Exploration of the mutual effects between cation–π and intramolecular hydrogen bond interactions in the different complexes of mesalazine with metal cations of alkali and alkaline-earth: a DFT study

In the present study, the density functional theory (DFT) method has been used to investigate the interplay effects between cation–π and intramolecular hydrogen bond (IMHB) interactions in the complexes formed by the mesalazine and metal cations (Li+, Na+, K+, Be2+, Mg2+ and Ca2+). The topological properties and the charge transfer values are estimated using the atoms in molecules (AIM) and natural bond orbital (NBO) analyses, respectively. The results indicate that the coupling simultaneously decreases the IMHB strength and increases the cation–π interaction. Our data also show that the strength of cation–π interactions enhances with increasing the charge-to-radius ratio of the cations, while the reverse results are observed for the IMHB interactions. Finally, the frontier molecular orbitals are applied to evaluate the conceptual DFT parameters such as energy gap, chemical hardness and electronic chemical potential of the complexes.