Jean-Claude Bunzli - Tuning the stoichiometry of lanthanide complexes with calixarenes: Bimetallic complexes with a calix[6]arene bearing ether-amide pendant arms

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  Ramirez,F.D.M., Charbonniere,L., Muller,G., Bunzli,J.C.G.   European Journal of Inorganic Chemistry  2004 (11) 2348-2355

  Abstract: A de-tert-butylated calix[6]arene   (A(6)L(6)) fitted with six ether-amide pendant arms was   synthesized and characterized in solution. NMR spectroscopic data   point to the six phenoxide units adopting an average D-6h   conformation on the NMR time scale. According to MM3 molecular   mechanics, and MOPAC quantum mechanical calculations, A(6)L(6) is   a ditopic ligand featuring two nonadentate coordination sites,   each built from three pendant arms, and extending in opposite   directions with one above, and the other under the main ring.   A(6)L(6) reacts with Ln(III) ions (Ln = La, Eu) in acetonitrile   to successively form 1:1 and 2:1 complexes. The isolated Eu-III   2:1 complex is luminescent (quantum yield: 2.5% in acetonitrile,   upon ligand excitation). In the solid state, the luminescence   decay is bi-exponential, with lifetimes equal to 1.66 and 0.46 ms   (upon direct metal excitation), pointing to the presence of two   differently coordinated metal ions, one with essentially no bound   water molecules, and the other one with two ligated water   molecules. According to molecular mechanics calculations, the   more stable isomer is indeed asymmetric with two nine-coordinated   metal ions. Both Eu-III ions are bound to three bidentate arms,   and one monodentate triflate anion, but one metal ion completes   its coordination sphere with two phenoxide oxygen atoms, and the   other one with two water molecules, consistent with IR   spectroscopic and luminescence data. In acetonitrile solution,   the two metal ion sites become equivalent, and the relatively   long lifetime (1.35 ms) is indicative of a coordination   environment free of water molecules. This work demonstrates, that   the stoichiometry of lanthanide complexes with calixarenes can be   tuned by a suitable choice of the narrow and/or wide rim   substituents. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451   Weinheim, Germany, 2004

  Address (URL): J INORG CHEM