Neutral CH and cationic CH donor groups as anion receptors

The design and synthesis of anion selective receptors and chemosensors continues to attract considerable interest within the supramolecular community. In recent years, increasing attention has focused on the use of neutral and cationic CH hydrogen bond donors as anion recognition elements. Over the last five years, motifs that support CHX (X = anion) hydrogen bonds have been actively used in various shape persistent macrocycles, foldamers and "molecular machines". This tutorial review highlights recent developments in host-guest chemistry based on the use of neutral and cationic CH hydrogen bond donors. Also discussed are various structural classifications, including alkyl CH, phenyl CH, triazole-based CH, imidazolium (CH)(+) and triazolium (CH)(+) hydrogen bond donor systems.