Synthesis, Spectroscopic Characterization, And Antimicrobial Evaluation Of A Novel Hydrazone Ligand And Its Transition Metal Complexes

A novel hydrazone ligand, (E)-N'-(4-fluoro-2-hydroxybenzylidene)-4-methoxybenzohydrazide, was synthesized by the condensation of 4-methoxybenzohydrazide with 4-fluoro-2-hydroxybenzaldehyde. This Schiff base ligand was further utilized to prepare a series of six transition metal complexes using Ni(II), Co(II), Cu(II), Pd(II), Mn(II), and Fe(II) ions. The structural elucidation of the ligand and its metal complexes was accomplished through a combination of analytical and spectroscopic techniques, including elemental analysis (CHN), Fourier-transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, proton and carbon nuclear magnetic resonance (¹H & ¹³C NMR), molar conductivity measurements, and magnetic susceptibility studies. The data confirm the ligand coordinates to the metal ions in a bidentate manner, typically via the azomethine nitrogen and phenolic oxygen atoms, forming complexes with proposed octahedral or square planar geometries. The synthesized compounds were evaluated for their in vitro antibacterial (against Gram-positive and Gram-negative strains) and antifungal activities. The results demonstrated that the metal complexes exhibited significantly enhanced antimicrobial potency compared to the free ligand, a phenomenon attributed to the chelation effect, which reduces polarity and enhances membrane permeability. Notably, the Cu(II) and Pd(II) complexes displayed the most promising broad-spectrum activity, suggesting their potential as leads for developing new antimicrobial agents.