Synthesis, structural characterization, electrochemical, optical, and DFT/TD-DFT investigation of a Cu(II) Schiff base complex

A square-planar copper(II) complex, denoted as [Cu(L)(HNA)]·DMF, was synthesized using the ligands (E)-(5-chloro-2-(((2-hydroxynaphthalen-1-yl)methylene)amino)phenyl)(phenyl)methanone and 2-hydroxy-1-naphthaldehyde. This complex was characterized by FT-IR and UV–Vis spectroscopy, as well as single-crystal X-ray diffraction. It crystallizes in a triclinic system with the space group. The geometric structure, vibrational frequencies, and electronic properties of the complex were calculated using density functional theory (DFT). For the non-metal atoms (C, H, N, O, Cl), the 6-31G + (d) basis set was applied, while for the Cu atom, the effective core potential (SDD) basis set was employed. Time-dependent density functional theory (TD-DFT) calculations were performed to study the nature of the UV–Vis transitions. A fragment-resolved hole–electron analysis was further employed to quantitatively characterize the charge-transfer excitations and distinguish between local and ligand-to-ligand charge-transfer transitions. In general, the theoretical results showed good agreement with the experimental data.