Very short OH⋯hydrogen bond in l-histidinium difluoride

The crystal structure of C6H11N3O22+·2F2− is reported. The structure contains a fluoride ion strongly H-bonded to a carboxylic O atom, a rare, very strong, hydrogen bond. The donor–acceptor distance is 2.3818(10) Å, the shortest value reported to date, considerably less than the sum of the van der Waals radii of the atoms implicated, as expected from a very strong hydrogen bond. The di-cation has an open conformation. There is an extensive H-bonding network between anions and cations assembling rings on the ac plane and chains in several directions. Two extra intermolecular interactions of the type CH⋯π are found, exhausting the aromatic π electron system ability to act as a proton acceptor.