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

In each of the title isomeric compounds, C(9)H(7.3)N·C(7)H(3.7)ClNO(4), (I), and C(9)H(8)N·C(7)H(3)ClNO(4), (II), of iso­quinoline with 3-chloro-2-nitro­benzoic acid and 4-chloro-2-nitro­benzoic 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 π–π inter­actions [centroid–centroid distances = 3.6389 (7)–3.7501 (7) Å], 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).