ELECTROCHEMICAL-BEHAVIOR OF [CP'2FE2S4] AND [CP'2FE2S4](PF6)2 (CP'=ETA-5-C5ME5) - STRUCTURAL-CHANGE OF THE FE2S4 CORE ACCOMPANIED BY A CHANGE OF REDOX STATE

Bulk electrolysis of Cp'2Fe2S4 in 0.1 M NH4PF6 in CH3CN at a peak potential for a one-electron-oxidation wave (+0.30 V vs SCE) gives a two-electron-oxidation product [Cp'2Fe2S4](PF6)2 in high yield, where an Fe2S4 core with a bidentate and a doubly bidentate mu-S2 ligands in the neutral species (A type species) changes to one with two doubly bidentate mu-S2 ligands in the dicationic species (B type species) during oxidation. Electrochemical and spectroscopic studies on the redox behavior of these neutral and dicationic species have shown that a total of six species, i.e. a neutral complex, a monocation, and a dication with A-type cores and the same with B-type cores, participate in the redox reactions between [Cp'2Fe2S4] and [Cp'2Fe2S4](PF6)2. The one-electronoxidation potential of [Cp'2Fe2S4] (E1/2 = +0.25 V vs SCE) is more positive than the one-electron-reduction potential of [Cp'2Fe2S4](PF6)2 (E1/2 = +0.15 V vs SCE), and the interconversion between A and B geometries of the Fe2S4 core is fast for monocations. Thus, an ECE-type process operates for the formation of [Cp'2Fe2S4](PF6)2 from [Cp'2Fe2S4]. The equilibrium constant for the electron transfer between [Cp'2Fe2S4] and [Cp'2Fe2S4](PF6)2 has been estimated.