Departamento de Química, Universidade Federal da Paraíba, João Pessoa-PB, Brazil - PDF

J. Braz. Chem. Soc., Vol. 2, No. 11, , Printed in Brazil Sociedade Brasileira de Química $ Article Novel Luminescent Eu 3+

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J. Braz. Chem. Soc., Vol. 2, No. 11, , Printed in Brazil Sociedade Brasileira de Química $ Article Novel Luminescent Eu 3+ -Indandionate Complexes Containing Heterobiaryl Ligands João B. M. Resende Filho, a Jannine C. Silva, a Juliana A. Vale, a Hermi F. Brito, b Wagner M. Faustino, a José G. P. Espínola, a Maria C. F. C. Felinto c and Ercules E. S. Teotonio*,a a Departamento de Química, Universidade Federal da Paraíba, João Pessoa-PB, Brazil b Departamento de Química Fundamental, Instituto de Química da Universidade de São Paulo, São Paulo-SP, Brazil c Instituto de Pesquisas Energéticas e Nucleares, Av. Prof. Lineu Prestes, 2242, Cidade Universitária, São Paulo-SP, Brazil Novos complexos indandionatos de fórmulas [Ln(aind) 3 e [Ln(bind) 3 O, (L: 1,10-fenantrolina (phen) ou 4,7-dimetil-1,10-fenantrolina (dmphen), Ln 3+ : Eu 3+ ou Gd 3+, aind: 2-acetil-1,3-indandionato e bind: 2-benzoil-1,3-indandionato) foram sintetizados e caracterizados por análise elementar, espectroscopia de absorção na região do infravermelho e análise termogravimétrica. Os dados de caracterização são consistentes com a presença de uma molécula de água de cristalização nas estruturas dos compostos [Ln(bind) 3 O, enquanto que nos complexos [Ln(aind) 3 a molécula de água atua como ligante. As geometrias dos complexos do íon Eu 3+, otimizadas pelo modelo SPARKLE/AM1, foram consistentes com os resultados experimentais de luminescência. As propriedades luminescentes dos compostos de Eu 3+ são discutidas em termos de parâmetros de intensidade experimentais (Ω 2 e Ω 4 ), taxas radiativas (A rad ) e não-radiativas (A nrad ) e eficiência quântica de emissão (η). Os maiores valores de η foram obtidos para os compostos O, refletindo a ausência de moléculas de água na primeira esfera de coordenação do íon Eu 3+. Novel Ln 3+ -indandionate complexes of formulas [Ln(aind) 3 and [Ln(bind) 3 O (L: 1,10-phenanthroline (phen) or 4,7-dimethyl-1,10-phenanthroline (dmphen), Ln 3+ : Eu 3+ or Gd 3+, aind: 2-acetyl-1,3-indandionate and bind: 2-benzoyl-1,3-indandionate) were synthesized and characterized by elemental analysis, infrared spectroscopy, and thermogravimetric analyses. The characterization data are consistent with the presence of a water lattice molecule in the [Ln(bind) 3. However, the data also suggest that the water acts as a coordinated molecule in the [Ln(aind) 3 ones. Theoretical geometries of the Eu 3+ -complexes have been optimized via the SPARKLE/AM1 Model for lanthanide complexes that are consistent with their luminescence experimental data. The photoluminescence properties of the Eu 3+ -compounds have been discussed in terms of experimental intensity parameters (Ω 2 and Ω 4 ), radiative (A rad ), and non-radiative (A nrad ) spontaneous emission coefficients. The higher values of emission quantum efficiency (η) of the reflect the absence of luminescence-quenching water molecule in their first coordination spheres. Keywords: lanthanides, 2-acyl-1,3-indandionates, 4,7-dimethyl-1,10-phenanthroline Introduction 2-acyl-1,3-indandiones (acind) compounds have been frequently used as precursor s molecules for the synthesis of novel compounds exhibiting biological activities and spectroscopic properties. 1-3 They are well known for their * microbial, anti-tumor, anti-inflammatory, anticoagulants, herbicides, and insecticide activities. 