Kinetic study of rare earth-edta-tiron mixed complex formation reaction in aqueous solution

Abstract

Mixed complex formation reactions of the EDTA-rare earth complex with tiron were studied by the temperature jump method. The two step mechanism involving the intermediate complexes of EDTA-rare earth-protonated tiron ion agreed reasonably with the concentration dependency of observed relaxation times. The values of the formation rate constants were the order of 10^5M^-1 sec^-1, which are two or three order less than the values is hydrated rare earth ions-murexide, -oxalic acid and -anthranic acid systems. The ligand-ligand interaction, electrostatic and steric repulsion, acts as the retarding effects in these mixed comlex formation reactions.