Abstract: The exploration of the NiX(2)/py(2)CO/Et(3)N (X = F, Cl, Br, I; py(2)CO = di-2-pyridyl ketone; Et(3)N = triethylamine) reaction system led to the tetranuclear [Ni(4)Cl(2){py(2)C(OH)O}(2){py(2)C(OMe)O}(2)(MeOH)(2)]Cl(2)·2Et(2)O (1·2Et(2)O) and [Ni(4)Br(2){py(2)C(OH)O}(2){py(2)C(OMe)O}(2)(MeOH)(2)]Br(2)·2Et(2)O (2·2Et(2)O) and the trinuclear [Ni(3){py(2)C(OMe)O}(4)]I(2)·2.5MeOH (3·2.6MeOH), [Ni(3){py(2)C(OMe)O}(4)](NO(3))(0.65)I(1.35)·2MeOH (4·2MeOH) and [Ni(3){py(2)C(OMe)O}(4)](SiF(6))(0.8)F(0.4)·3.5MeOH (5·3.5MeOH) aggregates. The presence of the intermediate size Cl(-) and Br(-) anions resulted in planar tetranuclear complexes with a dense hexagonal packing of cations and donor atoms (tetramolybdate topology) where the X(-) anions participate in the core acting as bridging ligands. The F(-) and I(-) anions do not favour the above arrangement resulting in triangular complexes with an isosceles topology. The magnetic properties of 1-3 have been studied by variable-temperature dc, variable-temperature and variable-field ac magnetic susceptibility techniques and magnetization measurements. All complexes are high-spin with ground states S = 4 for 1 and 2 and S = 3 for 3.
Abstract: The LaXO(3):Tb(3+) (X = Al(3+), Ga(3+), In(3+)) perovskite nanoparticles were obtained using the nonhydrolytic treatment (Bradley reaction) of the molecular precursors of the La(O(i)Pr)(3), Al(O(i)Pr)(3), Ga(O(i)Pr)(3), In(5)O(O(i)Pr)(13), and Tb(acac)(3), respectively. It was shown that crystal structure and morphology evolution in the LaXO(3), X = Al, Ga, In nano-oxide series depended on the size and chemical properties of the X-metal atom. Formation of the LaInO(3):Tb(3+) nanoparticles is distinctly less thermodynamically demanding on contrary to the LaAlO(3):Tb(3+) and LaGaO(3):Tb(3+) since it provided crystalline product directly in the solution synthesis at 202 °C, which is the lowest reported synthesis temperature for this compound up-to-date. This behavior was ascribed to the effects directly connected with the dopant substitution (exchange of bigger La(3+) cation with smaller Tb(3+)) as well as reduction of the particle size. The size effects are mostly reflected in the expansion of the cell volume, changes of the cell parameters as well as shifting and broadening of the Raman bands. Indirectly, size reduction has also an effect on the luminescence properties through the higher probability of presence of surface and net defects as well as heterogeneous distribution of the Tb(3+) ions caused by high surface-to-volume ratio. The prepared nanophosphors show basically green emission with exception of white-green in case of the LaInO(3):Tb(3+). Strong emission quenching was found in the latter case being most likely a consequence of the nonradiative energy transfer between Tb(3+) and In(3+) as well as the presence of defects. In comparison to the Pechini's method, the LaXO(3) nanoparticles required significantly lower annealing temperature (700 °C) necessary for complete crystallization. Generally the resulting particles are distinctly smaller (5 to 25 nm) and less agglomerated (50-100 nm) depending on the reaction conditions as well as thermal treatment. For the first time, it was shown that the LaGaO(3):Tb(3+) nanopowder has crystallized in the high-temperature rhombohedral R3c phase.
Abstract: Recent developments in scanning electron microscopy (SEM) have produced tabletop instruments capable of reasonable imaging resolution at less cost compared to conventional equipment. Combining the SEM with energy dispersive spectroscopy (EDS) allows the possibility of elemental analysis through detection of X-rays emitted from interaction between individual particles and the SEM electron beam, revealing their atomic composition. It's well known that exposure to inhalable particulate matter (PM) poses health risks and routine monitoring of the chemical content of these has been realized. Exposure information is of a general character but by combining the chemical build-up of monitored particles and knowledge of their inherent health effects will allow better risk assessment. An analysis technique using a tabletop SEM with EDS is demonstrated on particles collected onto nucleopore filters from urban, industrial and rural areas. Detailed characterization of the instruments analysis capabilities as applied to PM are described.
Abstract: Strontium titanate SrTiO3 thin films are highly perspective as gate dielectric material. Difference in volatility of the common homometallic precursors-strontium beta-diketonates and titanium alkoxides remains major hinder for preparation of high quality coatings based on this phase. An attractive alternative in its synthesis by MOCVD is provided by application of heterometallic mixed-ligand complexes, Sr2Ti2(beta-diket)4(OR)8(ROH)x. Mass-spectrometric study reveals, however, that none of these species can be considered a true single-source precursor. The relative stability of the molecules in solution and the congruence of in-situ release of homometallic species on evaporation are, on the other hand, crucial for the quality of the produced films and are strongly influenced by the nature of alkoxide ligands, OR. The historically first discovered representative of this heterometallic family, a sec-alkoxide derivative Sr2Ti2(thd)4(O(i)Pr)8, is in fact unexpectedly unstable, transforming in solution into Sr2Ti(thd)4(O(i)Pr)4((i)PrOH), which explains difficulties in keeping the correct stoichiometry using isopropoxide precursor. The primary alkoxide complexes, Sr2Ti2(thd)4(OR)8(ROH)2, R = Et, (n)Pr are also unstable yielding Sr4Ti2(thd)4(OR)8(ROH)2 on decomposition. The best solution stability and most uniform evaporation was observed for the iso-derivative, Sr2Ti2(thd)4(O(i)Bu)8, permitting to apply it in long term experiments under industrial process conditions. Present contribution provides detailed experimental comparison between and sec-and iso-alkoxide derivatives and sheds light on the influence of the ligand on molecular stability of a precursor and how it influences the quality of the derived oxide film, especially in relation to its electrophysical properties.
Abstract: The use of an inorganic perrhenate ligand in the structure of early-transition-metal alkoxide precursors permits to achieve uniform self-assembly of the primary nanoparticles produced by their hydrolysis. The latter has been carried out in a hydrocarbon reaction medium by the addition of water with vigorous stirring, either in the pure form or in solutions in parent alcohols. The self-assembly is guided by the surface charge enhanced by the presence of strongly coordinated anions as determined by zeta potential measurements. The aggregation process has been followed in real time by nanoparticle tracking analysis (NanoSight technique). The reaction products are spherical aggregates with a size that can be efficiently controlled through the polarity of the reaction medium. The produced nanobeads have been characterized by TEM, SEM-EDS, DLS, nitrogen adsorption, and FTIR. The coordination of metal centers has been investigated using EXAFS spectroscopy. The aggregates remain amorphous on thermal treatment of up to 700 °C (24 h treatment) but crystallize when treated at 1000 °C. This latter process is associated with the total loss of rhenium content and offers early-transition-metal oxides as products.
Abstract: Nanoparticles of a broad variety of main group and transition metal oxides appear to form exceptionally stable surface complexes with the ligands incorporating phosphate or phosphonate moiety. In the present work we demonstrate the formation and stability of such complexes on an example of BaTiO3 perovskite with the aid of scanning electron microscopy/energy dispersive spectroscopy, pH-metric titration, NMR and IR spectroscopy, dynamic light scattering, ζ potential, nanoparticle tracking analysis, thermogravimetric analysis, and radiometric measurements. Application of amino phosphonic acids as surface ligands provides nanoparticles with considerable solution stability in an aqueous medium at neutral pH and especially in the presence of electrolytes. This opens broad prospects of application for the thus produced nanoparticle dispersions in the domains of nano-optics and nanomagnetism. The same effect is observed even for surface complexation with nucleotides or phosphorylated proteins, using adenosine-triphosphate (ATP) and phosphocreatine (PCr) as model compounds, permitting the production of highly stable dispersions of specifically biologically targeted nanoparticles (particles supplied with predesigned biomolecular “coronaâ€) for use in magnetic resonance and optical imaging and even in drug delivery as supported by in vitro measurements. We have shown that the presented approach might be successfully broadened for other types of mixed metal oxide systems constituted of nanoparticles.
Abstract: Palladium (Pd) nanoparticles are recognized as components of airborne automotive pollution produced by abrasion of catalyst materials in the car exhaust system. Here we produced dispersions of hydrophilic spherical Pd nanoparticles (Pd-NP) of uniform shape and size (10.4 ± 2.7 nm) in one step by Bradley's reaction (solvothermal decomposition in an alcohol or ketone solvent) as a model particle for experimental studies of the Pd particles in air pollution. The same approach provided mixtures of Pd-NP and nanoparticles of non-redox-active metal oxides, such as Al(2)O(3). Particle aggregation in applied media was studied by DLS and nanoparticle tracking analysis. The putative health effects of the produced Pd nanoparticles and nanocomposite mixtures were evaluated in vitro, using human primary bronchial epithelial cells (PBEC) and a human alveolar carcinoma cell line (A549). Viability of these cells was tracked by vital dye exclusion, and apoptosis was also assessed. In addition, we monitored the release of IL-8 and PGE(2) in response to noncytotoxic doses of the nanoparticles. Our studies demonstrate cellular uptake of Pd nanoparticles only in PBEC, as determined by TEM, with pronounced and dose-dependent effects on cellular secretion of soluble biomarkers in both cell types and a decreased responsiveness of human epithelial cells to the pro-inflammatory cytokine TNF-α. When cells were incubated with higher doses of the Pd nanoparticles, apoptosis induction and caspase activation were apparent in PBEC but not in A549 cells. These studies demonstrate the feasibility of using engineered Pd nanoparticles to assess the health effects of airborne automotive pollution.
Abstract: Application of different solvating ligands drastically changes the composition and geometry of bimetallic sodium−tantalum pinacolates, forming insoluble and stable organic−inorganic hybrid materials through Van der Waals interactions. The loss of these neutral ligands on heating leads to contraction and densification of the structures, with formation of covalent metal−organic frameworks (MOFs) as intermediates, and resulting in direction-specific cracking and formation, on further thermal decomposition, of low-dimensional nanomorphologies—wires or plates of the same oxide material, containing well-crystalline monoclinic NaTaO3 as its major component. The crystallographic features of the precursor structures permitting us to control further morphological differentiation on the transformation to oxide material are identified.
Abstract: Strontium titanate SrTiO3 thin films have attracted interest as a possible gate dielectric material. Preparation of its high quality coatings is hindered by difference in volatility of the homometallic precursors – strontium beta-diketonates and titanium alkoxides. The only earlier known single-source precursor, a sec-alkoxide derivative Sr2Ti2(thd)4(OiPr)8, has limited volatility. Bimetallic primary alkyl chain complexes, Sr4Ti2O(thd)4(OR)10(ROH)2, R = Et, nPr, are stable and volatile, but possess a wrong composition. Highly volatile precursor Sr2Ti2(thd)4(OiBu)8 has been prepared using an iso-alkoxide, combining proper ligand size with the sterical requirements, and characterized by multivariate evaporation analysis. Its evaporation is associated with complete decomposition into homometallic species, which, however, are evaporated in a single step. This permits to successfully use this novel precursor for SrTiO3 thin film deposition by DLI-MOCVD technique in a sufficiently broad established temperature range. Using optimized experimental conditions, 100nm thick strontium titanate films with high permittivity have been successfully obtained on (1 0 0) Si.
Abstract: Nanoparticles of a Nd-doped LaAlO(3) perovskite can be obtained rapidly and with quantitative yield using the Bradley (ether elimination) treatment of a mixture of individual Ln(2)Al(2)(O(i)Pr)(12)((i)PrOH)(2), Ln = La, Nd, in acetophenone. The initially produced particles are poorly crystalline, but their crystallinity improves strongly on heating to 800 degrees C, which leads also to a controllable aggregation. The prepared nanoparticles are rather solution stable and can easily be surface-modified, which opens prospects for their use as phosphors in bioimaging applications. The precursors, bimetallic isopropoxides of rare earth elements and aluminum with a 1:1 composition, Ln(2)Al(2)(O(i)Pr)(12)((i)PrOH)(2), can be prepared with high yields via direct dissolution of metallic lanthanoids in a solution of aluminum isopropoxide in a toluene-isopropanol medium or through a short time reflux of "Ln(O(i)Pr)(3)" with 1 equiv of Al(O(i)Pr)(3) in toluene. In spite of good volatility and their proper composition, the Ln(2)Al(2)(O(i)Pr)(12)((i)PrOH)(2), Ln = La, Nd, do not act as single-source precursors in MOCVD, because of their quantitative transformation into LnAl(3)(O(i)Pr)(12) together with Ln(5)O(O(i)Pr)(13) on evaporation. These molecules are, however, present intact in solution according to variable temperature NMR studies, which permits application of them successfully as single source precursors in the synthesis of Ln:LaAlO(3) perovskite nanopowders with compositions thoroughly controlled through the conditions of the synthesis. Luminescent properties of the Nd:LaAlO(3) were examined and discussed in detail. The thermal population of the (4)F(5/2) and (2)H(9/2) states was found as a consequence of the grain size effect causing difficulties in heat dissipation. Moreover, luminescence behavior of the powder annealed at a lowest temperature shows well-defined short-range order.
Abstract: The first representatives of alkoxy-zircono-silsesquioxane compounds, dinuclear [Cy7Si7O12]Zr(ROH)(μ-OR)2Zr(ROH)[O12Si7Cy7], where R=nPr, nBu, tBu; Cy=c-C6H11, and [Cy*7Si7O12]Zr(μ-ROH)(μ-OR)2Zr [O12Si7Cy*7], R=tBu; Cy*=c-C5H9, have been prepared with quantitative yield by interaction of the corresponding zirconium alkoxides with the cycloalkyl-substituted cage silsesquioxanes in hexane. The Xray single crystal study of the n-butoxide derivative revealed that zirconium atoms are hexacoordinated with the 3 oxygen atoms of the cage ligand, 2 — from the bridging alkoxide groups and one — from the solvating alcohol molecule in the coordination sphere. The molecule is additionally supported by a hydrogen bond between the solvating alcohol and an oxygen atom belonging to the cage ligand coordinated by the other zirconium atom. The structures of produced silsesquioxanes display behavior typical for metal–organic frameworks as they crystallize initially as hexane clathrates, but lose the solvent on storage in inert atmosphere. This results in formation of empty channels situated along the c-axis.
Abstract: Interaction of M(acac)(2) with Ti(OEt)(4) associated with hydrolysis or thermolysis provides with high yields, through the decomposition of the initially formed M(2)Ti(2)(acac)(4)(OEt)(8), M = Ni (1), Co (2), poorly soluble Lindqvist-type products with the formula M(5)TiO(acac)(6)(OEt)(6), M = Ni (3), Co (4), Mg (5). The compounds 3-5 are isostructural and display a perfect statistical disorder between the OEt groups and 1/2 of the beta-diketonate, acac, ligand. The metal atoms constitute a regular octahedron, centered by the oxo-oxygen atom. There is only one symmetrically independent metal site, which imposes it to contain 1/6 of titanium and 5/6 of the divalent metal atom. The oxygen atoms on the surface of the octahedron are doubly bridging and are located above the twelve edges of the octahedron, as is usual for the Lindqvist-type structures. The coordination of the metal atoms is completed by a single terminal oxygen atom. The complexes 3-5 are volatile with decomposition, releasing only homometallic products into the gas phase in the case of 3 and 4, but with a considerable contribution of molecular evaporation in the case of 5. The intermediates 1 and 2 belong to the tetramolybdate, M(4)O(16), structure type. Highly soluble 1 and 2 can be considered as attractive molecular precursors for the incorporation of 3 and 4 into porous matrices for the preparation of combustion catalysts. Application of the same synthetic approach to n-propoxide complexes offers in a Co-Ti system a derivative with a different composition and resolved metal and ligand disorder, Co(4)Ti(2)O(acac)(4)(O(n)Pr)(10) (6), which, however, still follows the Lindquist type and displays high (tetragonal) symmetry for both the molecule and the crystal structure.
Abstract: Hierarchically porous hybrid microparticles, strikingly reminiscent in their structure of the silica skeletons of single-cell algae, diatoms, but composed of titanium dioxide, and the chemically bound amphiphilic amino acids or small proteins can be prepared by a simple one-step biomimetic procedure, using hydrolysis of titanium alkoxides modified by these ligands. The growth of the hierarchical structure results from the conditions mimicking the growth of skeletons in real diatoms--the self-assembly of hydrolysis-generated titanium dioxide nanoparticles, templated by the microemulsion, originating from mixing the hydrocarbon solvent and water on action of amino acids as surfactants. The obtained microsize nanoparticle aggregates possess remarkable chemical and thermal stability and are promising substrates for applications in drug delivery and catalysis. They can be provided with pronounced surface chirality through application of chiral modifying ligands. They display also high selectivity in sorption of phosphorylated biomolecules or medicines as demonstrated by (1)H and (31)P NMR studies and by in vitro modeling using (32)P-marked ATP as a substrate. The release of the adsorbed model compounds in an inert medium is a very slow process directed by desorption kinetics. It is enhanced, however, noticeably in contact with biological fluids modeling those of the tissues suffering inflammation, which makes the produced material highly attractive for application in medical implants. The developed synthetic approach has been applied successfully also for the preparation of analogous hybrid microparticles based on zirconium dioxide or aluminum sesquioxide.
