Spectroscopic and Quantum Chemical Studies of some Novel Mixed-Ligand Complexes of Fe(II) and Cu(II) and Investigation of their Antimicrobial Actvities

This study reports the synthesis, spectral characterization, quantum chemical studies, and biological activities of homo- and heteroleptic Fe(II) and Cu(II) complexes derived from 2-(4-bromobenzylidene)-aminophenol (L1). The ligand was prepared via a condensation reaction and characterized using FT-IR, UV-Visible spectroscopy, CHNS analysis, ¹H NMR, and ¹³C NMR. The complexes were synthesized in a 1:1 metal-to-ligand (M:L) ratio and characterized by melting point, UV-Vis, FT-IR, molar conductivity, and magnetic susceptibility measurements. FT-IR data confirmed bidentate coordination through oxygen and amide atoms, forming neutral complexes. Magnetic moments and electronic spectra support octahedral geometries for both Fe(II) and Cu(II) complexes. Molar conductance measurements indicated nonelectrolyte behavior in methanol. Key parameters from DFT (Density Functional Theory) calculations at the B3LYP/6–311++G(d,p) level are also reported. The Gauss View molecule imaging program was utilized to visualize the input data files as well as determine the HOMO–LUMO energies. The complexes exhibited notable antibacterial activity against both Salmonella and Staphylococcus. However, complexes C3 and C4 showed reduced activity against both bacteria, indicating that the homoleptic complexes of this ligand possess greater antibacterial efficacy. The ligand (L1) itself showed negligible activity against either bacterium. These results highlight the significant role of metal coordination in influencing biological activity.