Showing papers in "European Journal of Inorganic Chemistry in 2004"

Supramolecular Host‐Guest Systems in Zeolites Prepared by Ship‐in‐a‐Bottle Synthesis

Abstract: Zeolites have a microporous system defining large cavities interconnected by smaller windows. These cages can accommodate large molecules whose size, however, can be too big to cross the windows. The most important examples of these tridirectional zeolites are faujasites X and Y, but examples of other suitable zeolites are Beta, EMT and MCM-22. The inclusion of large guests inside the cavities starts from smaller precursors that can diffuse through the zeolite pores and then react inside the cavities to form the target guest. This microreview discusses the special characterisation techniques necessary to study these systems, differentiating those that serve to assess the identity and purity of the guests from those that address the internal vs. external location of the guests with respect to the zeolite host. It is organized by grouping the examples of ship-in-a-bottle synthesis according to the potential application of the system as catalysts, photocatalysts, sensors, in molecular machines, etc. Although proper credit is given to the pioneering reports on ship-in-a-bottle synthesis, the emphasis is placed on the most recent examples of the literature covering up to mid 2003. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Novel Supramolecular Frameworks Self-Assembled from One-Dimensional Polymeric Coordination Chains

Abstract: The novel supramolecular frameworks [Cd(BDC)(phen)(H2O)]n (2) and [Cd2(HBTC)2(phen)2]2n·nCd(HBTC)(phen)2 (3) have been synthesized by reaction of the metal source Cd(phen)2(NO3)2 (1) with benzene-1,4-dicarboxylic acid (H2BDC) and benzene-1,3,5-tricarboxylic acid (H3BTC), respectively in a mixed solution of DMF/C2H5OH/H2O. The three-dimensional supramolecular structure of 2 is constructed through hydrogen-bond and aromatic π−π interactions between adjacent metal-organic polymeric coordination chains. Conversely, interestingly, the supramolecular architecture 3 is formed by extending 1-D metal-organic polymeric coordination chains into a 3-D framework by hydrogen-bond interactions between polymeric coordination chains and metal-organic coordination complexes instead of by interchain hydrogen-bond interactions. Additionally, these three compounds exhibit strong fluorescence at room temperature in the solid state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Microwave‐Induced Polyol‐Process Synthesis of Copper and Copper Oxide Nanocrystals with Controllable Morphology

Abstract: Different morphologies of copper and copper oxide nanocrystallites, including radially arrayed whiskers, cubic particles and sphere particles, have been successfully synthesized by a microwave-induced method under ambient conditions. In aqueous solution containing different ethylene glycol concentrations, copper acetate hydrate produces different reduction products. The as-prepared copper and copper oxide crystallites were characterized by various techniques, including X-ray powder diffraction, transmission electron microscopy, selected-area electron diffraction and UV/Vis absorption spectroscopy. It was found that microwave irradiation plays a critical role in the formation of the products; temperature was also found to be important in the reaction. The irradiation time and copper acetate concentration also affect the morphology of the products. The possible formation mechanism is also discussed. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Switching of Molecular Spin States in Inorganic Complexes by Temperature, Pressure, Magnetic Field and Light: Towards Molecular Devices

Abstract: The spin crossover phenomenon in molecular inorganic compounds is one of the most spectacular examples of bistability phenomena leading to a switching between the high-spin and the low-spin states of the molecule by several means such as temperature, pressure, light and magnetic field (multi-property molecular switching). In the present microreview we report our most important findings, both experimental results and theoretical approaches, and discuss possible technological applications for each switching method as well as the recent synthesis of new spin crossover molecular materials. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Transition Metal Chemistry of Low Valent Group 13 Organyls

Abstract: The coordination of low-valent group 13 organyls EIR [E = Al, Ga, In; R = Cp*, C(SiMe3)3] to transition metals has attracted increasing interest over the past decade. Complexes and cluster compounds of these new ligands with a number of transition metals have been isolated and characterised. The EIR moiety is formally isolobal with CO and PR3 (R = alkyl, Cp*) or carbenes (R = chelating group) with varying σ-donor and π-acceptor properties depending on the organic group R as well as the group 13 metal E. In this review, different ways of forming M−E bonds such as substitution reactions of labile ligands or insertion of EIR into transition metal halide bonds are described. Furthermore, the reactivity of homoleptic complexes Ma(EIR)b is discussed, outlining the use of these new complex types in bond activation reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Complex Formation of ICL670 and Related Ligands with FeIII and FeII

