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  • 1
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; carbon-13 ; nitrogen-15 ; NMR ; lutetium(III) ; isothiocyanate ; complexation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A direct, low-temperature hydrogen-1, carbon-13, and nitrogen-15 nuclear magnetic resonance study of lutetium(III)-isothiocyanate complex formation in aqueous solvent mixtures has been completed. At −100°C to −120°C in water-acetone-Freon mixtures, ligand exchange is slowed sufficiently to permit the observation of separate1H,13C, and15N NMR signals for coordinated and free water and isothiocyanate ions. In the13C and15N spectra of NCS−, resonance signals for five complexes are observed over the range of concentrations studied. The13C chemical shifts of complexed NCS− varied from −0.5 ppm to −3 ppm from that of free anion. For the same complexes, the15N chemical shifts from free anion were about −11 ppm to −15 ppm. The magnitude and sign of the15N chemical shifts identified the nitrogen atom as the binding site in NCS−. The concentration dependence of the13C and15N signal areas, and estimates of the fraction of anion bound at each NCS−:Lu3+ mole ratio, were consistent with the formation of [(H2O)5Lu(NCS)]2+ through [(H2O)Lu(NCS)5]2−. Although proton and/or ligand exchange and the resulting bulk-coordinated signal overlap prevented accurate hydration number measurements, a good qualitative correlation of the water1H NMR spectral results with those of13C and15N was possible.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-8927
    Keywords: Carbon-13 ; nitrogen-15 ; NMR ; europium-nitrate complexes ; europium-isothiocyanate complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: 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) 2 1+ , 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) 2 1+ 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) 4 1- 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.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0749-1581
    Keywords: NMR ; 1H NMR ; 13C NMR ; 15N NMR ; 27Al NMR ; isothiocyanate ; complexes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A multinuclear magnetic resonance (NMR) study of the complexes of aluminum(III) with isothiocyanate ion in water-acetone mixtures has been completed. At temperatures low enough to slow proton and ligand exchange, separate resonance signals are observed for coordinated and bulk H2O (1H) and NCS- (13C, 15N), and Al3+ (27Al) in each complex. The 1H NMR spectra reveal six sets of signals for the complexes, [Al(H2O)6]3+ through [Al(H2O)(NCS)5]2-, including isomers for three of the species. Signal area measurements show a decrease in the Al3+ hydration number with increasing NCS- concentration, as this anion replaces water in the solvation shell. In the 27Al NMR spectra of these systems, signals for seven complexes, [Al(H2O)6]3+ through [Al(NCS)6]3-, are observed, with chemical shifts increasing by about 6 ppm with each additional NCS-. Although broadened somewhat by the Al(III) quadrupole, the 13C and 15N NMR spectra also reveal coordinated NCS- signals for these complexes, including 27Al—N13CS J-coupling in [Al(NCS)6]3-. Area evaluations of the 15N NMR signals provide an excellent complement to the 1H hydration number data. These NMR results demonstrate that a multinuclear approach to the study of solution complexes can provide detailed structural information about the species being formed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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