Intramolecular dynamics and molecular structure of europium(III) chelate complexes with crown ethers as studied by NMR spectroscopy

Sergey P. Babailov, Dmitry A. Mainichev, Lubov D. Nikulina, Svetlana S. Petrova

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Abstract

Earlier the intramolecular inversion of the 18-crown-6 molecules was found in the complex ion pairs [Ln(ptfa)2 (18-crown-6)]+ [Ln(ptfa)4]- (H2O)4 where Ln = La(1), Ce (2), Pr (3), Nd (4), and ptfa is 1,1,1-trifluoro-5,5-dimethyl-2,4- hexanedione. In this work the peculiarities of the molecular structure and dynamics were studied for [Eu(ptfa)2 (18-crown-6)]+ [Eu(ptfa)4]- (H2O)4 (5) by NMR spectroscopy techniques. Through VT-NMR spectra analysis the temperature dependence was obtained for the rate constant. The free energy ΔG (320) of 18-crown-6 ring inversion activation was found to be 65 ± 5 kJ mol-1 for 5 in CDCl3. This result is comparable with the earlier data [S.P. Babailov and D.A. Mainichev: J. Inclusion Phenom. Macrocyclic Chem. 43, 187-193 (2002)] for complexes 2, 3, 4 in deuterated toluene (ΔG(320)=65 ± 9, 64 ± 9, 64 ± 9 kJ mol-1 respectively). It was found by relaxation NMR spectroscopy that the effective distance between Ln and protons of the crown molecule is 4.5 ± 0.2 Å. The analysis of structural parameters testifies that the crown ether and chelated anions are in the first coordination sphere of a Ln cation. Obtained geometrical parameters show that the complex cations of Eu, Ce and Pr have similar spatial structures.

Original languageEnglish
Pages (from-to)73-78
Number of pages6
JournalJournal of Inclusion Phenomena and Macrocyclic Chemistry
Volume51
Issue number1
DOIs
Publication statusPublished - Feb 2005
Externally publishedYes

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Keywords

  • Complexes
  • Crown ethers
  • Dynamic NMR
  • Free energy of activation
  • Lanthanides
  • Molecular dynamics
  • Ring inversion
  • Structure

ASJC Scopus subject areas

  • Chemistry(all)
  • Condensed Matter Physics

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