Mixed chelates of some trivalent lanthanide ions containing (trans-1,2-cyclhexylenedinitrilo)tetraacetate and norleucinate

Abstract

Formation constants of mixed chelates with (trans-1,2-cyclohexylenedinitrilo)tetra-acetate (DCTA) as primary ligand and norleucinate (nle) as secondary ligand with metal ions La(III), Ce(III), Pr(III), Sm(III), Gd(III), Tb(III), Dy(III), Er(III), and Yb(III) have been determined by the modified potentiometricpH titration method of Irving-Rossotti in aqueous medium at (295±1) K and fixed ionic strength of μ=0.1M (NaClO4). Formation constants of binary complexes of the metal ions with the secondary ligand have also been determined under identical conditions. The mixed chelates were found to be more stable than the binary ones. The order of stabilities in terms of metal ions is La(III) Gd(III)<Tb(III)<Dy(III)<Er(III)<Yb(III) for binary and ternary complexes with a prominent “Gadolinium break”.