Hydrothermal Synthesis and Crystal Structure of a Keggin Polyoxometalate [Co^II（2,2′-bipy）2（H2O）]2[SiW^VI12O40]·2H2O

A Keggin-type tungstosilicate compound [CoII(2,2′-bipy)2(H2O)]2[SiWVI12O40]·2H2O 1 (bipy = bipyridine) was prepared by a hydrothermal method for the first time. Single-crystal X-ray diffraction revealed that 1 (C40H40Co2N8O44SiW12) crystallizes in the triclinic system, space group P1 with a = 10.4979(6), b = 13.3946(7), c = 13.5756(8), α = 70.0769(18), β = 68.910(3), γ = 74.186(4)o, V = 1649.84(16)3, Mr = 3688.95, Z = 1, Dc = 3.713 mg·m-3, μ = 21.432 mm-1, F(000) = 1644, S = 1.058, the final R = 0.0511 and wR = 0.1023 for 6523 observed reflections (I > 2σ(I)). Compound 1 consists of two coordinated cation fragments [CoⅡ(2,2′-bipy)2(H2O)]2+, one normal Keggin polyanion unit [SiWVI12O40]4- and two lattice water molecules. To be noted, each polyanion unit is linked to two cation fragments by its two surface terminal oxygen atoms and two cobalt atoms of two cation fragments forming an organic-inorganic hybrid unit in 1. Furthermore, the compound shows strong photo-luminescence property in the solid state at room temperature.