Redox behaviour of 4Fe-4S ferredoxin model arenethiolate complexes involving specific NH ? S hydrogen bonds assisted by a neighbouring phenyl group

The complexes [NMe4]2[Fe4S4(SC6H3Ph-6-NHCOR′-2)4]2–(R′= But1, Me 2 or CF33), [NMe4]2[Fe4S4(SC6H3Ph-6-NHCOR′-4)4]2–(R′= But4 or CF35) and [NMe4]2[Fe4S4(SC6H3Et-6-NHCOBut-2)4]2–6 were synthesized by ligand-exchange reactions of [NMe4]2[Fe4S4(SBut)4]2– with the corresponding organic disulfides. They have been characterized by IR and UV/VIS spectroscopy and by elemental microanalyses. From IR spectra in the solid state, the v(NH) shift (114 cm–1) of 1 from the band of the corresponding disulfide is larger than that of 6(87 cm–1). The results indicate that the phenyl group at the 6 position contributes to the strengthening of the NH ⋯ S hydrogen bond. The stabilization of the [Fe4S4(SR)4]––[Fe4S4(SR)4]2– redox potential of 1 compared with 6 is due to the co-operation of the aromatic ring and this hydrogen bond.