Jean-Claude Bunzli - Lanthanide triple helical complexes with a chiral ligand derived from 2,6-pyridinedicarboxylic acid

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  Publication Details (including relevant citation   information):

  Muller,G., Schmidt,B., Jiricek,J., Hopfgartner,G., Riehl,J.P.,   Bunzli,J.C.G., Piguet,C. Journal of the Chemical   Society-Dalton Transactions 2001 (18)   2655-21

  Abstract: The ligand   3-[2,6-bis(diethylcarbamoyl)pyridine-4-yl]-N-(tert-butoxycarbonyl)alanine   methyl ester (L-4) bearing a chiral group in the 4-position of   the pyridine ring has been synthesised and its interaction with   trivalent lanthanide ions studied. L-4 yields stable   [Ln(L-4)(3)](3+) Complexes in acetonitrile, with log beta (3) in   the range 19-20. The specific rotary dispersion of the complexes   is about ten times as large as that of the ligand alone,   consistent with triple helical structures in solution. NMR data   show the presence of only one time-averaged species in   acetonitrile solution with a trigonal symmetry, that is, the   helical P reversible arrowM interconversion is fast on the NMR   time scale. Circularly polarised luminescence on the Eu and Tb   triple helical complexes displays weak effects, pointing to only   a small diastereomeric excess in solution. High resolution   luminescence spectra of the Eu complex in the solid state reveal   a local symmetry derived from a trigonal arrangement around the   metal ion and the long D-5(0) lifetime (1.58 ms) is indicative of   the absence of water molecules bound in the inner co-ordination   sphere. Energy transfer processes in the luminescent Eu and Tb   triple helical complexes are discussed

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