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  • 1990-1994  (2)
  • 1994  (2)
  • Chemistry  (2)
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  • 1990-1994  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Variable-Temperature and -Pressure 31P-NMR Study of the Intramolecular PPh3 Migration in the Cluster Compound [Ir2Rh2(CO)11PPh3] (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 547-553 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of [Ir2Rh2(CO)12] with 1 mol-equiv. of PPh3 yields [Ir2Rh2(CO)11PPh3] (1) as a mixture of two isomers with the phosphine ligand axially bound either to one basal Rh-atom in the kinetically preferred isomer 1 R or to one basal Ir-atom in the thermodynamically preferred isomer 11. Both isomers are fluxional on the 13C-NMR time scale at low temperature due to CO scrambling. Around room temperature, a new type of fluxional process starts to operate which is responsible for the isomerisation 1R⇄11, i.e. the intramolecular migration of the reputedly inert PPh3 ligand from one metal centre to another. The activation volumes of conversions 1R → 11 and 11 → 1R are both positive, indicating that the migration of PPh3 is dissociative in character. This article reports the first application of variable pressure 31P-NMR to mechanistic studies.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770216
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Water exchange on the light lanthanide aqua ions [Pr(H2O)9]3+ and [Nd(H2O)9]3 +: A variable temperature and magnetic field 17O NMR study (1994)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 32 (1994), S. 739-745 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; 17O ; Nd3+ ; Pr3+ ; Water exchange ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 17O NMR relaxation rate measurements were made on aqueous perchlorate solutions of the light lanthanide ions Nd3+ and Pr3+, with the aim of measuring the kinetics of water exchange on these ennea aqua ions. Variable-temperature results at three magnetic fields show that the ‘kinetic’ effect is not the only contribution to the difference between the transverse and longitudinal relaxation rates. The results at high magnetic field allow lower limits, kex298 ≥ 5 × 108 S-1 and kex298 ≥ 4 × 108 s-1, to be determined for water exchange rates at 298.15 K on [Nd(H2O)9]3+ and [Pr(H2O)9]3+, respectively. These limits are consistent with our current understanding of water exchange on the lanthanide aqua ions, based on the change of relative stability of the ennea and octa aqua ions across the series.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260321207
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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