Synthesis, characterization, computational and biological investigation of Co(II), Ni(II) and Cu(II) complexes with 2-hydroxy-1-naphthaldehyde derived Schiff base ligand

Abstract A Schiff base ligand L 1 was synthesized via the condensation reaction between from 2-hydroxy-1-naphthaldehyde and 4-methoxyaniline. This Schiff base was employed for the preparation of metal complexes of type [M(L)2] in a 1:2 metal-to-ligand ratio (where M = Co(II) 2, Ni(II) 3 and Cu(II) 4. The ligand 1 and complexes 2–4 were characterized using elemental analysis and spectroscopic methods such FT-IR, UV-Vis, ¹H NMR, and mass spectrometry. The DFT methods at 6-31G(d, p) basis set and B3LYP function were employed for computational calculation. The computational calculations include geometry optimization, HOMO–LUMO analysis, molecular electrostatic potential mapping to get detailed insight into electronic structure and charge-transfer behaviour. The spectroscopic and computational calculation suggest mono-functional bidentate nature of ligand with coordination through azomethine nitrogen and deprotonated phenolic oxygen atoms. A distorted square planar geometry is tentatively proposed around metal ion in complexes. Nonlinear optical properties investigation revealed significant enhancement in polarizability and hyperpolarizability upon metal coordination. In-vitro antibacterial activities measured against E. coli, P. aeruginosa, and S. aureus using agar well diffusion method. Antibacterial activity measurement demonstrated superior inhibition zones for the metal complexes compared to the free ligand, with the Cu (II) complex showing the highest efficacy. Graphical Abstract