B3LYP density functional theory calculations were performed to quantify the binding affinities of six divalent first-row transition metals (Cr 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , and Cu 2+ ) for three well-known macrocyclic ligands (porphine, corrin, and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane [TMC]). Our calculations show that, as expected from the neutral, monoanionic, and dianionic characters of the TMC, corrin, and porphine ligands, respectively, the binding energy increases in the order TMC<corrin<porphine. This is because a more anionic ligand gives rise to greater electrostatic stabilization upon interaction with the metal cations. For all ligands, the binding energy increases in the order Mn 2+ <Cr 2+ ∼Fe 2+ <Co 2+ <Ni 2+ <Cu 2+ . Single occupation of all five d orbitals in the high-spin Mn 2+ complexes does not afford large stabilization due to either ligand-to-metal or metal-to-ligand charge transfer, thereby resulting in the minimum binding energies observed for Mn 2+ among the six different metal ions considered.