Coordination of fully substituted cyclopentano cucurbit[5]uril with alkaline earth cations in the presence of tetrachlorozincate anions

• Study the coordination of CyP5Q[5] and alkaline earth metal ions in the presence of [ZnCl4]2− anions by means of X-ray crystallography.
• [ZnCl4]2− anions form a honeycomb-like framework.
• Investigation to the analysis of the absorption capacities for CyP5Q[5] based supramolecular assemblies.

In this study, fully substituted cyclopentano cucurbit[5]uril (CyP5Q[5]) were coordinated with an alkaline earth cations (AE2+) in the presence of tetrachlorozincate anions ([ZnCl4]2−). Single-crystal X-ray diffraction analysis revealed that the CyP5Q[5]–Mg2+–[ZnCl4]2−–HCl interaction system yielded an Mg2+/Cl−@CyP5Q[5]-type molecular bowl, with a chloride anion in the cavity of the CyP5Q[5] moiety. The CyP5Q[5]–Ca2+ and Sr2+–[ZnCl4]2−–HCl interaction systems yielded isolated AE2+/CyP5Q[5]/AE2+-type molecular capsules, again with a chloride anion in the CyP5Q[5] cavity. A honeycomb effect was evident in all three systems, in which the of the [ZnCl4]2− anions surround the CyP5Q[5] molecules through outer surface interactions between Q[n] and electrostatic interactions with AE2+ cations, resulting in the formation of porous supramolecular assemblies. Direct coordination between Ba2+ and CyP5Q[5] yielded zigzag coordination polymers. The CyP5Q[5]/AE2+-based supramolecular assemblies (AE = Mg, Ca, Sr, Ba) presented different porous conformations and displayed differential absorption of volatile compounds.

The fully cyclopentano-substituted cucurbit[5]uril (CyP5Q[5]) was first reported in 2012. In the present work, we again selected CyP5Q[5] as a ligand, and investigated the coordination with alkaline earth cations (AE2+) in the presence of ZnCl2 in aqueous HCl solution. The experimental results revealed that CyP5Q[5] can coordinate with Mg2+, Ca2+, Sr2+, Ba2+ to form molecular bowl or capsule-like coordination complexes. Close inspection revealed that the different CyP5Q[5]/AE2+-based supramolecular assemblies included different sized pores that controlled their absorption properties.Figure optionsDownload as PowerPoint slide