Crystal structure and Hirshfeld surface analysis of 2-amino-pyridinium hydrogen phthalate

Amino-pyridine and phthalic acid are well known synthons for supra-molecular architectures for the synthesis of new materials for optical applications. The 2-amino-pyridinium hydrogen phthalate title salt, C₅H₇N₂ ⁺·C₈H₅O₄ ^-, crystallizes in the non-centrosymmetric space group P2₁. The nitro-gen atom of the -NH₂ group in the cation deviates from the fitted pyridine plane by 0.035 (7) Å. The plane of the pyridinium ring and phenyl ring of the anion are oriented at an angle of 80.5 (3)° to each other in the asymmetric unit. The anion features a strong intra-molecular O-H⋯O hydrogen bond, forming a self-associated S(7) ring motif. The crystal packing is dominated by inter-molecular N-H⋯O hydrogen bonds leading to the formation of 2₁ 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⋯O hydrogen bonds, forming layers parallel to the ab plane. Hirshfeld surface analysis and two-dimensional fingerprint plots were used to investigate and qu-antify the inter-molecular inter-actions in the crystal.