Synthesis, X-ray Structure, Spectroscopic Characterization, and Theoretical Prediction of the Structure and Electronic Spectrum of Eu(btfa)(3).bipy and an Assessment of the Effect of Fluorine as a beta-Diketone Substituent on the Ligand-Metal Energy Transfer Process.
The 2,2'-dipyridyl adducts of two europium beta-diketonate complexes, Eu(btfa)(3).bipy [btfa = 4,4,4-trifluoro-1-phenyl-2,4-butanedione, bipy = 2,2'-dipyridyl] and Eu(bzac)(3).bipy [bzac = 1-phenyl-2,4-butanedione], have been prepared. The crystal structure of the former with chemical formula EuC(40)H(26)O(6)N(2)F(9) has been solved by single-crystal X-ray diffraction methods. The complex crystallizes in the monoclinic space group P2(1)/n with a = 11.122(5) Å, b = 22.860(8) Å, c = 15.870(6) Å, beta = 102.62(3)(o), V = 3937(5) Å(3), and Z = 4. A single, eight-coordinate environment, which approximates a square antiprism, is found for the europium(III). The UV absorption spectra of both complexes were obtained from ethanol solutions and, in the case of Eu(btfa)(3).bipy, from a thin film. In both cases the absorption spectra are reasonably well predicted by the INDO/S-CI method using, for Eu(btfa)(3).bipy, both the X-ray data and that obtained through the SMLC/AM1 method as input geometry and, for Eu(bzac)(3).bipy, that obtained through the SMLC/AM1 method. There is a blue shift of the calculated spectra relative to the solution spectra and a slightly larger blue shift compared to the spectrum of the thin film. Both complexes are luminescent under near-UV excitation, and the spectra are in accord with the existence of a single emitting site in each. The increased quantum yield in the fluorinated complex is correlated with a decrease in the bipy-europium(III) distance, a closer match of the lowest ligand-centered triplet state (that level which is primarily responsible for the energy transfer from the ligands to the europium(III)), and the lower vibrational energy of the C-F bonds relative to the C-H bonds. In the fluorinated complex the calculations show that the lowest triplet level is primarily localized on the 2,2'-dipyridyl whereas in the nonfluorinated complex this is the second lowest triplet level.
Batista
Hélcio J.
HJ
Departamento de Química Fundamental and Departamento de Engenharia Química, Universidade Federal de Pernambuco, CEP 50740-540, Recife, PE, Brazil, and Department of Chemistry, University of Minnesota-Duluth, Duluth, Minnesota.
de Andrade
Antônio V. M.
AV
Longo
Ricardo L.
RL
Simas
Alfredo M.
AM
de Sá
Gilberto F.
GF
Ito
Nao K.
NK
Thompson
Larry C.
LC