Abstract
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.
Highlights
Cubane-shaped [Fe4S4] clusters represent a very interesting class of cofactors in biology and are involved in various functions in a cell’s life cycle.[1,2,3,4,5,6] Due to their mixed valent character with two ferric (FeIII) and two ferrous (FeII) iron atoms these clusters show extraordinary electrochemical properties which are crucial for their biological functions in electron transfer and redox catalysis reactions.[7]
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] 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-Electronic supplementary information (ESI) MS
Summary
Cubane-shaped [Fe4S4] clusters represent a very interesting class of cofactors in biology and are involved in various functions in a cell’s life cycle.[1,2,3,4,5,6] Due to their mixed valent character with two ferric (FeIII) and two ferrous (FeII) iron atoms these clusters show extraordinary electrochemical properties which are crucial for their biological functions in electron transfer and redox catalysis reactions.[7]. A convenient preparation method for the iodide cluster using iron pentacarbonyl, sulphur, iodine and an iodide salt has been reported by Pohl and co-workers (Scheme 1E).[30,31]
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