Synthesis, spectroscopic characterization, and thermal evaluation of metronidazole-based transition metal complexes

Abstract

The present study explores the synthesis, spectroscopic characterization, and thermal evaluation of a series of transition and post-transition metal complexes derived from metronidazole. Utilizing metronidazole as a bidentate ligand, coordination complexes were synthesized with metals including vanadium (IV), chromium (III), manganese (II), iron (III), cobalt (II), copper (II), zinc (II), platinum (II), palladium (II), and gold (III). The complexes were obtained through conventional solution-phase reactions and characterized comprehensively using elemental analysis, magnetic susceptibility, UV-Visible spectroscopy, infrared spectroscopy, electron spin resonance, and thermogravimetric analysis. The elemental analysis confirmed the metal-to-ligand stoichiometries, while magnetic measurements provided insight into oxidation states and coordination geometries, revealing structures such as square pyramidal (V), octahedral (Cr, Fe), tetrahedral (Mn, Co, Cu, Zn), and square planar (Pd, Pt). UV-Visible spectra exhibited characteristic d-d transitions and ligand-field absorptions supporting the inferred geometries. IR spectral shifts, particularly in the C=N stretching region, confirmed ligand coordination through the imidazole nitrogen, while the unaltered nitro group vibration indicated its non-involvement in bonding. ESR studies provided further evidence for paramagnetic behavior in Mn (II), Fe (III), and VO (IV) complexes, with calculated g-values consistent with high-spin configurations. Thermogravimetric analysis indicated multistep decomposition patterns, with final residues corresponding to thermally stable metal oxides. Activation energy values derived from Coats-Redfern plots demonstrated varied thermal stabilities across the complexes, with Cr (III), Fe (III), and Co (II) showing superior resistance to thermal degradation. These results not only expand the understanding of metronidazole’s coordination chemistry but also provide a foundational basis for the future development of metallo-drugs with potential antimicrobial or therapeutic applications.