Structure of the X-phase of 38% brominated betaine calcium chloride dihydrate.
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 P2(1)2(1)2(1) 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.
Vieira
L G
LG
Departamento de Física, Universidade do Minho, 4709 Braga codex, Portugal.
Hernandez
O
O
Ribeiro
J L
JL
Cousson
A
A
Kiat
J M
JM
Chaves
M R
MR
Almeida
A
A
Klöpperpieper
A
A