Design and Study of Novel Ni(II), Co(II), and Cu(II) Complexes With Hydrazone Ligand: Structural Characterization, DFT Analysis, and Assessment of Cytotoxic and Antioxidant Activities Supported by Molecular Docking Studies

A series of Ni(II), Co(II), and Cu(II) complexes with N ′ 1 , N ′ 2 ‐bis((E)‐1‐(pyridin‐2‐yl)ethylidene)oxalohydrazide (H 2 OHS) were synthesized and characterized using FT‐IR, UV–Vis, NMR, ESR, and thermal analyses. Density functional theory (DFT) calculations confirmed structural stability, electronic properties, HOMO–LUMO gaps, and charge‐transfer characteristics, supported by reduced density gradient (RDG) and noncovalent interaction (NCI) analyses. The complexes exhibited distinct geometries—octahedral for Ni(II), tetrahedral for Co(II), and square planar for Cu(II). Thermal degradation studies using Coats–Redfern and Horowitz–Metzger methods revealed high thermal stability. Biological evaluations demonstrated strong antimicrobial activity against Candida albicans , Staphylococcus aureus , E s cherichia coli , significant antioxidant potential (DPPH and ABTS), and potent cytotoxic effects against HepG2, MCF‐7, HCT116, and A549 cancer cell lines. Molecular docking studies confirmed strong ligand–receptor interactions, correlating with biological efficacy. These findings highlight the complexes' promising potential as multifunctional therapeutic agents in antimicrobial, antioxidant, and anticancer applications.