Dynamics of molecules intercalated in vanadium oxychloride: X-rays, NMR line widths and inelastic neutron scattering studies

Abstract

The structure and dynamics of molecular intercalates of the layer compound VOCl have been studied using X-rays, NMR and neutron scattering. Molecules containing nitrogen atoms enter between the sheets of Cl- ions which displace relative to each other to accommodate the intercalated molecules. This work mainly concerns pyridine and the methyl pyridines. The separation of the layers measured by X-rays indicates that the molecular axes are inclined to the layers, and this is confirmed through the observation of a NMR linewidth transition near 250K which shows that the molecules can reorient rapidly between a number of equivalent positions arising from the high symmetry of the environment of Cl- ions. A detailed analysis is given of motional averaging due to molecular reorientation in an orthorhombic cell. To account for the tilt and the rapid molecular motion, it is proposed that the molecules are attached to the layers only at the nitrogen atoms and are tilted from a perpendicular orientation by the pressure of the mutual attraction of the Cl- layers. Neutron scattering studies show that the methyl group rotation is weakly hindered.