Jean-Claude Bunzli - A Schiff-base bibracchial lariat ether forming a cryptand-like cavity for lanthanide ions

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  Gonzalez-Lorenzo,M., Platas-Iglesias,C., Avecilla,F.,   Geraldes,C.F.G.C., Imbert,D., Bunzli,J.C.G., de Blas,A.,   Rodriguez-Blas,T. Inorganic Chemistry  2003 42 (21) 6946-6954

  Abstract: We report here a structural and   photophysical study of lanthanide(III) complexes with the   di-deprotonated form of the bibracchial lariat ether   N,N'-bis(2-salicylaldiminobenzyl)-1,10-diaza-15-crown-5. The   X-ray crystal structures of [Ce(L-2-2H)](ClO4).0.5H(2)O (2) and   [Sm(L-2-2H)](ClO4).C3H8O (5b) show the metal ion being   nine-coordinated and deeply buried in the cavity of the dianionic   receptor. Thanks to the formation of a pseudomacrocycle through   pi-pi interaction between one of the phenol rings and one of the   benzyl rings, the complexes present a cryptand-like structure in   the solid state. H-1 and C-13 NMR studies on the La(Ill) complex   point that the solid state structure is essentially maintained in   acetonitrile solution. High-resolution laser-excited emission   spectra of the crystalline Eu(III) complex demonstrate the   presence of several coordination sites arising from different   conformations of the crown moiety. The ligand-to-Eu(III) energy   transfer is relatively efficient at low temperature, but back   transfer is implied in the deactivation process, especially at   room temperature, because the ligand triplet state lies at very   low energy. However, the low energy of the 3pipi* state provides   an efficient conversion of the visible light absorbed into   near-infrared light emitted by the Nd(III) ion

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