Magnetometry and transport Publications

Iron-containing pharmaceuticals, namely: (i) PreNatal with ferrous fumarate, (ii) Tardyferon® with ferrous sulfate, (iii) Fenules with water free ferrous sulfate, (iv) Iron Complex with iron glycinate, citrate, (v) Gentle Iron, (vi) Hema-Plex® and (vii) Iron Bisglycinate with iron (ferrous) bisglycinate chelate (iron compounds are given as declared by the manufactures) were studied by ⁵⁷Fe Mössbauer spectroscopy with X-ray diffraction and magnetization measurements for analysis of the iron state. The obtained results demonstrate that the iron compound announced by the manufacturer in each pharmaceutical is not homogeneous and exists as some modifications of this compound or results of its transformation/oxidation probably due to its instability. The presence of ferrous and ferric compounds is observed, and the relative ferric iron fractions are roughly determined for each pharmaceutical product. This analysis clearly shows the differences between the iron compounds proclaimed by the manufacturers and those obtained by Mössbauer spectroscopy. That justifies as to why this technique should be used for the control and analysis of the iron-containing pharmaceuticals.

1,3-Diphenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl-6,7-dicarbonitrile is an exceptionally stable electron-deficient organic radical with promising potential to be used as a building block in a range of electronic and spintronic materials. The radical has a fully reversible one-electron redox and is highly delocalized, with some spin density reaching as far as the nitrile groups. Two polymorphs, α and β, were identified and characterized by single-crystal X-ray diffractometry. Both polymorphs form one-dimensional (1D) π stacks. However, while in polymorph α radicals are located at evenly interplane distances (3.366 Å), in polymorph β radicals are located at alternate interplane distances (3.182 and 3.318 Å). Magnetic susceptibility measurements for polymorph α indicate strong antiferromagnetic interactions along the 1D regular chain. Magnetic susceptibility data cannot be fully fitted to the Bonner and Fischer model for the 2-300 K temperature range. The steeper rise in paramagnetism above 80 K was rationalized by temperature-dependent antiferromagnetic exchange interactions between radicals within the 1D π stacks, which is indeed supported by Density Functional Theory (DFT) calculations. A microscopic study of the magnetic topology of polymorph α together with the interpretation of its magnetic experimental data was pursued by using a First-Principles Bottom-Up approach. Minuscule changes in crystal packing upon changing the temperature significantly affect the magnetic interaction between spin-containing moieties. Temperature, therefore, is the key player in rationalizing the magnetism in polymorph α.

Numerous bio-organisms employ template-assisted crystallization of molecular solids to yield crystal morphologies with unique optical properties that are difficult to reproduce synthetically. Here, a facile procedure is presented to deposit bio-inspired birefringent crystals of xanthine derivatives on a template of single-crystal quartz. Crystalline sheets that are several millimeters in length, several hundred micrometers in width, and 300–600 nm thick, are obtained. The crystal sheets are characterized with a well-defined orientation both in and out of the substrate plane, giving rise to high optical anisotropy in the plane parallel to the quartz surface, with a refractive index difference Δn ≈ 0.25 and a refractive index along the slow axis of n ≈ 1.7. It is further shown that patterning of the crystalline stripes with a tailored periodic grating leads to a thin organic polarization-dependent diffractive meta-surface, opening the door to the fabrication of various optical devices from a platform of small-molecule based organic dielectric crystals.

Metal-organic Co(ii)-phenylalanine crystals were studied and were found to possess magnetic properties and long-range spin transport. Magnetic measurements confirmed that in the crystals there are antiferromagnetic interactions between Co(ii) and the lattice. The metal-organic crystals (MOCs) also present the chirality-induced spin selectivity (CISS) effect at room temperature. A long-range spin polarization is observed using a magnetic conductive-probe atomic force microscope. The spin polarization is found to be in the range of 35-45%.

We demonstrate here how nitrate salts of bivalent copper, nickel, cobalt, and manganese, along with an achiral organic ligand, assemble into various structures such as symmetrical double-decker flowers, smooth elongated hexagonal bipyramids, and hexagonal prisms. Large morphological changes occur in these structures because of different metal cations, although they maintain isomorphous hexagonal crystallographic structures. Metal cations with stronger coordination to ligands (Cu and Ni) tend to form uniform crystals with unusual shapes, whereas weaker coordinating metal cations (Mn and Co) produce crystals with more regular hexagonal morphologies. The unusual flower-like crystals formed with copper nitrate have two pairs of six symmetrical petals with hexagonal convex centers. The texture of the petals indicates dendritic growth. Two different types of morphologies were formed by using different copper nitrate-to-ligand ratios. An excess of the metal salt results in uniform and hexagonal crystals having a narrow size distribution, whereas the use of an excess of ligand results in double-decker morphologies. Mechanistically, an intermediate structure was observed with slightly concave facets and a domed center. Such structures most likely play a key role in the formation of double-decker crystals that can be formed by fusion processes. The coordination chemistry results in isostructural chiral frameworks consisting of two types of continuous helical channels. Four pyridine units from four separate ligands are coordinated to the metal center in a plane having a chiral (propeller-type) arrangement. The individual double-decker flower crystals are homochiral and a batch consists of crystals having both handedness.

3,3′,3′'-(Benzene-1,3,5-triyl)tris(1-phenyl-1H-benzo[e][1,2,4]triazin-4-yl) (1) is a C3-symmetrical triradical comprised of three Blatter radical units connected at the 1, 3, 5 positions of a central trimethylenebenzene core. This triradical has an excellent air, moisture, and thermal stability. Single-crystal XRD indicates that triradical 1 adopts a propeller-like geometry with the benzotriazinyl moieties twisted by 174.1(2)° and packs in 1D chains along the c axis to form an extensive network of weak intermolecular interactions. Frozen solution continuous wave (CW) EPR spectra and variable-temperature field-sweep echo-detected (FSED) spectra revealed an intramolecular ferromagnetic exchange within the spin system, supporting a quartet S = 3/2 ground state. DFT calculations further supported these experimental findings.

Utilizing the inherent ability of Lindquist-type hexaniobate cluster-anions, [Nb₆O₁₉]⁸⁻, to serve as oxo-donor ligands in complexes with transition-metal cations, we report the synthesis and characterization of the first all-inorganic “ferric” wheel, Li₄₈[(Nb₆O₁₉)₈Fe₈(OH)₈]·88H₂O, comprised of eight Fe atoms linked by eight hexaniobate cluster-anion ligands. Bond valence sum analysis of the X-ray structure and the synthesis conditions themselves indicate that the Fe atoms are in the +3 oxidation state. This is confirmed by magnetic susceptibility and electron paramagnetic resonance (EPR) measurements which indicate the presence of high spin (S = 5/2) Fe(iii) ions. In addition, magnetic susceptibility measurements reveal long-range superexchange antiferromagnetic interactions between the hexaniobate-ligand separated Fe³⁺ ions (J = −0.22 cm⁻¹). More generally, the results suggest the use of hexaniobate cluster-anions as linkers in the synthesis of other two- or three-dimensional polyoxometalate framework structures.

The spontaneous gelation of poly(4-vinyl pyridine)/pyridine solution produces materials with conductive properties that are suitable for various energy conversion technologies. The gel is a thermoelectric material with a conductivity of 2.2–5.0 × 10–6 S m–1 and dielectric constant ε = 11.3. On the molecular scale, the gel contains various types of hydrogen bonding, which are formed via self-protonation of the pyridine side chains. Our measurements and calculations revealed that the gelation process produces bias-dependent polymer complexes: quasi-symmetric, strongly hydrogen-bonded species, and weakly bound protonated structures. Under an applied DC bias, the gelled complexes differ in their capacitance/conductive characteristics. In this work, we exploited the bias-responsive characteristics of poly(4-vinyl pyridine) gelled complexes to develop a prototype of a thermal energy harvesting device. The measured device efficiency is S = ΔV/ΔT = 0.18 mV/K within the temperature range of 296–360 K. Investigation of the mechanism underlying the conversion of thermal energy into electric charge showed that the heat-controlled proton diffusion (the Soret effect) produces thermogalvanic redox reactions of hydrogen ions on the anode. The charge can be stored in an external capacitor for heat energy harvesting. These results advance our understanding of the molecular mechanisms underlying thermal energy conversion in the poly(4-vinyl pyridine)/pyridine gel. A device prototype, enabling thermal energy harvesting, successfully demonstrates a simple path toward the development of inexpensive, low-energy thermoelectric generators.

We describe an electrolytic process which successfully decrepitates (pulverizes) sintered Nd2Fe14B magnets in preparation for further recycling. Laboratory-scale measurements on magnets that had been removed from end-of-life hard disk drives demonstrate that cm-size magnet fragments, in electrical contact with a titanium cathode in a 2 M KOH solution, can undergo hydrogen decrepitation (HD) into powder with grain size 

The olefin metathesis reaction is among the most widely applicable catalytic reactions for carbon–carbon double bond formation. Currently, Mo– and Ru–carbene catalysts are the most common choices for this reaction. It has been suggested that an iron-based catalyst would be a desirable economical and biocompatible substitute of the Ru catalysts; however, practical solutions in this regard are still lacking. Here, we report the discovery and mechanistic studies of three-coordinate iron(II) catalysts for ring-opening metathesis polymerization of olefins. Remarkably, their reactivity enabled the formation of polynorbornene with stereoregularity and high molecular weight (>107 g mol–1). The polymerization in the presence of styrene revealed cross metathesis reactivity with iron catalysts. Mechanistic studies suggest the possible role of metal–ligand cooperation in formation of the productive catalyst. This work opens the door to the development of iron complexes that can be economical and biocompatible catalysts for olefin metathesis reactions.

We show that metal-organic frameworks, based on tetrahedral pyridyl ligands, can be used as a morphological and structural template to form a series of isostructural crystals having different metal ions and properties. An iterative crystal-to-crystal conversion has been demonstrated by consecutive cation exchanges. The primary manganese-based crystals are characterized by an uncommon space group ( P622 ). The packing includes chiral channels that can mediate the cation exchange, as indicated by energy-dispersive X-ray spectroscopy on microtome-sectioned crystals. The observed cation exchange is in excellent agreement with the Irving-Williams series (Mn < Fe < Co < Ni < Cu > Zn) associated with the relative stability of the resulting coordination nodes. Furthermore, we demonstrate how the metal cation controls the optical and magnetic properties. The crystals maintain their morphology, allowing a quantitative comparison of their properties at both the ensemble and single-crystal level.

Ceria (CeO2) and its solid solutions with Gd2O3 are technologically important and environmentally friendly materials with numerous interesting properties and important applications. Nevertheless, the magnetic properties of ceria are even today not fully understood, and magnetoelastic coupling in pure or doped ceria remains essentially unexplored. This has been so, in part, due to the difficulty of measuring very small magnetostrictive strains in weakly paramagnetic materials. During the last decade, however, technical advances have enabled sensitive and accurate measurements of sample deformation in high magnetic fields. Here, forced magnetostriction (MS) in Gd2O3-CeO2 solid solution ceramics (Ce1-xGdxO2-x/2, 0

Misfit layered compounds (MLCs) MX-TX2, where M, T = metal atoms and X = S, Se, or Te, and their nanotubes are of significant interest due to their rich chemistry and unique quasi-1D structure. In particular, LnX-TX2 (Ln = rare-earth atom) constitute a relatively large family of MLCs, from which nanotubes have been synthesized. The properties of MLCs can be tuned by the chemical and structural interplay between LnX and TX2 sublayers and alloying of each of the Ln, T, and X elements. In order to engineer them to gain desirable performance, a detailed understanding of their complex structure is indispensable. MLC nanotubes are a relative newcomer and offer new opportunities. In particular, like WS2 nanotubes before, the confinement of the free carriers in these quasi-1D nanostructures and their chiral nature offer intriguing physical behavior. High-resolution transmission electron microscopy in conjunction with a focused ion beam are engaged to study SmS-TaS2 nanotubes and their cross-sections at the atomic scale. The atomic resolution images distinctly reveal that Ta is in trigonal prismatic coordination with S atoms in a hexagonal structure. Furthermore, the position of the sulfur atoms in both the SmS and the TaS2 sublattices is revealed. X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and X-ray absorption spectroscopy are carried out. These analyses conclude that charge transfer from the Sm to the Ta atoms leads to filling of the Ta 5d z 2 level, which is confirmed by density functional theory (DFT) calculations. Transport measurements show that the nanotubes are semimetallic with resistivities in the range of 10–4 Ω·cm at room temperature, and magnetic susceptibility measurements show a superconducting transition at 4 K.

Cyclic 6-membered aromatic compounds such as benzene and azabenzenes (pyridine, pyridazine, and pyrazine) are known to be light-sensitive, affording, in particular, the Dewar benzene type of intermediates. Pyridine is known to provide the only Dewar pyridine intermediate that undergoes reversible ring-opening. We found that irradiation of photosensitive gels prepared from poly(4-vinyl pyridine) and pyridine at 254 or 312 nm leads to pyridine ring-opening and subsequent formation of 5-amino-2,4-pentadienals. We show that this light-induced process is only partially reversible, and that the photogenerated aminoaldehyde and aminoaldehyde-pending groups undergo self-condensation to produce cross-linked, conjugated oligomers that absorb light in the visible spectrum up to the near-infrared range. Such a sequence of chemical reactions results in the formation of gel with two distinct morphologies: spheres and fiber-like matrices. To gain deeper insight into this process, we prepared poly(4-vinyl pyridine) with low molecular weight (about 2000 g/mol) and monitored the respective changes in absorption, fluorescence, 1H-NMR spectra, and electrical conductivity. The conductivity of the polymer gel upon irradiation changes from ionic to electronic, indicative of a conjugated molecular wire behavior. Quantum mechanical calculations confirmed the feasibility of the proposed polycondensation process. This new polyacetylene analog has potential in thermal energy-harvesting and sensor applications.

Herein we report on a simplified synthesis of scarcely explored, terminally disubstituted electron-poor alkylidene cyclopent-2-en-4-ones through uncommon olefination. Secondary sulfones, activated by electron-withdrawing groups at the adjacent carbon atom, undergo K 2 CO 3 -promoted coupling with 4-acyloxy- and 4- tert -butylsilyloxycyclopent-2-en-1-ones giving directly, or after a separate dehydrosulfinylation step, alkylidene cyclopent-2-en-4-ones. A plausible mechanism for these transformations is proposed. Initially, β-arylsulfonyl esters as well as their acetyl or nitrile analogues are allylated by cyclopentenone derivatives via a tandem Michael addition of α-sulfonyl carbanions followed by proton migration and retro -Michael-type O-nucleofuge elimination. The primary allylation products are formed as two diastereomers whose configuration and conformation were elucidated using single crystal X-ray diffraction and NMR spectroscopy. Regardless of stereochemistry, both sets of diastereomers are subjected to Zaitsev-type retro -Michael vinylogous dehydrosulfinylation under either basic or thermal silica gel promoted conditions resulting in E/Z -alkylidene cyclopent-2-en-4-ones. In these reactions activated sulfones serve as bearing electron-withdrawing group alkylidene anion-radical synthons, whereas 4-oxy-substituted cyclopentenones represent cyclopent-2-en-4-one cation-radical surrogates.

Developing growth schemes for functional two-dimensional (2D) nanomaterials is of much interest, especially because synthetic conditions are often correlated with physical properties such as optical absorbance. Bi2Se3 is an interesting material because of its transition from a narrow gap semiconductor, for the thinnest structures, to a topological insulator, when the structures are at least six quintuple molecular layers (QLs), and its appealing photothermal, thermoelectric, and optical properties. Here, we developed a controlled colloidal synthesis based on oriented attachment to produce Bi2Se3 nanoplatelets with varying thicknesses. The synthesis scheme also enables the facile doping of the structures without noticeable intercalation. The variation in optical properties confirmed the higher concentration of charge carriers at the edge of the structures, which is due in this system to Se deficiency and low crystallinity. This research opens a way to tune the composition and thickness of nanostructured 2D Bi2Se3, an important functional material.

Formic acid (FA) is a promising hydrogen carrier that can play an instrumental role in the overall implementation of a hydrogen economy. In this regard, it is important to generate H₂ gas from neat FA without any solvent and/or additive, for which existing systems are scarce. Here we report the remarkable catalytic activity of a ruthenium 9H-acridine pincer complex for this process. The catalyst is unusually stable and robust in FA, even at high temperatures, and can catalyse neat FA dehydrogenation for over a month, with a total turnover number of 1,701,150. It can also generate high H₂/CO₂ gas pressures from neat FA (tested up to 100 bars). Mechanistic investigations and density functional theory studies are conducted to fully understand the molecular mechanism of the process. Overall, the high activity, stability, selectivity, simplicity and versatility of the system to generate a CO-free H₂/CO₂ gas stream and high pressure from neat FA makes it promising for large-scale implementation. 

Room-temperature, long-range (300 nm), chirality-induced spin-selective electron conduction is found in chiral metal–organic Cu(II) phenylalanine crystals, using magnetic conductive-probe atomic force microscopy. These crystals are found to be also weakly ferromagnetic and ferroelectric. Notably, the observed ferromagnetism is thermally activated, so that the crystals are antiferromagnetic at low temperatures and become ferromagnetic above ∼50 K. Electron paramagnetic resonance measurements and density functional theory calculations suggest that these unusual magnetic properties result from indirect exchange interaction of the Cu(II) ions through the chiral lattice.

3-(Phenyl)-1-(pyrid-2-yl)-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl (2) demonstrates the first example of polymorphism in the family of Blatter radicals. Two polymorphs, 2 alpha and 2 beta, have been identified and characterized by single crystal X-ray diffractometry and magnetic susceptibility measurements to investigate their magnetism-structure correlations. Both polymorphs form one-dimensional (1D) pi stacks of evenly spaced radicals with distinctly different pi-pi overlap modes. Within the 1D pi stacks, radicals are located at evenly interplanar distances, 3.461 angstrom for 2 alpha and 3.430 angstrom for 2 beta. Magnetic susceptibility studies indicate that both polymorphs exhibit antiferromagnetic interactions inside their 1D pi stacks. The magnetic susceptibility data are best interpreted in terms of a regular chain model of antiferromagnetically coupled quantum spins H = - 2J Sigma(i)(S-i) over right arrow.(Si+1) over right arrow) with exchange-interactions of J/k(B) = -36.7(3) K (-25.5(2) cm(-1)) for 2 alpha and J/k(B) = -72(3) K (-50(2) cm(-1)) for 2 beta. For polymorph 2 beta, a crossover on the magnetic susceptibility around 20 K suggests the presence of a phase transition, which might be related to dimerization of the radicals along the chain. DFT calculations support the experimental structure-magnetism results and the antiferromagnetic nature of the local interactions between radicals within the 1D pi stacks.

Host-guest solution chemistry with a wide range of organic hosts is an important and established research area, while the use of inorganic hosts is a more nascent area of research. In the recent past in a few cases, Keplerate type molybdenum oxide based porous, spherical clus-ters, shorthand notation {Mo132}, have been used as hosts for organic guests. Here we demonstrate the synthetically controlled encapsula-tion of first row transition metals (M = Mn, Fe, and Co) within a Keplerate cluster that was lined on the inner core with phosphate ani-ons, {Mo132PO4}. The resulting M2+x{Mo132PO4} host-guest complexes were characterized by 31P NMR and ENDOR spectroscopy that substantiated the encapsulation of the first-row transition metal guest. Magnetic susceptibility measurements showed that the encap-sulation of up to 10 equivalents showed little magnetic interaction between the encapsulated metals, indicating that each guest atom occupied a single site. Visualization of the capsules and differentiation of the Mo atoms of the capsule framework and the encapsulated transition metal was possible using spherical and chromatic double aberration-corrected electron microscopy combined with energy-filtered TEM (EFTEM) elemental maps. In addition, use of visible light induced XPS for chemically resolved electrical measurements (CREM) confirmed the successful encapsulation of M within {Mo132PO4} and furthermore showed photoinduced electron transfer from M to Mo. In the future such targeted electron transfer between host {Mo132} and a transition metal guest could be used as photo-initiated switches using inorganic compounds and for single site photocatalytic reactions in confined space.

The widespread crisis of plastic pollution demands discovery of new and sustainable approaches to degrade robust plastics such as nylons. Using a green and sustainable approach based on hydrogenation, in the presence of a ruthenium pincer catalyst at 150 °C and 70 bar H2, we report here the first example of hydrogenative depolymerization of conventional, widely used nylons and polyamides, in general. Under the same catalytic conditions, we also demonstrate the hydrogenation of a polyurethane to produce diol, diamine, and methanol. Additionally, we demonstrate an example where monomers (and oligomers) obtained from the hydrogenation process can be dehydrogenated back to a poly(oligo)amide of approximately similar molecular weight, thus completing a closed loop cycle for recycling of polyamides. Based on the experimental and density functional theory studies, we propose a catalytic cycle for the process that is facilitated by metal-ligand cooperativity. Overall, this unprecedented transformation, albeit at the proof of concept level, offers a new approach toward a cleaner route to recycling nylons.

