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 center dot 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 center dot C9H7NO, and the salt is 4-hydroxy-quinolinium 4-chloro-2-nitrobenzoate, C9H8NO+center dot C7H3ClNO4. In the compound, the acid and base molecules are held together by a short hydrogen bond [O center dot center dot center dot O = 2.4393 (15) angstrom], 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 center dot center dot center dot O and C-H center dot center dot center dot 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 pi-pi interactions [centroid-centroid distances = 3.5504 (8)-3.9010 (11) angstrom]. The layers are further linked by another C-H center dot center dot center dot O hydrogen bond, forming a three-dimensional network. Hirshfeld surfaces for the title compound mapped over shape-index and d orm were generated to visualize the intermolecular interactions.