Synthesis, characterization, and crystal structures of two 6-cobalt-containing dimeric polyoxoanions: [Co2(H2O)10Co4(H2O)2(B-α-XW9O34)2]8− (X = Ge and Si)

Two new polyoxotungstates K4Na4[Co2(H2O)10Co4(H2O)2(B-α-GeW9O34)2] · 28.5H2O (1) and K2Na6[Co2(H2O)10Co4(H2O)2(B-α-SiW9O34)2] · 17H2O (2) have been obtained in aqueous solution and characterized by IR, TG, element analysis, magnetism, electrochemistry and single-crystal X-ray analysis. The polyoxoanion frameworks of the two compounds consist of the sandwich-type polyoxoanion [Co4(H2O)2(B-α-XW9O34)2]8− (X = Ge and Si) covalently linked with two Co2+ cations by two μ2-O atoms. The magnetic properties of compound 1 have been studied by measuring its magnetic susceptibility in the temperature range 2.0–300.0 K, indicating the existence of intramolecular ferromagnetic Co–Co interactions. The electrochemical properties of the two compounds were detected in pH 3 buffer solutions, and three redox couples were detected in the multi-cobalt-substituted POMs.