Sigma-Hole Interactions in Anion Recognition

Sigma (sigma)-holes are electron-deficient regions that arise from the anisotropic distribution of electron density on the atom of group 14 (tetrels), 15 (pnictogens), 16 (chalcogens), and 17 (halogens) elements when covalently bonded to electron-withdrawing groups. Named after the donor atom's group, the sigma-hole interactions, halogen bonding, and chalcogen bonding with anionic species have found ground-breaking applications in anion supramolecular chemistry within the last decade. In this review, we feature key recent discoveries and advances across the whole range of sigma-hole interactions for anion recognition, from the familiar halogen bonding to the almost unknown pnictogen and tetrel bonding. In particular, the novel anion recognition properties and applications that result from the unique aspects of each sigma-hole interaction, together with detailed design considerations of anion-binding receptor motifs, are highlighted.