Synthesis, characterization, DFT optimization, and antimicrobial activities of Co(III) and Cd(II) complexes derived from pyridyl Schiff base ligand <i>N</i>-2-(6-methylpyridyl)-2-hydroxy-1-naphthaldimine

In the present investigation, two metal complexes of Co(III) and Cd(II) were readily synthesized from pyridyl Schiff base ligand <i>N</i>-2-(6-methylpyridyl)-2-hydroxy-1-naphthaldimine in methanol and characterized by FT-IR,¹H NMR, UV-Vis, and Mass spectroscopic methods. The spectral data indicated the coordination of metal ions by the pyridyl Schiff base ligand in a tridentate N, N, O mode. The complexes were assumed to adopt octahedral geometry. In complex <b>2</b>, an uncoordinated Cl^- anion is present, thereby balancing the charge of the complex. The electronic properties of Co(III) complex <b>2</b> and Cd(II) complex <b>3</b> have also been demonstrated by theoretical studies based on the DFT optimization. The reduced density gradient (RDG) plot reveals the strong binding with both metals. The antimicrobial activities of the pyridyl Schiff base ligand <b>1</b> and synthesized Co(III) complex <b>2</b> and Cd(II) complex <b>3</b> were studied against gram-negative bacteria. The <i>in vitro</i> antimicrobial study of Schiff base ligand <b>1</b>, Co(III) complex <b>2,</b> and Cd(II) complex <b>3</b> in <i>Escherichia coli</i> (ATCC 25922), <i>Salmonella typhi</i> (ATCC 6539), and <i>Shigella sonnei</i> (ATCC 25931) bacterial strains were investigated by performing the Kirby-Bauer disk-diffusion and well diffusion assays. Results indicated that the Cd(II) complex <b>3</b> shows better antibacterial activity against <i>Salmonella typhi</i>.