Pseudo-symmetries of the phases of (Et4N)(2)ZnBr4

The phase sequence of (Et4N)(2)ZnBr4 has been determined based on thermal a nalysis. Below the decomposition point (572 K) four phases are distinguishe d. The structures of three of the phases have been determined from 4-circle diffraction data at 240 (neutrons), 299 and 373 K (X-rays), respectively. The multiply twinned low-temperature phase (at 240 K) is characterized by a pseudo-orthorhombic lattice (monoclinic, P1a1, a = 17.6120(9) Angstrom, b = 8.8195(4) Angstrom, c = 16.1062(6) Angstrom and beta = 89.94(2)degrees), whereas the room-temperature phase (299 K: P42(1)c, a = 8.9874(6) Angstrom and c = 15,9774 Angstrom) and the first high-temperature phase (373 K: P4(2 )/nmc, a = 9.145(4) Angstrom and c = 15.835(8) Angstrom) belong to the tetr agonal crystal system. The transitions between the three phases are essenti ally connected with a stepwise ordering of the Et4N+ ions, whereas the posi tions of the heavy atoms change only slightly. Three Br-81 NQR lines are ob served between 77 and 204 K.