4,4'-Imino-dipyridinium bis-(hydrogen phthalate)

In the title salt, C(10)H(11)N(3) (2+)·2C(8)H(5)O(4) (-), doubly protonated 4,4'-dipyridylamine (dpa) cations participate in N-H⋯O hydrogen bonding with two hydrogen phthalate anions to form a neutral unit. Both anions contain an intramolecular O-H⋯O hydrogen bond. In the crystal structure, these units form two-dimensional layers through π-π stacking inter-actions with a centroid-to-centroid distance of 3.763 (3) Å. In turn, these layers aggregate in three dimensions by additional N-H⋯O hydrogen bonding. The assignment to the noncentrosymmetric space group P1 is corroborated by chemically unreasonable aromatic ring bond distances and poor K scale factor distributions for a disordered model in the centrosymmetric P space group.