THE MOLECULAR-STRUCTURES OF PENTABORANE(11), B5H11, AND HEXABORANE(12), B6H12, IN THE GAS-PHASE AS DETERMINED BY ELECTRON-DIFFRACTION AND AB-INITIO CALCULATIONS

The electron-diffraction patterns of gaseous arachno-B5H11 and arachno -B6H12 have been reanalysed. Inclusion of ab initio (MP2/6-31G) compu ted bond-length differences in the refinements afforded new optimum ge ometries with improved R factors (R(G) = 0.053 and 0.057, respectively ) compared with the structures reported previously. In contrast to the latter, the new geometries can be employed to calculate B-11 NMR chem ical shifts (DZ//GED level) which are in good agreement with the exper imental NMR data.