Selective Construction of Very Large Stacking-Interaction-Induced Molecular 8₁₈ Metalla-knots and Borromean Ring Using Curved Dipyridyl Ligands

Two molecular metalla-knots containing over 500 non-hydrogen atoms (especially 16 RhIII ions) and one molecular Borromean ring were obtained in high yields facilitated by multiple intermolecular interactions between their components. The syntheses rely on the strategic selection of the nonlinear dipyridyl ligand 2,7-di­(pyridin-4-yl)-9H-fluorene (L1) as precursor, and the structures of the assemblies were confirmed by detailed X-ray crystallographic analysis. Subsequently, replacing L1 with the bulkier ligand 4,4′-(9,9-dimethyl-9H-fluorene-2,7-diyl)­dipyridine (L2) led to the formation of three tetranuclear metallocycles in high yields on account of the weakened π–π stacking interactions between the naphthacene/anthracene and fluorene moieties, which in turn confirmed the significance of stacking interactions in the construction of the molecular 818 metalla-knots and the molecular Borromean ring.