Synthesis, Structure, Electrochemistry and Magnetism of Cobalt-, Nickel- and Zinc-Containing [M4(OH)3(H2O)2(α-SiW10O36.5)2]13- (M = Co2+, Ni2+, Zn2+)

Interaction of the trilacunary 9-tungstosilicate [A-α-SiW9O34]10- with cobalt(II), nickel(II) and zinc(II) ions in pH 9 aqueous medium at room temperature led to the formation of the respective M4-containing heteropolytungstates [M4(OH)3(H2O)2(α-SiW10O36.5)2]13- (M = Co2+ (1), Ni2+ (2), Zn2+ (3)). Polyanions 1-3 were characterized in the solid state by single-crystal XRD, FT-IR spectroscopy, thermogravimetric and elemental analysis. Electrochemical studies showed that the Co2+ ions in 1 can be oxidized to Co3+ and the CVs of the WVI centers of the polyanions are featured by well-defined and chemically reversible reduction waves. Magnetic measurements on 1 and 2 showed paramagnetism with complex ferromagnetic as well as antiferromagnetic interactions. A model was presented for extracting the exchange constants for the magnetic exchange interaction.