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.

Polyoxometalate (W/Mo) compounds connected via lanthanide cations with a three-dimensional framework, H2{ [K (H2O )2 ]2 [Ln (H2O )5 ]2 (H2M12O42 )}·nH2O : Synthesis, structures, and magnetic properties

Abstract: A series of 10 novel polyoxometalate (W/Mo) compounds connected via a trivalent lanthanide cation bridge, H2{[K(H2O)2]2[Ln(H2O)5]2(H2M12O42)}·nH2O (Ln = La, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu; M = W or W/Mo) (1−10), were designed and synthesized on the basis of the abduction of Al3+ in aqueous solution. X-ray diffraction analyses reveal that the structures of complexes 1−10 are three-dimensional frameworks assembled from the arrangement of H2M12O4210- (named paradodecmetalate-B) and Ln(H2O)53+ with two planes, which are constructed via the unification of H2M12O4210- and Ln(H2O)53+, along the [100] and [001] directions. Magnetic measurements reveal the paramagnetic properties and a strong ferromagnetic coupling between the two nearest-neighboring lanthanide cations, Ln3+ (Ln = Dy, Er), within the circle for compounds 2 and 4−9.

Selective transition-metal catalysis of oxygen delignification using water-soluble salts of polyoxometalate (POM) anions. part II. Reactions of α-[SiVW11O40]5- with phenolic lignin-model compounds

Abstract: When heated under anaerobic conditions, aqueous solutions of the polyoxometalate anion α-(SiVW 11 O 40 ] 5- (POM ox , 1), supplied as the salt K 5 [SiVW 11 O 40 ].12H 2 O, selectively delignify unbleached mixed-pine kraft pulps. During delignification, 1 is reduced hy residual lignin to α-[SiVW 11 O 40 ] 6- (POM red 2) : α-[SiVW 11 O 40 ] 5- + 1e- → α-[SiVW 11 O 40 ]6-, E o = +0.69V 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 cyclohexadienyl radicals and subsequently to cyclohexadienyl cations. Hydrolysis of these cationic intermediates results in alkyl-side-chain cleavage, a likely route to polymer degradation.

Synthesis, catalytic activity in oxidation reactions, and recyclability of stable polyoxometalate-centred dendrimers

Abstract: Nine- and 27-armed dendrimers with a peroxophosphotungstate core were synthesized by an ionic-bonding approach and used as air-stable, recoverable catalysts for oxidation reactions using hydrogen peroxide.

pH-Dependent syntheses of copper–quinoxaline–polyoxotungatate hybrids: variable role of Keggin-type polyanion in different pH conditions

Abstract: Four new hybrids based on the Keggin-type polyoxometalate, formulated as (Hbm)3(PW12O40)·4H2O (1) (bm = benzimidazole, which is synthesized in situ by quinoxaline), [Cu6(qx)9(PW12O40)2] (2), [Cu3(qx)5(PW12O40)(H2O)] (3) and [Cu4(qx)4(HPCuIIW11O39)]·1.5H2O (4) (qx = quinoxaline), were hydrothermally synthesized and structurally characterized by routine techniques and single-crystal X-ray diffraction. In 1, the [PW12O40]3− (PW12) clusters only act as counteranions and combine with the protonated organic ligand by electrostatic interactions. In 2, a 63 topological 2D layer is formed with the PW12 as the template. In 3, the PW12 anions link with four metal–organic chains via Cu–O weak interactions to construct a 3D framework. In 4, the Cu(II)-substituted Keggin unit as a hexadentate inorganic ligand coordinates with four Cu(I) ions from metal–organic chains and two O atoms from neighboring POMs to form a sandwich-like 2D layer. The structure difference of compounds 1–4 reveals that the self-assembly process is pH-dependent and the Keggin-type POM plays different role in different pH conditions.

Nb2O5 and Ta2O5 Thin Films from Polyoxometalate Precursors: A Single Proton Makes a Difference

Abstract: Thin film materials from water-based precursors follow the principals of green chemistry, leading to a more sustainable future in the energy intensive era in which we currently reside. While simple in practice, aqueous metal-oxide chemistry is complex at the molecular level. Here we develop the first water-based formation of Nb2O5 and Ta2O5 thin films; utilizing tetramethylammonium salts of [H2Ta6O19]6– and [H3Nb6O19]5– polyoxometalates. Although the clusters are structurally identical group V analogues and differ only by a single proton, this difference has a considerable influence on the quality of the films that are obtained. Through characterization of the solid-state precursor (single-crystal X-ray diffraction), the aqueous precursor solution (X-ray scattering), and the thin films (atomic force and scanning electron microscopies, X-ray diffraction, and reflectivity), we rationalize the important roles of cluster protonation that carry through all chemical processes from the precursor to the metal oxi...