Thermodynamic and Electrochemical Behaviour of Lanthanide Cryptates in N,N-Dimethylformamide

Article abstract of DOI:10.1039/DT9890000367

The stability of 222 (L¹), 221 (L²), 211 (L³) cryptates of samarium(III), europium(III), and ytterbium(III) and the corresponding complexes with the related monocycle, 22 (L⁴) have been determined in N,N-dimethylformamide by potentiometry using a competitive method with auxiliary alkali cations.Their electrochemical behaviour has also been investigated in the same solvent by polarography and cyclic voltammetry.The results clearly show the low stability of the trivalent cryptates.The electrochemical study of Ln(3+) ions with increasing amounts of ligand shows two different behaviours: (i) with L³, Ln(3+) ions are complexed as shown by the decrease of the reduction waves of Ln(3+) but no stabilization of Ln(2+) is observed; (ii) with L¹, L², and L⁴ the height of the reduction wave of Ln(3+) is not affected by the ligand concentration and the reduction occurs according to the scheme: Ln(3+) + e(1-) <*> Ln(2+) + L -> (2+).The differences δ between the redox potentials of the free and the complexed lanthanide(III) cations show an important stabilization of the divalent cryptates.Their stability constants have been calculated from the values of δ and the stability constants of trivalent complexes.While no particular ligand or cation selectivity is observed for the trivalent cryptates, this is not so for the reduced lanthanides which form the strongest complexes with L¹.The results are interpreted by size and solvation considerations.

Full text of DOI:10.1039/DT9890000367

View Article Online / Journal Homepage / Table of Contents for this issue

View Article Online

View Article Online

View Article Online