Symmetrical-Tetramethyl-Cucurbit[6]uril-Driven Movement of Cucurbit[7]uril Gives Rise to Heterowheel [4]Pseudorotaxanes.

Two novel heterowheel [4]pseudorotaxanes consisting of cucurbit[7]uril (Q[7]) and symmetrical-tetramethyl-cucurbit[6]uril (TMeQ[6]) were constructed via the multirecognition mechanism, in which Q[7] can rotate freely around the horizontal axis, while TMeQ[6] cannot. In the construction process, due to strong repulsive forces between carbonyl portals of two neighboring wheels, the dethreading and movement of the wheels along the axle was observed. The dissociation of the [4]pseudorotaxanes was also discussed.