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Linear 1,2-bis(pyridinium)ethane 'axles' and macrocyclic 24-membered crown ether 'wheels' (, and ) combine to form [2]pseudorotaxanes. These interpenetrated adducts are held together by N+...O ion-dipole interactions, a series of C-H...O hydrogen bonds and pi-stacking between electron-poor pyridinium rings of the axle and electron-rich catechol rings of the wheel. 1H NMR spectroscopy was used to identify the structural details of the interaction and to determine the thermodynamics of the binding process in solution. Analysis of nine of these adducts by single crystal X-ray crystallography allowed a detailed study of the non-covalent interactions in the solid state. A wide variety of structural changes could be made to the system. The versatility and potential of the template for the construction of permanently interlocked structures such as rotaxanes and catenanes is discussed.

Anionic wheels for cationic axles: Significant electrostatic ion–ion interactions dramatically increase the stability of interpenetrated molecules. In highly polar solvents, formation of [2]pseudorotaxanes is observed, in which crown ether wheels (see picture, red) having anionic sulfonate groups counter the pyridinium cations of the axle (blue).

The protonation of a cyclic tertiary amine, integrated into the structure of a dumbbell-shaped guest molecule, accelerates the sliding of the guest through the cavity of a crown ether macrocycle to yield a stable pseudo-rotaxane complex. The use of an amine with the appropriate ring size followed by a proton transfer reaction leads to the formation of an interlocked rotaxane species.