Crystal structure of 4-chloro-2-nitrobenzoic acid with 4-hydroxyquinoline: a disordered structure over two states of 4-chloro-2-nitrobenzoic acid-quinolin-4(1H)-one (1/1) and 4-hydroxyquinolinium 4-chloro-2-nitrobenzoate

The title compound, C9H7.5NO·C7H3.5ClNO4, was analysed as a disordered structure over two states, viz. co-crystal and salt, accompanied by a keto-enol tautomerization in the base molecule. The co-crystal is 4-chloro-2-nitrobenzoic acid-quinolin-4(1H)-one (1/1), C7H4ClNO4·C9H7NO, and the salt is 4-hydroxyquinolinium 4-chloro-2-nitrobenzoate, C9H8NO⁺·C7H3ClNO4 ^-. In the compound, the acid and base molecules are held together by a short hydrogen bond [O⋯O = 2.4393(15)Å], 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 interactions [centroid-centroid distances = 3.5504(8)-3.9010(11)Å]. 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 intermolecular interactions.