Self-Assembled Ring-in-Ring Complexes from Metal-Ligand Coordination Macrocycles and β-Cyclodextrin

We present a simple and efficient approach to ring-inring nanostructures from readily available starting materials through self-assembly process. The self-assembly tool kit includes divalent dipyridyl ligands, Pd(II) metal ions, and β-cyclodextrin (β-CD). A series of dipyridyl ligands are shown to form inclusion complexes with β-CD in aqueous solution as a result of hydrophobic interactions. On the other hand, the dipyridyl ligands can coordinate with Pd(II) to form symmetric multinuclear macrocyclic structures. When the bipyridyl ligands, Pd(II) metal ions, and β-CD are mixed together in solution, various self assembly geometries are obtained as a result of reversible errorchecking process that is enabled by the dynamic formation of metal-ligand coordination bond. In the case of bipyridyl ligands with flexible linkers, dinuclear coordination macrocycles M2L2 are formed and included in the cavity of β-CD to form ring-in-ring complexes. When more rigid bipyridyl ligands are used, a tetranuclear coordination macrocycle M4L4 prevails and shows no interaction with βCD, as apposed to the flexible ligand ones. The current findings provide a facile access to ring-in-ring complex through the self-assembly process and should facilitate the synthesis of more complex organic and supramolecular structures that would otherwise be difficult to obtain.