Theoretical and Empirical Relationships Between the Redox Potentials and 1 ( δ → δ *) Transition Energies of Quadruply Bonded Complexes

An analysis of the available electrochemical and electronic-sectroscopic data for quadruply metal–metal bonded complexes reveals that the 1 ( δ → δ *) transition energy is an approximately linear function of the difference between the electrode potentials at which they are reduced and oxidized to the bond-order 3. 5 complexes. A theoretical framework for interpreting this correlation is provided by extending to the redox potentials a simple zero-differential-overlap model previously applied to 1 ( δ → δ *) transition energies. It is suggested on the basis of this model that the simplicity of the empirical relationship between 1 ( δ → δ *) energies and redox potentials is a consequence of the particular one- and two-electron energy terms that characterize these complexes; a linear relationship is not required by theory.