Halide coordinated homoleptic Fe4S4X4(2-) and heteroleptic Fe4S4X2Y2(2-) clusters (X, Y = Cl, Br, I)-alternative preparations, structural analogies and spectroscopic properties in solution and solid state

摘要

New facile methods to prepare iron sulphur halide clusters Fe4S4X4(2-) from Fe(CO)(5) and elemental sulphur were elaborated. Reactions of ferrous precursors like tetrahalidoferrates(II) or simple ferrous halides with Fe(CO)(5) and sulphur turned out to be efficient methods to prepare homoleptic Fe4S4X4(2-) (X = Cl, Br) and heteroleptic clusters Fe4S4X4-nYn(2-) (X = Cl, Br; Y = Br, I). Solid materials were obtained as salts of BTMA(+) (= benzyltrimethylammonium); the new compounds containing Fe4S4Br4(2-) and Fe4S4X2Y2(2-) (X, Y = Cl, Br, I) were all isostructural to (BTMA)(2)Fe4S4I4 (monoclinic, Cc) as inferred from synchrotron X-ray powder diffraction. While the solid materials contain defined heteroleptic clusters with a halide X : Y ratio of 2 : 2, dissolving these compounds leads to rapid scrambling of the halide ligands forming mixtures of all five possible Fe4S4X4-nYn(2-) clusters as could be shown by UHR-ESI MS. The variation of X and Y allowed assignment of the absorption bands in the visible and NIR; the long-wavelength bands around 1100 nm were tentatively assigned to intervalence charge transfer (IVCT) transitions.