Polyoxoanions derived from [gamma-SiO4W10O32](8-)-containing oxo-centered dinuclear chromium(III) carboxylato complexes: Synthesis and single-crystal structural determination of [gamma-SiO4W10O32(OH)Cr-2(OOCCH3)(2)(OH2)(2)](5-)

The previously unknown heteropolyoxometalates [gamma-SiO4W10O32(OH)Cr-2(OOCR)(2)(OH2)(2)](5-) (R = H, CH3) have been prepared by the reaction of [gamma-SiO4W10O32](8-) With [Cr(OH2)(6)](3+) in formate or acetate buffer solution. Isolation of these new Cr-III-substituted polyoxometalates was accomplished both as Cs+ salts and as the Bu(4)N(+) salt for the acetate-containing anion. The compounds were characterized by elemental analysis, UV/vis, IR, and ESR spectroscopy, and cyclic voltammetry. The single-crystal X-ray structural analysis of (Bu(4)N)(3)H-2[gamma-SiO4W10O32-(OH)Cr-2(OOCCH3)(2)(OH2)(2)]. 3H(2)O [P2(1)2(1)2(1); a = 17.608(12), b = 20.992(13), c = 24.464(11) Angstrom; Z = 4; R = 0.057 for 6549 observed independent reflections] reveals that the two corner-linked CrO6 octahedra are additionally bridged by two acetate groups, demonstrating the relationship to the well-studied oxo-centered trinuclear carboxylato complexes of Cr-III.