The phases of [(CH3)4N](ClO4) at low temperature
| Autor: | Ramón Burriel, Elias Palacios, Paolo Ferloni |
|---|---|
| Rok vydání: | 2003 |
| Předmět: |
Phase transition
Stereochemistry Rietveld refinement Chemistry General Medicine Crystal structure General Biochemistry Genetics and Molecular Biology Crystallography Perchlorate chemistry.chemical_compound Polymorphism (materials science) Orthorhombic crystal system Single crystal Powder diffraction |
| Zdroj: | Acta Crystallographica Section B Structural Science. 59:625-633 |
| ISSN: | 0108-7681 |
| DOI: | 10.1107/s0108768103019013 |
| Popis: | The low-temperature crystal structures of tetramethylammonium perchlorate, [(CH_{3})_{4}N](ClO_{4}), are analysed. At 210 K, a collection of 376 unique reflections on a single crystal gave R = 0.0567 for space group P4/nmm, with a_{1} ={}8.2376 (14), c_{1} = 5.8256 (12) Å and Z = 2, where the ClO_{4} groups are disordered over four orientations. Below T_{c} = 170 K, these groups order in four sublattices, each ion gradually choosing one unique orientation. At 150 K, the crystal is microtwinned. 1389 unique reflections were refined in the orthorhombic space group P2_{1}2_{1}2, with a_{3} = 11.714 (3), b_{3} = 11.784 (3), c_{3} = 5.8265 (9) Å, Z = 4 and R = 0.087. At 30 K, Rietveld refinement gave the same structure as is found at 150 K, with a clear difference between a_{3} and b_{3} [a_{3} = 11.566 (2), b_{3} = 11.806 (2) and c_{3} = 5.729 (1) Å]. The structural models and the phase transition are explained on the basis of electrostatic octopole–octopole interactions among the ClO_{4} groups within layers perpendicular to the c axis. The order parameters of the low-temperature phase are discussed in relation to the structural results. |
| Databáze: | OpenAIRE |
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