Crystal structure of 4-chloro-2-nitro-benzoic acid with 4-hy-droxy-quinoline: a disordered structure over two states of 4-chloro-2-nitro-benzoic acid-quinolin-4(1H)-one (1/1) and 4-hy-droxy-quinolinium 4-chloro-2-nitro-benzoate.

The title compound, C(9)H(7.5)NO·C(7)H(3.5)ClNO(4), was analysed as a disordered structure over two states, viz. co-crystal and salt, accompanied by a keto-enol tautomerization in the base mol-ecule. The co-crystal is 4-chloro-2-nitro-benzoic acid-quinolin-4(1H)-one (1/1), C(7)H(4)ClNO(4)·C(9)H(7)NO, and the salt is 4-hy-droxy-quinolinium 4-chloro-2-nitro-benzoate, C(9)H(8)NO(+)·C(7)H(3)ClNO(4) (-). In the compound, the acid and base mol-ecules are held together by a short hydrogen bond [O⋯O = 2.4393†(15)†à ], in which the H atom is disordered over two positions with equal occupancies. In the crystal, the hydrogen-bonded acid-base units are linked by N-H⋯O and C-H⋯O hydrogen bonds, forming a tape structure along the a-axis direction. The tapes are stacked into a layer parallel to the ab plane via π-π inter-actions [centroid-centroid distances = 3.5504†(8)-3.9010†(11)†à ]. The layers are further linked by another C-H⋯O hydrogen bond, forming a three-dimensional network. Hirshfeld surfaces for the title compound mapped over shape-index and d (norm) were generated to visualize the inter-molecular inter-actions.