Received 29 April 2013
The crystal structure of the title compound, C5H4N2O2, is built of acid molecules located on a mirror plane. They form sheets stacked along the b-axis direction. The molecules interact via O-HN hydrogen bonds, forming  chains, and weak van der Waals interactions.
Data collection: KM-4 Software (Kuma, 1996); cell refinement: KM-4 Software; data reduction: DATAPROC (Kuma, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BT6903 ).
Kuma (1996). KM-4 Software. Kuma Diffraction Ltd, Wroclaw, Poland.
Kuma (2001). DATAPROC. Kuma Diffraction Ltd, Wroclaw, Poland.
Oxford Diffraction (2008). CrysAlis RED. Oxford Diffraction Ltd, Yarnton, England.
Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.
Starosta, W. & Leciejewicz, J. (2012). Acta Cryst. E68, m1065-m1066.