MOLECULAR-MOTION OF METHYL ROTOR IN A ZEOLITE - PROTON NMR LINESHAPESOF CH3CN-(2)HZSM-5 ADSORPTION COMPLEX

Proton lineshapes of methyl group in spatially isolated stoichiometric 1:1 CH3CN-(2)HZSM-5 adsorption complexes are shown as a function of t emperature. At 78 K, the methyl group dipolar lineshape is characteris tic of a fixed-axis tunneling planar rotator. With increasing temperat ure, one observes motional averaging associated with the reorientation of the symmetry axis of the hydrogen-bonded acetonitrile at the acid site. Since changes in dipolar anisotropy with temperature are determi ned by confinement interactions, lineshape measurements can be used to explore dispersion interactions in zeolitic frameworks. These interac tions are highly dependent on differences in size, geometry and rigidi ty of zeolite cavities. (C) 1998 Elsevier Science B.V. All rights rese rved.