1-(2-Methoxyphenyl)-3-phenyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (2) is a Blatter radical with a challenging structure-to-magnetism correlation. The nearly orthogonal 2-methoxyphenyl group disrupts the ability of the radical to form columns of pi-stacked molecules typically observed in organic radicals with extended pi-conjugated aromatic frameworks. The experimental magnetic susceptibility data are best interpreted in terms of an alternating antiferromagnetic Heisenberg linear chain model with(A1)J(exp)= 2J(A)= -6.74 cm(-1),(A2)J(exp)= 2 alpha J(A)= -2.70 cm(-1). Two possible 1D chains of alternating radicals (C1 and C2) were identified. However, owing to significant differences in the packing arrangement of the molecules and the similar lengths of the shortest intermolecular contacts within the chains, a convincing structure-to-magnetism correlation was not straightforward. DFT calculations reproduced with high accuracy the experimentally determined microscopic magnetic exchange interactions and showed beyond reasonable doubt that the observed magnetic susceptibility data are attributed to chain C2. Radicals within chain C2 are near perpendicular to each other (87.76 degrees) and form a herringbone pattern. There are two weak hydrogen interactions H3 center dot center dot center dot 4 and H23 center dot center dot center dot N1, both antiferromagnetic in nature and one shorter than the other (2.478vs.2.516 angstrom), that account for the experimentally determined exchange interactions (-6.74vs.-2.70 cm(-1)).

We report a room temperature protocol for the hydrogenation of various amides to produce amines and alcohols. Compared to the most previous reports for this transformation, which use high temperatures (typically, 100–200 oC) and H2 pressures (10-100 bar), this system proceeds under extremely mild conditions (RT, 5-10 bars of H2). The hydrogenation is catalyzed by well-defined ruthenium-PNNH pincer complexes (0.5 mol%) with potential dual modes of metal-ligand cooperation. An unusual Ru-amidate complex was formed and crystallo-graphically characterized. Mechanistic investigations indicate that the room-temperature hydrogenation proceeds predominantly via the Ru-N amido/amine metal-ligand cooperation.

Acridine-based PNP pincer complexes have been previously utilized for several environmentally benign catalytic processes. In light of the recent growth in interest in base-metal catalysis, we report here the synthesis of acridine-PNP pincer complexes of Ni, Co, Fe, and Mn. We also report here the noninnocent redox nature of these complexes that results in the dimerization of pincer complexes by forming a C-C bond at the C9 position of the acridine ring.

We envisaged that rapid thermal processing (RTP) widely used in semiconductor device fabrication can be employed for fabricating organic crystalline devices since heating and mass transfer are localized within a small area in RTP. This may result in crystal growth at the location relevant to organic device fabrication in situ, for which RTP has not been used so far. We utilized the RTP technique for the growth of high quality organic crystals from thin films of copper phthalocyanine (CuPc) and rubrene. The crystals were grown in situ on silicon surfaces, which were directly used for device fabrication (organic field effect transistors, OFETs, and organic phototransistors, OPTs). For CuPc devices, the mobility was 0.12 ± 0.11 cm2 V–1 s–1, on/off ratio of up to 106, and photo/dark current ratio of P > 105 (for OPT devices). The mobility of rubrene-based OFETs was 0.31 ± 0.15 cm2 V–1 s–1, on/off ratio of up to 105, and photo/dark current ratio of P ≈ 105. The mobilities are similar to those of previously reported single-crystalline CuPc and rubrene OFETs fabricated on untreated surfaces, and the photoresponses are stronger than those of the reported CuPc and rubrene OPTs. RTP is a general and efficient method to grow high quality organic crystals in situ, significantly advancing fabrication methodology for organic electronic and optoelectronic devices.

In view of their facile fabrication and recycling, functional materials that are built from small molecules ("molecular plastics") may represent a cost-efficient and sustainable alternative to conventional covalent materials. We show how molecular plastics can be made robust and how their (nano)structure can be tuned via modular construction. For this purpose, we employed binary composites of organic nanocrystals based on a perylene diimide derivative, with graphene oxide (GO), bentonite nanoclay (NC), or hydroxyethyl cellulose (HEC), that both reinforce and enable tailoring the properties of the membranes. The hybrids are prepared via a simple aqueous deposition method, exhibit enhanced mechanical robustness, and can be recycled. We utilized these properties to create separation membranes with tunable porosity that are easy to fabricate and recycle. Hybrids 1/HEC and 1/NC are capable of ultrafiltration, and 1/NC removes heavy metals from water with high efficiency. Hybrid 1/GO shows mechanical properties akin to covalent materials with just 2-10% (by weight) of GO. This hybrid was used as a membrane for immobilizing β-galactosidase that demonstrated long and stable biocatalytic activity. Our findings demonstrate the utility of modular molecular nanoplastics as robust and sustainable materials that enable efficient tuning of structure and function and are based on self-assembly of readily available inexpensive components.

We report here the activation of CO2 using two Mn-PNN pincer complexes that can exhibit different modes of metal-ligand cooperation amido/amino mode that involves [1,2]-activation of CO2 and dearomatization/aromatization mode that involves [1,3]-activation of CO2. We also compare their catalytic activity for CO2 hydrogenation.

1-Phenyl-3,7-bis(trifluoromethyl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (2), an exceptionally stable radical, was characterized by single crystal X-ray diffractometry and variable temperature SQUID magnetometry to investigate its structure-magnetism correlation. Radical 2 forms a 1D column of slipped pi-stacked molecules along the crystallographic a-axis. Within the columns, radicals are equidistantly separated by 3.57 angstrom. Magnetic susceptibility studies indicated that radical 2 obeys the Curie-Weiss law (C = 0.370 emu K mol(-1)) with local ferromagnetic interactions between radicals inside the 1D column (theta = 6.7 K). Fitting of the magnetic data revealed that the temperature dependence of chi T (5-300 K) was best described using the 1D regular linear ferromagnetic chain model with J/k = 9 K (6.3 cm(-1)), g(solid) = 2.0047. DFT calculations supported the assignment of the macroscopic 1D ferromagnetism to local interactions between slipped pi-stacked radicals along the a-axis of the 1D column.

Novel spin-electronic devices require electrodes that inject electrons with both high spin-polarization and perpendicular magnetic anisotropy (PMA). Several full-Heusler compounds are expected to be half-metallic ferromagnets, e.g. chemically-ordered L2(1) or B2 Co2MnSi. However, most cubic full-Heusler alloys have small magneto-crystalline anisotropy meaning that PMA is difficult to achieve in thin film geometries of devices. Addressing this limitation, Butler a al. (2014) calculate PMA and full spin-polarization in ultra-thin (2-3 nm) chemically-ordered Co2MnSi with an epitaxial coherent interface to rock-salt MgO (0 01). Experimentally, PMA in sputter-deposited ultra-thin films with full-Heusler compositions was reported though with adjacent layers of Pd or Pt.We investigate structural origins of such PMA using a test case of ultra-thin Co2MnSi films prepared by magnetron sputter-deposition, adjacent to a MgO layer to represent a tunneling barrier, and to a Pd buffer layer. We measure PMA, with an energy density of 7.8 +/- 1.8 Merg/cc at 5 K, when a Pd layer is adjacent to Co2MnSi, following annealing in a narrow temperature range, around 350 degrees C. This ferromagnetism originates from nanometer scale regions, below 5 nm in size, having a relatively low saturation magnetization, 550 +/- 50 emu/cc at low temperatures. Following thermal annealing, significant compositional intermixing between Co2MnSi films and adjacent layers, Co with Pd and Mn with MgO, was measured by electron energy-loss and angle resolved Xray photoelectron spectroscopies. Aberration-corrected transmission electron microscopy shows that Co2MnSi does not crystallize while at the interface with Pd, nanometer-scale crystallites of FCC solid solution CoPd with {1 1 1} texture are identified. We conclude that these Pd rich CoPd crystallites, characterized by large magnetostriction, are a source for PMA.

Commonly, iron(ii) and copper(i) complexes bind dioxygen (O-2) and then activate O-2 through a reductive reaction pathway. There is, however, significant interest in low temperature oxygenation with O-2 without the use of a sacrificial reductant. Here, earth-abundant metal complexes (Fe-II, Co-II, Ni-II and Cu-II) coordinated by two different tetra-dentate mono-carbon bridged bis-phenanthroline ligands, (1,10-Phen)(2)-2,2-CR1R2, where R-1 = n-butyl and R-2 = n-butyl or H were synthesized. The structures all showed the expected metal complexation in the equatorial plane by the bridged bis-phenanthroline ligands. For R-1 = n-butyl; R-2 = H, where the ligand has a tertiary carbon bridging group, fast intramolecular oxygenation occurred at the pseudobenzylic position. Depending on the transition metal the main products formed were oxygen bridged dimers of the metal complexes (Co and Fe) or metal complexes with a carbonyl moiety at the bridging pseudobenzylic position as a result of C-R-1 bond cleavage (Ni and Cu). The different product assemblages are explained by different reaction pathways that are metal specific. For quaternary carbon bridged ligands, R-1 = R-2 = n-butyl, the complexes catalytically activated C-H bonds of cyclohexene under catalytic conditions, showing higher effective turnover numbers at low catalyst loading. The reactivity observed is commensurate with a room temperature autooxidation reaction although the initiation of the free radical reaction is metal specific. In general labelling studies with O-18(2), UV-vis and EPR spectroscopy as well as cyclic voltammetry measurements led to a conclusion that the reaction pathways involved both C-H bond activation and O-2 activation.

Metal-ligand cooperation (MLC) by dearomatization/aromatization provides a unique way for bond activation, which has led to the discovery of various acceptorless dehydrogenative coupling reactions. However, most of the studies are based on pincer complexes with a central nitrogen donor. Aiming at exploration of the possibility of MLC by PCP-type pincer complexes, we report herein the synthesis, characterization, structure, and reactivity of pyridine-based PCP-Ru complexes. X-ray structures and DFT calculations indicate a carbenoid character of quaternized pyridine-based PCP-Ru complexes. These complexes undergo dearomatization by direct deprotonation, and the dearomatized complex can react with hydrogen, alcohols, or nitriles to regain aromatization via MLC.

Polyfluoroxometalates (PFOMs) that have a quasi Wells-Dawson structure and have low valent transition metal substitution at the so-called "belt" position, alpha(1)-[H2F6NaM(H2O)W17O55](q-), can reversibly interchange between dimeric and monomeric structures. The dimers have two unique M-mu O-W bridges between two PFOM units. The dimerization occurs through dehydration and was studied as a function of temperature using the visible spectrum that is sensitive to the wavelength and extinction coefficient of the d-d transition. The calculated thermodynamic parameters of the dimerization reaction were iteratively fitted using a function derived from the equilibrium constant and the Beer-Lambert law. Such reversible dimerization reactions have not been observed for similar alpha(1)-[P2M(H2O)W17O61](q-) structures, thus fluorine atoms in an axial position to the transition metal are apparently critical for dimerization by reducing the bond strength of the transition metal-aqua bond trans to the fluorine atom.

Base-metal-catalyzed dehydrogenative cross-coupling of primary alcohols to form cross-esters as major products, liberating hydrogen gas, is reported. The reaction is catalyzed by a pincer complex of earth-abundant manganese in the presence of catalytic base, without any hydrogen acceptor or oxidant. Mechanistic insight indicates that a dearomatized complex is the actual catalyst, and indeed this independently prepared dearomatized complex catalyzes the reaction under neutral conditions.

The rapid growth in demand for data and the emerging applications of Big Data require the increase of memory capacity. Magnetic memory devices are among the leading technologies for meeting this demand; however, they rely on the use of ferromagnets that creates size reduction limitations and poses complex materials requirements. Usually magnetic memory sizes are limited to 30-50 nm. Reducing the size even further, to the approximate to 10-20 nm scale, destabilizes the magnetization and its magnetic orientation becomes susceptible to thermal fluctuations and stray magnetic fields. In the present work, it is shown that 10 nm single domain ferromagnetism can be achieved. Using asymmetric adsorption of chiral molecules, superparamagnetic iron oxide nanoparticles become ferromagnetic with an average coercive field of approximate to 80 Oe. The asymmetric adsorption of molecules stabilizes the magnetization direction at room temperature and the orientation is found to depend on the handedness of the chiral molecules. These studies point to a novel method for the miniaturization of ferromagnets (down to approximate to 10 nm) using established synthetic protocols.

The magnetic properties of undoped, bulk CeO2 are not fully understood. In contrast to nanocrystalline ceria that exhibits paramagnetism attributed to Ce3+ at grain surfaces, bulk ceria is weakly paramagnetic, despite the absence of magnetic ions. In the present work, the magnetic susceptibility of bulk ceria ceramics doped with Lu3+, which has neither spin nor orbital angular momentum, was measured in order to assess the relative contributions of the crystal lattice, residual Ce3+ and oxygen vacancies to the overall bulk magnetization. We observed a magnetic response consisting of two parts: temperature independent (5-300 K) magnetic susceptibility, and Curie-Weiss paramagnetism. The temperature independent susceptibility decreases linearly with Lu content, and becomes diamagnetic at 30 mol% Lu. The Curie-Weiss magnetism visible at low temperatures was identified as resulting from a few ppm of Fe contaminant. However, Fe contamination does not contribute to the temperature independent paramagnetism. No contribution from Ce3+ could be detected. The fact that the magnetization decreases with Lu content, even though the concentration of oxygen vacancies, and the lattice defects associated with them, increases, indicates that neither is coupled to the magnetic field. Weak, temperature-independent paramagnetism in non-metals is usually attributed to a second order, Van Vleck-type magnetization. However, Van Vleck paramagnetism requires that the population of the first excited state be constant within the range of temperatures investigated. We discuss possible modifications of the large band gap electronic structure of undoped ceria which could account for our observations.

Homogeneous catalytic hydrogenation of esters to alcohols is an industrially important, environmentally benign reaction. While precious metal-based catalysts for this reaction are now well known, only very few catalysts based on first-row metal complexes were reported. Here we present the hydrogenation of esters catalyzed by a complex of earth-abundant manganese. The reaction proceeds under mild conditions and insight into the mechanism is provided based on an NMR study and the synthesis of novel Mn complexes postulated as intermediates.

Owing to their unique properties such as mechanical, optical, magnetic, nanomaterials attracted a great interest over the last two decades. Inorganic nanotubes, e.g. WS2, make an important class of nanomaterials with numerous potential applications. In the current work, a new synthetic strategy is developed to decorate the surface of WS2 nanotubes with FeWO4 nanoparticles. The FeWO4 nanoparticles were produced by first depositing amorphous iron oxide film onto the WS2 nanotubes' surface and, subsequently, high-temperature annealing (600 C-degrees). Careful analysis by electron microscopy; X-ray diffraction and other techniques were carried out. Based on these analyses, the growth mechanism of the hybrid nanostructures was elucidated. Magnetic measurements were employed to shed light on the magnetic behavior of the hybrid nanostructures. The orientation and position of the WS2 nanotubes decorated with the FeWO4 nanoparticles could be partially affected by applying a magnetic field using non-viscous solvents, like ethanol.

N-formylation of amines utilizing CO2 in the presence of reducing agents constitute an important methodology in organic synthesis. Presented herein is a selective N-formylation of amines with CO2 and H-2 catalyzed by complexes of Earth-abundant cobalt. A wide range of amines were converted to their corresponding formamides under CO2 and H-2 pressure, catalyzed by Co-PNP pincer complex, generating water as the sole byproduct.

The first example of base-metal-catalysed synthesis of amides from the coupling of primary amines with either alcohols or esters is reported. The reactions are catalysed by a new manganese pincer complex and generate hydrogen gas as the sole byproduct, thus making the overall process atom-economical and sustainable.

The first example of a base metal (manganese) catalyzed acceptorless dehydrogenative coupling of methanol and amines to form formamides is reported herein. The novel pincer complex (iPr-PN^HP)Mn(H)(CO)₂ catalyzes the reaction under mild conditions in the absence of any additives, bases, or hydrogen acceptors. Mechanistic insight based on the observation of an intermediate and DFT calculations is also provided.

How molecules in solution form crystal nuclei, which then grow into large crystals, is a poorly understood phenomenon. The classical mechanism of homogeneous crystal nucleation proceeds via the spontaneous random aggregation of species from liquid or solution. However, a non-classical mechanism suggests the formation of an amorphous dense phase that reorders to form stable crystal nuclei. So far it has remained an experimental challenge to observe the formation of crystal nuclei from five to thirty molecules. Here, using polyoxometallates, we show that the formation of small crystal nuclei is observable by cryogenic transmission electron microscopy. We observe both classical and non-classical nucleation processes, depending on the identity of the cation present. The experiments verify theoretical studies that suggest non-classical nucleation is the lower of the two energy pathways. The arrangement in just a seven-molecule proto-crystal matches the order found by X-ray diffraction of a single bulk crystal, which demonstrates that the same structure was formed in each case.

Three new three-dimensional (3D) Mn-II based metal-organic frameworks (MOFs) [{Mn(tda)(bpy)}(4)center dot 2CH(3)CN](n) (1), [Mn(tda)(b-pe) center dot xH(2)O] n (2) and [Mn(tda)(4-bpmh)center dot 2CH(3)CN](n) (3) have been solvothermally synthesized using MnCl2 center dot 4H(2)O, thiophene-2, 5-dicarboxylic acid (H2tda) and different pyridyl N, N'-donor spacer ligands [bpy = 4,4'-bipyridyl, bpe = 1,2-bis-(4-pyridyl) ethylene and 4-bpmh = N, N'-bispyridine-4-yl-methylene-hydrazine]. Structural study reveals twofold interpenetrated 3D pillar-layer structures for all three complexes, constructed from twodimensional (2D) Mn-carboxylate layers and neutral bipyridyl pillars. The 2D layers represent continuous extension of dinuclear [Mn-2(CO2)(4)N-4] nodes inter-connected via the tda ligands. Topological characterization represents a twofold inter-penetrated 6-connected uninodal net with pcu a-Po primitive cubic topology. Variable temperature magnetic measurements in the three complexes reveal the presence of similar antiferromagnetic interactions between neighbouring MnII ions, mediated through syn-syn carboxylate bridges. However, temperature dependent susceptibility plots taken at different magnetic fields show that the antiferromagnetic interactions observed in the complexes at lower magnetic fields are overcome by some inter-cluster interactions at higher magnetic fields. This interesting feature has also been perceived from field-dependent magnetization measurements and the hysteresis data.

The first example of a base-metal-catalyzed homogeneous hydrogenative coupling of nitriles and amines to selectively form secondary cross-imines is reported. The reaction is catalyzed under mild conditions by a well-defined (iPr-PNP)Fe(H)Br(CO) pincer pre-catalyst and catalytic tBuOK.

Xanthorhodopsin (xR) is a member of the retinal protein family and acts as a proton pump in the cell membranes of the extremely halophilic eubacterium Salinibacter ruber. In addition to the retinal chromophore, xR contains a carotenoid, which acts as a light-harvesting antenna as it transfers 40% of the quanta it absorbs to the retinal. Our previous studies have shown that the CD and absorption spectra of xR are dramatically affected due to the protonation of two different residues. It is still unclear whether xR can bind cations. Electron paramagnetic resonance (EPR) spectroscopy used in the present study revealed that xR can bind divalent cations, such as Mn²⁺ and Ca²⁺, to deionized xR (DI-xR). We also demonstrate that xR can bind 1 equiv of Mn²⁺ to a high-affinity binding site followed by binding of ∼40 equiv in cooperative manner and ∼100 equiv of Mn²⁺ that are weakly bound. SQUID magnetic studies suggest that the high cooperative binding of Mn²⁺ cations to xR is due to the formation of Mn²⁺ clusters. Our data demonstrate that Ca²⁺ cations bind to DI-xR with a lower affinity than Mn²⁺, supporting the assumption that binding of Mn²⁺ occurs through cluster formation, because Ca²⁺ cations cannot form clusters in contrast to Mn²⁺.

