Photoredox Chemistry in Oxide Clusters. Photochromic and Redox Properties of Polyoxometalates in Connection with Analog Solid State Colloidal Systems

Data on the electrochemical and photoredox chemistry of polyoxometalates of formula H 4 [SiW 12 O 40 ] and H 3 [PMo 12 O 40 ] are reported and analyzed in relation to those of related extended solids (WO 3 and colloidal WO 3 particles). These soluble multinuclear anions show reversible single-electron and multielectron reduction processes to yield blue mixed valent species. Similar reduced species can be obtained photochemically, with a concomitant oxidation of organic substrates. The reported photochromic behavior is similar to that of colloidal WO 3 particles. On the other hand, electrochemical potentials differ substantially from the flat band potential of WO 3 colloids. Finally, the title compounds are more stable and present the added advantage of having well-characterized monodisperse and controllable structures and tunable electrochemical properties.