Cucurbit[n]uril-based host–guest-metal ion chemistry: an emerging branch in cucurbit[n]uril chemistry

Cucurbit[n]urils (Q[n]s), a relatively new class of macrocyclic hosts with a rigid hydrophobic cavity and two identical carbonyl-fringed portals, have attracted much attention since the first member of the Q[n]-family, cucurbit[6]uril (Q[6]), was structurally identified in 1981 by Mock and co-workers. The interactions of the rigid cavities and negative portals of Q[n]s have resulted in the development of two almost mutually exclusive areas of study, namely Q[n]-based host–guest chemistry and Q[n]-based coordination chemistry. However, researches has revealed that Q[n]-based host–guest inclusion interactions may be influenced by metal ion coordination at the Q[n] portals, and in turn, coordination of metal ions at the Q[n] portals could be promoted by the formation of Q[n]-based inclusion host–guest complexes. Thus, this review provides an overview of related advances and achievements involving such a combination of Q[n]-based host–guest chemistry and Q[n]-based coordination chemistry, which could become an emerging branch, that is, Q[n]-based host–guest-metal ion chemistry. In particular, it could be useful in the treatment of wastewater, kinetic studies, drug delivery, the construction of novel supramolecular frameworks, metal-catalyzed reactions, recognition or response to metal cations, and so on.