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 1H spinlattice relaxation times and second moments of 1H-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 1H-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 120deg reorientational motion of the CH3 and NH+3 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 1H-NMR experimental results. (orig.)