Received 7 May 2009
The redetermined crystal structure of the title compound, C11H13N2O2+·Br-, is reported. Data collection at 100 K about three crystallographic axes resulted in a crystal structure with significantly higher precision in comparison to the two-dimensional data collected at 176 K [Takigawa et al. [(1966) Bull. Chem. Soc. Jpn, 39, 2369-2378]. The carboxyl group and indole ring system are planar, with maximum deviations of 0.002 (2) and 0.007 (2) Å, respectively, and make an angle of 70.17 (1)° with each other. The molecules are arranged in double layers of carboxyl and amino groups parallel to the ab plane, stabilized by an extensive network of N-HBr and O-HBr hydrogen bonds. The polar layer is held together by a network of three N-HBr hydrogen bonds and one O-HBr hydrogen bond. In the non-polar layer, the indole rings are linked mainly by electrostatic N-HC interactions between the polarized bond N-H (H is +) of the pyrrole unit and two of the ring C atoms (-) of the benzene rings of adjacent molecules. The distances of these electrostatic interactions are 2.57 and 2.68 Å, respectively. C-HO and C-H interactions are also present.
For a previous determination of the crystal structure of the title compound, see: Takigawa et al. (1966). Study of crystal structures of amino acids and their complexes has provided information about aggregation and the effect of other molecules on their interactions and molecular properties, see: Vijayan (1988); Prasad & Vijayan (1993). For the structure of histidine hydrochloride monohydrate, see: Takigawa et al. (1966). Donohue & Caron (1964). The structures of many amino acids with non-polar side chains feature a double-layered arrangement, see: Harding & Long (1968); Torii & Iitaka (1970, 1971, 1973).
Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell refinement: CrysAlis RED (Oxford Diffraction, 2008); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: AT2781 ).
The author gratefully acknowledges financial support from the University of Kwazulu-Natal. Thanks are also due to Ms C. Janse Van Rensburg for the mass spectrum analysis.
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