Crystal structure of a new mol-ecular salt: 4-amino-benzenaminium 5-carb-oxy-penta-noate

The asymmetric unit of the title mol-ecular salt (systematic name: 4-amino-anilinium 5-carb-oxy-penta-noate), C₆H₉N₂⁺·C₆H₉O₄^-, consists of half a 4-amino-benzenaminium cation (4-ABA) and half a 5-carb-oxy-penta-noate anion (5-CP); the other half of each ion is generated by inversion symmetry. Protonation of p-phenyl-enedi-amine (PPDA) leads to the formation of a 1:1 salt, but scrutiny of the crystal structure reveals that both of the amine groups of PPDA are partially protonated, with a half-occupied H atom. For the 5-CP anion, an H atom is positioned on an inversion center midway between two O atoms of inversion-related 5-CP ions. In the crystal, the 5-CP anions are linked by the O-H⋯O hydrogen bond to form chains propagating along the [1-10] direction. The chains are linked via N-H⋯O and N-H⋯N hydrogen bonds involving the 4-ABA cations, forming a three-dimensional supra-molecular framework. The title salt was also prepared by mechanochemical synthesis using liquid-assisted grinding (LAG). Its PXRD pattern matches that of the simulated pattern of the crystal structure of the title mol-ecular salt.