Peter T. Glink

Supramolecular daisy chains

Our childhoods may be recalled when a self-complementary cation, endowed with both a dibenzo[24]crown-8 macroring and a secondary dialkylammonium sidearm, self-assembles to form a two-component supramolecular architecture that is reminiscent of a daisy chain (depicted schematically on the right). This daisy-chain-like superarchitecture is stabilized by a combination of [N+ -H⋅⋅⋅O] hydrogen bonds and aryl-aryl stacking interactions.

THE GENESIS OF A NEW RANGE OF INTERLOCKED MOLECULES

Secondary dialkylammonium ions self-assemble with suitably sized macrocyclic polyethers, such as the well-known dibenzo-24-crown-8 and bis-p-phenylene-34-crown-10, into pseudorotaxane superstructures in (a) solution, (b) the solid state and (c) the ‘gas phase’.

The solid state structures of a [3]rotaxane and its [3]pseudorotaxane precursor

Abstract The solid state structures of a [3]pseudorotaxane — formed from a bis(azidomethyl)-substituted p -xylene-α,α′-dibenzylammonium dication and two dibenzo-24-crown-9 rings — and a [3]rotaxane derived from it — by two dipolar cycloadditions of the azidomethyl groups with di- t -butyl acetylenedicarboxylate — are described. The (super)structures are remarkably similar in their geometries and packing.

CONCEPT TRANSFER FROM THE LIFE SCIENCES INTO MATERIALS SCIENCE

The use of self-assembly processes, which are presided over by noncovalent bonding interactions, has led to the construction of a variety of mechanically-entwined and interlocked entities - namely, the so-called pseudorotaxanes, rotaxanes and catenanes - of nanometre size. Although these superstructures and structures are entirely unnatural in their forms, they have been constructed utilising approaches akin to those occurring in nature.