Showing papers on "Polyoxometalate published in 2000"
172 citations
TL;DR: The previously unknown titanium(IV)-containing mu-hydroxo dimeric heteropolytungstate (Bu4N)7[(PTiW11O39)2-OH] (TBA salt of H1) has been synthesized and shows higher catalytic activity than 2 for thioether oxidation by hydrogen peroxide in acetonitrile.
Abstract: The previously unknown titanium(IV)-containing μ-hydroxo dimeric heteropolytungstate (Bu4N)7[(PTiW11O39)2OH] (TBA salt of H1) has been synthesized, starting from H5PTiW11O40, and characterized by elemental analysis, multinuclear (31P, 17O, 183W) NMR, IR, FAB-MS, cyclic voltammetry, and potentiometric titration. 31P NMR reveals that H1 (δ −12.76) readily forms in MeCN from the Keggin monomer (POM), PTiW11O405- (2, δ −13.34), upon the addition of 1.5 equiv of H+, via the protonated species, P(TiOH)W11O394- (H2, δ −13.44). The ratio of H1, 2, and H2, which are present in equilibrium in MeCN solution at 25 °C, depends on the concentration of both H+ and H2O. The Ti−O−Ti linkage readily reacts with nucleophilic reagents, such as H2O and ROH, to yield monomeric Keggin derivatives. μ-Hydroxo dimer H1 shows higher catalytic activity than 2 for thioether oxidation by hydrogen peroxide in acetonitrile. The reaction proceeds readily at room temperature and affords the corresponding sulfoxide and sulfone in ca. quant...
138 citations
123 citations
TL;DR: In this article, a charge transfer (CT) salt was prepared from planar arene donors and planar polyoxometalates by attaching a cationic anchor onto the arene which then clings to the POM anion by Coulombic forces.
Abstract: Spherical polyoxometalates (POMs) such as M6O192- and SiM12O404- (with M = Mo or W) and planar arene donors (anthracenes and pyrenes) can be cocrystallized (despite their structural incompatibility) by attaching a cationic “anchor” onto the arene which then clings to the POM anion by Coulombic forces. As a result, novel charge-transfer (CT) salts are prepared from arene donors and Lindqvist-type [M6O19]2- and Keggin-type [SiM12O40]4- acceptors with overall 2:1 and 4:1 stoichiometry, respectively. The CT character of the dark-colored (yellow to red) crystalline materials is confirmed by the linear Mulliken correlation between the CT transition energies and the reduction potentials of the POM acceptors, as well as by the transient (diffuse reflectance) absorption spectra (upon picosecond laser excitation) of anthracene or pyrene cation radicals (in monomeric and π-dimeric forms). X-ray crystallographic studies reveal a unique “dimeric” arrangement of the cofacially oriented arene couples which show contact ...
116 citations
TL;DR: The p-styrenyl substituent borne by the organoimido-ligand in the Lindqvist derivative as discussed by the authors allows the polyoxometalate complex to be introduced as a pendant group in polystyrene compositions via conventional free radical-induced copolymerization.
114 citations
105 citations
TL;DR: In this paper, the incorporation of supra-molecular molybdenum polyoxometalates into sol-gel-derived silica is presented, which enables X-ray scattering experiments to provide information about the structure as well as the POM cluster distribution in the hybrid material.
