Thorium(iv) and uranium(vi) compounds of cucurbit[10]uril: from a one-dimensional nanotube to a supramolecular framework

Abstract

Cucurbit[10]uril {Q[10]} has the largest portal size and cavity in the series of Q[n] (n = 5–10) molecules. In contrast to its rich host–guest chemistry, its coordination chemistry is underdeveloped with only limited metal ions being investigated so far. In this work, we initiated the study of Q[10] complexes with Th(IV) and U(VI) ions in HCl solutions via a self-assembly approach. The coordination of Th(IV) ions with Q[10] led to the formation of a compound, {Th₄(Cl)₁₆(H₂O)₂₀(Q[10])}·nH₂O (Q[10]-Th), with a unique nano-tubular structure, while U(VI) ions facilitated the formation of a compound, [(UO₂)₂(Cl)₄(H₂O)₆]·(Q[10])₂·HCl·nH₂O (Q[10]-U), with a Q[10]-based supramolecular framework structure via intermolecular outer-surface and second-shell interactions. The structural and spectroscopic aspects of the two compounds together with their optical and thermal properties have been investigated. The successful preparation and characterization of the first two Q[10] compounds with Th(IV)/U(VI) ions highlighted the potential for further exploration of Q[10] coordination chemistry with actinide ions.