Intervalence Electron Transfer in Mixed Valence Diferrocenylpolyenes. Decay Law of the Metal−Metal Coupling with Distance

Abstract

A series of diferrocenylpolyenes of general formula Fc(CHCH)_nFc with n = 1−6 (Fc = ferrocenyl group) has been prepared and studied from the point of view of intervalence transitions in the mixed valence state. Well-resolved intervalence transitions are observed in dichloromethane upon partial electrolytic oxidation. Comproportionation constants have been determined from redox titration data and in some cases from electrochemical wave splitting. The corrected spectra of the mixed valence species have been deconvoluted to extract the parameters (position, intensity, width) of the intervalence bands, which allowed the determination of the metal−metal coupling (V_ab) through the bridging unit using Hush's formula. The decay of V_ab with distance is close to an exponential law with an exponent of 0.087 Å^-1, constituting one of the smallest attenuations reported so far. A small deviation to the exponential law is detected.