Violuric acid monohydrate: a definitive redetermination at 150 K

Abstract

A redetermination at 150 K of the structure of violuric acid monohydrate, C4H3N3O4·H2O, confirms that the space group is non-centrosymmetric Cmc21, despite indications from the intensity statistics and possible mol­ecular symmetry that it could be centrosymmetric Cmcm. Issues raised in the original reports [Craven & Mascarenhas (1964). Acta Cryst. 17, 407–414; Craven & Takei (1964). Acta Cryst. 17, 415–420] suggested either a disordered model or an ordered one with high thermal motion. The redetermination shows that an ordered model is correct, and the low-temperature data collection leads to normal displacement parameters. The precision of the structure is significantly improved in this new study. The violuric acid mol­ecule is entirely planar, and every atom in the structure lies on a crystallographic mirror plane. Violuric acid and water mol­ecules form hydrogen-bonded sheets.