Abstract: Complex formation of 4-[3,5-bis(2-hydroxyphenyl)-1,2,4-triazol-1-yl]benzoic acid (ICL670, H3Lx), 4-[3,5-bis(2-hydroxyphenyl)-1,2,4-triazol-1-yl]benzosulfonic acid (H3Ly), and 3,5-bis(2-hydroxyphenyl)-1-phenyl-1,2,4-triazole (H2Lz) with Fe3+ and Fe2+ was investigated in H2O and in H2O/DMSO mixtures by potentiometry, spectrophotometry and cyclic voltammetry. ICL670 has previously been considered as a promising drug for an oral treatment of iron overload. In this paper, the stability and redox properties of the various FeII and FeIII complexes were elucidated with a particular focus on their potential involvement in the generation of oxidative stress. The overall stability constants of [FeIII(Lx)] and [FeIII(Lx)2]3− (25 °C, 0.1 M KCl in H2O) are log β1 = 22.0 and log β2 = 36.9, respectively. The affinity of these ligands for Fe2+ is remarkably poor. In particular, the 1:2 complexes [FeII(Lx)2]4− and [FeII(Ly)2]4− were found to be less stable. As a consequence, the redox chemistry of the [FeIII(Lx)]/[FeII(Lx)]− and the [FeIII(Lx)2]3−/[FeII(Lx)2]4− couples differs significantly. [FeIII(Lx)2]3− is a very weak oxidizing agent (E1/2 is approximately −0.6 V versus NHE) and reduction of [FeIII(Lx)2]3− is not anticipated under physiological conditions. The reduction potential of the [FeIII(Lx)]/[FeII(Lx)]− couple is considerably less negative and was estimated to be +0.1 V (versus NHE). The possible roles of the various Fe complexes as catalysts for the Fenton reaction in biological media are discussed. The crystal structures of H3Lx, Na[Fe(Lz)2]·4EtOH, Na[Al(Lz)2]· 4EtOH, and [Cu(Lz)(pyridine)]2 were investigated by single-crystal X-ray diffraction, and the possible influence of the particular steric requirements of these ligands on the stability of the metal complexes has been analyzed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Effect of Substitution of Methyl Groups on the Luminescence Performance of Ir(III) Complexes: Preparation, Structures, Electrochemistry, Photophysical Properties and Their Applications in Organic Light-Emitting Diodes (OLEDs)

Abstract: A series of dimethyl-substituted tris(pyridylphenyl)iridium(III) derivatives [(n-MePy−n′-MePh)3Ir] [n = 3, n′ = 4 (1); n = 4, n′ = 4 (2); n = 4, n′ = 5 (3); n = 5, n′ = 4 (4); n = 5, n′ = 5 (5)] have been synthesized and characterized to investigate the effect of the substitution of methyl groups on the solid-state structure and photo- and electroluminescence. The absorption, emission, cyclic voltammetry and electroluminescent performance of 1−5 have also been systematically evaluated. The structures of 2 and 4 have been determined by a single-crystal X-ray diffraction analysis. Under reflux (> 200 °C) in glycerol solution, fac-type complexes with a distorted octahedral geometry are predominantly formed as the major components in all cases. Electrochemical studies showed much smaller oxidation potentials relative to Ir(ppy)3 (Hppy = 2-phenylpyridine). All complexes exhibit intense green photoluminescence (PL), which has been attributed to metal-to-ligand charge transfer (MLCT) triplet emission. The maximum emission wavelengths of thin films of 1, 3, 4 and 5 at room temperature are in the range 529−536 nm, while 2 displays a blue-shifted emission band (λmax = 512 nm) with a higher PL quantum efficiency (ΦPL = 0.52) than those of complexes 1 and 3−5; this is attributed to a decrease of the intermolecular interactions. Multilayered organic light-emitting diodes (OLEDs) were fabricated by using three (2, 3 and 4) of these IrIII derivatives as dopant materials. The electroluminescence (EL) spectra of the devices, which have the maximum peaks at 509−522 nm, with shoulder peaks near 552 nm, are consistent with the PL spectra in solution at 298 K. The devices show operating voltages at 1 mA/cm2 of 4.9, 5.6, 5.1, and 4.6 V for Ir(ppy)3, 2, 3, and 4, respectively. In particular, the device with 2 shows a higher external quantum efficiency (ηext = 11% at 1 mA/cm2) and brightness (4543 cd/m2 at 20 mA/cm2) than Ir(ppy)3 (ηext = 6.0% at 1 mA/cm2; 3156 cd/m2 at 20 mA/cm2) and other Ir(dmppy)3 derivatives, (dmppy = dimethyl-substituted ppy), under the same conditions. The methyl groups at the meta (Ph) and para (Py) positions to the Ir metal atom have a great influence on absorption, emission, redox potentials and electroluminescence. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Samarium(II) Iodide Mediated Reductions − Influence of Various Additives

Abstract: Samarium(II) iodide is a one-electron transfer reagent that has become highly appreciated as a mild and selective reducing agent in recent years. It has been found experimentally that various additives and co-solvents largely control the reactivity of SmI2. This microreview provides an overview of the current knowledge of the reagent SmI2 as a reducing agent, in particular with additives that increase its reactivity. The use of various proton sources is covered, as well as the effect of co-solvents. Furthermore, the very powerful reagent mixture SmI2/H2O/amine is also described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Multiproperty Molecular Materials: TTF-Based Conducting and Magnetic Molecular Materials

