Showing papers on "Polyoxometalate published in 1997"

A ruthenium-substituted polyoxometalate as an inorganic dioxygenase for activation of molecular oxygen

Abstract: The development of a procedure for the epoxidation of alkenes with molecular oxygen is an important industrial and synthetic goal. Non-radical activation of dioxygen by monooxygenase enzymes such as the iron-porphyrin-based cytochrome P-450 involves the insertion of one oxygen atom of O2 into the organic substrate while the other oxygen is reduced to water in the presence of an electron donor. Dioxygenase enzymes, on the other hand, catalyse insertion of both oxygen atoms without reducing agents. Oxidation of hydrocarbons with dioxygen catalysed by transition-metal compounds invariably proceeds by free-radical pathways rather than by dioxygenase-type reactions, and so do not allow the epoxidation of alkenes with molecular oxygen. The sterically hindered ruthenium tetramesityl porphyrin complex has been shown previously to activate dioxygen in a dioxygenase mode1. We describe here the use of the polyoxometalate {[WZnRu2(OH)(H2O)](ZnW9O34)2}11−(ref. 2) as a catalyst for non-radical molecular oxygen activation and alkene epoxidation. The polyoxometalate can be considered to act as an inorganic dioxygenase catalyst. The advantages of using inorganic catalysts such as polyoxometalates, as opposed to organometallic complexes, is their well documented stability against decomposition by self-oxidation3,4.

Synthesis of Ordered Aluminophosphate and Galloaluminophosphate Mesoporous Materials with Anion-Exchange Properties Utilizing Polyoxometalate Cluster/Surfactant Salts as Precursors

Abstract: Ordered nonlamellar mesoporous aluminophosphates and galloaluminophosphates have been synthesized by introducing phosphate linking groups to cluster/surfactants salts of prearranged AlO4Al12(OH)24(H2O)127+ (Al13) and GaO4Al12(OH)24(H2O)127+ (GaAl12) tridecamers. The Al13 and GaAl12 polyoxocations form a layered mesoscopic salt with the anionic surfactant sodium dodecylsulfate. Upon the reaction with a buffered hydrogen phosphate/dihydrogen phosphate solution the layers of clusters are transformed into a nonlayered, nearly hexagonal mesoscopic phase. Removal of the surfactant from the alumino- and galloaluminophosphates by anion-exchange results in mesoporous materials with BET surface areas up to 630 and 455 m2/g, respectively. FT-IR and 27Al and 31P MAS−NMR as well as 27Al → 31P cross-polarization experiments indicate that the phosphate treatment results in the formation of new bonds between aluminate and phosphate species. A fraction of the clusters are transformed leading to an increase in the number o...

Effects of pH and Mg:Ga Ratio on the Synthesis of Gallium-Containing Layered Double Hydroxides and Their Polyoxometalate Anion Exchanged Products

Abstract: We have synthesized a series of [Mg2+(1-x)M3+x(OH)2][TA2-(x/2)]·zH2O (M3+= Ga3+ or Al3+ and TA = C6H4(COO-)2) from mixed-metal chloride solutions with initial M3+ mole fractions of 0.20, 0.25, and 0.33, at constant pH values of 6.8, 7.7, 8.6, and 10.0. Terephthalate-containing products were obtained only under conditions that resulted in a Mg:M3+ ratio of 2:1 in the mixed metal hydroxide layers, indicating that a high layer charge density is necessary to incorporate terephthalate anions between the inorganic layers. Anion-exchange reactions were subsequently performed to produce LDHs intercalated with PW11O397- and H2W12O406- anions, yielding products that displayed sharp powder diffraction patterns. In each case, the surface area of the POM-intercalated product was found to be approximately 40−45 m2/g, indicating that the micropore system is totally blocked and that the materials are virtually nonporous; this may result from the high layer charge density of the LDH−terephthalate precursors.

New polyoxometalate promoted method of oxygen delignification

Abstract: The present paper examines the preliminary results of oxygen delignification of wood (pulping) and sulfate pulp (bleaching) in organic solvent - water media, in the presence of heptamolybdopentovanadophosphate anion [PMo 7 V 5 O 40 ] 8- .

[H2⊂(Mov2O4)6O4(μ2-OH)12(MoVIO3)4]6- and [Na⊂{(MoV2O4)3(μ2-OH)3H(PhP03)4}2]7-: A Further Example for the Validity of the Concept of Unit Construction in Polyoxometalate Chemistry

Abstract: Abstract The compound Na7[Na⊂{(MoV2O4)3(μ2-OH)3H(PhPO3)4}2] · 2N2H4 · 26 H2O (formulation with respect to the aggregate in the crystal) has been synthesized and characterized by single-crystal X-ray structure analysis (which alone does not allow the determination of the formula), UV/Vis/NIR/IR, 31P{1H}, 1H and 23Na NMR spectroscopy as well as magnetic susceptibility measurements. The compound is formed under similar conditions as (NH2Me2)6[H2⊂(MoV2O4)6O4(μ2-C)H)12(MoVIO3)4].Correspondingly, both cluster frame works are built up by the same {(MoV2O4)3(μ2-OH)3}3+ units.

Intercalation of Peroxomolybdate (VI) Anion into Layered Double Hydroxide and Its Reversible Transformation to Oxomolybdate (VI) Anion

Abstract: Peroxomolybdate (VI) anion with tartrate as a ligand ([Mo2O2(O2)4(C4H2O6)]4-, PMA) was intercalated into layers of Mg-Al type layered double hydroxide (LDH) by anion exchange reaction with terephthalate anion previously intercalated in the layers. The intercalation compounds were characterized by FT-IR, UV, X-ray diffraction and thermal analysis equipped with a mass spectroscope. Both in aqueous solution and in the LDH layers suspended in water, the peroxo groups (-O-O-) in PMA were released at 80°C to yield oxomolybdate(s) having a tartrate ligand, and the oxomolybdate(s) reverted to PMA by addition of hydrogen peroxide.

Hybrid Molecular Materials Formed by Magnetic and Conducting Networks Based on Inorganic Metal Complexes and Organic Donors

Abstract: The synthesis and physical characterization of new hybrid molecular materials formed by magnetic and organic networks are reported. The conducting molecular networks have been prepared from TTF and BEDT-TTF type donors. The inorganic magnetic component is formed by anion metal complexes of different nuclearities and dimensionalities (simple metal halides, polyoxometalate clusters and bimetallic oxalates).

Oxidative delignification of wood pulp or fibers using transition metal-substituted polyoxometalates

Abstract: A method for delignifying wood pulp and fiber is disclosed. The method comprises the steps of obtaining a wood pulp and exposing the wood pulp to a polyoxometalate of the formula V1 Mom Wn Nbo Tap (TM )q Xr Os !x- where l is 0-18, m is 0-40, n is 0-40, o is 0-10, p is 0-10, q is 0-9, r is 0-6, TM is a d-electron-containing transition metal ion, and X is a heteroatom, which is a p or d block element, where l+m+n+o+p≧4, l+m+q>0 and s is sufficiently large that x>0. The exposure is under conditions wherein the polyoxometalate is reduced. In a preferable form of the invention, the method additionally comprises the step of reoxidizing the polyoxometalate.