Boronate weak stabilizing effect

There is a weak electronic interaction between the ic-systems of adjacent sheets and that, with van der Waals forces operating, holds the sheets together. The delocalization of the ic electrons within each sheet provides the stability of the structure, which is 190 J moh more stable than the other principal allotrope, diamond. In diamond, each carbon atom exerts its valency of four in a tetrahedral manner, and the carbon-carbon distance is 154 pm, Le. that expected for a single covalent bond. The enthalpy of atomization of carbon is significantly larger than that of boron, reflecting the effect of the extra valence electron. 

Our group has devoted two articles for the study of systems where the chiral subunits are bonded to a boron or to a metallic atom (Scheme 3.28). In both cases, the weakness of the bonds formed can be easily broken. In the first case, a series of bisdiphenylborates and the effect of the fluoro substitution on the relative stability of the homo vs. heterochiral complexes have been studied by means of DFT calculations (B3LYP/6-31G ) [29]. In addition, the corresponding isoelectronic structures, in which the boron has been substituted by a carbon or a positively charged nitrogen, have been considered. In all the cases, the homo and heterochiral complexes present D2 and S4 symmetries, respectively. 

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