4-Chloro-2-nitro-benzoic acid-pyrazine (2/1).

In the title co-crystal, 2C(7)H(4)ClNO(4)·C(4)H(4)N(2), the pyrazine mol-ecule is located on an inversion centre, so that the asymmetric unit consists of one mol-ecule of 4-chloro-2-nitro-benzoic acid and a half-mol-ecule of pyrazine. The components are connected by O-H⋯N and C-H⋯O hydrogen bonds, forming a 2:1 unit. In the hydrogen-bonded unit, the dihedral angle between the pyrazine ring and the benzene ring of the benzoic acid is 16.55 (4)°. The units are linked by inter-molecular C-H⋯O hydrogen bonds, forming a sheet structure parallel to ([Formula: see text]04). A C-H⋯O hydrogen-bond linkage is also observed between these sheets.