A Size-Flexible Organometallic Box for the Encapsulation of Fullerenes.

A palladium-cornered molecular square with four pyrene-bis(imidazolylidene) bridging ligands is reported. This metallo-polygon can encapsulate C60 and C70 . The X-ray diffraction structures of the empty cage as well as the cages complexed with both fullerenes are described. The fullerene encapsulation produces perturbations in the structural parameters of the metallo-square, showing that it can adjust the shape of its cavity to the size of each fullerene.