Charge-Transfer Perturbations of the Electronic Contributions to Electron-Transfer Reactions. Enhanced Donor-Acceptor Couplings Mediated by Coordinated Ligands

Article abstract of DOI:10.1021/j100407a048

The factors contributing to variations in the adiabaticity of a series of Co(III)-Co(sep)(2+) (sep= (S)-1,3,6,8,10,13,16,19-octaazabicyclo<6.6.6>eicosane) cross-reactions have been investigated.Coordinated ligands can be effective in making the electron-transfer rates more adiabatic by altering the electronic structure of the complex and/or by contributing to intermolecular charge-transfer interactions.Alterations of the coordinated ligands change both the ligand field and the charge-transfer excited states of the Co(III) acceptor, and the contributions of each kind of excited state perturbation must be considered in evaluating rate patterns.For Co(NH3)5X(2+) oxidants, the inferred values of the electronic transmission coefficient, κ_el, increase systematically through the series X=CN, Cl, Br, N3, and I with the smallest value of κ_el being ca. 10^-3 and the largest approaching unity.Simple models are proposed which account for the variations in κ_el based on the perturbational effects of ligand to metal charge transfer and triplet ligand field excited states on the electron exchange integral coupling reactants and products.