1-Ethyl-3-methyl-1 H -imidazol-3-ium spiropentaborate

In the anion of the title compound, (C 6 H 11 N 2 )[B 5 O 6 (OH) 4 ], both six-membered borate rings adopt a flattened boat conformation with the spiro-B atom and its opposite O atom deviating from the remainders of the rings by 0.261 (3)/0.101 (2) and 0.160 (3)/0.109 (2) Å, respectively. The imidazolium cation also deviates from planarity due to rotation of the ethyl group (as indicated by the C—N—C—C torsion angle) by 71.4 (2)° out of the plane of the heterocycle. In the crystal, the anions are connected in a three-dimensional network through O—H...O hydrogen bonds, forming channels along the a- axis direction. The cations are situated in the channels, forming C—H...O hydrogen bonds with the anions.