Four new Mn-II- and Co-II-containing magnetic coordination polymers, [{Mn(Br-isa)(bpe)center dot 1/2H(2)O}(n) (1), (Co(Br-isa)(bpe)(1.5)center dot 1/2H(2)O}n (2), [{Mn(Br-isa)(4-bpmh)}(4)center dot 6H(2)O](n) (3), and [{Co(Br-isa)(4-bpmh)}(2)center dot 21/2H(2)O](n) (4)] [isa = isophthalic acid, bpe = 1,2-bis-(4-pyridyl)ethylene and 4-bpmh = N,N'-bispyridine-4-yl-methylene-hydrazine], have been synthesized at room temperature, using 5-bromo isophthalic acid (Br-H(2)isa) and two different N-donating ancillary ligands. The complexes have been characterized by single-crystal X-ray diffraction and other physicochemical techniques. Structure determination reveals two-dimensional (2D) coordination network architectures for all the complexes. In 1, 3, and 4, Mn-II and Co-II dinuclear units are connected via Br-H(2)isa ligands to form infinite 1D chains. The ancillary N,N'-donor spacer ligands interconnect the 1D chains into 2D coordination layers. Complex 2, on the other hand, can be viewed as being composed of cationic [{Co(bpe)}4](8+) square units that are joined by anionic Br-isa(2-) bridges into a 2D gridlike framework. Topology analysis shows an sql/Shubnikov tetragonal plane-net topology for complexes 1, 3, and 4, and an SP 2-periodic net (4, 4) Ia topology for complex 2. Complexes 1 and 3 show a field-dependent change in magnetic behavior which is confirmed from the susceptibility measurements at varying fields, field-dependent magnetization measurements, as well as from hysteresis data. Complex 2 exhibits a slow magnetization relaxation phenomenon manifested by the AC susceptibility measurements at different temperatures and frequencies. Finally, complex 4 exhibits a magnetic feature that can be interpreted as antiferromagnetic exchange interactions between two syn-syn carboxylate-bridged Co-II atoms.

Cotton is a promising basis for wearable smart textiles. Current approaches that rely on fiber coatings suffer from function loss during wear. We present an approach that allows biological incorporation of exogenous molecules into cotton fibers to tailor the material’s functionality. In vitro model cultures of upland cotton (Gossypium hirsutum) are incubated with 6-carboxyfluorescein–glucose and dysprosium–1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid–glucose, where the glucose moiety acts as a carrier capable of traveling from the vascular connection to the outermost cell layer of the ovule epidermis, becoming incorporated into the cellulose fibers. This yields fibers with unnatural properties such as fluorescence or magnetism. Combining biological systems with the appropriate molecular design offers numerous possibilities to grow functional composite materials and implements a material-farming concept.

The first example of base-metal-catalyzed dehydrogenative coupling of diols and amines to form cyclic imides is reported. The reaction is catalyzed by a pincer complex of the earth abundant manganese and forms hydrogen gas as the sole byproduct, making the overall process atom economical and environmentally benign.

Hydrogenation of nitriles to primary amines constitutes an atom-efficient and environmentally benign synthetic reaction. Herein we present a novel complex based on earth-abundant iron, and its application in the catalytic homogeneous hydrogenation of (hetero)aromatic, benzylic, and aliphatic nitriles to selectively form primary amines.

A non-classic complexation mode was discovered upon spectroscopic, thermodynamic, crystallographic and computational studies of a b-cyclodextrin/propionic acid complex. A "fully immersed" complexation phenomenon, where both the guest's hydrophobic and polar moieties are located inside the host and are stabilized by it, was found and calculated as the most favorable configuration.

The catalytic dehydrogenative coupling of alcohols and amines to form aldimines represents an environmentally benign methodology in organic chemistry. This has been accomplished in recent years mainly with precious-metal-based catalysts. We present the dehydrogenative coupling of alcohols and amines to form imines and H₂ that is catalyzed, for the first time, by a complex of the earth-abundant Mn. Detailed mechanistic study was carried out with the aid of NMR spectroscopy, intermediate isolation, and X-ray analysis.

The first example of a catalytic Michael addition reaction of non-activated aliphatic nitriles to α,β-unsaturated carbonyl compounds under mild, neutral conditions is reported. A new de-aromatized pyridine-based PNP pincer complex of the Earth-abundant, first-row transition metal manganese serves as the catalyst. The reaction tolerates a variety of nitriles and Michael acceptors with different steric features and acceptor strengths. Mechanistic investigations including temperature-dependent NMR spectroscopy and DFT calculations reveal that the cooperative activation of alkyl nitriles, which leads to the generation of metalated nitrile nucleophile species (α-cyano carbanion analogues), is a key step of the mechanism. The metal center is not directly involved in the catalytic bond formation but rather serves, cooperatively with the ligand, as a template for the substrate activation. This approach of "template catalysis" expands the scope of potential donors for conjugate addition reactions.

The use of carbon dioxide for synthetic applications presents a major goal in modern homogeneous catalysis. Rhodium-hydride PNP pincer complex 1 is shown to add CO₂ in two disparate pathways: one is the expected insertion of CO₂ into the metal-hydride bond, and the other leads to reductive cleavage of CO₂, involving metal-ligand cooperation. The resultant rhodium-carbonyl complex was found to be photoactive, enabling the activation of benzene and formation of a new benzoyl complex. Organometallic intermediate species were observed and characterized by NMR spectroscopy and X-ray crystallography. Based on the series of individual transformations, a sequence for the photocarbonylation of benzene using CO₂ as the feedstock was constructed and demonstrated for the production of benzaldehyde from benzene.

3-Adamantyl-1-phenyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl (4) crystallizes as chains of radicals where the spin bearing benzotriazinyl moieties are isolated from each other. Magnetic susceptibility studies in the 5-300 K temperature region indicate that radical 4 demonstrates typical paramagnetic behavior stemming from non-interacting S = 1/2 spins.

Various ruthenium(II) complexes with proximal oxophilic phenylselenium groups of the general formula [Ru^IIL^AL^B]X₂{L^A= L^B= 6,6′-bis[(4-methoxyphenyl)selanyl]-2,2′-bipyridine; 6,6′-bis[(nitrophenyl)selanyl]-2,2′-bipyridine; 3,6-bis(phenylselanyl)dipyrido[3,2-a:2′,3′-c]phenazine; L^A= 6,6′-bis(phenylselanyl)-2,2′-bipyridine, L^B= terpyridine} were prepared. The substitution patterns of these compounds were designed to have different electron-withdrawing/-donating properties or different binding motifs in comparison to the previously reported compound with L^A= L^B= 6,6′-bis(phenylselanyl)-2,2′-bipyridine. The research objective was to evaluate the potential of these compounds to activate ground-state molecular oxygen to form higher-valent Ru–O–Se bonds by cleavage of the O–O bond of O₂. All of the compounds prepared indeed activated O₂to form Ru–O–Se moieties, as observable by UV/Vis spectroscopy, mass spectrometry, or X-ray crystallography.

Azines (2,3-diazabuta-1,3-dienes) are a widely used class of compounds with conjugated C=N double bonds. Herein, we present a direct synthesis of azines from alcohols and hydrazine hydrate. The reaction, catalyzed by a ruthenium pincer complex, evolves dihydrogen and can be run in a base free version. The dehydrogenative coupling of benzylic and aliphatic alcohols led to good conversions and yields. Spectroscopic evidence for a hydrazine-coordinated dearomatized ruthenium pincer complex was obtained. Isolation of a supramolecular crystalline compound provided evidence for the important role of hydrogen bonding networks under the reaction conditions.

We report on Ru^(II)(μ²-O₂) nitrosyl pincer complexes that can return to their original Ru(0) state by reaction with mono-oxygen scavengers. Potential intermediates were calculated by density functional theory (DFT) and a mechanism is proposed, revealing a new type of metal-ligand cooperation consisting of activation of the O₂ moiety by both the metal center and the NO ligand. Reaction of the Ru(0) nitrosyl complex 1 with O₂ quantitatively yielded the crystallographically characterized Ru^(II) (μ²-O₂) nitrosyl complex 2. Reaction of 2 with the mono-oxygen scavengers phosphines or CO gave the Ru(0) complex 1 and phosphine oxides, or the carbonyl complex 3 (1 trapped by CO) and CO₂, respectively. Reaction of 2 with 1 equiv of phosphine at room temperature or -40 °C resulted in immediate formation of half an equivalent of 1 and 1 equiv of phosphine oxide, while half an equivalent of 2 remained unchanged. Overnight reaction at room temperature of 2 with excess CO (≤3 equiv) resulted in 3 and CO₂ gas as the only products. Reaction of 1 with 1 equiv of mono-oxygen source (dioxirane) at -78 °C yielded the Ru^(II)(μ²-O₂) complex 2. Similarly, reaction of the Ru(0) dearomatized complex 4 with O₂ led to the crystallographicaly characterized Ru^(II)(μ²-O₂) complex 5. Further reaction of 5 with mono-oxygen scavengers (phosphines or CO) led to the Ru(0) complex 4 and phosphine oxides or complex 6 (4 trapped by CO) and CO₂. When instead only 1 equiv of 5 was reacted with 1 equiv of phosphine at room temperature, immediate formation of half an equivalent of 4 and 1 equiv of phosphine oxide took place, while half an equivalent of 5 remained unchanged. When 5 reacted with an excess of CO (≤3 equiv), complex 6 and CO₂ gas were the only products obtained. DFT studies indicate a new mode of metal-ligand cooperation involving the nitrosyl ligand in the oxygen transfer process.

Herein we present a series of new α-iminopyridine-based iron-PNN pincer complexes [FeBr₂L_PNN] (1), [Fe(CO)₂L_PNN] (2), [Fe(CO)₂L_PNN](BF₄) (3), [Fe(F)(CO)₂L_PNN](BF₄) (4), and [Fe(H)(CO)₂L_PNN](BF₄) (5) with formal oxidation states ranging from Fe(0) to Fe(II) (L_PNN = 2-[(di-tert-butylphosphino)methyl]-6-[1-(2,4,6-mesitylimino)ethyl]pyridine). The complexes were characterized by a variety of methods including ¹H, ¹³C, ¹⁵N, and ³¹P NMR, IR, Mössbauer, and X-ray photoelectron spectroscopy (XPS) as well as electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopy, SQUID magnetometry, and X-ray crystallography, focusing on the assignment of the metal oxidation states. Ligand structural features suggest that the α-iminopyridine ligand behaves as a redox non-innocent ligand in some of these complexes, particularly in [Fe(CO)₂L_PNN] (2), in which it appears to adopt the monoanionic form. In addition, the NMR spectroscopic features (¹³C, ¹⁵N) indicate the accumulation of charge density on parts of the ligand for 2. However, a combination of spectroscopic measurements that more directly probe the iron oxidation state (e.g., XPS), density functional theory (DFT) calculations, and electronic absorption studies combined with time-dependent DFT calculations support the description of the metal atom in 2 as Fe(0). We conclude from our studies that ligand structural features, while useful in many assignments of ligand redox non-innocence, may not always accurately reflect the ligand charge state and, hence, the metal oxidation state. For complex 2, the ligand structural changes are interpreted in terms of strong back-donation from the metal center to the ligand as opposed to electron transfer. (Chemical Equation Presented).

A novel pincer ligand based on the pyrazine backbone (PNzP) has been synthesized, (2,6-bis(di(tert-butyl)phosphinomethyl)pyrazine), tBu-PNzP. It reacts with FeBr₂ to yield [Fe(Br)₂(tBu-PNzP)], 1. Treatment of 1 with NaBH₄ in MeCN/MeOH gives the hydride complex [Fe(H)(MeCN)₂(tBu-PNzP)][X] (X = Br, BH₄), 2·X. Counterion exchange and exposure to CO atmosphere yields the complex cis-[Fe(H)(CO)(MeCN)(tBu-PNzP)][BPh₄] 4·BPh₄, which upon addition of Bu₄NCl forms [Fe(H)(Cl)(CO)(tBu-PNzP)] 5. Complex 5, under basic conditions, catalyzes the hydrogenation of CO₂ to formate salts at low H₂ pressure. Treatment of complex 5 with a base leads to aggregates, presumably of dearomatized species B, stabilized by bridging to another metal center by coordination of the nitrogen at the backbone of the pyrazine pincer ligand. Upon dissolution of compound B in EtOH the crystallographically characterized complex 7 is formed, comprised of six iron units forming a 6-membered ring. The dearomatized species can activate CO₂ and H₂ by metal-ligand cooperation (MLC), leading to complex 8, trans-[Fe(PNzPtBu-COO)(H)(CO)], and complex 9, trans-[Fe(H)₂(CO)(tBu-PNzP)], respectively. Our results point at a very likely mechanism for CO₂ hydrogenation involving MLC.

The mechanism of the unique lactam formation from amines and water with concomitant H₂ liberation with no added oxidant, catalyzed by a well-defined acridine-based ruthenium pincer complex was investigated in detail by both experiment and DFT calculations. The results show that a dearomatized form of the initial complex is the active catalyst. Furthermore, reversible imine formation was shown to be part of the catalytic cycle. Water is not only the oxygen atom source but also acts as a cocatalyst for the H₂ liberation, enabled by conformational flexibility of the acridine-based pincer ligand. (Figure Presented).

Self-assembly of inorganic nanoparticles has been studied extensively for particles having different sizes and compositions. However, relatively little attention has been devoted to how the shape and surface chemistry of magnetic nanoparticles affects their self-assembly properties. Here, we undertook a combined experiment-theory study aimed at better understanding of the self-assembly of cubic magnetite (Fe3O4) particles. We demonstrated that, depending on the experimental parameters, such as the direction of the magnetic field and nanoparticle density, a variety of superstructures can be obtained, including one-dimensional filaments and helices, as well as C-shaped assemblies described here for the first time. Furthermore, we functionalized the surfaces of the magnetic nanocubes with light-sensitive ligands. Using these modified nanoparticles, we were able to achieve orthogonal control of self-assembly using a magnetic field and light.

Manganese(IV,V)-hydroxo and oxo complexes are often implicated in both catalytic oxygenation and water oxidation reactions. Much of the research in this area is designed to structurally and/or functionally mimic enzymes. On the other hand, the tendency of such mimics to decompose under strong oxidizing conditions makes the use of molecular inorganic oxide clusters an enticing alternative for practical applications. In this context it is important to understand the reactivity of conceivable reactive intermediates in such an oxide-based chemical environment. Herein, a polyfluoroxometalate (PFOM) monosubstituted with manganese, [NaH₂(Mn-L)W₁₇F₆O₅₅]^q-, has allowed the isolation of a series of compounds, Mn(II, III, IV and V), within the PFOM framework. Magnetic susceptibility measurements show that all the compounds are high spin. XPS and XANES measurements confirmed the assigned oxidation states. EXAFS measurements indicate that Mn(II)PFOM and Mn(III)PFOM have terminal aqua ligands and Mn(V)PFOM has a terminal hydroxo ligand. The data are more ambiguous for Mn(IV)PFOM where both terminal aqua and hydroxo ligands can be rationalized, but the reactivity observed more likely supports a formulation of Mn(IV)PFOM as having a terminal hydroxo ligand. Reactivity studies in water showed unexpectedly that both Mn(IV)-OH-PFOM and Mn(V)-OH-PFOM are very poor oxygen-atom donors; however, both are highly reactive in electron transfer oxidations such as the oxidation of 3-mercaptopropionic acid to the corresponding disulfide. The Mn(IV)-OH-PFOM compound reacted in water to form O₂, while Mn(V)-OH-PFOM was surprisingly indefinitely stable. It was observed that addition of alkali cations (K⁺, Rb⁺, and Cs⁺) led to the aggregation of Mn(IV)-OH-PFOM as analyzed by electron microscopy and DOSY NMR, while addition of Li⁺ and Na⁺ did not lead to aggregates. Aggregation leads to a lowering of the entropic barrier of the reaction without changing the free energy barrier. The observation that O₂ formation is fastest in the presence of Cs⁺ and ∼fourth order in Mn(IV)-OH-PFOM supports a notion of a tetramolecular Mn(IV)-hydroxo intermediate that is viable for O₂ formation in an oxide-based chemical environment. A bimolecular reaction mechanism involving a Mn(IV)-hydroxo based intermediate appears to be slower for O₂ formation.

The atom-efficient and environmentally benign catalytic hydrogenation of carboxylic acid esters to alcohols has been accomplished in recent years mainly with precious-metal-based catalysts, with few exceptions. Presented here is the first cobalt-catalyzed hydrogenation of esters to the corresponding alcohols. Unexpectedly, the evidence indicates the unprecedented involvement of ester enolate intermediates.

Organic derivatives of boronic acid are widely used reagents useful in various synthetic applications. A fundamental understanding and the exploration of new reaction pathways of boronic reagents with organometallic systems hold promise for useful advancement in chemical catalysis. Herein we present the reactions of simple boranes with dearomatized ruthenium pincer complexes based on PNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) or PNN (2-(di-tert-butylphosphinomethyl)-6-(diethylaminomethyl)pyridine) ligands. NMR studies revealed dehydrogenative addition of the borane B-H bond across the metal center and the ligand. Remarkably, new complexes were observed, which contain the boryl moiety at the benzylic carbon of the pincer ligand arm. X-ray crystal structures of new dearomatized boryl pincer complexes were obtained, and DFT calculations revealed mechanistic details of the adduct formation process through a dehydrogenative pathway. In addition, catalytic aryl-boron coupling reactions were explored. The new boryl pincer systems may possibly be useful in future postmodification techniques for ruthenium pincer complexes, as well as in catalytic B-B and B-C coupling reactions.

A compound combining the features of a molecular rotor and a photoswitch was synthesized and was shown to exist as three diastereomers, which interconvert via a reversible cyclic reaction scheme. Each of the three diastereomers was isolated, and by following the equilibration kinetics, activation barriers for all reactions were calculated. The results indicate that the properties of molecular switches depend heavily on their immediate chemical environment. The conclusions are important in the context of designing new switchable molecules and materials.

1-Phenyl-3-trifluoromethyl-1,4-dihydrobenzo[e] [1,2,4]triazin-4-yl is the first example of a hydrazyl radical that shows a reversible sharp spin transition fully completed within 5(1) K. The nominally first-order transition takes place at ca. 58(2) K and proceeds via subtle changes of intra- and interstack interactions between two similar structural phases. The low-temperature phase (5-60 K) is diamagnetic and has a singlet ground state (2J(exp) = -166.8 cm(-1), g(solid) = 2.0042, rho = 0.2%) stemming from a multicenter two-electron interaction. The high-temperature phase (60-300 K) is paramagnetic as a result of noninteracting S = 1/2 spins arising from weakly bound dimers.

A series of iron dicarbonyl complexes with bipyridine-based PNN pincer ligands were synthesized and characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ¹⁵N, ³¹P), IR spectroscopy, cyclic voltammetry, ⁵⁷Fe Mössbauer spectroscopy, XPS spectroscopy, and single-crystal X-ray diffraction. The complexes with the general formula [(R-PNN)Fe(CO)₂] (5: R-PNN=tBu-PNN=6-[(di-tert- butylphosphino)methyl]-2,2′-bipyridine, 6: R-PNN=iPr-PNN=6- [(diisopropylphosphino)methyl]-2,2′-bipyridine, and 7: R-PNN=Ph-PNN=6-[(diphenylphosphino)methyl]-2,2′-bipyridine) feature differently P-substituted PNN pincer ligands. Complexes 5 and 6 were obtained by reduction of the corresponding dihalide complexes [(R-PNN)Fe(X)₂] (1: R=tBu, X=Cl; 2: R=tBu, X=Br; 3: R=iPr, X=Cl; 4: R=iPr, X=Br) in the presence of CO. The analogous Ph-substituted complex 7 was synthesized by a reaction of the free ligand with iron pentacarbonyl. The low-spin complexes 5-7 (S=0) are diamagnetic and have distorted trigonal bipyramidal structures in solution, whereas in the solid state the geometries around the iron are best described as distorted square pyramidal. Compared to other structurally characterized complexes with these PNN ligands, shortened interpyridine C-C bonds of about 1.43 Å were measured. A comparison with known examples, theoretically described as metal complexes bearing bipyridine π-radical anions (bpy ^.-), suggests that the complexes can be described as Fe^I complexes with one electron antiferromagnetically coupled to the ligand-based radical anions. However, computational studies, at the NEVPT2/CASSCF level of theory, reveal that the shortening of the C-C bond is a result of extensive π-backbonding of the iron center into the antibonding orbital of the bpy unit. Hence, the description of the complexes as Fe ⁰ complexes with neutral bipyridine units is the favorable one. Innocent till proved guilty! Metrical parameters for the assignment of oxidation states of bipyridine ligands are challenged. A series of iron dicarbonyl complexes with bipyridine-based PNN pincer ligands were synthesized and fully characterized by various methods. Unusually short interpyridine C-C bonds were derived by X-ray diffraction (see scheme). The question if this is an effect of an intramolecular electron transfer or an effect of classical π-backbonding is addressed.

