Jean-Claude Bunzli - Lanthanide homobimetallic triple-stranded helicates: Insight into the self-assembly mechanism

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      Publication Details (including relevant citation   information):

      Elhabiri,M., Hamacek,J., Bunzli,J.C.G., Albrecht-Gary,A.M.   European Journal of Inorganic Chemistry  2004 (1) 51-62

      Abstract: The self-assembly mechanism leading to   the exclusive formation of a triple-stranded bimetallic helicate   upon reaction of Eu(III) with a ditopic hexadentate ligand L   bearing two carboxylate moieties has been fully elucidated in   water for a wide range of [Eu](tot)/[L](tot) ratios. Using a   fruitful combination of electrospray mass spectrometry,   potentiometry, UV/Vis spectrophotometry, luminescence, and (1)H   NMR spectroscopy, the final product Eu(2)L(3) and the   intermediate species EuL(2) and Eu(2)L(2) have been   characterised. The presence of terminal carboxylates in L   significantly reduces the electrostatic repulsions of the   coordination sites in Eu(2)L(2) and Eu(2)L(3) compared with the   corresponding complexes formed with analogous neutral ligands and   thus increases the stability of the L-europium(III) complexes.   Kinetic investigations carried out with an excess of L and with   an excess of Eu(III), show that the self-assembly proceeds   through either EuL(2) or Eu(2)L, intermediates depending on the   experimental conditions and leads to a pre-organized Eu(2)L(2)   complex by either a "braiding" or a "keystone" mechanism. In the   last step, a fast and efficient wrapping of the third ligand   strand leads to the target Eu(2)L(3) helicate. The overall   process is mainly governed by electrostatic interactions and   proceeds via a key double stranded intermediate helicate   Eu(2)L(2). To the best of our knowledge, as a result of the   fine-tuning of the coordination properties of L, we present one   of the most efficient and cooperative metal/ligand systems for   the spontaneous organization of a bimetallic triple-stranded   structure. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451   Weinheim, Germany, 2004)

      Address (URL): J INORG CHEM