A direct carbon-13 and nitrogen-15 NMR study of europium(III) complexation-nitrate and europium(III)-isothiocyanate complexation in aqueous solvent mixtures |
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Authors: | A. Fratiello V. Kubo-Anderson E. Bolanos O. Chavez J. Ortega R. D. Perrigan F. Reyes L. Saenz S. M. Stoll T. Thompson |
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Affiliation: | (1) Department of Chemistry and Biochemistry, California State University, Los Angeles, 90032 Los Angeles, California |
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Abstract: | A direct, low-temperature nuclear magnetic resonance spectroscopic study of europium(III)-nitrate contact ion-pairing has been completed, and preliminary results for europium(III)-isothiocyanate have been obtained. In water-acetone-Freon mixtures, at –110°C to –120°C, four15N NMR signals are observed for coordinated nitrate ion. Area evaluations of the signals and their concentration dependence indicate the formation of Eu(NO3)2+, Eu(NO3)21+, and two higher complexes, possibly the tetra-, with either the penta-or hexanitrato. This correlates well with similar15N NMR results obtained for Ce(III), Pr(III), Nd(III), and Sm(III). As a result of a higher dielectric constant, complex formation is significantly less in water-methanol mixtures, wheein only three complexes form with Eu(NO3)21+ dominating at the highest anion concentrations. Competitive complexing experiments in water-methanol also were made by35Cl NMR chemical shift and linewidth measurements, as well as15N NMR. Initial experiments with the Eu3+-NCS– system show four coordinated anion signals, displaced from the bulk anion peak by about –250 ppm and –2,500 ppm in the13C and15N NMR spectra, respectively. Area evaluations are consistent with the presence of Eu(NCS)2+ through Eu(NCS)41- in these solutions. A consideration of the chemical shifts identified the nitrogen atom as the site of binding in the NCS–. A discussion of these preliminary results, as well as those for several other metal-ions, will be presented. |
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Keywords: | Carbon-13 nitrogen-15 NMR europium-nitrate complexes europium-isothiocyanate complexes |
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