Abstract

The reaction of Cp(dppe)FeI with the ligands 2,2?- and 4,4?-dithiobispyridine (S2(PY)2) give the mononuclear or binuclear complexes of the type [Cp(dppe)Fe-S2(PY)2]PF6, [Cp(dppe)Fe-SPy]PF6 or [{Cp(dppe)Fe}2-?-SPy](PF6)2 depending on the reaction condition. Reaction of Cp(dppe)FeI with dithiobispyridines in presence of TlPF6 as halide abstractor and using CH2Cl2 as a solvent gives the complexes [Cp(dppe)Fe-4,4?-S2(PY)2)2 ]PF6 (1) and [CpFe(dppe)-2,2?-S2(PY)2]PF6 (2) whereas the same reaction using CH3OH as a solvent and NH4PF6 as the halide abstractor leads to the formation of the FeIII-thiolate complex [Cp(dppe)Fe-2,2?-SPy]PF6 (3) and the mixed-valence complex [Cp(dppe)FeIII-?SPy-FeII(dppe)Cp] (PF6)2 (4). Magnetic and ESR measurements are in agreement with one unpaired electron delocalized between them. Mössbauer data indicate clearly the presence of two different iron sites, each one of the N-bonded and S-bonded iron atoms, with intermediate oxidation state FeII-FeIII. An electron transfer intervalence absorption was observed for this complex at 780 nm (in CH2Cl2). By applying the Hush theory the intervalence parameters were obtained; ?=0.028, Hab= 361 cm-1 which indicate Class II Robin-Day. Estimation of the rate electron transfer affords a value kth = 6.5 × 106 s-1. Solvent effect on the intervalence transition follow the Hush prediction for high dielectric constants solvents which permit the evaluation of the outer and inner-sphere reorganizational parameters, which were analyzed and discussed. The electronic interaction parameters compare well with those found for electron transfer in metalloproteins. © 2000 Elsevier Science B.V.