STRUCTURE AND PHASE-TRANSITIONS IN [C(NH2)(3)]SBCL6 CRYSTALS

The crystal structure of [C(NH2)(3)]SbCl6 at 298 K (monoclinic, C2/m) and 240 K (monoclinic, P2(1)/a) has been determined. The structure con sists of isolated SbCl6- anions:and guanidinium cations. Differential scanning calorimetry, dilatometric and dielectric studies revealed two structural phase transitions; a first-order one at 351 K and a second -order one at 265 K. One of the two crystallographically non-equivalen t anions, SbCl6-(1), disordered in the room temperature phase is postu lated to contribute to the phase transition mechanism at 265 K.A ferro elastic domain structure is found below 351 K. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.