Abstract: New insight into the factors determining formation and stability of oxo-alkoxide carboxylates of titanium permits to design biocompatible systems for encapsulation of binary food quality inorganic dyes, such as Preussian blue, in a temperature-sensitive shell. The shells are formed spontaneously on hydrolysis of carboxylic acid-modified titanium alkoxides on the surface of water droplets containing the dye components. The complete dye is then prepared through mixing of pre-frozen encapsulated droplets which can be activated by heating to room temperature and also influenced by the storage time. The stable shells are obtained from longer chain carboxylates providing the micellar self-assembly derived constructions with increased colloid stability. The factors influencing the formation of individual crystalline oxoalkoxide carboxylates—a process competing with the micellar self-assembly and decreasing the stability of the oxo-alkoxide carboxylate shells are discussed with the starting point in the molecular structures of the known compounds and also the new complexes Ti6O6(OAc)6 (OiPr)6 C6H14 (1) and Ti12O12(OAc)6(OnPr)18 (2).
Abstract: The molecular structures of the species crystallizing from solutions of alkoxytitanasilsesquioxanes in hydrocarbons upon reflux confirm the partial release of solvating alcohol. They feature, however, distinctly the formation of a dinuclear core with preserved hexacoordination for the metal atoms. The active titanium centers in the silica-titania epoxidation catalysts, lacking the sterically demanding ligands, are thus quite probably also hexacoordinated.
Abstract: Investigation of the solvent and alkoxide precursor effect on the nonhydrolytic sol-gel synthesis of oxide nanoparticles by means of an ether elimination (Bradley) reaction indicates that the best crystallinity of the resulting oxide particles is achieved on application of aprotic ketone solvents, such as acetophenone, and of smallest possible alkoxide groups. The size of the produced primary particles is always about 5 nm caused by intrinsic mechanisms of their formation. The produced particles, possessing the composition of natural highly insoluble minerals, are biocompatible. Optical characteristics of the perovskite complex oxide nanoparticles can easily be controlled through doping with rare earth cations; for example, by Eu3+. They can be targeted through surface modification by anchoring the directing biomolecules through a phosphate or phosphonate moiety. Testing of the distribution of Eu-doped BaTiO3 particles, modified with ethylphosphonic acid, demonstrates their facile uptake by the plants with active fluid transport, resulting finally in their enhanced concentration within the cell membranes.
Abstract: An attempt to utilize a Co(II) cubane cluster as a building block to create extended frameworks results instead in the transformation of the cube into a dimer of dimers.
Abstract: The formation of nanoparticles in hydrolytic and non-hydrolytic reactions in organic media is treated as a borderline case of coordination chemistry equilibria. Metal cation complexes with O-donor ligands, such as metal alkoxides or beta-diketonates and carboxylates, experience normally no kinetic hinders in re-structuring and aggregation. The steps of hydrolysis and condensation constitute in this case parts of one and the same kinetic phenomenon. Introduction of oxo-ligands during the first steps of hydrolytic or thermal decomposition leads thus in homogeneous processes to well-defined oligonuclear oxo-species. The structure of the latter is originating from the densest possible packing of cations and ligands and is not in any mean related to the structure of the original precursor molecules. The oxo-alkoxide molecules serve apparently as nuclei for the formation of larger aggregates that become phase separated and can be referred to as Micelles Templated by Self-Assembly of Ligands. The core of the latter is practically always crystalline or at least short-order organized, while the shell is, in the hydrolytic approach, constructed of hydrated amorphous oxide and ligands that stabilize the colloid via interaction with the solvent. The thermal treatment either in solution or for a dry xerogel is thus indispensable for preparation of fully crystalline particles and offers also an opportunity to control the final size of the particles via further aggregation. To guarantee the formation of complex oxide nanoparticles, the conditions insuring phase separation for each component have to be achieved. This means that the use of stoichiometric or super-stoichiometric quantities of water is required together with a solvent guaranteeing minimal solubility of hydrolyzed species. The approaches to complex oxide phases and oxides doped with lanthanide cations are discussed.
Abstract: The paper represents a listing of results obtained by developing the original methods of controlled synthesis of cluster and mono-, bi- and trimetallic oxo-alkoxide derivatives of rhenium and d-elements of V-VI groups. The developed techniques of the synthesis of metal alkoxides include: (1) anodic dissolution of the metals in the alcohol media; (2) direct reaction of the rhenium (VII) oxide with alkoxide derivatives of the transition elements. By such techniques were obtained: Re4O4(OEt)(12), Re4O6((OPr)-Pr-i)(10); individual rhenium alkoxocomplexes: Re4O2(OMe)(16), Re4O6(OMe)(12), Re4O6-y(OMe)(12+y); bimetallic ReMoO2(OMe)(7), Re4-xMoxO6-y(OMe)(12+y), Re4-xWxO6-y(OMe)(12+y); Nb-2(OMe)(8)(ReO4)(2), Ta-2(OMe)(8)(ReO4)(2), Nb4O2(OMe)(14)(ReO4)(2), Ta4O2(OMe)(14)(ReO4)(2), Nb4O2(OEt)(14)(ReO4)(2), Ta4O2(OEt)(14)(ReO4)(2), alkoxocomplexes: Nb2-xTax(OMe)(8)(ReO4)(2), Nb4-xTaxO2(OMe)(14)(ReO4)(2), Nb4-xTaxO2(OEt)(14)(ReO4)(2). All compounds mentioned above are characterized with X-ray single crystal study, IR-spectroscopy, DTG. It has been shown, that thermal decomposition of alkoxide derivatives in inert or hydrogen atmosphere leads to formation nano-size powders of individual rhenium and its alloys at low temperature. Thermal decomposition in air leads to formation individual metal oxides or its solid solutions. It has been demonstrated that the alkoxide derivatives could be promising precursors for next generation catalysts manufacturing.
Abstract: The reactions of Ga(acac)(3) with salicylaldoxime (saoH(2)) and methyl-salicylaldoxime (Me-saoH(2)) in dichloromethane/hexane afforded the complexes [Ga(acac)(saoH)(2)] (1) and [Ga(acac)(3)][Ga(acac)(MesaoH)(2)] (2), respectively, in high yields. The crystal structures of I and 2 have been determined by single-crystal X-ray crystallography. Both complexes are mononuclear with the Ga(Ill) atoms being in octahedral environments surrounded by two bidentate chelate R-saoH(-) and one bidentate chelate acac(-) ligands. A [Ga(acac)(3)] moiety has co-crystallized along with the methylsalicylaldoximato complex. Characteristic IR as well as NMR data are discussed in terms of the nature of bonding in the structures of the two complexes. H-1 and C-13 NMR data in CDCl3 indicate that the salicylaldoximato, complexes isomerize in solution. (C) 2009 Elsevier Ltd. All rights reserved.
Abstract: Long-term storage at 0 A degrees C of a paraffin-sealed flask with commercial 70 wt% solution of zirconium n-propoxide in n-propanol resulted in crystallization of an individual oxoalkoxide complex Zr4O((OPr)-Pr-n)(14)((PrOH)-Pr-n)(2) in over 20% yield. The structure of this molecule can be described as a triangular Zr-3(mu(3)-O)(OR)(10)(ROH) core of 3 edge-sharing octahedrons with an additional Zr(OR)(4)(ROH) unit attached through a pair of (mu-OR) bridges. Mass spectrometric and H-1 NMR investigation of the commercial samples of the most broadly applied zirconium and hafnium n-propoxides and n-butoxides indicate the presence of analogous species in the commercial alkoxide precursors. The content of oxo-alkoxide species in the commercial precursors has been estimated to be similar to 20% for n-propoxide and similar to 35% for zirconium n-butoxide. A new route has been presented for synthesis of the individual crystalline mixed ligand precursor [Zr((OPr)-Pr-n)((OPr)-Pr-i)(3)((PrOH)-Pr-i)](2), from zirconium n-propoxide. A high yield has been observed (similar to 90%), indicative of an almost complete precursor transformation. Mass spectrometry has shown that the synthesized mixed ligand precursor is dimeric, which makes it an attractive alternative to zirconium n-propoxide. Addition of 1 eq of Acetylacetone to zirconium or hafnium alkoxide precursors results in formation of dimeric [M(OR)(3)(acac)](2) in high yields. These species have limited stability (much higher for Hf than for Zr) and transform in solution into hydrolysis-insensitive M(acac)(4) through very unstable M(acac)(3)(OR) intermediates containing 7-coordinated metal centers. This transformation can be followed kinetically in hydrocarbon solvents by H-1 NMR and is noticeably accelerated by addition of parent alcohols. The obtained results clearly reveal limited applicability of EXAFS and XANES techniques for the study of such systems, especially in the context of structure prediction.
Abstract: Modification of different zirconium propoxide precursors with H(2)dea was investigated by characterization of the isolated modified species. Upon modification of zirconium n-propoxide and [Zr(O(n)Pr)(O(i)Pr)(3)((i)PrOH)](2) with (1/2) a mol equivalent of H(2)dea the complexes [Zr(2)(O(n)Pr)(6)(OCH(2)CH(2))(2)NH](2) (1) and [Zr(2)(O(n)Pr)(2)(O(i)Pr)(4)(OCH(2)CH(2))(2)NH](2) (2) were obtained. However, (1)H-NMR studies of these tetranuclear compounds showed that these are not time-stable either in solution or solid form. The effect of this time instability on material properties is demonstrated by light scattering and TEM experiments. Modification of zirconium isopropoxide with either (1/2) or 1 equivalent mol of H(2)dea results in formation of the trinuclear complex, Zr{eta(3)mu(2)-NH(C(2)H(4)O)(2)}(3)[Zr(O(i)Pr)(3)](2)(iPrOH)(2) (3) countering a unique nona-coordinated central zirconium atom. This complex 3 is one of the first modified zirconium propoxide precursors shown to be stable in solution for long periods of time. The particle size and morphology of the products of sol-gel synthesis are strongly dependent on the time factor and eventual heat treatment of the precursor solution. Reproducible sol-gel synthesis requires the use of solution stable precursors.
Abstract: The tetragonal BaTiO3 nanopowder is synthesized in a solvent-less, efficient process by the thermolysis of a single [Ba2Ti2(thd)(4)(OnPr)(8)(nPrOH)(2)] precursor in a closed reactor at 700 degrees C under autogenous pressure, followed by combustion. This paper compiles the synthesis of the [Ba2Ti2(thd)(4)(OnPr)(8)(nPrOH)(2)] precursor, its analysis by mass spectrometry, and implementation for the fabrication of dielectric tetragonal BaTiO3 nanopowder by controlled efficient thermal decomposition. The as-prepared, intermediate, and final forms of the obtained nanomaterials are systematically analysed by XRD, Raman, and EDS measurements to gain structural and compositional information. Employing HR-SEM, TEM, and HR-TEM techniques, the morphological changes during the structural evolution of all the phases are pursued. The mechanistic elucidation for the fabrication of BaTiO3 nanopowder is developed on the basis of TGA and DTA data obtained for the initial [Ba2Ti2(thd)(4)(OnPr)(8)(nPrOH)(2)] reactant as well as the as prepared BaCO3 With amorphous Ti phase.
Abstract: The synthesis of Ba-Ti precursors was achieved by a self-assembly synthesis starting from barium metal, titanium n-propoxide and 2,2,6,6-tetramethyl-heptanedione (Hthd) in (PrOH)-Pr-n. The structure of the obtained Ba2Ti2(thd)(4)((OPr)-Pr-n)(8)((n)Pr0H)2 compound is of the M2M2’X-16 type-one of the most widespread for both the homo- and heterometallic tetranuclear alkoxide complexes. It remains unchanged in solution according to the NMR data, which are easily interpreted in terms of the same molecular structure as that revealed by crystallography for the solid state. In order to form BaTiO3 phase doped with 1% of the Eu3+ the heterometallic alkoxide complex of barium and titanium with the necessary amount of Eu dissolved in the reaction mixture were hydrolyzed by moist ethanol on reflux in 1 M solution in n-propanol. The obtained gels were dried in vacuum and have been heat treated at different temperatures (700-1100 degrees C). XRD measurements were performed in order to study the phase formation and grain size. TEM images have been taken for the morphology and grain size characterization. Emission spectra and decay times were measured for the description of the luminescence properties of the obtained system. (c) 2007 Elsevier B.V. All rights reserved.
Abstract: We have investigated the interaction of niobium and tantalum alkoxides with pinacol and are reporting here isolation and structural characterization of the products, attractive potential precursors of materials with hierarchical porosity. The general feature in the reactivity of alkoxide complexes with additional ligands is that stabilization of the complexes is achieved due to Bronsted acidity of the ligand and possibility of formation of hydrogen bonds in the structure. Presence of strong organic bases does not influence the complex formation. We were able to isolate, for example, highly moisture-sensitive ortho-pinacolates of Nb and Ta, M(O2C6H12)(2)(OC6H12OH), in the presence of excess of triethylamine. The earlier attempts to prepare these complexes were unsuccessful because of extremely high solubility and easy hydrolysis of these species. The first step in microhydrolysis of M(O2C6H12)(2)(OC6H12OH), M = Nb, Ta, independently of basicity of the medium provides M2O(O2C6H12)(2)(OC6H12OH)(4), even those highly moisture-sensitive in solution. The general conclusion of this work is that the Lewis acidity and blocking of the coordination sites by bulky alkoxide ligands does not play any important role. The reactivity of the species is not in any way hindered by the complete blocking of the metal centers.
Abstract: Trimetallic oxoalkoxide complexes (Nb0.7Ta0.3)(4)O-2(OMe)(14)(ReO4)(2) (1). (Nb0.3Ta0.7)(4)O-2(OMe)(14)(ReO4)(2) (II) and (Nb0.5Ta0.5)(4)O-2(OMe)(14()Re0(4))(2) (III) Were obtained by the interaction of rhenium heptoxide (VII) Re2O7 With niobium and tantalum alkoxides M-2(OMe)(10) (M = Nb, Ta) in toluene. The centrosymmetric molecules (I)-(III) can be considered as a product of condensation of two M-2(OMe)(9)(OReO3) molecules with the formation of two oxo-bridges. The specific feature of the structure is the uneven distribution of metal atoms in the crystallographic positions, where one symmetry-independent position, connected via mu-O with a perrhenate ReO4- group, is predominantly Occupied by niobium atoms, while the other one connected via alkoxide groups has a higher tantalum content. The distribution of Nb and Ta in the structure is truly even only for compound III. The niobium and tantalum content is varied to a different extent for I (less) and for II (more), which is apparently due to small differences in the sizes of these two cations, resulting in preferences for packing of different molecules in the structures. Thermal decomposition of (Nb1-xTax)(4)O-2(OMe)(14)(ReO4)(2)(x = 0.3, 0.5, 0.7) in air leads to the formation of crystalline species of solid solutions based oil tantalum and niobium oxides displaying semi-ordered pores with the size of 100-250 nm. In the dry nitrogen atmosphere, the decomposition leads to the amorphous complex oxides containing rhenium, niobium and tantalum. (C) 2008 Elsevier Inc. All rights reserved.
Abstract: Zirconia and titania nanoparticle sols were prepared, using either ligand-based precursor stabilization or acid stabilization routes. These sols were used to prepare microporous coatings on gamma-alumina substrates. The acetylacetonate-based particles have very small hydrodynamic diameters (1-2 nm), which lead to sol intrusion into the supports. As a result no appropriate membrane layer was formed. A microemulsion-based zirconia sol leads to a membrane that was selective in pervaporation dehydration of a water/n-butanol mixture. An optimized membrane showed stable separation performance for 120 days with a high selectivity toward water. Permporometry and gas permeation results on a titania membrane based on an acid-stabilized sol not only show microporosity, but also a significant contribution from defect flow.
Abstract: Systematic structural study of the molecules, resulting from microhydrolysis of heterometallic beta-diketonate alkoxides of barium and strontium (single-source precursors of perovskite oxide materials), demonstrates that the structures of these products result from a thermodynamically driven self-assembly of metal cations and ligands directed towards the most densely packed cores. The ratio between metal cations, and of the cations to bidentate heteroligands, is easily changed to enable the highest packing density. The key to the application of single-source precursors appears to be the use of stoichiometric or superstoichiometric water amounts together with solvents preventing diffusion of possible homometallic intermediates. Eu-doped BaTiO3 nanoparticles have been successfully obtained and characterized.
Abstract: A series of new dimeric complexes with composition [Ln(2)(hfa)(6)(4-cpyNO)(3)](2:3 adduct, Ln=Sm-III-Dy-III, Tm-III) were synthesized and fully characterized. X-ray diffraction data of [Tb-2(hfa)(6)(4-cpyNO)(3)]center dot CHCl3 confirmed the dimeric structure; Tb ions are nine-coordinated by six O atoms from three hfa-ligands and three O atoms from three bridging 4-cpyNO molecules. The photophysical properties (absolute quantum yields and luminescence lifetimes) of the Eu-III and Tb-III 2:3 adducts are presented and compared with those of the 2:2 adducts. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: A new non-hydrolytic, alkoxide-based route was developed to synthesize iron oxide nanocrystals. Surfactant-free thermal decomposition of the iron 2-methoxy-ethoxide precursors results in the formation of uniform iron oxide nanocrystals with an average size of 5.6 nm. Transmission electron microscope study shows that the nanocrystals are protected against aggregation by a repulsive surface layer, probably originating from the alkoxy-alkoxide ligands. Addition of oleic acid resulted in monodisperse nanocrystals with an average size of 4 nm. Mossbauer analysis confirmed that the nanocrystals mainly consisted of maghemite. Analysis of the magnetic hysteresis loop measurements and the zero field and field cooled measurements displayed an excellent fit to established theories for single-domain superparamagnetic nanocrystals and the size of the magnetic domains correlated well to the crystallite size obtained from transmission electron microscope. (C) 2007 Elsevier B.V. All rights reserved.
