R4/4 (30) rectangular rings in 2,5-dioxopiperazine-1,4-diacetic acid.

Molecules of the title 2,5-dioxopiperazinedione derivative, C(8)H(10)N(2)O(6), occupy centres of symmetry in the crystal structure. The six-membered ring has an almost planar conformation, with the substituent on nitrogen nearly perpendicular to the ring. The ideal geometry of the isolated molecule, as determined by ab initio HF-LCAO quantum-mechanical calculations, is slightly more puckered than that observed in the solid state. In the crystal structure, a strong hydrogen bond joins neighbouring molecules, thus forming a network of rectangular R(4)(4)(30) rings.