Polyoxometalate

About: Polyoxometalate is a research topic. Over the lifetime, 3493 publications have been published within this topic receiving 94123 citations. The topic is also known as: POM.

A Crown-Shaped Ru-Substituted Arsenotungstate for Selective Oxidation of Sulfides with Hydrogen Peroxide

Abstract: An acetate-bridged Ru-substituted arsenotungstate [H2 N(CH3 )2 ]14 [As4 W40 O140 {Ru2 (CH3 COO)}2 ]⋅22 H2 O (1) has been synthesized and structurally characterized. Four Ru atoms occupy the respective lacunary S2 sites of the crown-shaped polyanion [As4 W40 O140 ]28- , and each Ru atom is coordinated by one As atom and five μ2 -O atoms, comprising four from the S2 site and one from the acetate ligand. To the best of our knowledge, this coordination of the Ru atom, with an Ru-As bond length of 2.377(3)-2.387(3) A, is unprecedented in polyoxometalate (POM) chemistry. Notably, 1 exhibits high efficiency, excellent selectivity, and good recyclability for the oxidation of sulfides with hydrogen peroxide (H2 O2 ). Catalytic oxidation of various sulfides in the presence of 1 gives superior conversion and selectivity for sulfones in acetonitrile, whereas sulfoxides are obtained in methanol.

Ternary Porphyrinato Hf(IV) and Zr(IV) - Polyoxometalate Complexes.

Abstract: We report a facile, high-yield synthesis and characterization of discrete, ternary porphyrin–metal–polyoxometalate (por–M–POM) complexes where a group IV transition-metal ion is bound both to the porphyrin core and to the lacunary site of a Keggin POM, PW11O39–7. The remarkably robust complexes exploit the fact that HfIV and ZrIV are 7–8 coordinate and reside outside the plane of the porphyrin macrocycle, thus enabling the simultaneous coordination to meso-tetraphenylporphyrin (tpp) or meso-tetra(4-pyridyl)porphyrin (tpyp) and to the defect site in the Keggin framework. The physical properties of the (tpp)Hf(PW11O39)[tba]5, (tpyp)Hf(PW11O39)[tba]5, and (tpp)Zr(PW11O39)[tba]5 complexes are similar because the metal ions have similar oxidation states and coordination chemistry. This architecture couples the photonic properties of the porphyrin to the POM because the metal ion is incorporated into both frameworks. Thus, the ternary complexes can serve as a basis for the characterization of HfIV and ZrIV porphyrins bound to oxide surfaces through the group IV metal ions. The Hf(por) and Zr(por) bind strongly to TiO2 nanoparticles and indium tin oxide (ITO) surfaces, but significantly less binds to crystalline SiO2 or TiO2 surfaces. Together, the strong binding of the metalloporphyrins to the POM, nanoparticles, and the ITO surfaces, and paucity of binding to crystalline surfaces, suggests that the three-to-four open coordination sites on the Hf(por) and Zr(por) are predominantly bound at surface defect sites. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Selective Transition-Metal Catalysis of Oxygen Delignification Using Water-Soluble Salts of Polyoxometalate (POM) Anions.

Abstract: (POMred, 2) : α-[SiVW11 O40] 5+ 1e—> α-[SiVW 11 O40] 6-. E0= + 0.69 V vs. NHE, Model studies suggest that phenolic (hydroxylated phenyl) groups present in residual lignin are substrates for the reduction of 1. Reactions of 1 with phenolic arylglycerol β-aryl ethers and other phenolic lignin models suggest that anaerobic POM degradation of residual lignin may occur via sequential single-electron oxidation reactions of phenolic substructures, first to cyclohexodienyl radicals and subsequently to cyclohexadienyl cations. Hydrolysis of these cationic intermediates results in alkyl-side-chain cleavage, a likely route to polymer degradation.

Large Cation−Anion Materials Based on Trinuclear Ruthenium(III) Salts of Keggin and Wells-Dawson Anions Having Water-Filled Channels

Abstract: Reaction of the trinuclear ruthenium(III) cation [Ru3O(OOCCH3)6(CH3OH)3]+ with the Keggin-type [α-GeW11O39]8−, [α-SiW11O39]8−, and [α-SiMo12O40]4− and the Wells−Dawson-type [α-P2W18O62]6− polyanions in an aqueous, acidic medium resulted in plenary polyoxometalate-based materials K2Na[Ru3O(OOCCH3)6(H2O)3][α-GeW12O40]·10H2O (1), K3[Ru3O(OOCCH3)6(H2O)3][α-SiW12O40]·18H2O (2), K3[Ru3O(OOCCH3)6(H2O)3][α-SiMo12O40]·7H2O (3), and K2Na[Ru3O(OOCCH3)6(H2O)3]3[α-P2W18O62]·26H2O (4), respectively. All four materials, 1−4, crystallize as sodium and/or potassium salts in the monoclinic space group P21/n. Compounds 1−4 were characterized by IR, thermogravimetric analysis, and single-crystal/powder X-ray diffraction (XRD). The isolated solid-state frameworks, composed of cocrystallized trinuclear ruthenium cations and polyanions, exhibit nanosized voids filled with crystal waters. These water molecules can be removed reversibly upon heating under a vacuum, and powder XRD measurements demonstrated that the crystallinity o...