Advances in the lanthanide metallosupramolecular chemistry of the cucurbit[n]urils

• The synthesis and structures of cucurbit[n]uril lanthanide complexes are discussed.
• Emphasis is given to complex structural variation along the lanthanide series.
• The role of “structure inducers” in promoting complexation is discussed.
• Particular systems are able to discriminate between light and heavy lanthanides.

Lanthanide coordination complexes have attracted considerable attention because of their unique electronic, magnetic, and optical properties. Early work showed that the large size of lanthanide ions, their propensity for ionic bonding and steric dictates in the coordination sphere are crucial factors influencing the coordination number and geometry of individual lanthanide (Ln) complexes. This review provides an overview of recent advances and achievements in the chemistry of the lanthanides involving cucurbit[n]uril {Q[n]}ligands. The two preorganised (identical) carbonyl fringed portals in Q[n]s are each ideal for acting as a rigid platform for developing a variety of lanthanide-containing metallo-supramolecular assemblies. Further, the ability to employ Q[n]s with different portal sizes provides a means for influencing metal coordination behaviour. A range of examples in which the use of a “structure inducer” (often an anionic species or an organic molecule) is employed to promote the isolation of new Ln3+-Q[n] species is discussed. Particular Q[n] metal complex systems have been demonstrated to discriminate the light lanthanide cations from their heavier counterparts suggesting possible application in lanthanide separation processes.

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