Temperature-induced reversible single-crystal-to-single-crystal isomerisation of uranyl polyrotaxanes: an exquisite case of coordination variability of the uranyl center.

The first reversible solid-state single-crystal-to-single-crystal isomerisation mediated by the change of uranyl-ligand coordination modes, that is from seven-coordinated uranium(vi) of α-UP to six-coordinated uranium(vi) of the supramolecular isomer, β-UP, has been achieved in the uranyl polyrotaxane system by a temperature-induced strategy.