EDTA-Reduction of Water to Molecular Hydrogen Catalyzed by Visible-Light-Response TiO(2)-Based Materials Sensitized by Dawson- and Keggin-Type Rhenium(V)-Containing Polyoxotungstates

The synthesis and characterization of a Keggin-type mono-rhenium(V)- substituted polyoxotungstate are described. The dimethylammonium salt [Me(2)NH(2)](4)[PW(11)Re(V)O(40)] was obtained as analytically pure homogeneous black-purple crystals by reacting mono-lacunary Keggin polyoxotungstate with [Re(IV)Cl(6)](2-) in water, followed by crystallization from acetone at ca. 5 °C. Single-crystal X-ray structural analysis of [PW(11)Re(V)O(40)](4-) revealed a monomeric structure with overall T(d) symmetry. Characterization of [Me(2)NH(2)](4)[PW(11)Re(V)O(40)] was also accomplished by elemental analysis, magnetic susceptibility, TG/DTA, FTIR, UV-vis, diffuse reflectance (DR) UV-vis, and solution (31)P-NMR spectroscopy. Furthermore, [PW(11)Re(V)O(40)](4-) and the Dawson-type dirhenium(V)-oxido-bridged polyoxotungstate [O{Re(V)(OH)(α(2)-P(2)W(17)O(61))}(2)](14-) were supported onto anatase TiO(2) surface by the precipitation methods using CsCl and Pt(NH(3))(4)Cl(2). With these materials, hydrogen evolution from water in the presence of EDTA·2Na (ethylenediamine tetraacetic acid disodium salt) under visible light irradiation (≥400 nm) was achieved.