Zinc(II) complexes of salicylaldehyde-based ligands: synthesis, structural exploration, DFT, and biological evaluation

In the present study, octahedral complexes of Zinc(II) metal of the type [Zn(L¹⁻⁵)(H₂O)₃] (6–10) were prepared from ligands [H₂L¹⁻⁵] (1–5). Ligands were prepared by the condensation of salicylaldehyde derivatives with 6-amino-2,4-dichloro-3-methylphenol under refluxing in 1:1 composition. The compounds were investigated using various spectral and physicochemical techniques, including NMR, mass spectrometry, IR spectroscopy, powder XRD, melting point determination, and molar conductance measurements. The results obtained from these techniques established the tridentate behaviour of the ligands, which coordinate to the Zinc(II) metal ion through the deprotonated oxygen of the hydroxyl group and the azomethine nitrogen. DFT calculations of synthesized compounds were executed using B3LYP/LANL2DZ level of theory as implemented in Gaussian 16 without imposing any symmetry restrictions. The synthesized compounds were tested for their antimicrobial action using the serial dilution method, and the biological studies divulged that chelation adds to the antimicrobial activity of the compounds. Zinc(II) complex 9 was found to be the most potent against the tested microbes among the studied compounds. This observation depicts that these complexes may evident as remarkable active components in biomedical research and can be explored further for in-vivo studies.