Equilibrium study on Pd(II) chelates of mercapto carboxylic acids

The coordination of Pd(II) with a set of different mercapto and dimercapto compounds has been investigated by potentiometric titration at 25 degrees C in KCl 0.1 M. The ligand concentration ranged from 10(-4) M to 10(-3) M, and for each ligand concentration the 0.25, 0.50, 0.75 and 1.00 Metal/Ligand ratios were examined in the 2.5-11 pH range. Using KCl 0.1 M as an ionic strength medium the reported formation constants are implicitly referred to the complexation reaction starting from [PdCl4](2-) as is generally done for the aquo ion. On the bases of the estimated complexation stoichiometries some coordination models are proposed. The influence of -SH basicity, total charge of complexes and steric factors on the coordination properties of the various ligands is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.