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  • 1
    ISSN: 1572-8927
    Keywords: La(III) ; hydration ; proton ; NMR ; La-139 ; Cl-35
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A La(III) hydration study has been carried out for solutions of La(ClO4)3 and, in a preliminary way, La(NO3)3 in aqueous mixtures with acetone-d6 and Freon-12, using hydrogen-1, chlorine-35, and lanthanum-139 NMR spectroscopy. Low temperature, proton magnetic resonance experiments allowed the direct observation and area evaluation of separate signals for water molecules in the primary solvation shell of La(III) and in bulk medium. Measurements over a wide range of salt and solvent concentration gave a maximum La(III) hydration number of 6 and no evidence for inner-shell ion-pairing in La(ClO4)3 solutions. Chlorine-35 chemical shift and linewidth data in these solutions confirmed the absence of contact ionpairing. Hydration numbers of 3–4 for La(III) in several La(NO3)3 solutions clearly indicated inner-shell complex formation. Lanthanum-139 chemical shift and linewidth measurements for these systems revealed the presence of some process, possibly hydrolysis, in the La(ClO4)3 solutions at extremely high acetone-d6 concentrations.
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  • 2
    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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  • 3
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; carbon-13 ; nitrogen-15 ; cadmium-113 ; NMR ; infrared ; zinc(II) ; cadmium(II) ; isothiocyanate ; complexation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of zinc(II) and cadmium(II) complexes with isothiocyanate ion has been completed, using a low-temperature, multinuclear magnetic resonance technique that permits the observation of separate resonance signals for bound and free ligand, and Cd(II) metal ion. The Zn2+–NCS− complexes were studied by 1H, 13C, and 15N NMR spectroscopy. In the 1H spectra, the intensity of the coordinated water signal, corresponding to a Zn(II) hydration number of six in the absence of NCS−, decreases dramatically as this anion is added, indicating the complexing process involves more than a simple 1:1 ligand replacement. The 13C and 15N NMR spectra reveal signals for four species, most reasonably assigned to a series of tetrahedrally coordinated Zn2+–NCS− complexes. In the Cd2+–NCS− solution spectra, the 13C and 15N signals for four complexes also are observed and they are three line patterns, corresponding to a doublet from 113Cd J-coupling, and a dominant central peak, resulting from bonding to magnetically inactive Cd isotopes. The 113Cd spectra, showing signals for four complexes, correlate well in all respects with the 13C and 15N results, including coupling in specific cases. The spectral results for both metal ions reflect binding at the nitrogen atom of NCS−, with the complexes changing from an octahedral to a tetrahedral configuration when doing so. Confirming evidence for these conclusions also was provided by several infrared measurements of these metal–ion systems.
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  • 4
    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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  • 5
    ISSN: 0749-1581
    Keywords: 1H NMR ; 27Al NMR ; Al(ClO4)3 in aqueous dimethylformamide and urea ; Proton and ligand exchange ; Low-temperature studies ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A competitive solvation study of Al(III) in water-dimethylformamide (DMF) and water-urea mixtures was carried out by 1H and 27Al NMR spectroscopy. At temperatures low enough to slow proton and ligand exchange, separate 1H resonance signals were observed for bulk and coordinated ligand molecules, and for 27Al in different solvation complexes. The 1H NMR data confirmed hexacoordination of Al(III) at all concentrations, monodentate binding at the oxygen atom of both DMF and urea, preferential solvation by both organic ligands, the presence of steric hindrance to complexation, particularly by DMF, and the identification of the complexes responsible for the 27Al spectra. It also showed a non-equivalence of the amido groups in urea, in both the complex and free states, presumably owing to hindered rotation about the carbon - oxygen bond. In contrast to previous reports, the 27Al spectra for the water-DMF and water-urea solutions showed well resolved signals for the species [Al(H2O)n-6Ln]3+ (n = 0-6; L = DMF or urea), including two isomers for one of the water-urea complexes. The 27Al NMR data reflected the stronger preferential solvation by urea.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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