Synthesis, Spectroscopic Characterization, and Thermal Behavior of Co(II), Fe(III), and Mn(III) Complexes Derived from a Novel Schiff Base Ligand

This study presents the synthesis, spectroscopic characterization, and thermal analysis of novel Co(II), Fe(III), and Mn(III) complexes derived from a heterocyclic Schiff base ligand. The ligand, 2-(((4-((4-aminophenyl)sulfonyl)phenyl)imino)methyl)-6-methoxyphenol, was synthesized via the condensation of o-vanillin and dapsone in ethanolic medium under reflux conditions. The resulting Schiff base ligand was subsequently complexed with Co(II), Fe(III), and Mn(III) salts to form the corresponding metal complexes. These compounds were thoroughly characterized using elemental analysis, molar conductance measurements, and various spectroscopic techniques, including infrared (IR), ultraviolet-visible (UV-Vis), mass spectrometry, and ¹H nuclear magnetic resonance (NMR) spectroscopy. The IR spectra confirmed the bidentate coordination of the ligand to the metal centers through the phenolic oxygen and azomethine nitrogen atoms. Electronic spectral data suggested a square planar geometry for the Co(II) complex and octahedral geometries for the Fe(III) and Mn(III) complexes. Thermogravimetric analysis (TGA) was employed to investigate the thermal stability and decomposition patterns of the complexes under a nitrogen atmosphere at a heating rate of 10°C min⁻¹. The thermodynamic parameters, including activation energy (Eₐ), entropy change (ΔS), and free energy change (ΔF), were calculated using the Freeman-Carroll and Sharp-Wentworth methods. The results indicated that the Co(II) complex exhibited the highest thermal stability, followed by Mn(III) and Fe(III). The findings contribute to the understanding of Schiff base metal complexes and their potential applications in coordination chemistry, catalysis, and material science.