The nuclear quadrupole coupling of 10B and 11B in the carboranes B10C2H12

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Abstract
The nuclear quadrupole couplings of 10B and 11B in p‐carborane, p‐B10C2H12, were measured by the field cycling technique (nuclear quadrupole double resonance) at 77 K. The couplings are e2qQ/h(10B)=2980±40 kHz, e2qQ/h(11B)=1430±20 kHz, and η=0.49±0.03. Ab initio calculations of the electric field gradient tensors at the boron nuclei in o‐, m‐, and p‐carborane were performed. The results based on the Gaussian basis set (9s5p/4s)/[4s2p/2s] are in good agreement with the experimental couplings for p‐carborane and those for o‐ and m‐carborane obtained earlier by us. There are no reorientational jumps of the globular carborane molecules at 77 K on the nuclear quadrupole resonance time scale. The valence bond view of bonding in the carboranes is confirmed by the good correlation of experimental quadrupole coupling constants and those derived from the valence bond structures.