Spectroscopic and biological activity studies on tridentate Schiff base ligands and their transition metal complexes

Abstract

Schiff base ligands are prepared via condensation of pyridine-2,6-dicarboxaldehyde with 2-aminothiophenol (H₂L¹) and 2-aminobenzoic acid (H₂L²), respectively. The ligands are characterized based on elemental analysis, mass, IR and ¹H NMR spectra. Metal complexes are reported and characterized based on elemental analyses, IR, ¹H NMR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG and DTA). The molar conductance reveals that all the metal chelates are non-electrolytes except Th(IV) H₂L² complex which is 1:1 electrolyte . IR spectra show that H₂L¹ and H₂L² ligands behave as neutral tridentate ligands and bind to the metal ions via the two azomethine N and pyridine N. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral (Cr(III)- and Fe(III)-H₂L¹ and H₂L², Th(IV)-H₂L² and Mn(II)-H₂L¹ complexes) and triagonal bipyramidal (Co(II), Ni(II), Cu(II), Cd(II) and UO₂(II)-H₂L¹ and H₂L² and Mn(II)-H₂L² complexes). The thermal behaviour of these chelates is studied using TG and DTA techniques and the activation thermodynamic parameters are calculated using Coats-Redfern method. The synthesized ligands and their metal complexes were screened for their biological activity against bacterial species (Escherichia coli, P. vulgavis, B. subtilis and S. pyogones) and fungi (F. solani, A. niger and A. liavus). The activity data show that the metal complexes have antibacterial and antifungal activity more than the parent Schiff base ligands against one or more bacterial or fungi species.