Computation of the BF3 Affinity

The existence of numerous theoretical studies on the Lewis affinity of BF3 and on the nature of the dative bond in BF3 complexes, generally performed at high theoretical levels, illustrates that the choice of BF3 as a reference Lewis acid for constructing an affinity scale of Lewis bases is well founded, not only from the experimental but also from the computational point of view. Indeed, the electronic structure of BF3 is very simple, since this trigonal planar molecule contains only four first-row atoms. Calculations on the thermodynamics of BF3 complexes can significantly improve our knowledge of Lewis affinity, as illustrated below. 

It is possible to compute the BF3 Lewis affinity, at 0 and/or 298 K in the gas phase, of bases that are difficult to study experimentally, such as weak carbon n bases [41,42, 73], water [74] and diaminocarbenes [75]. 

Consequently, the Complete-Basis-Set QB3 results explain only 84% of the variance of the experimental results. The relative agreement rises to 93% when MejP is excluded. 

The BF3 affinity scale represents an improved version of the SbCls affinity scale (DN scale). The concept is similar but the methodology produces cleaner complexation reactions and consequently more accurate complexation enthalpies. Additionally, the BF3 affinity database is more comprehensive and more varied than the SbCls affinity database. Finally, compared with SbCls the electronic structure of BF3 is much simpler. 

Gay-Lussac, L.J. (1809) Memoire sur la combinaison des substances gazeuses, les unes avec les autres, Memoires de Physique et de Chimie de la Socidte d Arcueil, 2, 207-234. 

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