Proton NMR study of bis(tetramethylammonium) tetrachlorozincate at high pressures and low temperatures

Wide-line proton NMR studies on polycryst. bis(tetramethylammonium) tetrachlorozincate were carried out at high hydrostatic pressures up to 15 kbar at 77-300 K and at ambient pressure down to 4.2 K. A 2nd-moment transition is obsd. to occur starting around 161 K, the temp. for the V-VI phase transition. This transition temp. has a neg. pressure coeff. up to 2 kbar, beyond which it changes sign. At 77 K, the 2nd moment decreases to 4 kbar and then increases again as a function of pressure. The results are explained in terms of the dynamics of the $N(CH_3)_4$ groups