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

Abstract

Abstract The phase sequence of (Et4N)2ZnBr4 has been determined based on thermal analysis. Below the decomposition point (572 K) four phases are distinguished. The structures of three of the phases have been determined from 4-circle diffraction data at 240 (neu-trons), 299 and 373 K (X-rays), respectively. The multiply twinned low-temperature phase (at 240 K) is characterized by a pseudo-orthorhombic lattice (monoclinic, Plal, a = 17.6120(9] Å, b = 8.8195(4) Å, c = 16.1062(6) Å and ß=89.94(2)°), whereas the room-temperature phase (299 K:P421c, a = 8.9874(6)Åand c = 15.9774 Å) and the first high-temperature phase (373 K: P42 /nmc, a= 9.145(4) Å and c = 15.835(8) Å) belong to the tetragonal crystal system. The transitions between the three phases are essen-tially connected with a stepwise ordering of the Et4N+ ions, whereas the positions of the heavy atoms change only slightly. Three 81Br NQR lines are observed between 77 and 204 K.