Exploring N-Benzylidene-Isonicotinohydrazide Schiff Base and Its Ni(II), Cu(II), and Co(II) Complexes: Synthesis, Spectroscopic, Computational, and Molecular Docking Insights with the COVID-19 Protein Receptor

Abstract

A Schiff base ligand (L), N-benzylidene-isonicotinohydrazide (C₁₃H₁₁N₃O), was synthesized via the condensation of benzaldehyde and isoniazid in an ethanolic medium. The ligand was characterized by FT-IR, ¹HNMR, UV-Vis, ESI-MS, and elemental analysis, confirming its successful formation. Metal complexes of Ni(II), Co(II), and Cu(II) were synthesized by reacting the ligand with corresponding metal acetate salts under reflux conditions. Spectroscopic data revealed that coordination occurred through the azomethine nitrogen and carbonyl oxygen, as evidenced by shifts in characteristic IR bands. Electronic spectra and magnetic moment studies indicated that all three complexes adopted a distorted square planar geometry. Molar conductivity measurements confirmed their non-electrolytic nature. Density functional theory (DFT) calculations provided insight into the optimized geometries and electronic properties of the ligand and complexes, with HOMO-LUMO energy gap analysis suggesting enhanced reactivity upon complexation. Molecular docking of the free ligand and its metal complexes was performed against the SARS-CoV-2 main protease (PDB ID: 6XBH), yielding promising results.