Cation-π and anion-π interactions

In this review, we analyze the interaction of ions with aromatic rings from several points of view. We start with a short history of cation-pi and anion-pi interactions and continue with a description of the main forces involved in these interactions. The comprehension of these forces allows us to rationalize the requirement that both the ion and the aromatic compound should have improved the interaction. Some physical properties of both the aromatic rings and the interacting ion are directly related with the strength of the interaction. An interesting part of this review is the study of the interplay of the ion-pi interactions with other noncovalent forces. The strength of the ion-pi interaction is considerably influenced by the presence of hydrogen bonding or other weaker interactions. These influences can be used to tune the interaction, either weakening or strengthening it. We give some experimental examples that illustrate this point. (C) 2011 John Wiley & Sons, Ltd. WIREs Comput Mol Sci 2011 1 440-459 DOI: 10.1002/wcms.14