STUDIES ON KINETICS OF COMPLEXATION OF LANTHANIDE ALPHA-HYDROXYCARBOXYLATES WITH 1,10-PHENANTHROLINE

Kinetics of the coordination reaction of lanthanide (La-III,Eu-III) al pha-hydroxycarboxylates [LnL(3)(H2O)(2)] with 1,10-phenanthroline (phe n) in methanol-water (v/v, 3:2) were studied at 25 degrees C by calori metric titration. A one-step reaction process in accordance with the r ate law has been suggested. The reaction is found to be first order fo r both lanthanide alpha-hydroxycarboxylates and phen. We have evaluate d rate constants of the reactions. It is found that a linear free ener gy relationship exists between the stability constants of the lanthani de-alpha-hydroxycarboxylate-phen ternary complex and the rate constant s. It is also found that a linear free energy relationship exists betw een the rate constants of La-hydroxycarboxylate with phen and the acid strength of alpha-hydroxy-acid as primary ligand, but the linear free energy relationship does not exist in the Eu-alpha-hydroxycarboxylate -phen ternary complex. The influence of other factors upon the reactio n rate constants was also discussed. (C) 1997 Elsevier Science Ltd.