2-Aminoanilinium 2-carboxyacetate

In the crystal structure of the title compound, C6H9N2 +·C3H3O4 −, all the amino H atoms are involved in intermolecular N—H⋯O hydrogen bonds, which link the ions into double chains parallel to [101]. In the anion, an intramolecular O—H⋯O hydrogen bond is observed.

In the crystal structure of the title compound, C 6 H 9 N 2 + ÁC 3 H 3 O 4 À , all the amino H atoms are involved in intermolecular N-HÁ Á ÁO hydrogen bonds, which link the ions into double chains parallel to [101]. In the anion, an intramolecular O-HÁ Á ÁO hydrogen bond is observed.
Physicochemical properties such as the melting point, stability and solubility of an active pharmaceutical ingredient can be tuned through co-crystal formulation (Kapildev et al., 2011;Schultheiss & Newman, 2009). Co-crystal synthesis often relies on the acid-amide H-bonds interactions. Herein, we report the crystal structure of the title compound, 2-aminoanilinium 2-carboxyacetate.
The asymmetric unit of the title compound is composed of one 2-aminoanilinium cation and one 2-carboxyacetate anion  (Table 1).

Experimental
A mixture of benzene-1,2-diamine (2.0 mmol), malonic acid (2.0 mmol) in distilled water (20 ml) was added into a 50 ml flask and refluxed for 5 hours, then cooled and filtrated. The solution was evaporated slowly in the air. Colourless block crystals suitable for X-ray analysis were obtained after one week.

Refinement
All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.93-0.97 Å and with U iso (H) = 1.2 U eq (C). The amine and carboxylic H atoms were located in a difference Fourier map and refined freely. In the last stage of the refinement, they were restrained with the H-N1 = 0.90 (2) Å, H-N2 = 0.89 (2) Å and H-O4 = 0.82 (2) Å, and with U iso (H) = 1.5 U eq (N1, O4) or 1.2 U eq (N2). Fig. 1. The molecular structure of the title compound with displacement ellipsoids drawn at the 30% probability level.

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.