Synthesis,Characterization, and Crystal Structures of [N(CH3)4]2[B12H12] and [N(CH3)4]2[B12H12] · CH3CN

Bis(tetramethylammonium) dodecahydrododecaborate, (CH₃)₄N]₂B₁₂H₁₂], and bis(tetramethylammonium) dodecahydrododecaborate acetonitrile, (CH₃)₄N]₂B₁₂H₁₂] · CH₃CN, were synthesized and characterized via Infrared, ¹H and ¹¹B NMR spectroscopy. (CH₃)₄N]₂B₁₂H₁₂] crystallizes isopunctual to the alkali metal dodecaborates. The crystal structure of (CH₃)₄N]₂B₁₂H₁₂] · CH₃CN was determined from single crystal data and refined in the orthorhombic crystal system (Pcmn, no. 62, a = 898.68(8), b = 1312.85(9) c = 1994.5(1) pm, R(|F| , 4σ) = 5.9%, wR(F²) = 18.3%). Here, the geometry of the dodecaborate anion is that of an almost ideal icosahedron, less distorted than most other dodecaborates known. By low‐temperature Guinier‐Simon diffractometry phase transitions were detected for (CH₃)₄N]₂B₁₂H₁₂] and (CH₃)₄N]₂B₁₂H₁₂] · CH₃CN at –70 and –15 °C, respectively.