An approach to networks based on coordination of alkyl-substituted cucurbit[5]urils and potassium ions

Abstract

We introduce an approach for the synthesis of networks based on the coordination of alkyl-substituted cucurbit[5]uril (SQ[5]), dimethylcucurbit[5]uril (DMeQ[5]), 1,3-dicyclohexanocucurbit[5]uril (1,3-DCyHQ[5]), 1,2,4-tricyclohexanocucurbit[5]uril (1,2,4-TriCyHQ[5]), 1,2,3-cyclohexanocucurbit[5]uril (1,2,3-TriCyHQ[5]), and pentacyclopentanocucurbit[5]uril (PCyPQ[5]) with K⁺ ions in the absence of a structure inducer. These novel SQ[5]-K⁺-based networks feature trigonal-planar branches constructed from three SQ[5]s and K⁺ ions in a triangular manner, in which the coordination of each K⁺ ion to the five portal carbonyl oxygen atoms of one SQ[5] as well as to a bridging portal carbonyl oxygen from an adjacent SQ[5] draws the edges of three portals into close proximity. Thus, a 3-K⁺-cation junction is formed at each portal of the S[5] and there are four 3-K⁺-cation junctions in which one or two coordinated water molecule(s) are shared by the three K⁺ cations in the trigonal-planar branch. Detailed inspection of the relationship of the planes at the 3-K⁺ junction has revealed that the dihedral angles between the junction plane and the center junction plane have a strong influence on the supramolecular assembly of SQ[5] with K⁺ ions into 2D-networks or 3D-frameworks. Moreover, these dihedral angles determine the structural conformation of the SQ[5]-K⁺-based networks and the superimposition of 2D-networks in the compounds.