Structures of, and related consequences of deprotonation on, two C(s)-symmetric arachno nine-vertex heteroboranes, 4,6-X2B7H9 (X = CH2; S) studied by gas electron diffraction/quantum chemical calculations and GIAO/NMR.

Gas-phase structure determinations have been performed for arachno-4,6-(CH2)2B7H9 and arachno-4,6-S2B7H9 by combining quantum-chemical calculations and gas electron diffraction (GED) data. In addition, the monoanion derivatives of each of the aforementioned species have been studied using ab initio calculations. In all cases, comparison with experimental (11)B NMR chemical shifts have been achieved by calculating the appropriate NMR chemical shifts using GIAO-MP2 methods and the IGLO-II basis set for various geometries, both experimental and calculated. The NMR parameters calculated for the geometry obtained from the SARACEN GED refinement appeared to be quite reasonable, and in general, the fit between theoretical and experimental δ((11)B) NMR was found to be consistently good for all four species investigated.