STRUCTURE AND PROPERTIES OF FE4S4(2,6-BIS(ACYLAMINO)BENZENETHIOLATO-S)(4)](2-) AND FE2S2(2,6-BIS(ACYLAMINO)BENZENETHIOLATO-S)(4)](2-) - PROTECTION OF THE FE-S BOND BY DOUBLE NH-CENTER-DOT-CENTER-DOT-CENTER-DOT-S HYDROGEN-BONDS

Iron-sulfur clusters containing a singly or doubly NH...S hydrogen-bon ded arenethiolate ligand, [Fe4S4(S-2-RCONHC(6)H(4))(4)](2-) (R = CH3, t-Bu, CF3), [Fe4S4{S-2,6-(RCONH)(2)C6H3}(4)](2-), [Fe2S2(S-2-RCONHC(6) H(4))(4)](2-) (R = CH3, t-Bu, CF3), and [Fe2S2{S-2,6-(RCONH)(2)C6H3}(4 )](2-), were synthesized as models of bacterial [4Fe-4S] and plant-typ e [2Fe-2S] fenedoxins. The X-ray structures and IR spectra of (PPh(4)) (2)[Fe4S4{S-2,6-(CH3-CONH)(2)C6H3}(4)]. 2CH(3)CN and (NEt(4))(2)[Fe2S2 {S-2,6-(t-BuCONH)(2)C6H3}(4)] indicate that the two amide NH groups at the o,o'-positions are directed to the thiolate sulfur atom and form double NH...S hydrogen bonds. The NH...S hydrogen bond contributes to the positive shift of the redox potential of not only (Fe4S4)(+)/(Fe4S 4)(2+) but also (Fe4S4)(2+)/(Fe4S4)(3+) in the [4Fe-4S] clusters as we ll as (Fe2S2)(2+)/(Fe2S2)(3+) in the [2Fe-2S] clusters. The doubly NH. ..S hydrogen-bonded thiolate ligand effectively prevents the ligand ex change reaction by benzenethiol because the two amide NH groups stabil ize the thiolate by protection from dissociation.