Synthesis, characterization, and crystal structures of [N(CH3)(4)](2)[B12H12] and [N(CH3)(4)](2)[B12H12]center dot CH3CN

Bis(tetramethylammonium) dodecahydrododecaborate, [(CH3)(4)N](2)[B12H12], a nd bis(tetramethylammonium) dodecahydrododecaborate acetonitrile, [(CH3)(4) N](2)[B12H12]. CH3CN, were synthesized and characterized via Infrared,H-1 a nd B-11 NMR spectroscopy. [(CH3)(4)N](2)[B12H12] crystallizes isopunctual t o the alkali metal dodecaborates. The crystal structure of [(CH3)(4)N](2)[B 12H12]. CH3CN was determined from single crystal data and refined in the or thorhombic crystal system (Pcmn, no.62, a=898.68(8), b=1312.85(9) c = 1994. 5(1) pm, R([F], 4 sigma)= 5.9%, wR(F-2) = 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 diffr actometry phase transitions were detected for [(CH3)(4)N](2)[B12H12] and [( CH3)(4)N](2)[B12H12]. CH3CN at -70 and -15 degreesC, respectively.