Abstract: Two types of dimeric complexes [Ln(2)(hfa)(6)(mu(2)-O(CH2)(2)NHMe2)(2)] and [Ln(thd)(2)(mu(2),eta(2)-O(CH2)(2)NMe2)](2) (Ln = Y-III, Eu-III, Gd-III Th-III, Tm-III, Lu-III; hfa(-) = hexafluoroacetylacetonato, thd(-) = dipivaloylmethanato) are obtained by reacting [Ln(hfa)(3)(H2O)(2)] and [Ln(thd)(3)], respectively, with NN-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the Th-III compounds confirms their dimeric structure. The coordination mode of NN-dimethylaminoethanol depends on the nature of the beta-diketonate. In [Tb-2(hfa)(6)(mu(2)-O(CH2)(2)NHMe2)(2)], eight-coordinate Th-III ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1 center dot center dot center dot Tb2 separation of 3.684(1) angstrom. In [Tb(thd)(2)(mu 2,eta(2)-O(CH2)(2)NMe2)](2), the N,N-dimethylaminoethanol acts as chelating-bridging O,N-donor anion and the Th-III ions are seven-coordinate; the Th1 center dot center dot center dot Th1A separation amounts to 3.735(2) angstrom within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180 degrees C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The Eu-III and Tb-III dimers display metal-centered luminescence, particularly [Eu-2(hfa)(6)(O(CH2)(2)NHMe2)(2)] (quantum yield Q(Ln)(L) = 58%) and [Tb(thd)(2)(O(CH2)(2)NMe2)](2) (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and Eu-III- or Th-III-doped (0.01-0.1 mol%) Lu-III analogues, leads to the conclusion that both the beta-diketone and NN-dimethylaminoethanol ligands contribute significantly to the sensitization process of the Eu-III luminescence. The ancillary ligand increases considerably the luminescence of [Eu-2(hfa)(6)(O(CH2)(2)NHMe2)(2)], compared to [Ln(hfa)(3)(H2O)(2)], through the formation of intra-ligand states while it is detrimental to Th-III luminescence in both beta-diketonates. Thin films of the most luminescent compound [Eu-2(hfa)(6)(O(CH2)(2)NHMe2)(2)] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.
Abstract: Anodic oxidation of rhenium in ethanol in the presence of LiCl as a conductive additive results with high yield in formation of a new oxoethoxide cluster, Re4O4(OEt)(12). The structure of the planar centrosymmetric metal-oxygen core of this molecule is composed of four edge-sharing Re(V)O-6 octahedra. Eight electrons are available for the formation of metal-metal bonds indicated by five relatively short Re-Re distances within the Re-4-rhombus, a “planar butterfly†type cluster. The theoretical calculations are indicating relatively low contribution of metal-metal bonding in the stability of the core. The stability of the +V-oxidation state, unusual for rhenium alkoxides can be at least partially attributed to the size effects in the packing of ligands. The X-ray powder study indicates that treatment of Re4O4(OEt)(12) in ambient atmosphere rapidly transforms it into a mixed-valence derivative Re4O6(OEt)(10) with a structure related to the earlier investigated cluster Re4O6((OPr)-Pr-i)(10). Thermal decomposition of the latter rhenium oxoethoxide results in reduction to rhenium metal at as low temperatures as 380 degrees C, producing aggregates of metal nanoparticles with the average size of 3 nm.
Abstract: The amorphous bimetallic isopropoxides of variable composition LaZrnOx(OPri)(3+4n-2x), where it = 0.5-3 formed on interaction of the two homometallic isopropoxides, La5O((OPr)-Pr-i)(13) and Zr((OPr)-Pr-i)(4)((PrOH)-Pr-i), in solutions in parent alcohol crystallize slowly yielding a bimetallic oxoalkoxide La2Zr3O(OPri)(16) (1). In its molecule an octahedrally coordinated zirconium atom is connected via two mu(3)-OR and two mu-OR-groups with two lanthanum atoms of a tetrahedral [La2Zr2(mu(4)-O)] aggregate. This structure type has not been previously observed in the structures of pentanuclear alkoxide aggregates. The conditions leading to formation of I from solutions containing the homometallic alkoxides are outlined. (c) 2006 Elsevier B.V. All rights reserved.
Abstract: Niobium isopropoxide, Nb((OPr)-Pr-i)(5), is an attractive precursor of simple and complex niobium oxides in sol-gel technology. This compound cannot, unfortunately, be obtained by alcohol interchange starting from linear chain homologues such as Nb(OMe)(5) or Nb(OEt)(5). The equilibrium in the latter reaction favours formation of mixed-ligand complexes, [Nb-2(OR)(2)((OPr)-Pr-i)(8)], R = Me, Et. In particular, [Nb-2(OMe)(2)(OPri)(8)] (1) has been isolated in high yield from repeated treatment of Nb-2(OMe)(10) with excess of isopropanol. The X-ray single crystal study reveals a dinuclear structure containing a pair of edge-sharing octahedra with methoxide ligands in the bridging position. Infrared (IR) and mass spectroscopy (MS) studies confirmed the incomplete ligand substitution. The H-1-NMR spectra suggest equilibrium between different molecular forms in solution. Solvothermal interaction of 1 with La chips in toluene/isopropanol media results in formation of a mixture of LaNb2((OPr)-Pr-i)(13) and La2Nb4(mu(4)-O)(4)(OH)(2)(mu-(OPr)-Pr-i)(8)((OPr)-Pr-i)(8) (2).
Abstract: The modification of zirconium or hafnium alkoxides with diethanolamine, H(2)dea, leads to the formation of unique nona-coordinated Mmu-eta(3)-NH(C2H4O)(2)(3) cores. The mechanism is used to develop a self-assembly approach to the first thermodynamically stable zirconium-titanium and hafnium-titanium precursors, Zrmu-eta(3)-NH(C2H4O)(2)(3)[Ti((OPr)-Pr-i)(3)](2) (1) and Hfmu-eta(3)-NH(C2H4O)(2))(3)[Ti((OPr)-Pr-i)(3)](2) (2). Mass spectrometric characterization of these compounds demonstrates their volatility. In addition to the solution stability of these compounds the volatility makes them attractive single source precursors for MOCVD and ALD applications. These precursors are also interesting candidates for application in sol-gel synthesis of microporous materials as the stability of the core prevents self-assembly of ligands on the outer surface of the primary particles formed during the hydrolysis. A n-propoxide analog of 1 can be prepared from zirconium n-propoxide but does not yield any crystalline material. It is demonstrated that 1 can be prepared from [Zr((OPr)-Pr-n)((OPr)-Pr-i)(3) ((PrOH)-Pr-i)](2), however, with a lower yield compared to the use of zirconium isopropoxide. The single crystals obtained from systems containing zirconium isopropoxide, titanium isopropoxide and triethanolamine H(3)tea turned out to be Ti-2((OPr)-Pr-i)(2)(mu-eta(4)-NH(C2H4O)(3)(2))(2) (4). Theoretical calculations indicate that the octacoordinate Mmu-eta(4)-N(C2H4O)(3)(2) core, anticipated in reaction with H(3)tea, will have metal-nitrogen bonds that are too long for its stabilization. This explains why the formation of 4 is thermodynamically favored over the formation of heterometallic species. (c) 2006 Elsevier B.V. All rights reserved.
Abstract: The thermal decomposition of a ZrTi2[(OC2H4)(2)NH](3)(OC3H7)(6) precursor by the RAPET (reaction under autogenic pressure at elevated temperature) method provided the formation of crystalline zirconium titanate nanoparticles. These as-prepared nanoparticles are embedded in a carbon shell, which can be removed completely by calcination at 500 degrees C under air for 3 h, resulting in pure white crystalline nanoparticles. At a reaction temperature of 700 degrees C, the nanoparticles are mainly ZrTi2O6 (srilankite), whereas at 800 degrees C, the product is predominately Zr5Ti7O24. The structural, morphological, compositional, magnetic, and AC electrical properties are measured for the as-prepared ZrTi2O6 embedded in carbon (ZTEC), as well as the crystalline ZrTi2O6 nanoparticles (ZTN) obtained after sintering. The reaction mechanism is based on the decomposition products containing pyrrol and pyrazine. The presence of these compounds provides an understanding of the decomposition of the diethanolamine ligands and the formation of the nanoparticles in general.
Abstract: Niobium and tantalum oxo-ethoxo-perrhenates, (M4O2)-O-v(OEt)(14)(ReO4)(2), are easily obtained in high yields via interaction of metal ethoxides, M-v(OEt)(5), with rhenium heptoxide, Re2O7, in hydrocarbon solvents. The complexes have good solubility in hexane and toluene and are stable in solution at room temperature. Their molecular structures are based on a tetranuclear M-4(mu-O)(2)(mu-OR)(4)X-12 core, X = OR, ReO4, composed of two pairs of edge-sharing octahedra joined via two almost linear oxo-bridges containing a rectangular flat M-4-arrangement. The perrhenate ligands are attached in a centrosymmetric manner to the two opposite corners of the rectangle. (c) 2006 Elsevier Ltd. All rights reserved.
Abstract: Preparation of high purity dense coatings of perovskite materials, in particular (Ba,Sr)TiO3 and Ba(Ti,Nb)03, requires application of highly solution and even gas phase stable single-source precursors. We report here a new series of bimetallic alkoxide complexes of 1: 1 composition, M-II M-2(2)V(L)(2)(OEt)(12)(EtOH)(n), M-11=Sr, Ba, M-v=Nb, Ta, L=2,2,6,6-tetramethylheptanedionate (thd, n=2) or isopropylacetoacetate ((PrAcAc)-Pr-1, n=0). These products were characterized by X-ray single crystal study in the solid state for the Sr2Ta2(thd)(2)(OEt)(12)(EtOH)(2) as an example, and for all complexes by NMR in solution. Multivariate analysis of evaporation of these complexes by El-mass spectrometry shows that they are transformed into gas phase in the molecular form and display high gas phase stability. TG measurements reveal them to be thermally stable up to at least 280 degrees C and decompose at higher temperatures in a single step without separation of the components. The precursor transformations in solutions (through microhydrolysis) have also been studied. (C) 2007 Elsevier B.V All rights reserved.
Abstract: The continuous scaling down of devices dimensions, in silicon technology, imposes to replace silicon dioxide. Among the potential candidates for new capacitors, some perovskite structure materials (such as titanate or zirconate) show interesting characteristics. The first way to develop perovskite films is to use a mixture of two beta-diketonates by varying the solution’s cationic ratio. However, our previous results on SrZrO3 showed that a wide parametric study had to be carried on. Another way is to design novel heterometallic precursors that contain both cations on, the same molecule. The ligands could be chosen so that peculiar evaporation and decomposition temperatures could be obtained. Thus, perovskite films (SrZrO3) were deposited on plane Si(I 0 0) substrates by direct liquid injection MOCVD from two original heterometallic precursors Sr2Zr2(O ‘’ Pr)(8)(thd)(4)(†PrOH)2 and Sr2Zr2(thd)(4)((OPr)-Pr-i)(8). The oxide films were deposited at substrate temperature ranging from 550 to 900 degrees C. At the lowest temperatures (550 and 600 degrees C) the as-deposited films were amorphous. After a postannealing at 700 degrees C for 1 h under N-2/O-2, the films deposited at 550 degrees C were crystallized in the SrZrO3 orthorhombic phase. Crystallographic and chemical structures were controlled applying grazing X-ray diffraction and infrared spectroscopy measurements. Results are discussed with respect to experimental synthesis conditions. (c) 2007 Elsevier B.V. All rights reserved.
Abstract: Metathesis of solid GaCl3 with NaOEt/EtOH (1:3) provided, after separation of the NaCl precipitate, a solution containing oxoalkoxide chloride complexes of gallium. Residues from evacuation of the latter were redissolved in either toluene/ MeCN (solution 1) or toluene/pyridine (solution 2). Storage of the first solution provided crystals of Ga-5(mu(5)-O)(mu-OEt)(8)Cl-5 (1), and of the second solution - [Ga-12(mu(4)-O)(2)(mu(3)-O)(5)(mu-OEt)(10)-Cl12Py4]Py (2), both at room temperature and in relatively high yields. Compound 1 crystallizes as a vertically contracted tetragonal pyramid with the mu(5)-O ligand situated in the center of the equatorial plane defined by four trigonal bipyramidal coordinated gallium atoms. The axial Ga atom has octahedral coordination. All eight edges of the pyramid are capped by mu-OEt groups, and all the chloride ligands are situated in terminal positions. Crystals of [Ga-12(mu(4)-O)(mu(3)-O)(5)(mu- OEt)(10)Cl12Py4]Py (2) contain two [Ga-5(mu(4)-O)(mu(3)-O)(2)(mu-OEt)(5)- Cl5Py] fragments connected through a cyclic [Ga-4(mu(3)-O)(5)-Cl2Py2] unit with a mu(3)-O ligand in its center. Of the metal atoms, three possess tetrahedral, seven trigonal bipyramidal, and two octahedral coordination. The mass spectrum of I contains penta- and tetranuclear fragments. The spectrum of 2 contains heptameric fragments in addition to the pentanuclear fragments that are analogous to those in the spectrum of 1. The factors leading to formation of polymeric M(OR)(n) and related oligonuclear oxocomplexes are discussed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).
Abstract: The anodic dissolution of tin metal in absolute alcohols yields oxoalkoxides with the general formula Sn6O4(OR)(4) (R = Me (1), Et (2), i-Pr (3)) and orthoalkoxides with the general formula Sn(OR)(2) (R = n-Bu (4), C2H4OMe (5)). According to X-ray crystallographic data, the molecule of Sn6O4(OEt)(4) (2) is an octahedral [Sn-6] cluster with alternating oxo and OEt groups on its faces. The mass spectra of 1 and 2 indicate the presence of fragments of the hexanuclear oxoalkoxides.
Abstract: Bimetal alkoxo complexes of rhenium, niobium, and tantalum with the general formula M4O2(OR)(14)(ReO4)(2), where M = Nb or Ta and R = Me or Et, were prepared in similar to 80% yield by reacting niobium or tantalum alkoxide M(OR)(5) (R = Me or Et) with rhenium heptoxide Re2O7 in toluene. Comparative analysis of the molecular structures of the complexes was carried out by means of single-crystal X-ray diffraction and IR spectroscopy. The effect of the organic ligand and crystallization temperature on the geometry of the perrhenate group was studied. The solubility of the aforementioned alkoxo complexes in organic solvents increases with increasing hydrocarbon chain length of the ligand.
Abstract: The coordination chemistry of the ammonia solvated copper(II), zinc(II) and cadmium(II) ions has been studied in liquid and aqueous ammonia by means of EXAFS spectroscopy, and in the solid state by means of crystallography and EXAFS spectroscopy. The ammonia solvated copper(II) ion is six-coordinated in Jahn-Teller distorted octahedral configuration with Cu-N bond distances of 2.050(5), 2.060(5) and 2.064(7) angstrom in the equatorial plane, and of 2.31(2), 2.31(2) and 2.34(2) angstrom in the axial positions in solid [Cu(NH3)(6)](ClO4)(2), [Cu(NH3)(6)]Cl-2 and [Cu(NH3)(6)]Br-2, respectively, as determined by EXAFS. Solid [Cu(NH3)(6)](ClO4)(2) crystallizes in a cubic space group, Fm3m, which does not allow a Jahn-Teller distorted configuration, and the crystallographic result is instead six equidistant Cu-N bonds at 2.091(13) angstrom. Solid [Cu(NH3)(6)]Cl-2 crystallizes in a tetragonal space group, 14/mmm, with Cu-N bond distances of 2.068(7) and 2.24(2) in the equatorial and axial positions, respectively. The ammonia solvated copper(II) ion is also six-coordinated in Jahn-Teller distorted octahedral configuration in liquid and aqueous ammonia with Cu-N bond distances of 2.065(5) and 2.051(5) angstrom in the equatorial plane, and of 2.29(2) and 2.29(2) angstrom in the axial positions, respectively, as determined by EXAFS. The ammonia solvated zinc(II) ion is four-coordinated in tetrahedral configuration with mean Zn-N bond distances of 2.040(5) and 2.028(7) angstrom in solid [Zn(NH3)(4)](ClO4)(2) and aqueous ammonia solution, respectively, while the zinc(II) ion seems to be five-coordinated in liquid ammonia with a mean Zn-N bond distance of 2.117(7) angstrom, as determined by EXAFS. The ammonia solvated cadmium(II) ion is six-coordinated in octahedral configuration with mean Cd-N bond distances of 2.346(7), 2.350(7) and 2.347(7) angstrom in solid [Cd(NH3)(6)]Cl-2, liquid ammonia and aqueous ammonia solution, respectively, as determined by EXAFS. Solid [Cd(NH3)(6)]Cl-2 crystallizes in a cubic space group with six equidistant Cd-N bonds at 2.341(4) angstrom in a regular octahedron. (C) 2006 Elsevier B.V. All rights reserved.
Abstract: Heterometallic alkoxide complexes possessing a triangular M-3(mu-OR)(2)(mu-OR)(3) core are usually highly soluble in organic solvents and often display relatively high stability on transition into gas phase. Each metal atom is connected to four ligands within the core and needs two more donor atoms from the terminal ligands to complete octahedral coordination. This can be achieved for Ni(II), for example, by application of a bidentate chelating ligand such as the acetylacetonate one. Interaction of Ni(acac)2 with 1.5 eq. of [Zr((OPr)-Pr-i)(4)((PrOH)-Pr-i)](2) in toluene offers quantitatively [Zr((OPr)-Pr-i)(3)(acac)(2)] together with the bimetallic complex NiZr2(acac)((OPr)-Pr-i)(9) (1), possessing the desired structure and physical properties. (c) 2006 Elsevier B.V. All rights reserved.
