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  • Electronic Resource  (31)
  • Chemistry  (31)
  • General Chemistry  (4)
  • Hexaaquarhodium(III)  (1)
  • 11
    Electronic Resource
    Electronic Resource
    High-Pressure Stopped-Flow Study of the Kinetics of Base Hydrolysis of the Dichromate Ion by Hydroxide Ion, Ammonia, Water, and 2,6-Lutidine in Aqueous Solution (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 2445-2448 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Volumes of activation for the base hydrolysis of the dichromate anion have been measured at 298.2 K, using high-pressure stopped-flow spectrophotometry. The values of ΔV* (cm3 · mol-1), - 17.9 ± 0.6, - 19.2 ± 0.9, - 24.9 ± 0.9 and - 26.0 ± 0.7 for OH-, NH3, H2O and 2,6-lutidine, respectively, are consistent with an interchange mechanism with associative activation mode (Ia).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660809
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  • 12
    Electronic Resource
    Electronic Resource
    The Reaction Volume for the Equilibrium between the Lanthanide (III) ennea- and octaaqua lons as a diagnostic aid for their water-exchange mechanisms. Preliminary Communication (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1971-1973 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equilibrium between [Ce(H2O)9]3+ and [Ce(H2O)8]3+ has been followed in aqueous solution at 298 K by variable-pressure UV spectroscopy at 295 nm. The dervied volume of reaction for the dissociation of this enneaaqua ion is ΔV0 = +10.9 cm3. mol-1. This value, together with the previously determined activation volume, ΔV≠ = -6 cm3. mol-1, for H2O exchange on [Ln(H2O)8]3+ (Ln = Tb to Tm), allows the assignment of an associative interchange Ia mechanism on these octaaqua ions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710815
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  • 13
    Electronic Resource
    Electronic Resource
    Variable-Temperature and Variable-Pressure Kinetic and Equilibrium studies of formation and dissociation of [V(H2O)5NCS]2+ (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 1801-1808 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of formation and dissociation of [V(H2O)5NCS]2+ have been studied, as a function of excess metal-ion concentration, temperature, and pressure, by the stopped-flow technique. The thermodynamic stability of the complex was also determined spectrophotometrically. The kinetic and equilibrium data were submitted to a combined analysis. The rate constants and activation parameters for the formation (f) and dissociation (r) of the complex are: kf298/M-1 · S-1 = 126.4, kr298/s-1 = 0.82; ΔHf≠ /kJ · mol-1 = 49.1, ΔHr≠/kJ · mol-1 = 60.6; ΔSf≠/ J·K-1·mol-1= -39.8, ΔSr≠J·K-1·mol-1 = -43.4; ΔVf≠/cm3·mol-1 = -9.4, and ΔVr≠/cm3 · mol-1 =-17.9. The equilibrium constant for the formation of the monoisothiocynato complex is K298/M-1 = 152.9, and the enthalpy and entropy of reaction are ΔH0/kJ · mol-1 = - 11.4 and ΔS0/J. K-1mol-1 = +3.6. The reaction volume is ΔV0/cm3· mol-1 = +8.5. The activation parameters for the complex-formation step are similar to those for the water exchange on [V(H2O)6]3+ obtained previously by NMR techniques. The activation volumes for the two processes are consistent with an associative interchange, Ia, mechanism.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720816
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  • 14
    Electronic Resource
    Electronic Resource
    High-Pressure, High-Resolution Nuclear Magnetic Resonance (HPHR-NMR.): A Tool in Chemical KineticsPresented in part at the XVIIth International Conference on Coordination Chemistry in Hamburg, German Federal Republic, September 1976. (1977)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 60 (1977), S. 1124-1127 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In recent years the volume of activation Δ V* has become a powerful tool in chemical kinetics. High resolution NMR. spectroscopy is now one of the most common techniques used in the study of the kinetics of labile chemical systems. In order to measure Δ V* by this technique, we have built a 1H-probe-head, for a Fourier transform spectrometer, working up to 4 kbar and with a resolution of 0.6 Hz. The temperature is regulated and measured with an accuracy better than 0.2°. The high pressure probe-head has been tested on a chemical system showing a dissociative-associative crossover for the ligand substitution mechanism. It had been shown previously that the ligand exchange TaBr5 · L + *L ⇄ TaBr5 · *L + L proceeds via a D mechanism when L=Me2O, and via an Ia mechanism when L=Me2S. As expected, ΔV0* is positive (+30.5 ± 2.0 cm3 mol-1) for the dissociative process and negative (-12.6 ± 1.0 cm3 mol-1) for the associative one.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19770600335
