Halogenated closo-Dodecaborate Anions Stabilize Weakly Bound [(Me3NH)3X]2+ (X = Cl, Br) Dications in the Solid State

Cocrystallization of [Me3NH](2)[B12Y12] (Y = Cl, Br, I) with 1 equiv. of [Me3NH]X (X = Cl, Br) from acetonitrile/diethyl ether solution produced large colorless single crystals of [(Me3NH)(3)X][B12Y12]. Four different compounds of this type were prepared and structurally characterized. The compounds consist of weakly coordinating perhalogenated closo-dodecaborate [B12Y12](2-) dianions and unprecedented weakly bound discrete [(Me3NH)(3)X](2+) dications. The [(Me3NH)(3)X](2+) dications are built up from a central halide anion and three [Me3NH](+) cations bound by N-H center dot center dot center dot X hydrogen bonds. The cations have a pyramidal structure, as determined by X-ray diffraction, which is in contrast to quantum-chemical calculations, which predict a trigonal-planar structure. While the [(Me3NH)(3)Cl](2+) and [(Me3NH)(3)Br](2+) cations were easily prepared, attempts to synthesize the corresponding [(Me3NH)(3)F](2+) and [(Me3NH)(3)I](2+) cations failed. Three further crystal structures containing the angulated [(Me3NH)(2)X](+) cation stabilized by [B12Cl12](2-), [B12Br12](2-), or [Me3NB12Cl11](-) are reported as well.