Both metal-to-ligand charge transfer (MLCT) and oxidation (ionization) processes have been investigated for (NH3)(5)RuL(2+) complexes with L = pyridine, pyrazine, and protonated pyrazine. Calculations were carried out using ZINDO-95. Self-consistent-field molecular orbitals (MO’s) were obtained at the restricted Hartree-Fock level for the closed-shell ground state (t(2g))(6) (NH3)(5)RuL(2+) species. The MLCT wave functions and excitation energies were obtained by configuration interaction among all singlet configurations generated by single excitations from the highest 11 occupied MO’s to the lowest 11 unoccupied MO’s. We find that the Ru(II) d(pi) orbital is the HOMO for all three complexes. The results provide clear indication that the relative energies for removing an electron from the three types of t(2g) orbital depend on the effective distance that the electron is transferred. For relatively long-distance transfers (e.g., greater than or equal to 5 Angstrom as for intra- or intermolecular thermal or optical electron transfer to a weakly coupled Ru(III) site), the lowest energy process involves the d,orbital. In contrast, for the shorter range MLCT process, for which the electron interacts with the newly created hole to an extent determined by the relevant Coulomb and exchange integrals, the d(pi) orbital participates in the highest energy of the three possible t(2g) --> L(pi*) excitations. Accordingly, to the extent that the electronic coupling element for thermal or optical metal-to-metal electron transfer is enhanced by superexchange of the "electron" type involving the d(pi) orbital, the relevant MLCT intermediate state is not the lowest energy but rather the highest energy one. It also follows that an electron from the same symmetry orbital (d(pi)) is transferred in both optical and thermal electron transfer processes involving the Ru(II)-Ru(III) couples considered.