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-pi 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 pi-binding ability of the aromatic ligands, increasing significantly their pi-acidity and, consequently, enhancing the ability of the ring to interact favorably with anions. (C) 2013 Elsevier B.V. All rights reserved.