Controlled molecular motions in copper-complexed rotaxanes: An XAS study

The environment of the central metal of a molecular machine-like copper rot axane was observed by XAS experiments. The wheel of the rotaxane is a heter o-bischelating macrocycle containing both bidentate (phenanthroline) and te rdentate (terpyridine) moieties. The axle of the assembly contains only a b identate moiety. Applying an external chemical stimulus-oxidation of the me tal-increases the number of coordinating atoms required by the metal templa te from 4 to 5. This variation is consistent with the oscillation of the wh eel around the axle, leading thus to the most stable environment for the me tal in the Cu(II) rotaxane.