Transition Metal Ion-Directed Supramolecular Assembly of One- and Two-dimensional Polyrotaxanes Incorporating Cucurbituril

Abstract

This paper reports a synthetic strategy to construct one- and two-dimensional (ID and 2D) polyrotaxanes, in which a number of rings are threaded onto a coordination polymer, by the combination of self-assembly and coordination chemistry. Our approach to construct polyrotaxanes with high structural regularity involves threading a cucurbituril (CB) "bead" with a short "string" to form a stable pseudorotaxane, followed by linking the pseudorotaxanes with metal ions as "linkers" to organize into a ID or 2D polyrotaxane. A 4- or 3-pyridylmethyl group is attached to each end of 1,4-diaminobutane or 1,5-diaminopentane to produce the short "strings", which then react with the cucurbituril "bead" to form stable pseudorotaxanes. The reaction of the pseudorotaxanes with various transition metal ions including Cu-II, Co-II, Ni-II, Ag-I, and Cd-II produces ID or 2D polyrotaxanes, in which many molecular "beads" are threaded onto ID or 2D coordination polymers as confirmed by X-ray crystallography. The overall structure of a polyrotaxane is the result of inter-play among various factors that include the coordination preferences of the metal ion, spatial disposition of the donor atoms with respect to the CB beads in the pseudorotaxane, and the size and coordination ability of the counteranion.