ISSN:
1572-8927
Keywords:
139La NMR
;
lanthanide coordination
;
ion pairing
;
aqueous solutions
;
quadrupolar relaxation
;
solvation dynamics
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The interactions of the La(III) cations with three anions (X), nitrate, chloride and perchlorate, in aqueous solutions in the pH range 4.0–6.5, were studied by139La NMR spectroscopy. A single model, involving the formation of the contact ion-pair (inner-sphere complex) (LaX)2+ was successfully and quantitatively applied to the chemical shift and the transverse relaxation rate data. Both measurements gave values for the thermodynamic equilibrium constants of formation of (LaX)2+ (K th ) in good agreement (average K th =0.45±0.05; 0.15±0.09; 0.03±0.01, respectively for nitrate, chloride and perchlorate). The complexes are characterized by chemical shifts of −25, 22 and −3.1 ppm and by transverse relaxation rates of 11.2, 5 and 1.65 kHz respectively for nitrate, chloride and perchlorate. The139La quadrupolar relaxation rate is not controlled by the reorientational correlation time. This finding is discussed, and it is suggested that the very fast exchange of water molecules in the first coordination sphere of La(III) is responsible for the time fluctuation of the electric field gradient at the139La nucleus site.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00650870
Permalink
