A whole zoo of hydrogen bonds in one crystal structure: tris(isonicotinium) hydrogensulfate sulfate monohydrate

Depending on the reaction partner, the organic ditopic molecule isonicotinic acid (Hina) can act either as a Brønsted acid or base. With sulfuric acid, the pyridine ring is protonated to become a pyridinium cation. Crystallization from ethanol affords the title compound tris(4-carboxypyridinium) hydrogensulfate sulfate monohydrate, 3C₆H₆NO₂⁺·HSO₄^-·SO₄^2-·H₂O or [(H₂ina)₃(HSO₄)(SO₄)(H₂O)]. This solid contains 11 classical hydrogen bonds of very different flavour and nonclassical C-H...O contacts. All N-H and O-H donors find at least one acceptor within a suitable distance range, with one of the three pyridinium H atoms engaged in bifurcated N-H...O hydrogen bonds. The shortest hydrogen-bonding O...O distance is subtended by hydrogensulfate and sulfate anions, viz. 2.4752 (19) Å, and represents one of the shortest hydrogen bonds ever reported between these residues.