Abstract: The chemistry and physics of molecule-based materials are exciting subjects, and due to potential applications this area is being extensively investigated. Considerable effort is currently being made to design and to investigate new materials involving interplay or synergy between multiple physical properties. This microreview examines materials combining magnetism and electrical properties. Some fundamental background material is covered, together with a discussion of constraints on the design of molecular materials with these physical properties. Some examples from the literature are then related, in order to illustrate the achievements in this area. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Hydroxamic Acids − An Intriguing Family of Enzyme Inhibitors and Biomedical Ligands

Abstract: This review on hydroxamic acids deals with their efficacy as inhibitors of enzymes including cyclooxygenases, their synthesis, the complexity and structural diversity of their metal complexes, and their ability to act as effective nitric oxide donors. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Hydrothermal Syntheses, Crystal Structures and Photoluminescent Properties of Three Metal‐Cluster Based Coordination Polymers Containing Mixed Organic Ligands

Abstract: Three novel metal-cluster based coordination polymers (MCCPs) with formulae [Zn4(μ3-OH)2(H2O)2(sip)2(4,4′-bpy)2]·3H2O (MCCP-4), [Cd4(μ3-OH)2(H2O)2(sip)2(4,4′-bpy)4]·H2O (MCCP-5) and [Cd6(μ3-OH)4(μ2-OH2)2(OH2)2 (nip)4(4,4′-bpy)3]·3H2O (MCCP-6) [H2sip = 5-sulfoisophthalic acid, H2nip = 5-nitroisophthalic acid and 4,4′-bpy = 4,4′-bipyridyl] were hydrothermally synthesized and characterized by single-crystal X-ray diffraction studies. MCCP-4 crystallizes in the triclinic space group P with a = 10.106(2), b = 10.851(2), c = 11.125(2) A, α = 105.66(3), β = 112.63(3), γ = 98.18(3)°, V = 1041.8(4) A3, and Z = 2. MCCP-5 crystallizes in the monoclinic space group C2/c with a = 25.602(1), b = 16.571(1), c = 13.322(1) A, β = 92.524(1)°, V = 5646.4(2) A3, and Z = 4. MCCP-4 and -5 consist of similar [M4(μ3-OH)2]6+ tetranuclear building units that are joined through sip and 4,4′-bpy ligands to generate a two-dimensional structure (MCCP-4) and a three-dimensional structure (MCCP-5), respectively. MCCP-6 crystallizes in the triclinic space group P with a = 14.295(2), b = 14.472(2), c = 20.204(3) A, α = 73.362(3), β = 82.200(3), γ = 62.769(2)°, V = 3560.9(10) A3, and Z = 2. MCCP-6 contains unprecedented [Cd6(μ3-OH)4(μ2-OH2)2]8+ hexanuclear building units which are linked through nip and 4,4′-bpy ligands to afford a two-dimensional structure. The infrared spectroscopy, thermal stability and photoluminescence of the three complexes were studied. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The Dynamic Status Quo of Polyhedral Silsesquioxane Coordination Chemistry

Abstract: The chemistry of polyhedral oligomeric silsesquioxanes (POSS) has taken a tremendous leap over the past decade. New synthetic approaches have been developed, and new complexes based on elements throughout the periodic table have been synthesized and applied in catalytic processes such as alkene epoxidation, Oppenauer oxidation, alkene polymerization, Diels−Alders reactions and alkene metathesis. The use of silsesquioxane ligands as models for silica surface has provided an intimate knowledge of the reactions on the surface of this much-used support. New methods have been developed to incorporate silsesquioxanes into new materials. Encapsulation in siloxane polymers has provided precision supports for catalysts and controlled calcination has produced materials with well-defined metal oxide particles. This paper reviews the history and the latest developments of silsesquioxane chemistry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The "Rebound Controversy": An Overview and Theoretical Modeling of the Rebound Step in C-H Hydroxylation by Cytochrome P450

Abstract: C−H hydroxylation by the enzyme cytochrome P450 is one of Nature’s important and most ubiquitous processes. There is strong evidence that the mechanism proceeds by initial hydrogen abstraction, from the alkane, by the high-valent iron−oxo species of the enzyme, followed by a rebound of the alkyl radical to form the ferric−alcohol product complex (the Groves “rebound” mechanism). Nevertheless, the “rebound” mechanism is still controversial due to the ultrashort radical lifetimes deduced from radical-clock experiments. This review describes the main elements of the controversy and its updated resolution by theory, with an emphasis on the controversial rebound step. The theoretically derived model for alkane hydroxylation is found to involve two-state reactivity (TSR). In TSR, radicals are produced on two different spin-state surfaces, and thereafter they react differently; on the low-spin surface, the rebound proceeds with no product rearrangement and the lifetime of the radicals is ultrashort (or zero), while on the high-spin surface the barrier for rebound is substantial and the lifetime of the radical is sufficiently long that rearrangement may compete with product formation by rebound. A new valence-bond model is developed to model the rebound barrier on the high-spin surface and conceptualize its dependence on the nature of the alkyl radical. The possible intermediacy of carbocationic intermediates alongside radicals is discussed. It is shown that the TSR scenario provides a satisfactory rationale for the controversial findings in the field, and makes verifiable predictions. One of the predictions of TSR is that the ratio of unrearranged to rearranged products, [U/R], will be subject to an intrinsic isotope effect that is substrate-dependent. This prediction and its possible verification by experiment are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

