Metal-Organic Cages with Missing Linker Defects.

Self-assembled cages have been widely studied owing to their architectural aesthetics and diverse potential applications. Archimedean and Platonic structures are typically observed for these assemblies, but nonclassical architectures such as defective cages with missing edges/vertices are scarcely observed. We present here the controlled synthesis of defective coordination cages by employing steric hindrance of organic linkers to manipulate coordination modes of the assembled metal ions. Three chiral 1,1'-bi-2-naphthol (BINOL) derived bis-tridentate ligands L 1 - L 3 with pyridine-2,6-dicarboxamides (pcam) chelating moieties are therefore designed and synthesized, among which L 3 has a smaller steric hindrance on the coordinating sites relative to the other two linkers. Complexes of L 1 and L 2 with lanthanides affords the irregular Ln 8 ( L 1 ) 10 hexahedra with two missing edges and Ln 4 ( L 2 ) 5 tetrahedra with one missing edge, respectively, both of which contain a 1:1 mixture of Ln(pcam) 2 and Ln(pcam) 3 . In contrast, complex of L 3 produce the regular twisted Ln 6 ( L 3 ) 9 trigonal prisms without missing edges that contain only Ln(pcam) 3 vertices. The defective cage, especially the hexahedral cage featuring two missing linkers has more freedom to adjust its structural conformation, affording adaptable cavity to accommodate a range of guest molecules with sizes comparable or much larger than the cavity portals, such as anthracene, perylene, fullerene C 60 , BODIPY and leucocrystal violet, that are less accessible to the regular cage.