Self-Diffusion and Reorientation of Methylammonium Ions in (CH3NH3)2ZnCl4 Crystals as Studied by 1H-NMR

Differential thermal analysis, differential scanning calorimetry, and measurements of the H spin-lattice relaxation times and second moments of H-NMR absorptions were performed on methylammonium tetrachlorozincate (II) crystals over a wide temperature range. A solid-solid phase transition was located at 477 K. From the H-NMR experiments it was found that the cations undergo overall reorientation as well as three dimensional translational self-diffusion in the high-temperature phase. In the low-temperature phase, a 120° reorientational motion of the CH and NH groups of the cation about its C-N bond axis was detected. The parameters for the motional modes of the cations in the crystal were evaluated from the analysis of the H-NMR experimental results.