An Ni-4 single-molecule magnet: Synthesis, structure and low-temperature magnetic behavior

Abstract: The reaction of Ni(NO3)2·6H2O with H3thme (trihydroxymethylethane) in the presence of NaOMe leads to a tetranuclear Ni4 complex with a cubane-like structure. Intramolecular ferromagnetic interactions [J = 10 cm−1 based on H = −J(S1·S2 + S1·S3 + S1·S4 + S2·S3 + S2·S4 + S3·S4)] lead to an S = 4 ground state stabilized by 40 cm−1 from the first S = 3 excited state. Magnetization vs. field studies at different temperatures above 2 K suggest the presence of an axial magnetic anisotropy. Single-crystal magnetization measurements show a single-molecule-magnetic behavior below T = 0.5 K with fast relaxation of the magnetization due to resonant quantum tunneling. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The Electronic Structure of (Diiminopyridine)cobalt(I) Complexes

Abstract: DFT calculations show that square-planar (LCoR)-R-I complexes of a diiminopyridine ligand are best regarded as containing low-spin Co-II antiferromagnetically coupled to a ligand radical anion. The lowest triplet state, corresponding to a 3d(z)(2)-->pi* excitation, is calculated to be only a few kcal/mol above the ground state, and is thermally accessible. The anomalous H-1 NMR chemical shifts of the LCoR complexes are suggested to be due to thermal population of the triplet state at room temperature. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Zinc Guanidinate Complexes and Their Application in Ring‐Opening Polymerisation Catalysis

Abstract: The insertion reaction between 1 equiv. of carbodiimide, RN=C=NR, and the zinc bis(amide) [Zn{N(SiMe3)2}2] affords the homoleptic zinc(II) guanidinate compounds [Zn{(Me3Si)2NC(NR)2}2] (3, R = iPr; 4, R = Cy) in preference to the monosubstituted compounds. Compound 3 also results from the protonation reaction of 1 equiv. of the neutral guanidine (Me3Si)2NC(NiPr)(NHiPr) (2) with [Zn{N(SiMe3)2}2] or ZnMe2. In contrast, the N-dimethylguanidine analogue Me2NC(NiPr)(NHiPr) (1) reacts cleanly with 1 equiv. of ZnMe2 to afford the dimeric species [Zn{Me2NC(NiPr)2}Me]2 (5). Attempted protonation of the Zn-C bond in 5 with 2,6-di-tert-butylphenol resulted in preferential reaction at the Zn-N bond and formation of the mixed (aryloxo)methyl complex [Zn(OAr)M{Me2NC(NiPr)(NHiPr)}] (6), isolated as the guanidine adduct. Heating of 6, in an attempt to promote methane elimination, afforded a small amount of the dimetallic complex [{Zn(OAr)}2(-{Me2NC(NiPr)2})(-NMe2)] (7) as a result of the extrusion of NMe2- from the guanidine-based ligand. The amine-elimination reaction between [Zn{N(SiMe3)2}2] and 1 equiv. of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) proceeds smoothly to afford the mixed (guanidinate)(amide) complex [Zn(hpp){N(SiMe3)2}]2 (8), which forms a dimer in the solid state. Crystal structures of compounds 3-8 are reported and a preliminary study of the activity of 8 in the ring-opening polymerisation of lactide is described.

New porous lanthanide-organic frameworks: Synthesis, characterization, and properties of lanthanide 2,6-naphthalenedicarboxylates

Abstract: Three porous, 3-D coordination polymers [Pr4(NDC)6(H2O)6]·2H2O (1), [Eu4(NDC)6(H2O)5]·3H2O (2) and [Yb2(NDC)3(H2O)]·H2O (3) based on lanthanide 2,6-naphthalenedicarboxylates (NDC) were synthesized by hydrothermal reactions of lanthanide chlorides with NDC and their properties were investigated. Polymers 1, 2 and 3 differ in the coordination environment of the LnIII ions. Their 3-D networks are reminiscent of the shape of a compressed honeycomb, showing 1-D open channels. The guest water molecules and coordinating water molecules are enclathrated in the channels. The photophysical properties of the Eu3+ complex were investigated by high-resolution luminescence spectroscopy. The results indicate that there are four EuIII ion sites in complex 2, which is in accordance with the results of the single-crystal X-ray diffraction studies. Thermogravimetric and variable-temperature powder X-ray diffraction analyses show that the porous frameworks of this series of complexes are relatively stable. The framework remained even when the guest molecules were lost and did not collapse until the temperature reached 430 °C. The magnetic properties of 2 were also investigated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Main Chain Ferrocenyl Amides from 1‐Aminoferrocene‐1′‐carboxylic Acid

