Mechanochemical Synthesis, Characterization, and Antibacterial Evaluation of Ni(II) and Cu(II) Complexes Derived from a Schiff Base Ligand

Metal complexes derived from Schiff bases ligands stand at the forefront of research aiming to develop precise and potent therapeutic agents, owing to their exceptional effectiveness.In this study, naphthaldehyde-derived Schiff base Ligand (HL) was synthesized via a mechanochemical reaction between 2-hydroxy-1-naphthaldehyde and 4-iodoaniline.Subsequently, the ligand was further reacted with Ni(II) and Cu(II) ions using their respective metal salts to obtain homoleptic mononuclear complexes (C1 and C2).The composition of HL, C1, and C2 were determined using 1 H and 13 C NMR, UV-Vis, FTIR, CHN, and HRMS analyses.The results of these analyses revealed the ligand acted as bidentate mono-negative and chelate the metal ions through oxygen and nitrogen atoms of phenolate and azomethine moieties.Furthermore, the antibacterial potential of HL, C1, and C2 was assessed using in vitro disc diffusion techniques against selected bacteria, including Gram-positive Staphylococcus aureus and Streptococcus pyogenes, and Gram-negative Escherichia coli and Klebsiella pneumoniae, at concentration ranges of 10, 20, and 30 g/mL, in comparison to the positive control (ciprofloxacin).The antibacterial study demonstrated concentration-dependent activity, with the complexes surpassing the ligand in effectiveness against all tested bacteria at all concentrations.Notably, the Cu(II) complex, C2, exhibited superior activity compared to the Ni(II) complex, C1.C2 recorded higher zone of inhibition of 30.00.05 mm and 28.00.05mm on S. aureus and E. coli, respectively.These findings establish a robust foundation for further refining the lead compound to unlock its therapeutic potential in addressing the escalating challenge of bacterial resistance to antibiotics.