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Keywords:

  • lanthanide complexes;
  • lanthanide-induced shifts in NMR spectra;
  • molecular dynamics;
  • kinetics of chemical exchange;
  • free energy of activation;
  • dynamic NMR;
  • ethylenediaminetetraacetic acid;
  • EDTA;
  • two-site exchange;
  • aqueous solutions

1H nuclear magnetic resonance (NMR) measurements are reported for the D2O solutions of [Ln3+(EDTA4−)] complexes, where EDTA4− is ethylenediaminetetraacetate anion, Ln3+ = Tb3+ (I), Ho3+ (II), Tm3+ (III), Yb3+ (IV) and Lu3+ (V). Temperature dependencies of the 1H NMR spectra of paramagnetic I–IV have been analyzed using the dynamic NMR methods. It is found that the activation free energies (ΔG298 ) of the intermolecular EDTA ions exchange at [Ln3+(EDTA4−)] complexes are 60±3 (I), 66±3 (II), 69±3 (III) and 74±3 (IV) kJ/mol (at pD = 7). A monotonic increase of the free energy of chemical exchange processes along the series of lanthanide [Ln3+ (EDTA4−)] complexes is probably related to the lanthanide contraction. The obtained results indicate that coordination compounds I–IV may be considered as thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solution. Copyright © 2012 John Wiley & Sons, Ltd.