Abstract: The non-natural amino acid 1-aminoferrocene-1′-carboxylic acid is synthesised from ferrocene in eight steps. The folding and association phenomena of amido-substituted ferrocenes in the crystal as well as in solution are studied by X-ray crystallography, IR and NMR spectroscopy and DFT calculations. The amino acid is selectively protected at the amino group with the use of the fluorenyl-9-methoxycarbonyl (Fmoc) group. An amide-linked ferrocene dimer is prepared using the HOBt/DCC protocol for amide formation. In the crystal the dimer forms a hydrogen-bonded sheet structure, while in solution dynamic intramolecular hydrogen bonds are observed by VT 1H NMR and IR spectroscopy. The dynamic flipping process has been rationalised by DFT calculations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Hydrolytic Cleavage of DNA by Ternary Amino Acid Schiff Base Copper(II) Complexes Having Planar Heterocyclic Ligands

Abstract: The ternary copper(II) complexes [Cu(salgly)L] (L = phen, 1; dpq, 2), [Cu(salala)L] (L = phen, 3; dpq, 4) and [Cu(salphe)L] (L = phen, 5; dpq, 6), where salgly, salala and salphe are tridentate Schiff-base ligands derived from the condensation of salicylaldehyde with glycine, L-alanine and L-phenylalanine, respectively, are prepared and their nuclease activity studied (phen, 1,10-phenanthroline; dpq, dipyridoquinoxaline). The crystal structure of 3 displays a distorted square-pyramidal (4+1) coordination geometry in which the ONO-donor Schiff base is bonded to the metal atom in the basal plane. The chelating phen ligand displays an axial-equatorial mode of bonding. The complexes exhibit a d-d band near 670nm and a charge transfer band near 370nm in methanol. The one-electron paramagnetic complexes display axial EPR spectra in DMF glass at 77K, indicating a ${d_{x2-y2}} ^1$ ground state. The complexes are redox-active and exhibit a quasi-reversible CuII/CuI couple in DMF at approximately -0.6 V vs. SCE. They show catalytic activity in the oxidation of ascorbic acid by molecular oxygen. The ability of the complexes to bind calf thymus (CT) DNA follows the order: 2 \approx 4 \approx 6 > 1 \approx 3 \approx 5. Complexes 1-6 show oxidative DNA cleavage activity in the presence of mercaptopropionic acid as a reducing agent. All the complexes show hydrolytic cleavage activity in the absence of light or any reducing agent. The oxidative and hydrolytic DNA cleavage efficiencies follow the order: 2 \approx 4 \approx 6 > 1 \approx 3 \approx 5. The dpq complexes, which have a greater DNA binding ability, display enhanced nuclease activity than their phen analogues. The hydrolytic DNA cleavage rate of 1.8 h-1, observed for 2, is significantly high relative to most of the known copper-based synthetic hydrolases. Mechanistic pathways involved in the nuclease activity of the complexes are discussed.

Functionalization of Polyoxometalates by a Negatively Charged Bridging Ligand: The Dimeric [(SiW11O39Ln)2(μ-CH3COO)2]12− (Ln = GdIII, YbIII) Complexes

Abstract: The possibility of coupling lacunary polyoxometalates through a cationic center present in the vacancy by negatively charged organic ligands is demonstrated for the first time by single-crystal X-ray diffraction. The structure of the dimeric K12[{Yb(α-SiW11O39)(H2O)}2(μ-CH3COO)2]·38H2O complex, where two acetato ligands connect the ytterbium centers in a (η2, μ-1,1) fashion, is reported. Using gadolinium instead of ytterbium, both the isostructural dimeric compound K12[{Gd(α-SiW11O39)(H2O)}2(μ-CH3COO)2]·38H2O and the mononuclear sandwich complex [Gd(SiW11O39)2]13− can be selectively isolated, depending on the synthetic conditions. The magnetic properties of the dimeric gadolinium complex are presented. The influence of the nature of the rare-earth metal on the final compound is further highlighted by the fact that when praseodymium is used as the rare-earth element, only the sandwich compound can be obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Cyclopentadienyl RuII Complexes as Highly Efficient Catalysts for the N‐Methylation of Alkylamines by Methanol

Abstract: The ruthenium(II) half-sandwich complex [RuCl(η5-C5H5)(PPh3)2] (1) catalyses the reaction between methanol and alkylamines RNH2 or R1R2NH to afford RN(CH3)2 and R1R2NCH3 products, respectively. The reaction is quantitative and generally fast, at the methanol reflux temperature, for a wide spectrum of substrates. Starting from primary amines, the stepwise formation of RN=CH2, RNHCH3, and RN(CH3)2 has been observed. Both PPh3 and Cl− dissociation from 1 are key-steps in forming the effective catalytic species. The catalytic activity of several half-sandwich neutral or cationic complexes (2−15) related to 1 is also discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Phenyl 2‐Pyridyl Ketone and Its Oxime in Manganese Carboxylate Chemistry: Synthesis, Characterisation, X‐ray Studies and Magnetic Properties of Mononuclear, Trinuclear and Octanuclear Complexes

