Anion Recognition in Solution via Halogen Bonding

Abstract

An overview of the interactions between anions and electron-deficient, covalently bound halogens is presented. It might be anticipated that species such as halides and oxoanions would be good acceptors of halogen bonds because of their relatively high charge densities and nucleophilicities. The stabilities of the trihalide anions X3 (-) provide a clear indication that this is indeed the case. The thermodynamics of formation of the trihalides, and of analogous complexes between anions and monodentate haloorganics in organic solvent, are discussed in detail. Although the incorporation of multiple interacting groups to achieve high guest affinity has been a key principle of supramolecular chemistry for decades, it is only recently that multidentate halogen bond donors capable of anion recognition have been reported. This contribution highlights the range of architectures that have been employed as the basis for multidentate halogen bond donor design. Examples of selective and high-affinity anion recognition through halogen bonding, including implementations in polar, protic media, are discussed.