Anions and π-Aromatic Systems. Do They Interact Attractively?

Abstract

Hydrogen bonds and charge–charge interactions have been widely used (either alone or in combination) in the design of efficient and selective synthetic receptors for anions. Intuitively, the interaction between anions and π-aromatic systems is associated with a repulsive force. Consequently, for many years, anion-π interactions have been completely neglected as favorable non-covalent interactions for the construction of efficient anion receptors. Recently, however, theoretical studies indicate the existence of an attractive interaction between anions and certain type of π-acidic aromatic systems. These theoretical studies together with the observation of supramolecular complexes in the solid state in which anions are included in deep aromatic cavities have encouraged an in depth study of the anion-π interaction. Nowadays, the anion-π interaction is considered by several researchers a potential non-covalent interaction for the design of anion receptors. This chapter will provide an overview of recent theoretical investigations, performed since 2002, on anion binding involving six-membered aromatic rings. A series of experimental studies, carried out since 2004, also evidencing the existence of a possible attractive interactions betweens anions and six-membered aromatic moieties of host-guest systems in the solid state and in solution is also discussed.