1,3,7,8-Tetraphenyl-4,8-dihydro-1H-imidazolo[4,5g][1,2,4]benzotriazin-4-yl (5), 8-(4-bromophenyl)-1,3,7-triphenyl-4,8-dihydro-1H-imidazolo[4,5g][1,2,4]benzotriazin-4-yl (6), and 8-(4-methoxyphenyl)-1,3,7-triphenyl-4,8-dihydro-1H-imidazolo[4,5g][1,2,4]benzotriazin-4-yl (7) were characterized by using X-ray diffraction crystallography, variable-temperature magnetic susceptibility studies, and DFT calculations. Radicals 5-7 pack in 1D stacks made of radical pairs with alternate short and long interplanar distances. The magnetic susceptibility ( vs. T) of radicals 5 and 6 exhibit broad maxima at (50 +/- 2) and (50 +/- 4)K, respectively, and are interpreted in terms of an alternating antiferromagnetic Heisenberg linear chain model with average exchange-interaction values of J=-31.3 and -35.4cm(-1) (g(solid)=2.0030 and 2.0028) and an alternation parameter a=0.15 and 0.38 for 5 and 6, respectively. However, radical 7 forms 1D columns of radical pairs with alternating distances; one of the interplanar distances is significantly longer than the other, which decreases the magnetic dimensionality and leads to discrete dimers with a ferromagnetic exchange interaction between the radicals (2J=23.6cm(-1), 2zJ=-2.8cm(-1), g(solid)=2.0028). Magnetic exchange-coupling interactions in 1,2,4-benzotriazinyl radicals are sensitive to the degree of slippage and inter-radical separation, and such subtle changes in structure alter the fine balance between ferro- and antiferromagnetic interactions.

There is continuing interest in determining essential structural features of polymer gels, which display photoelectric and/or thermoelectric behavior. One such gel is the blend, poly(4-vinylpyridine-co-butyl methacrylate)/poly(4- vinylpyridine), dissolved in liquid pyridine. Following extended aeration of a three-component mixture, which serves as a model for the gel side chain interactions, crystallization of a new molecule, 4-isopropylpyridine hydroxide (IPPOH), occurs. X-ray diffraction, DFT modeling, and spectroscopy were used to determine the structural, electronic, and luminescent properties of the crystal. The crystal structure reveals molecules forming head-to-tail, hydrogen-bonded chains without base stacking or marked interchain interaction. The molecular chains are characterized by moderately long-lived, blue-violet luminescence excited in the near-UV. Because these photoluminescent properties resemble those of the gel from which the crystals are derived, we may posit similar structural features in the gel for which direct structural analysis is not available.

The tri-rhenium(VI) capped Wells-Dawson polyoxometalate, [Re₃P₂W₁₅O₆₂]^6- with quaternary ammonium cations was synthesized by reacting the trivacant lacunary species, [P₂W₁₅O₅₆]^12- with [ReOCl₃(PPh₃)₂] in an organic solvent. Elemental analysis by thermogravimetry and inductively coupled plasma mass spectroctrometry confirmed the substitution of three rhenium atoms, single-crystal X-ray diffraction as well as infra red spectroscopy showed the complete Wells-Dawson structure. The presence of all three rhenium atoms in one cap is indicated by ³¹P nuclear magnetic resonance spectroscopy and the electron spin resonance spectrum shows that the tri-rhenium(V) species with three unpaired electrons is low spin, S = 1/2.

Metal-ligand cooperation (MLC) plays an important role in catalysis. Systems reported so far are generally based on a single mode of MLC. We report here a system with potential for MLC by both amine-amide and aromatization- dearomatization ligand transformations, based on a new class of phosphino-pyridyl ruthenium pincer complexes, bearing sec-amine coordination. These pincer complexes are effective catalysts under unprecedented mild conditions for acceptorless dehydrogenative coupling of alcohols to esters at 35 degrees C and hydrogenation of esters at room temperature and 5 atm H-2. The likely actual catalyst, a novel, crystallographically characterized monoanionic de-aromatized enamido-Ru-II complex, was obtained by deprotonation of both the N-H and the methylene proton of the N-arm of the pincer ligand.

The synthesis of terminal as well as internal olefins was achieved by the one-step olefination of alcohols with sulfones catalyzed by a ruthenium pincer complex. Furthermore performing the reaction with dimethyl sulfone under mild hydrogen pressure provides a direct route for the replacement of alcohol hydroxy groups by methyl groups in one step.

An expedient approach to the synthesis of well soluble symmetrical dialkyl-substituted alpha-oligofurans containing up to 8 pi-conjugated furan heterocycles is reported. An ultimate symmetry and high solubility of these alpha-oligofurans were guaranteed using the 3,3'-diheptyl-2,2'-bifuran core and its symmetrical elongation through Suzuki-Miyaura or Stille cross-couplings. 3,3'-Diheptyl-2,2'-bifuran was prepared from 2,2'-bifuran-3,3'-dicarbaldehyde by the Wittig olefination and subsequent Pd/C-catalyzed transfer hydrogenation. The most appropriate access to 2,2'-bifuran-3,3'-dicarbaldehyde was achieved through a regioselective lithiation of 3-furanaldehyde acetal followed by CuCl2-induced homocoupling and deprotection. Single crystal X-ray analysis of 2,2'-bifuran-3,3'-dicarbaldehyde revealed anti-arrangement of the furan rings in planar molecules and an unexpected tight herringbone-type packing in crystals.

Air stable 1,3,7-triphenyl-1,4-dihydrothiazolo[5',4':4,5]benzo[1,2-e][1,2,4]triazin-4-yl packs in 1D pi stacks made of radical pairs with alternate short and long interplanar distances. The magnetic susceptibility exhibits a broad maximum at 73 +/- 5 K and is interpreted in terms of an alternating antiferromagnetic Heisenberg linear chain model with an average exchange interaction of J = -43.8 cm(-1) and an alternation parameter alpha = 0.3 (g(solid) = 2.0028). The enhanced overlap between the pi-extended SOMO orbitals leads to strong antiferromagnetic interactions along the chains (J(1) = -87.6 cm(-1) and J(2) = -26.3 cm(-1)).

The dearomatized complex cis-[Re(PNP^tBu*)(CO)₂] (4) undergoes cooperative activation of Cî - N triple bonds of nitriles via [1,3]-addition. Reversible C-C and Re-N bond formation in 4 was investigated in a combined experimental and computational study. The reversible formation of the ketimido complexes (5-7) was observed. When nitriles bearing an alpha methylene group are used, reversible formation of the enamido complexes (8 and 9) takes place. The reversibility of the activation of the nitriles in the resulting ketimido compounds was demonstrated by the displacement of p-CF ₃-benzonitrile from cis-[Re(PNP^tBu-N=CPh ^pCF3)(CO)₂] (6) upon addition of an excess of benzonitrile and by the temperature-dependent [1,3]-addition of pivalonitrile to complex 4. The reversible binding of the nitrile in the enamido compound cis-[Re(PNP ^tBu-HNC=CHPh)(CO)₂] (9) was demonstrated via the displacement of benzyl cyanide from 9 by CO. Computational studies suggest a stepwise activation of the nitriles by 4, with remarkably low activation barriers, involving precoordination of the nitrile group to the Re(I) center. The enamido complex 9 reacts via β-carbon methylation to give the primary imino complex cis-[Re(PNP^tBu-HN=CC(Me)Ph)(CO)₂]OTf 11. Upon deprotonation of 11 and subsequent addition of benzyl cyanide, complex 9 is regenerated and the monomethylation product 2-phenylpropanenitrile is released. Complexes 4 and 9 were found to catalyze the Michael addition of benzyl cyanide derivatives to α,β-unsaturated esters and carbonyls.

The aromatization-dearomatization reaction of pincer-type complexes prompted by protonation-deprotonation of the pincer "arm" is a key step in bond activation chemistry and atom-economic catalytic transformations. However, the possibility of double deprotonation of ancillary pincer ligands is rarely discussed in the literature. Here we report on square-planar cationic nickel(II) complexes of PNP^R type ligands (PNP = 2,6- bis[(dialkylphosphino)methyl]pyridine with R = ⁱPr, ^tBu), which can be readily transformed into the doubly deprotonated anionic species. The complexes [Ni(PNP^R)Cl]Cl (3, R = ⁱPr; 4, R = ^tBu) are readily prepared from the reaction of NiCl ₂·6H₂O and the PNP^R ligand in THF. Treatment of the cationic chloro complexes 3 and 4 with 2 equiv of MeLi gives the nickel(II) methyl complexes [Ni(PNP^R*)Me] (7, R = ⁱPr; 8, R = ^tBu), the asterisk indicates the deprotonated pincer arm). Reaction of 7 and 8 with an additional 1 equiv of MeLi gives the anionic complexes [Li(DME)₃][Ni(PNP^iPr**)Me] (9-DME, DME = 1,2-dimethoxyethane) and [Li(Et₂O)₂] [Ni(PNP^tBu**)(Me)] (10-Et₂O), respectively. Single-crystal X-ray diffraction studies exhibit doubly deprotonated PNP-pincer ligands coordinated to a nickel(II) center. DFT calculations, as well as multinuclear NMR spectroscopy and the X-ray structures, suggest a conjugated π-system with delocalization of the negative charge throughout the carbon backbone of the pincer ligand. The electrophilic attack of complex 9 by CO ₂ and tautomerization gives [Li][Ni(PNP^iPr*-COO)(Me) ] (11). The dearomatized complex that is formed contains an exocyclic methylene carbon atom and a carboxylate moiety adjacent to the second pincer arm.

Polymer-inorganic nanoparticle composites are an area of great research interest. Inorganic fullerene-like (IF) structures and inorganic nanotubes (INT) are used for producing composite materials with specific goals of reinforcement of the polymer and ameliorating its thermal stability. Here, a composite material containing INT and conducting polymer (polyaniline (PANI)) is synthesized by an in situ oxidative polymerization of the monomer in the presence of WS₂ nanotubes. The structure and electrical behavior of PANI/INT composite is studied and compared with the results of pristine PANI (synthesized under the same conditions without INT). Most remarkably, INT-WS₂ are found to play the role of an active doping agent. The highest conductivity is obtained for 0.85 wt% (ca. 0.06 at%) nanotubes content, two orders of magnitude higher than that of pristine PANI. This work suggests a new approach to control the host-guest interaction in the polymer nanocomposite via (Lewis) acid-base equilibrium. A composite material containing WS ₂ nanotubes (INT-WS₂) and conducting polymer (polyaniline (PANI)) is obtained by an in situ oxidative polymerization of the monomer in the presence of the INT-WS₂. Electron transfer from PANI to the INT-WS₂ is shown to produce a peak in the conductivity at 0.85 wt% (0.2 at%) of the nanotubes.

The synthesis and characterization of new iron pincer complexes bearing bipyridine-based PNN ligands is reported. Three phosphine-substituted pincer ligands, namely, the known ^tBu-PNN (6-((di-tert-butylphosphino) methyl)-2,2′-bipyridine) and the two new ⁱPr-PNN (6-((di-iso-propylphosphino)methyl)-2,2′-bipyridine) and Ph-PNN (6-((diphenylphosphino)methyl)-2,2′-bipyridine) ligands were synthesized and studied in ligation reactions with iron(II) chloride and bromide. These reactions lead to the formation of two types of complexes: mono-chelated neutral complexes of the type [(R-PNN)Fe(X)₂] and bis-chelated dicationic complexes of the type [(R-PNN)₂Fe]²⁺. The complexes [(R-PNN)Fe(X)₂] (1: R = ^tBu, X = Cl, 2: R = ^tBu, X = Br, 3: R = ⁱPr, X = Cl, and 4: R = ⁱPr, X = Br) are readily prepared from reactions of FeX₂ with the free R-PNN ligand in a 1:1 ratio. Magnetic susceptibility measurements show that these complexes have a high-spin ground state (S = 2) at room temperature. Employing a 2-fold or higher excess of ⁱPr-PNN, diamagnetic hexacoordinated dicationic complexes of the type [( ⁱPr-PNN)₂Fe](X)₂ (5: X = Cl, and 6: X = Br) are formed. The reactions of Ph-PNN with FeX₂ in a 1:1 ratio lead to similar complexes of the type [(Ph-PNN)₂Fe](FeX₄) (7: X = Cl, and 8: X = Br). Single crystal X-ray studies of 1, 2, 4, 6, and 8 do not indicate electron transfer from the Fe^II centers to the neutral bipyridine unit based on the determined bond lengths. Density functional theory (DFT) calculations were performed to compare the relative energies of the mono-and bis-chelated complexes. The doubly deprotonated complexes [(R-PNN*)₂Fe] (9: R = ⁱPr, and 10: R = Ph) were synthesized by reactions of the dicationic complexes 6 and 8 with KO ^tBu. The dearomatized nature of the central pyridine of the pincer ligand was established by X-ray diffraction analysis of single crystals of 10. Reactivity studies show that 9 and 10 have a slightly different behavior in protonation reactions.

A cationic Rh(III) aryl-methyl complex, bearing a thiophosphoryl-based SCS-type pincer ligand, undergoes facile migratory insertion upon addition of CO, thereby affording a Rh(III) aryl-acetyl complex. This reactivity diverges from that of structurally analogous Rh(III) aryl-methyl complexes of phosphine-based PCP- and PCN-type pincer ligands, which have been previously shown to undergo C-C reductive elimination upon addition of CO, thereby giving C-C agostic Rh(I) complexes. A comparative DFT study of CO migratory insertion in the SCS and PCP complexes reveals that the difference in reactivity originates from the higher electrophilicity of the sulfur atoms of the SCS ligand relative to the phosphorus atoms of the PCP ligand. This leads to decreased Rh → CO π back-donation in the SCS system, resulting in CO labilization and facilitating the metal-to-CO methyl migration. In the PCP system it leads to stronger Rh-CO bonding, which enhances OC → Rh → arene σ donation, thereby weakening the Rh-C_ipso bond and facilitating metal-to-C_ipso methyl migration.

A comparative study of two structural isomers highlights the advantages of bifuran vs. bithiophene units in conjugated systems, such as higher fluorescence, solubility, and increased stability of the oxidized species. Importantly, we have found that the small bifuran unit bestows the advantages found in longer oligofurans, and should be considered in the rational design of π-conjugated systems.

Benzyl cations are highly reactive compounds involved as intermediates in various chemical and biochemical processes. In this work metal coordination was utilized to stabilize different coordinated modes of benzyl cations, including methylene arenium (MA), π-benzyl, and σ-benzyl complexes. Two bidentate ligand frameworks, diphenylphosphinoethane (dppe) and di-tert- butylphosphinopropane (dtpp), were studied. η²-Coordination to Pd(II) allows for the characterization and studies of the reactivity of the otherwise unobserved methylene arenium species under ambient conditions. The relative stability and electronic structure of the three forms of the coordinated benzyl molecule, η²-MA, η¹-σ- benzylic, and η³- π-benzylic, were investigated experimentally and computationally. The MA and π-benzylic structures are preferred in the absence of counteranions, while the dtpp bulky ligand contributes to stabilization of the methylene arenium form. Counteranions have a significant influence on the relative stability. The triflate anion stabilizes the σ-benzylic form upon coordination to the metal center or the methylene arenium form as a result of compensation of positive charge on the MA ring. Use of the noncoordinating BArF counteranion promotes conversion to the π-benzylic form.

A (PNP)Co(i)methyl diamagnetic complex formally loses an H atom from the pincer ligand, exhibiting a long-range metal–ligand cooperation in what may be considered as an unusual example of “C–H cleavage”. Spectroscopic data indicate that the product is a neutral Co(i) complex with a radical delocalized in the ligand backbone.

We report the first transistor based on inorganic nanotubes exhibiting mobility values of up to 50 cm² V^-1 s^-1 for an individual WS₂ nanotube. The current-carrying capacity of these nanotubes was surprisingly high with respect to other low-dimensional materials, with current density at least 2.4 × 10⁸ A cm^-2. These results demonstrate that inorganic nanotubes are promising building blocks for high-performance electronic applications.

Despite considerable interest in ruthenium carbonyl pincer complexes and their substantial catalytic activity, there has been relatively little study of the isoelectronic ruthenium nitrosyl complexes. Here we describe the synthesis and reactivity of several complexes of this type as well as the catalytic activity of complex 6. Reaction of the PNP ligand (PNP = 2,6-bis( ^tBu₂PCH₂)pyridine) with RuCl ₃(NO)(PPh₃)₂ yielded the Ru(II) complex 3. Chloride displacement by BAr^F- (BAr^F- = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) gave the crystallographicaly characterized, linear NO Ru(II) complex 4, which upon treatment with NaBEt ₃H yielded the Ru(0) complexes 5. The crystallographically characterized Ru(0) square planar complex 5·BF₄ bears a linear NO ligand located trans to the pyridilic nitrogen. Further treatment of 5·BF₄ with excess LiOH gave the crystallographicaly characterized Ru(0) square planar, linear NO complex 6. Complex 6 catalyzes the dehydrogenative coupling of alcohols to esters, reaching full conversion under air or under argon. Reaction of the PNN ligand (PNN = 2-(^tBu ₂PCH₂)-6-(Et₂NCH₂)pyridine) with RuCl₃(NO)(H₂O)₂ in ethanol gave an equilibrium mixture of isomers 7a and 7b. Further treatment of 7a + 7b with 2 equivalent of sodium isopropoxide gave the crystallographicaly characterized, bent-nitrosyl, square pyramidal Ru(II) complex 8. Complex 8 was also synthesized by reaction of PNN with RuCl₃(NO)(H₂O)₂ and Et₃N in ethanol. Reaction of the "long arm" PN²N ligand (PN ²N = 2-(^tBu₂PCH₂-)-6-(Et ₂NCH₂CH₂)pyridine) with RuCl ₃(NO)(H₂O)₂ in ethanol gave complex 9, which upon treatment with 2 equiv of sodium isopropoxide gave complex 10. Complex 10 was also synthesized directly by reaction of PN²N with RuCl ₃(NO)(H₂O)₂ and a base in ethanol. A noteworthy aspect of these nitrosyl complexes is their preference for the Ru(0) oxidization state over Ru(II). This preference is observed with both aromatized and dearomatized pincer ligands, in contrast to the Ru(II) oxidation state which is preferred by the analogous carbonyl complexes.

Rare cases of directly observed reductive elimination (RE) of methyl halides from Rh^III complexes are described. Treatment of the coordinatively unsaturated complexes [(^tBuPNP)Rh(CH ₃)X][BF₄] (1-3, X = I, Br, and Cl; ^tBuPNP = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine) with coordinating and noncoordinating compounds results in the formation of the corresponding free methyl halides and Rh^I complexes. The rate increase of CH ₃I and CH₃Br RE in the presence of polar aprotic solvents argues in favor of an S_N2 RE mechanism. However, the RE of CH ₃Cl is faster in polar protic solvents, which argues in favor of a concerted C-Cl RE. The RE of methyl halides from complexes 1-3 is induced by steric factors, as treatment of the less bulky complexes [(ⁱPrPNP) Rh(CH₃)X][BF₄] (19-21; X = I, Br, Cl, respectively) with coordinating compounds leads to the formation of the adducts complexes rather than RE of the methyl halides. The accumulated evidence suggests that the RE process is nonassociative.

The oxidation of alcohols to carboxylic acids is an important industrial reaction used in the synthesis of bulk and fine chemicals. Most current processes are performed by making use of either stoichiometric amounts of toxic oxidizing agents or the use of pressurized dioxygen. Here, we describe an alternative dehydrogenative pathway effected by water and base with the concomitant generation of hydrogen gas. A homogeneous ruthenium complex catalyses the transformation of primary alcohols to carboxylic acid salts at low catalyst loadings (0.2 mol%) in basic aqueous solution. A consequence of this finding could be a safer and cleaner process for the synthesis of carboxylic acids and their derivatives at both laboratory and industrial scales.

The synthesis of novel PNN ruthenium pincer complexes based on 2,2′-dipyridinemethane phosphine derivatives, as well as on 2,2′-oxobispyridine phosphine ligands, and their reactivity toward dearomatization and cyclometalation are described. The dearomatized compounds 7a,b undergo cyclometalation to yield complexes 8a,b. In order for cyclometalation to proceed, the coordination sphere around the Ru center has to rearrange, and this depends on the flexibility of the system, showing that the cyclometalation is qualitatively faster in the case of the dimethyl derivative 7a than in the case of the spyrocyclopentyl derivative 7b. The cyclometalation occurs diastereoselectively and leads to only one diastereomer of the cyclometalated compounds. In the case of the 2,2′-oxobispyridine complex 6c, the dearomatized complex was too unstable to be isolated; however it was possible to isolate and characterize a stable dicarbonyl-dearomatized ruthenium(II) complex, 9c, when the deprotonation was performed under a CO atmosphere. Dearomatization of 6a under CO also led to dicarbonyl-dearomatized ruthenium(II) complex 9a, which slowly rearranged into the dicarbonyl-aromatized ruthenium(0) complex 10a. These complexes were tested in catalytic alcohol-amine coupling, esterification of primary alcohols, and hydrogenation of secondary amides. Moderate activity was observed in hydrogenation of amides to alcohols and amines and low activity in the other transformations, owing mainly to the formation of stable cyclometalated compounds.

