Structures, magnetic and catalytic properties of three sandwich-type silicotungstates containing tetranuclear copper(II) clusters.

Three sandwich-type silicotungstates, formulated as [Cu4(H2O)2(SiW9O34)2] x 12 NH4 x 22 H2O (1), [Cu4(H2O)2(SiW9O34)2] x 12 NH4 x 11 H2O (2) and {[Cu(NH3)4]2[Cu(H2O)4][Cu4(H2O)2(SiW9O34)2]} 2[Cu(NH3)4(H2O)] x 2 NH4 x 6 H2O (3), were synthesized by microwave irradiation and hydrothermal reaction. Crystal structural analysis reveals that 1-3 possess the same dimeric polyoxoanions [Cu2SiW9O34(H2O)]2(12-) featuring tetranuclear copper(II) clusters. Magnetic studies indicate that the Cu4 clusters exhibit ferromagnetic coupling interactions. Investigation on their catalytic activity for the oxidation of ethylbenzene suggests that catalytic activity of 1-3 is closely related to the acidity of complexes and the existence of unsaturated coordination sites in the complex.