NMR in molecular crystals

Abstract

The 1H, 19F and 13C relaxation times of fluoroadamantane C10H15F are measured over a wide temperature range. These relaxation times are analysed with two dynamical descriptions: an isotropic rotational diffusion and a Frenkel jump model. In this jump model, the structural equilibrium positions are taken into account and therefore two molecular motions are able to explain adequately the experimental results obtained in the plastic phase: a three-fold uniaxial rotation around the dipolar C-F axis and a tumbling reorientation of this axis between <111> cubic axes. The refinements are first carried out using 1H and 19F NMR results in conjunction with the residence time deduced from the dielectric relaxation. Finally, by introducing the 13C NMR results obtained in the plastic phase a precise determination of the two residence time can be made from the NMR results alone.