Biological activity studies on metal complexes of novel tridentate Schiff base ligand. Spectroscopic and thermal characterization

Metal complexes of novel Schiff base (HL) ligand, prepared via condensation of 4-aminoantipyrine and 2-aminophenol, are prepared. The ligand is 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, ESR spectra and thermal analyses (TG, DTG and DTA). From the elemental analyses, 1:1 [M]:[ligand] complexes are prepared with the general formulae [M(L)Cl(H2O)2]·yH2O (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), y = 3–4), [Fe(L)Cl2(H2O)]·3H2O and [Th(L)Cl(H2O)2]Cl2·3H2O. The molar conductance data reveal that all the metal chelates are non-electrolytes (except Th(IV) complex, it is 2:1 electrolyte). IR spectra show that HL is coordinated to the metal ions in a uninegatively tridentate manner with NNO donor sites of the azomethine-N, amino N and deprotonated phenolic-O. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral. The thermal behaviour of these chelates shows that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters are calculated from the DTG curves using Coats–Redfern method. The synthesized ligand, in comparison to its metal complexes is screened for its antibacterial activity against bacterial species, Escherichia coli, Pseudomonas putida, Exiguobacterium acetylicum and Bacillus simplex. The activity data show that the metal complexes to be more potent/antibacterial than the parent Shciff base ligand against one or more bacterial species.

Graphical abstractMetal complexes of novel Schiff base (HL) ligand; prepared via condensation of 4-aminoantipyrine and 2-aminophenol, are prepared. The ligand and its metal complexes are characterized based on elemental analysis, mass, IR and 1H NMR spectra, solid reflectance, magnetic moment, molar conductance, ESR spectra and thermal analyses. The complexes are prepared with the general formulae [M(L)Cl(H2O)2]·yH2O (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), y = 3–4), [Fe(L)Cl2(H2O)]·3H2O and [Th(L)Cl(H2O)2]Cl2∣3H2O. IR spectra show that HL is coordinated to the metal ions in a uninegatively tridentate manner with NNO donor sites of the azomethine-N, amino N and deprotonated phenolic-O. The complexes are octahedral. The thermal behaviour of these chelates is studied. The synthesized ligand, in comparison to its metal complexes is screened for their antibacterial activity against bacterial species, Escherichia coli, Pseudomonas putida, Exiguobacterium acetylicum and Bacillus simplex.Figure optionsDownload full-size imageDownload as PowerPoint slide