Crystal structure of 1H,1′H-[2,2′-biimid­azol]-3-ium hydrogen tartrate hemi­hydrate

In the crystal of the title hydrated salt, C₆H₇N₄⁺·C₄H₅O₆⁻·0.5H₂O, the bi­imidazole monocation, 1H,1′H-[2,2′-biimidazol]-3-ium, is hydrogen bonded, via N—H...O, O—H...O and O—H...N hydrogen bonds, to the hydrogen tartrate anion and the water mol­ecule, which is located on a twofold rotation axis, forming sheets parallel to (001). The sheets are linked via C—H...O hydrogen bonds, forming a three-dimensional structure. There are also C=O...π inter­actions present [O...π distances are 3.00 (9) and 3.21 (7) Å], involving the carbonyl O atoms and the imidazolium ring, which may help to consolidate the structure. In the cation, the dihedral angle between the rings is 11.6 (2)°.