Jean-Claude Bunzli - A water-stable and strongly luminescent self-assembled non-covalent lanthanide podate

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  Publication Details (including relevant citation   information):

  Edder,C., Piguet,C., Bunzli,J.C.G., Hopfgartner,G. Journal of   the Chemical Society-Dalton Transactions  1997 (24) 4657-4663

  Abstract: The segmental ligand   2-(6-carboxypyridin-2-yl)-1,1'-dimethyl-2'-(5-methylpyridin-2-yl)-5,   benzimidazole) (L-9 reacted with an equimolar mixture of Ln(III)   (Ln = La or Eu) and Zn-II in basic conditions to give selectively   the self-assembled dinuclear non-covalent podates   [LnZn(L-9-H),(3)](2+). Electrospray mass spectrometry and proton   NMR spectroscopy show that [LnZn(L-9-H),(3)](2+) adopt the   expected head-to-head triple-helical structure with Zn-II   pseudo-octahedrally co-ordinated by the bidentate binding units   of the three segmental ligands and Ln(III) occupying the   remaining facial pseudo-tricapped trigonal prismatic site   produced by the wrapped unsymmetrical tridentate units. Upon UV   irradiation, solutions of [EuZn(L-9-H),(3)](2+) in acetonitrile   or in water produce strong red luminescence. The Eu (D-5(0),)   lifetime and quantum yield indicate that Eu-III is efficiently   protected from external interactions for complex concentration in   the range 10(-4)-10(-8) M and that no solvent molecule enters the   first co-ordination sphere. Electrospray mass spectrometry   combined with high-resolution emission spectroscopy confirm that   the structure of the dinuclear triple-helical complex   [EuZn(L-9-H),(3)](2+) is maintained at low concentration which   strongly contrasts with the lipophilic analogous non-covalent   lanthanide podates [EuZn(L-i),(3)](5+) {i = 7 or 8;   2-[6-(organo)pyridin-2-yl]-1,1'-dimethyl-2'-(5-methylpyridin-2-yl)-5,5'-methyle nebis(1H-benzimidazole)}   which are decomplexed in acetonitrile for concentrations below   10(-5) M. Detailed photophysical studies have established that   [EuZn(L-9-H),(3)](2+) works as an efficient UV-->VIS   light-converting device in the solid state and in water

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