Fe4S4I42- has been prepared in tetrahydrofuran (THF) solution by the reaction of Fe, S8, I2, and Me3NCH2Ph+TI-, and isolated as black, fairly air-stable crystals of (Me3NCH2Ph)2Fe4S4I4 (1) in nearly quantitative yield. 1 reacts with iron and iodine or with elemental sulfur and Fel2 in CH2Cl2 solution to form Fe6S6I62- which was isolated as black crystals of (Me3NCH2Ph)2Fe6S6I6 (5). In THF solution Fe6S6I62- is converted to Fe4S4I42- which was isolated as Fe(THF)6Fe4S4I4·4 THF (3). Evidence is presented for an equilibrium between Fe2S2I42- and Fe4S4I42-, Fel42- and sulfur when iron, sulfur, iodine and Et4N+I- react (with the required stoichiometry) to form Fe2S2I42- in CH2Cl2 solution. From this solution (Et4N)6(Fe4S4I4)2Fe2S2I4 (6 ) crystallizes as black needles (tetragonal, P42bc, a = 2467.9, b = 1653.8 pm, Z = 4). Crystals of 6 consist of the discrete anions Fe4S4I42- and Fe2S2I42- and Et4N+ cations. The [Fe4S4]2+ core does not exhibit the usually observed core distortion. This clearly demonstrates that additional ligands (THF, CH3CN, iodide ions etc.) strongly reduce the stability of iodine substituted Fe/S clusters (except [Fe4S4]2+ cores!). The biological relevance of the observed rearrangements is discussed.
Crystal structure of Escherichia coli YfhJ protein, a member of the ISC machinery involved in assembly of iron-sulfur clusters