Abstract: In this article, we report a simple, one-stage, efficient synthetic method for the growth of carbon sausages filled with in situ formed tungsten oxide nanorods (CSTON), without any external catalyst. The thermal dissociation of tungsten(VI) isopropoxide, 5% w/v in isopropanol at 700 degrees C in a closed Swagelok cell in an inert atmosphere yielded a CSTON product. The product is characterized by SEM, TEM, EDAX, C, H, N, S analysis, TGA, Raman spectroscopy, and HR-TEM. The assignment of the structure of the sausages as a carbon shell, with the central part being the WOx, is based on SAEDS spectra. The same reaction was also conducted at a lower temperature closer to the temperatures of solvothermal reactions, at 350 degrees C. The reaction yielded WOx nanorods with a diameter ranging from 10 nm to 50 nm and a length of up to 6 mu m.
Abstract: The synthesis and structural determination of three new heterometallic molybdenum complexes, one with cobalt and two with nickel and two of these with beta-diketonate ligands and one with amino alcohol ligands, are presented. The reaction of cobalt acetylacetonate with [MoO(OMe)(4)] provides [Co2Mo2O2(acac)(2)(OMe)(10)] (1) and [MoO(acac)(OMe)(3)] (4), and the reaction of nickel acetylacetonate with [MoO(OMe)(4)] provides [Ni2Mo2O2(acac)(2)(OMe)(10)] (2) and 4. The reaction of [Ni(ORN)(2)] (R-N = CHMeCH2NMe2) with [MoO(OMe)(4)] yields [Ni2Mo2O2(ORN)(2)(OMe)(10)] (3). The two new oxomolybdenum complexes undergo ether elimination upon storage to give the corresponding dioxo complexes [MoO2(acac)(OMe)](2) (5) and [MoO2(ORN) (OMe)](2) (6). Compounds 3 and 4 could also be obtained from the reaction of’stoichiometric amounts of Hacac with [MoO(OMe)(4)] and [MoO2(OMe)(2)], respectively. The local structure around the nickel atom in compound 2 in solution and compound 3 in the solid state and in toluene/hexane solution has been determined by means of EXAFS spectroscopy. The complexes are intended to be used as single-source precursors, which are attractive in coatings and for the preparation of mesoporous materials; its application for the synthesis of nickel molybdate by sol-gel processing is therefore reported. The oxide material obtained from 3 displays a uniform grain size and a large surface area. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Abstract: The modification of different zirconium propoxide and hafnium propoxide precursors with 2,2,6,6,-tetramethyl-3,5- heptanedione (Hthd) was investigated by characterization of the isolated modified species. The complexes [Zr((OPr)-Pr-n)(3)(thd)](2), [Zr((OPr)-Pr-n)((OPr)-Pr-i)(2)(thd)](2), Zr((OPr)-Pr-i)(thd)(3), [Hf((OPr)-Pr-n)(3)(thd)](2), and Hf((OPr)-Pr-i)(thd)(3) were isolated and characterized. The structure of the n-propoxide analogue of Zr((OPr)-Pr-i)(thd)(3) could not be refined, but its existence was clearly demonstrated by XRD and H-1 NMR. The modification of the propoxide precursors involves mono- and trisubstituted intermediate compounds and does not involve a disubstituted compound; thus, the commercial product that is claimed to be “Zr((OPr)-Pr-i)(2)(thd)(2)†and is most commonly used for the MOCVD preparation of ZrO2 does not exist. No evidence was found for the presence of such a compound in either zirconium- or hafnium-based systems. Formation of the dimeric hydroxo-di-thd-substituted complex, [Hf(OH)((OPr)-Pr-i)(thd)(2)](2), which could be isolated only for hafnium-based systems, occurs on microhydrolysis. All heteroleptic intermediates are eventually transformed to the thermodynamically stable Zr(thd)(4) or Hf(thd)(4). The compounds obtained from isopropoxide precursors showed a higher stability than those with n-propoxide ligands or a combination of both types. In addition, it is important to note that residual alcohol facilitates the transformation and strongly enhances its rate. The unusually low solubility and volatility of M-IV(thd)(4) has been shown to be due to close packing and strong van der Waals interactions in the crystal structures of these compounds.
Abstract: Ionic or ionogenic alkoxides are attractive potential catalysts for polymerization reactions. Direct interaction between CoCl2 and [Ta(OMe)(5)] produced, by self-assembly, a small amount of ionic aggregate clathrate with acetonitrile, [Co2Ta2(OMe)(12)(MeCN)(4)](2+) [CoCl3(MeCN)](2)(-) center dot 2MeCN(1). The structure of 1 contains a planar M-4(mu(3)-OR)(2)(mu-OR)(4)-core that can be considered as a fragment of hexagonal packing of metal and ligand atoms completed by 6 (3 + 3) terminal alkoxide ligands at the tantalum and 4 (2 + 2) terminal acetonitrile molecules at the cobalt atoms that are bearing the (+1) positive charge each. A rational synthesis of this compound was achieved by reaction between [NaTa(OMC)(6)] with four equivalents of CoCl2 in toluene/acetonitrile to give a new crystallographic form (Co2Ta2(OMe)(12)(MeCN)(4)] [CoCl3(MeCN)](2) (2), not containing interstitial solvent molecules. (C) 2006 Elsevier B.V. All rights reserved.
Abstract: Dissolution of BaO in 90-95% MeOH provides [Ba(OH)(2)(H2O)(2)](MeOH)(2) (1) as rectangular platelet crystals. Interaction of BaO or Ba(OH)2 with 98-100% methanol results in the formation of needle shaped crystals of [Ba(OH)2(MeOH)2](MeOH) (2). The structure of I is composed of planar layers of tetragonally distorted [Ba(OH)(4/2)(H2O)(4/2)] cubes altered by the layers of alcohol molecules oriented in the direction perpendicular to the metal hydroxide layers. The structure of 2 is formed by layers of distorted antiprisms of Ba(mu(3)-ROH)(mu-OH)(4)(mu-ROH)(2)(ROH)] and [Ba(mu(3)-ROH)(2)(p-ROH)(2)(mu-OH)(4)] composition. IR spectra of 1 and 2 are in good agreement with the observed structures. The structures of compounds 1 and 2 are compared with those of Ba(OH)(2) (.) nH(2)O (n = 1, 3). (c) 2006 Elsevier Ltd. All rights reserved.
Abstract: Microporous zirconia-titania composite membranes have been fabricated by sol-gel processing using diethanolamine-modified precursor solutions. Microporous materials made from powders calcined at 400 degrees C show type I nitrogen sorption behavior. Supported similar to 0.1 mu m thick membranes (see figure) exhibit molecular-sieving properties and are expected to have great potential for separation and reaction applications under harsh conditions.
Abstract: Uniform nanocrystalline mesoporous mixed cobalt-nickel spinel phases displaying unimodal pores in the 7-12 nm range and relatively high specific surface areas up to 83 m(2)/g were prepared by a novel low temperature synthesis approach in which the desired metal oxide stoichiometries were introduced on a molecular level by reacting heterometallic alkoxide precursors in the presence of supramolecular liquid crystalline phases. The resultant phases, composed mainly of ca. 8-11 nm uniform cobalt-nickel spinel nanoparticles, were highly promising as low-temperature hydrocarbon combustion catalysts investigated in a model reaction of propane oxidation. (c) Wiley-VCH Verlag GmbH & Co.
Abstract: Iron oxide doped silica films and powders with highly ordered mesostructures of extraordinary temperature stability (up to 1000 degrees C) and iron loading of up to 6 atom% were produced by the use of novel iron alkoxide-coordinated surfactants. Wormhole-like, 2d-centered rectangular, orthorhombic and lamellar mesostructures were obtained by variation of the molar ratios of the metal-surfactant complexes. The influence of a subsequent heat treatment was studied by GI-SAXS, TEM, XRD, and nitrogen sorption techniques. The molecular composition of the films was studied by XPS and EXAFS.
Abstract: This paper summarizes recent literature data and presents new experimental data on the mechanisms of chemical modification, hydrolysis and polycondensation of the alkoxides and demonstrates possibilities to approach new classes of materials, exploiting these mechanisms. Low reactivity of silicon alkoxides is improved by either basic catalysis exploiting an S(N)2 mechanism or acidic catalysis facilitating a proton-assisted S(N)1 mechanism as well as by modification with chelating ligands. Metal alkoxides are much stronger Lewis bases compared to silicon alkoxides and the acidity of water is strong enough to achieve their rapid hydrolysis via proton-assisted S(N)1 pathway even in the absence of additional catalysts. Introduction of the modifying chelating ligands is leading generally to increased charge distribution in the precursor molecules. Modifying chelating ligands are also appreciably smaller than the alkoxide ligands they replace. The modification with chelating ligands is thus facilitating the kinetics of hydrolysis and polycondensation. The size and shape of the primary particles formed in sol-gel treatment of metal alkoxides are defined not by kinetic factors in their hydrolysis and polycondensation but by the interactions on the phase boundary, which is in its turn directed by the ligand properties. The products of the fast hydrolysis and condensation sequence consist of micelles templated by self-assembly of ligands (mainly oxo-species). This concept provides explanations for commonly observed material properties and allows for the development of new strategies for the preparation of materials. We discuss the formation of inverted micelles, obtained by the appropriate choice of solvents, which allows for the formation of hollow spheres. The modifying beta-diketonate ligands act as the surfactant and form an interface between the hollow sphere and the solvent. Retention of ligands inside the gel particles is possible only if ligands possessing both chelating and bridging properties are applied. Application of such ligands, for example, diethanolamine, permits to prepare new transition metal oxide based microporous membranes.
Abstract: The coordination chemistry of solvated Ag-I and Au-I ions has been studied in some of the most strong electron-pair donor solvents, liquid and aqueous ammonia, and the P donor solvents triethyl, tri-n-butyl, and triphenyl phosphite and tri-n-butylphosphine. The solvated AgI ions have been characterized in solution by means of extended X-ray absorption fine structure (EXAFS), Raman, and Ag-107 NMR spectroscopy and the solid solvates by means of thermogravimetry and EXAFS and Raman spectroscopy. The AgI ion is two- and three- coordinated in aqueous and liquid ammonia solutions with mean Ag - N bond distances of 2.15(1) and 2.26(1) angstrom, respectively. The crystal structure of [Ag(NH3)(3)] ClO4, 0.47 NH3 (1) reveals a regular trigonal-coplanar coordination around the AgI ion with Ag - N bond distances of 2.263(6) angstrom and a Ag center dot center dot center dot Ag distance of 3.278(2) angstrom separating the complexes. The decomposition products of 1 have been analyzed, and one of them, [Ag( NH3) 2] ClO4, has been structurally characterized by means of EXAFS, showing [ Ag( NH3) 2] units connected into chains by double O bridges from perchlorate ions; the Ag center dot center dot center dot Ag distance is 3.01( 1) angstrom. The linear bisamminegold(I) complex, [Au(NH3)(2)](+), is predominant in both liquid and aqueous ammonia solutions, as well as in solid [Au(NH3)(2)]BF4, with Au - N bond distances of 2.022(5), 2.025- 5), and 2.026(7) angstrom, respectively. The solvated Ag-I ions are three- coordinated, most probably in triangular fashion, in the P donor solvents with mean Ag-P bond distances of 2.48 - 2.53 angstrom. The AuI ions are three- coordinated in triethyl phosphite and tri-n-butylphosphine solutions with mean Au - P bond distances of 2.37(1) and 2.40(1) angstrom, respectively.
Abstract: We present the results of the RAPET (reaction under autogenic pressure at elevated temperatures) dissociation of CoZr2(acac)(2)((OPr)-Pr-i)(8) at 700 degrees C in a closed Swagelok cell under an applied magnetic field of 10 T. It produces a mixture of carbon-coated and noncoated metastable ZrO2 nanoparticles, bare metallic Co nanoparticles, and bare carbon. The same reaction in the absence of a magnetic field produces spherical Co and ZrO2 particles in sizes ranging from 11 to 16 nm and exhibiting, at room temperature, metastable phases: fcc for cobalt and a tetragonal phase for zirconia. The metastable phases of Co and ZrO2 are manifested because of a carbon shell of similar to 4 nm thickness anchored to their surfaces. The effect of an applied magnetic field to synthesize morphologically different, but structurally the same, products is the key topic of the present paper.
Abstract: Modification of the liquid Ni(ORN)(2) R-N = C2H4NMe2, with stoichiometric or sub-stoichiometric amounts of carboxylic acids, HCOOH or CH3COOH, results in formation of crystalline heteroleptic complexes Ni-6(OH)(2)(ORN)(6)(OCOR)(2) R = H (1) CH3 (3) with the core structure closely analogous to that observed earlier for hexanuclear titanium (IV) alkoxide carboxylates and derived from hexagonal packing of the donor atoms. (c) 2005 Elsevier Ltd. All rights reserved.
Abstract: Interaction of molybdenum oxomethoxide and bismuth chloride in toluene/acetonitrile media leads to the formation of an unusual ionic salt [MO(OMe)(5)(CH3CN)]Bi2Cl7 (1), providing the first example of an isolated mononuclear alkoxide cation, [Mo(OMe)(5)(CH3CN)](+) with rather uniform Mo-O(Me) bond lengths. The product can be isolated with moderate yields and only from solutions with considerable excess of the molybdenum reactant (Mo:Bi ≈ 2: 1) after refluxing of the reaction mixture, which indicates disproportionation of MoO(OMe)(4) in solution into MoO2(OMe)(2) and Mo(OMe)(6) as a crucial step in its formation. (C) 2005 Elsevier B.V. All rights reserved.
Abstract: Metal alkoxide and β-diketonate complexes are broadly recognized as versatile precursors of high-purity glass and ceramic materials in the sol-gel technology. By applying reactants containing various metal atoms in the proper ratio and assuring their conservation through sol-gel treatment, single-source precursors (SSP) provide an efficient approach to complex materials. Simple and cost-efficient routes to SSP can be developed by applying the concept of geometrical molecular structure design, which is based on the choice of a type proper of molecular structure and its completion with ligands, providing the necessary number of donor atoms for the chosen core as well as sterical protection.
Abstract: This article reports on the fabrication of WO3 nanorods using an efficient straightforward synthetic technique, without a catalyst, and using a single precursor. The thermal dissociation of WO(OMe)(4) at 700 degrees C in a closed Swagelok cell under an air/inert atmosphere yielded W18O49 nanorods. Annealing Of W18O49 at 500 degrees C under an air atmosphere led to the formation of pure WO3 nanorods. The obtained products are characterized by morphological (scanning electron microscopy and transmission electron microscopy), structural (X-ray diffraction analysis, high-resolution scanning electron microscopy, and Raman spectroscopy), and compositional [energy-dispersive X-ray and elemental (C, H, N, S) analysis] measurements. The mechanism of the formation of nonstoichiometric W18O49 nanorods is supported by the measured analytical data and several control experiments.
Abstract: interaction of FeX3, X = Cl, Br with 3 equiv. of NaOEt in toluene/ethanol media provides mixtures of iron (III) oxoethoxide, Fe5O(OEt)(13), and its halide alkoxide analogs. The latter have been identified by mass-spectrometric study as Fe5O(OEt)(12)X and Fe5O(OEt)(11)X-2. Application of FeBr3 as a starting material leads to much more pure samples of Fe5O(OEt)(13) isolated with higher yields. (c) 2005 Elsevier B.V. All rights reserved.
Abstract: The conventional Gross reaction for the formylation of the tetrapropoxythiacalix[4]arene using TiCl4 affords the 18-(chloromethyl)-28-hydroxy-25,26,27-tripropoxythiacalix[4]arene substituted in the meta-position of the macrocycle. The p-tetraformyl-tetrapropoxythiacalix[4]arene, which is an interesting intermediate to the upper-rims functionalization of thiacalixarenes, was prepared with a very good yield using BuLi and N-formylpiperidine. (C) 2004 Published by Elsevier Ltd.
Abstract: The acidic properties of mono- and bimetal Re and Mo oxide clusters immobilized in microporous NaY zeolite were studied using the temperature-programmed desorption technique. It was established that the strength of acidic sites at the clusters decreases in the series ReMoO6 > ReO3 > MoO3. It was found that the acidic properties of the clusters correlate with their catalytic activity in the conversion of methanol.
Abstract: The tetrameric hydrolysis products of zirconium(IV) and hafnium(IV), the zirconyl(IV) and hafnyl(IV) ions, [M-4(OH)(8)(OH2)(16)(8+)], often labelled MO2+.5H(2)O, are in principle the only zirconium(IV) and hafnium(IV) species present in aqueous solution without stabilising ligands and pH larger than zero. These complexes are furthermore kinetically very stable and do not become protonated even after refluxing in concentrated acid for at least a week. The structures of these complexes have been determined in both solid state and aqueous solution by means of crystallography, EXAFS and large angle X-ray scattering (LAXS). Each metal ion in the [M-4(OH)(8)(OH2)(16)](8+) complex binds four hydroxide ions in double hydroxo bridges, and four water molecules terminally. The M-O bond distance to the hydroxide ions are markedly shorter, ca. 0.12 Angstrom, than to the water molecules. The hydrated zirconium(IV) and hafnium(IV) ions only exist in extremely acidic aqueous solution due to their very strong tendency to hydrolyse. The structure of the hydrated zirconium(IV) and hafnium(IV) ions has been determined in concentrated aqueous perchloric acid by means of EXAFS, with both ions being eight-coordinated, most probably in square antiprismatic fashion, with mean Zr-O and Hf-O bond distances of 2.187(3) and 2.160(12) Angstrom, respectively. The dimethyl sulfoxide solvated zirconium(IV) and hafnium(IV) ions are square antiprismatic in both solid state and solution, with mean Zr-O and Hf-O bond distances of 2.193(1) and 2.181(6) Angstrom, respectively, in the solid state. Hafnium(IV) chloride does not dissociate in N,N’-dimethylpropyleneurea, dmpu, a solvent with good solvating properties but with a somewhat lower permittivity (epsilon=36.1) than dimethyl sulfoxide (epsilon=46.4), and an octahedral HfCl4(dmpu)(2) complex is formed.
