Co-ordination compounds, of Boron

It is in the field of the co-ordination compounds of boron that some of the most conflicting results have been obtained. It is however generally recognized that the transformation of the sp hybridization of the boron atom to an sp hybridized state on complex formation results in a shift to high field. In our laboratories, we have designated this chemical-shift difference between the free and complexed boron acceptor molecule as the A value. We have found it very convenient to use this A value although it is not always applicable, e.g., in borane BH3, which exists as the dimer, diborane, and in phenylborane, PhBH2, which we have not yet isolated in the free state. 

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