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.

Amine-modified silica NH2–(CH2)x–SiO2 (x = 0, 2, 3) as support for cobalt-substituted polyoxometalate TBA4HPW11CoO39: Effect of the nature of the support on the oxidation activity

Abstract: Acidic tetra-n-butylammonium (TBA) salts of Keggin type transition-metal-monosubstituted polyoxometalate TBA 4 HPW 11 CoO 39 (Co-POM) have been chemically anchored to the amino-modified silica (NH 2 –(CH 2 ) x –SiO 2 , x = 0, 2, 3) containing 40–710 μmol NH 2 -groups per 1 g of support. The interaction of Co-POM with NH 2 –(CH 2 ) x –SiO 2 was studied by DR-UV–vis spectroscopy. Spectroscopic data revealed that the type of interaction between Co-POM and support depends on the amount of anchored functional NH 2 -groups. It was found that Co-POM was attached to NH 2 –(CH 2 ) x –SiO 2 support both by the electrostatic NH 3 + ⋯Co-POM − and dative (Si–OH⋯Co-POM) bonding. Both the amount of anchored NH 2 -groups and the distance between NH 2 -group and surface of silica affect the nature of the interaction between Co-POM and surface functional groups. The increase of the amount of anchored NH 2 –(CH 2 ) 3 -groups leads to decrease in the contribution of dative bonding Si–OH⋯Co-POM and an increase in the contribution of electrostatic bonding NH 3 + ⋯Co-POM − . The activity of the immobilized Co-POM was tested in benzyl alcohol oxidation with oxygen in CH 3 CN medium. It was found that catalytic activity and stability of Co-POM depend on the nature of interaction between Co-POM and surface groups of support that is adjustable both by the amount of anchored functional NH 2 -groups on silica support and the distance between NH 2 -group and surface of silica.

Two three-dimensional porous frameworks built from metal-organic coordination polymer sheets pillared by polyoxometalate clusters

Abstract: Two new porous frameworks [Ni(bix)2][VW12O40]·(H2bix)·H2O (1) and [Co(bix)2][VW12O40]·(H2bix)·2H2O (2) (bix = 1,4-bis(imidazol-1-ylmethyl)-benzene) composed of Keggin polyoxometalates (POMs) and metal–organic coordination polymer sheets have been successfully obtained, and characterized by elemental analysis, IR spectra, thermal gravimetric analysis, and single crystal X-ray diffraction. Structural analysis reveals that the 2D metal–organic coordination polymer sheets in the two compounds are constructed from the transition-metal (TM) cations and the flexible N-donor ligand bix, which are further pillared by POM clusters into the 3D porous frameworks. Powder X-ray diffraction (PXRD) patterns of 1 indicate the structural integrity of the framework in aqueous solution with a wide pH range of 1 to 11, and in common organic solvents (methanol, ethanol and DMF). Photocatalytic studies indicate that compounds 1 and 2 are not only active photocatalysts for degradation of rhodamine B (RB), but very stable and easily separated from the photocatalytic system for reuse as well.

Synthesis and characterisation of mesoporous hybrid silica-polyoxometalate aerogels for photocatalytic degradation of rhodamine B and methylene blue

Abstract: Mesoporous silica aerogel/polyoxometalate hybrids were successfully synthesised under mild conditions, and were investigated towards photocatalytic degradation of Rhodamine B and Methylene ...

A first principles study of water oxidation catalyzed by a tetraruthenium-oxo core embedded in polyoxometalate ligands.

Abstract: We present a computational study addressing the catalytic cycle of a recently-synthesized all-inorganic homogeneous catalyst capable to promote water oxidation with low overpotential and high turnover frequency [Sartorel et al., J. Am. Chem. Soc., 2008, 130, 5006; Geletii et al., Angew. Chem., Int. Ed., 2008, 47, 3896]. This catalyst consists of a tetraruthenium-oxo core [Ru4O4(OH)2·(H2O)4]6+capped by two polyoxometalate [SiW10O36]8− units. The reaction mechanism underpinning its efficiency is currently under debate. We study a reaction cycle involving four consecutive proton-coupled electron transfer (PCET) processes that successively oxidize the four RuIV–H2O units of the initial state (S0) to the four RuV-OH centers of the activated intermediate (S4). The energetics of these electrochemical processes as well as the structural and electronic properties of the reaction intermediates are studied with ab initio Density Functional Theory (DFT) calculations. After characterizing these reaction intermediates in the gas phase, we show that the solvated tetraruthenate core undergoes a solvent-induced structural distortion that brings the predicted molecular geometry to excellent agreement with the experimental X-ray diffraction data. The calculated electronic properties of the catalyst are instead weakly dependent on the presence of the solvent. The frontier orbitals of the initial state as well as the electronic states involved in the PCET steps are shown to be localized on the tetraruthenium-oxo core. The reaction thermodynamics predicted for the intermediate reaction steps is in good agreement with the available cyclic voltammetry measurements up to S3, but the calculated free energy difference between the initial and the activated state (S0/S4) turns out to be significantly lower than the thermodynamic limit for water oxidation. Since the oxidizing power of the S0/S4 couple is not sufficient to split water, we suggest that promoting this reaction would require cycling between higher oxidation states.