Abstract: Polyoxometalates (POMs) of transition metals (e.g., molyb-denum, vanadium) have been a center of research interest for several decades, as they exhibit a great variety of structures and a rich diversity of fascinating properties. [1] The structures range from relatively simple, like the Keggin ion, [2] to extremely complex, such as the wheel-shaped [3±5] and ball-shaped molybdate clusters [6] prepared by Müller et al., of which the latter possess 154, 176, 248, or 132 metal centers per cluster. Their architectures are not only well-defined, relatively easy to produce, and beautiful, but these compounds also exhibit the electronic, electrochemical, magnetic, and optical qualities typical of mixed-valence molybdenum oxide compounds , which creates potential for many applications. In most cases, pure POMs are quite difficult to handle from a materials science point of view. For example, the problem of too high a solubility in water is encountered, together with low pH and redox stability. In addition, the cluster cavities of most POMs are filled with water of crystallization, which cannot be removed without destroying the structures. [9,10] There is also the inherent problem of lacking access to all inner sites of the clusters, which is necessary for application of these compounds, for example in catalysis. There are only a few examples of POMs which possess a permeable structure representing a pore system providing accessibility to the inner surface comparable to those of porous silica. [9±16] The reason for this is simply the fact that POMs are crystalline, and a sol-gel process similar to the synthesis of silica [17,18] is not yet known for the fabrication of molybdenum trioxide. The introduction of POMs into a sol-gel-derived silica matrix [7,19] or their immobilization in pre-formed porous materials [20,21] was used to solve these problems. In this publication we present the incorporation of supra-molecular molybdenum polyoxometalates into sol-gel-derived silica. Two types of molybdenum polyoxometalates were synthesized according to the preparation method published by Mül-ler et al. [4] The sol-gel process to produce the POM±sil-ica hybrid material produces amorphous, optically clear objects (monoliths) in variable size and form (see also Fig. 6a). Due to the presence of the polyoxometalate these monoliths are deeply colored. The higher electron density of POMs, compared with that of the silica matrix, enables X-ray scattering experiments to provide information about the structure as well as the POM cluster distribution in the hybrid material. The small-angle X-ray scattering (SAXS) diffraction pattern of the …
96 citations
TL;DR: In this article, the polyoxometalate P2Mo18O626− was used for the electroreduction of H2O2 by the polyoxide polygonalates.
85 citations
77 citations
TL;DR: In this paper, a new heterogeneous catalyst prepared by immobilisation of polyoxometalates on chemically modified hydrophobic mesoporous silica gel has been successfully applied to the selective epoxidation of olefins with 15% aqueous H2O2 without the use of organic solvent.
61 citations
TL;DR: In this paper, the role of hydroxyl radical in the polyoxometalate-mediated photocatalytic oxidation of aqueous chlorinated organic compounds was investigated using kinetic probes.
Abstract: The present study reports the development of kinetic probes to determine the possible role of hydroxyl radicalsin the polyoxometalate-mediated photocatalytic oxidation of aqueous chlorinated organic compounds.Photocatalytic oxidation of the model chloroaromatic 1,2-dichlorobenzene (DCB) was carried out in oxygenated,illuminated solutions of three contrasting polyoxometalates (POMs), H
TL;DR: In this paper, the polyoxometalate H5PV2Mo10O40 (1) is deposited on cotton cloth, polyacrylic fiber, nylon fiber, carbon powder (Ambersorb 572), and the Japanese “self-deodorizing” fabric Smoklin by immersion of these materials in aqueous solutions of 1 followed by evaporation of the water.
TL;DR: In this paper, a polyoxometalate-based organic/inorganic film, composed of cetyl pyridinum 11-molybdovanadoarsenate (CPMVA) molecules, has been studied.
Abstract: The preparation, structure, and electrochemical and electrocatalytical properties of a new polyoxometalate-based organic/inorganic film, composed of cetyl pyridinum 11-molybdovanadoarsenate (CPMVA) molecules, have been studied. Cyclic potential scanning in acetone solution led to a stable CPMVA film formed on a highly oriented pyrolytic graphite (HOPG) surface. X-ray photoelectron spectroscopy, scanning tunneling microscopy, and cyclic voltammetry were used for characterizing the structure and properties of the CPMVA film. These studies indicated that self-aggregated clusters were formed on a freshly cleaved HOPG surface, while a self-organized monolayer was formed on the precathodized HOPG electrode. The CPMVA film exhibited reversible redox kinetics both in acidic aqueous and in acetone solution, which showed that it could be used as a catalyst even in organic phase. The CPMVA film remained stable even at pH >7.0, and the pH dependence of the film was much smaller than that of its inorganic film (H4AsMo...
TL;DR: The novel, dimeric polyoxometalate has been characterized by 31P NMR spectroscopy and single-crystal X-ray diffraction and can be viewed as a fused dimer of two lacunary moieties leading to a cigar-shaped structure with four belts and two caps.
Abstract: The novel, dimeric polyoxometalate [{(P2O7)Mo15O45}2]8- has been characterized by 31P NMR spectroscopy and single-crystal X-ray diffraction. The 30-molybdobispyrophosphate contains two eclipsed diphosphate ions with linear P−O−P bonds (180.0(10)°). The polyanion can be viewed as a fused dimer of two lacunary [(P2O7)Mo15O48] moieties leading to a cigar-shaped structure with four belts and two caps.
