A new sandwich-type polyoxometalates containing mixed transition metals, [Cd2Zn2(H2O)2(P2W15O56)2]16−: Syntheses, spectrochemical characterization and its electrocatalytical activity comparison with [M4(H2O)2(P2W15O56)2]16− (M = Cd2+ and Zn2+) and [P2W15O

•This compound is a new polyoxometalates containing mixed transition metals.•The cadmium ions are located in external position at M4O16 metal centers.•This mixed-metal polyoxometalate can catalyze electrochemical reduction of NO2−.•By reducing the number of cadmium ions, catalytic efficiency increases.

The mixed-metal sandwich-type polyoxometalate [Cd2Zn2(H2O)2(P2W15O56)2]16− (abbreviated Cd2Zn2P4W30) has been synthesized and characterized by FT-IR, 31P NMR, 113Cd NMR spectroscopies, cyclic voltammetry (CV) and elemental analysis. The electrochemical behavior of this sandwich-type complex in aqueous solution has been investigated, and also systematic comparisons of that have been made by [M4(H2O)2(P2W15O56)2]16− (M = Cd2+ and Zn2+) (abbreviated M4P4W30) and [P2W15O56]12− (abbreviated P2W15). All these compounds show successive reduction processes of the tungsten centers in a negative potential range, but in some cases, the electrochemistry involves redox reactions originating from cadmium ions. These sandwich-type complexes have efficient electrocatalytic activities towards the reduction of nitrite. However, there is a significant decrease in efficiency as the number of cadmium centers in the complex increases.

Graphical abstractThe syntheses, spectroscopic characterization and electrochemical properties of a new sandwich-type polyoxometalates containing mixed transition metals are reported. Electrocatalytic reductions of nitrite by this compound was investigated in detail by using cyclic voltammetry.Figure optionsDownload full-size imageDownload as PowerPoint slide