Polymorphism and multiple twinning of (Et4N)(2)ZnCl4

The phase sequence of (Et4N)(2)ZnCl4 has been determined based on thermal analysis and Cl-35 NQR spectroscopy. On cooling two phase transitions are observed at 223.0(5) and 217.7(9) K. respectively. On heating only one phase transition is found at 228.4(3) K. Therefore three phases are distinguished below the decomposition point (556(5) K) with a metastable phase in the temperature region 217-229 K. a twinned low-temperature phase below and a disordered high-temperature phase above this region. respectively. The structure of the low-temperature phase has been determined from X-ray 4-circle diffraction data. The space group of this phase is C2ca (Aba2) with a = 11.366(6) A. b = 13.347(4) A and c = 15.246(6) Angstrom at T = 190 K. From the group-subgroup relations between the high- and the low-temperature phase the structure of the intermediate phase has been derived and confirmed by the analysis of the transition entropies.