Synthesis, characterization and antimicrobial studies of Fe(II), Cu(II) and Cr(II) complexes of (E)-2-hydroxy-5-nitro-N-ethylbenzylideneamine

Abstract

The escalating problem of antimicrobial resistance has renewed interest in metal coordinated curative agents, particularly Schiff base transition metal complexes, which combine structural versatility with promising biological activity. In this study, a Schiff base ligand, (E)-2-hydroxy-5-nitro-N-ethylbenzylideneamine, was prepared through condensation of 2-hydroxy-5-nitrobenzaldehyde with aminoethane in refluxing ethanol, and then reacted with Fe(II), Cu(II), and Cr(II) salts in a 2:1 molar ratio to yield their corresponding metal complexes. The synthesized ligand and complexes were characterized by Fourier-transform infrared (FT-IR) spectroscopy, magnetic susceptibility measurements, melting point determination, and solubility tests. FT-IR data confirmed Schiff base formation via the C=N stretching band at 1565 cm⁻¹ and established metal coordination through characteristic M–N and M–O vibrations in the complexes, pointing to bidentate coordination through the imine nitrogen and phenolic oxygen donor atoms. Magnetic moment values of ~5.9 B.M. for Fe(II), ~4.9 B.M. for Cr(II), and ~1.9 B.M. for Cu(II) were recorded, consistent with high-spin octahedral geometry for Fe(II) and Cr(II), and square planar or distorted tetrahedral geometry for Cu(II). Antimicrobial screening against Aspergillus niger and Salmonella spp. using the agar well diffusion method revealed that all complexes outperformed the free ligand. The Fe(II) and Cu(II) complexes each recorded a maximum inhibition zone of 24 mm against Salmonella spp., while the Cr(II) complex achieved 22 mm against both test organisms at 1000 μg/mL. The improved bioactivity is ascribed to chelation effects that raise lipophilicity and facilitate penetration of microbial membranes. These findings indicate that the synthesized complexes hold real promise as candidates for novel antimicrobial agents.