ORIENTATIONS AND REORIENTATIONAL DYNAMICS OF METHANOL ENCLATHRATED IN BETA-QUINOL (HYDROQUINONE) FROM DIELECTRIC AND H-1, H-2, AND C-13 NMR-STUDIES

Dielectric measurements of methanol-β-quinol clathrate between 5 and 300 K show two widely separated relaxation regions associated with relaxation of the components of the methanol dipole moment parallel and perpendicular to the c axis of the crystal. Both are sensitive to the methanol content of the cages. For high methanol content, both components tend to become ordered below the transition at 66 K. NMR studies over a wide range of temperature were made of the H line shape in CH3OD-C6D6O2, D quadrupole coupling constant (DQCC) in CD3OH-C6H 6O2 and spin-lattice relaxation of H in CH 3OH-C6H6O2 and D in CD 3OH-C6H6O2. A 13C chemical shift anisotropy of σ∥-σ⊥= 20.6 ppm for CH3OH in a single crystal was obtained at 302 K. The DQCC in CH3OD was 109 kHz at 302 K. The results are consistent with a model of six preferred orientations of methanol, three related by 120° rotation about the c axis and three generated approximately by inversion of the first three through the cage center. In the preferred orientations, the COH plane is parallel to c and the angle of 32° between the CO bond and c below 100 K increases to ∼40° at 300 K. © 1979 American Institute of Physics.