title: Tetra-gonal polymorph of 5,5-dichloro-barbituric acid.
abstract: The tetra-gonal polymorph of 5,5-dichloro-barbituric acid (m.p. 478 K), C(4)H(2)Cl(2)N(2)O(3), forms an N-H⋯O hydrogen-bonded tape structure along [001]. Two tapes related by a twofold rotation axis are associated via Cl⋯O contacts [3.201 (1) Å], and four such chain pairs are arranged around a fourfold roto-inversion axis. The crystal structures of the monoclinic and ortho-rhom-bic polymorphs have been reported previously [Gelbrich et al. (2011 ▶). CrystEngComm, 13, 5502-5509].
authors.affiliation: Institute of Pharmacy, University of Innsbruck, Innrain 52c, 6020 Innsbruck,  Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Gelbrich
authors.forename: Denise
authors.initials: D
authors.lastname: Rossi
authors.forename: Ulrich J
authors.initials: UJ
authors.lastname: Griesser