ISSN : 2348 - 8948

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Volume : 6 Issue :12 Month : December (2018)
Page Numbers : 621-632

Potentiometric Studies On The Formation Equilibria Of Ternary Complexes Of Lead (Ii), Cadmium (Ii), And Mercury (Ii) With Maleic Acid And L-Phenylalanine In Dimethylformamide-Water Mixture

Meti Mengistu melese, Fedlu Kedir Sabir, Hadgu Hailekiros Belay*
The stability constants of ternary complexes of Pb(II), Cd(II) and Hg(II) ions with Maleic Acid (MA) and L Phenylalanine (F) were determined pH metrically in the concentration range of 0ā€“50 % v/v in Dimethylformamide-Water Mixtures maintaining an ionic strength of 0.16 mol lāˆ’1 using NaNO3 as an electrolyte at 303.0 K. The Value of āˆ† log K that is responsible for the extra stability of ternary complexes was discussedbased on statistical parameters and the nature of the species formed. The formation of various ternary species was established by modeling studies using the computer program MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The species detected are MLXH2, ML2X and HML2XH2for Pb (II), ML2XH, ML2XH2 and MLX2H3for Cd (II) and ML2XH, ML2XH2and MLX2 for Hg (II). The relative stabilities of the mixed ligand complexes were compared with those of the binary complexes. The enhanced stability associated with the ternary complex is attributed to chelate effect, stacking interactions and hydrogen bonding.Influence of the solvent on the speciation was discussed based on the dielectric constant of the medium. The stability of the mixed ligand complexesis discussed in terms of the molecular structure of Maleic acid and L- Phenylalanine as well as the nature of the metal ion.
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