Popis: |
The new clusters (X)2[Fe4S4(SCH2tib4] (XEt4N, Ph4P) have been synthesized with a sterically encumbered and benzyl-type thiolate ligand, in order to study its influence on the formation and stability of the oxidized state [Fe4S4]3+. Both clusters exhibit a stable redox couple in CH2Cl2, and the oxidized (Ph4P) [Fe4S4(SCH2tib)4] can be generated in solution by chemical oxidation. EPR and 1H NMR studies show that this species is unstable in solution at room temperature and that it decomposes, possibly by way of a transient [3Fe4S]+ state. The isotropic shift, longitudinal relaxation time and temperature dependence of the SCH2 protons' resonance have been analyzed both in the [4Fe4S]2+ and [4Fe4S]3+ states, and compared to results available on the same oxidation state centers in [4Fe4S] proteins. |