Syntheses and Characterization of γ-[SiW10M2S2O38]6- (M = MoV, WV). Two Keggin Oxothio Heteropolyanions with a Metal−Metal Bond

Abstract
The oxothio polyanions γ-[SiW10M2S2O38]6- (M = MoV, WV) were obtained through stereospecific addition of the dication [M2S2O2]2+ (M = Mo, W) to the divacant γ-[SiW10O36]8- anion in dimethylformamide. These compounds were isolated as crystals and are stable in usual organic solvents and in aqueous medium from pH = 1 to pH = 7. NEt4Cs3H2[SiW10Mo2S2O38]·6H2O (a γ-isomer derived from the α Keggin structure capped by the [Mo2S2O2]2+ fragment containing a metal−metal bond) crystallizes in the triclinic space group P1̄ with a = 12.050(3) Å, b = 12.695(2) Å, c = 20.111(4) Å, α = 74.35(2)°, β = 86.83(2)°, γ = 63.50(2)°, Z = 2. NEt4Cs5[SiW12S2O38]·7H2O is isostructural and crystallizes in the triclinic space group P1̄ with a = 12.197(4) Å, b = 12.714(3) Å, c = 20.298(3) Å, α = 74.75(1) Å, β = 86.48(2)°, γ = 61.80(2)°, Z = 2. 183W NMR spectra of Li+ salts in aqueous solution agree with the solid state structures and reveal 100% purity for both anions. Polarographic, infrared and UV−vis data are also given.

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