Incremental Binding Free Energies in Mg2+ Complexes: A DFT Study

Abstract

Density functional theory has been employed to evaluate the incremental binding energies, enthalpies, entropies, and free energies for the reactions of Mg2+ with water, methanol, formamide, and formate. The B3LYP/6-31+G* calculations on the Mg2+ complexes show that the metal ion can accommodate no more than three negatively charged formates. For the neutral-ligand complexes, magnesium prefers to bind to methanol and formamide rather than water when the number of ligands is less than four, but it prefers water to methanol and formamide for complexes with five or six ligands. These results have been rationalized in terms of steric crowding of the ligands around the metal ion and charge transfer from the ligand(s) to Mg2+. These two factors result in attenuation of the Mg−O bond distance and, hence, reduction in the electrostatic and polarization energies, which dominate the incremental binding energy. An empirical scheme, employing the incremental binding energies for Mg2+−single-type-ligand complexes, has been developed to accurately predict the total binding energy of Mg2+−mixed-ligand clusters.