OXOVANADIUM(IV) COMPLEXES OF MERCAPTOCARBOXYLIC ACIDS

Complex formation between oxovanadium(IV) and a series.of aliphatic me rcaptocarboxylic acids (mercaptoacetic, 2- and 3-mercaptopropionic, 2- mercaptosuccinic, and meso-2,3-dimercaptosuccinic) was studied in aque ous solution by potentiometric and spectroscopic (EPR and electronic a bsorption) techniques. A comparison with the complexes of the correspo nding hydroxycarboxylic acid analogues was also made. The most interes ting finding is that VO2+ has a similar affinity to the rather soft th iolate-S donors as to the hard alcoholate-0 donors, if these donors ar e in chelatable position with a hard carboxylate group. The bidentate mercaptocarboxylates form (CO2-, S-)-co-ordinated mono and bis complex es, while bis complex formation is rather hindered with the tridentate 2-mercaptosuccinic acid. Due to the high denticity of the ligand, 2,3 -dimercaptosuccinic acid readily forms oligomeric species via the co-o rdination of all potential donor groups.