TL;DR: The hexamolybdopyrophosphate [(O3POPO3)Mo6O18(H2O)4]4- (1) has been characterized by 31P NMR, IR, elemental analysis, and single-crystal X-ray diffraction.
Abstract: The hexamolybdopyrophosphate [(O3POPO3)Mo6O18(H2O)4]4- (1) has been characterized by 31P NMR, IR, elemental analysis, and single-crystal X-ray diffraction. This polyoxoanion consists of a six-membe...
TL;DR: A novel amino acid salt of 18-Molybdodiphosphate formulated (Lys)2H6[P2Mo18O62]·16H2O was synthesized and its structure characterized.
TL;DR: In this article, the authors showed that the redox environment of silver can be controlled with high definition by the heteropolyanion monolayer matrix, and they showed that a small amount of cesium (Ag:Cs=9:1) in the silver phosphomolybdate salt did not appreciably alter the packing in the ordered AgCs(9: 1)3PMo12O40 monolayers, but did produce a measurable shift of the NDR values to −0.68
TL;DR: In this paper, the voltammetric behavior obtained on addition of Li+ can be simulated according to a reaction scheme involving an extensive series of reversible potentials and equilibrium constants.
TL;DR: The Group 14 derivatized polyoxometalate series [LNbOEMe3]3− (L=α-{PW11O39}7−; E=Si, Ge, Sn, Pb) can be prepared from the n-Bu4N+ salt of the niobium substituted Keggin ion [L NbO]4− and Me3EOTf (OTf=O3SCF3) (53-76% yield) as discussed by the authors.
TL;DR: In this article, the electrochemical properties of these compounds were characterized by elemental analysis, IR, UV/Vis and 31P NMR spectroscopy, and it was shown that only the iron(III) and the copper(II) ions within the complexes are reducible in the same potential domain as the molybdenum(VI) moieties.
Abstract: The complexes formed by [(1)-2,3-P2Mo2W15O61]10– with vanadium(IV), manganese(II), cobalt(II), nickel(II), copper(II), and zinc(II) were synthesized. They were characterized by elemental analysis, IR, UV/Vis and 31P NMR spectroscopy. Their electrochemical studies are complemented by those of the previously synthesized iron(III)- and Mo(VI)-substituted complexes. Among the main conclusions from the electrochemistry of all these compounds, it can be pointed out that only the iron(III) and the copper(II) ions within the complexes are reducible in the same potential domain as the molybdenum(VI) moieties. In the case of the iron(III) complex, it has been possible to obtain a reversible overall three-electron process on the first wave of the oxometalate by varying the pH of the solution. In contrast, copper can be deposited from the corresponding complex. Substitution of [(1)-2,3-P2Mo2W15O61]10– with vanadium(IV), manganese(II), iron(III), cobalt(II), nickel(II), copper(II), zinc(II) and molybdenum(VI) gives a series of complexes in which the trimetallic moiety constituting one of the ‘‘caps’’ of the polyoxometalate contains cations different from the remaining tungsten skeleton. The electrochemical properties of these complexes are modulated by this particular constitution.
TL;DR: In this article, direct halogenations of polyoxometalates [NaPW11O39]6− and [PW9O34]9− led to a molecular metal oxide with a fully brominated face (see picture).
Abstract: Direct halogenations of polyoxometalates [NaPW11O39]6− and [PW9O34]9− led to [PW9O28Br6]3−, a molecular metal oxide with a fully brominated face (see picture). This methodology creates new opportunities for systematic chemistry at polyoxometalate surfaces.
TL;DR: In this paper, the reduction of colloidal solutions of polyhydroxo complexes of Pd(II) in the presence of Mo(VI, W(VI), V(V), and Nb(V) polyoxo anions is described.
Abstract: Sols containing Pd(0) clusters with polyoxo anions are prepared by the reduction of colloidal solutions of polyhydroxo complexes of Pd(II) in the presence of Mo(VI), W(VI), V(V), and Nb(V) polyoxo anions. The cluster sizes varied within the limits of 1–10 nm depending on the nature of the polyoxo anion. The stability of sols toward coagulation depends on the ratio between the palladium and polyoxo anion amounts in solution and on the composition of the solvent. Supported Pd catalysts are obtained by the adsorption of particles from sols; Pd can exist in these catalysts as individual particles or associates or form filamentary structures.
