Synthesis, Structural, DFT, Molecular Docking, and Biological Evaluation of New Fe(III) and Ni(II) Mixed-Ligand Complexes Based on Imidazoleacetic Acid and Benzimidazole

This study investigates the synthesis, characterization, and biological evaluation of novel metal complexes formed by Imidazoleacetic acid (IA) and an Benzimidazole-based ligand (BZ) with Fe(III) and Ni(II) ions. A comprehensive array of characterization methods, including elemental analysis, IR spectroscopy, magnetic moment measurements, electronic spectra, mass spectrometry, thermal analysis, and DFT calculations, confirmed a 1:1:1 (M:IA:BZ) stoichiometry. Both FeIABZ and NiIABZ complexes exhibited octahedral geometry, with one and two water molecules coordinated to the Fe(III) and Ni(II) centers, respectively. PXRD analysis of FeIABZ and NiIABZ revealed predominantly amorphous structures, with NiIABZ showing relatively higher crystallinity and larger nanocrystallite size (∼21.4 nm) compared to FeIABZ (∼17.0 nm). DFT calculations revealed that metal coordination resulted in a decrease in the energy gap and an increase in the complexes' softness, enhancing their predicted biological activity. The FeIABZ and NiIABZ complexes displayed significant antimicrobial activity, with both demonstrating superior efficacy against Gram-positive and Gram-negative bacteria compared to their free ligands. Their performance was comparable to the standard antibiotic Chloramphenicol. Moreover, these complexes exhibited notable antifungal activity against Candida albicans and Aspergillus niger. Minimal inhibitory concentration (MIC) values further validate the enhanced antimicrobial properties of the metal complexes. In addition to these effects, the complexes showed promising anti-inflammatory activity, with the NiIABZ demonstrating the highest potency, approaching the IC₅₀ of the standard drug. Molecular docking studies against DNA gyrase B indicated that the NiIABZ exhibited the highest binding affinity, forming multiple hydrogen bonds with key amino acid residues, suggesting a strong antibacterial potential.