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 [Co₉(OH)₃(H₂O)₆(PO₄)₂(B-α-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, [Co₉(OH)₃(H₂O)₆(HPO₄)₂(B-α-PW₉O₃₄)₃]^16– (Co₉-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 Co₉-P. The experimental results were supported by computational studies.