Jean-Claude Bunzli - Selective self-assembly of hexameric ****- and heteropolymetallic lanthanide wheels: Synthesis, structure, and photophysical studies

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  Chen,X.Y., Bretonniere,Y., Pecaut,J., Imbert,D., Bunzli,J.C.,   Mazzanti,M. Inorganic Chemistry 2007  46 (3) 625-637

  Abstract: A rational approach to the formation   of pure heteropolymetallic lanthanide complexes that uses a   two-step assembly strategy and exploits the different size   requirements of the two metals included in the final structure is   described. The investigation of the assembly of [LnL(2)](Otf) (L   = 2,2':6',2 ''-terpyridine-6-carboxylate) complexes into   hexametallic rings hosting an additional hexacoordinated   lanthanide cation was crucial for the development of this   strategy. The formation and size of the cyclic assembly are   controlled by the ionic radius and by the coordination number of   the lanthanides. The rather high luminescence quantum yield of   the heptaeuropium complex (25%) indicates that the ring structure   is well adapted to include highly luminescent lanthanide   complexes in nanosized architecture. The use of a stepwise   synthetic strategy leads to the selective assembly of large   heteropolymetallic rings. The addition of a smaller lanthanide   ion to the [EuL2](Otf) complex in anhydrous acetonitrile leads   selectively to heterometallic species with the Eu ions located on   the peripheral sites and the smaller ion occupying only the   central site. The high selectivity is the result of the different   size requirements of the two metal sites present in the cyclic   structure. The heterometallic structure of the isolated [Lu   subset of(EuL2)(6)](Otf)(9) complex was confirmed by X-ray   diffraction and by high resolution solid-state photophysical   studies. The described synthetic approach allowed us to obtain   the first example of selective assembly of two different   lanthanide ions in a large polymetallic structure characterized   in solution and in the solid state and will make the isolation of   planned dimetallic combinations presenting different lanthanide   emitters in the peripheral sites possible

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