Redox-Controlled Selective Docking in a [2]Catenane Host

The docking by neutral and charged guests selectively
in two geometrically
different binding pockets in a dynamic [2]­catenane host is demonstrated
in the solid state by manipulating its redox chemistry. The change
in redox properties, not only alters the affinity of the host toward
neutral and charged guests, but it also induces a profound change
in the geometry of the host to accommodate them. X-ray crystallography,
performed on the two different 1:1 complexes, demonstrates unambiguously
the fact that the [2]­catenane host provides a uniquely different binding
pocket wherein a methyl viologen dication is stabilized by interacting
with a bipyridinium radical cation, despite the presence of Coulombic
repulsions.