1-Ethyl-3-methyl-1H-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.