Remarkable Influence of Structures around Rhenium (V) Centers Constructed in Polyoxotungstates for Methanol Dehydrogenation under Visible Light Irradiation

The synthesis and characterization of 1-Dawson-type mono-rhenium (V)-substituted polyoxotungstate, [1-P2W17ReO62] (1), are described. The dimethylammonium salt of 1, [Me2NH2]7[1-P2W17ReO62]·9H2O (Me2NH2-1), was obtained as analytically pure homogeneous black-blue crystals by reacting mono-lacunary 1-Dawson polyoxotungstate with [ReCl6] in CH3COOH/CH3COOLi buffer, followed by crystallization via a vapor diffusion from acetonitrile/ethanol. Characterization was also accomplished by X-ray crystallography, elemental analysis, TG/DTA, FTIR, UV-vis, and solution P NMR spectroscopy; these results showed that the polyoxoanion 1 was a monomeric -Dawson structure, in which the rhenium(V) ion was coordinated to the monovacant site of [1-LiP2W17O61], resulting in an overall C1 symmetry. The polyoxoanion 1, [O{Re(OH)(2-P2W17O61)}2] (2), and [-PW11ReO40] (3) showed the Original Research Article British Journal of Applied Science & Technology, 4(16): 2302-2319, 2014 2303 hydrogen evolution from methanol under visible light irradiation (400nm) in the presence of titanium dioxide. The activities were remarkably depended on the rhenium (V) sites in 1–3; polyoxoanion 2 possessing the dirhenium(V)-oxido-bridged site showed the highest activities among these complexes.