SYNTHESES AND CHARACTERIZATION OF GAMMA-[SIW(10)M(2)S(2)O(38)](6-) (M=MO-V, W-V) - 2 KEGGIN OXOTHIO HETEROPOLYANIONS WITH A METAL-METAL BOND

The oxothio polyanions gamma-[SiW(10)M(2)S(2)O(38)](6-) (M = MO(V), W- V) were Obtained through stereospecific addition of the dication [M(2) S(2)O(2)](2+) (M = MO, W) to the divacant gamma-[SiW10O36](8-) anion i n dimethylformamide. These compounds were isolated as crystals and are stable in usual organic solvents and in aqueous medium from pH = 1 to pH = 7. NEt(4)Cs(3)H(2)[SiW10Mo2S2O38]. 6H(2)O (a gamma-isomer derive d from the alpha Keggin structure capped by the [Mo2S2O2](2+) fragment containing a metal-metal bond) crystallizes in the triclinic space gr oup <P(1)over bar> with a = 12.050(3) Angstrom, b = 12.695(2) Angstrom , c = 20.111(4) Angstrom, alpha = 74.35(2)degrees, beta = 86.83(2)degr ees, gamma = 63.50(2)degrees, Z = 2. NEt(4)Cs(5)[SiW12S2O38]. 7H(2)O i s isostructural and crystallizes in the triclinic space group <P(1)ove r bar> with a = 12.197(4) Angstrom, b = 12.714(3) Angstrom, c = 20.298 (3) Angstrom, alpha = 74.75(1) Angstrom, beta = 86.48(2)degrees, gamma = 61.80(2)degrees, Z = 2. W-183 NMR spectra of Li+ salts in aqueous s olution agree with the solid state structures and reveal 100% purity f or both anions. Polarographic, infrared and W-vis data are also given.