Three Zn(II)/Cd(II) complexes constructed by pyridine Schiff base ligands: crystal structures, spectral properties, and Hirshfeld surface analysis

Three pyridyl Schiff base complexes (1–3) were produced through the reactions of zinc(II) or cadmium(II) ions as coordination centers with the rigid N2 ligands. The above ligands were synthesized via a reflux method by condensing pyridine aldehydes (2-pyridinecarboxaldehyde, 6-methoxypyridine-2-carbaldehyde, 8-quinolinecarbaldehyde) and anilines (3-methoxy-4-methylaniline, 2-phenoxyaniline). The structures and morphologies of these three complexes were characterized by X-ray single-crystal diffraction, infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy, and SEM–EDX. X-ray diffraction revealed that the central metals in all three complexes are tetrahedrally coordinated with a distorted tetrahedral geometry, and their supramolecular structures were illustrated. Theoretical calculations, including Hirshfeld surface analysis, energy frameworks, and energy level distributions, were performed to quantitatively analyze intermolecular interactions and electronic configurations. Fluorescence emission spectra were measured under an excitation wavelength of 360 nm, revealing maximum emission peaks at 508.6, 503.8, and 551.2 nm for the three complexes, respectively, which demonstrates the influence of different ligand structures on the fluorescence properties of the complexes.