Nickel(II) and Copper(II) Complexes of Ampicillin-Based Schiff Base Ligands: Synthesis, Characterization, and Antimicrobial Evaluation

Matthew B. Mshelia, Mohammed B. Fugu, Ibrahim Waziri*, Grema A. Mala, Abubakar A. Ahmed, Ibrahim M. Wakil and Naomi P. Ndahi
Department of Pure and Applied Chemistry, University of Maiduguri, P.M.B. 1069, Maiduguri,
Nigeria

*Corresponding author’s Email: waziriibrahim@unimaid.edu.ng, doi.org/10.55639/607.02010083


ABSTRACT

Two Schiff base ligands (HL1 and HL2) were synthesized through the condensation of ampicillin with 2-nitrobenzaldehyde and 2-hydroxy-1 naphthaldehyde, respectively, and subsequently complexed with Nickel(II) and Copper(II) ions to afford four new metal complexes (NiL1, CuL1, NiL2, and CuL2). The ligands and complexes were characterized using melting point determination, solubility tests, FTIR, UV–Visible spectroscopy, mass spectrometry, elemental analysis, and conductivity measurements. Spectroscopic data confirmed coordination through the azomethine nitrogen and the carbonyl oxygen of the amide group, with characteristic shifts in ν(C=N), ν(C=O), and ν(C–O) bands supporting tridentate chelation. Electronic spectra revealed ligand-cantered transitions for the free ligands and the appearance of d–d/LMCT bands in the metal complexes, suggesting octahedral coordination environments. The antimicrobial activities of the compounds were assessed against selected Gram-positive and Gram-negative bacteria (S. aureus, S. pyogenes, E. coli, S. typhi) and the fungal strain C. albicans. The complexes exhibited markedly higher activity than the free ligands, with CuL2 and NiL1 showing the broadest and most potent inhibition profiles. Structure activity analysis indicates that increased π-conjugation (HL2-series) and the borderline Lewis acidity of Cu enhance biological potency. Overall, these results demonstrate the potential of ampicillin-derived Schiff base complexes as promising scaffolds for the development of new antimicrobial agents

Keywords:
Schiff base ligands,
Metal complexes,
Ampicillin derivatives,
Antimicrobial activity.

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