4, Therefore, 2-acyl- 1,3-indandiones have been inspired intensive theoretical and experimental investigations The significant interest in the investigation of the indandionate complexes has been increased in the last decade This kind of cyclic ligands presents a good chelating ability owing to the existence of three carbonyl Vol. 2, No. 11, 2014 de Resende Filho et al groups, which has contributed to obtain different d-metal complexes with high thermodynamic and photophysical stabilities. Most of the studies on d-metal complexes with the acind ligand have been concerned with structural and magnetic properties However, there are only a few works reporting on Ln 3+ -complexes with these ligands, for example, the first structural characterization and photoluminescent as well as electroluminescent properties of the Ln 3+ -complexes containing 2-acyl-1,3-indandionates ligands have been reported by our group. 11,12 Moreover, Li et al. 13 have reported similar study on the Eu 3+ -complexes containing the 2-(2,2,2-trifluoroacethyl)-1-indone (TFI) ligand, which presents correlated structure with the 2-acyl- 1,3-indandionate ligands. Lanthanide diketonate complexes containing heterobiaryl ligands have been the subject of extensive studies in the literature ranging from synthesis, characterization, and their photoluminescent properties to sensor applications Although the great coordinating ability of bidentate 1,10-phenanthroline and 4,7-dimethyl- 1,10-phenanthroline ligands through the two nitrogen atoms to the Ln 3+ ions, up to now, to our knowledge, no work has been reported on luminescent properties of complexes containing indandionate and heterobiaryl as ancillary ligands. Furthermore, the relatively rigid structure of the heteroaryl ancillary ligands may contribute to minimize the luminescence quenching of the europium ion via thermal vibrations. Based on the above considerations, in this work, we have reported the synthesis and spectroscopic studies of the novel [Ln(aind) 3 (L) and [Ln(bind) 3 (L)] H 2 O complexes, where aind = 2-acetyl-1,3-indandione, bind = 2-benzoyl-1,3-indandione, Ln = Eu 3+ or Gd 3+, and L = 1,10-phenanthroline or 4,7-dimethyl-1,10- phenanthroline (Figure 1). In addition, theoretical structures of the Eu 3+ complexes were optimized by semiempirical quantum-mechanical calculations and their optical properties have been investigated on the basis of experimental intensity parameters. Experimental Materials and methods The solvents (acetone and ethanol), 1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline and lanthanide oxides (Ln 2 O 3 ) were purchased from Aldrich Co. and used without previous treatment. Hexahydrated lanthanide chlorides, LnCl 3 6H 2 O, were prepared by reaction between Ln 2 O 3 and hydrochloric acid purchased from Aldrich Co acetyl-1,3-indandione (aind), 2-benzoyl-1,3-indandione (bind) ligands, and [Ln(aind) 3 ], [Ln(bind) 3 ] precursor complexes were synthesized according to the procedures as reported in the literature. 4,11 Elemental analyses (C, H, and N) were carried out using a Perkin Elmer 2400 elemental microanalyzer. Infrared (IR) spectra were recorded from 400 to 4000 cm 1 on a Shimadzu FT-IR spectrophotometer model IRPRESTIGE-21 using KBr pellets. Excitation and emission spectra of the Ln 3+ -complexes in solid state were recorded at liquid nitrogen temperature on a Fluorolog-3 spectrofluorometer (Horiba) with excitation and emission double grating 0.22 m monochromators, and a 40 W Xenon lamp as excitation source and R928P PMT as detector. All spectra were recorded using a detector mode correction. The second-order diffraction of the source radiation was eliminated using a cut-off filter. Luminescence decay curves of the Eu 3+ -complexes in the solid state were recorded at low temperature (77 K) using the same equipment but operating on the phosphorescence mode with pulsed Xenon lamp as excitation source. The luminescence instruments were fully controlled by the FluorEssence program. All the luminescence data of the samples were measured in quartz tube of 2 mm in diameter. TG curves were recorded from 30 to 900 C using a Shimadzu DTG-60H thermobalance with a heating rate 10 C min 1 under a nitrogen atmosphere. Synthesis of the Ln 3+ -complexes with heteroaromatic ligands Figure 1. Structural formulas of the ligands: (a) 2-acetyl-1,3-indandione (aind), (b) 2-benzoyl-1,3-indandione (bind), (c) 1,10-phenanthroline (phen), and (d) 4,7-dimethyl-1,10-phenanthroline (dmphen). Lanthanide indandionate complexes containing ancillary ligands were synthesized by mixing acetonic solutions of the corresponding hydrated complexes, [Ln(aind) 3 ] or [Ln(bind) 3 ], with phen or dmphen ligands in the molar ratio of complex:ligand (1:1.3). The resulting solutions were stirred for 1 h at room temperature (ca. 27 C). Later on, these solutions were stand up until the total evaporation of solvent. The prepared 2082 Novel Luminescent Eu 3+ -Indandionate Complexes Containing Heterobiaryl Ligands J. Braz. Chem. Soc. yellow solids were washed thoroughly with cold ethanol and dried under reduced pressure. (phen) (1): g, yield 68%; FT IR (KBr, cm 1 ): 348(w), 3443(w), 307(w), 291(w), 2920(w), 286(w), 1681(m), 1643(m), 1622(s), 18(s), 1467(s), 1363(m), 1340(m), and 732(s). Anal. Calc. for C 4 H 31 EuN 2 : C, 9.28, H, 3.43, and N, Found: C, 9.71; H, 3.3, and N, O (2): g, yield 72%; FT-IR (KBr, cm 1 ): 3429(w), 30(w), 292(w), 2920(w), 1694(m), 1618(s), 187(s), 168(s), 164(s), 1448(s), 1420(s), 1340(m), and 741(m). Anal. Calc. for C 60 H 37 EuN 2 : C, 6.64; H, 3.40, and N, 2.. Found: C, 6.3, H, 3.44, and N, [Gd(aind) 3 (phen) (3): g, yield 6%; FT IR (KBr, cm 1 ): 324(w), 3433(w), 307(w), 291(w), 2922(w), 2866(w), 286(w), 1682(m), 1643(m), 1622(s), 187(s), 1467(s), 1364(m), 1340(m), and 73(s). Anal. Calc. for C 4 H 31 GdN 2 : C, 8.94, H, 3.41, and N, 3.0. Found: C, 9.63, H, 4.1, and N, [Gd(bind) 3 O (4): g, yield 8%; FT IR (KBr, cm 1 ): 344(w), 303(w), 3032(w), 2926(w), 1694(m), 1636(m), 1616(s), 187(s), 168(s), 164(s), 1448(s), 1423(s), 1340(m), and 741(m). Anal. Calc. for C 60 H 37 GdN 2 : C, 6.32, H, 3.38, and N, 2.4. Found: C, 6., H, 3.34, and N, (s), 18(s), 164(s), 140(s), 1421(s), 1342(m), and 736(m). Anal. Calc. for C 62 H 41 GdN 2 : C, 6.84, H, 3.63, and N, Found: C, 6.92, H, 3.7, and N, Results and Discussion Characterization The results of the elemental analysis (C, H, and N) are consistent with the monohydrated formulas of Ln(aind) 3 L H 2 O and Ln(bind) 3 L H 2 O complexes, where Ln = Eu 3+ or Gd 3+. The infrared spectra of the Ln 3+ -complexes (Figure 2) exhibit two bands at around 160 and 1690 cm 1 assigned to the ν(c=o) stretching modes, due to the coordinated and noncoordinated carbonyl groups, respectively. These data are in agreement with the FT-IR spectral data of precursor-hydrated complexes, 11 suggesting that the 2-acyl-1,3-indandione ligands are coordinated to Ln 3+ ions through oxygen atoms of the carbonyl groups in bidentate mode. Moreover, the absorption bands at around 1468 and 1423 cm 1 indicate that the phen and dmphen ligands act as chelating agents, coordinating to the Ln 3+ ion through the nitrogen atoms. 19,20 The complexes also exhibit absorption bands in the spectral range cm 1 assigned to ν(o H) stretching of the water molecule (Figure 2). Interestingly, FT-IR spectra of the [Ln(aind) 3 L H 2 O] compounds exhibit narrow peaks at around 360 cm 1, while the [Ln(bind) 3 L] H 2 show only one broad absorption band. These data give (): g, yield 7%; FT-IR (KBr, cm 1 ): 364(w), 302(w), 3068(w), 1691(m), (s), 1643(s), 1620 (s), 183(s), 1467(s), 139(m), 1340(m), and 72(s). Anal. Calc. for C 47 H 3 EuN 2 : C, 60.06, H, 3.73, and N, Found: C, 60.26, H, 3.71, and N, O (6): g, yield 8%; FT-IR (KBr, cm 1 ): 343(w), 30(w), 1693(m), 1629(m), 1612(m), 18(s), 164(s), 1448(s), 1421(s), 1361(m), and 736(m). Anal. Calc. for C 62 H 41 EuN 2 : C, 66.13, H, 3.64, and N, Found: C, 66.28, H, 3.48, and N, 2.2. [Gd(aind) 3 (7): g, yield 60%; FT-IR (KBr, cm 1 ): 3442(w), 3068(w), 168(m), 164(m), 1620(s), 18(s), 1467(m), 137(m), 1340(m), and 729(m). Anal. Calc. for C 47 H 3 GdN 2 : C, 9.74, H, 3.71, and N, Found: C, 60.32, H, 3.61, and N, [Gd(bind) 3 O (8): g, yield %; FT-IR (KBr, cm 1 ): 3441(w), 303(w), 1691(m), 1629(s), Figure 2. FT-IR absorption spectra of the Eu 3+ -complexes recorded in the range of cm 1 in KBr pellets. Vol. 2, No. 11, 2014 de Resende Filho et al evidences that the water molecule is coordinated to the Ln 3+ ion only in the [Ln(aind) 3 L H 2 O] complexes. Similar spectral profiles have also been observed for La 3+ and Tb 3+ complexes using EDTA as ligand that present coordinated and non coordinated water molecules, respectively. 