799765-05-2Relevant academic research and scientific papers
Tuning the stoichiometry of lanthanide complexes with calixarenes: Bimetallic complexes with a calix[6]arene bearing ether-amide pendant arms
Ramirez, Flor De Maria,Charbonniere, Loic,Muller, Gilles,Buenzli, Jean-Claude G.
, p. 2348 - 2355 (2004)
A de-tert-butylated calix[6]arene (A6L6) fitted with six etheramide 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, A6L6 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. A6L6 reacts with LnIII ions (Ln = La, Eu) in acetonitrile to successively form 1:1 and 2:1 complexes. The isolated EuIII 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 EuIII 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. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
