Heteroligand complexes of some rare earth metals with CDTA and unsaturated dicarboxylic acids

Abstract

Potentiometric evidence has been cited for the formation of heteroligand 1:1:1, ternary and 1:1:1:1, quaternary species in the systems M(III)-CDTA-CCA/MIA and M(III)-CDTA-CCA-MIA, respectively (M(III) = La(III), Pr(III), Nd(III), Gd(III) or Dy(III); CDTA = cyclohexanediaminetetra-acetic acid; CCA = citraconic acid and MIA = maleic acid). The protonated mixed ligand complexes, existing in the low pH range, appear to undergo deprotonation resulting in the formation of normal chelates at comparatively higher pH. The formation constants log K MLL′ and log K MLL′L″, respectively, for ternary and quaternary species, formed by simultaneous addition of the ligands to the metal ion and deprotonation constants,-log K A H , for protonated ternary species have been evaluated at 27 ± 1°C and ionic concentration (μ) = 0.1 M KNO 3. The order of relative stabilities is La(III) < Pr(III) < Nd(III) < Gd(III) < Dy(III).