A versatile template for the formation of [2]pseudorotaxanes. 1,2-Bis(pyridinium)ethane axles and 24-crown-8 ether wheels

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Abstract
Linear 1,2-bis(pyridinium)ethane ‘axles’ and macrocyclic 24-membered crown ether ‘wheels’ (24C8, DB24C8 and DN24C8) 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 π-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.