A multinuclear nuclear magnetic resonance study of methylammonium nitrate

Abstract

Deuterium nmr line shapes in the solid II phase of methylammonium nitrate (MAN) indicate that motion of the cation is restricted to internal rotations of the ND3 group about the C—N axis. In the high temperature plastic phase, solid I, of MAN, 2H, 14N, and 17O nmr results demonstrate that both the cation and anion undergo rapid overall rotations that result in complete averaging of all nuclear quadrupolar interactions. Spin-lattice relaxation results imply that rotations of the cation and anion are anisotropic and that the overall rotations are strongly coupled in both the solid I and liquid phases. At the melting point, overall rotations of the cation are only slightly faster in the liquid phase than in the solid I phase. In the solid I phase, in-plane rotations of the nitrate ion are about twice as rapid as end-over-end rotations of the C3 axis. In the neat liquid, rotations of the NO3− ion are more isotropic, with overall rotations being slightly faster than rotations about the symmetry axis.