Preparation, characterization and biological activity of novel metal-NNNN donor Schiff base complexes

Novel Schiff base (H2L) ligand is prepared via condensation of benzil and triethylenetetraamine. 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, and thermal analyses (TG, DTG and DTA). 1:1 [M]:[H2L] complexes are found from the elemental analyses data having the formulae [M(H2L)Cl2]·yH2O (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II)), [Fe(H2L)Cl2]Cl·H2O, [Th(H2L)Cl2]Cl2·3H2O and [UO2(H2L)](CH3COO)2·2H2O. The metal chelates are found to be non-electrolytes except Fe(III), Th(IV) and UO2(II) complexes are electrolytes. IR spectra show that H2L is coordinated to the metal ions in a neutral tetradentate manner with 4Ns donor sites of the two azomethine N and two NH groups. The geometrical structures of these complexes are found to be octahedral. The thermal behaviour of these chelates is studied where the hydrated complexes lose 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 using Coats–Redfern method. The ligand (H2L), in comparison to its metal complexes, is screened for its antibacterial activity. The activity data show that the metal complexes have antibacterial activity more than the parent Schiff base ligand and cefepime standard against one or more bacterial species.