The rate of exchange reactions taking place between the Ce(edta)” complex and Pb2+, Ni2+, and Co2+ ions in general increases with increasing H+ and metal ion concentration. On the basis of the rate equations obtained, it was assumed that the exchange reactions proceed via the dissociation of the protonated Ce(Hedta) complex as well as by the direct attack of the metal ions on the Ce(edta)- and Ce(Hedta) complexes. In the Ce(edta)--Pb2+ system the results have been explained by the fast formation and slow transformation of the binuclear complex Ce(edta)Pb+, in which presumably only an acetate group is coordinated to the Pb2+ ion. The rate of exchange between Ce(edta)- and Ni2+ (as well as Co2+) is inversely proportional to the Ce3+ ion concentration. This has been explained by the much lower water-exchange rate of the Ni2+(aq) and Co2+(aq) ions compared to that of the Ce3+(aq) ion. The rate of exchange taking place by the direct attack of the metal ions on the complex is linearly proportional to the water-exchange rate of these ions. This presumably resulted from the formation of an intermediate complex, where one of the iminodiacetate groups of edta is coordinated to the Ce3+ ion while the other one is coordinated to the attacking Ni2+ or Co2+ ion.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry