Polypyridinic ligand coordination to Zn2+ and Hg2+ metal ions

The thermodynamic parameters for the complexation reaction between Zn2+ and Hg2+ with the mixed amino-polypyridinic ligands tris[(2-pyridyl)methyl]amine (TPA) and 6,6-bis–bis (pyridylmethyl)aminomethyl]-2,2-bipyridine (BTPA) have been obtained in anhydrous DMSO by using spectrophotometry, polarography, potentiometry and titration calorimetry. Complexes with stoichiometry 1:1 have been observed in all cases but Hg-TPA system, for which 1:2 complex is also formed. As found in water, both delta G and delta H become more favorable when going down along the group. From a comparison of data with those reported for other metal ions in DMSO (Co2+, Ag2+, Cd2+) and in water as solvent, it is shown that TPA is more selective towards Hg2+ in water than in DMSO and that the selectivity of BTPA in DMSO is much higher towards Cd2+ and Hg2+ ions with respect to Zn2+.