Cations as Lewis Acids in the Gas Phase

There is a large array of cations that have been studied in the gas phase for their interaction with Lewis bases (generally neutral organic molecules) and are still being actively investigated today. The most studied is the proton [1-6]. This special cation will not be dealt with in this chapter (however, see Section 1.3 in Chapter 1), since the proton and its transfer serve to define the Bronsted acids and bases, as opposed to Lewis acids and bases, which do not exchange protons. Moreover, although the proton and a cation with an empty orbital may be seen as identical from the point of view of the Lewis theory, the special electronic structure of the proton (in fact the absence of any electron) makes the proton affinity and basicity scales completely different, qualitatively and quantitatively, from any other cation scales. 

A significant part of the studies of the interaction of gas-phase metal cations with organic molecules was devoted to their chemical reactivity bond insertion, bond cleavage, elimination and so on. This aspect is not considered here, although some of these reactions may be used as indirect routes for the formation of cation/molecule adducts. 

Apart from the proton, experimental studies have focused primarily on the binding of alkali metal cations and transition metal monocations. Few studies have considered alkaline 

Lewis Basicity and Affinity Scales Data and Measurement Christian Laurence and Jean-Fran9ois Gal 2010 John Wiley Sons, Ltd 

The research field is, in principle, not restricted to monocharged cations so the thermochemistry of multicharged cations, resulting from the solvation (addition of several molecules) of alkaline earth dications (Mg +, Ca +, etc.), has been studied [7]. Nevertheless, such studies are severely limited by competitive electron transfer, since the second ionization energy of a metal is usually much greater than that of molecules, and the charge exchange reaction 

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