Estudos espectroscópicos e estruturais de complexos B-dicetonatos de íons lantanídeos com ligantes fosfinóxidos

• Ano de defesa: 2014
• Autor(a) principal: Pereira, Dariston Kleber Sousa
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal da Paraíba; Brasil; Química; Programa de Pós-Graduação em Química; UFPB
• Palavras-chave em Português: Lantanídeos; Luminescência; B-dicetonatos; Fosfinóxidos; Transferência de carga; Lanthanides; Luminescence; B-diketonates; Phosphine oxides; Charge transfer; CIENCIAS EXATAS E DA TERRA::QUIMICA
• Link de acesso: https://repositorio.ufpb.br/jspui/handle/tede/9226

This work reports spectroscopic and structural investigations of the complexes presenting the formulas [Ln(TTA)3L2], [Ln(DBM)3L], [Ln(TTA)2(NO3)L2], [Ln(DBM)2(NO3)L2] and [Ln(DBM)(NO3)2(HMPA)2], where Ln: Eu3+ or Tb3+, TTA: 2-thenoyltrifluoroacetonate, DBM: dibenzoylmethanate and L: HMPA (hexamethylphososphoramide) or TPPO (Triphenylphosphine oxide). The compounds were characterized by complexometric and elemental analysis and single crystal X-ray diffraction. The spectroscopic properties of the complexes were studied by diffuse reflectance and luminescence spectroscopies. Formation of positronium in the complexes were also investigated. In order to obtain a synergy between theory and experiment, DFT calculations were performed, for geometry optimization and to obtain DBM triplet states energies, using B3LYP, B97D, M06-2X, PBE1PBE, CAM-B3LYP and ω-B97XD functionals, in both gas phase and in acetone solvent. X-ray data showed that the replacement of DBM molecules by nitrate ions promotes stronger intramolecular interactions, which influence the compounds melting points. The diffuse reflectance and excitation spectra suggest the presence of ligant-to-metal charge transfer states (LMCT) of low energy in DBM containing Eu3+ complexes. The replacement of DBM ligands by nitrate ions decrease the energy of these LMCT states. This decrease is duo to the lower polarizability of the nitrate ion which promotes a greater charge donor effect on the other ligands, reducing the energy of the LMCT state. Positron annihilation results showed that positronium formation in compounds containing both DBM and phosphine oxides decreases when the former are replaced by nitrate ions, due to the increase of electron density donation from the ligands to the metal center, decreasing the phosphinoxides positronium formation capacity. DFT calculation provided relatively satisfactory results for geometry optimization and in obtaining DBM triplet states energies. These results indicate that the replacement of B-diketonate ligands by less polarizable species, such as nitrate, has a great influence on the structural and spectroscopic properties of the investigated compounds.