2-Hydroxy-3-nitrobenzamide

The asymmetric unit of title compound, C7H6N2O4, contains two molecules, one of which has a disordered nitro group with an occupancy ratio of 0.517 (9):0.483 (9) for the O atoms. Both molecules contain an intramolecular O—H⋯O hydrogen bond. In the crystal, both molecules form inversion dimers linked by pairs of N—H⋯O hydrogen bonds, resulting in R 2 2(8) ring motifs. The dimers are connected by further N—H⋯O links and weak C—H⋯O interactions, resulting in a layered motif.

The asymmetric unit of title compound, C 7 H 6 N 2 O 4 , contains two molecules, one of which has a disordered nitro group with an occupancy ratio of 0.517 (9):0.483 (9) for the O atoms. Both molecules contain an intramolecular O-HÁ Á ÁO hydrogen bond. In the crystal, both molecules form inversion dimers linked by pairs of N-HÁ Á ÁO hydrogen bonds, resulting in R 2 2 (8) ring motifs. The dimers are connected by further N-HÁ Á ÁO links and weak C-HÁ Á ÁO interactions, resulting in a layered motif.
The title compound consists of two molecules in the asymmetric unit. The O-atoms of nitro group in one of the molecules are disordered over two sites with occupancy ratio of 0.517 (9):0.483 (9). In both molecules the hydroxy group form intramolecular H-bonding with the O-atom of amide group, thus completing ring motifs R 1 1 (6) (Bernstein et al., 1995). The H-atoms of NH 2 groups behave differently. One H-atom forms dimer, whereas the other is used in linkage of the dimers.
It is intersting that both molecules form dimers among themselves through the intermolecular H-bonds of N-H···O type with ring motifs R 2 2 (8). The dimers of both molecules are connected to each other through the same type of intermolecular H-bonding (Fig. 2). The molecules are stabilized in the form of two dimensional polymeric sheets due to intera as well as intermolecular H-bonding (Table 1).

Experimental
A solution of 2-hydroxybenzamide (1.37 g, 0.01 mol) in ethylacetate (EtOAc) (25 ml) was added dropwise to a nitrating mixture of HNO 3 (1.89 g, 0.03 mol) and H 2 SO 4 (1.96 g, 0.02 mol) with constant stirring while the temperature was kept below 278 K. Then reaction mixture was stirred at room temperature for 4-5 h. The resulting mixture was refluxed for 1 h, cooled, neutralized with aq. NaHCO 3 (10%) and extracted with EtOAc (3 × 25 ml). The organic layers were combined, dried over anhydrous Na 2 SO 4 , filtered and concentrated under reduced pressure to afford a reddish brown solid. The column chromatographic purification with 0, 2.5, 5 and 7.5% EtOAc in petrol (0.5 L each) over a silica gel packed column (25.5 cm) afforded brown prisms of (I).

Refinement
The H-atoms were positioned geometrically, with O-H = 0.82 Å for hydroxy groups. The coordinates of all other H-atoms were refined with U iso (H) = 1.2U eq (carrier).
supplementary materials sup-2 Figures Fig. 1. View of (I) with displacement ellipsoids drawn at the 50% probability level. H-atoms are shown by small spheres of arbitrary radius. Hydrogen bonds are symbolized by dashed lines. Fig. 2. The partial packing of (I) which shows that molecules form dimers and the dimers are interlinked forming two dimensional polymeric sheets.