Jean-Claude Bunzli - Importance of the chromophore orientation to the ligand-to-metal energy transfer in lanthanide complexes with pendant-arm fitted cyclen derivatives

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  Publication Details (including relevant citation   information):

  Zucchi,G., Scopelliti,R., Bunzli,J.C.G. Journal of the   Chemical Society-Dalton Transactions 2001  (13) 1975-1985

  Abstract: Comparative solid state structural   studies of three lanthanide macrocyclic complexes derived from   1,4,7,10-tetraazacyclododecane with pendant arms bearing amide   co-ordinating groups have been performed in order to evaluate the   parameters influencing the co-ordination polyhedron and to assess   the importance of the geometric factor in energy transfer   processes. In all the investigated structures the co-ordination   geometry is a mono-capped twisted square antiprism, a situation   commonly observed for similar compounds. High resolution   luminescence spectra of the europium complexes are consistent   with a tetragonal site symmetry for the metal ion. An analysis of   the presented crystal structures and of previously reported ones   indicates that (i) the relative orientation of the O-4 and N-4   planes is not determined by the co-ordinated solvent molecule and   (ii) the twist angle between them is mainly dictated by the   flexibility of the pendant arms. Interpretation of the   luminescence properties of the complexes of Sm(III), Eu(III) and   Tb(III) can be made from the structural parameters found in the   solid state and in solution (by NMR spectroscopy). Both the   energy parameter (i.e. the gap between the ligand triplet state   and the metal ion excited state) and the geometric parameter   (i.e. the donor-acceptor distance and the orientation of the   choromophore) have to be taken into account to explain the   results obtained in terms of the efficiency of the L-->Ln   intra-molecular energy transfer. Furthermore, the correlative   comparison between structural and luminescent properties shows   how inter-molecular interactions in the solid state can be a   prominent factor in the effectiveness of this transfer

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