title: Tetra-n-butyl-ammonium bromide: a redetermination at 150 K addressing the merohedral twinning.
abstract: The redetermined, low temperature (150 K), structure of tetra-n-butyl-ammonium bromide, (C(4)H(9))(4)N(+)·Br(-), has been found to be merohedrally twinned via twin law -1 0 0, 0 - 1 0, 1 0 1. The structure was previously determined, with low precision, no inclusion of H atoms and only the bromide ion refined with anisotropic displacement parameters, by Wang et al. (1995 ▶). Mol. Cryst. Liq. Cryst. Sci. Tech. A, 264, 115-129. The redetermined structure has considerably improved precision in all geometrical parameters, has all non-H atoms refined anisotropically, H atoms included, and is isomorphous with the iodide analogue. The structure is otherwise routine, with the shortest cation to anion contacts being between the bromide anion and the CH atoms close to the ammonium nitro-gen centre at a distance of ca. 2.98-3.11 Å. Each anion makes eight such contacts to four different anions. The n-butyl chains are fully extended, adopting an all-anti conformation with approximate S(4) point symmetry.
authors: Chemistry Department, Loughborough University, Loughborough, LE11 3TU,  England.
authors: Mark R J
authors: MR
authors: Elsegood