Crystal structure and Hirshfeld surface analysis of 2-aminopyridinium hydrogen phthalate

Aminopyridine and phthalic acid are well known synthons for supramolecular architectures for the synthesis of new materials for optical applications. The 2-aminopyridinium hydrogen phthalate title salt, C5H7N2+-C8H5O4-, crystallizes in the non-centrosymmetric space group P2(1). The nitrogen atom of the -NH2 group in the cation deviates from the fitted pyridine plane by 0.035 (7) angstrom. The plane of the pyridinium ring and phenyl ring of the anion are oriented at an angle of 80.5 (3)degrees to each other in the asymmetric unit. The anion features a strong intramolecular O-H center dot center dot center dot O hydrogen bond, forming a self-associated S(7) ring motif. The crystal packing is dominated by intermolecular N-H center dot center dot center dot O hydrogen bonds leading to the formation of 2(1) helices, with a C(11) chain motif. They propagate along the b axis and enclose R-2(2)(8) ring motifs. The helices are linked by C-H center dot center dot center dot O hydrogen bonds, forming layers parallel to the ab plane. Hirshfeld surface analysis and two-dimensional fingerprint plots were used to investigate and quantify the intermolecular interactions in the crystal.