Crystal structures of isoquinoline-3-chloro-2-nitrobenzoic acid (1/1) and isoquinolinium 4-chloro-2-nitrobenzoate

In each of the title isomeric compounds, C9H7.3N.C7H3.7ClNO4, (I), and C9H8N.C7H3ClNO4, (II), of iso-quinoline with 3-chloro-2-nitro-benzoic acid and 4-chloro-2-nitro-benzoic acid, the two components are linked by a short hydrogen bond between a base N atom and a carboxy O atom. In the hydrogen-bonded unit of (I), the H atom is disordered over two positions with N and O site occupancies of 0.30 (3) and 0.70 (3), respectively, while in (II), an acid-base interaction involving H-atom transfer occurs and the H atom is located at the N site. In the crystal of (I), the acid-base units are connected through C-H...O hydrogen bonds into a tape structure along the b-axis direction. Inversion-related adjacent tapes are further linked through pi-pi interactions [centroid-centroid distances = 3.6389 (7)-3.7501 (7) angstrom], forming a layer parallel to (001). In the crystal of (II), the acid-base units are connected through C-H...O hydrogen bonds into a ladder structure along the a-axis direction. The ladders are further linked by another C-H...O hydrogen bond into a layer parallel to (001).