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Theory of adiabatic Hexaamminecobalt-Self-Exchange

R. G. Endres, M. X. LaBute, D. L. Cox

physics.chem-pharXiv:physics/0212010

Abstract

We have reexamined the thermally induced Co(NH3)62+/3+ [Co(II/III)] redox reaction using the first principles density-functional-theory method, semiclassical Marcus theory, and known charge transfer parameters. We confirm a previously suggested mechanism involving excited state (2Eg) of Co(II) which becomes lower than the ground state (4T1g) in the transition state region. This lowers the transition state barrier considerably by about 6.9 kcal/mol and leads to a spin-allowed and adiabatic electron exchange process. Our calculations are consistent with previous experimental results regarding the spin-excitation energy (3T1g) of Co(III), and the fact that an optical absorption peak (2Eg) of the Co(II) species could not be found experimentally. Our rate is of order 6 10-3 1/Ms and hence 2 orders of magnitude faster than determined previously by experiments.

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