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.

Sequential Halogen Bonding with Ditopic Donors: σ-Hole Evolutions upon Halogen Bond Formation

“…Because of its strength and directionality, halogen bonding (XB) , is currently investigated as a hydrogen bond analogue, where the halogen atom acts as the electrophile. This interaction plays a crucial role in many areas of supramolecular chemistry and crystal engineering, such as anion receptors, , organocatalysis, , molecular conducting , and magnetic materials, , solid state polymerization, , liquid crystals , and gels, luminescent compounds, , etc. Competition cases , when halogen bonding is faced with hydrogen bonding , have been reported in many instances, highlighting the strength of the halogen bonding and the cases of orthogonal XB and HB in proteins …”

Solution Studies of a Water-Stable, Trivalent Antimony Pnictogen Bonding Anion Receptor with High Binding Affinities for CN–, OCN–, and OAc–

“…Up to three of these sites can be induced. The stabilizing interaction that results from an electron donor interacting with this site has been termed a pnictogen bond (PnB), in analogy to the closely related halogen (XB) and chalcogen (ChB) bonds − which have been employed in the design of anion receptors. ,− ,− An important feature of these supramolecular interactions that distinguishes them from formal Lewis acids such as BX 3 , AlX 3 , or PnX 5 (Pn = pnictogen, X = halogen) is that they form with minimal geometric reorganization which results in reversible PnB, ChB, or XB formation without an activation barrier. , These receptors have been applied to form supramolecular capsules to mimic biological molecules, as cross-membrane anion transporting agents, ,,, and as catalysts in substitution reactions. , …”