ELECTROCHEMICAL PARAMETRIZATION OF METAL-COMPLEX REDOX POTENTIALS, USING THE RUTHENIUM(III) RUTHENIUM(II) COUPLE TO GENERATE A LIGAND ELECTROCHEMICAL SERIES

A ligand electrochemical parameter, EL(L), is described to generate a series which may be used to predict M(n)/M(n − 1) redox potentials by assuming that all ligand contributions are additive. In this fashion it performs a purpose similar to that of the Dq parameter in electronic spectroscopy. The parameter is defined as one-sixth that of the Ru(III)/Ru(II) potential for species RuL6 in acetonitrile. The EL(L) values for over 200 ligands are presented, and the model is tested over a wide range of coordination complexes and organometallic species. The redox potential of a M(n)/M(n − 1) couple is defined to be equal to Ecalc= SM[ΣEL(L)] + IM. The values of SM and IM, which are tabulated, depend upon the metal and redox couple, and upon spin state and stereochemistry, but, in organic solvents, are generally insensitive to the net charge of the species. Consideration is given to synergism, the potentials of isomeric species, and the situations where the ligand additivity model is expected to fail. In this initial study, the redox couples are restricted almost exclusively to those involving the loss or addition of an electron to the t2g (in Oh) sublevel. © 1990, American Chemical Society. All rights reserved.