21,22 Thermogravimetric curves of the (dmphen) and (Figure 3) show that these systems undergo thermal decomposition in consecutive steps. The curves show the first weight loss in the temperature range from 60 to 110 o C that correspond to 1.6% for O and 2.1% for, which are in agreement with the release of water molecules. However, it can be observed in Figure 3 that the complex exhibits a shorter dehydration interval ( o C) than the (dmphen)] O) complex, in which the dehydration process occurs from 40 to 10 o C (see insert Figure 3). These data corroborate with the FT-IR results, indicating that the water molecules are acting as ligand in the former complex. Similar behavior has been observed in the thermal and FT-IR studies of the Ln 3+ -EDTA complexes, as reported by Gigante et al.. 22 Figure 3 also shows that the anhydrous compounds undergo consecutive weight loss starting from 20 o C, yielding the lanthanide oxides, for example, Eu 2 O 3, that is in agreement with theoretical values: 1.3% (calc. 18.7%) and 16.4% (calc. 1.6%) for and, respectively. model for Eu(III) and other lanthanide ions implemented in the software package MOPAC ,24 Water molecule was not considered in the last complexes, since the FT-IR and thermogravimetric data indicate that the water molecule is out of the first coordination sphere. The calculated structures of the and O complexes are shown in Figure 4, while those ones for the similar complexes with phen ligand are presented in Supporting Information (Figure S1). Theoretical structural studies Theoretical molecular structures of the and O complexes, where L = phen or dmphen, were optimized using the reparameterized latest version of the SPARKLE/AM1 Figure 3. Thermogravimetric curves of the (solid line) and O (dashed line) complexes. Figure 4. Theoretical geometries of the Eu 3+ -complexes optimized by the SPARKLE/AM1 model: (a) and (b) O. The optimized structures reveal that the indandionate ligands are characterized by the planarity of 1,3-indandione moieties. In addition, the substituent phenyl groups in the bind ligands are twisted from the 1,3-indandione moieties at around angles of 29 and 40. The less pronounced twist is observed in the phenyl group that belongs to the bonded molecule more distant from heteroaromatic ligand. This behavior reflects the steric hindrance on the ligands due to the heteroaromatic one in the first coordination sphere. Thus, the phenyl groups are orientated to minimize steric repulsion among ligands. Therefore, the steric hindrance due to the substituent phenyl groups of the ligand is enough to avoid water coordination to the lanthanide ion compared to the complexes. The coordination polyhedron, EuN 2 O 6, for the L] H 2 O complexes can be described as distorted 2084 Novel Luminescent Eu 3+ -Indandionate Complexes Containing Heterobiaryl Ligands J. Braz. Chem. Soc. square antiprismatic geometries (Figure 4b, Figure S1). A square face contains four oxygen atoms from indandionate ligands, another one presenting two oxygen atoms from indandionate and two nitrogen atoms belong to phen or dmphen ligand. The coordination polyhedron of the complex, EuN 2 O 7, is better described as a distorted monocapped square antiprismatic geometry, with oxygen atom from water molecule occupying the capping position (Figure 4a, Figure S1). The bond lengths of Eu 3+ -O(indandionate), and Eu 3+ -N(heteroaromatic) in the complexes are around 2.38 and 2.1 Å, respectively. These structural data are close to those obtained for [Eu(isovind) 3 (EtOH), 11 as well as other Eu 3+ compounds with bipy and phen ligands Photoluminescent properties of the Gd 3+ -compounds The phosphorescence spectra of the analogous [Gd(aind) 3 and [Gd(bind) 3 were recorded at 77 K with excitation monitored at 370 nm for S 0 transition, in order to estimate the triplet state