Equilibrium studies of mercury(II) complexes with penicillamine

The complex-formation equilibria of mercury(II) with penicillamine have bee n investigated in acidic and neutral conditions. A liquid-liquid extraction method using dithizone as auxiliary ligand was applied for the determinati on of the stability constants of three differently protonated 1:2 metal/lig and complexes formed at pH < 3. Evidence has been found by potentiometry an d confirmed by Raman spectroscopy for the existence of 1:3 metal/ligand com plex besides 1:1 and 1:2 species at pH > 4. The stability constants of HgL3 H3- and HgL2H- complexes as well as the macroscopic protonation constants o f the ligand were determined from pH-metric data. The binding sites in the complexes with a special regard to the possible role of -COO- and -NH2 grou ps in the coordination have been discussed. (C) 1999 Elsevier Science B.V. All rights reserved.