Boron nuclear quadrupole couplings and localized electronic wave functions in the boron clusters o-carborane and o-silaborane

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Abstract
The 11B nuclear quadrupole couplings in ‘‘o‐silaborane’’ [1,2‐dimethyl‐1,2‐ disila‐closo‐ dodeca‐ borane(12), B10Si2(CH3)2H10] were measured at 77 K with a nuclear quadrupole double resonance spectrometer with rapidly switched magnet. Three 11B transitions were found which were assigned by comparison with ab initio calculations of the electric field gradients. The surprising difference in the order of the quadrupole couplings of equivalent borons in o‐silaborane and the corresponding carbon compound o‐carborane (B10C2H12) is explained by the different valence bond structures of the two boron clusters which were obtained by localization of the electronic wave functions.