Crystal structure of 4-amino-pyridinium 5-(5-chloro-2,4-dinitrophenyl)-1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate hemihydrate.

The title mol-ecular salt, C5H7N2 (+)·C12H8ClN4O7 (-)·0.5H2O, crystallizes as a hemihydrate. The two rings in the barbiturate anion are not coplanar but make a dihedral angle of 43.17 (16)°. The two nitro groups deviate from the ring to which they are attached; the nitro group ortho with respect to the ring junction is more deviated [39.3 (4)°] than that in the para position [4.2 (5)°], probably to overcome steric hindrance. As a result of this, the latter nitro group is more involved in delocalizing the negative charge of the anion than the former nitro group. In the crystal, the cations and anions are linked via N-H⋯O hydrogen bonds forming zigzag chains along [10-1]. The chains are linked by O-H⋯O and C-H⋯O hydrogen bonds, forming slabs lying parallel to (10-1). Further C-H⋯O hydrogen bonds link the slabs, forming a three-dimensional structure.