Halogen bonding between complementary organic monolayers was directly observed in an organic environment using force spectroscopy. This non-covalent interaction is significantly affected by the nature of the organic media. We also demonstrated the effect of lateral packing interactions on the optical properties of the monolayers.x

7-(Fur-2-yl) benzotriazinyl 1 is the first example of a hydrazyl radical dimer with a thermally accessible triplet state. The triplet exciton (vertical bar D vertical bar = 0.018 cm(-1), vertical bar E vertical bar = 0.001 cm(-1)) was observed by solid-state VT-EPR spectroscopy between 5 and 140 K. VT crystallography, DFT calculations and magnetic susceptibility studies reveal a strong temperature dependence of the intra-dimer exchange interaction with J/k similar to -254 + 0.0007T(2).

Lubricating nanoparticles: The effect of doping semiconductor hollow closed-fullerene-like nanoparticles of MoS ₂ and WS ₂ has been overlooked to date. Rhenium doping of these nanoparticles leads to a marked increase in the nanoparticle's conductivity, reduced agglomeration, and a great reduction in friction and wear (see picture) that approaches superlubricity.

The PNS pincer-type ligand 1 and the novel Ru(PNS) complexes 2-8 were synthesized and characterized. The (PNS)RuH(Cl)CO complex 2 was prepared by reaction of ligand 1 with RuH(Cl)CO(PPh ₃) ₃. 2 reacted with KHMDS (potassium bis(trimethylsilyl)amide) to form the symmetrical dimeric complex 4 via the intermediacy of the dearomatized complex (PNS*)Ru(H)CO 3, in which deprotonation of the benzylic-S "arm" took place. Reaction of 2 with excess NaH gave the dimeric 4, by a formal intermolecular attack of the benzylic "arm" on a second ruthenium center. Complex 4 underwent spontaneous transformation in solution to the dinuclear complex 5 via C-S bond cleavage, resulting in the loss of a S-bound ^tBu group. Treatment of 2 with KHMDS in the presence of PEt ₃ resulted in the trapping of intermediate 3 in the form of the dearomatized complex 8. Reaction of 2 with LiHBEt ₃ gave the trans-dihydride complex 6, which reacted with CO ₂ to give the formato complex 7, in which the formato ligand is located trans to the hydride. Complexes 2, 4, and 5 were also investigated as catalysts for the dehydrogenative coupling of alcohols with amines.

Taking advantage of the synthetic availability and solubility of long oligofurans, their reactivity toward dienophiles was studied as a model for the rarely investigated reactivity of long conjugated systems. Unlike oligoacenes, the reactivity of oligofurans decreases or remains constant with increasing chain length. Terminal ring cycloadducts of oligofurans are kinetically and thermodynamically favored, whereas central ring cycloadducts are preferred in oligoacenes, because of the different driving forces in the two reactions: π-conjugation in oligofurans and aromatization/dearomatization in oligoacenes.

An antimony(V) containing α-Keggin type acidic polyoxometalate, H ₄PSbMo ₁₁O ₄₀, was prepared by reacting NaMoO ₄, H ₃PO ₄ and Sb ₂O ₃ in the presence of aqua regia to appraise its reactivity compared to the well known vanadate analog, H ₄PVMo ₁₁O ₄₀. Characterization was by X-ray diffraction, MALDI-TOF MS, IR, UV-vis and ³¹P NMR spectroscopy. Catalytic redox reactions, such as oxidative dehydrogenation using O ₂ and N ₂O as terminal oxidants were studied and showed very different reactivity of H ₄PSbMo ₁₁O ₄₀ versus H ₄PVMo ₁₁O ₄₀. It was found by DFT calculations that in contrast to analogous H ₄PVMo ₁₁O ₄₀ where vanadium centered catalysis is observed, in H ₄PSbMo ₁₁O ₄₀ catalysis is molybdenum and not antimony centered.

We report here that the undesired hydrodehalogenation in cross-coupling reactions with fluorinated substrates involves water as a possible hydrogen source. Moreover, the product distribution (hydrodehalogenation vs carbon-carbon coupling) can be controlled by varying the phosphine substituents. Significant hydrodehalogenation occurs prior to the formation of Ar _F-Pd(II)-Br complexes. DFT calculations were used to evaluate a direct hydrodehalogenation route with a phosphine and water. These findings provide new mechanistic insight into aryl-Br bond activation with fluorinated substrates and selective arene functionalization.

In this work, we prepared a series of new conjugated polyselenophenes that, in the 3,4-positions of the selenophene ring, have oxygen or sulfur substituents bridged by a phenylene moiety. Such substitution of a conjugated backbone produces a skeleton that has only planar units, does not have stereo centers, and offers the potential to structurally modify the polymer without impairing its conjugation. The reported polyselenophenes exhibit significantly different properties as a function of the heteroatom. The selenophene backbone combined with a phenylene periphery creates the rare combination of a low-band gap, low HOMO energy level, and a flat skeleton, which is desired for many optoelectronic applications. The properties of the phenylene-bridged polyselenophenes were compared with those of their polythiophene analogs. The polyselenophenes obtained in this work have a lower band gap and higher planarity than polythiophenes and their monomers electropolymerize more easily. Theoretical studies support the experimental findings about rigidity and band gap changes.

The superconducting critical temperature, T _C, of thin Nb films is significantly modified when gold nanoparticles (NPs) are chemically linked to the Nb film, with a consistent enhancement when using 3 nm long disilane linker molecules. The T _C increases by up to 10% for certain linker length and NP size. No change is observed when the nanoparticles are physisorbed with nonlinking molecules. Electron tunneling spectra acquired on the linked NPs below T _C typically exhibit zero-bias peaks. We attribute these results to a pairing mechanism coupling electrons in the Nb and the NPs, mediated by the organic linkers.

The complex bis(acetonitrile)bis(triphenylphosphine)ruthenium(II) sulfate [Ru(PPh ₃) ₂(NCCH ₃) ₂(SO ₄)], fully characterized spectroscopically and by a single crystal X-ray study, catalyzes at 110 °C the direct transformation of primary alcohols to the corresponding acetals with liberation of molecular hydrogen. The formation of acetals proceeds via direct substitution of the hydroxy group of the hemiacetal intermediate by an alcohol molecule. The closely related bis(triphenylphosphine) ruthenium(II) acetate [Ru(PPh ₃) ₂(OAc) ₂] catalyzes the conversion of primary alcohols to the corresponding esters rather than acetals.

The new, structurally characterized hydrido carbonyl tetrahydridoborate iron pincer complex [(iPr-PNP)Fe(H)(CO)(?1-BH4)] (1) catalyzes the base-free hydrogenation of ketones to their corresponding alcohols employing only 4.1 atm hydrogen pressure. Turnover numbers up to 1980 at complete conversion of ketone were reached with this system. Treatment of 1 with aniline (as a BH3 scavenger) resulted in a mixture of trans-[(iPr-PNP)Fe(H)2(CO)] (4?a) and cis-[(iPr-PNP)Fe(H)2(CO)] (4?b). The dihydrido complexes 4?a and 4?b do not react with acetophenone or benzaldehyde, indicating that these complexes are not intermediates in the catalytic reduction of ketones. NMR studies indicate that the tetrahydridoborate ligand in 1 dissociates prior to ketone reduction. DFT calculations show that the mechanism of the iron-catalyzed hydrogenation of ketones involves alcohol-assisted aromatization of the dearomatized complex [(iPr-PNP*)Fe(H)(CO)] (7) to initially give the Fe0 complex [(iPr-PNP)Fe(CO)] (21) and subsequently [(iPr-PNP)Fe(CO)(EtOH)] (38). Concerted coordination of acetophenone and dual hydrogen-atom transfer from the PNP arm and the coordinated ethanol to, respectively, the carbonyl carbon and oxygen atoms, leads to the dearomatized complex [(iPr-PNP*)Fe(CO)(EtO)(MeCH(OH)Ph)] (32). The catalyst is regenerated by release of 1-phenylethanol, followed by dihydrogen coordination and proton transfer to the coordinated ethoxide ligand.

The electronic properties, rigidity, and planarity of conjugated polymers of the PEDOT type were tuned by changing the conjugated backbone from polythiophene to the more rigid polyselenophene and by replacing one or both oxygen atoms in the ethylenedioxy bridge (peripheral ring) with sulfur. While the band gaps of the obtained polyselenophenes are similar to 1.4 eV, the orbital energy levels shift significantly because of changes in the electronic nature of the peripheral ring and the peak-width of the absorbance spectrum varies because of changes to backbone rigidity.

Electron-rich PNP-and PNN-type ruthenium(II) hydrido borohydride pincer complexes, [RuH(BH₄)(^tBu-PNP)] (tBu-PNP = (2,6-bis(di-tert-butylphosphinomethyl)pyridine) (5) and [RuH(BH ₄)(^tBu-PNN)] (^tBu-PNN = 2-di-tert- butylphosphinomethyl-6-diethylaminomethylpyridine) (6), were prepared from their corresponding N2-bridged dinuclear Ru(II) complexes [(^tBu-PNP) RuCl₂]₂(μ-N₂) (3) and [(^tBu-PNN) RuCl₂]₂(μ-N₂) (4), respectively. The X-ray structure of 5 reveals a BH₄ -anion η2 coordinated to ruthenium through two bridging hydrides. A variable-temperature ¹H NMR study of 6 exhibits interesting fluxional behavior of the BH4 -ligand. Similarly, the Ru(II) hydrido borohydride complex 9, in which the BH₄ -moiety is coordinated in a η1 bonding mode, was obtained by reaction of [RuCl ₂(PPh₃)(ⁱPr-PNP)] (iPr-PNP = 2,6-bis(diisopropylphosphinomethyl)pyridine) (8) with two equivalents of NaBH4 at room temperature. The hydrido borohydride pincer complexes 5, 6, and 9 catalyze the acceptorless dehydrogenative coupling of primary alcohols to esters and the dehydrogenation of secondary alcohols to the corresponding ketones, accompanied by evolution of hydrogen gas. The reactivity follows the order 6 > 9 > 5. With the hydrido borohydride complex 6 as catalyst, high yields (up to 98%) and high turnover numbers (TON∼1000) were obtained in the dehydrogenation of primary alcohols under mild and neutral conditions. In addition, 6 effectively catalyzes the hydrogenation of nonactivated aromatic and aliphatic esters to the corresponding alcohols with TON ∼200 under a relatively mild pressure of dihydrogen and neutral and homogeneous conditions. Thus, an efficient homogeneous catalytic system for the dehydrogenation- hydrogenation reactions of alcohols is developed, which is relevant to the current interest in hydrogen storage.

A series of new low-band-gap thieno- or selenolo-fused polyselenophenes (P5 and P6) and selenolo-fused polythiophene (P4) (as well as previously reported thieno-fused polythiophene, P3) was prepared systematically by electropolymerization (P4-P6) and by solid-state polymerization (P3, P5 and P6). The 2,5-dibrominated monomers (3Br(2), 5Br(2), and 6Br(2)) undergo solid-state polymerization under slight heating and produce insoluble P3, P5, and P6 as black conducting powders. The spectroelectrochemically measured optical band gaps of P4-P6 films are 0.96, 0.72, and 0.76 eV, respectively. DFT calculations performed on P3-P6 provide excellent estimations of the experimental band gaps of these polymers. The band gap of the polyselenophenes (P5 and P6) is 0.2 eV lower than that of the corresponding polythiophenes (P3 and P4). We introduced a new scheme for band gap control in conjugated polymers by replacing the sulfur atom with a selenium atom in the main and/or peripheral ring, which leads to significant and predictable changes in the band gap of the polymers. This is due to the lower aromaticity of a selenophene ring compared to a thiophene ring. Thus, we have achieved band gap control in very low band gap (similar to 0.7-1.0 eV) polymers through the use of different combinations of selenium and sulfur atoms in the main and peripheral rings.

Treatment of 7,8-benzo[h]quinoline (bhq-H, 1) and 10-methyl benzo[h]quinoline (bhq-Me, 3) with [Rh(C₂H₄) ₂(THF)₂][BF₄] resulted in double C-H activation of aliphatic and aromatic C-H bonds, yielding the Rh(III) complexes 4 and 5, respectively. The structures of 4 and 5 were revealed by X-ray diffraction. The reaction of 1 with two other slightly different rhodium precursors, [Rh(olefin)_n(THF)₂][BF₄] (COE (n = 2), COD (n = 1)), led to completely different products, a dinuclear complex 7 and a trinuclear complex 6, respectively, which were characterized by X-ray diffraction. Complex 6 exhibits a rare linear Rh-Rh-Rh structure. Utilizing excess of 1 with [Rh(COD)(THF)₂][BF₄] led to the formation of a new product 8 with no C-H bond activation taking place. Additional C-H activation products of 1, cationic and neutral, in the presence of P ⁱPr₃ (9a, 9b and 10) are also presented.

A highly active iron catalyst for the hydrogenation of carbon dioxide and bicarbonates works under remarkably low pressures and achieves activities similar to some of the best noble metal catalysts. A mechanism is proposed involving the direct attack of an iron trans‐dihydride on carbon dioxide, followed by ligand exchange and dihydrogen coordination.

Reductions made easy: A highly efficient iron catalyst effects the homogeneous hydrogenation of ketones under very mild conditions (see scheme). A mechanism including the insertion of the ketone into the Fe-H bond, followed by addition of hydrogen to a dearomatized intermediate is proposed.

Figure Presented: New pincer ruthenium complexes (2-6) based on the new bipyridine-NHC ligand 1 were prepared and studied, resulting in an efficient catalytic hydrogenation of esters to the corresponding alcohols under mild conditions. Reaction of the ligand 1 with RuH(Cl)CO(PPh₃) ₃, followed by reaction with one equivalent of the base KHMDS, gave the mixed phosphine-NHC complex 2, incorporating a C-H-activated bipyridine ligand. Complex 2 has an octahedral structure containing two phosphorus atoms trans to each other, a hydride trans to the NHC ligand, and CO trans to the C-H-activated carbon of the bipyridine ligand. Using the precursor complex Ru(p-cymene)Cl₂(CO), reaction with 1 followed by treatment of the intermediate product with one equivalent of KHMDS resulted in formation of the dichloride pincer complexes 3a and 3b, which are in equilibrium, as indicated by variable-temperature ¹H NMR. Complex 3a is an octahedral, neutral, and symmetric complex with the CO ligand positioned trans to the central pyridine group of the pincer ligand and the two chlorides trans to each other, as indicated by single-crystal X-ray diffraction. Complex 3b is cationic, with an outer-sphere chloride. Reaction of the NHC ligand 1 with LiHMDS at low temperature followed by addition of RuH(Cl)CO(PPh₃)₃ resulted in the mixed phosphine-NHC complex 4, which has an octahedral structure containing phosphorus trans to the hydride, a CO trans to the NHC ligand, and an outer-sphere chloride. Chloride substitution by BAr^F- gave the X-ray-characterized complex 5. Deprotonation of complex 4 with KHMDS resulted in formation of the dearomatized complex 6. The in situ prepared 6 (from complex 4 and an equivalent of base) is among the best catalysts known for the hydrogenation of nonactivated esters to the corresponding alcohols under mild conditions.

Sequential addition of CO molecules to cationic aryl-hydrido Rh ^III complexes of phosphine-based (PCP) pincer ligands was found to lead first to C-H reductive elimination and then to C-H oxidative addition, thereby demonstrating a dual role of CO. DFT calculations indicate that the oxidative addition reaction is directly promoted by CO, in contrast to the commonly accepted view that CO hinders such reactions. This intriguing effect was traced to repulsive JT interactions along the aryl-Rh-CO axis, which are augmented by the initially added CO ligand (due to antibonding interactions between occupied Rh d_π orbitals and occupied π orbitals of both CO and the arene moiety), but counteracted by the second CO ligand (due to significant π back-donation). These repulsive interactions were themselves linked to significant weakening of the π-acceptor character of CO in the positively charged rhodium complexes, which is concurrent with an enhanced o-donating capability. Replacement of the phosphine ligands by an analogous phosphinite-based (POCOP) pincer ligand led to significant changes in reactivity, whereby addition of CO did not result in C-H reductive elimina-tion, but yielded relatively stable mono- and dicarbonyl aryl-hydrido POCOP-Rh ^III complexes. DFT calculations showed that the stability of these complexes arises from the higher electrophilicity of the POCOP ligand, relative to PCP, which leads to partial reduction of the excessive π-electron density along the aryl-Rh-CO axis. Finally, comparison between the effects of CO and acetonitrile on C-H oxidative addition revealed that they exhibit similar reactivity, despite their markedly different electronic properties. However, DFT calculations indicate that the two ligands operate by different mechanisms.

The complex (PNP)Ir^I(CH₂COCH₃) 2 (PNP = 2,6-bis((di-tert-butylphosphino)methyl)pyridine) was prepared by reaction of the dearomatized, electron-rich complex (PNP)Ir^I(COE) (1; PNP* = deprotonated PNP, COE = cyclooctene) with acetone. Upon treatment with CO, complex 2 undergoes a surprising elimination of acetone to form the dearomatized species (PNP)Ir^I(CO) (4), involving proton migration from the ligand "arm" to the acetonyl moiety. DFT studies reveal that this process occurs via the square-pyramidal intermediate 2+CO, formed upon CO coordination to 2, in which the acetonyl moiety is located at the apical position prior to proton migration. Reaction of 2 with H₂ (D₂) indicates an equilibrium between complex 2 and the nonaromatic (PNP)Ir^III(H) (CH₂COCH₃) complex 2b, which is the species that actually activates H₂ to exclusively form the trans-dihydride (PNP)Ir ^III(H)₂(CH₂COCH₃) (5a) and activates D₂ to form the trans-hydride-deuteride 5b with benzylic-D incorporation, as also corroborated by DFT studies. Interestingly, benzene C-H activation by complex 2 results in formation of the complex (PNP)Ir ^I(C₆H₅) (6a) and elimination of acetone. DFT studies show that the benzene C-H bond is actually activated by the dearomatized "bare" (PNP)Ir^I intermediate 2c, formed upon acetone elimination from 2.

The oxygenation of sulfides to the corresponding sulfoxides catalyzed by H₅PV₂Mo₁₀O₄₀ and other acidic vanadomolybdates has been shown to proceed by a low-temperature electron transfer-oxygen transfer (ET-OT) mechanism. First, a sulfide reacts with H ₅PV₂Mo₁₀O₄₀ to yield a cation radical-reduced polyoxometalate ion pair, R₂^+·, H₅PV^IVV^VMo₁₀O₄₀, that was identified by UV-vis spectroscopy (absorptions at 650 and 887 nm for PhSMe ^+· and H₅PV^IVV^VMo ₁₀O₄₀) and EPR spectroscopy (quintet at g = 2.0079, A = 1.34 G for the thianthrene cation radical and the typical eight-line spectrum for V^IV). Next, a precipitate is formed that shows by IR the incipient formation of the sulfoxide and by EPR a VO²⁺ moiety supported on the polyoxometalate. Dissolution of this precipitate releases the sulfoxide product. ET-OT oxidation of diethylsulfide yielded crystals containing [V(O)(OSEt₂)_x(solv)_5-x]²⁺ cations and polyoxometalate anions. Under aerobic conditions, catalytic cycles can be realized with formation of mostly sulfoxide (90%) but also some disulfide (10%) via carbon-sulfide bond cleavage.

