Structure of the X-phase of 38% brominated betaine calcium chloride dihydrate

• Published in: Acta crystallographica. Section B, Structural science Vol. 57; no. 3; pp. 296 - 302
• Main Authors: Vieira, L. G., Hernandez, O., Ribeiro, J. L., Cousson, A., Kiat, J.-M., Chaves, M. R., Almeida, A., Klöpperpieper, A.
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01.06.2001; Blackwell
• Subjects: Aliphatic, non-condensed and condensed benzenic, and alicyclic compounds; betaine; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Organic compounds; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; symmetry; Temperature dependence; Molecular structure; Phase transformations; Neutron diffraction; Calcium compounds; Experimental study; Quaternary ammonium compound; Betaine; Ambient temperature; Chlorides; Saturated aliphatic compound; Bromides; Carboxylates; Organic compounds; Low temperature; Hydrates; Polymorphism; Crystal structure
• ISSN: 0108-7681; 1600-5740
• DOI: 10.1107/S0108768101001525

The structures of the high‐ and low‐temperature phases of 38% brominated BCCD [betaine (trimethylammonioacetate) calcium chloride dihydrate], the latter being known as the X‐­phase, have been determined by single‐crystal neutron diffraction at 295 and 20 K, respectively. The symmetry of the X‐phase is described by the P212121 space group. The distortion with respect to the high‐temperature Pnma phase is characterized by anti‐symmetric displacements of the betaine molecules as well as of the Ca octahedra. On the basis of a symmetry‐mode analysis, we propose an interpretation of the direct phase transition that occurs around 80 K between these two phases.