Mixed-Valence Compounds
Organic mixed-valence (MV) compounds are helpful samples to elucidate adiabatic electron transfer (ET) processes.[1] MVs usually consist of at least two equivalent redox centers linked by an unsaturated bridge, which allows the redox centers to interact electronically. Robin and Day classified such compounds into three groups with respect to their electronic coupling.[2] MVs belonging to Robin-Day class II are able to undergo an optically induced charge transfer from one charged redox center to the other. This transmission can be observed by steady state spectroscopy resulting in the so called intervalence charge transfer (IV-CT) band. An analysis of the IV-CT band according to the generalized Mulliken-Hush theory provides the fundamental parameters of charge transfer reactions including the Marcus reorganization energy and the electronic coupling.[3]
Chart 1: Adiabatic Gibbs energy surface of a Robin-Day class II MV and its ET pathways. The black arrows represent the solvent dipols. The size of the redox centers represent changes of geometry in different redox states.[1]
[1] Lambert, C.; Heckmann, A. Angew. Chem., Int. Ed. 2011, accepted.
[2] Robin, M. B.; Day, P. Adv. Inorg. Chem. Radiochem. 1967, 10, 247-422.
[3] Heckmann, A.; Amthor, S.; Lambert, C. Chem. Commun. 2006, 2959-2961.
