Density functional theory using the B3LYP hybrid functional has been employed to study the formation of [Cu-II(TPA(H))(O-2(-))](+) and [Cu-II(TPA(MeO))(O-2(-))](+) (TPA = tris(2-pyridylmethyl)amine) in two different solvents, THF and EtCN. The thermodynamics of solvent coordination as well as that of the overall reactions with O-2 has been computed. The formations of [Cu-II(TPA(H))(O-2(-))](+) in THF and of [Cu-II(TPA(MeO))(O-2(-))](+) in both THF and EtCN are found to be initiated from the [Cu-I(TPAR)]+ species, that is, the Cu complex possessing an empty coordination site. In contrast, the formation of [Cu-II(TPA(H))(O-2(-))](+) in EtCN is found to be initiated from the [Cu-I(TPA(H))(EtCN)](+) species, that is, one solvent molecule being coordinated to Cui. In general, good agreement is found between theoretical and experimental results. The high accuracy of the B3LYP functional in reproducing experimental thermodynamic data for the present type of transition metal complexes is demonstrated by the fact that the differences between measured and computed thermodynamic parameters (Delta G degrees, Delta H degrees, and -T Delta S degrees, in most cases are less than 2.0 kcal mol(-1). An attempt was made to investigate the kinetics of the formation of [Cu-II(TPA(H))(O-2(-))](+) in THF and EtCN. Computed free energies of activation, Delta G(double dagger), are in good agreement with experimental results. However, an analysis of the partitioning of the free energy barriers in enthalpic and entropic contributions indicates that the computationally studied reaction pathway might differ from the one observed experimentally.