Abstract: Rhenium and molybdenum oxide clusters were synthesized from the Re2O3(OMe)(6), ReMoO2(MeO)(7), and Mo2O2(OMe)(8) oxomethoxide complexes. The nanomaterials obtained were studied by the FTIR, DTA, EXAFS, and H-2-TPR techniques. It was established that, in microporous NaY zeolite, the oxomethoxide, complexes lose their ligands, so that only metal suboxide cores penetrate into the intracrystalline space, where they reside as nanosized clusters. It was found that the reduction of the clusters depends strongly on their size and the location in the matrix. The matrix environment also affects the transitions between different oxidation states of Re and Mo and the degree of reduction of their oxides.
Abstract: Interaction of Ni(acac)(2) with 2 eq. of Al((OPr)-Pr-i)(3) in toluene on reflux with subsequent modification with 2 eq. of acetylacetone offers with quantitative yields a new heterometallic complex, NiAl2(acac)(4)((OPr)-Pr-i)(4) (1), characterized by X-ray single crystal study and variety of spectroscopic techniques. Uniform NiAl2O4-coatings were obtained on Al2O3 substrates by dip-coating from toluene solutions of 1 with subsequent thermal treatment and characterized by X-ray powder, SEM and AFM studies. Powder samples were obtained by hydrolysis of solutions of 1 in the moist air and characterized by TG and X-ray powder data.
Abstract: The stabilizing and destabilizing mechanism in the action of acetylacetone on zirconium propoxide precursors is revealed; the nature of heteroleptic intermediates provides an explanation.
Abstract: Interaction of the commercial “Zr((OPr)-Pr-n)(4)†with an excess of (PrOH)-Pr-i provides in high yields a new solid crystalline but highly soluble precursor Zr-2(mu-(OPr)-Pr-n)(2)((OPr)-Pr-i)(6)((PrOH)-Pr-i)(2) (2). Interaction of 1 eq. of 2 with 1 eq. of Co(acac)(2) results in quantitative transformation into a mixture of Co2Zr2((OPr)-Pr-n)(4)((OPr)-Pr-i)(6)(acac)(2) (3), with a structure representing a fragment of hexagonal packing of metal atoms and alkoxide ligands (typical for derivatives of primary alcohols), and Zr-2((OPr)-Pr-i)(6)(acac)(2) (4). Reaction of 1 eq. of homoleptic zirconium isopropoxide, Zr-2((OPr)-Pr-i)(8)((PrOH)-Pr-i)(2) (1), with 1 eq. of Co(acac)(2) provides a new complex CoZr2((OPr)-Pr-i)(8)(acac)(2) (5) having a linear chain structure (characteristic of sec-alcohol derivatives) in quantitative yield. Microhydrolysis of a mixture of 1.5 eq. of 2 and 1 eq. of Co(acac)(2) gave in moderate yield CoZr3O((OPr)-Pr-n)(3)((OPr)-Pr-i)(5)(acac)(4) (6), with a tetrahedral CoZr3O core characteristic of zirconium sec-oxoalkoxides. Modification of a solution of barium and zirconium isopropoxides in toluene (Ba:Zr=1:1) with 1.5 eq. of Hacac results almost quantitatively in a mixture of insoluble Ba(acac)(2) and soluble and volatile heterometallic alkoxide Ba2Zr4((OPr)-Pr-i)(18)(acac)(2) (7). Addition of 2 eq. of Hthd to a mixture of barium and zirconium n-propoxides in toluene (Ba:Zr=1:1) gives highly soluble and volatile complex Ba2Zr2(thd)(4)((OPr)-Pr-n)(8)((PrOH)-Pr-n)(2) (8). Reaction of the in situ obtained Ba(thd)(2) with 0.5 eq. of 2 provided almost quantitatively another highly soluble and volatile precursor Ba2Zr2(thd)(4)((OPr)-Pr-n)(2)((OPr)-Pr-i)(6) (9). Addition of 2 eq. of Hthd to a mixture of strontium and zirconium isopropoxides in toluene (Sr:Zr=1:1) gives highly soluble complex Sr2Zr2(thd)(4)((OPr)-Pr-i)(8) (10) volatilized on heating via complete decomposition into Sr(thd)(2), Zr(thd)(2)((OPr)-Pr-i)(2) and non-volatile products. Bimetallic hydroxo-isopropoxides of strontium and barium, Sr2Zr2(OH)(2)((OPr)-Pr-i)(10)((PrOH)-Pr-i)(4) (11) and Ba2Zr2(OH)(2)((OPr)-Pr-i)(10)((PrOH)-Pr-i)(6) (12), have been obtained in good yields via microhydrolysis of solutions of isopropoxides in toluene/isopropanol media. All compounds have been characterized by a variety of spectroscopic techniques, and compounds 1-9 and 11-12 also by X-ray single crystal studies. The principles in construction of zirconium alkoxides-products of thermodynamically controlled molecular self-assembly- and their stability and reactivity are discussed in connection with the sterical role played by the chosen ligands.
Abstract: The thermal decomposition of the methoxide complexes MoO(OMe)(4) (I), Re4O6(OMe)(12) (II) and (Re1-xMox)O-6(OMe)(12) (0.24 less than or equal to x less than or equal to 0.55) (III) in hydrogen and nitrogen at T less than or equal to 800degreesC and in air at temperatures T less than or equal to 400degreesC have been monitored by thermal analysis, X-ray powder diffraction and scanning electron microscopy. Heating of I, II and III in air yields orthorhombic MoO3, ReO3 and a mixture of these two phases, respectively. Thermal treatment of I and II in nitrogen, using heating rates of 20 K min(-1) or faster, yields the same products as in air, while applying slower heating rates of I and thermal treatment of III in nitrogen yield the tetragonal modification Of MoO2 and (Re1-xMox)O-2 (with 0.24 less than or equal to x less than or equal to 0.55), respectively. Heat treatment of I, II and III in hydrogen yields fine powders of Mo, Re or a Re-Mo alloy (having the structure of the sigma-phase) at surprisingly low temperatures, around 520, 240 and 360 degreesC for I, II and III, respectively. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: New heterometallic interesting trinuclear, Zreta(3), mu(2)-NH(c(2)H(4)O(2)(3)[Ti((OPr)-Pr-i)(3)](2) encountering a nona-coordinated central zirconium atom crystallizes at -30 degreesC from a solution of zirconium and titanium isopropoxides and diethanolamine (Zr:Ti:L = 1:23) in hydrocarbons. Due to its solution stability, this structurally characterized compound is an attractive potential precursor in sol-gel technique for the preparation of mixed metal oxide materials. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: The article describes the principles of the Single Source Precursor approach to inorganic materials and introduces the Geometrical Molecular Structure Design Concept (MSDC) based on the choice of a proper molecular structure type for the desired precursor and completing it with ligands providing both the necessary number of donor atoms and the sterical protection of the chosen core. Application of MSDC is illustrated with examples taken from development of new approaches in the synthesis of oxide and sulfide catalysts and ferroelectric oxide materials.
Abstract: Rhenium and molybdenum oxomethoxide complexes Re2O3(OMe)(6), ReMoO2(MeO)(7), and Mo2O2(OMe)(8) were used as precursors to prepare highly dispersed mono and bimetallic oxide species supported on the microporous NaY zeolite and mesoporous SiO2 and Al2O3. The prepared materials were characterized by the use of FTIR, NH3-TPD, and H-2-TPR techniques. It was shown that, upon loading into microporous zeolite, oxomethoxide complexes loose their ligands so that just metal suboxide cores remains in the intracrystalline voids as the nanosized oxide clusters. The obtained clusters reveals both acidic and redox properties. The maximum amount of NH3 adsorbed per bimetallic species could be used as a characteristic of both availability of acid sites and oxide dispersion. Reducibility of these species depends strongly on both their location in the matrix and the size. The matrix texture also affects the transitions between different valent states of Re and Mo as well as the metal reduction extent. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: A new class of heterometallic heteroleptic alkoxides, (M2Ta2)-Ta-II(acac)(2)(OEt)(12), M-II=Co, Ni, has been used as single-source precursors in order to obtain nanophase powders and films. (M2Ta2)-Ta-II(acac)(2)(OEt)(12) was prepared via interaction of M-II(acac)(2), M-II=Co, Ni, with Ta(OEt)(5), in toluene and characterized structurally by single-crystal X-ray diffraction, IR and NMR spectroscopy. Oxide films were deposited by spin coating on Si- and SiO2-substrates. Multiple layers, with intermittent heat treatment, were applied to increase the thickness. After annealing at different temperatures and time, the films were characterized by powder X-ray diffraction and SEM. The films were homogeneous and the thickness could be varied between 0.14 mum and 0.67 mum, depending on solution concentration (0.20 - 0.28 M) and number of layers ( 3 - 6). The nanophase powders were also studied at different annealing temperatures. Powder X-ray diffraction of the films coated on Si- substrate and the nanophase powders revealed the presence of CoTa2O6 and Co3O4 phases for the cobalt-tantalum precursor. NiTa2O6 and NiO phases were detected by powder X-ray diffraction with the nickel-tantalum precursor. Atomic force microscopy revealed the oxide films on the Si- substrate to be very smooth and the root mean square roughness was 2.4 nm for a three-layer oxide film with a thickness of 0.50 mum.
Abstract: Prolonged storage of solutions in the Al(OPri)(3)-Ta(OPri)(5)-(PrOH)-Pr-i system containing additional (PrOH)-Pr-n leads to crystallization with minor yields of a new aluminium. oxopropoxide, Al11O6(OPrn)(10)(OPri)(10)(OR)(ROH)(2) (R=Pr-i, Pr-n) (1). Interaction of Al(OPri)(3) with Mg(acac)(2) (in a 1:1 ratio) in toluene on refluxing leads to formation of Al5Mg4O3(OH)(3)(OPri)(8)(acac)(6).0.5PhMe (2) in minor yields. Both molecules contain two pentanuclear cores [M-5(mu(4)-O)(mu3-O)(mu-OX)(6)(Y)(4)] (X = H, Pr-n, Y = OPri, acac/2) and differ only in the manner in which they are attached to each other, i.e., via the central [Al(mu(3)-O)(2)(mu-O)(2)(OR)] unit in 1, and via a common [Al-(mu(3)-O)] edge and an, additional (mu-OH)-group in 2. The core structures in the molecules of aluminium and iron oxoalkoxides are discussed. (C) 2003 Elsevier Ltd. All rights reserved.
Abstract: Oxoisopropoxide complexes of niobium, Nb6O8((PrO)-Pr-i)(14)((PrOH)-Pr-i)(2) (I), and rhenium, Re4O6((OPr)-Pr-i)(10) (II), were isolated as by-products of anodic oxidation of these metals in (PrOH)-Pr-i in the presence of LiCl as conductive additive. The common feature of both structures consists in the occurrence in their molecules of an M4O16 planar core formed in the formal absence of M-M bonding for I and in the presence of electron-deficient but surprisingly short (Re-Re 2.52-2.54 Angstrom) metal-metal bonds in II. The stability of this core for the oxoalkoxide derivatives of rhenium(V,VI) and niobium(V) and poor stability for those of tantalum(V) are discussed based on the results of quantum-chemical calculations. (C) 2003 Elsevier B.V. All rights reserved.
Abstract: The reaction of Ph2Si(OH)(2)(1) with pyridine led to the formation of the pyridinium adduct (HO)Ph2SiOSiPh2O(PyH) (2). The complex contains one free silanol group and another silanol group is bonded to the amine via hydrogen bonding. The analogous reaction Of (c-C6H11)(7)Si7O9 (OH)(3) (3) with pyridine afforded the salt [PyH][(c-C6H11)(7)Si7O9(OH)(2)(2)H] (4). Both pyridinium derivatives have been characterised by X-ray diffraction. In complex 4 the anion consists of two silsesquioxane fragments connected by intermolecular hydrogen bonding. (C) 2003 Elsevier B.V. All rights reserved.
Abstract: Interaction of divalent metal acetylacetonates, M(acac)(2), M = Mg, Co, with titanium methoxide, Ti(OMe)(4), in 1: 1 ratio in toluene provides with practically quantitative yield a new family of heterometallic alkoxide complexes with general composition M2Ti2(acac)(4)(OMe)(8), M = Mg (1), Co (2). The structure of these nearly spherically shaped molecules contains both metals in octahedral coordination, one acac-ligand being attached to each metal atom. Both I and 2 are highly soluble in hydrocarbon solvents and display considerable volatility with distinct fragmentation patterns starting from molecular ions in the mass-spectra, which makes them perspective precursors of titanate materials in sol-gel and MOCVD techniques. (C) 2003 Elsevier B.V. All rights reserved.
Abstract: Spherical Co and ZrO2 particles in the size range of 11-16 nm, exhibiting at room temperature metastable phases, fee for cobalt, and tetragonal for zirconia, were synthesized, by the reaction under autogenic pressure at elevated temperature (RAPET) technique. The tetragonal phase in ZrO2 was obtained without doping the ZrO2 with trivalent impurities. Using high-resolution transmission electron microscopy and selected area energy-dispersive X-ray analysis it is manifested that a carbon shell of similar to4 nm thickness is formed on the surface of Co and ZrO2 nanocrystallites. This carbon shell is responsible for stabilizing the high-temperature metastable phases at room temperature. These two products were obtained by the dissociation of CoZr2(acac)(2)((OPr)-Pr-i)(8) at 700 degreesC under its autogenic pressure.
Abstract: In this article, we present results of the RAPET dissociation of MoO(OMe)(4) at 700 degreesC in a closed Swagelok cell. The reaction produces molybdenum dioxide nanoparticles (20 nm) coated with carbon (20 nm). We have also carried out the same reaction under an applied magnetic field of 10 T. This reaction yielded different products. It produces a mixture of comparatively larger (50 nm) molybdenum dioxide nanoparticles and separated uncoated carbon particles (20-30 nm).
Abstract: The reaction of Mn(acac)(3) with 3 eq. of Al((OPr)-Pr-i)(3) in toluene at reflux provided with minor yield single crystals of MnAl2(acac)(3)((OPr)-Pr-i)(4)(OAc)(C7H8)(0.5) (1), incorporating into the molecular structure the acetate ligand originating from oxidation of the (OPr)-Pr-i-groups. 1 was obtained with high yield (76%) via the reaction of Mn(acac)(3) with 2.2 eq. of Al((OPr)-Pr-i)(3) with subsequent addition of 1 eq. of HOAc to the reaction mixture cooled to room temperature. The analogs of 1, CoAl2(acac)(3)((OPr)-Pr-i)(4)(OAc)(C7H8)(0.5) (2), and ZnAl2(acac)(3)((OPr)-Pr-i)(4)(OAc)(C7H8)(0.5) (3), were obtained with almost quantitative yields by reaction of the corresponding M-II(acac)(2) with 2 eq. of Al((OPr)-Pr-i)(3) in toluene at reflux with subsequent addition of 1 eq. of Hacac and 1 eq. of HOAc after cooling the reaction mixture to the room temperature. In the molecules 1-3 the late transition metal atom is tetrahedrally coordinated (eta(2)-acac plus 2 bonds to mu-(OPr)-Pr-i-groups), and the Al atoms have a slightly distorted octahedral coordination (hexacoordinated) (eta(2)-acac plus 3 bonds to mu-(OPr)-Pr-i-groups plus one bond to mu-OAc-group). 1-3 are stable to solvolysis in toluene and are volatile under reduced pressure. Thermal decomposition of CoAl2(acac)(3)((OPr)-Pr-i)(4)(OAc)(C7H8)(0.5) leads to nanoparticles of CoAl2O4, while homogeneous coatings of the spinel can be easily obtained using MOCVD.
Abstract: Addition of two equivalents of tris(2-hydroxy-3,5-dimethylbenzyl)amine (H(3)Lig) to the solution of MoO2(acac)(2) in MeOH results in the formation of anionic complex, which precipitates as LigH(4)[MoO(2)Lig], a yellow crystalline solid. Crystal structure determinations reveal that the asymmetric unit consists of one [MoO(2)Lig](-) anion, one H(4)Lig(+) cation and two molecules of solvent. Three phenoxide groups of the tetradentate ligand are bonded to cis-MoO22+ -ion in xy-plane, while the amino nitrogen atom completes the distorted octahedral coordination. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: Heterometallic nanocomposite oxide catalysts have been obtained by impregnation of NaY zeolite with toluene solutions of a structurally characterized heterometallic heteroleptic alkoxide, Co2Nb2(acac)(2)(OMe)(12). EXAFS studies showed the molecular structure of the complex to be preserved and the coordination of the late transition metal atom in the ready nanocomposite very close to that in the original complex. A silsesquioxane complex has been used in order to prepare a zeolite nanocomposite analogue and this proved successful with very similar EXAFS spectra to the ready nanocomposite, indicating the usefulness of the sils-esquioxanes as molecular analogues of zeolites. (C) 2004 Elsevier B.V. All rights reserved.
