Modeling of the Redox Properties of (Hexaamine)cobalt(III/II) Couples.

The thermodynamics (redox potentials) and kinetics (electron transfer rates) of (hexaamine)cobalt(III/II) redox couples are interpreted in terms of steric strain induced by the ligand systems. The intersections of potential energy curves (strain energy versus metal−ligand distance plots of pairs of conformers) of the oxidized and reduced forms of a wide range of (hexaamine)cobalt(III/II) couples are related to the inner sphere reorganization (ΔH⧧), and correlated with experimentally determined electron self-exchange rates. The minima of these potential energy curves of the reduced and oxidized forms are correlated with the reduction potentials. The perturbation by electronic effects due to differences in nucleophilicity along the series ammonia, primary amine, secondary amine, tertiary amine has been accounted for. The redox potentials of the couples studied (E° = −0.6V to +0.8 V; vs SHE), the electron self-exchange rates (10-7s-1−103s-1), the Co3+−N distances (1.94−2.05 A), and the ligand field strengths...