Complexation of cerium group lanthanide ions (Ce, Pr, Nd, Sm) with L-malic acid in aqueous solutions was studied by pH-metric titration at a malic acid : lanthanide concentration ratio of 1 : 2, in the pH range of 3.0 to 9.0, and at ionic strength of 0.1 mol/l (KCl). The composition and the stability constants of L-malate complexes and hydroxo complexes of lanthanides were determined.

Complexation of Cerium Group Lanthanides with L-Malic Acid under an Excess of Metal Ions

Complexation of Nd3+ and Sm3+ ions with L-malic acid (H3Mal) in aqueous solutions (I = 0.1 mol/l KCl) was studied by pH-metric titration at the molar concentration ratios of H3Mal : lanthanide equal to 1 : 2, 1 : 1, 2 : 1 in the pH range 2.8–9.5. Mathematical modeling of composite equilibrium processes was used to determine the compositions and stability constants of Nd(III) and Sm(III) L-malate complexes. It was found that in addition to the 1 : 1 and 1 : 2 complexes with different degree of deprotonation, the protonated L-malate complexes and hydroxo complexes of these metals were also formed. The Sm3+ and Nd3+ ions were established to behave differently during complexation with H3Mal.

Different Complexation of Nd3+ and Sm3+ with L-Malic Acid

We report here on the coordination properties of a series of lanthanide cations (Ln=La, Nd, Eu, Tb, Er) with a tripodal homoditopic ligand L, which is bearing three diamido-dihydroxamate arms anchored on a tertiary amine. The complexes of L with lanthanides were studied in a MeOH/H2O (80/20 by weight) solvent and a marked size-discriminating effect depending on the intramolecular interactions was observed in the tripodal dinuclear lanthanide edifice. Positive cooperative effects favour the formation of the bimetallic LLn2 complexes compared with the monometallic analogues for the heavier lanthanide cations (Eu, Tb, Er), while the lighter ones (La, Nd) show a decrease of cooperative interactions in the corresponding bimetallic species. Moreover, increased levels of heterobimetallic complexes are detected for Ln(III) pairs containing a lighter Ln(III) ion and a heavier one. In contrast with the adjunctive ligand exchange reported for LFe2 and CDTA, the corresponding substitution reaction for LLn2 occurs according to a disjunctive mechanism. Our work thus highlights the importance of the balance between the rigidity of a tripodal structure and the flexibility of the side arms to accommodate two trivalent cations in a supramolecular ensemble. 

https://hal.science/hal-03767785/document

H.S. Rana

Papers

Potentiometric studies on stepwise biligand complex formation La(III), Pr(III) or Nd(III)-cyclo hexane-1, 2-diaminotetraacetic acid-hydroxy acid