An Overview of Lewis Basicity and Affinity Scales

The impossibility of establishing a universal scale of Lewis basicity does not prevent the determination of the quantitative behavior of Lewis bases, thanks to scales constructed against particular Lewis acids: BF(3), 4-FC(6)H(4)OH, I(2), Li(+), Na(+), K(+), Al(+), Mn(+), CpNi(+), and CH(3)NH(3)(+). These scales encompass important types of bonds formed in a Lewis acid-base adduct: the dative bond, the conventional and ionic hydrogen bonds, the halogen bond and cation-molecule bonds for metal cations of groups 1, 7, 10, 11, and 13. Moreover, although these scales are generally not interrelated, there exist family-dependent relationships that permit ranking, in a rather general order, of bases belonging to a given chemical family, for example, the family of oxygen bases. Therefore, the skepticism about the quantitative usefulness of the Lewis concept of acids and bases is no longer founded