Coordination of alkaline-earth metal ions to hexanohydroxyhexanomethylcucurbit[6]uril and formation of tubular coordination polymers

The interaction of alkaline-earth cations (AE2+) with hexanohydroxyhexanomethylcucurbit[6]uril (HHQ[6]) in the presence of CdCl2 in aqueous HCl solution was investigated. Single crystal X-ray diffraction analysis revealed that the interaction results in the formation of one-dimensional coordination polymers of HHQ[6] with AE2+ (Ca, Sr or Ba). In addition, compounds containing Ca and Sr are isomorphous. Moreover, the compound obtained from the HHQ[6]–MgCl2–CdCl2–HCl system contained only a metal-free HHQ[6]-based supramolecular assembly. ITC experiments showed that the interaction between HHQ[6] and Mg2+ could not be effectively measured, and that the interaction of Ca2+ or Sr2+ with HHQ[6] are driven by ΔH and ΔS, whereas the interaction between Ba2+ and HHQ[6] is driven by ΔH.

Graphical abstractInteraction of alkaline-earth cations (AE2+) with hexanohydroxyhexanomethylcucurbit[6]uril (HHQ[6]) in the presence of CdCl2 in aqueous HCl results in the formation of one-dimensional coordination polymers of HHQ[6] with AE2+ (Ca, Sr or Ba).Figure optionsDownload full-size imageDownload as PowerPoint slide