The ligand electrochemical series, E(L)(L), has been developed for many hundreds of ligands, and provides an accurate prediction of metal-centered redox potentials for coordination complexes. Semiempirical methods are used in conjunction with second-order perturbation theory to provide a new method to factorize the E(L)(L) parameter and extract a new and general measure of the sigma- and pi-donating and pi-accepting properties of a ligand.