On the use of theoretical tools in the study of photophysical properties of the new Eu(fod)3 complex with diphenbipy

Article abstract of DOI:10.1016/j.cplett.2005.10.114

The synthesis, characterization, spectroscopic, and fluorescence properties of Eu(fod)₃ ? 2H₂O and Eu(fod)₃ ? diphenbipy (fod = 6,6,7,7,8,8, 8-heptafluoro-2,2-dimethyl-3,5-octadionate, diphenbipy = 4,4′-diphenyl-2,2′-dipyr

Full text of DOI:10.1016/j.cplett.2005.10.114

Chemical Physics Letters 418 (2006) 337–341
www.elsevier.com/locate/cplett
On the use of theoretical tools in the study of photophysical
properties of the new Eu(fod)3 complex with diphenbipy
a
b
c,
*
Edjane R. dos Santos , Marcos A.C. dos Santos , Ricardo O. Freire
,
c
a
a
Severino A. Ju´nior , Ledjane S. Barreto , Maria E. de Mesquita
a
Departamento de Quı´mica, UFS, 49100-000, Sa˜o Cristo´va˜o, SE, Brazil
b
Departamento de Fı´sica, UFS, 49100-000, Sa˜o Cristo´va˜o, SE, Brazil
Departamento de Quı´mica Fundamental, UFPE, 50590-470 Recife, PE, Brazil
c
Received 30 August 2005; in final form 22 October 2005
Available online 23 November 2005
Abstract
The synthesis, characterization, spectroscopic, and fluorescence properties of Eu(fod)3 Æ 2H2O and Eu(fod)3 Æ diphenbipy
(fod = 6,6,7,7,8,8, 8-heptafluoro-2,2-dimethyl-3,5-octadionate, diphenbipy = 4,40-diphenyl-2,20-dipyridyl) are described. New spectro-
scopic studies of these complexes are presented based on theoretical and experimental analyses of the intensity parameters, X2 and
X4, and on the maximum splitting of the 7F1. The geometries calculated by Sparkle/AM1 model was used to calculate the 7F1 manifold
splitting (DE0–1) and the intensity parameters X2, X4 based on the Simple Overlap Model (SOM). The reconciliation among the data from
the theoretical 7F1 manifold splitting, and the intensity parameter certifies the reliability of the models used in the theoretical calculations.
ꢀ 2005 Elsevier B.V. All rights reserved.
1. Introduction
demands a lower computational effort makes possible the
theoretical project of lanthanide complexes with high lumi-
nescence since it permits to treat a great number of lantha-
nide complexes in a relatively short period of time.
Additionally, this new version is capable of calculating
High luminescent europium (III) complexes with b-dik-
etones and o-phenantroline-N-oxide ligands have been syn-
thesized and suggested as promising light conversion
molecular devices (LCMD) [1]. For the obtainment of an
efficient LCMD it is necessary the optimization of the lumi-
nescence process [2] that consists in an initial stage, where
the light in the UV region is absorbed by the ligands
(antenna effect [3]). After this the energy is transferred, gen-
erally from the triplet state of the ligand to the excited state
of the lanthanide ion, and in the last stage the excited lan-
thanide ion decays to the ground state via photon emission
in the visible region.
the coordination polyhedron of Pr+3 [7], Eu+3, Gd+3
,
Tb+3 [6], Dy+3 [8], Tm+3 [9] and Yb+3 [10] ions complexes
with the same accuracies of the ab initio/effective core
potential calculations [6].
The Sparkle/AM1 model, as tool for design of new
LCMDs, has been applied in an intense way to calculate
the ground state geometry of the lanthanide complexes
[11–13]. These geometries are used to predict some spectro-
scopic properties, such as singlet and triplet energies, and
electronic spectra of lanthanide complexes [11–13]. With
these quantities it is possible to build rate equations that
involve the energy transfer mechanism to calculate the
quantum yields [4] for these complexes.
Some recent papers, where theoretical tools were used
for the design of new europium complexes with a high
quantum yield have been published by our group [4,5].
The development of a new Sparkle/AM1 model [6] which
In this Letter, we report the synthesis, characterization
and spectroscopic properties of the Eu(fod)3 Æ diphenbipy
(fod = 6,6,7,7,8,8, 8-heptafluoro-2,2-dimethyl-3,5-octadio-
nate, diphenbipy = 4,40-diphenyl-2,20-dipyridyl). Theoreti-
*
Corresponding author. Fax: +55 81 2126 8442.
E-mail addresses: rfreire@ufpe.br (R.O. Freire), mesquita@ufs.br
(M.E. de Mesquita).
0009-2614/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.cplett.2005.10.114

