Spectrophotometric and potentiometric study on platinum(II) chelates of mercapto carboxylic acids

The coordination of Pt(II) with different mercapto and dimercapto compounds has been studied using both potentiometric titration at 25 degreesC in KCl 0.1 M and UV-Vis spectroscopy. The slow complex formation kinetics has bee n followed spectrophotometrically for several days on samples with differen t ligand molar fractions ranging from 0.1 to 1, keeping the ligand and meta l concentration below 8 x 10(-4) M. For the potentiometric titration, the l igand concentrations were kept constant at 10(-3) M, and the 0.25, 0.5, 0.7 5 and 1.00 metal/ligand ratios were titrated in the pH range 2.5-11 for eac h ligand. The solutions were kept in a thermostatted bath at 25 degreesC fo r 2 days before titration. The stabilization of the absorbance values under these conditions after 2 days, and the back titration with hydrochloric ac id 0.1 M, led us to conclude that the proper equilibrium complex formation is reached under these conditions. Using KCl 0.1 M as an ionic strength med ium, the reported formation constants are referred to the complexation reac tion starting from [PtCl4](2-). Some models are proposed on the basis of th e estimated stoichiometries. (C) 2000 Elsevier Science B.V. All rights rese rved.