Novel luminescent Eu3+-indandionate complexes containing heterobiaryl ligands

ARTICLE

Novel luminescent Eu³⁺-indandionate complexes containing heterobiaryl ligands

João B. M. Resende Filho^I; Jannine C. Silva^I; Juliana A. Vale^I; Hermi F. Brito^II; Wagner M. Faustino^I; José G. P. Espínola^I; Maria C. F. C. Felinto^III; Ercules E. S. Teotonio^{*, I}

^IDepartamento de Química, Universidade Federal da Paraíba, 58051-970 João Pessoa-PB, Brazil

^IIDepartamento de Química Fundamental, Instituto de Química da Universidade de São Paulo, 05508-900 São Paulo-SP, Brazil

^IIIInstituto de Pesquisas Energéticas e Nucleares, Av. Prof. Lineu Prestes, 2242, Cidade Universitária, 05508-000 São Paulo-SP, Brazil

ABSTRACT

Novel Ln³⁺-indandionate complexes of formulas [Ln(aind)₃L(H₂O)] and [Ln(bind)₃L]∙H₂O (L: 1,10-phenanthroline (phen) or 4,7-dimethyl-1,10-phenanthroline (dmphen), Ln³⁺: Eu³⁺ or Gd³⁺, 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)₃L]∙H₂O compounds. However, the data also suggest that the water acts as a coordinated molecule in the [Ln(aind)₃L(H₂O)] ones. Theoretical geometries of the Eu³⁺-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 Eu³⁺-compounds have been discussed in terms of experimental intensity parameters (Ω₂ and Ω₄), radiative (A_rad), and non-radiative (A_nrad) spontaneous emission coefficients. The higher values of emission quantum efficiency (η) of the [Eu(bind)₃L]∙H₂O compounds 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

RESUMO

Novos complexos indandionatos de fórmulas [Ln(aind)₃L(H₂O)] e [Ln(bind)₃L]∙H₂O, (L: 1,10-fenantrolina (phen) ou 4,7-dimetil-1,10-fenantrolina (dmphen), Ln³⁺: Eu³⁺ ou Gd³⁺, 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)₃L]∙H₂O, enquanto que nos complexos [Ln(aind)₃L(H₂O)] a molécula de água atua como ligante. As geometrias dos complexos do íon Eu³⁺, otimizadas pelo modelo SPARKLE/AM1, foram consistentes com os resultados experimentais de luminescência. As propriedades luminescentes dos compostos de Eu³⁺ são discutidas em termos de parâmetros de intensidade experimentais (Ω₂ e Ω₄), 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 [Eu(bind)₃L]∙H₂O, refletindo a ausência de moléculas de água na primeira esfera de coordenação do íon Eu³⁺.

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.^4,5 Therefore, 2-acyl-1,3-indandiones have been inspired intensive theoretical and experimental investigations.^6-11

The significant interest in the investigation of the indandionate complexes has been increased in the last decade.^6-12 This kind of cyclic ligands presents a good chelating ability owing to the existence of three carbonyl 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.^6-10 However, there are only a few works reporting on Ln³⁺-complexes with these ligands, for example, the first structural characterization and photoluminescent as well as electroluminescent properties of the Ln³⁺-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 Eu³⁺-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.^14-17 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 Ln³⁺ 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)(H₂O)] and [Ln(bind)₃(L)]∙H₂O complexes, where aind = 2-acetyl-1,3-indandione, bind = 2-benzoyl-1,3-indandione, Ln = Eu³⁺ or Gd³⁺, and L = 1,10-phenanthroline or 4,7-dimethyl-1,10-phenanthroline (Figure 1). In addition, theoretical structures of the Eu³⁺ complexes were optimized by semi-empirical 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 (Ln₂O₃) were purchased from Aldrich Co. and used without previous treatment. Hexahydrated lanthanide chlorides, LnCl₃·6H₂O, were prepared by reaction between Ln₂O₃ and hydrochloric acid purchased from Aldrich Co.¹⁸ 2-acetyl-1,3-indandione (aind), 2-benzoyl-1,3-indandione (bind) ligands, and [Ln(aind)₃(H₂O)₂], [Ln(bind)₃(H₂O)₂] 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 Ln³⁺-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 450 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 Eu³⁺-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 ºC using a Shimadzu DTG-60H thermobalance with a heating rate 10 ºC min^-1 under a nitrogen atmosphere.

