Synthesis and Thermal Study of Co (II), Ni (II), Cu (II) Mixed Ligand Complexes Using Histidine As Tridentate Ligand

Abstract

The mixed ligand complexes of Co (II), Ni (II) and Cu (II) with histidine (His.) and 8- hydroxyquinoline (Qui.) have been synthesized and characterized.The resulting complexes were characterized by vibrational and electronic spectral data, thermogravimetric studies , metal analysis and molar conductance measurements. The histidine acts as tridentate ligand, coordinating through the two nitrogen atoms of imidazole ring and the amino group and carboxylate oxygen whereas 8-hydroxyquinoline shows a bidentate nature and the coordination occurs through nitrogen of imine group and oxygen of phenol group. The experimental data suggest that a mononuclear octahedral structure with general formula (M (His.)(Qui.) H2O ) where M= Co (II), Ni (II) and (Cu (His.)(Qui.)H2O) .H2O, thermo gravimetric studies reveal the presence of coordinated water molecules in all complexes. The molar conductance measurements reveal non-electrolytic nature of complexes. Mixed ligand complexes of 8-hydroxyquinoline and o-hydroxybenzylidene-1-phenyl-2, 3-dimethyl-4-amino-3- pyrazolin-5-on with Fe (II), Co (II), Ni (II) and Cu (II) ions were synthesized , the molar conductivity of the complexes in DMF solution have non-electrolyte behavior and 8-hydroxyquinoline coordinate through the nitrogen and oxygen atoms. therefore, the complexes have tetrahedral configuration. (12) Several mixed ligand Ni(II),Cu(II) and Zn(II) complexes of 2- amino-3-hydroxypyridine(AHP) and imidazoles viz.,, imidazole (him), benzimidazole (bim), histamine(hist) and L- histidine(his) have been synthesized and characterized, the geometry becomes tetrahedral when mixed ligand complexes are fomed with him, bim and hist for Cu(II) and Zn(II). All Ni (II) and Cu (II) / Zn (II) histidine mixed ligand complexes have octahedral geometry.The complexes exhibited considerable amount of antibacterial activity and Cu (II) complexes cleave DNA yielding scission of the sugar- phosphate backbone . (13) Mixed ligand Zr(IV) complexes prepared with 8-hydroxyquinoline as a primary ligand and amino acids such as L-alanine/L - serine/glycine as a secondary ligand. Zr(II) was used due to its high coordination number and ability to form stable complexes. These complexes were characterized and screened for their antibacterial, antifungal and cytotoxic properties . (14) Kinetics and mechanism of thermal decomposition of o-vanilline-L-histidine complexes of some transition metal ions in which histidine acts as a tridentate ligand and an octahedral structure for the complexes has been reported . (15) Synthesis, structural, coordination and thermal stability studies of mixed ligand complexes of histidine with other ligands (adenine/guanine/ethylenediamine, diethylenetriamine or N,N,N , N ,, ,N ,,, -pentamethyldiethylenetriamine, glycine or L-alanine, histamine and diethylglyoxime) have been carried out .