TL;DR: Oxidation of a variety of compounds, including methionine (Met), using a complex formed between dirhodium(II) acetate and the lacunary form of phosphotungstic acid as the catalyst is effective over a wide range of conditions, including pH 2-10.
TL;DR: In this paper, a polyoxometalate anions with unusual chemical composition and structural features could be prepared by carefully tuning the synthetic procedures by using anions of dihydroxy-p-benzoquinones, benzene carboxylic acids, methylene diphosphonic acid, and phosphono-carboxyl acid as ligands.
Abstract: New polyoxometalate anions with unusual chemical composition and structural features could be prepared by carefully tuning the synthetic procedures. Polyoxometalate anions containing a high amount of Te or Se or residues of acetic acid, fumaric acid, succinic acid, diglycolic acid or thio-diacetic acid as ligands have been characterized by X-ray structure analysis. Coordination polymers with one-dimension ally, two-dimensionally and three-dimensionally infinite structural characteristics could be prepared employing anions of dihydroxy-p-benzoquinones, benzene carboxylic acids, methylene diphosphonic acid, and phosphono-carboxylic acids. Coordination polymers with chain-like or layer-like structure carrying negative excess charge as well as compounds with an open framework structure have been studied.
TL;DR: In this article, the authors discuss protonation, oligomerization, and condensation reactions of vanadate(V), molybdate(VI), and tungstate(VI).
Abstract: Publisher Summary This chapter discusses protonation, oligomerization, and condensation reactions of vanadate(V), molybdate(VI), and tungstate(VI). The elements vanadium, molybdenum, and tungsten in their high oxidation states form the stable oxyanions [VO4]3-, [MoO4]2-, and [WO4]2-. In aqueous solution, these ions are easily protonated and show a strong tendency to form polyoxoanions by oxygen bridging, and the release of water molecules. Depending on pH and concentration, a great variety of ions can form in each case, giving rise to complex systems of simultaneous equilibria, which have proved difficult to characterize with certainty. The molybdate(VI) system, in particular, needs further clarification regarding the existence of some polyions. More kinetic and thermodynamic data would also help to improve the understanding of these systems and lead to a general inclusive explanation of the mechanism of polyoxoanion formation. In this respect, new information about some structural preferences of the different metals in mixed polyoxoanions is a useful addition to known facts regarding polyoxometalate structures.
TL;DR: In this paper, the monolacunar structure of the Keggin polytungstate anion [GeW11O39]8− having the capacity of functioning as the coordinating ligand for the uranium U4+ cation, and the formation of the complex polyto-state anions of the [U(GeW 11O39)2]12− type was established.
Abstract: The starting point of this study is the monolacunar structure of the Keggin polytungstate anion [GeW11O39]8−having the capacity of functioning as the coordinating ligand for the uranium U4+ cation, and the formation of the complex polytungstate anions of the [U(GeW11O39)2]12− type. The pH range of the complex formation was established and the stability constants were calculated by the electrophoresis method. By applying the molar ratio method to spectrophotometry, the molar ratio of polyoxometalate ligands and U4+ cations have been found to have the values of 1:1 and 2:1, respectively.
Patent•
06 Jul 2000TL;DR: In this paper, a new polyoxometalate compound and polymers comprising recurring monomers of those compounds are provided, where the compounds are formed by replacing at least one oxide of the starting polyoxide with an organoimido (NR) group bonded to the polyoxometricalate via a triple bond to the nitrogen atom.
Abstract: New polyoxometalate compounds and polymers comprising recurring monomers of those compounds are provided. The compounds are formed by replacing at least one oxide of the starting polyoxometalate with an organoimido (NR) group bonded to the polyoxometalate via a triple bond to the nitrogen atom. The R of the (NR) group comprises a reactive functional group which renders the compound readily polymerizable, alone or with other monomers (e.g., divinylbenzene), to form the inventive polymers. Additionally, a countercation (e.g., bis(tetra-n-butylammonium)) can be mixed with the polyoxometalate compounds in order to neutralize the negative charge thereof as well as to make those compounds more soluble in organic solvents.
TL;DR: In this paper, a molecular molybdenum oxychloride anion [Mo 2 O 5 Cl 4 ] 2− as a tetra-n -butylammonium salt was shown to have a relatively long Mo-Mo distance.