Controlling the ON/OFF threading of a terpyridine containing [2]pseudorotaxane ligand via changes in coordination geometry.

A 1,2-bis(pyridinium)ethane type axle containing a terpyridine chelate group, when combined with 24-membered crown ethers, forms [2]pseudorotaxanes, the stability of which can be controlled by coordination of metal ions with different geometries.