9-Cobalt(Ii)-Containing 27-Tungsto-3-Germanate(Iv): Synthesis, Structure, Computational Modeling, And Heterogeneous Water Oxidation Catalysis

The 9-cobalt(II)-containing trimeric, cyclic polyanion [Co-9(OH)(3)(H2O)(6)(PO4)(2)(B-alpha-GeW9O34)(3)](21-) (1) was synthesized in an aqueous phosphate solution at pH 8 and isolated as a hydrated mixed sodium-cesium salt. Polyanion 1 was structurally and compositionally characterized in the solid state by single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, as well as thermogravimetric and elemental analyses. The magnetic and electrochemical properties of 1 were also studied and compared with those of its phosphorus analogue, [Co-9(OH)(3)(H2O)(6)(HPO4)(2)(B-alpha-PW9O34)(3)](16-) (Co-9-P). The electrochemical water oxidation activity of the cesium salt of 1 under heterogeneous conditions was also studied and shown to be superior to that of Co-9-P. The experimental results were supported by computational studies.