Pseudosymmetry in tetradecyltrimethylammonium bromide

Acta Cryst. (2003). E59, o1151–o1152

Tetradecyltrimethylammonium bromide is commonly used as a surfactant and germicide. A single crystal grown serendipitously from the residual detergent used to wash laboratory glassware was analyzed showing that the long organic molecules are packed in layers with the tetradecyl chains adopting an extended zigzag form. These long chains are parallel within a layer and antiparallel in alternate layers. This packing emulates a c-halved unit cell in space group P2₁/m, but it is not supported by the diffraction data, as many reflections with l = 2n +1 showed weak, but significant, intensity. Refinement in the half cell in P2₁ or P2₁/m resulted in unrealistic bond lengths and displacement parameters. Including all the data and refining in space group P2₁/c revealed the true structure.