BORON NUCLEAR-QUADRUPOLE COUPLINGS AND LOCALIZED ELECTRONIC WAVE-FUNCTIONS IN THE BORON CLUSTERS O-CARBORANE AND O-SILABORANE

The B-11 nuclear quadrupole couplings in ''o-silaborane'' [1,2-dimethy l-1,2- disila-closo- dodecaborane(12), B10Si2(CH3)(2)H-10] were measur ed at 77 K with a nuclear quadrupole double resonance spectrometer wit h rapidly switched magnet. Three B-11 transitions were found which wer e assigned by comparison with ab initio calculations of the electric f ield gradients. The surprising difference in the order of the quadrupo le couplings of equivalent borons in o-silaborane and the correspondin g 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. (C) 1995 American I nstitute of Physics.