2-Amino-3-nitrobenzoic acid

The title compound, C7H6N2O4, is approximately planar (r.m.s. deviation = 0.026 Å for the 13 non-H atoms). The molecular structure is stabilized by intramolecular N—H⋯O hydrogen bonds, which generate S(6) ring motifs. In the crystal, molecules are linked via intermolecular N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds into a three-dimensional network.


Experimental
The attempt to prepare organotin(IV) carboxylate complexes by heating under reflux the mixture of 2-amino-3-nitrobenzoic acid (2 mmol) and dimethyltin(IV) oxide (4 mmol) for 4 h in 50 ml of methanol was unsuccessful. The resulting orange solution was filtered and orange crystals were obtained after 2 weeks. Unfortunately, the crystals obtained were found to be the starting material (2-amino-3-nitrobenzoic acid) with the melting point of 482 K.

Refinement
Atoms H1O4, H1N2 and H2N2 were located in a difference Fourier map and refined freely with O-H = 0.83 (2) Å and N-H = 0.875 (18) and 0.893 (17) Å. The remaining H atoms were positioned geometrically and refined using a riding model with C-H = 0.95 Å and U iso (H) = 1.2 U eq (C). Fig. 1

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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.