The Binding Interactions between Cyclohexanocucurbit[6]uril and Alkyl Viologens Give Rise to a Range of Diverse Structures in the Solid and the Solution Phases.

The binding interactions between the cyclohexanocucurbit[6]uril (Cy6CB6) host and a series of dialkyl-4,4'-bipyridinium (viologen) dicationic guests were investigated in the solution phase, using (1)H NMR spectroscopy, and in the solid phase, using X-ray diffraction methods. In D2O solution, methyl viologen (MV(2+)) and ethyl viologen (EV(2+)) form 1:1 complexes in which the bipyridinium aromatic nucleus is partially included inside the Cy6CB6 cavity. Propyl viologen (PV(2+)), butyl viologen (BV(2+)), pentyl viologen (FV(2+)), and heptyl viologen (HV(2+)) form 2:1 complexes with Cy6CB6, in which each of the viologen aliphatic chains is included by a host molecule. In the solid state, EV(2+) forms a polypseudorotaxane via pseudorotaxane interdigitation of Cy6CB6 hosts. The PV(2+) guest forms a dumbbell-shaped structure with a Cy6CB6 host residing over each of the terminal propyl groups of the guest. In contrast to this, the BV(2+) guest and Cy6CB6 form a different polypseudorotaxane structure in which dumbbell-shaped structures, formed by two host molecules interacting with a single guest, are interconnected through metal-host coordination.