Exploring Metal Complexes: Synthesis, Spectral Characterization, Molecular Docking, and Biological Evaluation Studies of a Schiff Base Derived From N′-((2-Hydroxyphenyl)(phenyl)methylene)-4-methylbenzohydrazide

The Schiff base ligand (HL), N '-((2-hydroxyphenyl)(phenyl)methylene)-4-methylbenzohydrazide, was synthesized via the condensation reaction of (2-hydroxyphenyl)(phenyl) methanone and 4-methylbenzohydrazide in methanol. Reacting HL with metal salts of Cu2+ and La3+ in a 2:1-M ratio yielded metal complexes of Cu2+ and La3+, denoted as ML2 (M = Cu) and ML2Cl (M = La). The obtained metal complexes were further subjected to the following characterization techniques: elemental analysis, conductivity, magnetic susceptibility, powder X-ray diffraction, FTIR, NMR, TGA, and electronic spectral studies. The tridentate nature of HL was validated by FTIR and NMR investigations. Spectroscopic data suggested an octahedral structure for the complexes, which was further supported by electronic spectral analysis and magnetic susceptibility measurements. Powder X-ray diffraction revealed their crystalline nature, whereas thermal analysis indicated sequential decomposition of water, anions, and ligand molecules. An octahedral shape was confirmed by the axial symmetry of the ML2 ESR spectra, which showed g(||) > g(perpendicular to) > 2.0023. Studies on antibacterial activity against B. subtilis, E. coli, and E. faecalis showed that HL exhibited strong activity against E. faecalis and B. subtilis but lower efficacy against E. coli. Although ML2Cl showed maximum activity against B. subtilis and E. faecalis, ML2 was most effective against B. subtilis and E. faecalis. Molecular docking experiments confirmed strong ligand-protein binding by evaluating binding interactions, energy profiles, and molecular distances. ML2 demonstrated the most stable interaction with the lowest binding energy, suggesting its enhanced biological activity compared to ML2Cl. The DFT experiments confirmed the optimized structures, and their energy levels including HOMO, LUMO, MESP, and MESP bar, as well as global reactivity parameters.