338
E.R. dos Santos et al. / Chemical Physics Letters 418 (2006) 337–341
cal tools such as Sparkle/AM1 model (used for predicting
the ground state geometries) and Simple Overlap Model
(SOM) [14] (used to calculate the F1 manifold splitting
ZINDO package [18]. We have used a point charge of
+3e to represent the trivalent europium ion.
7
(DE0–1) and the intensity parameters X2, X4) have been
used to explain the influence of the ligand field in the stud-
ied complexes.
3.2. Intensity parameters
From the emission spectrum, we have determined the
value of the experimental 7F1 manifold splitting as well
as the experimental intensity parameters X2 and X4 by
2. Experimental details
7
7
using the 5D0 ! F2 and 5D0 ! F4 transitions, respec-
tively, and by expressing the emission intensity
I = ⁄xAradN in terms of the areas under the emission
curve. Here, ⁄x is the transition energy, Arad is the corre-
sponding coefficient of spontaneous emission and N is the
population of the emitting level (5D0). The magnetic dipole
2.1. Sample
The Eu(fod)3 Æ 2H2O complex and diphenbipy were pur-
chased from Aldrich and used as received. The complex
Eu(fod)3 Æ diphenbipy was prepared adding 40 ml of a
warm ethanolic solution of diphenbipy (1 mmol) to an eth-
anolic solution containing 1 mmol of Eu(fod)3 Æ 2H2O. The
pure products were obtained by repeated crystallization
from hexane and dried over P2O5 under reduced pressure
(less than 1 mmHg). The purity of the compounds was
achieved by CHN elemental analysis.
7
5D0 ! F1 allowed transition was taken as reference. The
Arad is given by
4e2x3
3ꢀhc3
X
2
7
5
Arad
¼
v
Xkh FJ kUðkÞk D0i .
ð1Þ
k
The appropriate reduced matrix elements of Eq. (1) were
taken from [19], and an average index of refraction of 1.5
was used in the Lorentz local field correction, v. The pro-
cedure for the calculation of the theoretical F1 manifold
splitting intensity parameters, Xk, is described in [20].
2.2. Measurements
7
The elemental analysis was measured by means of a
CHNS–O analyzer Flash 1112 Series EA Thermo Finni-
gam. The infrared spectra were recorded from 4000 to
400 cmꢀ1 using a spectrophotometer model BRUKER
IFS 66 with conventional KBr technique. The absorption
spectra were recorded on a Perkin–Elmer UV–Visible spec-
trophotometer Lambda 6 model 2688–002. The lumines-
cence spectra at room temperature and 77 K were
obtained in an ISS PC1ꢁ Spectrofluorometer. The excita-
tion device is equipped with a 300 W xenon lamp and a
holographic grating. The emission is collected in a 25 cm
monochromator with resolution of 0.1 nm equipped with
a photomultiplier. The excitation and emission slit width
4. Results and discussion
The analytical data are in accordance with the proposed
formulae of Eu(fod)3 Æ diphenbipy, the UV–Vis absorption
spectrum has shown three bands in 207, 251 and 288 nm
(Table 1). The free diphenbipy shows two bands in 208
and 250 nm. The inexistence of the band in 250 nm (char-
acteristic of the diphenbipy ligand) in the spectrum of the
Eu(fod)3 Æ 2H2O complex and the presence of this band in
the spectrum of Eu(fod)3 Æ diphenbipy, is indicative that
the water molecules are substituted by diphenbipy ligand
in the first sphere of coordination of the Eu+3 ion.
were
0.5 mm,
both
monochromators
having
1200 grooves/mm.
The IR data show that the band due to the mCN is
shifted to lower frequencies (about 1343.40 cmꢀ1) as com-
pared to the free ligand (1584.12 cmꢀ1) band due to the
coordination of this ligand by means the CN group of
diphenbipy. The spectrum also shows that there is no coor-
dination of water molecules in this complex because in our
observation the water molecules is lost upon heating at
90 ꢂC in vacuum over P2O5.
3. Theoretical details
3.1. Geometry optimization and calculation of the transition
energies
The ground state geometry of the Eu(fod)3 Æ 2 H2O and
Eu(fod)3 Æ diphenbipy complexes were calculated with the
Sparkle/AM1 model [6], implemented in the MOPAC93r2
package [15]. The MOPAC keywords used were: PRE-
CISE, GNORM = 0.25, SCFCRT = 1.D-10 (in order to
increase the SCF convergence criterion) and XYZ (the
geometry optimizations were performed in Cartesian
coordinates).
The luminescence spectra of the Eu(fod)3 Æ 2H2O and
Eu(fod)3 Æ diphenbipy complexes in the solid state are
Table 1
Photophysical data for Eu(fod)3 Æ 2H2O and Eu(fod)3 Æ diphenbipy com-
plexes in the solid statea and solutionb
For Eu(fod)3 Æ 2H2O and Eu(fod)3 Æ diphenbipy com-
plexes we have calculated their singlet and triplet excited
states using configuration interaction single (CIS) based
on the intermediate neglect of the differential overlap/spec-
troscopic (INDO/S) technique [16,17] implemented in
Complex
Absorptionb
Luminescencea
kmax (nm)
kemis (nm)
kexc (nm)
Eu(fod)3 Æ 2H2O
Eu(fod)3 Æ diphenbipy
291
288
611
612
340
340

