Transition metal and organometallic anion complexation agents

Anions are ubiquitous species, and therefore, their sensing is of considerable interest. Anion receptors containing electrochemically active groups such as ferrocene or cobaltocenium, or optically active groups such as ruthenium(II) bipyridyl derivatives, allow the binding of anions to be detected by a physical response at the metal centre. These systems have been incorporated into various acyclic, macrocyclic and calix[4]arene frameworks, many of which include an amide hydrogen-bonding group. Anions may be recognised in a range of environmental conditions, with some receptors even being active in aqueous solution. The incorporation of new transition metal and organometallic systems has led to the development of several new strategies in anion recognition.