Tetra­ethyl­ammonium 7,12-di­cyano-1-carba-closo-dodeca­borate

In the title compound, C₈H₂₀N⁺·C₃H₁₀B₁₁N₂⁻, the carborane anion cage displays nearly-perfect C_s symmetry, with the two CN groups lying on a noncrystallographic mirror plane that bis­ects the cage. In the crystal, the anions form extended chains along the a-axis direction, with C—H...N hydrogen bonds linking consecutive anions. The C[triple bond]N bond lengths (and B—C[triple bond]N angles) in the nitrile moities are 1.1201 (19) Å, 178.60 (15)° and 1.1433 (17) Å, 179.45 (15)°, similar to those observed in organic nitriles. A hydrogen bond between a methylene H atom of the cation and the N atom in one of the nitrile groups of the anion is the closest contact between the anion and cation, at 2.52 Å.