From Ligand to Bioactive Complex: Crystal Structure of ligand and DPPH Radical-Scavenging Enhancement in an Iron(III) Hydrazone Schiff Base

Abstract

A new HYDRAZONE SCHIFF BASE, N’-[(1E)-1-(5-bromo-2-hydroxyphenyl)Ethylidene]Pyridine-3- Carbohydrazide (H2L), was synthesized from 5-bromo-2-Hydroxyacetophenone and Nicotinic acid Hydrazide, and its Iron(III) complex was prepared. The ligand was characterized by single-crystal X-ray diffraction, ¹H/¹³C NMR, and both compounds were studied by IR, UV-Vis, and molar conductivity measurements. Spectroscopic data indicate that, following amide-iminol tautomerization, the ligand coordinates through the iminol oxygen, azomethine nitrogen, and pyridine nitrogen atoms, giving an octahedral iron(III) center that is non-electrolytic and stable in DMF. DPPH assays showed enhanced radical-scavenging activity for the complex relative to the free ligand (IC50 = 2.6 vs 4.8 mg mL⁻¹), though both remained less active than ascorbic acid. The compounds also displayed selective antibacterial activity, favoring Gram-positive strains (S. aureus, E. faecalis) over E. coli. These results highlight the role of metal coordination in enhancing the bioactivity of hydrazone Schiff bases and support iron(III) complexes as promising candidates for new bioactive coordination compounds.