Encapsulation of anions: Macrocyclic receptors based on metal coordination and anion–π interactions

Supramolecular chemistry of anions is a topic of continuous interest due to vital role of anions in many key chemical and biological processes. The dominant functional groups for constructing anion binding receptors are amides and amines/ammonium cations, where the key interaction to bind the anion is the hydrogen bond. This review covers systems where the binding of the anion with the receptor is through anion–π interactions, i.e., the non-covalent forces between electron-deficient aromatic systems and anions. Moreover, this review is focused to those receptors where coordination metals play a prominent role thanks to two very important characteristics: first, they are crucial for the synthesis and assembly of the receptor and, secondly, they strongly change the π-binding ability of the aromatic ligands, increasing significantly their π-acidity and, consequently, enhancing the ability of the ring to interact favorably with anions.

BF4− encapsulated into a square host with electron deficient aromatic walls.Figure optionsDownload high-quality image (76 K)Download as PowerPoint slideHighlights
► Supramolecular architectures based on electron-deficient aromatic ligands are useful for the encapsulation of anions.
► The importance of the transition metal is crucial to enhance the π-acidity of the aromatic ligands.
► Theoretical calculations are useful to evaluate the effect of the ligand coordination on the strength of the anion–π interaction.
► Structural and theoretical studies come together to explain weak interactions.