SYNTHESIS, SPECTROSCOPIC CHARACTERIZATION AND ANTIMICROBIAL EVALUATION OF QUERCETIN AND 2-METHYLIMIDAZOLE MIXED-LIGAND COBALT(II) AND NICKEL(II) COMPLEXES

Abstract

Two new mixed-ligand complexes, [Co(Que)₂(2-MeIm)₂] and [Ni(Que)₂(2-MeIm)₂], were synthesized and characterized by elemental analysis, FTIR, UV-Vis, TGA, magnetic susceptibility, and molar conductance measurements. Quercetin coordinates as a dianionic bidentate O,O-donor, while 2-methylimidazole acts as a neutral monodentate N-donor, yielding anhydrous octahedral geometries (μeff = 4.81 B.M. for Co(II); 3.14 B.M. for Ni(II)). Both complexes exhibited markedly enhanced antimicrobial activity against Gram-positive (S. aureus), Gram-negative (E. coli, K. pneumoniae, P. aeruginosa), and fungal (A. niger) strains compared to free ligands, with zones of inhibition reaching 17–22 mm at 200 mg/mL (vs. 8–14 mm for ligands). The results validate the beneficial role of metal coordination in improving the lipophilicity and biological performance of quercetin-based systems.