organic compounds
Crystals of a second polymorph of violuric acid monohydrate [systematic name: pyrimidine-2,4,5,6(1H,3H)-tetrone monohydrate], C4H3N3O4·H2O, have higher density and a more extensive hydrogen-bonding arrangement than the previously reported polymorph. Violuric acid and water molecules form essentially planar hydrogen-bonded sheets, which are stacked in an offset ...ABCABC... repeat pattern involving no ring-stacking interactions.