Intermolecular dynamics and paramagnetic properties of ethylenediaminetetraacetate complexes with the yttrium subgroup rare earth elements using nuclear magnetic resonance

¹H nuclear magnetic resonance (NMR) measurements are reported for the D ₂O solutions of [Ln ³⁺(EDTA ^4-)] ^- complexes, where EDTA ^4- is ethylenediaminetetraacetate anion, Ln ³⁺ = Tb ³⁺ (I), Ho ³⁺ (II), Tm ³⁺ (III), Yb ³⁺ (IV) and Lu ³⁺ (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 (ΔG ^∥ ₂₉₈) of the intermolecular EDTA ions exchange at [Ln ³⁺(EDTA ^4-)] ^- 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 [Ln ³⁺ (EDTA ^4-)] ^- 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.