The structure and Hirshfeld surface analysis of the 4-amino 3-nitrobenzoic acid triclinic polymorph

By preparation of 4-amino-3-nitrobenzoic acid (4-A3NBA-P) in the triclinic crystal form in contrast to known monoclinic crystals polymorphism of this compound has been established. The monoclinic form is called polymorph I, while triclinic crystals are designated as polymorph II. In the former polymorph, 4-A3NBA molecules are associated with the 3D network by H-bonds, while in the case of the latter polymorph, the H-bonded layers are incorporated into crystal structure by π•••π interactions. Therefore, Hirshfeld surface analyses indicate that the percentage of the O•••H/H•••O interactions of polymorph II (~ 39.1%) is less than that of polymorph I (54.5%). The TG-DTA studies attest that there is no “polymorph II → polymorph I” phase transition.