Jean-Claude Bunzli - Dimeric complexes of lanthanide(III) hexafluoroacetylacetonates with 4-cyanopyridine N-oxide: Synthesis, crystal structure, magnetic and photoluminescent properties

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  Eliseeva,S.V., Ryazanov,M., Gumy,F., Troyanov,S.I., Lepnev,L.S.,   Bunzli,J.C.G., Kuzmina,N.P. European Journal of Inorganic   Chemistry 2006 (23) 4809-4820

  Abstract: A series of new mixed-ligand   lanthanide complexes [Ln-(hfa)(3) (4-cpyNO)](2) (Ln =   Sm-III-Ho-III and Tm-III hfa(-) = hexafluoroacetylacetonate;   4-cpyNO = 4-cyanopyridine N-oxide) have been synthesised by   treating the corresponding lanthanide hexafluoroacetylacetonates   with 4-cpyNO (molar ratio 1:1) in chloroform. Single-crystal   X-ray analysis revealed that [Tb(hfa)(3)(4-cpyNO)](2) and   [Ho(hfa)(3)(4-cpyNO)](2) are isostructural and are comprised of   two types of symmetrically independent dimetallic molecules.   Within a dimer, the eightfold-coordinated metal atoms are bridged   by two 4-cpyNO ligands through the oxygen atoms of the N-oxide   groups. The magnetic susceptibility data for the Gd-III and   Tb-III complexes indicate the presence of weak antiferromagnetic   interactions within the dimetallic Ln(2)O(2) units. The thermal   stability of the [Ln(hfa)(3)(4-cpyNO)](2) adducts was studied by   thermogravimetric analysis and their volatility estimated from   sublimation experiments under reduced pressure. The   photoluminescent properties were measured for solid samples upon   excitation at 330-360 nm. The mixed-ligand complexes of Sm-III,   Eu-III, Tb-III, Dy-III and Tm-III exhibit metal-centred   luminescence in the entire visible spectral range with   characteristic pink, red, green, yellow and blue emission,   respectively. The introduction of ancillary 4-cpyNO molecules   into the coordination sphere of the lanthanide(III) ions was   found to significantly affect their luminescence quantum yields.   [Eu(hfa)(3)(4-cpyNO)](2) thin films on quartz substrates were   obtained by the vacuum evaporation technique and their   photoluminescent properties were found to be enhanced when   compared with those of the bulk samples. This suggests that these   dimers could be good candidates for the fabrication of emitting   layers for light-emitting diodes. (c) Wiley-VCH Verlag GmbH &   Co

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