Jean-Claude Bunzli - In search for mononuclear helical lanthanide building blocks with predetermined properties: Lanthanide complexes with diethyl pyridine-2,6-dicarboxylate

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  Renaud,F., Piguet,C., Bernardinelli,G., Bunzli,J.C.G.,   Hopfgartner,G. Chemistry-A European Journal  1997 3 (10) 1660-1667

  Abstract: The ligand diethyl   pyridine-2,6-dicarboxylate (L-5) reacts with Ln(III) in   acetonitrile to successively give the complexes [Ln(L-5)(i)](3+)   (Ln = La to Lu, i = 1-3), Spectroscopic investigations (ES-MS,   UV/Vis, NMR) show that the 1:3 complexes [Ln(L-5)(3)](3+) have   poor stability in solution and exist as a mixture of rapidly   interconverting conformers, Variable-temperature NMR data show   that the helical P reversible arrow M interconversion and dynamic   on-off equilibria of the ester side arms both control the   observed average structure in solution. Contrary to similar   lanthanide building blocks possessing benzimidazole or   carboxamide side arms, [EU(L-5)(3)](3+) has a sizable quantum   yield in anhydrous acetonitrile; this has been attributed to an   improved ligand --> Eu-III energy transfer resulting from a   good energetic match between the ligand- and metal-centered   excited states. Pure 1:3 complexes cannot be isolated in the   solid state, but crystalline 1:2 complexes [Ln(L-5)(2)](TfO)(3) .   nH(2)O have been prepared, The X-ray crystal structure of   [Eu(L-5)(2)(TfO)(2)(OH2)]TFO (1) reveals two meridionally   tricoordinated ligands L-5 but the long Eu-O(ester) bonds imply   only weak interactions between the carbonyl groups of the ester   side arms and Eu-III, providing a limited protection of the   metallic site. The photophysical studies show that nonacoordinate   Eu-III in 1 binds an additional water molecule to give a   decacoordinate complex in the solid state, thus confirming the   accessibility of the metallic site for Further complexation

  Address (URL): WOS:A1997YA85600012