Synthesis, spectroscopic characterization, thermal decomposition and antimicrobial studies of manganese(III), iron(III) and cobalt(III) complexes with Schiff base derived from thiophene-2-carboxaldehyde and 2-aminobenzoic acid

A Schiff base namely N-(2-thiophenyl methylene)-2-aminobenzoic acid (HNTA) has been prepared by condensation of thiophene-2-carboxaldehyde with 2-aminobenzoic acid in 1 : 1 molar ratio. Manganese(III) iron(III) and cobalt(III) complexes of this Schiff base have been synthesized and characterized on the basis of elemental analysis, molar conductance, IR, UV-Vis, H-1 NMR, FAB mass, magnetic measurements, thermogravimetric analysis and XRD studies. The IR spectral data show that the ligand is coordinated to the metal ion in a tridentate manner with ONS donor sites of the carboxylate oxygen, azomethine nitrogen and thiophene ring sulphur atom. Magnetic moment measurements and electronic spectral data suggest a distorted octahedral geometry for manganese(III) complex and six-coordinated octahedral geometry for iron(III) and cobalt(III) complexes. Proton NMR spectral data reveal that the carboxylate proton displaced during complexation. The thermal decomposition studies of iron(III) complex show three stage decomposition and for each stage, kinetic parameters have been evaluated using Coats-Redfern equation. XRD patterns of the ligand and its cobalt(III) complex show orthorhombic crystal system. The ligand and the metal complexes are evaluated for antibacterial and antifungal activities against various bacterial and fungal strains.