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Abstract:
Proton and fluorine FT wide line dipolar spectra of a single crystal of KHF2 have been recorded for various orientations of the magnetic field H0. Due to the small H-F distance in the bifluoride ion, the proton intermolecular splitting is unusually large (maximum splitting 293 kHz) yielding exceptionally well-resolved 5-line spectra (arbitrary orientation of H0). The splitting allows an unusually precise determination of the proton-fluorine distance rH−F. The result, is in good agreement with neutron diffraction data and confirms that the proton occupies a symmetric position between the hydrogen bonded fluorine atoms. The calculated proton intermolecular broadening fully accounts for the angular dependence of the width of the various lines in the dipolar spectrum. The fluorine wide-line spectrum shows a clear asymmetry due to the anisotropy of the magnetic shielding. From the experimental spectra one is able to deduce the principal values of the shielding tensor: σxx = -59.7 ± 5, σγγ = −43.4 ± 5 and σzz = +32.5 ± 5 ppm relative to C6F6. (z is along the bond axis; y is perpendicular to the bond and to the plane where the ions are arranged; y is perpendicular to the bond in that plane).
