Crystal structure of bis(tetra-n-butylammonium)dodecamolybdosulfate(VI)-(2–), [NBun4]2[SMo12O40]

Abstract

The structure of [NBuⁿ₄]₂[SMo₁₂O₄₀] has been determined by the single-crystal X-ray method: cubic, space group Fm3m, a= 18.824(1)Å and Z= 4. The structure model was refined by full-matrix least squares to R= 0.0607 and R′= 0.0585 for 320 independent reflections and 32 variables. The heteropolyion [SMo₁₂O₄₀]^2–1 contained in the crystals is a typical Keggin molecule with point symmetry 3m and located at sites of crystallographic Fm3m symmetry in two equally weighted orientations related by inversion at the S atom. The geometry is compared with those of the isomorphous Keggin molecules [PMo₁₂O₄₀]^3–2, [SiMO₁₂O₄₀]^4–3 and [GeMo₁₂O₄₀]^4–4 as a function of the nature of the central heteroatom and in relation to the relative stability 123 < 4 in aqueous solution.