Synthesis, Spectroscopic Characterization, and Antibacterial Activity of Cu[II], Cu[I] and Ag[I] Complexes of 5-methoxy- and 5-difluoromethoxy-2-mercaptobenzimidazoles

Copper [II], copper[I], and silver[I] complexes of 5-methoxy-2-mercaptobenzimidazole [MTZ] and 5-[difluoromethoxy]-2-mercaptobenzimidazole [FMZ] were synthesized and characterized by elemental analysis, infrared and NMR spectroscopy, and magnetic susceptibility measurements. The complexes exhibited thermal stability, melting/decomposing above 340°C, and were readily soluble in polar aprotic solvents such as DMSO and DMF. The analytical and spectral data confirmed 1:1 metal-to-ligand stoichiometries, with coordination occurring through the azomethine nitrogen and thiol sulphur atoms. The magnetic susceptibility data indicated paramagnetic behaviour for Cu[II] and diamagnetism for Cu[I] and Ag[I] complexes. The in vitro antibacterial activity of the complexes was evaluated using the agar well diffusion method against Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Salmonella typhi. Among the synthesized compounds, AgMTZ displayed the highest and broadest antibacterial activity, followed by AgFMZ and CuMTZ, suggesting that metal ion type and ligand substitution significantly influence bioactivity. These findings reveal the potential of methoxy- and difluoromethoxy-substituted benzimidazole–metal complexes as promising antimicrobial agents with tunable activity profiles.