Abstract: The use of phenyl 2-pyridyl ketone [(ph)(2-py)CO] and its oxime [(ph)(2-py)CNOH] in manganese benzoate chemistry has been investigated. The reaction of an excess of (ph)(2-py)CNOH with Mn(O2CPh)2·2H2O affords the mononuclear complex [MnII(O2CPh)2{(ph)(2-py)CNOH}2]·1.2H2O (1·1.2H2O) in high yield. The MnII ion is coordinated by two monodentate benzoates and two N,N′-bidentate chelating (ph)(2-py)CNOH molecules in a cis-cis-trans fashion. The comproportionation reaction between Mn(O2CPh)2·2H2O and NnBu4MnO4 (3:1) in the presence of (ph)(2-py)CNOH in MeCN/EtOH/CH2Cl2 leads to the isolation of the mixed-valent cluster [Mn8O2(OH)2(O2CPh)10{(ph)(2-py)CNO}4]· 4CH2Cl2 (2·4CH2Cl2) in about 55% yield. A second synthetic procedure that leads to pure 2 involves the reaction between the known starting material (NnBu4)[Mn4IIIO2(O2CPh)9(H2O)] and four equivalents of the oxime ligand in CH2Cl2. The centrosymmetric octanuclear molecule contains four MnII and four MnIII ions held together by two μ4-O2− ligands and two μ3-OH− ions to give the unprecedented [Mn8(μ4-O)2(μ3-OH)2]14+ core, with peripheral ligation provided by ten PhCO2− (two η1, four syn,syn η1:η1:μ2 and four η1:η2:μ3) and four η1:η1:η1:μ2 (ph)(2-py)CNO− ions. The 1:1 reaction between Mn(O2CPh)2·2H2O and the ketone (ph)(2-py)CO affords the trinuclear complex [Mn3(O2CPh)6{(ph)(2-py)CO}2] (3) in more than 80% yield. As judged from single-crystal X-ray crystallography, the complex adopts a linear structure with one η1:η2:μ2 and two η1:η1:μ2 benzoates spanning each pair of metal ions. The terminal MnII ions are capped by bidentate chelating (ph)(2-py)CO ligands. The three complexes have been characterised by IR spectroscopy. The CV study of complex 2 in CH2Cl2 reveals irreversible reduction and oxidation processes. The magnetic properties of 2 and 3 have been studied by variable-temperature dc magnetic-susceptibility techniques. As the temperature approaches zero, the value of the χMT product for 2 approaches zero and, thus, the octanuclear complex has an S = 0 ground state. This S = 0 ground state is explained in terms of the magnetic behaviour of the central, butterfly-like [Mn4III(μ3-O)2]8+ subcore. The results for 3 reveal weak antiferromagnetic coupling, with J = −2.7 cm−1 for adjacent MnII ions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Crystal Engineering of the Coordination Architecture of Metal Polycarboxylate Complexes by Hydrothermal Synthesis: Assembly and Characterization of Four Novel Cadmium Polycarboxylate Coordination Polymers Based on Mixed Ligands

Abstract: Four novel compounds, [Cd(tp)(bpp)]n (1), [Cd(tp)(bpy)]n (2), [{Cd4(bpa)4(bpy)6}·(bpy)0.5·7H2O]n (3) and [Cd2{(Htp)(tp)1.5}(bpe)]n (4) [tp = terephthalate, bpp = 1,3-bis(4-pyridyl)propane, bpy = 4,4′- bipyridine, bpa = 4,4′-biphenyldicarboxylate, bpe = 1,2-bis(4-pyridyl)ethane], of cadmium(II) polycarboxylate coordination polymers based on mixed ligands were obtained by a hydrothermal method. Complex 1 (C21H18CdN2O4) crystallizes in the orthorhombic Pbca space group [a = 11.9401(0) A, b = 16.8148(3) A, c = 20.2743(3) A, and Z = 8]. Complex 2 (C18H12CdN2O4) belongs to the monoclinic C2/m space group [a = 20.299(3) A, b = 10.720(1) A, c = 11.764(2) A, β = 110.944(2)°, and Z = 6]. Complex 3 (C121H98Cd4N13O23) belongs to the monoclinic P21/c space group [a = 23.2208(0) A, b = 11.8103(1) A, c = 45.4670(6) A, β = 104.516(1)°, and Z = 4]. Complex 4 (C32H23Cd2N2O10) belongs to the monoclinic P21/n space group [a = 6.9896(1) A, b = 22.6294(1) A, c = 19.7738(3)A, β = 99.380(1)°, and Z = 4].The CdII centers in the four compounds are bridged by mixed polycarboxylate ligands with bpy and related species to form the twofold parallel interpenetration topology of an undulating 2D 44 net for 1, a twofold interpenetration topology of a 3D α-Po net for 2, a fourfold interpenetration topology of a 3D 5-connected borazone 4664 net for 3 and an interesting 3D spiral pipe-like structure with a bolt for 4. These four compounds exhibit strong fluorescent emissions at 549 and 582 nm (λex = 532 nm) for 1, 493 nm (λex = 360 nm) for 2, 413 and 424 nm (λex = 315 nm) for 3 and 350 nm (λex = 220 nm) for 4 in the solid state at room temperature. These are novel structural topologies and could be significant in the field of photoactive materials. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

