Spectroscopic elucidation and enhanced antibacterial activity of benzimidazole–thioether complexes with some first-row transition metals

Abstract

This study reports the synthesis, characterization, and biological evaluation of a new benzimidazole derivative, 2-((benzylthio)methyl)-1H-benzimidazole (L), and its coordination complexes with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). The ligand was synthesized in two steps, while its metal complexes were prepared in 1:1 and 2:1 ligand-to-metal ratios. Characterization by FT-IR, UV–Vis, NMR, and magnetic susceptibility measurements confirmed that the coordination geometry varies with the ligand-to-metal ratio. All 1:1 (L: M) metal complexes adopt tetrahedral structures. Conversely, when a 2:1 (L:M) ratio is employed, Mn(II), Co(II), and Ni(II) ions form octahedrally coordinated complexes, whereas Cu(II) and Zn(II) ions favor square-planar coordination. The antimicrobial activity of the synthesized compounds was tested against Staphylococcus aureus and Escherichia coli. The free ligand exhibited weak antibacterial activity, whereas its metal complexes—particularly Cu(II)—showed markedly enhanced inhibition zones. KEY WORDS: Benzimidazole, Coordination chemistry, Antimicrobial activity, NMR, Copper complexes Bull. Chem. Soc. Ethiop. 2026, 40(11), 2459-2472                              DOI: https://dx.doi.org/10.4314/bcse.v40i11.13