The reduction potentials of a series of polypyridine complexes of Mo0, Os(II), Re(I), and Ru(II), some nitrosyl Os(II) and Ru(II) complexes, and a series of dinitrosylmolybdenum species are parametrized with the SIGMAE(L)(L) parameter. The slope, S(L), and intercept, I(L), of the linear correlations are shown to relate to metal-ligand coupling and interligand coupling through the metal center.