Studies on mixed ligand complexes involving ligands of biological importance [Ni(II), Zn(II) or Cd(II)-1,10-phenanthroline — or 2,2′-bipyridyl-histidine]
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The formation of mixed ligand complexes of the title metal ions with 1,10-phenanthroline (Phen) or 2,2′-bipyridyl (Bipy) in presence of histidine (His) has been studied pH-metrically. The stepwise formation of 1∶1∶1 mixed ligand complexes has been inferred from the potentiometric titration curves. Initially, a 1∶1 metal—Phen or—Bipy complex is formed in the lower buffer region and then the addition ofHis takes place resulting in 1∶1∶1 ternary complex formation. The formation constants (K MAL ) of the resulting mixed ligand complexes have been calculated at 30±1°C (μ=0.1 KNO3) and the values have been found to be higher than the formation constants of 1∶2 and lower than those of 1∶1 metal—His complexes. The order of stability in terms of metal ions follows the order, Ni(II)>Zn(II)>Cd(II).
KeywordsHistidine Phen KNO3 Potentiometric Titration Ternary Complex
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