Structural and Physico-Chemical Study of New Keggin Polyoxometalates with Mixed Adenda

Reactions between [alpha-PVMo10O39](8-) mono-lacunary Keggin monovanado-deca-molybdophosphate and transition metal cations Mn2+, Fe3+, Co2+, Ni2+ and Cu2+ in aqueous solution results in the formation of new polyoxometalate complexes, with the stoichiometry metal: ligand by 1:1. New complexes were isolated as potassium salts, i.e. K8-n[Mn+(H2O)PVMo10O39]center dot xH(2)O. The molecular formula of complexes was determined by elemental and thermo-gravimetric analysis, UV-Vis, FT-IR, Raman, EPR spectroscopy and X-ray diffraction. The investigation results strongly suggest a Keggin-type structure with mixed addenda of new complexes in which the transition metal cations are coordinated by five oxygen atoms of the cavity of lacunary polyoxometalate anions and sixth oxygen atom originates in the water molecule in distorted Oh symmetry. Some of new complexes, K-6[Ni(H2O)PVMo(10)O39]center dot x H2O (x = 16,21) and K-6[Cu(H2O)PVMo10O39]center dot 17H(2)O, crystallized in monoclinic system, space group P2(1)/c. The electrocatalytic activity of the K-6[Cu(H2O)PVMo10O39]center dot 17H(2)O compound towards H2O2 was evidenced.