energies (T 1 ) of the indandionate ligands. The Gd 3+ -compounds were used for this propose because the lowest excited energy level of Gd 3+ ion ( 6 P 7/2 ) is too high to receive energy from the ligands. In addition, the Gd 3+ radius is similar to the Eu 3+ ion, therefore, Gd 3+ complexes mimetize both geometry and intraligand energy level structures of Eu 3+ -complexes. Figure S2 shows the phosphorescence spectra of the Gd 3+ compounds, which exhibit broad emission bands in the spectral range from 440 to 60 nm assigned to the T S 0 transition centered on the indandionate ligands. The first T 1 excited state energies of the ligands were estimated as the energies correspond to the 0-0 phonon transitions from the phosphorescence spectra of the [Gd(aind) 3, and [Gd(bind) 3 with values of cm 1 (46. nm), and cm 1 (447.0 nm), respectively. These results suggest that both the aind and bind ligands have appropriated T 1 state energies, which play most important role in intramolecular ligand-tometal energy transfer process. Although, the S 1 and T 1 energy levels of the 1,10-phenanthroline ligand and its derivative are usually located at around and cm 1, respectively, 29 the main role of these ligands in lanthanide diketonate complexes is only to act as ancillary ones. 30 Photoluminescent properties of the Eu 3+ -compounds Figure shows the excitation spectra of the and recorded at 77 K in the spectral range nm with emission monitored on the hypersensitive transition at 611 nm. These spectra are dominated by two intense broad absorption bands in the spectral range from nm, which are assigned to the S 0 and S 0 S 2 transitions centered on the acind ligands. These bands are overlapped with the absorption bands assigned to the S 0 transition of the phen and dmphen ligands at 300 nm. The spectral profiles of the Eu 3+ -compounds (Figure ) indicate that the S 0 and S 0 S 2 transitions are approximately located in the 1,3-indandionate moieties. These results are in agreement with those ones observed for similar complexes, as reported in the literature. 11 Figure also presents some characteristic narrow absorption bands assigned to the 7 F 0 2S+1 L J intraconfigurational transitions of the Eu 3+ ion. These bands exhibit lower intensity than those ones, which correspond to the intraligand transitions, corroborating the efficient sensitization process via antenna effect. Figure. Excitation spectra of the Eu 3+ -compounds recorded at 77 K in the spectral range 20-0 nm, under emission at around 612 nm. (a) (phen) and O and (b) and O. The emission spectra of the and were recorded at 77 K in Vol. 2, No. 11, 2014 de Resende Filho et al. 208 the spectral range from 420 to 730 nm, under excitation centered on indandionate ligand, S 0 transitions (at 370 nm), as shown in Figure 6. The luminescent spectra display only the characteristic emission narrow bands that are assigned to the 7 F J transitions of the Eu 3+ ion, where J = 0, 1, 2, 3, and 4. 31,32 Figure 6. Emission spectra of the Eu 3+ -complexes recorded at 77 K in the spectral range of nm, under excitation at 370 nm. The local ligand field effect of the Eu 3+ -complexes has been qualitatively investigated based on the splitting and relative emission intensities of the 7 F J(0-4) transitions. Table 1 presents the intraconfigurational-4f 6 transitions and their Stark (2J + 1)-components. The presence of the only one emission band assigned to 7 F 0, as well as three stark components for 7 F 1 indicate that the Eu 3+ is located at low symmetry environment (C n, C nv or C s ). 33 These optical data corroborate with the fact that the intensity of the band assigned to transition is higher than that of the assigned to 7 F 1 one, 27 which are in close agreement with the distorted coordination polyhedra obtained from theoretical modeling for both Eu 3+ -complexes (Figure 4, Figure S1). The absence of broad phosphorescence bands arising from the indandionate ligands (Figure 6) emphasizes the presence of an
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