9-Amino­acridin-10-ium 4-amino­benzo­ate dihydrate

The asymmetric unit of the title hydrated salt, C(13)H(11)N(2) (+)·C(7)H(6)NO(2) (−)·2H(2)O, consists of two independent 9-amino­acridinium cations, two 4-amino­benzoate anions and four water mol­ecules. Both 9-amino­acridinium cations are essentially planar, with maximum deviations of 0.034 (1) and 0.025 (2) Å, and are protonated at the pyridine N atoms. The 4-amino­benzoate anions are approximately planar, with dihedral angles of 9.16 (19) and 5.4 (2)° between the benzene ring and the carboxyl­ate group. In the crystal, the two independent anions are connected by N—H⋯O hydrogen bonds, forming a layer parallel to (100). The layers are connected through the cations by N—H⋯N and N—H⋯O hydrogen bonds. The water mol­ecules, which form O—H⋯O hydrogen-bonded chains along the b-axis direction, connect the anions and the cations by O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds. The crystal structure also features π–π inter­actions [centroid–centroid distances = 3.6343 (9)–3.8366 (10) Å] and a C—H⋯π inter­action.