On structural phase transitions in the (C5H12N)(2)SbCl5 crystals

The results of the X-ray (at 295 and 355 K), dilatometric, differential sca nning calorimetry and dielectric studies on a new piperidinium crystal, (C5 N12N)(2)SbCl5, are presented. The anionic sublattice of the crystal is buil t up of infinite (SbCl52-)(n) chains composed of SbCl63- distorted octahedr a connected with each other by corners. In voids of anionic sublattice two crystallographic ally independent piperidinium cations are located. At 295 K they are both in chair conformation. The compound undergoes three first-o rder phase transitions at 378.5 K (I --> II), 339.5 K (II --> III) and 205 K (III --> IV). The mechanisln of the (II --> III) transition (Pna2(1) --> P2(1)2(1)2(1))was proposed based on the X-ray data. It is associated with c hanges in the conformation of the N(1) cation. In phase (III) its conformat ion changes to twist boat. The physical properties of this crystal are comp ared to those found for the other piperidinium crystals of the (C5H12N)(2)M X5 (M = Sb, Bi; X = Cl, Br) type. (C) 2000 Elsevier Science B.V. All rights reserved.