A ditopic 1,2-bis(2,2′-bipyridyl-6-yl)ethyne ligand, L, has been synthesized for the first time by consecutive Suzuki and Sonogashira coupling reactions either in a one- or two-step synthesis. Coordination of L with some first-row transition metals, Fe, Mn and Co showed a very rich structural diversity that can be obtained with this ligand. Reaction of L with Mn ^II(OAc)₂ yielded a dimanganese(ii) complex, [Mn ₂L(μ-OAc)₃]PF₆, (1) where the two somewhat inequivalent trigonal-bipyramidal Mn atoms separated by 3.381 Å are bridged by L and three acetate moieties. A similar reaction of L with Mn ^III(OAc)₃ yielded a very different dimanganese complex [Mn₂L′(OH)(OAc)₂(DMF)₂]PF ₆·DMF (2) where L′ is a E-1,2-bis(2,2′-bipyridyl- 6-yl)ethene fragment that was formed in situ. The L′ ligand bridges between the two Mn centers, despite its trans configuration, which leads to a very strained ethene bridging moiety. The Mn atoms are also bridged by two acetate ligands and a hydroxy group that bridges between the Mn atoms and the ethene fragment; DMF completes the octahedral coordination around each Mn atom which are separated by 3.351 Å. A comproportionation reaction of L with Mn^II(OAc)₂ and n-Bu₄NMnO₄ yielded a tetramanganese compound, [Mn₄(μ₃-O)₂(OAc) ₄(H₂O)₂L₂](PF₆) ₂·2CH₃CN (3). Compound 3 has a dimer of dimers structure of the tetranuclear Mn core that consists of binuclear [Mn ₂O(OAc)₂L]⁺ fragment and a PF₆ anion. BVS calculations indicate that 3 is a mixed-valent 2Mn^II plus 2Mn^III compound where two [Mn^II₂O(OAc) ₂L]⁺ fragments are held together by Mn^III-O inter-fragment linkers which have a distorted octahedral geometry. The Mn atoms in the [Mn₂O(OAc)₂L]⁺ fragments have a capped square-pyramid configuration where an aqua ligand is capped on one of the faces. Although the aqua ligand is well within a bonding distance to a carbon atom of the proximal ethyne bridge, there does not appear to be an oxygen-carbon bond formation, rather the ligand is constrained in this position, as deduced by the observation that the bond lengths and angles of the ligand are essentially the same as those for the free ligand, L. Reaction of L with perchlorate or triflate salts of Fe(ii), Mn(ii) and Co(ii) in dry acetonitrile yielded binuclear triple helicate structures (2:3 metal to L ratios) [Fe₂L ₃](CF₃SO₃)₄·CH₃CN (4), [Mn₂L₃](ClO₄)₄·1. 7CH₃CN·1.65EtOEt (5) and [Co₂L₃] (ClO₄)₄·2CH₃CN·2EtOEt (6) where each M(ii) center with a slightly distorted octahedral geometry is bridged by three of the ditopic ligands. The M-M distances varied; 5.961 Å (Mn), 6.233 Å (Co) 6.331 Å (Fe). Reaction of L with Co(ClO ₄)₂·6H₂O in wet acetonitrile yielded a dicobalto(iii) compound, [Co₂L′₃(O) ₂](ClO₄)₂·H₂O (7), with two types of L′ fragments; one bridging between the two Co centers and two non-bridging ligands, each bonded to a Co atom via one bipyridyl group where the other is non-bonding. The octahedral coordination sphere around each Co atom is completed by the formation of a cobalt-carbon bond from the two carbon atoms of the ethene moiety of the bridging ligand and by a hydroxy moiety that is also bonded to the ethene group of the non-bridging ligand. Reaction of L with Co(ClO₄)₂·6H₂O in dry acetonitrile in the presence of Et₃N yielded the tetracobalto(ii) complex {[Co ₂L₄(OH)₄](ClO₄)₄} ₂ (8) with a unique twisted square configuration of cobalt ions with Co-Co distances of 3.938 to 4.131 Å. In addition to the L bridging ligand the Co atoms are linked by hydroxy moieties. Some preliminary catalytic studies showed that the Mn compounds 1 and 2 were active (high yield within 3 min) for alkene epoxidation with peracetic acid and hydrogen peroxide dismutation (catalase activity).

We describe an experimental and theoretical consideration of photoexcited proton transfer in a poly(4-vinyl pyridine)/pyridine gel. Evidence was found for two states of a multiple state process analyzed by DFT modeling. According to the latter, following irradiation at 385 nm, the proton donor is the CH group of the polymer main chain and the proton acceptor is the nitrogen of the polymaric pyridine side chain. Proton transfer is made possible through the assistance of a mobile pyridine solvent molecule acting as a transfer vehicle. Proton transfer promotes both a geometrical rearrangement of the vinyl side chain as well as electronic density redistribution. The photoproduct intermediate - the hydrogen-bonded complex between the protonated solvent pyridine molecule and the deprotonated polymeric pyridine side chain - is identified by its Curie law magnetic susceptibility, ESR spectrum, and fluorescence lifetime measurements. The proton transfer from the nitrogen of the solvent pyridine molecule to the pyridine side chain nitrogen, producing pyridinium, is a thermodynamically favorable relaxation process and occurs without an energy barrier. The protonation of nitrogen on the polymeric side chain was detected by solid state NMR spectroscopy performed on a ¹⁵N-polymer enriched gel. The calculations and experimental data suggest a central role for the gel solvent molecule as a catalytic agent and proton transfer vehicle. The process suggested by DFT modeling may have relevance for photosensitive devices in part due to the fact that we have been able to show that long-lived paramagnetism may be included among the inducible properties of soft polymer gels.

A series of cationic, neutral, and anionic Pd^II and Pt ^II PNP (PNP = 2, 6-bis-(di-tert-butylphosphinomethyl)pyridine) complexes were synthesized. The neutral, dearomatized complexes [(PNP*)MX] (PNP* = deprotonated PNP; M= Pd, Pt; X = Cl, Me) were prepared by deprotonation of the PNP methylene group of the corresponding cationic complexes [(PNP)MX][Cl] with 1 equiv of base (KN(SiMe₃)₂ or ^tBuOK), while the anionic complexes [(PNP*)MX] ^-Y⁺ (PNP* = double-deprotonated PNP; Y = Li, K) were prepared by deprotonation of the two methylene groups of the corresponding cationic complexes with either 2 equiv of KN(SiMe₃)₂ or an excess of MeLi. While the reaction of [(PNP)PtCl][Cl] with an excess of MeLi led only to the anionic complex without chloride substitution, reaction of [(PNP)PdCl][Cl] with an excess of MeLi led to the methylated anionic complex [(PNP*)PdMe]^-Li⁺. NMR studies, X-ray structures, and density functional theory (DFT) calculations reveal that the neutral complexes have a broken aromatic system with alternating single and double bonds, and the deprotonated arm is bound to the ring by an exocyclic CdC double bond. The anionic complexes are best described as a π system comprising the ring carbons conjugated with the exocyclic double bonds of the deprotonated "arms". The neutral complexes are reversibly protonated to their cationic analogues by water or methanol. The thermodynamic parameters.δ H, δ S, and δ G for the reversible protonation of the neutral complexes by methanol were obtained.

We report on the observation of an anisotropic magnetic dipolar interaction that results from binding PbSe nanoparticles (NPs) to GaAs surfaces by an organic linker. The observed dependence of the blocking temperature on the alignment of the linking molecule relative to the surface normal indicates that the anisotropy is caused by the attachment of the organic linker to the NPs. The presented results may serve as a strategy for fine-tuning the magnetic interactions and anisotropy on surfaces.

3,4-Dimethoxytellurophene (5) was synthesized via a new ring construction reaction. The crystal structure of 5 is characterized by unusually short Te center dot center dot center dot Te distances. The electropolymerization of 5 probably produces some amount of poly-5. Since the product was unstable under experimental conditions, a definitive assignment could not be made. However, the UV-vis spectrum recoded during electropolymerization of 5 shows an absorption peak at 679 nm with an onset at 820 nm (1.51 eV), closely matching the calculated band gap of poly-5.

Magnetic susceptibility measurements of WO3 crystals hydrogen doped on the surface suggest 2D local non-percolated superconductivity with an onset temperature of 120 K. Observed zero field cooled vs. field cooled magnetization response is characteristic of type II superconductivity. The diamagnetic response at the critical temperature is field dependent, and is suppressed by a magnetic field of similar to 1700 Oe.

The synthesis of a series of new ruthenium complexes based on the new PONOP ligands 1 and 10 ((C₅H₃N-1,3-(OPR₂) ₂: 1, R = ⁱPr; 10, R = ^tBu) is presented, including the stable trans-dihydride complexes (ⁱPr-PONÖP)Ru(H) ₃(PPh₃) (4) and (rBu-PONOP)Ru(H)₂(CO) (12) and the stable Ru(0) complexes (R-PONOP)Ru(CO)₂ (6, R = ⁱPr; 15, R = ^tBu). A surprisingly stable 16-electron Ru(0) complex (13) was formed by deprotonation of 12 with KO^tBu. Complex 13 reacts with H₂ to afford the cis-dihydride complex 12a, which isomerized to the trans-dihydride 12. Complex 13 reacted with CO to afford the saturated Ru(0) complex 15. Reaction of complex 12 with water led to hydrolysis of the phosphinite PONOP ligand and rearrangement to a dimeric product (14). Reaction of the trans-dihydride complex 4 with the electrophiles PhCOCl, Mel, and MeOTf led to abstraction of one of the hydride ligands, forming the monohydride complexes (ⁱPr-PONOP)Ru(H)(PPh₃)(X) (X = Cl (2), I (8a), OTf (8b)) together with benzaldehyde in the case of 2. Similarly, 12 afforded the monohydride complexes (^tBu-PONOP)Ru(H)(CO)(X) (X = Cl (11), OTf (17), I (18)). Reaction of the Ru(0) complexes 6 and 15 with water resulted in hydrolysis of the O - P bond and formation of the zwitterionic complexes 7 and 16. Treatment of 2 and 11 with MeOTfor Mel resulted in abstraction of the chloride ligand rather than the hydride, forming complexes 8a, b and 17, 18, respectively. Additional syntheses of complexes based on ligands 1 and 10 are presented.

Rhodium complexes based on the electron-withdrawing PCP-type pincer ligand dipyrrolylphoshi-noxylene (DPyPX, ^PyrPCP) were synthesized and their reactivity was studied. Reaction of Rh^I(^pyrPCP)PR ₃ (2) (R = Et (a). Ph (b); Pyr (pyrrolyl, NC₄H ₄) (c); Pyd (pyrrolydinyl, NC₄H₈) (d)) with MeI was strongly dependent on the sterics and nucleophilicity of PR3. Complex 2a (PEt₃ cone angle, Θ^o, 132°) reacted with MeI to give isomers of Rh^ΠI(^PyrPCP)Me(I)PEt₃, 3. Reaction of 2b (Θ^o_PR3 = 145°, R = Pyd (2d), Ph (2b), Pyr (2c)) with MeI was accompanied by release of PPh₃ and is thought to proceed via the 14e intermediate Rh^I(^PyrPCP). While the PPyd₃ complex 2d reacted with MeI to give [Rh ^ΠI(^PyrPCP)Me(I)₂][MePPyd₃], 4a, the PPyr₃ complex 2c did not react, owing to Steric hindrance around Rh¹ and the low nucleophilicity of PPyr₃. The aptitude of complexes 2 toward activation of H₂ was also examined. Our results support the involvement of 14e intermediates in the olefin hydrogenation process. The ancillary ligand substitution at the Rh^I center of 2 was found to proceed by an associative mechanism. ML₅ d⁸ intermediates were clearly detected by ³¹P{ ¹H} NMR at 213 K during equilibrium between 2a and 2c.

We model the interaction of side-chain and end-chain groups of poly(4-vinylpyridine) by a 5:1 molar ratio mixture of 4-isopropylpyridine (side-chain model) and 4-propylpyridine (end-chain model). We find that the 4-isopropylpyridine in the mixture is oxidized in a slow air flow to produce 4-isopropylpyridine hydroperoxide which in turn precipitates as lamellar crystals with monoclinic structure. The fact that the peroxide group is exchanged for the hydrogen of the tertiary carbon demonstrates the high activity of the latter and gives strong support for its involvement in the self-protonation mechanism proposed earlier for the poly(4-vinylpyridine)/pyridine gel.

Reaction of nickel (II) perchlorate with the ligand N,N′-bis-(3,5-dipiperidin-1-yl-[2,4,6]triazin-1-yl)-pyridin-2-ylmethyl-ethane-1,2-diamine yields an octahedral Ni(II) high-spin complex 1 ([C₄₀H₅₆N₁₄Ni(H₂O)(CH₃OH)](ClO₄)₂(CH₃OH)₂) with moderate zero-field splitting (ZFS) axial distortion parameter D/k_B = 5.37 K. The ligand contributes a N4 donor set; the remaining two coordinating positions are occupied by coordinating solvents molecules. Exchange of the coordinating solvents molecules in complex 1 to thiocyanate moieties leads to formation of complex 2 ([C₄₀H₅₆N₁₄Ni(NCS)₂](CHCl)₃) with an extended parameter D/k_B = 8.80 K. The analysis of the structural and magnetic properties of complexes 1 and 2 led to the design of dinuclear complex 3 ([C₄₀H₅₆N₁₄NiN₃]₂(ClO₄)₂(CH₃OH)₂), where two azido groups were utilized as bridging ligands. The double azido bridges in complex 3 cross each other to form a rarely observed non-coplanar (N₃)₂ structure. The magnetic behavior of complex 3 reveals ferromagnetic coupling interactions characterized by J/k_B = 23.25 K, D₁/k_B = 7.90 K, D₂/k_B = 0.54 K.

Manganese(II) complexes, Mn₂L¹₃(ClO₄)₄, MnL¹(H₂O)₂(ClO₄)₂, MnL²(H₂O)₂(ClO₄)₂, and {(μ-Cl)MnL²(PF₆)}₂ based on N,N′-bis(2-pyridinylmethylene) ethanediamine (L¹) and N,N′-bis(2-pyridinylmethylene) propanediamine (L²) ligands have been prepared and characterized. The single crystal X-ray diffraction analysis of Mn₂L²₃(ClO₄)₄ shows that each of the two Mn(II) ion centers with a Mn-Mn distance of 7.15 Å are coordinated by one ligand while a common third ligand bridges the metal centers. Solid-state magnetic susceptibility measurements as well as DFT calculations confirm that each of the manganese centers is high-spin S = 5/2. The electronic structure obtained shows no orbital overlap between the Mn(II) centers indicating that the observed weak antiferromagentism is a result of through space interactions between the two Mn(II) centers. Under different reaction conditions, L¹ and Mn(II) yielded a one-dimensional polymer, MnL¹(H₂O)₂(ClO₄)₂. Ligand L² when reacted with manganese(II) perchlorate gives contrarily to L¹ mononuclear MnL²(H₂O)₂(ClO₄)₂ complex. The analysis of the structural properties of the MnL²(H₂O)₂(ClO₄)₂ lead to the design of dinuclear complex {(μ-Cl)MnL²(PF₆)} where two chlorine atoms were utilized as bridging moieties. This complex has a rhomboidal Mn₂Cl₂ core with a Mn-Mn distance of 3.726 Å. At room temperature {(μ-Cl)MnL²(PF₆)} is ferromagnetic with observed μ_eff = 4.04 μ_B per Mn(II) ion. With cooling, μ_eff grows reaching 4.81 μ_B per Mn(II) ion at 8 K, and then undergoes ferromagnetic-to-antiferromagnetic phase transition.

An investigation of the optical and magnetic properties of a unique hydrogen-linked conjugate nanostructure, comprised of superparamagnetic gamma-Fe2O3 nanoparticles (NPs) and near-infrared PbSe nanocrystal quantum dot (NQD) chromophores, is reported. The results show retention of the NQDs' emission quantum efficiency and radiative lifetime, and only a small red shift of its band energy, upon conjugation to the dielectric surroundings of gamma-Fe2O3 NPs. The study also shows the sustain-ability of the superparamagnetism of the NPs after conjugation, with only a slight decrease of the ferromagnetic-superparamagnetic transition temperature with respect to that of the individual NPs. Thus, the conjugate nanostructure can be considered as a useful medical platform when PbSe NQDs act as fluorescent tags, while the gamma-Fe2O3 NPs are used as a vehicle driven by an external magnetic field for targeted delivery of tags or drugs.

Nonthermal crystallization of amorphous barium titanate (BTO) was initiated by a monochromatic x-ray microbeam from a synchrotron radiation source. Following x-ray exposure, micron-sized BTO single crystals with a true square pyramid shape appeared on the surface of an amorphous BTO substrate-free film. The location and size of the areas in which crystal growth appeared fit well the x-ray microbeam path and size, respectively. A plausible mechanism of x-ray induced initiation of nonthermal crystallization in BTO is proposed. The observed phenomenon holds promise for materials engineering at nanoscale and crystallization of amorphous materials in situations where heating must be avoided.

Adsorption-induced magnetization of binding PbS self-assembled nanoparticles (NP) on GaAs surfaces by an organic linker was studied. The magnetization is anisotropic and the magnetic moment reaches saturation for a magnetic field of 2000 Oe applied parallel to the surface. The results also show the dependence of the measured magnetic moment on the density of 4.2 nm diameter PbS nanoparticles, when the field is applied parallel to the surface. The observed dependence of anisotropy on the alignment of the linking molecule, relative to the surface normal, indicates that the anisotropy is caused by the attachment of the organic to the NPs. The orientation of the organic molecule relative too the NPs surface normal is found to coincide with the direction of the magnetic anisotropy.

Reaction of [Pd(TFA)₂] (1; TFA = trifluoroacetate) with 2 equiv of benzyldiisopropylphosphine resulted in formation of the metalated complex [Pd {C₆H₄(CH₂PⁱPr₂)}{(C ₆H₅CH₂)PⁱPr₂ }(TFA)] (2). The dinuclear trifluoroacetate complex [Pd(C₆H₄(CH ₂PⁱPr₂)}[TFA)]₂ (3) was formed when the reaction was performed with an equimolar amount of the phosphine. Both complexes were structurally characterized. Reduction of the cyclometalated palladium complex 2 with sodium metal in THF gave a mixture of cis and trans isomers of the dimetalated bis(o-benzyldiisopropylphosphine)palladium(II) (6a,b) and bis(benzyldiisopropylphosphine)palladium(0) (7). A mechanism for the reduction process is presented. Treatment of the reaction mixture of 6a,b and 7 with an equimolar amount of hydrochloric acid led to a mixture of 7, [Pd(C ₆H₄(CH₂PⁱPr₂)Ji(C ₆H₅CH₂)PⁱPr₂}(Cl)] (9), [Pd{(C₆H₅CH₂)PⁱPr₂J ₂(H)(Cl)] (8), [Pd((C₆H₅CH₂)-P ⁱPr₂}₂(Cl)₂] (4), and both isomeric forms of [Pd(C₆H₄(CH₂PⁱPr ₂)}₂] (6a,b). All complexes were independently prepared and fully characterized. The addition of another 1 equiv of hydrochloric acid to this reaction mixture resulted in the exclusive formation of 4. Reduction of 4 with sodium metal in THF cleanly yielded the Pd⁰ complex 7 in high yields, offering a new, facile, and high-yield route toward the synthesis of dicoordinated bis(phosphine) Pd⁰ complexes. Reaction of 7 with an equimolar amount of HCl led to the clean formation of [PdJ(C₆H ₅CH₂)PⁱPr₂}₂(H)(Cl)] (8). The addition of another 1 equiv of HCl led to the quantitative formation of 2 and H₂. Reactions of 9 and an equimolar amount of NaBHEt3 cleanly yielded complex 7, which was also exclusively formed by treatment of 4 with 2 equiv of NaBHEt3. Mixtures of the cis and trans isomers 6a,b were formed by the addition of 2 equiv of (lithiobenzyl)diisopropylphosphine to benzene solutions of bis(diethyl sulfide)palladium dichloride (5) at room temperature.

The crystal structure of the new cationic Rh-1 complex trans-[Rh(CO)(2)(L)(2)]BF4 (L=alpha(2)-(diisopropyl-phosphino)isodurene) wag found to exhibit a nonlinear OC-Rh-CO fragment and weak intramolecular C-H center dot center dot center dot Rh interactions. These interactions, which have also been shown to occur in solution, have been examined by density functional theory calculations and found to be inextricably linked to the presence of the distorted OC-Rh-CO fragment. This linkage has also been demonstrated by comparison with a highly similar Rh-1 complex, in which these C-H center dot center dot center dot Rh interactions are absent. Furthermore, the presence of these weak interactions has been shown to have a significant effect on the reactivity of the metal center.

Surprisingly, despite its very high mobility in a single crystal, rubrene shows very low mobility in vacuum-sublimed or solution-processed organic thin-film transistors. We synthesized several rubrene analogues with electron-withdrawing and electron-donating substituents and found that most of the substituted rubrenes are not planar in the solid state. Moreover, we conclude (based on experimental and calculated data) that even parent rubrene is not planar in solution and in thin films. This discovery explains why high mobility is reported in rubrene single crystals, but rubreneshows very low field-effect mobility in thin films. The substituted rubrenes obtained in this work have significantly better solubility than parent rubrene and some even form films and not crystals after evaporation of the solvent. Thus, substituted rubrenes are promising materials for organic light-emitting diode (OLED) applications.

Carbon powder was produced by a pulsed arc ignited between two carbon electrodes submerged in ethanol, and was comprised of both micro- and nano-particles. The measured magnetic properties of the mixed "raw" powder at 20 and 300 K were: saturation magnetization M-s similar to 0.90-0.93 emu/g, residual magnetization M-r = 0.022 and 0.018 emu/g, and coercive force H-c = 11 and 8 Oe, respectively The data lead to conclusion that the powder consisted of ferromagnetic particles with a critical temperature much higher than 300 K. Magnetic particles in solution were separated by means of bio-ferrography It was found that the magnetically separated particles included chains of similar to 30-50 nm diameter spheres, and nanotubes and nanorods with lengths of 50-250 nm and diameters of 2030 nm. In contrast, the residual particles which passed through the bio-ferrograph consisted of 1 pm and larger micro-particles, and nano-particles without any definite shape. (c) 2007 Elsevier Ltd. All rights reserved.