Abstract: The stable E- and Z-isomers of 10-membered azocrown ether have been isolated and studied by X-ray, (HNMR)-H-1 and UV-Vis methods. Their structures in a solid state indicate. the stretched conformation for trans-isomer and unstressed for cis-isomer. The concerted effect of azo-group pi-conjugation with benzene residue and steric strain of molecular conformation results in the observed stability of isomers.
Abstract: Molybdenum and tungsten oxoalkoxides [MO(OMe)(4)]; M=Mo, W and rhenium heptaoxide (Re2O7) reacted at room temperature with thiocarbonyl compounds such as N,N-dimethylthioformamide (DMTF), producing the crystalline metal sulfides MoS2, WS3 and Re2S7, respectively. The reaction mechanism involves, as the first step, the coordination of DMTF to a metal via the sulfur donor atom, followed by the subsequent metathesis of the latter with the doubly bonded oxygen atom. The final product is, depending on reaction conditions, a colloidal metal sulfide or up to 0.1 mm large metal sulfide crystals. By carrying out the reaction within a mesoporous alumina matrix, supported metal sulfide catalysts were obtained in one step. These catalysts were tested for catalytic hydrodesulfurization and their activity compared with catalysts prepared by traditional methods. Reaction of nickel and zinc acetylacetonates and aminoalkoxides with DMTF in hydrocarbon media was found to provide colloids and, on aging,. ne powder precipitates of NiS and ZnS.
Abstract: Interaction of 4 equiv. CoCl2 with 6 equiv. of NaOC2H4OEt in toluene/HOC2H4OEt medium provided Co4Cl2(OC2H4OEt)(6) (1) with practically quantitative yield. Reaction of Co(acac)(2) with Ti(OMe)(4) in 1:1 ratio in toluene gave Co-4(OMe)(2)(acac)(6)(MeOH)(2) (2) with moderate yields. The same reaction for Zn(acac)(2) resulted in formation of Zn-4(OMe)(2)(acac)(6)(C7H8) (3), The structures of 1-3 contain planar tetranuclear cores of M-4(mu(3)-OR)(2)(mu(2)-OR)(4) type ([Ti(OMe)(4)](4) type structure), where the metal atoms are pentacoordinated in 1, hexacoordinated in 2, and both penta- and hexacoordinated in 3. The magnetic measurements have revealed competing ferromagnetic and antiferromagnetic interactions between the 4 Co(II) atoms in 1, but only ferromagnetic in 2. (C) 2003 Elsevier Ltd. All rights reserved.
Abstract: Thiacalixarenes bearing phenylazo or ethynylic groups on the lower rims were prepared and fully characterized. The functional groups were chosen for their ability to increase the electron delocalisation over the molecule and to form metal complexes. The formation of complexes between phenylazothiacalixarenes and metal salts (Zn2+, Ag+...), and the synthesis of platinum acetylides from ethynylthiacalixarenes were investigated. Preliminary studies on optical limiting properties for both ligands and complexes is reported. Clamping levels of similar to4 muJ at 532 nm, were observed for both tetra( pentylphenylethynyl) tetrapropoxythiacalix[4] arene (150 mM in THF, 99% transmission) and the platinum complex (30 mM in THF, 83% transmission). A second functionalisation (upper rims) with metal alkoxide groups has also been investigated in order to prepare hybrid materials incorporating the optically active molecule. The same macrocycle core was thus bifunctionalised, and used for its optical properties on one side and as a precursor of an inorganic network for hybrid materials on the other.
Abstract: General principles of formation and stability of the heterometallic alkoxides existing due to Lewis Acid-Base interaction, isomorphous substitution and heterometallic metal-metal bonds are discussed. The molecular structure design approach based on the choice of a proper molecular structure type and completing it with the ligands, providing both the necessary number of donor atoms and the sterical protection of the metal oxygen core, is presented. Its applications in prediction of the composition and structure of single source precursors of inorganic materials are demonstrated for such classes of compounds as oxoalkoxides, alkoxide beta-diketonates, alkoxide carboxylates, derivatives of functional alcohols, metallatranes and metallasiloxanes.
Abstract: Porous nickel and cobalt oxides were prepared using their alkoxides as inorganic precursors. The stabilization of the meso-structure is especially critical for divalent elements such as Ni and Col which do not form any network structure, like silicates. The lack of a network-forming multivalent bond is the probable reason why no stable mesoporous oxides have been synthesized for divalent elements yet. Here we have reported our attempt to synthesize porous oxides of Ni and Co. Octadecylamine has been used as the organic structure-directing agent. The product obtained was put under solvent extraction and calcination at various temperatures to remove the surfactant, followed by characterization using XRD, TEM and BET measurements. The FT/IR and thermal analyses (TGA and DSC) were also carried out for supporting information, such as extent of removal of surfactant from the pores of the metal oxide. A relatively better surface area has been obtained for the Co oxide, but in Ni the surface area found is not as good. A possible reason for that has been discussed. The porous (solvent extracted) cobalt oxide has been used as a catalyst in the oxidation reaction of cyclohexane in mild conditions. The catalyst has shown relatively better conversion of cyclohexane into cyclohexanone and cyclohexanol than the nanostructured cobalt oxide catalyst of regular structure. (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: Interaction of Co(acac)(2) with 2 eq. of Ti((OPr)-Pr-i)(4) in hexane leads to an equimolar mixture of the new heterometallic complex [Co2Ti2(acac)(2)((OPr)-Pr-i)(10)] (1) and the known heteroleptic alkoxide Ti-2(acac)(2)((OPr)-Pr-i)(6). When redissolved in (PrOH)-Pr-i 1 is destroyed, forming [Co-2(acac)(4)((PrOH)-Pr-i)(2)] (2) as the only isolable crystalline product. Reaction of Co( acac) 2 with 3 eq. of Ta((OPr)-Pr-i)(5) gives [Co2Ta2((OPr)-Pr-i)(14)] (3) together with Ta(acac)((OPr)-Pr-i)(4). Reaction of Ni(acac)(2) with 4 eq. of Nb((OPr)-Pr-i)(5) produces the heterometallic complex [NiNb2((OPr)-Pr-i)(12)] (4). Reactions of M(acac)(2) (M = Co, Ni, Mg and Zn) with Al((OPr)-Pr-i)(3) in 1 : 2 ratios provides access to [MAl2((OPr)-Pr-i)(4)(acac)(4)] [M = Co (5), Ni (6), Mg (7)] and [Zn2Al2((OPr)-Pr-i)(6)-( acac)(4)] (8) respectively. When redissolved in (PrOH)-Pr-i, [NiAl2((OPr)-Pr-i)(4)(acac)(4)] (6) is destroyed, forming a mixture of [Ni-2(acac)(4)((PrOH)-Pr-i)(2)] (9), Al((OPr)-Pr-i)(3) and Al(acac)(3). Interaction of M(acac)(2), (M = Co, Ni) with metal isopropoxides in (PrOH)-Pr-i as well as their recrystallization from (PrOH)-Pr-i give 2 and 9 respectively. 5-7 are unstable in the hydrocarbon solution on heating, decomposing with formation of [M2Al2((OPr)-Pr-i)(6)(acac)(4)], along with Al(acac)(3) and heterometallic alkoxide species. Mg(acac)(2) was found to recrystallize unchanged from the solutions of Ti((OPr)-Pr-i)(4) in toluene. The solution structure and stability of the heterometallic complexes has been investigated by UV-Vis spectroscopy and NMR, and the details of their decomposition on sublimation by mass-spectroscopy. The factors influencing the formation and stability of heterometallic complexes originating from the reactions of divalent metal acetylacetonates with metal isopropoxides are discussed.
Abstract: The crystal structure of N,N-dimethylthioformamidium hexachlorohafnate(IV), (CH3)(2)NCHSH(2)[HfCl6], obtained by dissolution of anhydrous hafnium( IV) chloride in N, N-dimethylthioformamide and storage under ambient atmosphere, has been determined from single crystal X-ray diffraction data. The bond distance distribution within the N, N-dimethylthioformamidium ion is similar to that in N, N-dimethylthioformamide molecules strongly bound to metal ions, but significantly different from that in pure N, N-dimethylthioformamide. The hafnium( IV) ion coordinates six chloride ions in a near-regular octahedral arrangement with a mean Hf-Cl bond distance of 2.447 Angstrom. The packing in the crystal structure shows clearly the presence of hydrogen bonds of the X-(H)...Cl type, X = C and S, which are sufficiently strong and directional to hold the structure together. The structures of the hexachlorohafnate(IV), [HfCl6](2-), and hexachlorozirconate( IV), [ZrCl6](2-), ions in N,N-dimethylthioformamide solution have been determined by means of EXAFS, giving mean Hf-Cl and Zr-Cl bond distances of 2.44(1) and 2.45(1) Angstrom, respectively. The infrared spectrum of solid (CH3)(2)NCHSH(2)[HfCl6] has been analysed and compared with the data for free and strongly coordinated N, N-dimethylthioformamide.
Abstract: Hydrolysis of (M2M2V)-M-II(acac)(2)(OMe)(12), M-II=Co or Ni and M-V=Nb or Ta, in dry toluene, subsequent evaporation of the solvent, and heating to 500 C, provides access to a catalytically active oxide. The thermogravimetry (TG) analyses of the thermal behaviour of the hydrolysed alkoxides show three distinct steps. The first weight loss occurs at 120degreesC, the second at 390degreesC, and the third at 480degreesC. The weight is constant at 67% of original weight from 480 to 900 C. The powder X-ray patterns of the Co-Ta hydrolysed alkoxide show that powder heated to 500degreesC is amorphous but powder heated to 900degreesC revealed the presence of an equimolar mixture of (CoTa2O6)-Ta-II and (Co4Ta2O9)-Ta-II. Gelation and further transformation on thermal treatment were found to occur in the same way for Co2Ta2(acac)(2)(OMe)(12), Ni2Ta2(acac)(2)(OMe)(12), and Co2Nb2(acac)(2)(OMe)(12). Interaction of Co2Ta2(acac)(2)(OMe)(12) solution with NaY 12 Angstrom A zeolite was found to be an exothermic reaction providing access to a nanocomposite compound. The latter has been investigated with the aid of EXAFS spectroscopy. The interaction with NaY 12 Angstrom zeolite was found to occur in the same way for Co2Nb2(acac)(2)(OMe)(12) .
Abstract: The interaction of Co(acac)(2) with Al((OPr)-Pr-i)(3) in 1:1 ratio in toluene on reflux provided with quantitative yield a new heterometallic heteroleptic alkoxide complex, Co2Al2((OPr)-Pr-i)(6)(acac)(4)(I), displaying the so far unprecedented linear chain structure with a M’(mu-OR)(2)M(mu-OR)(2)M(mu-OR)(2)M’core. I appears to be a promising precursor for cobalt oxide-cobalt spinel nanocomposite materials. (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: Alkoxylation of the rhenium heptoxide, Re2O7, with the bimetallic niobium-tantalum methoxide, NbTa(OMe)(10), provided, dependent on the reaction conditions, either (Nb,Ta)(2)(OMe)(8)(ReO4)(2) (1) or (Nb,Ta)(4)O-2(OMe)(14)(ReO4)(2) (II). Niobium and tantalum are distributed very uniformly between the correspondent positions in the molecular structure of I (only one symmetry independent position present for M-v atoms). In the structure of II, the metal atom position connected to the perrhenate ligand has higher niobium content, while that connected to alkoxide groups and the oxoligand has higher tantalum content. Possible reasons for this difference and its influence on the decomposition behavior of I and II on vacuum sublimation are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.
Abstract: Crystals of magnesium oxomethoxoniobate, MgNb2O2(OMe)(10)(MeOH)(4) (1), resulting from partial decomposition of bimetallic alkoxoniobate, MgNb2(OMe)(12) (.) 2MeOH (2), have been isolated with moderate yields from solutions obtained by interaction of magnesium and niobium niethoxides in MeOH. Compound 1 is a non-volatile product, insoluble in hydrocarbons and poorly soluble in alcohol. The Structure of its molecule is analogous to that of Ti-4(OMe)(16), the positions connected to two tridentate OR-groups being Occupied by Mg atoms and those connected to one tridentate-OR-group-by those of Nb. The analysis of the M-O bond lenghts permits I to be considered as [Mg(ROH)(2)](2)(2+) [NbO(OR)(5)](2)(2-). Compound 2 in analogy to the corresponding tantalum derivative is a noii-crystallizing viscous volatile liquid. Its mass-spectrum contains the products corresponding to elimination of Nb(OR)(5), and R2O. The structural difference for niobium and tantalum oxoalkoxides can be explained by the ability of only niobium atoms to form terminal bonds to oxygen atoms (’niobyl’ groups). (C) 2002 Elsevier Science Ltd. All rights reserved.
Abstract: The octanuclear complex of bismuth ethoxide ethanol solvate, [Bi(OEt)(3)](8) (.) (7 + x)EtOH (1) has been isolated on crystallization from the ethanol solution of the products from the BiCl3 metathesis with NaOEt. The molecule of 1 is a [Bi-8] cycle with a crown shape (analogous to that of S-8 in the elementary sulfur), and is built up of seven [Bi(mu-OEt)(4)(OEt)] tetragonal pyramids and one [Bi(mu-OEt)(4)(OEt)(EtOH)] octahedron. The ring is surrounded by EtOH molecules forming hydrogen bonds with the terminal OEt-groups. (C) 2002 Elsevier Science B.V. All rights reserved.
Abstract: Thermal decomposition of complex oxomethoxo compounds Nb4O2(OMe)(14)(ReO4)(2) (I) and Ta4O2(OMe)(14)(ReO4)(2) (II) has been investigated. The decomposition of (II) at temperatures exceeding 100 degreesC results in the formation of MeOMe, MeOCH2OMe, MeOH, and H2O vapor and is accompanied by sublimation at temperatures over 135 degreesC. Plausible mechanisms of the processes studied are discussed. A new bimetallic methoxo compound, Nb-2(OMe)(8)(ReO4)(2) (III), was synthesized by interaction between Re2O7 and Nb-2(OMe)(10) in toluene solution and its structure was determined by means of an X-ray single-crystal study. The structure can be considered as a product of substitution for terminal methoxo groups with two perrhenate groups in dimeric Nb-2(OMe)(10) molecules. Decomposition of 11 in an inert atmosphere at 900 degreesC gave a Re-Ta mixed oxide phase, supposedly based on the L-Ta2O5 structure. Decomposition of I and III under similar conditions leads to the formation of rhenium-niobium oxide phases. The results obtained provide a basis for the alkoxide approach to the synthesis of oxide and metallic rhenium-based materials.
Abstract: The reaction of FeBr2 with three equivalents of NaOtBu in THIF affords the first heterometallic Fe-II alkoxide, [(THF)NaFe(OtBU)(3)](2) (1), to be structurally characterised. The central core of the structure is an M2O6M’(2) fragment with C-2 symmetry. The compound is shown to be promising as a new precursor for magnetic iron oxide Fe3O4, ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany. 2002).
Abstract: The structure and vibrational spectra of the dimethyl sulfoxide solvated thallium(III) ion have been studied in a dimethyl sulfoxide solution and in the solid state. X-ray crystallography shows a trigonal unit cell, space group R (3) over bar (No. 148), for the [TI(dmso)(6)](ClO4)(3) Compound with Z = 3, a = b = 11.9764(13) [11.8995(9)] Angstrom, c = 20.802(2) [20.467(2)] Angstrom, and V = 2584.0(5) [2509.9(4)] Angstrom (3) at 295 [150] K. The crystal structure comprises a highly symmetric hexakis(dimethyl sulfoxide)thallium(III) ion, with thallium in a 3 symmetry site and a TI-O bond distance of 2.224(3) Angstrom at 295 K. The octahedral TlO6 kernel is compressed along the threefold axis with an O-Tl-O bond angle of 96.20(11)degrees. The Tl-O-S bond angle of 120.7(2)degrees corresponds to a Tl . . .S distance of 3.292(2) Angstrom. One perchlorate ion centered on the (3) over bar axis was described by a statistically disordered model. A low-temperature EXAFS study (10 K) resulted in the TI-O and Tl . . .S distances of 2.221(4) and 3.282(6) Angstrom, respectively, consistent with a Tl-O-S bond angle of 120(1)degrees. The low Debye-Waller factors confirm a regular coordination without the disorder of the dimethyl sulfoxide ligands, which would have resulted from the alternative choice of space group R3 for the crystal structure. Raman and infrared spectra have been recorded and assigned, with the bands at 435 and 447 cm(-1) corresponding to the vibrational frequency of the symmetric and asymmetric TI-O stretching modes, respectively. EXAFS data of a 0.5 mol dm(-3) thallium(III) trifluoromethanesulfonate in a dimethyl sulfoxide solution were consistent with that of a hexasolvated ion with mean Tl-O and Tl . . .S distances of 2.22(1) and 3.33(2) Angstrom, respectively, which correspond to a mean Tl-O-S bond angle of 124(2)degrees. The anomalously large disorder parameter for the TI-O distances is consistent with a weal, pseudo-Jahn-Teller effect. The Tl-205, C-13, and H-1 NMR spectra of the complex in solution show single signals at 1886, 39.5, and 2.3 ppm, respectively.
Abstract: The interaction of Co(acac)(2) and Ta(OMe)(5) in dry toluene led to formation of crystalline [Co2Ta2(acac)(2)(OMe)(12)] 1 and [Ta(acac)(OMe)(4)] 2 complexes. If the starting material is not completely water-free the products obtained are [Co-4(acac)(6)(OMe)(2)(MeOH)(2)] 3 and Co(acac)(2). 2MeOH 4 due to hydrolysis of Ta(OMe)(5) producing free methanol and thus altering the reaction pathway. The interaction of M-II(acac)(2), M-II=Co, Ni, Zn or Mg, and M-V(OMe)(5), M-V=Ta or Nb, in dry toluene was found generally to provide (M2M2V)-M-II(acac)(2)(OMe)(12) 5-8, a new class of heterometallic heteroleptic alkoxide complexes. The crystal structures of 1-8 have been determined.
