Poised on the brink between a bistable complex and a compound.

[reaction: see text] An enmeshed supramolecular complex, based on a semi-dumbbell-shaped component containing an asymmetrically substituted tetrathiafulvalene site and a 1,5-dioxynaphthalene site for encirclement by a cyclobis(paraquat-p-phenylene) ring component and with a "speed bump" in the form of an thiomethyl group situated between the two recognition sites, has been self-assembled. This complex is a mixture in acetone solution of two slowly interconverting [2]pseudorotaxanes, one of which is on the verge of being a [2]rotaxane at room temperature.