The first highly conductive polyselenophene, namely, poly(3,4-ethylenedioxyselenophene) (PEDOS), was synthesized by taking advantage of a novel method for efficiently contracting the selenophene ring. PEDOS shows a relatively low band gap (1.4 eV), very high stability in the oxidized state, and a well-defined spectroelectrochemistry.

In this work, we present a complete and detailed experimental characterization and theoretical study of a variety of coordinated S-nitrosothiols (RSNOs), such as cysteine derivatives, mercaptosuccinic acid, benzyl thiol, and phenyl thiol. Some of them are extremely unstable and sensitive in free form. Strikingly, in contrast with free S-nitrosothiols, we found that, upon coordination to iridium, they become very stable even in aqueous solutions. The study of these coordinated complexes provides further insight on the elucidation of structural aspects dealing with the nature of the S-N bond in RSNOs, a fact which still remains a matter of controversy.

Terminal oxo complexes of transition metals have critical roles in various biological and chemical processes. For example, the catalytic oxidation of organic molecules, some oxidative enzymatic transformations, and the activation of dioxygen on metal surfaces are all thought to involve oxo complexes. Moreover, they are believed to be key intermediates in the photocatalytic oxidation of water to give molecular oxygen, a topic of intensive global research aimed at artificial photosynthesis and water splitting. The terminal oxo ligand is a strong π-electron donor, so it readily forms stable complexes with high-valent early transition metals. As the d orbitals are filled up with valence electrons, the terminal oxo ligand becomes destabilized. Here we present evidence for a dⁿ (n > 5) terminal oxo complex that is not stabilized by an electron withdrawing ligand framework. This d⁶ Pt(iv) complex exhibits reactivity as an inter- and intramolecular oxygen donor and as an electrophile. In addition, it undergoes a water activation process leading to a terminal dihydroxo complex, which may be relevant to the mechanism of catalytic reactions such as water oxidation.

A rare case of BAr_F anion cleavage (BAr_F^- = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) by a metal complex is described. Reaction of the Rh(I) dinitrogen complexes 5a,b and 6a,b, based on the phosphinite pincer ligands {C₆H₄[OP( _tBu)₂]₂} (2), with 2 equiv of AgBAr_F at room temperature resulted in B-C bond cleavage of one of the BAr_F anions and aryl transfer to afford the Rh(III) aryl complexes 7 and 8, respectively. The X-ray structure of 8 revealed a square-pyramidal geometry with a coordinated acetone molecule. The aryl transfer occurred as a result of electrophilic attack by unsaturated Rh(III) on one of the aryl rings of the BAr_F anion. Utilizing different solvents yielded the same product, except when CH₃CN was used, in which case one-electron oxidation took place, yielding complex 9. Treatment of 6a,b with 1 equiv of AgX (X = BAr _F, BF₄, PF₆) resulted in a one-electron oxidation to yield the paramagnetic Rh(II) complexes 9-11, respectively. Complex 11 was characterized by X-ray diffraction, revealing a mononuclear square-planar Rh(II) complex.

The new pyridine-based sulfoxide pincer ligand 1 (2-(diethylaminomethyl)-6- (tert-butylsulfinylmethyl)pyridine = S(O)NN) reacts cleanly with Rh ₂(COE)₄Cl₂ to form the neutral water- and air-stable Rh¹ complex [Rh(S(O)NN)(NCCH₃)], 1. The cationic complexes [Rh(S(O)NN(NCCH₃)][BF₄] (2) and [Ir(S(O)NN)(COE)][BF₄] (5) were obtained by the reaction of 1 with the appropriate metal precursors. The corresponding carbonyl complexes [Rh(S(O)NN)(CO)][PF₆] (4) and [Ir(S(O)NN)(CO)][BF₄] (7) exhibit vCO in the IR spectra that shows that ligand 1 is a relatively poor a-donor ligand compared to the more common PNP-type ligands, resulting in rather electron-poor metal centers. The carbonyl compounds can be deprotonated to the remarkably stable dearomatized complexes Rh(S(O)NN*)(CO) (8) and Ir(S(O)NN*)(CO) (9). DFT studies on 8 revealed a high electron derealization over the pyridine ring system and the sulfur atom, which explains the high stability of 8 toward reprotonation. Complete protonation of 8 was achieved in acetic acid.

The cationic, pincer-type complexes [(SNS)Ir(COE)][BF₄] (1) and [(SNS)Rh(COE)][BF₄] (2) (SNS = 2,6-bis(t-butylthiomethy1)pyridine; COE = cyclooctene) complexes were prepared, and their structure and reactivity were studied. They are fluxional at room temperature as a result of "arm" hemilability, which can be frozen at low temperatures. Reaction of complex 1 with H₂ resulted in a dimeric dihydride complex [(SNS)Ir(H₂)]₂[BF₄]₂ (3) in which the sulfur atoms bridge between two metal centers. The Rh complex 2 did not react with H₂. Both the carbonyl complexes [(SNS)Ir(CO)][BF ₄] (5) and [(SNS)Rh(CO)][BF₄] (6) show differences in the IR stretching frequencies in solution vs. solid states, which are a result of uncommon metal-metal interactions between square planar d⁸ systems in the solid state. Complexes 1, 3, 5 and 6 were structurally characterized by X-ray crystallography. A network of hydrogen bonds involving the BF ₄^- counter anion and hydrogen atoms of complex 5 was observed.

Aiming at the generation of a silanone intramolecularly bound to platinum, we prepared pincer-type PSiP silanol Pt(II) complexes. While a stable silanone complex was not isolated, unusual reactivity modes, involving its possible intermediacy, were observed. Treatment of the new PSiH₂P-type ligand (o-iPr₂PC₆H₄)₂SiH₂ (7) with (Me₂S)₂Pt(Me)Cl yields the pincer-type hydrosilane complex [{(o- iPr₂PC₆H₄)₂SiH}PtCl] (8), which upon Ir(I)-catalyzed hydrolytic oxidation gives the structurally characterized silanol complex [{(o- iPr₂PC₆H ₄)₂SiOH}PtCl] (3). Complex 3, comprising in its structure the nucleophilic silanol fragment and electrophilic Pt(II)-Cl moiety, exhibits dual reactivity. Its reaction with the non-nucleophilic KB(C₆F ₅)₄ in fluorobenzene leads to the ionic complex [{(o- iPr₂PC₆H₄)₂SiOH}Pt]⁺ [(C₆F₅)₄B]^- (9), which reacts with CO to yield the structurally characterized [{(o- iPr₂PC ₆H₄)₂SiOH}PtCO]⁺ [(C ₆F₅)₄B]^- (10). Treatment of 3 with non-nucleophilic bases leads to unprecedented rearrangement and coupling, resulting in the structurally characterized, unusual binuclear complex 11. The structure of 11 comprises two different fragments: the original O-Si-Pt(II)-Cl pattern, and the newly formed silanolate Pt(II)-H pattern, which are connected via a disiloxane bridge. Complex 9 undergoes a similar hydrolytic rearrangement in the presence of iPr₂NEt to give the mononuclear silanolate Pt(II)-H complex 17. Both these rearrangement-coupling reactions probably involve the inner-sphere generation of an intermediate silanone 14, which undergoes nucleophilic attack by the starting silanol 3 to yield complex 11, or adds a water molecule to yield complex 17. X-ray diffraction studies of 3, 10, and 11 exhibit a very short Si-Pt bond length (2.27-2.28 Å) in the neutral complexes 3 and 11 that elongates to 2.365 Å in the carbonyl complex 10. A significantly compressed geometry of the silanolate platinum(II)-hydride fragment B of the binuclear complex 11 features a Pt(2)-O(2)-Si(2) angle of 100.4 (3)° and a remarkably short Pt(2)⋯Si(2) [2.884 (3) Å] distance.

In the present work the formation of several primary aliphatic coordinated nitrosamines by reaction of the extremely reactive K[IrCl5(NO)] in acetonitrile solution with the corresponding amine is described. Complete characterization, including X-ray diffraction determinations for some examples, are reported, and experimental evidence of their stability. Density functional theory calculations (DFT) helped to understand the role of the coordination environment of these complexes and to support, with excellent correlation with the experimental data, the proposed reaction pathways and stability studies. Complexes containing the highly unstable primary nitrosamines as ligands are generally scarce, and moreover, to our knowledge, our group has recently reported the first examples of isolated primary nitrosamines coordinated to the metal center only through the NO moiety.

Both closed and open framework structures were designed for copper complexes with N,N′-bis-pyridin-2-ylmethyl-ethane-1,2-diamine (2-bpen)-based ligands. The design included substitution at the bridging aliphatic nitrogen atoms by reaction with cyanuric chloride to yield the 3,5-dichloro-2,4,6-triazine derivative. The chloride atoms on the triziane rings were further substituted by either electron donating amines, or an electron withdrawing thiomethyl moiety. The substitution of bridging nitrogen atoms by more electron donating aminated 2,4,6-triazines led to the formation of copper(II) complexes with closed square pyramidal architecture. On the other hand, substitution of bridging nitrogen atoms by the more electron withdrawing 2,4,6-triazines with thioether groups led to the formation of square planar or tetrahedral copper complexes with an open framework architecture whose specific structure and oxidation state depended on the anion.

The Rh^III complex [(PNP)Rh(CN)(CH₃)][I] 5, obtained by oxidative addition of methyl iodide to [(PNP)Rh(CN)] 2, reacts selectively in two pathways: In aprotic solvents C-I reductive elimination of methyl iodide followed by its electrophilic attack on the cyano ligand takes place, giving the methyl isonitrile RhI complex [(PNP)Rh(CNCH₃)][I] 3, while in protic solvents C-C reductive elimination of acetonitrile takes place forming an iodo RhI complex [(PNP)RhI] 9. Reaction of 2 with ethyl iodide in aprotic solvents gave the corresponding isonitrile complex, while in protic solvents no reactivity was observed. The selectivity of this reaction is likely due to a hydrogen bond between the cyano ligand and the protic solvent, as observed by X-ray diffraction, which retards electrophilic attack on this ligand.

(Figure presented) Head over EELS: Reaction of O₂ with a hexa-iron(II)-substituted polyoxometalate in water yields a polyoxometalate with "end-on" hydroperoxo groups, {Fe^III-O₂H}, at the terminal positions. The hydroperoxo moiety, stabilized by hydrogen bonding with water, is unusual for its long O-O bond and nearly linear Fe-O-O bond angle. Electron energy-loss spectroscopy (EELS) is used to determine the oxidation state of iron.

The crystallographic surface structure of thermal vapor grown Cs-X WO3 0.005

We describe a hydrogen-bonded poly(4-vinyl pyridine)-based dielectric material, in which conductivity can be induced due to the presence of side-chain protonated species that form spontaneously when the polymer is dissolved in pyridine. The conductivity of the proton conductive gel can be controlled by direct irradiation at the proton-transfer center: a reversible change of conductivity was observed in response to the on/off switching of 385 nm wavelength radiation. Over most of the range of intensities used, the proton conductivity exhibited a bimolecular character. We present a model of the protonated pyridine side-chain unit in the ground and excited states (DFT level). In the ground state, the protonated pyridine moiety has a cyclic, conjugated structure.

The synthesis and characterization of several Pt(ii) complexes, including formyl complexes, based on the PCP-type pincer ligands C₆H ₄[CH₂P(iPr)₂]₂ (^iPrPCP) and C₆H₄[CH₂P(tBu)₂]₂ (^tBuPCP) are described. The chloride complex (^iPrPCP)PtCl (6) and the unsaturated cationic complexes [(PCP)Pt]⁺X^- (X = OTf^-, BF₄^-) (1, 7), based on both PCP ligands, were prepared and the latter reacted with carbon monoxide to give the corresponding cationic carbonyl complexes [(PCP)Pt(CO)]⁺X^- (X = OTf^-, BF₄^-) (2, 8a). Hydride nucleophilic attack on both carbonyl complexes resulted in rare neutral platinum formyl complexes (^iPrPCP)Pt(CHO) (3) and (^tBuPCP)Pt(CHO) (9). Complex 3 undergoes decarbonylation to the corresponding hydride complex within hours at room temperature, while the bulkier complex 9 is more stable and undergoes complete decarbonylation only after 3-4 d. This observation demonstrates the very significant steric effect of the ligand on stabilization of the corresponding formyl complexes. Reaction of complex 9 with triflic acid resulted in the carbonyl complex [(^tBuPCP)Pt(CO)]⁺ OTf^- (8b) with liberation of H₂, an unusual transformation for a metal formyl. Reaction with methyl triflate resulted in the Fischer carbene-type complex, the methoxy-methylidene [(^tBuPCP)Pt(CHOCH ₃)]⁺OTf^- (11). The X-ray structures of complexes 2, 6, 8a and 11 were determined.

We prepared the first σ-bonded metal complexes of widely utilized organic dyes, perylene tetracarboxylic acid diimides (PDIs). These 1,7-dipalladium PDI complexes were synthesized by C-Br oxidative addition of 1,7-dibromo-N,N′-dicyclohexyl PDI (Br₂PDI) to Pd(0) phosphine complexes bearing triphenylphosphine and bischelating 1,2-bis(diphenylphosphino) ethane (dppe). The structures of Pd-PDI complexes were elucidated by single-crystal X-ray analysis. Surprisingly, despite direct attachement of two late transition metal centers, Pd-PDI systems are highly fluorescent (Φ = 0.65 and 0.22 for triphenylphosphine and dppe systems, respectively). This is rationalized in terms of weak electronic interactions between the metal centers and PDI π-system, as revealed by TD-DFT calculations.

This contribution describes the reactivity of Pt(PEt₃) ₄ with (4-bromo-phenyl)-pyridin-4-yl-diazene. η²- Coordination of Pt(PEt₃)₂ to the N=N moiety is kinetically preferable and followed by an aryl-halide bond activation process. This quantitative transformation proceeds under mild reaction conditions in solution and in the solid state. Mechanistic studies in solution indicate that the metal insertion into the aryl-halide bond is the rate-determining step. The reaction obeys first-order kinetics in the η²-coordination complex with ΔG^‡_298K = 24.6 ± 1.6 kcal/mol, ΔH^‡ = 26.5 ± 1.6 kcal/mol, and ΔS ^‡ = 6.6 ± 5.0 eu. No effect on the reaction progress and NMR line shape has been observed in the presence of excess PEt₃. However, competition experiments with the η-coordination complex and PhBr reveal that the product ratio can be altered by the presence of PEt₃, indicating that the two aryl-halide bond activation processes proceed via different mechanistic pathways. Numerical analysis of a series of competition experiments fits a reaction scheme involving a unimolecular transformation from the η²-coordination complex to the product of aryl-halide oxidative addition. This "ring-walking" process is kinetically accessible as shown by density functional theory (DFT) calculations at the PCM:PBEO/SDB-cc-pVDZ/PBE0/SDD level of theory.

Reaction of the aryl-monophosphine ligand α²- (diisopropylphosphino)isodurene (1) with the Rh^I precursor [Rh(coe)₂(acetone)₂]BF₄ (coe = cyclooctene) in different solvents yielded complexes of all three common oxidation states of rhodium, depending on the solvent used. When the reaction was carried out in methanol a cyclometalated, solvent-stabilized Rh^IIIalkylhydride complex (2) was obtained. However, when the reaction was carried out in acetone or dichloromethane a dinuclear η⁶-arene Rh^II complex (5) was obtained in the absence of addedredox reagents. Moreover, when acetonitrile was added to a solution of either the Rh^II or Rh ^III complexes, a new solvent-stabilized, noncyclometalated Rh ^I complex (6) was obtained. In this report we describe the different complexes, which were fully characterized, and probe the processes behind the remarkable solvent effect observed.

CO(mpletely) unexpected: The oxidative addition of CH bonds to transition‐metal ions usually requires high electron density at the metal center, and therefore strong π‐acceptor ligands, such as carbon monoxide, are normally expected to inhibit such reactions. Hence surprisingly, an electron‐poor cationic RhI system is observed in which addition of a CO ligand can actually promote oxidative addition of a strong CH bond (see scheme).

Novel estrogen-conjugated pyridine-containing Gd(III) and Eu(III) contrast agents (EPTA-Gd/Eu) were designed and effectively synthesized. Convenient to administration and MRI experiments, both EPTA-Gd and EPTA-Eu are soluble in water. The EPTA-Gd selectively binds with a micromolar affinity to the estrogen receptor and induces proliferation of human breast cancer cells. The EPTA-Gd is not lethal and does not cause any adverse effects when administrated intravenously. It enhances T₁ and T₂ nuclear relaxation rates of water and serves as a selective contrast agent for localizing the estrogen receptor by MRI.

The potential triple-halogen-bond acceptor, sym-triiodo-trifluorobenzene IFB (1), has been co-crystallized with a series of bipyridyl derivatives (2-4) to gain insight to the factors controlling formation of multiple halogen bonds with a single aromatic system. Co-crystals 5-7 were obtained that consistently contained two N⋯I halogen bonds. The reluctance to the formation of a supramolecular assembly having a third N⋯I halogen bond does not depend on the size of the bispyridine donor systems (2-4). Apparently, there are limitations to the number of halogen bonds that can be formed with a single aromatic halogen donor. The solid-state structure of co-crystal (5) contains short I⋯F contacts of 2.96 and 3.05 A. DFT calculations were performed at the PBE0/(apc1-aSDBDZ)//PBEO/(pc1-SDBDZ) level of theory to investigate the nature of the interaction between the pyridine nitrogen and IFB (1). These calculations reveal a weakening of N⋯I interactions as more pyridine moieties coordinate to the IFB (1), which might be a contributing factor to the consistent formation of two rather than three N⋯I halogen bonds.

The formation of gold crystallites on the surface of S ₈ promotes diffusion of electrons and determines the conductive properties of the shell-core nanosystems. Conducting probe atomic microscopy and four-probe resistance measurements confirmed that Au/S ₈ shell-core systems exhibit electrical conductivity on the micro- as well as on the nanoscale in contrast to non-covered S ₈ crystals, which are insulating. The conductivity of Au/S ₈ systems on the microscale was measured to be 10 ±1 S-cm ^-1. In XPS measurements, a single peak at 163.6 eV was observed for bulk S ₈ whereas an additional peak corresponding to a binding energy of 161.4 eV appeared for S ₈ adsorbed on a Au substrate. This is interpreted to mean that a chemical reaction has taken place. A process which results in adsorption of uniform gold nanolayers on needle shaped or fibrous S ₈ crystallites is under investigation.

The Rh(II) mononuclear complexes [(PNP^tBu)RhCl][BF₄] (2), [(PNP^tBu)Rh(OC(O)CF₃)][OC(O)CF₃] (4), and [(PNP^tBu)Rh(acetone)][BF₄]₂ (6) were synthesized by oxidation of the corresponding Rh(I) analogs with silver salts. On the other hand, treatment of (PNP^tBu)RhCl with AgOC(O)CF ₃ led only to chloride abstraction, with no oxidation. 2 and 6 were characterized by X-ray diffraction, EPR, cyclic voltammetry, and dipole moment measurements. 2 and 6 react with NO gas to give the diamagnetic complexes [(PNP^tBu)Rh(NO)Cl][BF₄] (7) and [(PNP^tBu)Rh(NO) (acetone)]-[BF₄]₂ (8) respectively. 6 is reduced to Rh(I) in the presence of phosphines, CO, or isonitriles to give the Rh(I) complexes [(PNP^tBu)Rh(PR₃)][BF₄] (11, 12) (R = Et, Ph), [(PNP^tBu)Rh(CO)][BF₄] (13) and [(PNP^tBu)Rh(L)] [BF₄] (15, 16) (L = tert-butyl isonitrile or 2,6-dimethylphenyl isonitrile), respectively. On the other hand, 2 disproportionates to Rh(I) and Rh(III) complexes in the presence of acetonitrile, isonitriles, or CO. 2 is also reduced by triethylphosphine and water to Rh(I) complexes [(PNP ^tBu)RhCl] (1) and [(PNP^tBu)Rh(PEt₃)][BF ₄] (11). When triphenylphosphine and water are used, the reduced Rh(I) complex reacts with a proton, which is formed in the redox reaction, to give a Rh(III) complex with a coordinated BF₄, [(PNP ^tBu)Rh(Cl)(H)(BF₄)] (9).

Electrical resistivity and Hall measurements, of pellets compacted from IF-WS₂ nanoparticles and 2H-WS₂ powder were done. Electrical transport measurements were carried out on pellets by the van der Pauw method in a wide temperature range. Arrhenius plots for conductivities of the WS₂ samples (2H, IF and IF+treatment) exhibit marked variations in (∂ ln ∂T^-1)/∂T^-1 with temperature. Resistivity of IF-WS₂ pellets is higher than that of 2H-WS ₂ pellets. It was found that the electrical properties of IF-WS ₂ powder vary with aposteriory heat treatment under vacuum. The ¹H NMR measurements show that the prepared product contains water (and possibly some hydrogen) molecules that occupy the voids in the central part of the fullerene-like nanoparticles and the nanopores between the adhering IF-WS₂ particles. Defects in the IF-WS₂ structure, arising due to the strain release during the folding of the layers, may result in additional sites for the absorbed water.

