Networks of intermolecular interactions involving nitro groups in the crystals of three polymorphs of 9-aminoacridinium 2,4-dinitrobenzoate ⋅ 2,4-dinitrobenzoic acid

We report on the crystal structures of three polymorphs of 9-aminoacridinium 2,4-dinitrobenzoate ⋅ 2,4-dinitrobenzoic acid (I, II and III). Single-crystal X-ray diffraction measurements show that the title compound forms three polymorphs with the space groups P21/n (I) and P 1 ¯ (II and III). The asymmetric units of all the polymorphs consist of 9-aminoacridinium cation, the 2,4-dinitrobenzoate anion and the 2,4-dinitrobenzoic acid molecule. The neutral and ionic forms of 2,4-dinitrobenzoic acid are linked via O–H⋯O hydrogen bonds with a D graph-set motif, forming monoanionic dimers. The amine and carboxylic acid moieties are linked via N–H⋯O, O–H⋯O and C–H⋯O hydrogen bonds. The acridinium skeletons in the crystal packing form π-stacked columns, whereas the monoanionic dimers of 2,4-dinitrobenzoic acid are linked by different types of intermolecular interactions, especially those involving nitro groups. To the best of our knowledge, the crystal structure of 9-aminoacridinium 2,4-dinitrobenzoate ⋅ 2,4-dinitrobenzoic acid is the first in which the appearance of monoanionic dimers of 2,4-dinitrobenzoic acid has been documented.