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  • 1
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; nitrogen-15 ; chlorine-35 ; NMR coordination ; Lu(ClO4)3 ; Lu(NO3)3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A coordination study of Lu(III) has been carried out for the nitrate and perchlorate salts in aqueous mixtures of acetone-d6 and Freon-12 by1H,15N and35Cl NMR spectroscopy. At temperatures lower than −90°C, proton and ligand exchange are slow enough to permit the direct observation of1H resonance signals for coordinated and free water molecules, leading to an accurate measure of the Lu(III) hydration number. In perchlorate solution, in the absence of inner-shell ion-pairing, Lu(III) exhibits a maximum coordination number of six over the allowable concentration range of study, contrasting markedly with the report of values of six to nine or greater as determined by a similar NMR method. The absence of contact ion-pairing was confirmed by35Cl NMR chemical shift and linewidth measurements. Extensive ion-pairing was observed in the nitrate solutions as reflected by the lower Lu(III) hydration numbers of two to three in these systems, the observation of two coordinated water signals, and15N NMR signals for two complexes. The1H and15N NMR spectra and the hydration number could be accounted for by the presence of (H2O)4Lu(NO3)2+ and (H2O)2Lu(NO3) 2 1+ .
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  • 2
    ISSN: 1572-8927
    Keywords: Nitrogen-15 ; chlorine-35 ; NMR ; cerium nitrate ; complexation ; water acetone mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of the complex formation which occurs between cerium(III) and nitrate ions in aqueous solvent mixtures has been carried out by a direct, low-temperature, nitrogen-15 (15N) NMR technique. At temperatures in the range of −95 to −110°C, ligand exchange is slow enough to permit the observation of separate15N NMR signals for bulk nitrate, and this anion in the cerium(III) principal coordination shell. In water-acetone-Freon-12 mixtures, the spectra reveal the nitrato complexes do not form consecutively. Rather, signals are observed for Ce(NO3)2+, Ce(NO3) 2 1+ , and only two other higher order complexes, even at very high NO 3 − to Ce(III) mole ratios. Signal area evaluations were used to identify the possible higher order complexes. At comparable salt concentrations in aqueous-methanol mixtures, only Ce(NO3)2+ and Ce(NO3) 2 1+ are formed, reflecting a decreased tendency for complexation in media of higher dielectric constant.
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  • 3
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; nitrogen-15 ; chlorine-35 ; NMR ; erbium nitrate ; complexation ; acetone ; methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The extent of inner-shell ion-pair formation of Er3+ with nitrate ion in aqueous mixtures has been studied by nitrogen-15 (15N) NMR spectroscopy. At low temperature, exchange is slow enough to permit the direct observation of15N signals for nitrate ions in the Er3+ solvation shell and in bulk medium. In water-acetone mixtures,15N NMR signals for the mono-and bis complexes are observed at low nitrate to Er3+ mole ratios, but only the bis complex is evident at higher anion concentrations. No spectral evidence for the tris complex was seen at any nitrate concentration. In water-methanol-acetone mixtures, signals for the mono and bis complexes persist even at higher nitrate concentrations, indicating a reduced tendency to ion-pair with increasing dielectric constant. Preliminary15N NMR results are presented for the nitrate complexes of other paramagnetic lanthanide ions.
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  • 4
    ISSN: 1572-8927
    Keywords: Carbon-13 ; nitrogen-15 ; chlorine-35 ; NMR ; samarium(III) ; isothiocyanate ; Sm3+ − NCS− complexes ; water–acetone–Freon ; water–methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Multinuclear magnetic resonance studies of trivalent lanthanide inner-shell ion-pairing with nitrate and isothiocyanate are continuing. For NCS− solutions in water–acetone–Freon mixtures at low temperature, generally −100 to −125°C, ligand exchange is slow enough to permit the observation of 13C and 15N NMR signals for coordinated and free anions. For samariuni(III) solutions, four coordinated NCS−signals, displaced about +35 ppm and +250 ppm from free anion, are observed in the 13C and 15N NMR spectra, respectively. The 13C and 15N NMR data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Sm(NCS)2+ through Sm(NCS) 4 1 . The coordination numbers reach a maximum of about three moles of NCS− per mole of Sm(III) with both nuclides, a result confirmed by spectral appearance showing the dominance of Sm(NCS)3 at the highest concentration studied. An analysis of the chemical shifts indicates that binding occurs at the nitrogen atom of NCS−. In water–methanol, due to the higher dielectric constant of such mixtures, coordination was less extensive. A competitive binding study with Ci− by 35Ci NMR demonstrated conclusively the superior coordinating ability of NCS−.
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  • 5
    ISSN: 1572-8927
    Keywords: carbon-13 ; nitrogen-15 ; chlorine-35 ; NMR ; cerium(III)–isothiocyanate complexes ; water–acetone–Freon ; water–methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of lanthanide complexation with isothiocyanate is underway using a multinuclear magnetic resonance technique. For isothiocyanate solutions in water–acetone–Freon mixtures at low temperature, −85–−125°C, ligand exchange is slow enough to permit the observation of 13C and 15N NMR signals for coordinated and free anions. For the Ce3+–NCS− system, four coordinated anion signals, displaced from the free anion signal by about +450 to +550 ppm for 15N and +50 to +80 ppm for 13C, are observed. The 13C and 15N spectral data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Ce(NCS)2+ through Ce(NCS)1- 4. In water–methanol, the extent of complexing is decreased, presumably because of the higher dielectric constant of this medium. In addition, the results of a competitive study of NCS− and Cl− ion binding, carried out using 35Cl NMR, is presented.
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