Crystallographic, antibacterial, and in silico studies of Ni(II) and Cu(II) Schiff base complexes derived from 2-acetylpyridine

Two Schiff base complexes, namely Ni(L1)(NCS)₂ (2) and Cu(L1)(NCS).SCN (3) (where L1 = [N,N′-bis(1-(pyridin-2-yl)ethylidene)propane-1,3-diamine]) have been synthesized through condensation of L1 with metal acetates using a 2:1 ratio, in the presence of sodium thiocyanate, NaSCN. The complexes were characterized by elemental analysis, IR, UV–Vis, magnetic moment, as well as molar conductivity. The crystal structures of complexes 2 and 3 were successfully characterized by single crystal X-ray crystallography. The Ni atom in 2 is in a distorted octahedral environment while the Cu atom in 3 is in an environment lying between square pyramidal and trigonal bipyramidal; in both complexes the NCS⁻ is acting as terminal ligand. Both complexes were paramagnetic. Density functional theory (DFT) calculations were performed at the B3LYP/LanL2DZ level of theory to explore the quantum chemical properties of the ligand and its metal complexes. The calculations proceed with the 3D crystal structure characterization of the complexes, and the correlation between theoretical and experimental results were discussed. NBO analysis was used to determine the strength of donor–acceptor interactions in metal complexes. The antibacterial activity of the synthesized compounds was screened in vitro against two strains of Gram-positive (Staphylococcus (S.) aureus, Staphylococcus (S.) haemolyticus) and three strains of Gram-negative (Shigella (S.) sonnei, Salmonella (S.) typhimurium, Enterobacter (E.) aerogenes) bacteria, and showed no activity. The binding affinity of the synthesized complexes in the binding site of S. aureus tyrosyl-tRNA was investigated using molecular docking, and the outcomes showed a good agreement with experimental results.