Explicit Solvent Effect on Cation-π Interactions: A First Principle Investigation

Sequential attachment of water molecules to cation-pi (Li+-benzene, K+-benzene, and Mg2+-benzene) systems reveals that the cation-pi interaction strength varies in opposite direction depending on the site of solvation of the cation-pi system. Solvation of the metal ion decreases its interaction energy with the pi system, while the solvation of the pi system increases its interaction energy with the metal ion. The cation binding to benzene clearly enhances the ability of aromatic protons to participate in hydrogen bonding with water molecules. The distance between the metal ion and centroid of the benzene inherently varies with the position of water molecules in the vicinity of cation-pi complex. Reduced variational space (RVS) analysis on bare and solvated cation-pi complexes indicates that the major contributions to the total interaction energy are coming from the polarization and charge transfer energy terms of the pi system. Topological atoms in molecules (AIM) analysis is performed to evaluate the nature of the cation-pi interaction. Good correlations are observed between interaction energies and charge density at the cage critical point of the cation-pi complexes.