THE CO(NH3)62+/3+ EXCHANGE-REACTION - GROUND-STATE VERSUS THERMALLY EXCITED PATHWAYS

The electron-exchange reaction involving the Co(NH3)6(2+) and Co(NH3)6(3+) has been analyzed on the basis of electronic structure calculations. Equilibrium and inner-shell transition-state geometries, activation energies, multiplet splittings, and spin-orbit coupling coefficients have been evaluated by using the results of ab initio electronic structure calculations for the separate reactants (at both the SCF(UHF) and correlated (UMP2) levels) in conjunction with empirical values for atomic spin-orbit matrix elements and the known value of the multiplet splitting for the Co3+ reactant. Electron-transfer matrix elements have been obtained from INDO calculations for the Co(NH3)6(2+)/CO(NH3)6(2+) transition-state supermolecule complex corresponding to apex-to-apex, edge-to-edge, and face-to-face relative orientation of the reactants. Combining this information with previous estimates of solvent reorganization energy and coordination sphere breathing frequencies, we have estimated a value of approximately 10(-4) for the orientationally averaged electronic transmission factor associated with the ground-state spin-or-bit-enhanced pathway. The calculations suggest that an alternative thermally excited pathway will not be competitive at room temperature. The present results are compared with earlier analyses of kinetic data which suggest k(el) greater-than-or-similar-to 10(-2).