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 1H NMR spectroscopy, and in the solid phase, using X-ray diffraction
methods. In D2O solution, methyl viologen (MV2+) and ethyl viologen (EV2+) form 1:1 complexes in which
the bipyridinium aromatic nucleus is partially included inside the
Cy6CB6 cavity. Propyl viologen (PV2+), butyl viologen (BV2+), pentyl viologen (FV2+), and heptyl viologen
(HV2+) form 2:1 complexes with Cy6CB6, in which each of
the viologen aliphatic chains is included by a host molecule. In the
solid state, EV2+ forms a polypseudorotaxane via pseudorotaxane
interdigitation of Cy6CB6 hosts. The PV2+ 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
BV2+ 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.