Chalcogen (Ch) elements of group 16 of the periodic table typically form neutral organic compounds such as chalcogenone R₁R₂CCh, chalcogeno-ethers R₁–Ch–R₂, and chalcogen oxides R₁–(ChO)–R₂, with anisotropic distribution of the electron density that determines the presence, on the Ch atom's surface, of areas of higher and lower electron density where the electrostatic potential can be negative and positive, respectively.¹  Regions of positive, or less negative, electrostatic potential, commonly named σ-holes, are frequently disposed opposite to these R₁–Ch bonds and can attractively interact with electron-rich sites such as Nu atoms and anions possessing a lone pair (Lp) of electrons, in the formation of the so-called chalcogen bonds (ChB, Scheme 16.1).