title: 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.
abstract: 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.
authors.affiliation: 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.
authors.forename: Hélcio J.
authors.initials: HJ
authors.lastname: Batista
authors.forename: Antônio V. M.
authors.initials: AV
authors.lastname: de Andrade
authors.forename: Ricardo L.
authors.initials: RL
authors.lastname: Longo
authors.forename: Alfredo M.
authors.initials: AM
authors.lastname: Simas
authors.forename: Gilberto F.
authors.initials: GF
authors.lastname: de Sá
authors.forename: Nao K.
authors.initials: NK
authors.lastname: Ito
authors.forename: Larry C.
authors.initials: LC
authors.lastname: Thompson