Abstract: The interaction of Ta-2(OMe)(10) with Re2O7 in toluene in 1:2 ratio provided an approach to a new bimetallic complex, Ta-2(OMe)(8)(ReO4)(2)(I), which in its solid state structure and solution behavior displayed a close analogy to the homometallic M-2(OMe)(10), M=Nb, Ta, and to M2O2(OMe)(8), M=MO, W, complexes. (C) 2001 Elsevier Science B.V. All rights reserved.
Abstract: The reaction of Al2Cl6 with an excess of Ph2Si(OH)(2) in THF in the presence of pyridine yielded new anionic and cyclic aluminosiloxanes: the structure of the anionic complex is composed of separated pyridinium cations and aluminosiloxane anions dth a tetrahedral arrangement around the Al atom, which is similar to that in natural aluminosilicates; the core of the cyclic aluminosiloxane is a twelve-membered Al2Si4O6 ring in a chair conformation, which contains a Cl group on each of the two Al atoms.
Abstract: Soluble Ni(II) alkoxides, namely the dimethylaminoisopropoxide clathrate with toluene, Ni(eta (2)-ORN)(2).C7H8 (I) and the solvent free crystalline Ni(ORN)(2) (R-N = CHMeCH2NMe2) species (II), obtained by sublimation of I in vacuo, were characterized by X-ray diffraction. The reaction between Ni(ORN)(2) and copper carboxylates such as propionate and copper acetate hydrate in hydrocarbons afforded [CuNi2(O2CEt)(3)(ORN)(3)((ROH)-O-N)] (III) and [Ni(Ni0.25CU0.75)(2)(mu (3)-OH)(mu -OAc)(eta (1)-OAc)(2)(mu, eta (2) -ORN)(2)(eta (2)-(ROH)-O-N)] (IV), respectively. The structures of I and II are based on square planar molecules of the trans isomer. The structure of IV corresponds to triangular aggregates with a M-3(mu (3)-OH) central core. The remarkable feature is the presence of three types of coordination sphere, one metal is coordinated octahedrally and corresponds to nickel and the other two have square pyramidal and square planar coordinations, respectively, and an electronic density corresponding to Cu (75%) and Ni (25%). The monodentate behavior of the two acetato ligands is stabilized by intramolecular hydrogen bonding involving the hydroxyl functionalities of the mu (3)-hydroxo (2.776(9) Angstrom) and the solvated aminoalcohol ligand (2,573(6) Angstrom). Magnetic data in the 20-300 K temperature range for III and IV account for three uncoupled metal centers at high temperature whereas ferromagnetic exchange interactions are likely below 20 K. (C) 2001 Elsevier Science Ltd. All rights reserved.
Abstract: The anodic oxidation of molybdenum metal in MeOH at both low anodic and cathodic current density (0.025 A/cm(2)) and electrolyte temperatures kept below 20 degreesC provides sn efficient approach to Mo(OMe)(6) (I). W(OMe)(6) (II) can be obtained from the electrolytes, prepared via anodic dissolution of tungsten, by fractional crystallization. The symmetrically independent units in the structures of I and II, being isomorphous, follow the C-1 (slightly distorted D-2d) symmetry. Theoretical calculations performed for a free molecule of I indicate that this low symmetry may be the result of the packing of the molecules in the crystal, structure and also an inherent property imposed by the bonding in this compound. Crystal data for I: Mo(OMe)(6) at 22 degrees C, a = 7.0976(13), b = 6.6103(12), and c = 12.286(2) Angstrom, beta = 90.068(3)degrees, V= 576.41(18) Angstrom (3), monoclinic P2/n, Z = 2. Crystal data for II: W(OMe)(6) at 22 degreesC, a = 7.1164(19), b = 6.6414(18), and c = 12.304(3) Angstrom, beta = 90.047(5)degrees, V = 581.5(3) Angstrom (3), monoclinic P2/n, Z = 2.
Abstract: The interaction of the individual M-4(acac)(4)(mu (3)-OMe)(4)(MeOH)(4) complexes, M = Co, Ni in toluene;methanol media provided crystals of (Co,Ni)(4)(acac)(4)(mu (3)-OMe)(4)( MeOH)(4) (I) - the product of co-crystallization of isomorphous products. The oxidation of a MeOH solution of I in air in the presence of NaOAc and aminoalcohols as catalysts gave Co2Ni2(acac)(4)(mu (3)-OMe)(4)(OAc)(2) (II), an individual heterometallic derivative. The interaction of Mg(OCH(CH3)CH2NMe2)(2) with Cu(acac)(2) in toluene/methanol media produced Mg-4( acac)(4)(mu (3)-Me)(4)( MeOH)(4) (III) as the only isolatable product. The starting Co and Ni homometallic complexes as well as the heterometallic CoNi complex II were used to prepare the zeolite-supported oxide catalysts which exhibited extremely high activity towards methanol oxidation. (C) 2001 Elsevier Science Ltd. All rights reserved.
Abstract: The anodic oxidation of rhenium metal in isopropanol at temperatures not exceeding 20 degreesC provides with good yields the crystalline Re4O6(O-i Pr)(10) (I) complex, the molecular structure of which is built up around a practically ideal (Re-Re 2.52-2.54 Angstrom) planar rhombus of metal atoms, being thus connected by five equivalent metal-metal bonds in a system with only six cluster electrons. (C) 2001 Elsevier Science B.V. All rights reserved.
Abstract: The reaction of Re2O7 with MeOH at room temperature leads to a fine black powder. A product with the same crystal structure, according to X-ray powder data, was obtained in the form of single crystals on storage of solutions of Re2O3(OMe)(6), obtained by anodic oxidation of Re metal. It was identified as Re4O6(OMe)(12) (1) by an X-ray single crystal study. A mixed-valence complex of analogous composition and structure, Re4O6-y (OMe)(12+y) (2), earlier erroneously described as Re4O2(OMe)(16), can be obtained via anodic dissolution of Re in MeOH using high current densities. The heterometallic members of this family, Re4-xMxO6-y(OMe)(12+y) [M = Mo (3), W (4); x less than or equal to 0.55, y < 1.0], were obtained by interaction of Re2O7 with MO(OMe)(4) or M(OMe)(6) in toluene at reflux. Mo-poor samples of 3 (x <less than or equal to> 0.25) could also be obtained on storage of solutions prepared by anodic oxidation of Re, in the presence of MoO(OMe)(4). The reaction of Re2O7 with Nb(OMe)(5) or Ta(OMe)(5) in refluxing toluene gave M-4(mu -O)(2)(mu -OMe)(4)(OMe)(14)(ReO4)(2) [M = Nb (5), Ta (6)] as the only crystalline products. The compounds 1-6 are insoluble in organic solvents and display a remarkable resistance to ambient atmosphere, making them attractive precursors for soft chemical preparation of rhenium metal and alloy powders.
Abstract: The anodic oxidation of Re metal in MeOH (Me = CH3) provides a mixture of Re2O3(OMe)(6) and Re(V) oxoalkoxides that on storage or on heating give insoluble and air stable Re4O6-y(OMe)(12+y)(I). I can be also obtained by reaction of Re2O7 with MeOH. In the presence of MoO(OMe)(4), a heterometallic complex ReMoO2(OMe)(7)(II) is formed as intermediate, the final product being Re4-xMoxO6-y(OMe)(12+y)(III). The electrosynthesis in the presence of WO(OMe)(4) gives Re4-xWxO6-y(OMe)(12+y)(IV) only at very high Re : W ratios in solutions and the W content varies in one and the same sample. The dissolution of Re2O7 in the solutions of MO(OMe)(4), M = Mo,W in toluen on reflux yields Re4-xMxO6-y(OMe)(12+y) with uniform Re : M distribution. The cocrystallization of MoO(OMe)(4) and WO(OMe)(4) yields (Mo,W)O(OMe)(4) (V) with almost uniform Mo : W distribution. The thermal decomposition of II and III in inert atmosphere gives fine powder of the (Re,Mo)O-2 phase. The reduction with hydrogen gas converts II and III into an ultrafine powder of Re-Mo alloy at temperatures below 400 degreesC. The latter can be sintered into compact metal at 800-900 degreesC.
Abstract: The microhydrolysis of VO(OEt)(3) on interaction with atmospheric moisture in the absence of other solvents than the compound itself leads to crystallization of a greenish black crystalline compound. The latter was identified as V6O7(OEt)(12), (I), a member of the hexavanadate family, with the aid of an X-ray single crystal study (space group R-3, a = b = 17.483(11), c = 11.273(10) Angstrom, alpha = beta = 90, gamma = 120 degrees). The V6O19 core is highly symmetric and situated on the cross section of the crystallographic elements of symmetry. The carbon atoms of each ethoxy group are disordered between two positions arising from two different orientations possible for it. (C) 2000 Elsevier Science S.A. All rights reserved.
Abstract: No complex formation can be observed between molybdenum(VI) oxoalkoxides and the alkoxides of niobium(V) or tantalum(V) at room temperature. The bimetallic derivatives of molybdenum(V), Mo4M2O8((OPr)-Pr-i)(14), where M=Nb 1 and Ta 2, were instead isolated on cooling from the solutions of the isopropoxides in toluene subjected to a short-time reflux. The X-ray single crystal study showed both 1 and 2 to be built of ((PrO)-Pr-i)(3)M(mu-(OPr)-Pr-i)(3)MoO(mu-O)(2)MoO(mu-(OPr)-Pr-i)(2)MoO(m u-O)(2)MoO(mu-(OPr)-Pr-i)(3)M((OPr)-Pr-i)(3) non-linear chain molecules with 2 Mo-Mo bonds (2.5836(8) Angstrom) and short but non-bonding Mo-M distances (3.1791(8) Angstrom for 1 and 3.1746(8) Angstrom for 2). According to NMR and EXAFS data this structure becomes very fluxional or might even be partially broken into homometallic components in hydrocarbon solutions. The oxidation of 2 with traces of oxygen leads to the formation of Mo3Ta2O8((OPr)-Pr-i)(10) 3. Compound 3 can be isolated in a pure form from the reaction of MoO((OPr)-Pr-i)(4) with Ta((OPr)-Pr-i)(4)(OMe) 6: the presence of methoxide ligands leads to the formation of additional oxoligands via non-reductive thermolysis leading to the formation of a (CH3)(2)C(OMe)(2) ketal as organic byproduct. The molecules of 3 are 5-member rings with a MoO(mu-O)(2)MoO fragment in the basis (Mo-Mo 2.5730(13) Angstrom), coupled to two (mu-(OPr)-Pr-i)(2)Ta((OPr)-Pr-i)(3) fragments that are joined together by an oxomolybdate ligand (mu-O)(2)MoO2. According to NMR-spectroscopic data the aggregate is preserved and rigid in solution. Mo4Ta4O16((OPr)-Pr-i)(12) 4 was found to be one of the products of complete oxidation of 2 (and 3) on prolonged contact with dry oxygen. The thermal treatment of the solutions of MoO((OPr)-Pr-i)(4) and WO((OPr)-Pr-i)(4) in toluene yields (Mo4O8)-O-V(Mo,W)O-VI(2)2((OPr)-Pr-i)(12) 5 with a molecular structure very close to its homometallic analog Mo6O10((OPr)-Pr-i)(12). The complete X-ray single crystal study was carried out for the sample of 5 with (Mo4O8)-O-V(Mo0.45W0.55)O-VI(2)2((OPr)-Pr-i)(12) composition.
Abstract: Complex formation between molybdenum and tantalum alkoxides has been achieved via activation of the homometallic species, both being Lewis acids, by either partial hydrolysis or partial thermolysis in hydrocarbon media. The crystal structures of the products formed, Mo2Ta4O8(OMe)(16) (I) and Mo4Ta2O8((OPr)-Pr-1)(14) (II) respectively, are described. (C) 2000 Elsevier Science S.A. All rights reserved.
Abstract: The paper introduces a formal security model for a microprocessor hardware system. The model has been developed as part of the evaluation process of the processor product according to ITSEC assurance level E4. Novel aspects of the model are the need for defining integrity and confidentiality objectives on the hardware level without the operating system or application specification and security policy being given, and the utilization of an abstract function and data space. The security model consists of a system model given as a state transition automaton on infinite structures and the formalization of security objectives by means of properties of automaton behaviors. Validity of the security properties is proved. The paper compares the model with published ones and summarizes the lessons learned throughout the modeling process.
Abstract: The approach based on isomorphous substitution permitted preparation of (Co, Ni)(4)(acac)(4)(mu (3)-OMe)(4) (MeOH)(4)(I) via interaction of individual M-4(acac)(4)(mu (3)-OMe)(4)(MeOH)(4) in toluene/methanol media. The oxidation of I in air in solution in MeOH in the presence of NaOAc and aminoalcohols as catalysts gives Co2Ni2-(acac)(4)(mu (3)-OMe)(4)(OAc)(2)(II). The symmetrization reaction between a complex formed by a hard Pearson acid and a soft Pearson base and that formed by a soft acid and a hard base led to CuNi2(OCOC2H5)(3)(ORN)(3)-((ROH)-O-N)(III) and Ni(Ni0.25Cu0.75)(2)(mu (3)-OH)(mu (2)-OAc)(OAc)(2)(mu (2), eta (2)-ORN)(3)(eta (2)-(ROH)-O-N)(IV) R-N = CH(CH3)-CH2NMe2 via interaction of Ni(ORN)(2) with copper propionate and copper acetate hydrate respectively in hydrocarbon media.
Abstract: The alkoxides of molybdenum and other heavy transition elements such as Ta or Nb were found to be unreactive towards each other. The bimetallic derivatives could be obtained either via partial hydrolysis that gave Mo2Ta4O8(OMe)(16) (I) or via partial thermolysis that provided access to Mo4Ta2O8((OPr)-Pr-i)(1)4 (II), Mo3Ta2O8((OPr)-Pr-i)(10) (III), Mo4Ta4O16((OPr)-Pr-i)(12) (IV), Mo4Nb2O8((OPr)-Pr-i)(14) (V) and Mo4W2- xMo(x)O(10)((OPr)-Pr-i)(12) (VI). I-VI can be isolated only from hydrocarbon media as the presence of alcohols leads to precipitation of insoluble homometallic derivatives of molybdenum. The cathodic reduction of MoO(OR)(4) (R = Me, Et) in the presence of LiCl and M(OR)(5) (M = Nb, Ta) leads only to formation of LiMo2O2(OMe)(7)(MeOH) (VII) or LiMo2O2(OEt)(7) (VIII) respectively.
Abstract: The partial hydrolysis of a mixture of molybdenum and tantalum methoxides (Mo:Ta = 1:2) with stoichiometric amounts of water yields a new bimetallic complex Mo2Ta4O8(OMe)(16) (I) on crystallization from toluene. The molecules of I appear to be a combination of two MoO2((OPr)-Pr-i)(2) units with the earlier described Ta4O4((OPr)-Pr-i)(12) core. The thermal reduction of a mixture of MoO((OPr)-Pr-i)(4) and Ta-2((OPr)-Pr-i)(10) (in a 1:1 Mo:Ta ratio) followed by oxidation of the products by dry oxygen, provides access to Mo4Ta4O16((OPr)-Pr-i)(12) (II). The same procedure, using LiMo2O4((OPr)-Pr-i)(4)(OC2H4OMe) instead of MoO((OPr)-Pr-i)(4), yielded trimetallic LiMo4Ta3O14((OPr)-Pr-i)(9)(OC2H4OMe)(3) (III) in minor yields. The molecular structure of II can be described as a distorted cube, the corners of which are occupied in turn by [((PrO)-Pr-i)(3)Ta(mu-O)(3)] octahedra and [MoO(mu-O)(3)] tetrahedra sharing common vertexes. The molecular structure of III can be derived from that of II by replacing one [(iPrO)(3)Ta(mu-O)(3)] octahedron with an [Li(mu,eta(2)- OC2H4OMe)(3)] trigonal prism (the coordination number of the three Mo atoms is then increased to six). (C) 2000 Elsevier Science Ltd. All rights reserved.
Abstract: Upon oxidation by dry oxygen of electrolytes produced by anodic stripping of rhenium in a methanol solution of MoO(OMe)(4) in the presence of the electroconductive LiCl until Re : Mo >= 4 : 1, brown-black crystals separate slowly. The precipitate is unstable in air. Its X-ray powder diffraction pattern is virtually unchangeable, but the rhenium-to-molybdenum ratio is variable and close to the metal ratio in the electrolyte. An X-ray structure experiment on an Re : Mo approximate to 9 : 1 single crystal showed that the crystal is structurally built of tetranuclear, nearly planar molecules M4O6-y(OMe)(12+y) (M = Re, Mo). The M atoms are bonded through oxo bridges along two opposite sides of the rectangle and pairs of methoxide bridges along the other two sides. The remaining three positions in the coordination sphere of the metal are occupied by two terminal alkoxo groups and the oxygen atom (trans to the alkoxide bridge), which are disordered to positions corresponding to the terminal oxo and alkoxo groups. For all M atoms, the occupancy of the alkoxo group position is smaller than the value calculated according to the assumption that only rhenium(V) (molybdenum(VI)) atoms are present in the structure, which is indicative of the presence of rhenium(VI).
