Jean-Claude Bunzli - Role of the ancillary ligand N,N-dimethylaminoethanol in the sensitization of Eu-III and Tb-III luminescence in dimeric beta-diketonates

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  Eliseeva,S.V., Kotova,O.V., Gumy,F., Semenov,S.N., Kessler,V.G.,   Lepnev,L.S., Bunzli,J.C.G., Kuzmina,N.P. Journal of Physical   Chemistry A 2008 112 (16)   3614-3626

  Abstract: Two types of dimeric complexes   [Ln(2)(hfa)(6)(mu(2)-O(CH2)(2)NHMe2)(2)] and   [Ln(thd)(2)(mu(2),eta(2)-O(CH2)(2)NMe2)](2) (Ln = Y-III, Eu-III,   Gd-III Th-III, Tm-III, Lu-III; hfa(-) =   hexafluoroacetylacetonato, thd(-) = dipivaloylmethanato) are   obtained by reacting [Ln(hfa)(3)(H2O)(2)] and [Ln(thd)(3)],   respectively, with NN-dimethylaminoethanol in toluene and are   fully characterized. X-ray single crystal analysis performed for   the Th-III compounds confirms their dimeric structure. The   coordination mode of NN-dimethylaminoethanol depends on the   nature of the beta-diketonate. In   [Tb-2(hfa)(6)(mu(2)-O(CH2)(2)NHMe2)(2)], eight-coordinate Th-III   ions adopt distorted square antiprismatic coordination   environments and are O-bridged by two zwitterionic   N,N-dimethylaminoethanol ligands with a Tb1 center dot center dot   center dot Tb2 separation of 3.684(1) angstrom. In [Tb(thd)(2)(mu   2,eta(2)-O(CH2)(2)NMe2)](2), the N,N-dimethylaminoethanol acts as   chelating-bridging O,N-donor anion and the Th-III ions are   seven-coordinate; the Th1 center dot center dot center dot Th1A   separation amounts to 3.735(2) angstrom within centrosymmetric   dimers. The dimeric complexes are thermally stable up to 180   degrees C, as shown by thermogravimetric analysis, and their   volatility is sufficient for quantitative sublimation under   reduced pressure. The Eu-III and Tb-III dimers display   metal-centered luminescence, particularly   [Eu-2(hfa)(6)(O(CH2)(2)NHMe2)(2)] (quantum yield Q(Ln)(L) = 58%)   and [Tb(thd)(2)(O(CH2)(2)NMe2)](2) (32%). Consideration of energy   migration paths within the dimers, based on the study of both   pure and Eu-III- or Th-III-doped (0.01-0.1 mol%) Lu-III   analogues, leads to the conclusion that both the beta-diketone   and NN-dimethylaminoethanol ligands contribute significantly to   the sensitization process of the Eu-III luminescence. The   ancillary ligand increases considerably the luminescence of   [Eu-2(hfa)(6)(O(CH2)(2)NHMe2)(2)], compared to   [Ln(hfa)(3)(H2O)(2)], through the formation of intra-ligand   states while it is detrimental to Th-III luminescence in both   beta-diketonates. Thin films of the most luminescent compound   [Eu-2(hfa)(6)(O(CH2)(2)NHMe2)(2)] obtained by vacuum sublimation   display photophysical properties analogous to those of the   solid-state sample, thus opening perspectives for applications in   electroluminescent devices

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