14: The Cation–π Interaction

The cation–π interaction has long been recognized as a powerful force that can contribute strongly to intermolecular interactions. It has been well documented in the gas phase, in solution, and in the solid state. In the present chapter, we present a brief overview of the fundamental nature of the cation–π interaction, describing work that establishes both the nature and the potential magnitude of the interaction. We then describe a number of systems in which cation–π interactions play a key role in determining a solid state packing arrangement. It is clear that the cation–π interaction can play an important role in molecular crystals, both in explaining observed packing patterns and in rationally designing molecular solids.