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 reactio n of [gamma-SiO4W10O32](8-) With [Cr(OH2)(6)](3+) in formate or acetat e buffer solution. Isolation of these new Cr-III-substituted polyoxome talates was accomplished both as Cs+ salts and as the Bu(4)N(+) salt f or the acetate-containing anion. The compounds were characterized by e lemental analysis, UV/vis, IR, and ESR spectroscopy, and cyclic voltam metry. The single-crystal X-ray structural analysis of H-2[gamma-SiO4W 10O32-(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 654 9 observed independent reflections] reveals that the two corner-linked CrO6 octahedra are additionally bridged by two acetate groups, demons trating the relationship to the well-studied oxo-centered trinuclear c arboxylato complexes of Cr-III.