Synthesis of the Ln³⁺-complexes with heteroaromatic ligands

Lanthanide indandionate complexes containing ancillary ligands were synthesized by mixing acetonic solutions of the corresponding hydrated complexes, [Ln(aind)₃(H₂O)₂] or [Ln(bind)₃(H₂O)₂], 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 ºC). Later on, these solutions were stand up until the total evaporation of solvent. The prepared yellow solids were washed thoroughly with cold ethanol and dried under reduced pressure.

[Eu(aind)₃(phen)(H₂O)] (1): 0.2482 g, yield 68%; FT-IR (KBr, cm^-1): 3485(w), 3443(w), 3057(w), 2951(w), 2920(w), 2856(w), 1681(m), 1643(m), 1622(s), 1585(s), 1467(s), 1363(m), 1340(m), and 732(s). Anal. Calc. for C₄₅H₃₁EuN₂O₁₀: C, 59.28, H, 3.43, and N, 3.07. Found: C, 59.71; H, 3.35, and N, 2.74.

[Eu(bind)₃(phen)]∙H₂O (2): 0.4230 g, yield 72%; FT-IR (KBr, cm^-1): 3429(w), 3055(w), 2952(w), 2920(w), 1694(m), 1618(s), 1587(s), 1568(s), 1564(s), 1448(s), 1420(s), 1340(m), and 741(m). Anal. Calc. for C₆₀H₃₇EuN₂O₁₀: C, 65.64; H, 3.40, and N, 2.55. Found: C, 65.35, H, 3.44, and N, 2.84.

[Gd(aind)₃(phen)(H₂O)] (3): 0.2088 g, yield 56%; FT-IR (KBr, cm^-1): 3524(w), 3433(w), 3057(w), 2951(w), 2922(w), 2866(w), 2856(w), 1682(m), 1643(m), 1622(s), 1587(s), 1467(s), 1364(m), 1340(m), and 735(s). Anal. Calc. for C₄₅H₃₁GdN₂O₁₀: C, 58.94, H, 3.41, and N, 3.05. Found: C, 59.63, H, 4.15, and N, 2.66.

[Gd(bind)₃(phen)]∙H₂O (4): 0.2042 g, yield 58%; FT-IR (KBr, cm^-1): 3445(w), 3053(w), 3032(w), 2926(w), 1694(m), 1636(m), 1616(s), 1587(s), 1568(s), 1564(s), 1448(s), 1423(s), 1340(m), and 741(m). Anal. Calc. for C₆₀H₃₇GdN₂O₁₀: C, 65.32, H, 3.38, and N, 2.54. Found: C, 65.55, H, 3.34, and N, 3.24.

[Eu(aind)₃(dmphen)(H₂O)] (5): 0.1050 g, yield 57%; FT-IR (KBr, cm^-1): 3564(w), 3502(w), 3068(w), 1691(m), (s), 1643(s), 1620 (s), 1583(s), 1467(s), 1359(m), 1340(m), and 725(s). Anal. Calc. for C₄₇H₃₅EuN₂O₁₀: C, 60.06, H, 3.73, and N, 2.98. Found: C, 60.26, H, 3.71, and N, 3.01.

[Eu(bind)₃(dmphen)]∙H₂O (6): 0.1030 g, yield 58%; FT-IR (KBr, cm^-1): 3435(w), 3055(w), 1693(m), 1629(m), 1612(m), 1585(s), 1564(s), 1448(s), 1421(s), 1361(m), and 736(m). Anal. Calc. for C₆₂H₄₁EuN₂O₁₀: C, 66.13, H, 3.64, and N, 2.49. Found: C, 66.28, H, 3.48, and N, 2.52.

[Gd(aind)₃(dmphen)(H₂O)] (7): 0.1630 g, yield 60%; FT-IR (KBr, cm^-1): 3442(w), 3068(w), 1685(m), 1645(m), 1620(s), 1585(s), 1467(m), 1357(m), 1340(m), and 729(m). Anal. Calc. for C₄₇H₃₅GdN₂O₁₀: C, 59.74, H, 3.71, and N, 2.97. Found: C, 60.32, H, 3.61, and N, 3.12.

