Structure of double Keggin-Ti/W-mixed polyanion [(A-β-GeTi3W9O37)2O3]14− and multielectron-transfer-based photocatalyic H2-generation

[(A-β-GeW9Ti3O37)2O3]14− (1a) is isolated as K+/Na+/H+ salt, K9NaH4[(β-GeW9Ti3O37)2O3]·40.5H2O (1), and characterized by single-crystal X-ray structural and 183W NMR spectral analyses in comparison with [(A-α-GeW9Ti3O37)2O3]14− (2a) previously isolated as K9H5[(α-GeW9Ti3O37)2O3]·16H2O (2). Two isomers of 1a and 2a have local symmetry of D3h and are stable in aqueous solutions at least at pH values of ≤7. The photocatalytic H2-formation for the dehydrogenative oxidation of methanol (CH3OH → H2 + HCHO) with 1 and 2 is investigated with a help of electronic and ESR spectra and electrochemistry, and is explained in terms of the two-electron reduction of protons at the central TiIII–O–TiIII linkage of the corner-shared TiO6 octahedra connecting two half molecules.

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