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  • 15
    Electronic Resource
    Electronic Resource
    Volumes of Activation for Dimethylsulfoxide and N,N-Dimethylformamide Exchange with Hexasolvates of Aluminium (III) and Gallium (III) Ions in Deuterionitromethane SolutionHigh-pressure NMR. kinetics, part 10. For part 9 see [1]. (1980)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 63 (1980), S. 268-276 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-pressure 1H-NMR. has been used to determine volumes of activation (ΔV#) for solvent exchange with [M(S)6]3+ ion (M = Al(III), Ga(III); S = dimethylsulfoxide (DMSO) and N,N-dimethylformamide (DMF)) in [2H]3-nitromethane solution. For Al(III),Δ V# = + 15.6 ± 1.4 (S = DMSO, 358.5 K) and ΔV# = + 13.7 ± 1.2 cm3mol-1 (S = DMF, 354.5 K), whilst for Ga(III), ΔV# = + 13.1 ± 1.0 (S = DMSO, 334.6 K) and ΔV# = +7.9 ± 1.6 cm3mol-1 (S= DMF, 313.8 K). Variable temperature studies over a temperature range of 107.2 K (Al(III)) and 101.1 K (Ga(III)) were carried out for solvent exchange with [M(DMF)6]3+ ions in [2H]3-nitromethane solution, using stopped-flow NMR, and conventional linebroadening, and gave ΔH# = 88.3 ± 0.9 and 85.1 ± 0.6 kJ+ mol-1, and ΔS# = 28.4 ± 2.7 and 45.1 ± 1.9 JK-1 mol-1 for Al(III) and Ga(III) ions respectively. All of these results are consistent with dissociative modes of activation.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19800630127
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  • 16
    Electronic Resource
    Electronic Resource
    Adducts of Niobium (V) and Tantalum (V) Halides. XVPart XIV: [1].. Ligand Exchange of the Adducts with Some Phosphoryl CompoundsAbstracted, in part, from the Ph. D. Thesis of C. M. P. Favez, University of Lausanne, 1976. (1977)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 60 (1977), S. 2695-2702 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ligand exchange MX5·L + *L⇌MX5·*L + L for the octahedral adducts MX5·L, in an inert solvent (CH2Cl2 or CHCl3) with neutral ligands, proceeds via a dissociative D mechanism when M = Nb, X = Cl and L = phosphoryl compound. A dissociative interchange Id mechanism is suggested when M = Nb or Ta, and X = F. A first order rate law and positive values for ΔS* (+4 to +14 cal K-1 mol-1) are observed for the exchanges on the pentachloride adducts. However, a second order rate law and large negative values for ΔS* (-15 to -24 cal K-1 mol-1) are found for the intermolecular neutral ligand exchange (measured by 1H-NMR.) and for the intramolecular fluorine exchange (measured by 19F-NMR.) reactions on the pentafluoride adducts. The fluorine exchange is 2 to 5 times faster than the ligand exchange. The exchanges, on the pentachloride and on the pentafluoride adducts, are slowed down with increasing donor strength of the phosphoryl compound.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19770600820
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  • 17
    Electronic Resource
    Electronic Resource
    Magnetic-Field-Dependent Electronic Relaxation of Gd3+ in Aqueous Solutions of the Complexes [Gd(H2O)8]3+, [Gd(propane-1,3-diamine-N,N,N′,N′-tetraacetate)(H2O)2]-, and [Gd(N,N′-bis[(N-methylcarbamoyl)methyl]-3-azapentane-1,5-diamine-3,N,N′-triacetate)(H2O)] of interest in magnetic-resonance imaging (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 2129-2146 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: EPR Spectra have been measured for aqueous solutions of a series of Gd3+ complexes at variable temperature and a range of magnetic fields; S-band (0.14 T), X-band (0.34 T), Q-band (1.2 T), and 2-mm-band (5.0 T). The major contribution to the observed line widths is magnetic-field-dependent and is interpreted as being due to the modulation of the zero-field splitting produced by distortion of the complexes from perfect symmetry. The transverse and longitudinal relaxation matrices for an 8S ion with such an interaction have been calculated using Redfield theory with vector-coupling methods, and diagonalised numerically to obtain relaxation rates and intensities for the degenerate transitions which contribute to the multiplet. The observed line width, which is inversely proportional to the magnetic field at low temperatures, is best described by the intensity-weighted mean transverse relaxation time for the four transitions with non-zero intensity. A least-squares fit of the data yields the square of the zero-field splitting tensor, Δ2, and a correlation time, τv, with activation energy, Ev. The physical significance of these parameters and the extent of validity of the theoretical approach are considered. The parameters are used to predict the magnetic-field dependence of the longitudinal and transverse electronic relaxation times, which are discussed in the context of their relevance to 1H-NMR relaxivity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760524
