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6Li NMR Spectroscopy

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David B Collum – One of the best experts on this subject based on the ideXlab platform.

Gillian R. Goward – One of the best experts on this subject based on the ideXlab platform.

  • An Improved Understanding of Li+ Hopping Pathways and Rates in Li3Fe2(PO4)3 Using Selective Inversion 6Li NMR Spectroscopy
    The Journal of Physical Chemistry C, 2013
    Co-Authors: Danielle L. Smiley, L. J. M. Davis, Gillian R. Goward
    Abstract:

    6Li selective inversion NMR experiments are used to reveal Li ion exchange rates and energy barriers for Li ion hopping in monoclinic Li3Fe2(PO4)3. The three crystallographically unique Li sites in this material are well resolved by magic-angle spinning, thus allowing for the examination of all three exchange processes. We have revisited this material using selective inversion to probe dynamics, and energy barriers over the temperature range 268–397 K are found to be 0.37 ± 0.07, 0.53 ± 0.02, and 0.52 ± 0.03 eV for the three unique exchange pairs. The results presented here are consistent with the known Li3Fe2(PO4)3 crystal structure. The selective inversion experiment is more robust than 2D EXSY for the determination of energy barriers by NMR; this can be attributed to the efficiency of the one-dimensional technique, and an exchange model that accounts for multisite exchange and fast spin–lattice relaxation. Moreover, bond valence sum density maps provide a meaningful depiction of lithium ion diffusion p…

  • an improved understanding of li hopping pathways and rates in li3fe2 po4 3 using selective inversion 6Li NMR Spectroscopy
    Journal of Physical Chemistry C, 2013
    Co-Authors: Danielle L. Smiley, L. J. M. Davis, Gillian R. Goward
    Abstract:

    6Li selective inversion NMR experiments are used to reveal Li ion exchange rates and energy barriers for Li ion hopping in monoclinic Li3Fe2(PO4)3. The three crystallographically unique Li sites in this material are well resolved by magic-angle spinning, thus allowing for the examination of all three exchange processes. We have revisited this material using selective inversion to probe dynamics, and energy barriers over the temperature range 268–397 K are found to be 0.37 ± 0.07, 0.53 ± 0.02, and 0.52 ± 0.03 eV for the three unique exchange pairs. The results presented here are consistent with the known Li3Fe2(PO4)3 crystal structure. The selective inversion experiment is more robust than 2D EXSY for the determination of energy barriers by NMR; this can be attributed to the efficiency of the one-dimensional technique, and an exchange model that accounts for multisite exchange and fast spin–lattice relaxation. Moreover, bond valence sum density maps provide a meaningful depiction of lithium ion diffusion p…

Klaus Dr Bronstert – One of the best experts on this subject based on the ideXlab platform.

Danielle L. Smiley – One of the best experts on this subject based on the ideXlab platform.

  • An Improved Understanding of Li+ Hopping Pathways and Rates in Li3Fe2(PO4)3 Using Selective Inversion 6Li NMR Spectroscopy
    The Journal of Physical Chemistry C, 2013
    Co-Authors: Danielle L. Smiley, L. J. M. Davis, Gillian R. Goward
    Abstract:

    6Li selective inversion NMR experiments are used to reveal Li ion exchange rates and energy barriers for Li ion hopping in monoclinic Li3Fe2(PO4)3. The three crystallographically unique Li sites in this material are well resolved by magic-angle spinning, thus allowing for the examination of all three exchange processes. We have revisited this material using selective inversion to probe dynamics, and energy barriers over the temperature range 268–397 K are found to be 0.37 ± 0.07, 0.53 ± 0.02, and 0.52 ± 0.03 eV for the three unique exchange pairs. The results presented here are consistent with the known Li3Fe2(PO4)3 crystal structure. The selective inversion experiment is more robust than 2D EXSY for the determination of energy barriers by NMR; this can be attributed to the efficiency of the one-dimensional technique, and an exchange model that accounts for multisite exchange and fast spin–lattice relaxation. Moreover, bond valence sum density maps provide a meaningful depiction of lithium ion diffusion p…

