2-Hydr-oxy-5-nitro-benzaldehyde.

The title compound, C(7)H(5)NO(4), is essentially planar, with a maximum deviation from the mean plane of 0.0116 (11) Å for the hydr-oxy O atom. The mol-ecular and crystal structure are stabilized by intra- and inter-molecular inter-actions. An intra-molecular O-H⋯O hydrogen bond generates a six-membered ring, producing an S(6) ring motif. The C-H⋯O inter-actions result in the formation of C(5) chains and R(2) (2)(8) rings forming an approximately planar network parallel to (10). These planes are inter-connected through π-π inter-actions [centroid-centroid distance 3.582 (2) Å].