Tungsten polyoxometalate

Hydrogen peroxide is an inexpensive oxidant, but it requires a catalyst to effect oxidation of an alcohol to the ketone. Removal of the catalyst then becomes an issue. Ronny Neumann of the Weizmann Institute of Science reports (J. Am. Chem. Soc. 2004,126, 884) the development of a hybrid organic-tungsten polyoxometalate complex that is not soluble in organic solvents, but that nonetheless catalyzes the hydrogen peroxide oxidation of alcohols to ketones. The solid catalyst is removed by filtration after the completion of the reaction. The catalyst retained its activity after five recyles. 

In dilute acid solutions, molybdenum and tungsten form many polyoxometallate ions. 

Polyoxometalate anions, especially those of hexavalent molybdenum and tungsten interact with rare-earth cations to generate a seemingly endless variety of complexes in which the rare earths function as encrypted cations, as core heteroatoms, or as linkers of polyoxometalate fragments to yield discrete anionic assemblies currently incorporating as few as 8 and as many as 164 metal centers,... 

Polyoxometallate ions containing tungsten form an enormous range of compounds, which have been reviewed extensively. They may be subdivided into (1) isopolyanions containing W as the dominant and frequently the only metal component, and (2) heteropolyanions where other metals and/or nonmetal atoms may be present in the core structure. 

Cluster Compounds Inorganometallic Compounds Containing Transition Metal Main Group Elements Heterogeneous Catalysis by Metals Oxidation Catalysis by Transition Metal Complexes Polyoxometalates Tungsten Organometallic Chemistry. Tungsten Proteins. 

Solid-state reference electrodes for potentiometric sensors are currently under research. The main problem to be faced in developing this type of electrode lies in connecting the ionic conducting (usually aqueous) solution with an electronic conductor. Since the reference electrode has to maintain a defined potential, the electrochemical reaction with components of the electrolyte has to be avoided. Oxides, mixed oxides, and polyoxometalate salts of transition elements can be proposed for preparing solid-state reference electrodes. Tested compounds include tungsten and molybdenum oxides (Guth et al., 2009). 

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