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

Zeitschrift Fur Naturforschung Section a-a Journal of Physical Sciences 55(9-10): 801-809

Autoren/Herausgeber: Sondergeld P
Fueß H
Mason SA
Ishihara H
Schmahl WW
Erschienen: 2000

The phase sequence of (Et4N)(2)ZnBr4 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 (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 tetragonal crystal system. The transitions between the three phases are essentially connected with a stepwise ordering of the Et4N+ ions, whereas the positions of the heavy atoms change only slightly. Three Br-81 NQR lines are observed between 77 and 204 K.