2-(2-Amino-4-nitrophenyl)-7-nitro-4H-3,1-benzoxazin-4-one

In the title compound, C14H8N4O6, the benzoxazin-4-one fused-ring system (r.m.s. deviation = 0.018 Å) is coplanar with the attached benzene ring [dihedral angle = 0.81 (4)°], there being an intramolecular N—H⋯N hydrogen bond between them. Each nitro group is twisted out of the plane of the attached benzene ring [O—N—C—C torsion angles = 167.94 (11) and 170.38 (11)°]. In the crystal, amine–nitro N—H⋯O hydrogen bonds lead to centrosymmetric dimeric aggregates that are connected into a three-dimensional architecture by oxazinyl–nitro C—H⋯O and π–π interactions [inter-centroid distance between the oxazinyl and terminal benzene rings = 3.5069 (7) Å].

The use of the EPSRC X-ray crystallographic service (Coles & Gale, 2012) at the University of Southampton, England, and the valuable assistance of the staff there is gratefully acknowledged. JLW acknowledges support from CAPES (Brazil). Structural studies are supported by the Ministry of Higher Education (Malaysia) and the University of Malaya through the High-Impact Research scheme (UM.C/HIR/ MOHE/SC/3).
Supporting information for this paper is available from the IUCr electronic archives (Reference: HG5375).

Synthesis and crystallization
The title compound was obtained from the reaction of 2-amino-4-nitrobenzoic acid with 4-chlorobenzenesulfonyl chloride (1 mmol of each) in refluxing acetone (20 ml) for 30 min. The reaction mixture was rotary evaporated and the residue was recrystallized from MeOCH 2 CH 2 OH. Crystals used in the structure determination were grown by slow evaporation of its MeOCH 2 CH 2 OH solution; M.pt: 474-475 K (dec.).

Refinement
Intensity data was collected at the National Crystallographic Service, England (Coles & Gale, 2012). The C-bound H atoms were geometrically placed (C-H = 0.95 Å) and refined as riding with U iso (H) = 1.2U eq (C). The N-bound H atoms were located from a difference map and refined with N-H = 0.88±0.01 Å, and with U iso (H) = 1.2U eq (N).
In (I), Fig. 1, the atoms comprising the benzoxazin-4-one fused-ring system are co-planar (r.m.s. deviation = 0.018 Å) and form a dihedral angle of 0.81 (4)° with the attached benzene ring. The co-planarity between the ring systems is accompanied by an intramolecular N2-H···N3 hydrogen bond, Table 1. Both nitro groups are twisted out of the plane of the attached benzene rings as seen in the values of the O1-N1-C1-C2 and O6-N4-C12-C11 torsion angles of 167.94 (11) and 170.38 (11)°, respectively.

Figure 2
A view in projection down the b axis of the unit-cell contents for (I). The N-H···O, C-H···O and π-π interactions are shown as blue, orange and purple dashed lines, respectively. Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(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.