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  • 1985-1989  (4)
  • 1988  (4)
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  • 1985-1989  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Oxygen-17 nuclear magnetic resonance kinetic study of water exchange on the lanthanide(III) aqua ions (1988)
    s.l. : American Chemical Society
    Inorganic chemistry 27 (1988), S. 1973-1979 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00284a028
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    High-pressure NMR kinetics. Part 34. Variable-temperature and variable-pressure NMR kinetic study of solvent exchange on hexaaquaruthenium(3+) and -(2+) and hexakis(acetonitrile)ruthenium(2+) (1988)
    s.l. : American Chemical Society
    Inorganic chemistry 27 (1988), S. 873-879 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00278a025
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The solution structure and reactivity of decavanadate (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1406-1420 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxygen-exchange reaction of V10O286- with bulk water has been followed by time-dependent 17O-NMR spectroscopy (buffered solutions, pH ∼ 5.5, [V10]total ∼ 0.17m, T = 298 K). It is shown that all seven structurally different sites of O-atoms are kinetically similar but, in contrast to earlier studies, not identical (6 h ≤ ‘t1/2’ ≤ 11 h). The kinetic similarity of the various structural sites implies the some (but not full) O scrambling is involved. Two possible mechanisms with a ‘half-bonded’ and an ‘open’ intermediate are discussed in detail to interpret the experimental results. A computer simulation of the exchange reaction based on these models is presented. It is shown that the ‘half-bonded-intermediate’ mechanism is consistent with the experimental data and the following parameters are calculated: formation of the intermediate: k1 = 5.8 · 10-3 s-1, k-1 = 6.7 · 10-2 s-1, [intermediate]∞ ≈ 8%; all activated O-atoms exchange within the lifetime of the intermediate (τ ∼ 15 s), and the calculated exchange rate of the intermediate (k2 ≥ 0.60 s-1) is consistent with earlier assumptions (k2 ≈ 0.5 s-1). It is shown that a simulation based on the ‘open-intermediate’ mechanism results in kinetic parameters which are not consistent with the kinetics of the formation of cyclic metavanadates ((VO3-)n, n = 4,5) from decavanadate, since the required formation rate is by a factor ∼ 102 too fast, and the equilibrium concentration of metavanadates is by a factor of ∼ 2 too large (under the conditions of the O-exchange experiments of decavanadate (T = 298 K, [V10]total ≈ 0.17m, pH ∼ 5.55) the total amount of metavanadates present is ∼ 8%, with [(VO3-)4]/[(VO3-)5] ∼ 4:1; a qualitative analysis of the kinetics of the formation of metavanadates (vo kinetics; the exact mechanism of the back-reaction (at least second-order) is not known with certainty) leads to k1 ≥ 4·10-5 s-1). O exchange of decavanadates via equilibrated metavanadates would lead to full scrambling of the O sites and is not consistent with the observed differences in the exchange rates. From the qualitative kinetic parameters of the metavanadate formation kinetics, it can be concluded that any contribution of an ‘open’ or an ‘metavanadate’ mechanism is of the order of 1-2% at most.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710605
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Intramolecular Dynamics of Five-coordinate iron Carbonyl Complexes with olefinic ligands as studied by variable-pressure 1H-NMR spectroscopy (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1458-1466 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Variable-pressure 1H-NMR Spectroscopy has been used to study the fluxionality of some five-coordinated Fe complexes in solution. For [Fe(CO)2 1,3-cyclooctadiene (PPh3)], the CO site exchange is known (by analogy with [Fe(CO)3(1,3-cyclooctadiene)]) to be a non-dissociative process, and an activation volume of ca. 0 cm3.mol-1 was indeed obtained. However, for [Fe(CO2){2,3-η:O-σ-(7,7-dimethoxybicyclo[2.2.1]hept-2-ene)}(PPh3)], the activation volume of +5 cm3 mol-1 suggests that an unprecedented dissociation process is responsible for the CO site exchange. The molecular structure of [Fe(CO)2(1,3-cyclooctadiene)(PPh3)] was ascertained by single-crystal X-ray diffractometry. The crystals are triclinic, space group P1, a = 9.606(3), b = 16.795(2), c = 7.743(8) Å, α = 97.83(4), β = 109.63(4), γ = 83.37(2)°. The structure determination has shown that the complex possesses a tetragonal pyramidal coordination, with the endocyclic C=C bond and PPh3 occupying basal sites.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710609
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    Paper (German National Licenses)
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