Preparation, crystal structure and optical spectroscopy of the rare earth complexes (RE3+=Sm, Eu, Gd and Tb) with 2-thiopheneacetate anion

Ercules E.S. Teotonio, Hermi F. Brito, Maria Cláudia F.C. Felinto, Larry C. Thompson, Victor G Young, Oscar L. Malta

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Abstract

Rare earth complexes with the formulae Sm(TPAC)3·3H 2O, Eu2(TPAC)6·5.25H2O and RE(TPAC)3·3.5H2O (where RE=Gd and Tb), and TPAC=2-thiopheneacetate) have been synthesized and characterized by complexometric titration, elemental analyses, infrared spectroscopy, and X-ray crystallography. Infrared data suggested the presence of both bridging and chelating TPAC anions. The crystal structure of the [Eu2(TPAC) 6·(H2O)3]·2.25H2O complex in the solid state, determined by X-ray diffraction, revealed that it crystallizes in the orthorhombic crystal system (space group Aba2), with two crystallographically independent Eu3+ centers (Eu1 and Eu2). These europium centers are held together by one bidentate bridging and two tridentate bridging carboxylate groups. The existence of two Eu3+ centers was also supported by the emission spectrum. The luminescence properties of the RE-TPAC complexes were investigated by measuring the excitation and emission spectra, and the intramolecular ligand-to-rare earth energy transfer mechanisms were discussed. The emission spectra of the Eu3+ and Tb3+ ions displayed only narrow bands arising from 5D07F0 and 5D07F 0-4 transitions, respectively, indicating an efficient luminescence sensitization of these ions by the TPAC 'antenna'. On the other hand, the emission spectrum of the Sm3+-complex displayed a broad band from the phosphorescence of the TPAC ligand which overlapped the 4f5- intraconfigurational transitions. The theoretical intensity parameters Ωλ (λ=2 and 4), maximum splitting of the 7F1 state (ΔE) and the ratio between the 5D07F0 and 5D 07F2 transition intensities (R 02) were calculated based on the X-ray crystalline structure for the Eu3+-complex, and a comparison with experimental data were made. The emission quantum efficiency (η) of the D5 emitting level of the Eu 3+ ion was also determined.

Original languageEnglish (US)
Pages (from-to)85-94
Number of pages10
JournalJournal of Molecular Structure
Volume751
Issue number1-3
DOIs
StatePublished - Sep 15 2005

Bibliographical note

Funding Information:
This research was supported by grants from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq-RENAMI).

Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.

Keywords

  • 2-Thiopheneacetate
  • Crystalline structure
  • Intensity parameters
  • Intramolecular energy transfer
  • Rare earths

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