In the title compound, C5H6N2O4, the molecules lie across a crystallographic mirror plane. The compound lacks traditional hydrogen-bond donors, and hence crystals are held together by unusual C= O⋯ O, O⋯ C and weak C—H⋯ O interactions, forming layers. Adjacent layers are arranged in an antiparallel manner, yielding an ABA layer sequence. The intermolecular contacts are quite short; a topological analysis of charge density based ...