Equilibria with the thallium(III)triethylenetetraminehexaacetate anion [Tl(ttha)](3-) in aqueous solution

The equilibria involving the thallium(III) triethylenetetraminehexaacetate complex [Tl(ttha)](3-) were studied. Its stability constant was estimated u sing UV-VIS spectrophotometry for the ligand exchange occurring between bro mide and ttha in the pH range from 0 to 10. The protonated complex [Tl(H-3 ttha)] 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 dif ferent metal ions. In the case of copper the stability constant was also me asured spectrophotometrically. The complex formation in solution was verifi ed in two cases by matrix-assisted laser desorption ionisation time-of-flig ht mass spectrometry. The results obtained are discussed and compared with those of other similar ligands. (C) 2000 Elsevier Science B.V. All rights r eserved.