4-Methyl­pyridinium 4-hy­droxy­benzoate

In the crystal structure of the title salt, C₆H₈N⁺·C₇H₅O₃⁻, the anions and cations are linked by classical N—H...O hydrogen bonds. The anions are connected by pairs of C—H...O hydrogen bonds into inversion dimers and further linked by classical O—H...O hydrogen bonds. Weak π–π inter­actions [centroid–centroid distances = 3.740 (3) and 3.855 (3) Å] also occur. The dihedral angle between the CO₂⁻ group and the benzene ring to which it is attached is 20.95 (8)°.

2-Phenyl­ethanaminium 4-hy­droxy­benzoate

In the title salt, C₈H₁₂N⁺·C₇H₅O₃⁻, the cation is disordered over two orientations with site occupancies of 0.565 (7) and 0.435 (7). In the anion, the carboxyl­ate group makes the dihedral angle of 4.19 (18)° with the benzene ring. In the crystal, the ions are connected by N—H...O and O—H...O hydrogen bonds, forming a three-dimensional network.

1H-Benzotriazole–4-hy­droxy­benzoic acid (1/1)

The asymmetric unit of the title compound, C₆H₅N₃·C₇H₆O₃, comprises independent benzotriazole and 4-hydroxybenzoic acid molecules. The dihedral angle between the benzene ring and the benzotriazole ring system is 15.18 (7)°. The mean plane of the carb­oxyl group is twisted at an angle of 18.55 (1)° with respect to the benzene ring. The crystal structure is stabilized by weak inter­molecular N—H...N, O—H...N, O—H...O and C—H...O inter­actions, forming a three-dimensional network.