Five Transition-Metal-Substituted Polyoxometalates: Syntheses, Structures and Electrochemical Properties

A series of transition metal, such as Ni/Mn/Zn, substituted sandwich-type polyoxometalates, H9Na(enMe)3[Ni4(H2O)2(PW9O34)2]·31H2O (1), H8Na2[Ni4(H2O)2(PW9O34)2]·34H2O (2), H8Na2[Mn4(H2O)2(PW9O34)2]·29H2O (3), H4Na6[Mn4(H2O)2(PW9O34)2]·41H2O (4), H5Na7[Zn4(H2O)2(GeW9O34)2]·25H2O (5) have been synthesized under mild hydrothermal conditions and characterized by IR spectra, thermogravimetric analysis, elemental analysis, single-crystal X-ray diffraction and powder X-ray diffraction, respectively. The structure analysis reveals that 1–5 contain a similar sandwich-type polyoxoanion unit [M4(H2O)2(XW9O34)2]10−/12− (M = Ni2+/Mn2+/Zn2+; X = PV/GeIV), which are further linked by Na+ cations to form 1- to 3-D structures, respectively. Furthermore, the electrochemical properties of 1, 4 and 5 have been studied in 0.5 mol L−1 Na2SO4/H2SO4 supporting electrolyte, and show that 1, 4 and 5 possess comparatively apparent catalytic activities toward the NaNO2 or H2O2 reduction.