Equilibria with the thallium(III)triethylenetetraminehexaacetate anion [Tl(ttha)]3− in aqueous solution Original Research Article

The equilibria involving the thallium(III) triethylenetetraminehexaacetate complex [Tl(ttha)]3− were studied. Its stability constant was estimated using UV–VIS spectrophotometry for the ligand exchange occurring between bromide and ttha in the pH range from 0 to 10. The protonated complex [Tl(H3ttha)] is a weak acid allowing the determination of the stability constant of the heterobinuclear complexes [MTl(ttha)]− (M = Co, Ni, Cu, Zn, Cd and Pb) by use of alkalimetric titrations of the above acid in presence of different metal ions. In the case of copper the stability constant was also measured spectrophotometrically. The complex formation in solution was verified in two cases by matrix-assisted laser desorption ionisation time-of-flight mass spectrometry. The results obtained are discussed and compared with those of other similar ligands.