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  • 1985-1989  (16)
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  • 11
    Electronic Resource
    Electronic Resource
    Direct measurement of a prominent outer-sphere electron self-exchange: kinetic parameters for the hexaaquaruthenium(II)/(III) couple determined by oxygen-17 and ruthenium-99 NMR (1985)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 107 (1985), S. 312-317 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00288a005
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  • 12
    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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  • 13
    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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  • 14
    Electronic Resource
    Electronic Resource
    Dimethylformamide-Exchange Mechanism on Some First-Row Divalent Transition-Metal IonsPart 33 of the series ‘High-Pressur NMR Study’. Part 32: [1].Taken in part from the diploma work of C. Cossy, Université de Lausanne, 1983.This work was presented in part at the 24th International Conference on Coordination Chemistry, Athens, Greece, August 1986. (1987)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 70 (1987), S. 1516-1525 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of temperature on the dimethylformamide exchange on Mn(DMF)2+6 and Fe(DMF)2+6 has been studied by 13C- and 17O-NMR, respectively, yielding the following kinetic parameters: k298 equals; (2.2±0.2). 106 S-1, ΔH≠ = 34.6 ± 1.3 kJ mol-1, ΔS≠ = -7.4 ± 4.8 J K-1mol-1 for Mn2+ and K298 = (9.7 ± 0.2).105 S-1, Delta;H≠ = 43.0 ± 0.9 kJ mol-1, ΔS≠ = + 13.8 ± 2.8 J K-1mol-1 for Fe2+. The volumes of activation, ΔV≠ in cm3mol-1, derived from high-pressure NMR on these metal ions, together with the previously published activation volumes for Co2+ and Ni2+ (+2.4 ± 0.2 (Mn2+), +8.5 ± 0.4 (Fe2+) +9.2 ± 0.3 (Co2+), + 9.1 ± 0.3 (Ni2+)) give evidence for a dissociative activation mode for DMF exchange on these high-spin first-row transition-metal divalent ions. The small positive ΔV≠ value observed for DMF exchange on Mn2+ seems to indicate that a mechanistic changeover also occurs along the series, (probably from Id to D), as for the other solvents previously studied (Ia to Id, for H2O, MeOH, MeCN). This changeover is shifted to the earlier elements of the series, due to more pronounced steric crowding for dimethylformamide hexasolvates.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19870700608
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  • 15
    Electronic Resource
    Electronic Resource
    Variable-Temperature and Variable-Pressure 17O-NMR Study of Water Exchange of Hexaaquaaluminium(III)Part 25 of the series ‘High-Pressure NMR Kinetics’. Part 24: [1].These results are part of the Ph. D. thesis of D. H.-C., University of Lausanne, 1984. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 545-554 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transverse relaxation rate of H2O in Al(H2O)63+ has been measured as a function of temperature (255 to 417 K) and pressure (up to 220 MPa) using the 17O-NMR line-broadening technique, in the presence of Mn(II) as a relaxation agent. At high temperatures the relaxation rate is governed by chemical exchange with bulk H2O, whereas at low temperatures quadrupolar relaxation is prevailing. Low-temperature fast-injection 17O-NMR was used to extend the accessible kinetic domain. The samples studied contained Al3+ (0.5 m), Mn2+ (0.2-0.5 m), H+ (0.2-3.1 m) and 17O-enriched (20-40%) H2O. Non-coordinating perchlorate was used as counter ion. The following H2O exchange parameters were obtained: kex298 = (1.29 ± 0.04) s-1, ΔH* = (84.7 ± 0.3) kJ mol-1, ΔS* = +(41.6 ± 0.9) J K-1 mol-1, and ΔVex* = +(5.7 ± 0.2) cm3 mol-1, indicating a dissociative interchange, Id, mechanism. These results of H2O exchange on Al(H2O)63+ are discussed together with the available complex-formation rate data and permit also the assignment of Id mechanisms to these latter reactions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680302
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  • 16
    Electronic Resource
    Electronic Resource
    Water Exchange on Hexaaquavanadium(III): a Variable-Temperature and Variable-Pressure 17O-NMR Study at 1.4 and 4.7 TeslaPart 24 of the series ‘High-Pressure NMR Kinetics’. Part 23: [1].These results are part of the Ph. D. thesis of A. H., University of Lausanne, 1984. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 508-521 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Water exchange on hexaaquavanadium (III) has been studied as a function of temperature (255 to 413 K) and pressure (up to 250 MPa, at several temperatures) by 17O-NMR spectroscopy at 8.13 and 27.11 MHz. The samples contained V3+ (0.30-1.53 m), H+ (0.19-2.25 m) and 17O-enriched (10-20%) H2O. The trifluoromethanesulfonate was used as counter-ion, and, contrary to the previously used chloride or bromide, CF3SO3- is shown to be non-coordinating. The following exchange parameters were obtained: kex298 = (5.0 ± 0.3) · 102 s-1, ΔH* = (49.4 ± 0.8) kJ mol-1, ΔS* = -(28 ± 2) JK-1 mol-1, ΔV* = -(8.9 ± 0.4) cm3 mol-1 and Δβ* = -(1.1 ± 0.3) · 10-2 cm3 mol-1 MPa-1. They are in accord with an associative interchange mechanism, Ia. These results for H2O exchange are discussed together with the available data for complex formation reactions on hexaaquavanadium(III). A semi-quantitative analysis of the bound H2O linewidth led to an estimation of the proportions of the different contributions to the relaxation mechanism in the coordinated site: the dipole-dipole interaction hardly contributes to the relaxation (less than 7%); the quadrupolar relaxation, and the scalar coupling mechanism are nearly equally efficient at low temperature (∼ 273 K), but the latter becomes more important at higher temperature (75-85% contribution at 360 K).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680224
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