Selective anion recognition by covalent organic cages

Recent studies on selective anion recognition employing covalent organic cage hosts are reviewed. Cage-like host molecules with convergent anion binding sites (positively charged or neutral moieties), including protonated azacryptands, prism-like cages, tetrahedral cages, and more complex cage structures, are demonstrated. We focus on anion selectivity as described by comparison binding constants between hosts and anions in solution, and examine the factors affecting anion selectivity in terms of multiple and cooperative non-covalent interactions, shape complementarity, and size matching between hosts and anions.