Different packing motifs in the crystal structures of three mol-ecular salts containing the 2-amino-5-carb-oxy-anilinium cation: C7H9N2O2 +·Cl-, C7H9N2O2 +·Br- and C7H9N2O2 +·NO3 -·H2O.

The syntheses and crystal structures of three mol-ecular salts of protonated 3,4-di-amino-benzoic acid, viz. 2-amino-5-carb-oxy-anilinium chloride, C7H9N2O2 +·Cl-, (I), 2-amino-5-carb-oxy-anilinium bromide, C7H9N2O2 +·Br-, (II), and 2-amino-5-carb-oxy-anilinium nitrate monohydrate, C7H9N2O2 +·NO3 -·H2O, (III), are described. The cation is protonated at the meta-N atom (with respect to the carb-oxy group) in each case. In the crystal of (I), carb-oxy-lic 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. Inter-molecular inter-actions 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 mol-ecules form undulating chains. Taken together, alternating (001) slabs of organic cations plus anions/water mol-ecules result. Hirshfeld surfaces and fingerprint plots were generated to give further insight into the inter-molecular inter-actions 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.