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Free keywords:
lanthanides; beta-diketonates; luminescence; thin films; photophysics
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.
