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.

Preferential catalytic hydrogenation of aromatic compounds versus ketones with a palladium substituted polyoxometalate as pre-catalyst

Abstract: A palladium-substituted polyoxometalate having a Keggin structure, supported on γ-alumina or active carbon, was used as a catalyst precursor for catalytic hydrogenation. The catalyst system enabled fast hydrogenation of arenes at 30 bar H2 and 230 °C. Most interesting was the finding that arenes could be selectively reduced in the presence of distal ketone groups under similar conditions, 30 bar H2 and 200 °C. For example, 1-phenyl-2-propanone yielded 1-cyclohexyl-2-propanone with no reduction of the ketone moiety. Additionally, aromatic compounds with vicinal (conjugated) ketone moieties underwent complete hydrogenation to saturated hydrocarbons and catalytic McMurry coupling was observed for aliphatic aldehydes.

Design and analysis of chain and network structures from organic derivatives of polyoxometalate clusters.

Abstract: Polyoxometalate (POM) clusters derivatized with aniline groups exhibit distinct interactions with counterions and with each other. These interactions lead to the assembly of the clusters into chains and networks upon crystallization. Two cluster types were examined, [W(6)O(25)H(AsC(6)H(4)-4-NH(2))(2)](5-) and [Mo(12)O(46)(AsC(6)H(4)-4-NH(2))(4)](4-). The X-ray crystal structures were solved for the mixed salts containing [C(NH(2))(3)](+)/Na(+), Ag(+)/H(+), or Cu(2+)/H(+) as counterions. The X-ray crystal structures reveal that the POM clusters are linked together by hydrogen bonds or POM-metal ion-POM linkages. The roles of the counterions, solvents, and organic groups in the formation of specific crystalline architectures are discussed. Strongly interacting counterions form bonds to the oxo ligands of the POM and connect them into tetrameric units and/or into one-dimensional chains. The hydrogen bonding strength of the solvent influences the formation of hydrogen bonds between the aniline groups and oxo ligands of the cluster. The aniline groups played differing roles in the final structures: they were either nonbonding, bonded to a counterion, or involved in hydrogen bonding. Depending on the bonding interactions, the architecture of the cluster salts may be significantly altered.

New approach to the synthesis of an organopolymolybdate polymer in aqueous media by linkage of multicarboxylic ligands.

Abstract: The reaction of molybdates with multicarboxylic ligands resulted in the crystalline materials of [Na8(MoVI10O32EDTA)(H2O)35]n (1) and (NH4)8n[MoVI10O32PDTA]n(H2O)30n (2) (EDTA = 1,2-diaminoethanetetraacetate; PDTA = 1,3-diaminopropanetetraacetate). In the two compounds, decamolybdate clusters are covalently linked by multicarboxylic ligands to form unusual meso-helical chains. For the first time, the synthesis of an organopolyoxometalate polymer is realized in aqueous media, which opens a green chemical approach to the fabrication of polyoxometalate-based polymers. The photochromic properties of 1 in the poly(vinyl alcohol) film displayed reddish-brown coloration upon UV irradiation, providing a new coloration material for photochromic films.

Polyoxometalate‐Based Bottom‐Up Fabrication of Graphene Quantum Dot/Manganese Vanadate Composites as Lithium Ion Battery Anodes

Abstract: Lithium ion battery (LIB) electrodes require a stable connection between a redox-active metal oxide for charge storage and an electrically conductive (often carbon-based) material for charge transport. As charge transfer within the metal oxide is often a performance-limiting factor, one promising concept is the linking of charge transfer and charge storage components on the nanoscale. This would maximize the interfacial contact area and improve charging/discharging behavior. This work presents a one-step, room-temperature route giving nanostructured manganese vanadium oxide/graphene quantum dot (GQD) composite electrodes. Manganese vanadium oxide clusters are used as solution-processable precursors, which are deposited on GQDs using a sonication-driven conversion leading to electroactive, lightweight composites. Incorporation of the composites as anodes in LIBs shows high electrochemical performance featuring discharge capacities of 970 mAh g−1 over 100 cycles with coulombic efficiencies near 100 %. The study shows how 3d-metal oxide/GQD nanostructures can be accessed by a scalable sonication route starting from soluble, chemically tunable metal oxide clusters and graphene quantum dots.