| Abstract
| - Two types of dimeric complexes [Ln2(hfa)6(μ2-O(CH2)2NHMe2)2] and [Ln(thd)2(μ2,η2-O(CH2)2NMe2)]2 (Ln= YIII, EuIII, GdIII, TbIII, TmIII, LuIII; hfa- = hexafluoroacetylacetonato, thd- = dipivaloylmethanato) areobtained by reacting [Ln(hfa)3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in tolueneand are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms theirdimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of theβ-diketonate. In [Tb2(hfa)6(μ2-O(CH2)2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismaticcoordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with aTb1···Tb2 separation of 3.684(1) Å. In [Tb(thd)2(μ2,η2-O(CH2)2NMe2)]2, the N,N-dimethylaminoethanol actsas chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1···Tb1A separationamounts to 3.735(2) Å within centrosymmetric dimers. The dimeric complexes are thermally stable up to180 °C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The EuIII and TbIII dimers display metal-centered luminescence, particularly[Eu2(hfa)6(O(CH2)2NHMe2)2] (quantum yield= 58%) and [Tb(thd)2(O(CH2)2NMe2)]2 (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and EuIII- or TbIII-doped(0.01−0.1 mol %) LuIII analogues, leads to the conclusion that both the β-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillaryligand increases considerably the luminescence of [Eu2(hfa)6(O(CH2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2],through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both β-diketonates.Thin films of the most luminescent compound [Eu2(hfa)6(O(CH2)2NHMe2)2] obtained by vacuum sublimationdisplay photophysical properties analogous to those of the solid-state sample, thus opening perspectives forapplications in electroluminescent devices.
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