(S)-1-Methoxycarbonyl-3-(4-nitrophenyl)propan-2-aminium bromide

In the crystal structure of the title compound, C10H13N2O4 +·Br−, intermolecular N—H⋯Br and N—H⋯(O,Br) hydrogen bonds link the cations and anions into a two-dimensional network parallel to the ab plane.


Comment
The construction of metal-organic coordination compounds has attracted much attention owing to potential functions, such as permittivity, fluorescence, magnetism and optical properties (Fu, Zhang et al., 2008;Xiong et al., 1999;. Amino acid derivatives constitute a class of excellent ligands for the construction of novel metal-organic frameworks (Fu et al., 2007;Xie et al., 2002;Chen et al., 2000). We report here the crystal structure of the title compound.
The title compound is built up from a Branion and a protonated amino group cation (Fig.1). The nitro group and the benzene ring are nearly coplanar being twisted to each other by 2.39 (6)°. The S absolute configuration at C8 is deduced from the synthetic pathway and confirmed by the X-ray analysis.
The crystal packing is stabilized by N-H···Br and N-H···O H-bonds (Table 1) building an infinite two-dimensional network parallel to ab plane (Fig.2).

Experimental
Under nitrogen protection, methyl 2-amino-3-(4-nitrophenyl)propanoate (30 mmol), nitric acid (50 mmol) and sulfuric acid (20 mmol) were added in a flask. The mixture was stirred at 110 °C for 3 hours. The resulting solution was poured into ice water (100mL), then filtered and washed with distilled water. The crude product was recrystallized with distilled water by adding 4ml HBr to yield colourless needle-like crystals, suitable for X-ray analysis.

Refinement
C-bound H atoms were positioned geometrically and treated as riding, with C-H = 0.93 Å (aromatic), C-H = 0.96 Å (methyl), C-H = 0.97 Å (methylene) and C-H = 0.98 Å (methine), with U iso (H) = 1.2U eq (C) and U iso (H) = 1.5U eq (methyl). The H atoms of amine group were located in difference Fourier maps and at the last stage of refinement they were treated as riding, with U iso (H) = 1.5U eq (N). Fig. 1

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.