With open arms: A ruthenium PNN complex (see scheme) catalyzes the hydrogenation of esters in high yields under neutral conditions. The analogous PNP complex is less active. A mechanism is proposed based on the hemilabile nature of the PNN ligand which allows a vacant site to be created by decoordination of the CH2NEt2 arm.

Reaction of the PNN ligand ((2-(di-tert-butylphosphinomethyl)-6- diethylaminomethyl)pyridine) with 1 equiv. of anhydrous FeCl₂ in THF results in the formation of (PNN)FeCl₂ (1). The cationic complex [(PNN)Fe(THF)Cl](PF₆) (2) was obtained by chloride abstraction from 1 with 1 equiv. of TlPF₆. Similarly, the PNP-type complexes 3 and 4 were obtained from FeCl₂ with 1 equiv. of t-Bu-PNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) and i-Pr-PNP (2,6-bis(di-iso-propylphosphinomethyl)pyridine), respectively. Complexes 1 and 3 were characterized by X-ray diffraction and elemental analyses. In both structures the Fe(II) centers exhibit a distorted square pyramidal geometry comprising two chloride ligands and one tridentate PNN or PNP ligand. The magnetic properties of the paramagnetic complexes 1-4 are discussed.

A study that illustrates the straightforward chemical modulation of the optical absorbance of a thermally monolayer in air by exploitation of redox properties of metal complex, is presented. The monolayers have been demonstrated as thermally robust, and 25 Os²⁺/Os³⁺ redox cycles. the solution-surface electron transfer process induced changes in the molecular properties of the monolayer have been monitored by UV/vis transmission spectroscopy. This siloxane-basaed monolayers and surface chemistry could open up new opportunities in interfacial engineering and the formation of monolayer-based memory devices.

Benzyl cations are unstable intermediates involved in various chemical and biological processes. Two extreme resonance forms of these cations include positive charge localization at the methylene carbon or delocalization in the ring, the latter, nonaromatic form, termed "methylene arenium". The preparation of the discrete methylene arenium compound, stabilized by coordination to a metal (palladium) center, is described. It was fully characterized, including by X-ray diffraction. Reactivity patterns, resulting from charge distribution in the ring, were observed. Upon controlled release of the methylene arenium compound into solution, it demonstrates aromatic benzyl cation reactivity.

Here we show that self-assembled monolayers on gold of double-stranded DNA oligomers interact with polarized electrons similarly to a strong and oriented magnetic field. The direction of the field for right-handed DNA is away from the substrate. Moreover, the layer shows very high paramagnetic susceptibility. Interestingly, thiolated single-stranded DNA oligomers on gold do not show this effect. The new findings are rationalized based on recent results in which high paramagnetism was measured for diamagnetic films adsorbed on diamagnetic substrates.

Direct magnetization measurements of thin gold films are presented. These measurements integrate the signal from the thin film under study and the magnetic contribution of the film's interface with the substrate. The diamagnetic contribution to the signal from the bulk substrate is of the same order as the noise level. We find that thin gold films can exhibit positive magnetization. The character of their magnetic behavior is strongly substrate dependent. (c) 2006 American Institute of Physics.

Electrical resistivity and Hall effect measurements of pellets compacted from fullerene-like WS2 nanoparticles (IF-WS2) and bulk 2H-WS2 powder were carried out using the van der Pauw method over a wide temperature range. In addition IF-WS2 pellets were annealed at elevated temperatures under vacuum in a specially designed system. Arrhenius plots for the conductivities of the WS2 samples (2H, IF and IF+annealing) exhibit marked uprise of partial derivative In (sigma T-1)/partial derivative T-1 with temperature. The resistivity of the non-annealed IF-WS2 pellets is higher by 2-8 orders of magnitude than that of 2H-WS2 pellets, whereas the resistivity of the annealed IF pellets is higher than that of the non-annealed ones. Hall Effect measurements at 300 K show p-type conductivity and similar carrier concentration for both types of materials. The carrier mobility of 2H-WS2 platelets is found to be in the range of the reported values. However, IF-WS2 pellets have shown an unusually low mobility for a semiconducting material. The experimental data was found to be in a good agreement with a model used for analyzing the conductivity of polycrystalline semiconductors, which takes into consideration fluctuations of the barrier heights among the different nanoparticles as well as within a single nanoparticle boundary. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Coordinated C-nitrosochloroalkanes were obtained by electrophilic addition of K[IrCl5NO] to cyclooctene or dicyclopentadiene; in the last case, the crystal structure of trans-[IrCl4(CH3CN)(syn-1-chloro-2-nitroso-1,2-dihydrodicyclopentadiene)] was determined by X-ray diffraction. Although the reaction between NOCl and alkenes is well-known, there are Very few examples of clean electrophilic addition of coordinated NO+ to alkenes.

The reaction of the cationic (PNP)Ir(I)(cyclooctene) complex (1) (PNP = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine) with 2-butanone or 3-pentanone results in the selective, quantitative activation of a β C−H bond, yielding O,C-chelated complexes. Calculations show that the selectivity is both kinetically (because of steric reasons in the rate determingin step (RDS)) and thermodynamically controlled, the latter as a result of carbonyl oxygen coordination in the product. The RDS is formation of the η2-C,H intermediates from the complexed ketone intermediates. Water has a strong influence on the regioselectivity, and in its presence, reaction of 1 with 2-butanone gives also the α terminal C−H activation product. Computational studies suggest that water can stabilize the terminal α C−H activation product by hydrogen bonding, forming a six-membered ring with the ketone, as experimentally observed in the X-ray structure of the acetonyl hydride aqua complex.

Unusual reactions are reported, in which the aromatic PNP ligand (PNP = 2,6-bis-(di-tert-butylphosphinomethyl)pyridine) acts in concert with the metal in the activation of H2 and benzene, via facile aromatization/dearomatization processes of the ligand. A new, dearomatized electron-rich (PNP*)Ir(I) complex 2 (PNP* = deprotonated PNP) activates benzene to form the aromatic (PNP)Ir(I)Ph 4, which upon treatment with CO undergoes a surprising oxidation process to form (PNP*)Ir(III)(H)CO 6, involving proton migration from the ligand “arm” to the metal, with concomitant dearomatization. 4 undergoes stereoselective activation of H2 to exclusively form the trans-dihydride 7, rather than the expected cis-dihydride complex. Our evidence, including D-labeling, suggests the possibility that the Ir(I)−Ph complex is transformed to the dearomatized Ir(III)(Ph)(H) (independently prepared at low temperature), which may be the actual intermediate undergoing H2 activation.

Supporting Information. The CIF file that was originally made available as Supporting Information for this paper was from a different, unrelated paper. The correct CIF file was made available under the Supporting Information link for this communication on August 15, 2005.

An efficient, environmentally benign method for the preparation of esters from alcohols under mild, neutral conditions without the need for carboxylic acid derivatives and condensing agents was developed. Catalyst design, based on new Ru(II) hydrido carbonyl complexes incorporating electron-rich PNP and PNN ligands has resulted in the novel complex (I) which is an outstanding catalyst for the dehydrogenation of primary alcohols to esters and H2 under neutral conditions.

New platinasiloxanes were synthesized and their reactivity was studied. Oxidative addition of (HSiMe₂)₂O to Pt(PEt ₃)₃ led to dehydrogenation and quantitative formation of the four-membered platinacyclosiloxane [(PEt₃)₂Pt- ((SiMe₂)₂O)] which was characterized by X-ray diffraction. This complex was stable towards non-polar substrates and aerobic conditions, but reacted readily with electrophiles and Lewis acids. Reaction with MeI resulted in ring opening, while MeOTf gave an oxonium complex, with retention of the platinacycle structure. A complex resulting from BF₃ coordination to the ring oxygen atom was also obtained. An unprecedented open-chain diplatinasiloxane containing the Pt-Si-O-Si-O-Si-Pt fragment was formed by oxidative addition of H-SiMe₂-O-SiMe₂-O- SiMe₂-H to Pt(PEt₃)₃ and it was characterized by X-ray diffraction.

A series of the first C-metalated diazoalkane complexes of Pt, based on pincer-type PCN and PCP ligands (PCP = C6H3[CH2P(iPr)(2)](2); PCN = C6H3[CH2P(tBu)(2)](CH2)(2)N(CH3)(2)), with the general formula (PCX)Pt[C(N-2)RI (2, X = N, R = Ph; 3, X = N, R = SiMe3; 5, X = P, R = Ph) were prepared via direct nucleophilic attack of RCN2-Li+ at the metal center. These remarkably stable complexes were characterized by H-1, P-31{H-1}, and C-13 NMR and IR spectroscopy. Complex 2 was also characterized by single-crystal X-ray crystallography. Reactions of the C-metalated diazoalkane Pt complexes with Cu(I) (reported to catalyze decomposition of diazoalkanes) were strongly influenced by the nature of the pincer ligand. Bimolecular coupling to generate diphenylacetylene and (PCP)Pt-OTf (6) was observed in the case of the rigid PCP-based complex 5, while the hemilabile PCN-based complex 2 was converted to an ylide-bridged dimeric structure, the formation of which was promoted by the decoordination of the ligand amine arm. In addition, formation of the stable metalsubstituted azine-type binuclear complex 10, generated by reaction of 2 with Rh-2(OAc)(4), is described.

The study of the effect of self-assembled organic monolayers on the critical current in thin superconducting Nb films is presented. Correlation is found between the coverage of the adsorbed layer and the critical current. A large change of up to 50% in the critical current by the well-organized monolayers is observed. The phenomenon is explained by the adsorption-induced electric field effect diminishing the surface pinning force.

The title compound, a new fluorinated stilbazole-based chromophore combines hydrocarbon (HC) donor and perfluorocarbon (PFC) acceptor sites in one rigid-rod-type conjugated molecule. The bifunctional stilbazole derivative combines several possibilities of weak, medium, and strong intermolecular interactions leading to an attractive crystal packing. The chromophore shows strong pi-pi stacking behavior in solution, while its crystal structure consists of an infinite unimolecular network involving both interchain pi-pi stacking and (NBr)-Br-... halogen bonding. The latter Lewis acid-base interactions do not play a dominant role in controlling the solution optical properties. In the solid state, the molecules are aligned in one-dimensional infinite head-to-tail chains as a result of attractive halogen bonding. Adjacent chains are oriented in opposite directions.

Cooperative effects generate new electronic and magnetic properties in closed packed organized organic layers. In layers made from chiral molecules, unexpectedly large electronic dichroism is observed, which manifests itself as spin specific electron transmission. For many thiolated molecules self-assembled on gold, a surprisingly large ferromagnetism is observed. All the observations can be rationalized by assuming orbital ferromagnetism of the organic thin layer. This is a new type of magnetism that is caused by the formation of closed packed layers of organic molecules on metal. In particular, charge transfer occurs between the substrate and the adsorbed layer. This charge is responsible for the appearance of magnetism.

The cyclo-octasulfur (S₈) molecule is presented as the basis for conductive Au/S₈ macrocrystalline systems. Photolysis of 4,4′-dithiodipyridine in pyridine/water solution was used for the production of S₈ microcrystals. The mechanism of the photochemical reaction was verified by X-ray crystallography. The polymorphism of S ₈ can be used for shape-controlled crystallization.

MgB2 superconducting wires were produced by the Mg diffusion method. Scanning electron microscopy (SEM), optical microscopy, dispersive X-ray analysis (EDS), and XRD diffraction were used to study the physical structure and content of the wires. Magnetic properties (T-c(m), H-c1, H-c2, J(c) by the Bean model) were obtained with a SQUID magnetometer, and transport properties (T-c(r), H-c2, resistivity and residual resistivity ratio) were measured using a standard four-lead configuration. The V-I characteristics of the wires close to the critical temperature showed a staircase response, which was attributed to the presence of weak links, creating phase slip centers. The origin of those weak links is discussed in relation to their formation and structure.

New electronic and magnetic properties are induced by the adsorption of close-packed monolayers of thiols on gold. In layers made from chiral molecules, unexpectedly large electronic dichroism is observed, which manifests itself as spin-specific electron transmission. For many thiolated molecules self-assembled on gold, a surprisingly large ferromagnetism is observed. All the observations can be rationalized by assuming orbital ferromagnetism of the organic thin layer. This is a new type of magnetism, induced by the formation of a closed packed layer of organic molecules on metal. The adsorption results in charge transfer between the substrate and the adsorbed layer, which is the origin of this magnetism.

The magnetization of an ensemble of isolated lead grains of sizes ranging from 4 to 1000 nm is measured. A sharp disappearance of the Meissner effect with a lowering of the grain size is observed for the smaller grains. This is a direct observation by magnetization measurement of the occurrence of a critical particle size for superconductivity, which is consistent with Anderson's criterion.

Meissner fraction in the superconducting state of lead archaeological artifacts is used to evaluate the mass of the uncorroded metal in the sample. Knowing the total mass of the sample, the mass of all corrosion products is established. It is shown that this mass correlates with the archaeological age of the lead artifacts over a time span of similar to2500 years. Well-dated untreated lead samples from Tel-Dor, the Persian period, Caesarea, the Byzantine and the Crusader periods as well as contemporary data were used to establish the dating correlation. This new chemical dating method is apparently applicable to lead artifacts buried in soils with pH >6.5. In such soils the corrosion process is very slow and the corrosion products, mainly PbO and PbCO3, accumulate over hundreds of years. The method presented is in principle non-destructive.

Unique occurrence of magnetism is shown, in which magnetism appears ex nihilo, when organic molecules are self-assembled as monolayers on gold substrate. The molecules as well as the substrate, when they stand alone, are diamagnetic. Using a superconducting quantum interference device type magnetometer we obtained direct evidence that close-packed organized thio-organic films adsorbed on gold substrates possess magnetic properties at room temperature. The films studied show very high specific magnetization, up to many tens Bohr magnetons per adsorbed molecule, with a very small hysteresis. It is highly anisotropic and shows almost no temperature dependence. The magnetism observed is related to charge transfer between the organic layer and the metal substrate. Yet, the uniqueness here is that many spins are polarized per adsorbed molecules. The magnetic effect is related to the two dimensional organization of the organic molecules on the metal substrate which might explain the high anisotropy. (C) 2003 American Institute of Physics.

Layered metal disulfides - MoS2 and WS2 in the form of fullerene-like (IF) nanoparticles and in the form of platelets (crystallites of the 2H polytype) have been intercalated by exposure to alkali metal (potassium and sodium) vapor using a two-zone transport method. The composition of the intercalated systems was established using X-ray energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). X-ray powder diffraction (XRD) analysis and transmission electron microscopy (TEM) of the samples, which were not exposed to the ambient atmosphere, showed that they suffered little change in their lattice parameters. On the other hand, after exposure to ambient atmosphere, substantial increase in the interplanar spacing (3-5 Angstrom) was observed for the intercalated phases. Insertion of one to two water molecules per intercalated metal atom was suggested as a possible explanation for this large expansion along the c-axis. The modifications in magnetic and transport properties of the intercalated materials were investigated, and are believed to occur via charge transfer from the alkali metal to the conduction band of the host lattice. Restacking of the MS2 layers after prolonged exposure to the atmosphere and recovery of the pristine compound properties were observed as a result of deintercalation of the metal atoms.

Layered metal disulfides-MS₂ (M = Mo, W) in the form of fullerene-like nanoparticles and in the form of platelets (crystallites of the 2H polytype) have been intercalated by exposure to alkali metal (potassium and sodium) vapor using a two-zone transport method. The composition of the intercalated systems was established using X-ray energy dispersive spectrometer and X-ray photoelectron spectroscopy (XPS). The alkali metal concentration in the host lattice was found to depend on the kind of sample and the experimental conditions. Furthermore, an inhomogeneity of the intercalated samples was observed. The product consisted of both nonintercalated and intercalated phases. X-ray diffraction analysis and transmission electron microscopy of the samples, which were not exposed to the ambient atmosphere, showed that they suffered little change in their lattice parameters. On the other hand, after exposure to ambient atmosphere, substantial increase in the interplanar spacing (3-5 Å) was observed for the intercalated phases. Insertion of one to two water molecules per intercalated metal atom was suggested as a possible explanation for this large expansion along the c-axis. Deintercalation of the hydrated alkali atoms and restacking of the MS₂ layers was observed in all the samples after prolonged exposure to the atmosphere. Electric field induced deintercalation of the alkali metal atoms from the host lattice was also observed by means of the XPS technique. Magnetic moment measurements for all the samples indicate a diamagnetic to paramagnetic transition after intercalation. Measurements of the transport properties reveal a semiconductor to metal transition for the heavily K intercalated 2H-MOS₂. Other samples show several orders of magnitude decrease in resistivity and two- to five-fold decrease in activation energies upon intercalation. These modifications are believed to occur via charge transfer from the alkali metal to the conduction band of the host lattice. Recovery of the pristine compound properties (diamagnetism and semiconductivity) was observed as a result of deintercalation.

The experimentally observed ferromagnetism in MgB2 in the normal state is attributed to microphase-separated inclusions of iron. This magnetic character is also observed when the iron content of the samples is reduced below 20 mug/g, however in these samples the diamagnetism of MgB2 is apparent and is measured. It is found experimentally that the diamagnetic susceptibility at room temperature of B element, MgB2, and MgB4 is close to the ratio 1:2:4, suggesting that the diamagnetism in these borides is confined to the boron atoms. This observation supports a picture in which the two electrons of Mg are donated to B in MgB2.

It is known that Cs_xWO₃, 0.3 ≥ x ≥ 0.19, is a 3D superconductor. Below x = 0.19 a transition from a metal to an insulator occurs and for x = 0.10, for example, no superconductivity is observed. We find, however, that for x ≤ 0.05 superconductivity reappears. For x = 0.005 nominal concentration we observe a critical transition T_c to the superconducting state at 5.9 K. This is observed in magnetic measurements, where a pronounced Meissner effect is present. X-ray photoelectron spectroscopy and transport measurements indicate that the SC state is confined to mesoscopic islands, some 10 nm thick on the surface of the Cs_xWO₃ doped crystals. The bulk of the crystal is practically pure WO₃. Thus during the high temperature crystal growth process, there is a redistribution of the Cs dopant as it migrates to the surface of the WO₃ crystals. From these observations, we conclude that upon reduction of the Cs nominal concentration below x = 0.05, a 2D superconductor is formed, while for x ≥ 0.19, the Cs_xWO₃ bronze is a 3D superconductor.

The crystal structure and the magnetic properties of the W1-xNbxO3-delta, (x

Composites consisting of MgB2 and Al, 11% by volume, undergo a transition-to-superconductivity onset at T-C = 38 K, close to the value reported for pure MgB2. The transition appears to have broadened, as determined by both magnetic and transport measurements, possibly due to the proximity effect and disorder. Spatially resolved tunnelling spectroscopy at 4.2 K shows a distribution of gap structures, from Bardeen-Coopel-Schrieffer-like spectra with 2 Delta /k(B)T(C) = 3.2 to spectra that are typical for proximity superconductors.

WO3 crystals were doped with Na on the surface to similar to7% nominal atomic concentration. Scanning tunneling microscopy and spectroscopy were employed, together with magnetization measurements, in the study of these crystals. Tunneling experiments reveal superconducting islands, 20-150 nm in size, covering about 10% of the surface, the rest of which is insulating. Magnetization measurements show that the superconducting phase formed at the surface has a critical temperature of 91 K, while tunneling spectroscopy yields superconducting gaps having values up to 2 Delta /kT(c) similar to 4. Presumably most of the sodium is concentrated in these islands and therefore they are metallic in nature, above 30% in atomic concentration. This material is therefore a noncuprate superconductor with a high critical temperature.

CuInSe₂ single crystals prepared by the traveling heater method were investigated by synchrotron X-ray diffraction. Three sample types were investigated: as-grown, n-type; samples converted to p-type by annealing with Se; and samples subjected to an electric field leading to n⁺/p/n transistor formation. Clear evidence for the thermally-assisted electromigration mechanism proposed for electric-field induced transistor formation was observed. The observations provide important support for the model of ion migration-mediated self-stabilization of CuInSe₂-based solar cells.

Scanning tunneling spectroscopy along with magnetization measurements were employed in the study of Na-doped WO3. The magnetization data suggest that a superconducting phase is formed below T-C = 91 K. Tunneling experiments reveal islands, 20-150 nm in size, having a superconductor-like density of states. These islands cover about 10% of the surface, the rest of which is insulating, and exhibit spectroscopic gaps having values up to 2 Delta/kT(C) similar to 4. Therefore this material seems to be a non-cuprate superconductor with a high critical temperature.