Abstract
The various physico-chemical studies were made on the complex-formation equilibria between In (III) and sulfhydryl-containing bidentate ligands, such as 2-aminoethanethiol (2-mercaptoethylamine, MEA), 3-mercaptopropionic acid (MPA), and mercaptoacetic acid (thioglycolic acid, TGA). The insoluble and stable complex, InL3, was formed during the titration of the MEA-In (III) solution. The complex formation of In (III) with MPA and TGA was investigated by potentiometric titration over a wide range of the metal concentration. Calculation of the titration data of the MPA-In (III) system indicated that MPA formed the In2L3, In3L4, and In3 (OH) L4 species together with the mononuclear species. In the higher concentration, non-charged species, In3 (OH) L4, was precipitated. In the alkaline solution, the carboxyl group was eliminated from the coordination sphere and the InL4 species was formed. These observations in the MPA-In (III) system were similar to those of the cysteine case. Since TGA forms the stable complex with fivemembered chelate ring, the InL4 or hydrolyzed species were not formed even in the alkaline solution. Calculation indicated the formation of the InL3, In2L3, and In3L5 species in the TGA system.
