Nuclear Quadrupole Interaction in Boron Compounds

The quadrupole coupling constants of B11 in some boron compounds are investigated in detail. A Townes-and-Dailey type of interpretation for boron trimethyl gives better agreement with experiment than a detailed molecular orbital calculation, but it is pointed out that this agreement is to be regarded as fortuitous. It is concluded that if localized LCAOMO functions are formed from undistorted atomic orbitals to describe a bond, they lead to an underestimation of the field gradient at the nucleus due to the electrons. For borine carbonyl, an estimation of the ionic character of the BC bond is made from the observed quadrupole coupling constant of B11. With this estimate, the dipole moment associated with the BH3 group is obtained from the observed dipole moment of the whole molecule. The dipole moment of the BH3 group is also calculated using localized LCAOMO's for the BH bonds. This calculation gives the correct sign of the observed dipole moment, but overestimates its magnitude. Some comments are made on the quadrupole interaction tensor for B11 in kernite using a molecular orbital approach.