Synthesis, characterization and crystal structure of dimeric polyoxometalates based on the [γ-SiW10O36]8− units

The dimeric polyoxometalate Na7K3[{γ-SiW10O34}2(μ2-O)2Ni(H2O)2] · 18H2O (1) has been successively obtained in an aqueous solution system. Compound 1 represents the first dimeric polyoxometalates accommodating a nickel ion between the two [γ-SiW10O36]8− units which are fused together in an asymmetrical mode to constitute the unprecedented tungsten-oxo fragment. Compound 1 was characterized by IR spectrum, UV spectrum, elemental analyses and single-crystal X-ray diffraction. The IR spectrum of 1 indicates that the γ-type polyoxoanion exists in the dimeric compound. The UV spectra also could be used to confirm that polyoxoanions existing in the compound are the Keggin structure.