The phases of [(CH3)4N](ClO4) at low temperature

• Published in: Acta crystallographica. Section B, Structural science Structural science, 2003-10, Vol.59 (5), p.625-633
• Main Authors: Palacios, Elías, Burriel, Ramón, Ferloni, Paolo
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Exact sciences and technology; phase transitions; Physics; powder diffraction; Rietveld refinement; Structure of solids and liquids; crystallography
• ISSN: 0108-7681; 1600-5740
• DOI: 10.1107/S0108768103019013

The low‐temperature crystal structures of tetramethylammonium perchlorate, [(CH)N](ClO), are analysed. At 210 K, a collection of 376 unique reflections on a single crystal gave for space group , with 8.2376 (14),  (12) Å and , where the ClO groups are disordered over four orientations. Below  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 , with  (3), 11.784 (3),  (9) Å, and . At 30 K, Rietveld refinement gave the same structure as is found at 150 K, with a clear difference between and [ (2),  (2) and  (1) Å]. The structural models and the phase transition are explained on the basis of electrostatic octopole–octopole interactions among the ClO groups within layers perpendicular to the axis. The order parameters of the low‐temperature phase are discussed in relation to the structural results.