Self-assembled ring-in-ring complexes from metal-ligand coordination macrocycles and β-cyclodextrin

Ring-in-ring nanostructures can be assembled from readily available starting materials, including dipyridyl ligands, (en)Pd(NO₃)₂, and β-cyclodextrin (β-CD). When a series of dipyridyl ligands are mixed with β-CD and Pd(II) in aqueous solution, various self-assembled geometries can be obtained as a result of a combination of hydrobic interactions and metal-ligand coordinations. In the cases of dipyridyl ligands with flexible linker, dinuclear coordination macrocycles M₂L₂ are formed and included in the cavity of β-CD to form ring-in-ring complexes. When more rigid dipyridyl ligands are used, a tetranuclear coordination macrocycle M₄L₄ prevails and shows no interaction with β-CD, as apposed to the flexible ones.