Polyoxoanions Derived from [gamma-SiO(4)W(10)O(32)](8-)-Containing Oxo-Centered Dinuclear Chromium(III) Carboxylato Complexes: Synthesis and Single-Crystal Structural Determination of [gamma-SiO(4)W(10)O(32)(OH)Cr(2)(OOCCH(3))(2)(OH(2))(2)](5-).