Jean-Claude Bunzli - Proton NMR, luminescence and electrochemical study of 18-membered Schiff-base macrocyclic lanthanum(III) complexes

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      Publication Details (including relevant citation   information):

      Platas,C., Avecilla,F., de Blas,A., Rodriguez-Blas,T.,   Bunzli,J.C.G. Journal of the Chemical Society-Dalton   Transactions 1999 (11) 1763-1771

      Abstract: An NMR, electrochemical and   photophysical study has been made of lanthanide(nr) complexes   with a 18-membered hexadentate Schiff-base N4O2   polyoxaazamacrocycle L-1 derived from the condensation of   2,6-bis(2-aminophenoxymethyl)pyridine and 2,6-diformylpyridine,   as well as their interaction with the chelating agents   1,10-phenanthroline and 2,2'-bipyridine. Separation of the   contact and pseudocontact contributions to the observed H-1 NMR   lanthanide-induced shift values point to an isostructural series   of [Ln(L-1)][ClO4](3) (Ln = La-Eu, except Pm) in acetonitrile.   The interaction of the lanthanum(III) complex with   1,10-phenanthroline and 2,2'-bipyridine was demonstrated by the   use of different spectroscopic techniques and the stability   constant for the 1,10-phenanthroline adduct was calculated from   H-1 NMR data. Upon excitation through the metal excited levels,   the terbium(III) complex displays the typical luminescence   originating from the excited D-5(4) level, while the adduct with   1,10-phenanthroline presents emission upon excitation through the   ligand bands. The reaction of   2,6-bis(2-aminophenoxymethyl)pyridine and 2,6-diformylpyridine   and the perchlorate of Gd-III or Tb-III in ethanol solution   yielded a reduced macrocycle L-2 instead of the expected   complexes of L-1. Electrochemical studies in acetonitrile   solution showed that the reduction of the imine groups is   favoured when the ionic radius of the lanthanide(III) ion   decreases

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