Coordination Pattern of Two Imidazole-Chalcone Hybrid Ligands and Reactivity Analysis of TheirTransition Metal (II) Complexes by Density Functional Theory

AbstractA DFT study of the coordination behavior of two imidazole-based chalcone ligands: 2-[1-(3-(1H-imidazol-1-yl)propylimino)-3-(phenylallyl)]phenol and 2-[1-(3-(1H-imidazol-1-yl)propylimino)-3-4-nitrophenylallyl]phenol (herein dubbed HL1 and HL2 respec-tively) toward Co2+, Cu2+, Ni2+ and Zn2+ ions, and reactivity analysis of the resulting complexes is reported. The dispersion-corrected DFT (DFT-D3), conceptual DFT, quantum theory of atoms-in-molecules (QTAIM), molecular electrostatic potential (MEP) and the non-covalent interaction (NCI) index approaches were used. Both HL1 and HL2 are found to utilize variable imidazole ring-based donor sites to coordinate with metal ions, contrary to some earlier studies asserting that these species only act as tridentate ligands bearing a unique set of donor atoms toward metal (II) ions. Interestingly, the Ni (II) complexes of both ligands and the Zn (II) complex of HL1 turned out to be organometallic species. Diverse non-covalent intramolecular interactions were elucidated in all compounds, playing key roles in molecular integrity. Our results also showed that HL2 and its complexes are more reactive than their HL1 counterparts, owing to their higher electrophilicity indices. Moreover, whereas the metal ion center (except the Zn(II) ion) in all complexes studied are liable to attack by nucleophiles, the car-bon and oxygen atoms of the phenolic moiety alongside the chloride ligands, are most favorable sites for electrophilic attack.