REDOX BEHAVIOR OF 4FE-4S FERREDOXIN MODEL ARENETHIOLATE COMPLEXES INVOLVING SPECIFIC NH-CENTER-DOT-CENTER-DOT-CENTER-DOT-S HYDROGEN-BONDS ASSISTED BY A NEIGHBORING PHENYL GROUP

The complexes [NMe(4)](2)[Fe4S4(SC(6)H(3)Ph-6-NHCOR'-2)(4)](2-) (R' = Bu(t) 1, Me 2 or CF3 3), [NMe(4)](2)[Fe4S4(SC(6)H(3)Ph-6-NHCOR'-4)(4)] (2-) (R' = Bu(t) 4 or CF3 5) and [NMe(4)][Fe4S4(SC(6)H(3)Et-6-NHCOBu(t )-2)(4)](2-) 6 were synthesized by ligand-exchange reactions of [NMe(4 )](2)[Fe4S4(SBu(t))(4)](2-) with the corresponding organic disulfides. They have been characterized by IR and UV/VIS spectroscopy and by ele mental microanalyses. From IR spectra in the solid state, the v(NH) sh ift (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 pheny l 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-oper ation of the aromatic ring and this hydrogen bond.