DFT studies of the interactions between the [Ca(H2O)5]2+ cation and monofunctional oxo, aza, sulfur and phosphorous ligands

Abstract

Quantum chemical calculations using the B3LYP/6-311++G(d,p) method were performed to determine the affinity of the [Ca(H2O)5]2+ cation for several monofunctional ligands. Four sets of ligands were studied: with oxygen binding atom (phosphoryl, amide, carboxylic acid, ketone, aldehyde, ether, alcohol, enol), nitrogen (imine, thiocyanic acid, nitrile, amine and ammonia), sulfur (thiocarbonyl, thioether and thioalcohol) and phosphorous (phosphine) binding atom. Compounds that bind via a double bonded oxygen atom have the strongest metal–ligand interaction, followed by compounds binding via nitrogen, singly bonded oxygen atom, sulfur and phosphine. The ligand with the strongest interaction, phosphine oxide, has an ionic resonance form with a negative charge on the binding oxygen atom that highly contributes to the hybrid geometry, what favors the interaction. The Energy Decomposition Analysis (EDA) of the interaction energy between the [Ca(H2O)5]2+ cation and the ligand shows that the electrostatic term is the major component of the interaction and represents at least 43.66% of the total interaction energy. The covalent component represents at least 28.09% of the total interaction energy. Along the set of compounds studied, the electrostatic component varies more than twice the covalent term. The repulsive and the dispersion components are roughly constant in all complexes.