1D‐Polyoxometalate‐Based Composite Compounds − Design, Synthesis, Crystal Structures, and Properties of [{Ln(NMP)6}(PMo12O40)]n (Ln = La, Ce, Pr; NMP = N‐methyl‐2‐pyrrolidone)

Abstract: The structures of three 1:1 composite compounds prepared with the polyoxometalate (POM) [PMo12O40]3− and the cations [Ln(NMP)6]3+ [Ln = La (1), Ce (3), Pr (2); NMP = N-methyl-2-pyrrolidone] exhibit two types of zig-zag chains with alternating cations and anions through Mo−Ot−Ln−Ot−Mo links in the crystal. The compounds were characterized by IR, UV, and ESR spectroscopy, single-crystal X-ray structural analysis, and by a study of their thermal properties. In all the compounds, the La3+, Pr3+, and Ce3+ centers are eight-coordinate with the oxygen atoms in bicapped trigonal-prismatic geometries. The variation of the average Ln−O separations along the La, Ce, and Pr series is consistent with the effects of the lanthanide contraction. The results of the single-crystal X-ray diffraction analyses and the IR spectroscopic studies are in agreement and both show the metal cation units are coordinatively bonded to the Keggin clusters. The UV spectra of the title compounds suggest that their structures are entirely disrupted in dilute solution. Low-temperature ESR spectra indicate that thermal electron delocalization occurs among the Mo atoms in the three compounds. The results of cyclic voltammetry (CV) show that compounds 1, 2, and 3 all undergo five two-electron reversible reductions and that the [PMo12O40]3− anions are the active centers for electrochemical redox reactions in solution, while the corresponding cations have only a small effect on the electrochemical properties. Studies of magnetic properties show that 1 is diamagnetic, while 2and 3 exhibit antiferromagnetic Pr−Pr or Ce−Ce exchange interactions. In addition to the results of CV, the average bond lengths and the magnetic properties of compound 3 indicate that the oxidation state of cerium is III in the compound of formula [{Ce(NMP)6}(PMo12O40)]n. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Comparative Electrochemical Study of Unsubstituted and Substituted Bis(phthalocyaninato) Rare Earth(III) Complexes

Abstract: The electrochemistry of homoleptic substituted phthalocyaninato rare earth double-decker complexes M(TBPc)2 and M(OOPc)2 [M = Y, La...Lu except Pm; H2TBPc = 3(4),12(13),21(22),30(31)-tetra-tert-butylphthalocyanine, H2OOPc = 3,4,12,13,21,22,30,31-octakis(octyloxy)phthalocyanine] has been comparatively studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in CH2Cl2 containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). Two quasi-reversible one-electron oxidations and three or four quasi-reversible one-electron reductions have been revealed for these neutral double-deckers of two series of substituted complexes, respectively. For comparison, unsubstituted bis(phthalocyaninato) rare earth analogues M(Pc)2 (M = Y, La...Lu except Pm; H2Pc = phthalocyanine) have also been electrochemically investigated. Two quasi-reversible one-electron oxidations and up to five quasi-reversible one-electron reductions have been revealed for these neutral double-decker compounds. The three bis(phthalocyaninato)cerium compounds display one cerium-centered redox wave between the first ligand-based oxidation and reduction. The half-wave potentials of the first and second oxidations and first reduction for double-deckers of the tervalent rare earths depend on the size of the metal center. The difference between the redox potentials of the second and third reductions for MIII(Pc)2, which represents the potential difference between the first oxidation and first reduction of [MIII(Pc)2]−, lies in the range 1.08−1.37 V and also gradually diminishes along with the lanthanide contraction, indicating enhanced π−π interactions in the double-deckers connected by the smaller, lanthanides. This corresponds well with the red-shift of the lowest energy band observed in the electronic absorption spectra of reduced double-decker [MIII(Pc′)2]− (Pc′ = Pc, TBPc, OOPc).