Abstract: The colorless needle-shaped crystals of a new heterometallic 2-methoxyethoxide, BaMo2O5(OC2H-4OMe)(4)(HOC2H4OMe) (1), have been obtained by the saturation of barium 2-methoxyethoxide solution in 2-methoxyethanol with the crystalline MoO2(OC24H,OMe)(2). The precipitation started when the Ba:Mo ratio achieved a 1:2 value and the precipitate formed contained BaMoO4 as an admixture thus indicating that the formation of oxo species led partially even to formation of inorganic molybdates. Molecules of 1 involve the metal-oxygen framework quite typical of trinuclear homo- and heterometallic alkoxide species. The rather high coordination number of the barium atom (10) and the lengths of the observed interatomic distances permit to suggest that this atom in 1 forms predominantly ionic bonds and, therefore, complex 1 can be formulated as [Ba(HOC2H4OMe)](2+) [Mo2O5(OC2H4OMe)(4)](2-). (C) 1998 Elsevier Science Ltd. All rights reserved.
Abstract: The review provides a description of main events in the development of chemistry of metal alkoxides in Russian and summarizes the results obtained by the authors. The studies of solubility and vapor pressure in the M(OR)(n)-ROH (R = Li, Mg, Ca, Sr, Ba, Tl) systems permitted the determination of the composition of the solvates formed and the optimization of the isolation conditions for distinct derivatives. The electrochemical synthetic approach to the alkoxide and 2-methoxyethoxide derivatives of III-VIII Group elements has been elaborated. Improvement of the MCln with NaOR metathesis conditions led to practically quantitative yields of alkoxides. The examples of the structures of polynuclear oxoalkoxides, earlier erroneously considered to be orthoderivatives, i.e. ‘M(OR)(n)’, are given. It has been stated that among the alkoxoderivatives of Zr and I-If these are only M(OC2H4OMe)(4) and M(OR)(4) . ROH (R = Pr’, Bu’) that exist as individual compounds, while the samples of those with different R contain oxocomplexes of M3O(OR)(10) and M4O(OR)(14) composition. The questions connected with the origin of oxogroups in the molecules of alkoxides and their influence on the properties of the samples are discussed. The irreproducibility of the physicochemical constants for the samples (physical state, melting points, solubility in alcohols, intensity of coloration) is caused by different ‘chemical’ (synthetic procedures, isolation conditions) and thermal prehistory and storage times; it originates from the difference in their molecular composition (different fractions of different types of oligomeric and polymeric [M(OR)(n)](m) and MxOy(OR)(z) aggregates). Formation of bimetallic alkoxides is studied using the plotting of 20 degrees C solubility isotherms in M(OR)(n)- M’(OR)(m)-Solvent systems. Different kinds of systems are considered and the composition and structure of bimetallic complexes and oxocomplexes, originating from their decomposition, are described. Decomposition of alkoxomolybdates and -tungstates in solutions may result in crystallization of complex oxides as the final products. The example of MTiO3 (M = Mg, Ba) oxide preparation is discussed as most illustratively demonstrating the need in studies of metal alkoxides interaction in solution for the optimization of synthesis of oxides by the sol-gel technique. (C) 1998 Elsevier Science Ltd. All rights reserved.
Abstract: Liquid samples of MoO((OPr)-Pr-i)(4) (I), kept at room temperature in complete isolation from oxygen and moisture, nearly completely solidify after approximately 2 months of storage. GLC-MS analysis of the liquid residue showed it containing approximately equal amounts of (PrOH)-Pr-i and acetone and excess of (Pr2O)-Pr-i. Multinuclear NMR (C-13, O-17 and Mo-95) investigation of this reaction in solution in toluene proved that acetone and ether elimination occur simultaneously. The solid product of the reaction was identified as Mo6O10((OPr)-Pr-i)(12) (II). (C) 1998 Elsevier Science Ltd. All rights reserved.
Abstract: Molybdenum oxomethoxide and ethoxide are found to react very rapidly with aldehydes and ketones in both alcohol and hydrocarbon media transforming the latter into acetals and ketals respectively. The colloid solution of the molybdenum blue usually formulated as “MoO2.88. H2Oâ€appears to be the major inorganic product of this reaction. The reaction mechanism includes presumably formation of a semiacetal molybdate and its subsequent decomposition with elimination of acetal. Different reaction pathways of metal alkoxides interaction with aldehydes and ketones are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.
Abstract: In order to obtain new organic-inorganic hybrid materials the method exploiting the phenomenon of polymer crazing was investigated. Polypropylene and polyethyleneterephtalate films were subjected to crazing to achieve high porosity. Incorporation of hydrated oxides of Mo and W in porous polymer matrix was performed by hydrolysis of alkoxides in pores using counterflow diffusion technique. It was shown that peculiarities of the hydrolysis of the initial compounds affect significantly the distribution of substances inside porous polymer matrix and the possibility of accumulation of inorganic component inside the film. Mo matter in contrast to W is easily incorporated in the polymer matrix to form a well-defined layer. These samples demonstrated high photosensitivity.
Abstract: The studies of zirconium isopropoxide solvate, Zr((OPr)-Pr-i)(4).-(PrOH)-Pr-i(I), interaction with molybdenum oxoisopropoxide in different solvents ((HOPr)-Pr-i, hexane) revealed I to be the only isolable crystalline product in alcohol. In hexane I crystallized from Zr-rich solutions (up to Zr:Mo = 1:2 ratio). From the solutions with Zr:Mo = 1 :2 ratio repeatedly dried in vacuo and subsequently redissolved in hexane, the crystallization of Zr3Mo8O24((OPr)-Pr-i)(12)((PrOH)-Pr-i)(4)(II) occurred slowly with 12% yield. II can be recrystallized from hexane, but is destroyed by (PrOH)-Pr-i which causes the formation of I. Thermal decomposition of II in air at 800 degrees C (2 h) gives a single phase ZrMo2O8(III). Hydrolysis studies of hexane solutions, prepared in a manner analogous to those, from which II was obtained, showed that single-phase samples of III could be obtained when a thin layer of solution was left for hydrolysis and evaporation of solvent in a moist air and then annealed at 800 degrees C (2 h). The same kind annealing of a xerogel, obtained by hydrolysis with water solutions in (PrOH)-Pr-i and subsequent drying at 100 degrees C gave a complex mixture of phases where III was not even the major component. No Zr-W complex was isolable under analogous conditions. From the xerogel, obtained by hydrolysis with H2O/(PrOH)-Pr-i, ZrO2 and WO3 crystallized separately on heating. Only traces of ZrW2O8(IV) were obtained along with individual oxides when 1% water in ether was applied for hydrolysis. Molecular precursor is therefore crucial for obtaining III, IV.
Abstract: The study of the side products of the anodic dissolution of molybdenum and tungsten metals in alcohols in the presence of LiCl showed them to be [LiMo2O2(OMe)(7)(MeOH)] 1 in the case of MeOH and [LiMo2O4(OEt)(5)(EtOH)] 2 in EtOH. Treatment of 2 with an excess of (PrOH)-O-1 gave [LiMo2O4(OPr1)(5)((PrOH)-O-1)] 3, the structure of which was confirmed by a study of [LiMo2O4(OPr1)(4)(OC2H4OMe)(2)] 4, the product of partial substitution of OR groups in 3 by 2-methoxyethoxide ligands. Reaction of 2 with an excess of MeOC2H4OH led to an equimolar mixture of [MoO2(OC2H4OMe)(2)] and [LiMoO2(OC2H4OMe)(3)] 5. In (PrOH)-O-1 a crystalline product identified as [Mo6O10(OPr1)(12)] 6 was isolated. Anodic oxidation of tungsten in MeOH gave a mixture of homometallic W(OMe)(6) and [WO(OMe)(4)]. Electrosynthesis in EtOH gave as major product an amorphous glass-like mass (after separation of crystalline [WO(OEt)(4)] by filtration and subsequent drying of the filtrate in vacuo). Treatment of the latter with an excess of HOC2H4OMe led to crystallization of [LiWO2(OC2H4OMe)(3)(2) . 2Li(HOC2H4OMe)(2)](2+)[W6O19](2-) 7. Complexes 1, 4 and 7 were characterized by X-ray single-crystal studies. A GLC-mass spectrometric study of the composition of organic side products indicated that the processes were associated with formation of ethers, alkyl halides, aldehydes or ketones and their derivatives. The nature of the possible side reactions was deduced on the basis of the data obtained.
Abstract: The hydrolysis of solutions, containing either LiMo2O4(OPri)(5)((PrOH)-Pr-i) and ‘’La(OPri)(3)†or LiOPri and La2Mo4O8(OPri)(14) in 1:1 ratio, in toluene or (PrOH)-Pr-i, by water solutions in isopropanol, leads to formation of monolythic gels. The latter can be converted by drying and heat treatment at 600 degrees C into a fine powder of pure alpha-LiLaMo2O8 phase, which is transformed into beta-LiLaMo2O8 powder by annealing at 800 degrees C. The sintering of the pellets pressed under 4 bar pressure of alpha-LiLaMo2O8 powder at 800 degrees C for 2 h converts them into pieces of beta-LiLaMo2O8 transparent ceramics, thus providing a route to LiLnMo(2)O(8) laser waveguide materials.
Abstract: Various routes to Ni-II-aminoalkoxides have been investigated. A nickel isopropoxide derivative 1 was prepared by anodic dissolution of the metal in the presence of LiCl as electrolyte. Alcoholysis reactions of 1 with 1-dimethylamino-2-propanol afforded the homoleptic nickel(II) aminoalkoxide 2 together with a Ni-Li species 3. 2 was also obtained by metathesis reactions between sodium alkoxide and the nickel hexammine complex whereas the reaction between the latter and the aminoalcohol led to an halide solvate, cis-NiCl2(eta(2)-ROH)(2), 4. The various compounds were characterized by elemental analysis, FT-IR and UV-vis spectroscopies as well as by X-ray diffraction for 3 and 4. 3 corresponds to [Li((PrOH)-O-i)Ni(eta(2)-OCHMeCH2NMe2)Cl](2) and the overall structure can be seen as two [Ni(eta(2)-OCHMeCH2NMe2)(2)Cl](-) moieties assembled by Li((PrOH)-O-i)(+). The lithium atom is 4-coordinate due to its interaction with the oxygen atoms of the aminoalkoxide ligands. Nickel is 5-coordinate with a distorted tetragonal pyramidal stereochemistry, one nitrogen being in the apical position. The metal displays a distorted octahedral surrounding for the NiCl2 adduct 4. The bond distances vary in the order Ni-OR < Ni-N approximate to Ni-O(H)R < Ni-Cl for 3 and 4. The various compounds (except 1) are soluble in organic media. (C) 1997 Elsevier Science Ltd.
Abstract: The reaction of lanthanum isopropoxide with the isopropoxide of molybdenum(VI), MoO(OPri)(4), in 1:2 molar ratio in hexane, leads to the formation of the mixed-metal hexanuclear complex La2Mo4O4(mu(4)O)(4)(mu-OPri)(8)(OPri)(6) (1), formally derived from the dioxomolybdenum species MoO2(OPri)(2). The molecule of 1 contains an unusual tetragonal bipyramidal La2Mo4 metal core supported by four tetradentate oxobridging ligands binding two neighbouring molybdenum and both lanthanum atoms each. Complex 1 readily decomposes either in solution in iso-propanol or on heating in uacuo to 90 degrees C. The mechanism of the latter process is discussed.
Abstract: The direct electrochemical synthesis of zirconium (la) and hafnium (Ib) alkoxides, M(OPri)(4) . (PrOH)-O-i, Zr(OBu(i))(4) . Bu(i)OH (4a) and M(OR)(4), where R = Et (2a,b), Bu(n) (3a), Bu(S) (5a), C(2)H(4)OMe (6a,b) has been carried out by anodic oxidation of metals in anhydrous alcohols in the presence of LiCl as a conductive additive to give quantitative yields. The solubility polytherms and dissociation pressure of la,b have been investigated. It has been proved by means of chemical analysis, X-ray powder, and IR spectral studies that the desolvation of 1a,b and Sn(OPri)(4) . (PrOH)-O-i (1c) is accompanied by the formation of amorphous oxocompounds M(3)O(OPri)(10). On the basis of H-1 NMR data it has been proved that the structure of the latter is analogous to that of known triangular cluster molecules M(3)(mu(3)-O)(mu(3)-OR)(mu-OR)(3)(OR)(6), where M = Mo, W, U. Mass-spectral data and the determined physicochemical characteristics of 1-5 permit to conclude that the samples of composition M(OR)(4), where M = Zr, Hf, and 2, 3, 5 contain tri- and tetranuclear oxocomplexes M(3)O(OR)(10) and M(4)O(OR)(14), respectively, along with Zr(OR)(4) oligomers of different molecular complexity.
Abstract: The new heterobimetallic methoxide [ReMoO2(OMe)(7)] 1 is obtained in 62% yield by hexane extraction from the electrolyte prepared by anodic oxidation of Re metal in a methanolic solution of [MoO(OMe)(4)] in the presence of LiCl as electrolyte; the molecule of 1 consists of two [MO(OMe)(5)] octahedra with three shared mu-OMe groups; while 1 shows high volatility and under such conditions remains intact, mass spectrometry indicates complete dissociation into homometallic species in the gas phase.
Abstract: The reaction between barium ethoxotetratitanate with various hydroxo ligands shows a tendency for the destruction of the heterometallic alkoxide with precipitation of an insoluble barium derivative. Novel heteroleptic complexes Ba2Ti2(thd)2(OEt)10(EtOH)4 (I), Ba2Ti2(thd)4-(mu3-OEt)2(mu-OEt)4(OEt)2(EtOH)2 (II), and Ba2Ti2(acac)4(OEt)8 (III) were obtained in a high yield by reactions between alkoxides and beta-diketonates and/or by adding a beta-diketone to a mixture of alkoxides. II crystallizes in the triclinic system, space group P1 with the unit-cell parameters a = 9.94(8), b = 14.696(5), c = 15.909(7) angstrom, alpha = 100.57(3), beta = 105.36(5), gamma = 108.27 (4)-degrees, Z = 1, R = 0.053, R(w) = 0.061 for 2550 reflections. The molecular structure of II is based on a centrosymmetric rhombus, each metal bearing a diketonate ligand. Ba and Ti are 7- and 6-coordinated, respectively. The Ba-O bond distances range from 2.572(8) to 3.008(6) angstrom, with the Ba-O(thd) < Ba-OR almost-equal-to Ba-OHR almost-equal-to Ba-mu2-OR < Ba-mu3-OR. The Ti-O distances vary from 1.861(7) to 2.067(6) angstrom according to Ti-mu2-OR < Ti-OR < Ti-O(thd). The solvate is stabilized by H-bonding.
Abstract: The X-ray single-crystal studies of [MTi-2(OR)(9)(2)] (M = Ca, Ba; R = Et) obtained from-EtOH solutions in 1:4 metal-titanium ratios show that these complexes, both in the-solid state and in solution, are composed of symmetric molecules, in which the central eight-coordinated metal atom is bound to two face-sharing bioctahedral [Ti-2(OR)(9)] groups.
Abstract: The reaction of lanthanum isopropoxide with 2 equivalents of triethanolamine leads to a novel ‘diatrane’ complex H3La[(OC2H4)3N]2; its reaction with Nb(OPri)5 provides a soluble and volatile mixed-metal species [La(OC2H4)3N2Nb(OPri)43] whose molecular structure is based on a central ‘diatrane’ core with eight-coordinate lanthanum while all niobium centres are six-coordinate.
Abstract: The hexanuclear complex of calcium oxo ethoxide ethanol solvate, [Ca6O2(OEt)8].14EtOH 1 has been isolated after the prolonged refluxing of an ethanol solution of calcium ethoxide in the presence of the oxygen in air and studied by X-ray diffraction; the metal-oxygen framework is built of two [Ca4O4] cubes sharing a common [Ca2O2] face, which involves both oxo groups.
Abstract: MoO(OMe)4 has been prepared by anodic oxidation of molybdenum metal in anhydrous methanol containing LiCl as an electrolyte. The X-ray single crystal study showed the complex to consist of pseudo-centrosymmetric dimeric molecules, [MoO(OMe)3(mu-OMe)]2. The general effect of the M(mu-OR)2M ring upon the arrangement of bonds with increased multiplicity is discussed in this and related molecules.
Abstract: An X-ray structural study of the crystals isolated from the solutions obtained by the reaction of Ba metal with Ti(OPr(i))4 in isopropyl alcohol has been carried out; the crystals of the compound, which is a precursor for the synthesis of BaTiO3, contain molecules of two different kinds [Ba4Ti4O4(OR)16(ROH)4] and [Ba4Ti4O4(OR)16(ROH)3], where R = Pr(i).
Abstract: Conductometric titration curves of MO(OR)4 and MO2(OR)2 (M = Mo, W; R = Et, (i)Pr, C2H4OMe) by sodium (or lithium) alkoxides have ultimately proved the existence of the (1:1) bimetallic complexes in alcohol solutions. Upon evaporation of the solvents from the solutions, decomposition of the complexes occurs, accompanied by the elimination of ether, resulting in the precipitation of Na2MoO4; the molybdenum derivatives decompose more readily than the corresponding tungsten species. Under special conditions the crystals of [NaWO(OEt)5(EtOH)2]2 (I) and [NaMo2O4(OR)5(ROH)]2 [R = (i)Pr (VI), Et (VIII)] complexes have been isolated. [NaMoO2(OC2H4OMe)3]2 (XI) proved to be the only stable complex. Solubility isotherms in the systems WO(OEt)4-M(OEt)n-EtOH and MoO2(OC2H4OMe)2-M(OC2H4OMe)n-MeOC2H4OH (M = Na, Bi) were measured which allowed us to establish the regions of stability of the complexes. The nature of the M-O bonding in the synthesized bimetallic complexes is discussed on the basis of their crystal structures and IR spectra.
