The stability of palladium(II) complexes with sulphur-containing ligands Original Research Article

The stability constants of the palladium(II) complexes with sulphur-containing acids HnL :thioglycolic acid, methylthioglycolic acid, l-cysteine, d,l-penicillamine, S-methyl-l-cysteine, d,l-methionine, and d,l-ethionine, were determined using potentiometric pH titrations and spectrophotometric measurements at 25°C and I = 1.00(NaClO4). The anionic complexes PdBr42− and Pd(SCN)42− were used for this purpose as they give the complexes PdL and PdL2 in the pH range 2–8 with liberation of hydrogen ions from the protonated ligands. The stability constants were also obtained in 1 M HClO4 using spectrophotometric measurements. The agreement between the values obtained by both methods are within 0.1 logarithmic unit. The spectral data of the complexes are given and compared with those of the glycine complexes. The palladium(II) complexes with thiolate and thioether ligands are more stable relative to those of mercury(II), the latter showing a much larger selectivity.