Centrosymmetric and non-centrosymmetric packing of aligned molecular fibers in the solid state self assemblies of cyclodextrin-based rotaxanes
Date
2006
Authors
Cieslinski, M.
Steel, P.
Lincoln, S.
Easton, C.
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Journal article
Citation
Supramolecular Chemistry, 2006; 18(6):529-536
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Marta M., Steel, Peter J., Lincoln, Stephen F., Easton and Christopher J
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Abstract
Two [2]-rotaxanes each comprising α-cyclodextrin as the rotor, and with either 3,3′-difluoro- or 3,3′-dichloro-stilbene as the axle and trinitrophenylamino substituents as the blocking groups at the 4- and 4′-positions, were prepared and their structures analyzed in solution and the solid state using <sup>1</sup>H NMR spectroscopy and X-ray crystallography, respectively. With each rotaxane, in solution the stilbene rotates freely within the cyclodextrin annulus. In the solid state the 3,3′-dichlorostilbene- based rotaxane adopts two very similar conformations, each having the chlorines in the anti,anti -orientation. By comparison, the 3,3′-difluorostilbene- based rotaxane adopts anti,anti-, anti,syn- and syn,syn-orientations of the substituents. The crystal packing of each rotaxane displays aligned molecular fibers, which are centrosymmetrically orientated in the case of the difluoride due to the head-to-head/tail-to-tail alignment of the cyclodextrins. By contrast, all of the cyclodextrins in the dichloride are aligned head-to-tail along a single axis to give a polar, non-centrosymmetric crystal. © 2006 Taylor & Francis.
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© 2006 Taylor & Francis