Electronic Structures and Reactivities of Corrole−Copper Complexes

Abstract: The spectroscopic and electrochemical examination of the mononuclear copper complexes of 5,10,15-tris(pentafluorophenyl)corrole and 5,10,15-tris(2,6-dichlorophenyl)corrole (1a and 2a, respectively) and of the corresponding dinuclear corrole dimers 1b and 2b reveal the existence of two almost degenerate electronic states. The lower state consists of copper(III) ions coordinated by closed-shell corrolato trianions and the higher state is composed of copper(II) ions chelated by open-shell corrolato dianions. The contributions from both states are evident in the molecular structure of monomeric and mononuclear 2a, which displays a distorted square-planar coordination geometry around the metal ion and short Cu−N bond lengths typical of copper(III), together with some non-equivalence of the Cα−Cmeso bond lengths that might reflect the open-shell character of the macrocycle. The latter state is most likely to be responsible for the dimerization process. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Chemical Vapor Deposition of Niobium Disulfide Thin Films

Abstract: Atmospheric pressure chemical vapor deposition (APCVD) of niobium sulfide coatings was achieved on glass substrates from the reaction of NbCl5 and S(SiMe3)(2), tBu(2)S(2), tBuSH, or HSCH2CH2SH at 250-600degreesC. The niobium sulfide films grown at temperatures above 500degreesC were crystalline, and powder X-ray diffraction showed that two polytypes of NbS2 were produced. The sulfur precursor used is fundamental to the polytype of NbS2 obtained; films that are grown from the APCVD reaction of NbCl5 and S(SiMe3)(2) or tBu(2)S(2) at 500-600degreesC crystallize into the 1T structure, whereas those grown from the APCVD reaction of NbCl5 and tBuSH or HSCH2CH2SH at 500-600 degreesC crystallize into the 3R structure. Energy dispersive X-ray analysis (EDXA) studies gave elemental ratios close to the expected 1:2 ratio for Nb:S. Scanning electron microscopy (SEM) revealed surface morphologies consistent with an island growth mechanism. The films were also characterized using Raman and X-ray photoelectron spectroscopy, both of which showed differences consistent with the formation of the two polytypes, 1T and 3R-NbS2.

A Rational Self‐Sacrificing Template Route to β‐Bi2O3 Nanotube Arrays

Abstract: Arrayed β-Bi2O3 nanotubes (NTs) were synthesized for the first time through a rational “self-sacrificing template” route, simply by oxidizing the precursor metallic bismuth NT arrays in air at 200−220 °C for 14−18 h. XRD, TEM, and HRTEM characterizations show that the prepared β-Bi2O3 samples are all phase pure and the β-Bi2O3 NTs have uniform diameters of approximately 3−6 nm and lengths up to several micrometers. The optical absorption and photoluminescence (PL) characteristics of the prepared samples were investigated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Heteroatom‐Substituted Group 4 Bis(indenyl)metallocenes

Abstract: The synthesis, characterization and applications of heteroatom-substituted group 4 bis(indenyl)metallocene complexes is reviewed. In recent years, an increasing number of group 4 metallocenes with electronically modified cyclopentadienyl ligands have been reported with, in some cases, considerably altered catalytic properties. This microreview focuses on bis(indenyl) complexes of titanium, zirconium and hafnium that contain nitrogen, oxygen and sulfur atoms directly bonded to the five- or six-membered rings of the indenyl ligand framework. The catalytic performance is briefly reviewed, with emphasis on catalytic olefin polymerization. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Supramolecular hydrogen-bond structures and magnetic interactions in basal-apical, dinuclear, azide-bridged copper(II) complexes

Abstract: The synthesis, characterisation, X-ray single crystal structures and magnetic properties of three new basal-apical mu(2)-1,1-azide-bridged complexes [(CuLN3)-N-1](2) (1), [(CuLN3)-N-2](2) (2) and [(CuLN3)-N-3](2) (3) with very similar tridentate Schiff-base blocking ligands {HL1 = N-[2-(ethylamino) ethyl] salicylaldimine; HL2 = 7-(ethylamino)-4-methyl-5-azahept-3-en-2-one; HL3 = 7-amino-4-methyl-5-azaoct-3-en-2-one} have been reported [complex 1: monoclinic, P2(1)/c, a = 8.390(2), b = 7.512(2), c = 19.822(6) Angstrom, beta = 91.45(5)degrees; complex 2: monoclinic, P2(1)/c, a = 8.070(9), b = 9.787(12), c = 15.743(17) A, beta = 98.467(10)degrees; complex 3: monoclinic, P2(1)/n, a = 5.884(7), b = 16.147(18), c = 11.901(12) Angstrom, beta = 90.050(10)degrees]. The structures consist of neutral dinuclear entities resulting from the pairing of two mononuclear units through end-on azide bridges connecting an equatorial position of one copper centre to an axial position of the other, The copper ions adopt a (4+1) square-based geometry in all the complexes. In complex 2, there is no inter-dimer hydrogen-bonding. However, complexes 1 and 3 form two different supramolecular structures in which the dinuclear entities are linked by H-bonds giving one-dimensional systems. Variable temperature (300-2 K) magnetic-susceptibility measurements and magnetisation measurements at 2 K reveal that all three complexes have antiferromagnetic coupling. Magneto-structural correlations have been made taking into consideration both the azido bridging ligands and the existence of intermolecular hydrogen bonds. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).