[Gd(bind)₃(dmphen)]∙H₂O (8): 0.0980 g, yield 55%; FT-IR (KBr, cm^-1): 3441(w), 3053(w), 1691(m), 1629(s), 1612(s), 1585(s), 1564(s), 1450(s), 1421(s), 1342(m), and 736(m). Anal. Calc. for C₆₂H₄₁GdN₂O₁₀: C, 65.84, H, 3.63, and N, 2.47. Found: C, 65.92, H, 3.57, and N, 2.67.

Results and Discussion

Characterization

The results of the elemental analysis (C, H, and N) are consistent with the monohydrated formulas of Ln(aind)₃L·H₂O and Ln(bind)₃L·H₂O complexes, where Ln = Eu³⁺ or Gd³⁺.

The infrared spectra of the Ln³⁺-complexes (Figure 2) exhibit two bands at around 1560 and 1690 cm^-1 assigned to the ν(C=O) stretching modes, due to the coordinated and non-coordinated 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 Ln³⁺ 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 Ln³⁺ ion through the nitrogen atoms.^19,20 The complexes also exhibit absorption bands in the spectral range 4000-3200 cm^-1 assigned to ν(O-H) stretching of the water molecule (Figure 2). Interestingly, FT-IR spectra of the [Ln(aind)₃L·H₂O] compounds exhibit narrow peaks at around 3560 cm^-1, while the [Ln(bind)₃L]·H₂O compounds show only one broad absorption band. These data give evidences that the water molecule is coordinated to the Ln³⁺ ion only in the [Ln(aind)₃L·H₂O] complexes. Similar spectral profiles have also been observed for La³⁺ and Tb³⁺ complexes using EDTA as ligand that present coordinated and non-coordinated water molecules, respectively.^21,22

Thermogravimetric curves of the [Eu(aind)₃(dmphen)(H₂O)] and [Eu(bind)₃(dmphen)]∙H₂O compounds (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 ºC that correspond to 1.6% for [Eu(bind)₃(dmphen)]∙H₂O and 2.1% for [Eu(aind)₃(dmphen)(H₂O)], which are in agreement with the release of water molecules. However, it can be observed in Figure 3 that the [Eu(aind)₃(dmphen)(H₂O)] complex exhibits a shorter dehydration interval (60-130 ºC) than the [Eu(bind)₃(dmphen)](H₂O) complex, in which the dehydration process occurs from 40 to 150 ºC (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 Ln³⁺-EDTA complexes, as reported by Gigante et al..²²

Figure 3

Theoretical structural studies

Theoretical molecular structures of the [Eu(aind)₃L(H₂O)] and [Eu(bind)₃L]∙H₂O complexes, where L = phen or dmphen, were optimized using the reparameterized latest version of the SPARKLE/AM1 model for Eu(III) and other lanthanide ions implemented in the software package MOPAC2012.^23,24

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 [Eu(aind)₃(dmphen)(H₂O)] and [Eu(bind)₃(dmphen)]∙H₂O complexes are shown in Figure 4, while those ones for the similar complexes with phen ligand are presented in Supporting Information (Figure S1).

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 40º. 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 [Eu(aind)₃L(H₂O)] complexes.

The coordination polyhedron, EuN₂O₆, for the [Eu(bind)₃L]·H₂O complexes can be described as distorted 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 [Eu(aind)₃L(H₂O)] complex, EuN₂O₇, 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 Eu³⁺-O(indandionate), and Eu³⁺-N(heteroaromatic) in the complexes are around 2.38 and 2.51 Å, respectively. These structural data are close to those obtained for [Eu(isovind)₃(EtOH)(H₂O)],¹¹ as well as other Eu³⁺-compounds with bipy and phen ligands.^25-28

Photoluminescent properties of the Gd³⁺-compounds

The phosphorescence spectra of the analogous [Gd(aind)₃L(H₂O)] and [Gd(bind)₃L]∙H₂O compounds were recorded at 77 K with excitation monitored at 370 nm for S₀→S₁ transition, in order to estimate the triplet state energies (T₁) of the indandionate ligands. The Gd³⁺-compounds were used for this propose because the lowest excited energy level of Gd³⁺ ion (⁶P_7/2) is too high to receive energy from the ligands. In addition, the Gd³⁺ radius is similar to the Eu³⁺ ion, therefore, Gd³⁺-complexes mimetize both geometry and intraligand energy level structures of Eu³⁺-complexes. Figure S2 shows the phosphorescence spectra of the Gd³⁺-compounds, which exhibit broad emission bands in the spectral range from 440 to 650 nm assigned to the T→S₀ transition centered on the indandionate ligands.

