Coordination versatility and enhanced bioactivity of Co2+, Cu2+ and Cd2+ complexes derived from pyridyl Schiff base: structural, electronic and electrochemical insights

A Schiff base ligand, H₂L, was obtained from the condensation of pyridine-2,6-dicarbohydrazide and cinnamaldehyde and was further complexed with Co²⁺, Cu²⁺, and Cd²⁺ ions. The coordination complexes were then analyzed by normal spectroscopic/microscopic analyses (FT-IR, UV-visible, ¹H-NMR, ¹³C-NMR, ESR, PXRD, EDX, and TEM) and other conventional physicochemical analyses (C.H.N microanalysis, molar conductivity, and elemental analysis, molar conductivity) beside (TG/DTA) thermal analysis. Structural analysis revealed mononuclear octahedral geometries for the Co²⁺ and Cd²⁺ chelates through pincer ONO chelation, while the Cu²⁺ complex showed a ligand-supported dinuclear square planer arrangement via two NO hydrazone scaffolds. Computational studies based on the DFT theory postulated the reactivity and spectral trends for the free ligand and metal chelates. The electrochemical properties for the ligand and its complexes were analyzed using cyclic voltammetry and revealed quasi-reversible/irreversible electrochemical behaviors. Biological analyses confirmed the efficiency of the Schiff base and its metal complexes for antibacterial, antifungal, DPPH-antioxidant, and DNA-binding capabilities and exhibited in-vitro cytotoxicity towards HepG2 and MCF-7 cell lines.