B. Bednarska-Bolek

Structure and phase transition in the (C5H10NH2)SbCl6?(C5H10NH2)Cl crystal

Differential scanning calorimetry, dilatometric, dielectric dispersion and linear birefringence measurements have been used to study the phase transition at 202 K in the (C5 H10 NH2 )SbCl6 (C5 H10 NH2 )Cl crystal. The x-ray studies show that at room temperature it crystallizes in the orthorhombic symmetry (space group Pccn ), whereas below 202 K the structure changes its symmetry to monoclinic (P 21 /c ). The mechanism of the phase transition is connected both with the disordering of the piperidinium cations and the essential change in the NH...Cl hydrogen bond system. The title crystal exhibits the ferroelastic domain structure in the monoclinic phase.

Structure, phase transitions and molecular motions in ferroelastic (C4H8NH2)SbCl6·(C4H8NH2)Cl

The crystal structure at 293 K of the new pyrrolidinium chloroantimonate (V) analogue, (C4H8NH2)SbCl6(C4H8NH2)Cl, has been determined by x-ray diffraction as monoclinic, space group P21/c, Z = 8. The crystal is built up of isolated SbCl6- anions, two types of inequivalent pyrrolidinium cation and isolated Cl- ions. It undergoes five solid-solid phase transitions: at 351/374 K of first-order type (cooling/heating, respectively), at 356 and 152 K second order and at 135/141 and 105/134 K first order, detected by differential scanning calorimetry, dilatometric and dielectric measurements. The ferroelastic domain structure appears between 152 and 135 K. The proton nuclear magnetic resonance second moment and spin-lattice relaxation time of polycrystalline samples were studied over the temperature range 27-410 K. The order-disorder mechanism of the phase transitions at 105 and 374 K connected with the reorientational motion of the pyrrolidinium cations has been confirmed.

Ferroelastic phase transitions in triethylammonium and piperidinium chloroantimonate(V)

Abstract Preliminary x-ray diffraction, IR, Raman and dielectric studies of (C5H10NH2)SbCl6 and [(C2H5)3NH]SbCl6 are reported. The former crystal undergoes three phase transitions: at 294, 310 and 369 K, whereas latter crystal one transition at 336 K. Both salts reveal ferroelastic domain structure at room temperature. Dynamic of the organic cations is suggested to contribute to ferroelastic-paraelastic phase transitions at 369 K (piperidinium salt) and 336 K (triethylammonium one).