  • an improved understanding of li hopping pathways and rates in li3fe2 po4 3 using selective inversion 6Li NMR Spectroscopy
    Journal of Physical Chemistry C, 2013
    Co-Authors: Danielle L. Smiley, L. J. M. Davis, Gillian R. Goward
    Abstract:

    6Li selective inversion NMR experiments are used to reveal Li ion exchange rates and energy barriers for Li ion hopping in monoclinic Li3Fe2(PO4)3. The three crystallographically unique Li sites in this material are well resolved by magic-angle spinning, thus allowing for the examination of all three exchange processes. We have revisited this material using selective inversion to probe dynamics, and energy barriers over the temperature range 268–397 K are found to be 0.37 ± 0.07, 0.53 ± 0.02, and 0.52 ± 0.03 eV for the three unique exchange pairs. The results presented here are consistent with the known Li3Fe2(PO4)3 crystal structure. The selective inversion experiment is more robust than 2D EXSY for the determination of energy barriers by NMR; this can be attributed to the efficiency of the one-dimensional technique, and an exchange model that accounts for multisite exchange and fast spin–lattice relaxation. Moreover, bond valence sum density maps provide a meaningful depiction of lithium ion diffusion p…

Lara R Liou – One of the best experts on this subject based on the ideXlab platform.

  • Solution structures of lithium amino alkoxides used in highly enantioselective 1,2-additions.
    Journal of the American Chemical Society, 2014
    Co-Authors: Angela M. Bruneau, Lara R Liou, David B Collum
    Abstract:

    Lithium ephedrates and norcarane-derived lithium amino alkoxides used to effect highly enantioselective 1,2-additions on large scales have been characterized in toluene and tetrahydrofuran. The method of continuous variations in conjunction with 6Li NMR Spectroscopy reveals that the lithium amino alkoxides are tetrameric. In each case, low-temperature 6Li NMR spectra show stereoisomerically pure homoaggregates displaying resonances consistent with an S4-symmetric cubic core rather than the alternative D2d core. These assignments are supported by density functional theory computations and conform to X-ray crystal structures. Slow aggregate exchanges are discussed in the context of amino alkoxides as chiral auxiliaries.

  • lithium phenolates solvated by tetrahydrofuran and 1 2 dimethoxyethane structure determination using the method of continuous variation
    Journal of the American Chemical Society, 2009
    Co-Authors: Timothy S De Vries, Lara R Liou, Jocelyn M Gruver, Anandarup Goswami, Emily Jayne, David B Collum
    Abstract:

    The method of continuous variation in conjunction with 6Li NMR Spectroscopy was used to characterize lithium phenolates solvated by tetrahydrofuran and 1,2-dimethoxyethane. The strategy relies on the formation of ensembles of homo- and heteroaggregated phenolates. The symmetries and concentration dependencies of the heteroaggregates attest to the aggregation numbers of the homoaggregates. The structurally diverse phenols afford substrate- and solvent-dependent combinations of lithium phenolate monomers, dimers, trimers, tetramers, and pentamers. We discuss the refinement of protocols for characterizing O-lithiated species. Computational studies examine further the substituent and solvent dependencies of aggregation.

  • structures of β amino ester enolates new strategies using the method of continuous variation
    Journal of the American Chemical Society, 2008
    Co-Authors: Lara R Liou, Anne J Mcneil, Gilman E S Toombes, David B Collum
    Abstract:

    The solution structures of four enolates derived from β-amino esters are investigated using 6Li NMR Spectroscopy in conjunction with the method of continuous variation (method of Job). Ensembles of homo- and heteroaggregated enolates are generated by mixing enantiomers of a single enolate (R/S mixtures), opposite antipodes of two different enolates (R/S′ mixtures), and the same antipodes of two different enolates (R/R′ mixtures). The numbers of observable aggregates and their dependence on the mole fraction of the two enolates confirm the hexamer assignments. Inherent symmetries observable in the 6Li NMR spectra show the stereochemistry of chelation about the hexagonal drum.