Synthesis and characterization of Schiff bases derived from cephalexin and their theoretical study in the formation of coordination complexes with metal ions

Ligand was prepared for Schiff base derived from cephalexin and cinnamaldehyde, and its transition metal complexes with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). The ligand was prepared via condensation under reflux conditions in ethanol using glacial acetic acid as catalyst. Complexes were obtained in 1:1 metal-to-ligand ratio and characterized by elemental analysis, UV–Vis, FTIR, NMR, mass spectrometry, magnetic susceptibility, and molar conductivity. Spectroscopic results indicate bidentate coordination through azomethine nitrogen and carbonyl oxygen atoms, forming octahedral geometries for most complexes, while Co(II) exhibited tetrahedral geometry. Antimicrobial screening against Staphylococcus aureus, Escherichia coli, and Candida albicans revealed enhanced activity of metal complexes compared to the free ligand, attributed to chelation and increased lipophilicity. Density functional theory (DFT) calculations using B3LYP and LANL2DZ/6-31+G(d,p) basis sets provided optimized geometries and electronic properties. HOMO–LUMO energy gaps indicated higher stability of the ligand relative to its complexes, while quantum descriptors supported their reactivity trends. Molecular electrostatic potential analysis identified electrophilic and nucleophilic sites responsible for biological interactions. Overall, metal coordination significantly improved biological activity and altered electronic structure, suggesting potential pharmaceutical applications of these Schiff base metal complexes in coordination chemistry and drug design research applications fields studies. KEY WORDS: Antibacterial, Cephalexin, Schiff-base, Transition metal complexes, Cinnamaldehyde Bull. Chem. Soc. Ethiop. 2026, 40(7), 1433-1445. DOI: https://dx.doi.org/10.4314/bcse.v40i7.4