Different packing motifs in the crystal structures of three mol­ecular salts containing the 2-amino-5-carb­oxy­anilinium cation: C(7)H(9)N(2)O(2) (+)·Cl(−), C(7)H(9)N(2)O(2) (+)·Br(−) and C(7)H(9)N(2)O(2) (+)·NO(3) (−)·H(2)O

The syntheses and crystal structures of three mol­ecular salts of protonated 3,4-di­amino­benzoic acid, viz. 2-amino-5-carb­oxy­anilinium chloride, C(7)H(9)N(2)O(2) (+)·Cl(−), (I), 2-amino-5-carb­oxy­anilinium bromide, C(7)H(9)N(2)O(2) (+)·Br(−), (II), and 2-amino-5-carb­oxy­anilinium nitrate monohydrate, C(7)H(9)N(2)O(2) (+)·NO(3) (−)·H(2)O, (III), are described. The cation is protonated at the meta-N atom (with respect to the carb­oxy group) in each case. In the crystal of (I), carb­oxy­lic acid inversion dimers linked by pairwise O—H⋯O hydrogen bonds are seen and each N—H group forms a hydrogen bond to a chloride ion to result in (100) undulating layers of chloride ions bridged by the inversion dimers into a three-dimensional network. The extended structure of (II) features O—H⋯Br, N—H⋯Br and N—H⋯O hydrogen bonds: the last of these generates C(7) chains of cations. Overall, the packing in (II) features undulating (100) sheets of bromide ions alternating with the organic cations. Inter­molecular inter­actions in the crystal of (III) include O—H⋯O, O—H⋯(O,O), N—H⋯O, N—H⋯N and O—H⋯N links. The cations are linked into (001) sheets, and the nitrate ions and water mol­ecules form undulating chains. Taken together, alternating (001) slabs of organic cations plus anions/water mol­ecules result. Hirshfeld surfaces and fingerprint plots were generated to give further insight into the inter­molecular inter­actions in these structures. The crystal used for the data collection of (II) was twinned by rotation about [100] in reciprocal space in a 0.4896 (15):0.5104 (15) ratio.