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  • 18
    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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  • 19
    Electronic Resource
    Electronic Resource
    Mechanisms of Water Exchange between Lanthanide(III) Aqua Ions [Ln(H2O)n]3+ and bulk water: A Molecular Dynamics Simulation Approach Including High-Pressure Effects (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 285-294 
    Details
    ISSN: 0947-6539
    Keywords: computer simulations ; high-pressure chemistry ; lanthanide complexes ; ligand exchange ; mechanistic studies ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the microscopic mechanisms of the water exchange reaction between the hydration shells of lanthanide(III) ions (Ln = Nd, Sm, Yb) and bulk water by means of molecular dynamics simulations. In contrast to the residence time of a water molecule in the first hydration shell (τres (1st shell) = 1577, 170 and 410 ps for Nd3+, Sm3+ and Yb3+, respectively), that in the second hydration shell is nearly independent of the type of the cation and amounts to 12-18 ps. Along the lanthanide series a change in the coordination number from 9 to 8 is coupled to a changeover in the water exchange mechanism. The observed water exchange events on the [Nd(H2O)9]3+ aqua ion follow a dissociatively activated Id mechanism via an eightfold-coordinated transition state of square antiprismatic geometry. The lifetime of the transitory square antiprism varies between virtually 0 and 10 ps. The assignment of an Id mechanism (instead of a limiting D mechanism) is supported by the existence of a preferential arrangement between the exchanging water molecules (1800) and by the fact that the calculated average activation volume ΔV≠ = + 4.5 cm3 mol-1 is clearly smaller than the estimated activation volume ΔV≠lim ≈ΔV0 = + 7.2 cm3 mol-1 for a limiting D process. In the case of Sm3+ a ninth water molecule exchanges frequently between the first hydration shell and the bulk and maintains the coordination equilibrium between a [Sm(H2O)8]3+ and a [Sm(H2O)9]3+ aqua ion. The resulting trajectory pattern of incoming and leaving water molecules is an alternation of elimination and addition reactions and cannot be classified into the scheme of D, I or A mechanisms for substitution processes. The reaction volume ΔV0 for the coordination equilibrium [Sm(H2O)8]3+ + H2O → [Sm(H2O)9]3+ can be evaluated consistently both by a thermodynamic and a geometric approach. The observed exchange events for [Yb(H2O)8]3+ exhibit the characteristics of an Ia mechanism. The water exchange takes place via a transition-state geometry close to that of a tricapped trigonal prism and involves a slightly negative activation volume.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020309
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  • 20
    Electronic Resource
    Electronic Resource
    17O-NMR, EPR and NMRD Characterization of [Gd(DTPA-BMEA)(H2O)]: A Neutral MRI Contrast Agent (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2017-2021 
    Details
    ISSN: 1434-1948
    Keywords: MRI ; GdIII complexes ; NMR spectroscopy ; NMRD ; Lanthanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study including variable-temperature and -pressure, multiple-field 17O NMR, EPR and NMRD has been performed on the MRI contrast agent, [Gd(DTPA-BMEA)(H2O)]. The water exchange rate [kex298 = (0.39 ± 0.02) × 106 s-1] and the activation volume (ΔV≠ = +7.4 ± 0.4 cm3 mol-1), hence the mechanism, are identical to those for [Gd(DTPA-BMA)(H2O)]. The longer rotational correlation time of [Gd(DTPA-BMEA)(H2O)], as obtained from a global analysis of 17O-NMR, EPR and NMRD data, and compared to that of [Gd(DTPA-BMA)(H2O)], can be explained by water molecules hydrogen-bonded to the ether oxygen atoms of the ligand side chain.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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