Metallosupramolecular cages are a promising class of discrete molecular containers that exhibit highly selective guest encapsulation for applications in molecular separations,1 catalysis2 and the stabilisation of reactive species.3 The rational design of organic ligand binding modes and corresponding metal coordination geometries leads to the predictable self-assembly of complex architectures. Metallosupramolecular cages enclose a central cavity that features a distinct microenvironment for host-guest interactions. The aim of this study is to synthesise chiral metal organic cages for the enantioselective discrimination of chiral guest molecules.
Here, we employed chiral amino acid motifs on the capping positions of 3,3’-bipyridine based ligands to achieve chiral induction on the metal centres. A homochiral T-symmetric [M4L6] tetrahedral cage (M= ZnII, CoII) was successfully self-assembled via this strategy. Upon subsequent guest encapsulation of a lanthanoid hexanitrate anion, the tetrahedron reassembled into a homochiral [M5L6] trigonal bipyramidal cage with D3-symmetry. This reassembly to form the (ΔΔΔΔΔ)-[LnIII(NO3)6 ⊂ M5L6]n+ cage proceeds via a templating effect around the central [LnIII(NO3)6]3- anion. This trigonal bipyramidal cage design is robust, as we see encapsulation across the lanthanoid series. We report the successful characterisation of a series of 17 trigonal bipyramidal cages via single-crystal X-ray diffraction. Thus, lanthanoid ions were successfully abstracted from solution by the rearrangement of a tetrahedral metallosupramolecular cage into a trigonal bipyramidal cage.