• Fojud, Zbigniew
• Czarnecki, Piotr
• Małuszyńska, H.
• Wąsicki, Jan

Abstract

<p>The crystal structure of bis(thiourea) pyridinium iodide (T2PyI) was previously determined at 295 and 110 K [Prout, Heyes, Dobson, McDaid, Maris, Mueller & Seaman (2000). Chem. Mater. 12, 3561-3569] and the two phases were described in the space groups Cmcm and P21 cn, respectively. Because differential scanning calorimetry revealed two phase transitions, at 161 and 141 K, a redetermination of the structure of T2pyI at 295, 155 and 110 K has been undertaken, and the following sequence of space groups obtained: Cmcm (I) C2cm (II) P21 cn (III). The high- (I) and low-temperature (III) phases confirmed the results reported in the previous study. In the new intermediate phase II, the mirror plane perpendicular to the x axis vanishes and the crystal structure loses the centre of symmetry. In phases I and II the pyridinium cations are strongly dynamically disordered, while in the low-temperature phase III the cations are well ordered. In all three phases the thiourea-iodine hydrogen-bonded sublattice is very well ordered. Dielectric measurements show that the intermediate and low-temperature phases are ferroelectric and that 161 K is the Curie point of a new ferroelectric crystal. © 2008 International Union of Crystallography.</p>

Topics

• impedance spectroscopy
• compound
• inclusion
• phase
• Hydrogen
• phase transition
• differential scanning calorimetry
• space group