Interaction over three redox centers at conjugated oligomeric ferrocenes with N=2 to 6 nuclei

Two types of conjugated oligo(hexylferrocene), composed of almost equivalent nuclei, showed the same number of voltammetric waves as number of nuclei (N=2 to 6) because of the generation of multiple mixed-valence states. This finding was inconsistent with the theoretical analysis for a linear assembly of identical nuclei, in that at most four waves are observed for an even number of nuclei and three waves for an odd number of nuclei. The greater number of voltammetric waves than that predicted by the theory is ascribed to the generation of complicated mixed-valence states or to an increase in the asymmetry of the electronic distribution. It can be explained neither by the inequality of the chemical potential at the marginal redox sites nor by the inequality of the interaction energy at the marginal sites, A solution for the appearance of more waves was given by introducing a redox interaction between every second nucleus for formation of the mixed-valence state. The interaction over three redox centers is based on the idea that the mixed-valence state formed by a coupling of the closest neighbor donor and the closest neighbor acceptor is further stabilized by another closest donor or acceptor. Thermodynamic analysis successfully reproduced the experimental formal potentials as a function of three interaction energies which were common to a series of the complexes.