Structural investigations on Cs-2[B12H12]

The crystal structure of Cs-2[B12H12] has been determined from X-ray single -crystal data collected at room temperature. Dicesium dodecahydro-closo-dod ecaborate crystallizes as colourless, face-rich crystals (cubic, Fm (3) ove r bar; a = 1128.12(7) pm: Z = 4). Its synthesis is based on the reaction of Na[BH4] with BF3(O(C2H5)2) via the decomposition of Na[B3H8] in boiling di glyme, followed by subsequent separations, precipitations (with aqueous CsO H solution) and recrystallizations. The crystal structure is best described as anti-CaF2-type arrangement with the Cs+ cations in all tetrahedral inte rstices of the cubic closest-packed host lattice of the icosahedral [B12H12 ](2-)-cluster dianions. The intramolecular bond lengths are in the range us ually found in closo-hydroborates: 178 pm for the B-B and 112 pm for the B- H distance. Twelve hydrogen atoms belonging to four [B12H12](2-) icosahedra provide an almost perfect cuboctahedral coordination sphere to the Cs+ cat ions, and their distance of 313 pm (12x) attests for the salt-like characte r of Cs-2[B12H12] according to (3)(infinity){(Cs+)(2)([B12H12](2-))} The B- 11{H-1}-NMR data in aqueous (D2O) solution are delta = -12,70 ppm ((1)J(B-H ) = 125 Hz), and delta = -15,7 ppm (linewidth: Delta nu(1/2) = 295 Hz) for the solid state B-11-MAS-NMR.