8-Hy­droxy-5,7-dimethyl­quinolin-1-ium hydrogen sulfate

The quinoline ring system of the title salt, C₁₁H₁₂NO⁺·HSO₄⁻, is essentially planar, with a maximum deviation of 0.054 (2) Å for all non H atoms. In the crystal, the cations and anions are linked via N—H...O, O—H...O and weak C—H...O hydrogen bonds, and are stacked respectively in columns along the a axis. π–π stacking inter­actions, with centroid–centroid distances of 3.5473 (12) and 3.6926 (12) Å, are also observed. The crystal studied was an inversion twin with refined components of 0.43 (7):0.57 (7).

8-Hy­droxy-5,7-dimethyl­quinolin-1-ium chloride dihydrate

In the title hydrated salt, C₁₁H₁₂NO⁺·Cl⁻·2H₂O, the quinoline ring system is essentially planar, with a maximum deviation of 0.005 (1) Å for all non-H atoms. In the crystal, the three components are linked by O—H...O, N—H...O, O—H...Cl and weak C—H...O hydrogen bonds, forming a layer structure parallel to the ac plane. The crystal structure is further stabilized by π–π stacking inter­actions, with centroid–centroid distances of 3.5213 (6) and 3.7176 (6) Å.

2,3-Diamino­pyridinium hydrogen malonate

In the title mol­ecular salt, C₅H₈N₃⁺·C₃H₃O₄⁻, the cation is essentially planar, with a maximum deviation of 0.005 (1) Å for all non-H atoms. In the anion, an intra­molecular O—H...O hydrogen bond generates an S(6) ring. In the crystal, the cations and anions are connected via N—H...O hydrogen bonds and a weak C—H...O inter­action, forming layers parallel to the ab plane.