| Résumé | A method is presented for detecting multiple xenon atoms in cavities of solid-state inclusion compounds using ¹²⁹Xe double quantum NMR spectroscopy. Double quantum filtered ¹²⁹Xe NMR spectra, performed on the xenon clathrate of Dianin's compound were obtained under high-resolution Magic-Angle Spinning (MAS) conditions, by recoupling the weak ¹²⁹Xe-¹²⁹Xe dipole-dipole couplings that exist between xenon atoms in close spatial proximity. Because the ¹²⁹Xe-¹²⁹Xe dipole-dipole couplings are generally weak due to dynamics of the atoms and to large internuclear separations, and since the ¹²⁹Xe Chemical Shift Anisotropy (CSA) tends to be relatively large, a very robust dipolar recoupling sequence was necessary, with the symmetry-based SR26¹¹₄ dipolar recoupling sequence proving appropriate. We have also attempted to measure the ¹²⁹Xe-¹²⁹Xe dipole-dipole coupling constant between xenon atoms in the cavities of the xenon-Dianin's compound clathrate and have found that the dynamics of the xenon atoms (as investigated with molecular dynamics simulations) as well as ¹²⁹Xe multiple spin effects complicate the analysis. The double quantum NMR method is useful for peak assignment in ¹²⁹Xe NMR spectra because peaks arising from different types of absorption/inclusion sites or from different levels of occupancy of single sites can be distinguished. The method can also help resolve ambiguities in diffraction experiments concerning the order/disorder in a material. |
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