Different packing motifs in the crystal structures of three molecular salts containing the 2-amino-5-carboxyanilinium cation: C₇H₉N₂O₂ ⁺·Cl⁻, C₇H₉N₂O₂ ⁺·Br⁻ and C₇H₉N₂O₂ ⁺·NO₃ ⁻·H₂O

Abstract

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.