The first T₁ 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)₃L(H₂O)], and [Gd(bind)₃L]∙H₂O compounds with values of 21906 cm^-1 (456.5 nm), and 22371 cm^-1 (447.0 nm), respectively. These results suggest that both the aind and bind ligands have appropriated T₁ state energies, which play most important role in intramolecular ligand-to-metal energy transfer process. Although, the S₁ and T₁ energy levels of the 1,10-phenanthroline ligand and its derivative are usually located at around 30000 and 22000 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 Eu³⁺-compounds

Figure 5 shows the excitation spectra of the [Eu(aind)₃L(H₂O)] and [Eu(bind)₃L]∙H₂O compounds recorded at 77 K in the spectral range 250-590 nm with emission monitored on the ⁵D₀→⁷F₂ hypersensitive transition at 611 nm. These spectra are dominated by two intense broad absorption bands in the spectral range from 270-470 nm, which are assigned to the S₀→S₁ and S₀→S₂ transitions centered on the acind ligands. These bands are overlapped with the absorption bands assigned to the S₀→S₁ transition of the phen and dmphen ligands at 300 nm. The spectral profiles of the Eu³⁺-compounds (Figure 5) indicate that the S₀→S₁ and S₀→S₂ 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 5

The emission spectra of the [Eu(aind)₃L(H₂O)] and [Eu(bind)₃L]∙H₂O compounds were recorded at 77 K in the spectral range from 420 to 730 nm, under excitation centered on indandionate ligand, S₀→S₁ transitions (at 370 nm), as shown in Figure 6. The luminescent spectra display only the characteristic emission narrow bands that are assigned to the ⁵D₀→⁷F_J transitions of the Eu³⁺ ion, where J = 0, 1, 2, 3, and 4.^31,32

The local ligand field effect of the Eu³⁺-complexes has been qualitatively investigated based on the splitting and relative emission intensities of the ⁵D₀→⁷F_J(0-4) transitions. Table 1 presents the intraconfigurational-4f⁶ transitions and their Stark (2J + 1)-components. The presence of the only one emission band assigned to ⁵D₀→⁷F₀, as well as three stark components for ⁵D₀→⁷F₁ indicate that the Eu³⁺ 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 ⁵D₀→⁷F₂ transition is higher than that of the assigned to ⁵D₀→⁷F₁ one,²⁷ which are in close agreement with the distorted coordination polyhedra obtained from theoretical modeling for both Eu³⁺-complexes (Figure 4, Figure S1).

The absence of broad phosphorescence bands arising from the indandionate ligands (Figure 6) emphasizes the presence of an efficient luminescence sensitization occurring via antenna effect. The efficient intramolecular energy transfer mechanism from aind and bind ligands to the Eu³⁺ ion in the complexes is characterized by: (i) strong absorption of S₀→S₁ transition of the 2-acyl-1,3-indandione ligands; (ii) intersystem cross by the non-radiative processes S₁→T; (iii) energy transfer of the T₁→(⁵D₁, ⁵D₀), and (iv) efficient radiative process from the ⁵D₀→⁷F_J(0-4) transitions.^34-35

