Dodecahydro-closo-undecaborate [B11H12](-)

DFT-calculations of the geometries of the closo-anion [B11H11](2-) in its g round state and in the transition state of its skeletal rearrangement and o f the protonated species [B11H12](-) in its ground state were performed at the B3LYP/6-31++G(d,p) level. The corresponding NMR shifts were computed on the basis of the optimized geometry by the GIAO method at the same level. Calculated and observed NMR data are in good agreement and thus prove the s tructure of [B11H12](-), previously deduced from 2D-NMR spectra. The additi on of water, ethanol, and pyridine to [B11H12](-) at low temperature gave t he nido-species [B11H13(OH)](-), [B11H13(OEt)](-), and [B11H12(py)](-), res pectively. The structures of these anions were investigated by NMR methods and the last two of them by crystal structure analyses of appropriate salts . The course of the addition reactions can be rationalized on the basis of the structurally characterized reaction components.