Acta Crystallographica Section B

Structural Science

Volume 64, Part 5 (October 2008)

research papers

Acta Cryst. (2008). B64, 567-572 [ doi:10.1107/S0108768108018223 ]

Redetermination of the structure and dielectric properties of bis(thiourea) pyridinium iodide - a new ferroelectric inclusion compound

H. Maluszynska, P. Czarnecki, Z. Fojud and J. Wasicki

Abstract: 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 P2₁cn, 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) [rightwards arrow] C2cm (II) P2₁cn (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.

Keywords: thiourea inclusion compounds; ferroelectricity; phase transitions.


	Structure factor file (CIF format) (56.8 kbytes) [ doi:10.1107/S0108768108018223/ws5061Isup2.fcf ] Contains datablock I

	Structure factor file (CIF format) (49.5 kbytes) [ doi:10.1107/S0108768108018223/ws5061IIsup3.fcf ] Contains datablock II

	Structure factor file (CIF format) (103.5 kbytes) [ doi:10.1107/S0108768108018223/ws5061IIIsup4.fcf ] Contains datablock III

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