Structural investigation of trimethylammonium tetrachloromercurate

Titelangaben

Amami, Mongi ; van Smaalen, Sander ; Ben Salah, Abdelhamid ; Helluy, Xavier ; Sebald, Angelika:
Structural investigation of trimethylammonium tetrachloromercurate.
In: Journal of Solid State Chemistry. Bd. 177 (2004) Heft 8 . - S. 2961-2970.
ISSN 0022-4596
DOI: https://doi.org/10.1016/j.jssc.2004.05.012

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Abstract

The temperature dependence of the crystal structure of TrMA2HgCl4 (TrMA=trimethylammonium) is studied by single-crystal and powder X-ray diffraction between 161 and 373 K. Below room temperature, we did not find significant changes of the crystal structure. The phase transition at 325 K is described by a rotation of one of the two independent TrMA+ cations by 40° around the N–H axis, resulting in major rearrangements in the network of hydrogen bonds. A large change of the volume of the unit cell is found at the phase transition at 357 K, resulting in damage to the single crystals. Powder diffraction then shows that this transition can be described as a α–β transition between the α and β-K2SeO4 structure types. Structure refinements employing alternatively restrictions by the space group and additional restrictions by the {C3} non-crystallographic site symmetry for the TrMA+ cations show that significant deviations from {C3} symmetry of the TrMA+ cations do not exist at any temperature. The molecular dynamics and orientational disorder were studied by the maximum entropy method applied to the X-ray data. The diffraction results are corroborated by temperature dependent {NMR} experiments.