Jean-Claude Bunzli - Stereocontrolled Self-Assembly and Self-Sorting of Luminescent Europium Tetrahedral Cages

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      Yan,Liang Liang, Tan,Chun Hong, Zhang,Guang Lu, Zhou,Li Peng,   B nzli,Jean-Claude G., Sun,Qing Fu Journal of the American   Chemical Society 2015 137 (26)   8550-8555

      Abstract: Coordination-directed self-assembly   has become a well-established technique for the construction of   functional supramolecular structures. By contrast to the most   often exploited transition metals, trivalent lanthanides LnIII   have been less utilized in the design of polynuclear   self-assembled structures despite the wealth of stimulating   applications of these elements. In particular, stereochemical   control in the assembly of lanthanide chiral cage compounds is   not easy to achieve in view of the usually large lability of the   LnIII ions. We report here the first examples of stereoselective   self-assembly of chiral luminescent europium coordination   tetrahedral cages and their intriguing self-sorting behavior. Two   pairs of R and S ligands are designed based on the   pyridine-2,6-dicarboxamide coordination unit, bis(tridentate) L1   and tris(tridentate) L2. The corresponding chiral Eu4(L1)6 and   Eu4(L2)4 topological tetrahedral cages are independently   assembled based on edge-capping and face-capping design   strategies, respectively. The chirality of the ligand is   transferred during the self-assembly process to give either ? or   ? metal stereochemistry. The self-assembled cages are   characterized by NMR, high-resolution ESI-Q-TOF-MS and, in one   case, by X-ray crystallography. Strict control of   stereo-selectivity is confirmed by CD spectroscopy and NMR   enantiomeric differentiation experiments. Narcissistic   self-sorting is observed in the self-assembly process when the   two differently shaped ligands L1 and L2 are mixed. More   impressively, distinct self-sorting behavior between Eu4(L1)6 and   Eu4(L2)4 coordination cages is observed for the first time when   racemic mixtures of ligands are used. We envisage that chiral   luminescent lanthanide tetrahedral cages could be used in   chiroptical probes\sensors and enantio-selective catalysis

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