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Digitale Medien

Interactions of La(III) with anions in aqueous solutions. A139La NMR study (1992)

Chen, Zhigang ; Detellier, Christian

Springer

Journal of solution chemistry 21 (1992), S. 941-952

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ISSN: 1572-8927

Schlagwort(e): 139La NMR ; lanthanide coordination ; ion pairing ; aqueous solutions ; quadrupolar relaxation ; solvation dynamics

Quelle: Springer Online Journal Archives 1860-2000

Thema: Chemie und Pharmazie

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00650870

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Digitale Medien

23Na nuclear magnetic resonance study of the complexation of sodium tetraphenylborate by [5,5]-dibenzo-30-crown-10 in nitromethane, acetonitrile, acetone and pyridine (1990)

Brière, Kathleen M. ; Graves, Helen P. ; Rana, Tariq S. ; [weitere]

Chichester : Wiley-Blackwell

Journal of Physical Organic Chemistry 3 (1990), S. 435-442

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ISSN: 0894-3230

Schlagwort(e): Organic Chemistry ; Physical Chemistry

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: The nature of the (Na-DB30C10)+ complex has been studied by 23Na NMR in four non-aqueous solvents: nitromethane (NM), acetonitrile (AN), acetone (AC) and pyridine (PY). The equilibrium constant of formation (Kf) of (Na-DB30C10)+ in AC, AN and PY was determined at 300 K: log Kf = 3·9 ± 0·3, 3·4 ± 0·5 and 3·0 ± 0·1, respectively. In cases such as in pyridine, where exact values of the rate constants for the chemical exchange could not be calculated, limiting values were determined giving k-1 (the rate constant for complex dissociation) 〉 6·6 × 10-4 s-1 and kc (the rate constant for the formation of the complex) 〉 5 × 107 l mol-1 s-1. Evidence was found for the formation of a 2 : 1 (Na2-DB30C10)+2 complex in nitromethane. It has been previously shown that for (Na-DB24C8)+ the first coordination sphere of Na+ is exclusively filled by the oxygens of the crown ether, whereas for (Na-DB18C6)+ there is participation of at least one solvent molecule. The first coordination sphere of Na+ in (Na-DB30C10)+ consists of one or several molecules of solvent in addition to a number of oxygens from the crown ether. The soft wrapping of the Na+ by DB30C10 is in constrast with the hard wrapping of Na+ by DB24C8 and of K+ by DB30C10.

Zusätzliches Material: 4 Ill.