A new Mo/V-oxide-based cationic species templated by Keggin polyoxotungstates (4-) and its catalytic activity in benzene hydroxylation

Three new polyoxotungstate-templated Mo/V-oxide-based organic–inorganic hybrid compounds, [Mo2V2O9(bpy)6][XW12−xVxO40] (X = Si(1) and Ge(2), x = 0; X = P(3), x = 1) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. They are isomorphic and consist of Keggin polyoxotungstate anions and a novel Mo/V-oxide-based cationic species, [Mo2V2O9(bpy)6]4+. The cationic species exhibits a finite Z-shaped chain, which is composed of corner-sharing {MoO4N2}. Octahedra and {VO2N4} octahedra via V–O–Mo–O–Mo–O–V mode. Electrochemical measurements of 1 and 3 show that three pairs of semi-reversible redox peaks are corresponding to redox processes of W and Mo centers. 1 and 3 are active catalysts for the hydroxylation of benzene with oxygen as the oxidant. Most interestingly, their active sites are on the cation [Mo2V2O9(bpy)6]4+ instead of the Keggin polyoxotungstate anions.