Icosahedral Carbaboranes with Peripheral Hydrogen–Chalcogenide Groups: Structures from Gas Electron Diffraction and Chemical Shielding in Solution

Samples of closo-1,2-(EH)2-1,2-C2B10H10 (E = S, Se) have been prepared; in the case of E = Se for the first time. Their semi-experimental equilibrium molecular structures were established by the concerted use of quantum-chemical computations and gas elec¬tron diffraction (GED). A method has been developed and implemented to quantify the contribution of experimental data to each refined structural parameter. The accuracy of the experimental structures, as well as those computed at the MP2 level, were gauged by com¬parison of experimental 11B NMR chemical shifts with quantum-chemically computed ones; the inclusion of electron correlation (GIAO-MP2) provides superior results. For geometrical predictive purposes, the remaining group VI elements were considered and the icosahedral structures for E = O and Te were also computed; for E = O the same model chemistries were used as for E = S, while for E = Te similar approaches as for E = Se were employed.