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

The stability constants of the palladium(II) complexes with sulphur-contain ing acids HnL:thioglycolic acid, methylthioglycolic acid, L-cysteine, D,L-p enicillamine, S-methyl-L-cysteine, D,L-methionine, and D,L-ethionine, were determined using potentiometric pH titrations and spectrophotometric measur ements at 25 degrees C and I=1.000(NaClO4). The anionic complexes PdBr42- a nd Pd(SCN)(4)(2-) were used for this purpose as they give the complexes PdL and PdL2 in the pH range 2-8 with PdBr42- 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 valu es obtained by both methods are within 0.1 logarithmic unit. The spectral d ata of the complexes are given and compared with those of the glycine compl exes. The palladium(II) complexes with thiolate and thioether ligands are m ore stable relative to those of mercury(II), the latter showing a much larg er selectivity. (C) 2000 Elsevier Science B.V. All rights reserved.