Supramolecular chemistry: molecular recognition and self-assembly using rigid spacer-chelators bearing cofacial terpyridyl palladium(II) complexes separated by 7 A.

Partially and fully aromatic molecular spacers bearing two symmetrically bound terpyridyl chelators have been prepared. These spacer-chelators were constructed to dispose the two terpyridyl ligands and their complexes with square planar metals cofacially with a separation of about 7 A between the two metals. Dipalladium(II) complexes of these spacer-chelators were prepared and characterized. These palladium complexes readily form large molecular rectangles with a linear linker such as 4,4'-dipyridyl. The dichlorodipalladium complex of the partially reduced spacer-chelator is capable of incarcerating planar aromatic and coordination compounds as guests. A crystal structure showing the incorporation of 9-methylanthracene has been determined. A 9-methylanthracene lies completely within the approximately 7 A space provided by the cleft formed by the two cofacially disposed chloro-palladium-terpyridyl units. The crystal structure shows additional pi-stacking interactions between a second 9-methylanthracene and neighboring receptors.