Structure and stability of carboxylate complexes. Part 18. Stability constants of the copper(II) complexes of some thiodialkanoates

Abstract

Potentiometric studies of the complexation of Cu^II with 2.2′-thiodiacetate, 3.3′-thiodipropanoate, and 4.4′-thiodibutanoate have been carried out at 25.0 °C in a 3 mol dm^–3(sodium) perchlorate medium. Two different titration techniques are used which enable alternative methods of calculation of the results to be applied. The results show the formation of 1 : 1 complexes with both the ligand and the monoprotonated ligand in each case, and in addition the 1 : 2 species in the case of thiodiacetate. Combined potentiometric and spectroscopic evidence shows that, in both thiodibutanoate species, the ligand is unidentate through an oxygen-donor atom; the protonated species show increasing bidentate behaviour as the potential chelate-ring size is decreased from seven to five members. In the remaining unprotonated species the ligands are bi-(thiodiacetate) and tri-dentate (thiodipropanoate).