Judd-Ofelt intensity parameters (Ω_λ = 2.4), radiative (A_rad), non-radiative (A_nrad) rates, and emission quantum efficiency (η) of the ⁵D₀ emitting level of the Eu³⁺ complexes have been quantitatively obtained from the luminescence decay curves and emission spectral data (Table 2). The luminescence decay curves (Figure S3) were recorded by monitoring the emission intensity of the hypersensitive ⁵D₀→⁷F₂ transition under excitation of the S₀→S₁ transition centered on the 2-acyl-1,3-indandionate ligands at 370 nm. The curves were well-adjusted to a single exponential function, yielding the ⁵D₀ lifetimes values (τ) equal to 0.459, 0.465, 0.229, and 0.594 ms for [Eu(aind)₃(phen)(H₂O)], [Eu(bind)₃(phen)]∙H₂O, [Eu(aind)₃(dmphen)(H₂O)] and [Eu(bind)₃(dmphen)]∙H₂O (Table 2), respectively. While using these data, the total decay rates were determined according to the expression: A_total = 1/τ. The radiative rates (A_rad) were determined using the ⁵D₀→⁷F_2,4 transitions (forced electric dipole) and the ⁵D₀→⁷F₁ transition (magnetic-dipole) as internal reference.^36,37 The values of both radiative and noradiative rates for [Eu(aind)₃L(H₂O)], and [Eu(bind)₃L]∙H₂O complexes are presented in Table 2. When τ values of these complexes were compared with the corresponding ones of precursor hydrated complexes, it was observed a considerable decrease in both A_rad and A_nrad rates. The decrease in A_nrad values might be attributed to the water molecules substitution by the auxiliary phen and dmphen ligands in the first coordination sphere of the Eu³⁺ ion (Table 2), that reduce the multiphonon decays, also observed for the other Eu³⁺-indandionate complexes, as reported in the literature.^11,12 The lower values of A_nrad for [Eu(bind)₃L]∙H₂O compounds compared to those observed for [Eu(aind)₃L(H₂O)] are a direct consequence of the multiphonon decay, because the water molecule is not coordinated to the Eu³⁺ ion.

Moreover, the luminescence quantum efficiency was determined using the expression η = A_rad/(A_rad + A_nrad). Table 2 shows that the higher values were observed for the [Eu(bind)₃L]·H₂O compounds than the [Eu(aind)₃L(H₂O)] ones, indicating the absence of water molecules in the first coordination of Eu³⁺ ion, which decrease significantly the luminescence quenching effect.

The experimental intensity parameters Ω₂ and Ω₄ for the complexes were directly determined from the A_rad values of the ⁵D₀→⁷F₂ and ⁵D₀→⁷F₄ transitions, respectively.^35,36 These parameters depend on the local geometry and the ligating atoms polarizabilities in the first coordinating sphere around the metal central ion.³⁷ As observed in Table 2, the values of Ω₂ for the complexes containing heteroaromatic phen and dmphen ligands are lower than those ones calculated for the hydrated precursor compounds.¹¹ This result suggests that the chemical environment polarizabilities have decreased when phen and dmphen ligands substitute water molecules in the first coordination sphere of the Eu³⁺ ion, which have contributed to a significant decrease in the emission rate assigned to the ⁵D₀→⁷F₂ transition. These values are similar to those found for europium 2-acyl-1,3-indandionate complexes containing triphenylphosphine oxide ligand.¹¹ The values of Ω₄ exhibit similar behavior, suggesting that the sensibility of the ⁵D₀→⁷F₄ transition has also been changed with the polarizability and chemical environment.

Conclusions

In the current work, we have reported the synthesis, characterization, and photoluminecent properties of [Ln(aind)₃L(H₂O)] and [Ln(bind)₃L]∙H₂O coordination compounds (Ln : Eu³⁺ or Gd³⁺). The FT-IR data suggest that the water molecule is coordinated to the Ln³⁺ ion in the case of 1, 3, 5, and 7 complexes. The photoluminescence data are consistent with coordination polyhedra calculated via SPARKLE/AM1 model for the [Ln(aind)₃L(H₂O)] and [Ln(bind)₃L]∙H₂O complexes. The structural differences and the absence of water molecules in the first coordination sphere have great impact on the luminescence quantum efficiency (η) of the Eu³⁺-complexes, decreasing the luminescence quenching in the intramolecular energy transfer process.

Supplementary Information

The luminescence decay curves of the Eu³⁺-complexes are available free of charge at http://jbcs.sbq.org.br as PDF file.

Acknowledgements

This research was supported by grants from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Instituto Nacional de Ciência e Tecnologia-Nanotecnologia para Marcadores Integrados (INCT-INAMI), FACEPE-PRONEX, Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP No. 2003/07178-8) and, Financiadora de Estudos e Projetos (FINEP).

Submitted on: March 13, 2014

Published online: August 26, 2014

FAPESP has sponsored the publication of this article.

Supplementary Information

The supplementary material is available in pdf: [Supplementary material]

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Publication Dates

• Publication in this collection
  13 Nov 2014
• Date of issue
  Nov 2014

History

• Received
  13 Mar 2014
• Accepted
  26 Aug 2014