Computational investigation of tetraamine–derived Schiff base ligands and their Cu(II) and Zn(II) complexes

Abstract

The theoretical quantum chemical methods were employed to design tetraamine–based Schiff bases and investigate their interaction with Cu²⁺ and Zn²⁺ ions. Three ligands were designed from the possible condensation product of [1,1′–biphenyl]–3,4,3′,4′–tetraamine with thiophene–2–carbaldehyde (L1), 2–furaldehyde (L2), and 1H–indole–3–carbaldehyde (L3). The geometric optimizations, in conjunction with interaction analyses, elucidated the pronounced binding affinity of the ligands for metal ions, with Cu(II) complexes displaying a significantly greater affinity in comparison to their Zn(II) analogs. Molecular orbital evaluations suggested robust metal–ligand interactions, whereby Cu(II) complexes demonstrated enhanced stability in contrast to Zn(II) complexes, which indicated increased reactivity, thereby implying a potential for augmented biological efficacy. Electrostatic potential (ESP) mapping further corroborated the binding affinities of the complexes by illustrating the regions of electrostatic interactions. Furthermore, non-covalent interaction (NCI) analysis provided comprehensive insights into the nature and strength of the forces governing metal–ligand binding, revealing that the stronger interactions in Cu(II) complexes account for their enhanced stability. These theoretical insights provide significant direction for prospective experimental investigations of Schiff base metal complexes in the realms of biomedical and catalytic applications.