NMR Studies on the Motion of Dimethylammonium Ions in [(CH3)2NH2]2SnCl6 and [(CH3)2NH2]2TeCl6 as well as Their Partially Deuterated Analogs

The temperature dependences of proton spin-lattice relaxation time, T1 and of the second moment of 1H NMR absorptions were studied in dimethylammonium hexachlorostannate(IV), hexachlorotellurate(IV), and their partially deuterated analogs. From X-ray powder patterns taken at room temperature, the tellurium(IV) complex was found to be isomorphous with the tin(IV) complex. For the tellurium complex, a phase transition was located at 169 K by DTA experiments. By 1H NMR, two kinds of motions, the reorientation of the methyl groups about their respective C - N bond axis and the 180° flip motion of the whole cation about its two fold pseudosymmetry axis, were observed for the cation in the crystals. The activation energies were evaluated for these motional modes. Besides these two motions, large-amplitude librations or small angle reorientations of the cation about its pseudosymmetry axis are deduced to take place at high temperatures.