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

In each of the title isomeric compounds, C₉H_7.3N·C₇H_3.7ClNO₄, (I), and C₉H₈N·C₇H₃ClNO₄, (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) Á], 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).