E.R. dos Santos et al. / Chemical Physics Letters 418 (2006) 337–341
339
5
fluorescence from the D0 level of the Eu+3 ion is strongly
quenched by coupling with the OH vibration [22].
As we can observe in Fig. 2, the coordination polyhe-
dron of the Eu(fod)3 Æ 2H2O complex is formed by six oxy-
gens from the b-diketones ligands and two oxygens from
water molecules. For the Eu(fod)3 Æ diphenbipy complex
the coordination polyhedron is composed by six oxygens
from the b-diketones ligands and two nitrogens from the
diphenbipy ligand. Tables 2 and 3 show the Sparkle/
AM1 spherical coordinates of the Eu(fod)3 Æ 2H2O and
Eu(fod)3 Æ diphenbipy, respectively.
The optimized geometry obtained from the Sparkle/
AM1 model is shown in Fig. 2.
The experimental and theoretical values of the DE0–1
and Xk (k = 2,4) are shown in Table 4. The DE0–1 calcula-
tion is used in order to obtain the value of the charge factor
g, which enters into the Xk expression, because the DE0–1
Fig. 1. Emission spectra of: (a) Eu(fod)3 Æ 2H2O and (b) Eu(fod)3 Æ
diphenbipy complexes in the solid state, at 77 K.
shown in Fig. 1a and b, respectively. The presence of the
7
5D0 ! F0 transition can be used as a good diagnostic of
the crystallinity and purity of the compounds of [21]. Since
the band is not splitted by the ligand field effect, any split-
ting observed is necessarily due to a multiplicity of Eu+3
sites. However, a single symmetrical peak is observed in
both complexes, which strongly indicates that only one
Eu+3 site is present in both samples. The intensity ratio
7
7
I(5D0 ! F2)/I(5D0 ! F1) is 11.98 to the complex
Eu(fod)3 Æ diphenbipy complex, which is higher than that
of the complex with water (7.96). These data indicate that
5
7
the intensity of the D0 ! F2 is markedly enhanced by
complexing with diphenbipy (Fig. 1b). The complex
Eu(fod)3 Æ diphenbipy shows a very lower symmetry for
the Eu+3 ion than that for the Eu(fod)3 Æ 2H2O, because
the transitions 5D0 ! F2 and 5D0 ! F0 have considerable
intensities and the 7F1 and 7F2 manifolds are clearly totally
split. The substitution of water molecules by diphenbipy
ligand in the Eu(fod)3 Æ 2H2O complex increases the
luminescence intensities because it is well known that
7
7
Fig. 2. Calculated ground state geometry of (a) Eu(fod)3 Æ 2H2O and
(b) Eu(fod)3 Æ diphenbipy complexes.

340
E.R. dos Santos et al. / Chemical Physics Letters 418 (2006) 337–341
Table 2
5. Conclusion
Spherical atomic coordinates for the Sparkle/AM1 coordination polyhe-
dron of the Eu(fod)3 Æ 2H2O complex
We have synthesized the europium diphenbipy complex.
The coordination was determined from the chemical ana-
lytical data and from the changes in the IR, UV–Vis spec-
tra observed after the substitution of the two water
molecules in the first sphere of the coordination of Eu+3
ion by the diphenbipy ligand.
The substitution of the water molecules by diphenbipy
in the Eu(fod)3 Æ 2H2O complex has led to an increase in
the intensity of the luminescence which can be associated
to the low symmetry on the site.
˚
Atom
R (A)
h (ꢂ)
0.00
/ (ꢂ)
0.00
7.85
70.39
278.10
212.66
131.98
298.21
135.98
188.52
Eu3+
0.00
2.38
2.38
2.38
2.38
2.38
2.38
2.39
2.39
O (fod) (1.258, 2.2)
O (fod) (1.258, 2.2)
O (fod) (1.258, 2.2)
O (fod) (1.258, 2.2)
O (fod) (1.258, 2.2)
O (fod) (1.258, 2.2)
O (H2O) (1.258, 0.6)
O (H2O) (1.258, 0.6)
85.57
82.65
69.62
70.37
145.27
152.31
81.97
4.53
The charge factors and the polarizability appear beside the ion (g, a in
The high value of the X2 intensity parameter for the
complex with diphenbipy reflects the hypersensitive behav-
3
10ꢀ24 A ).
˚
7
ior of the 5D0 ! F2 transition and indicates that the Eu+3
ion is in a high polarizable chemical environment.
The reconciliation among the data from the theoretical
7F1 manifold splitting, and the intensity parameter certifies
the reliability of the models used in the theoretical
calculations.
Table 3
Spherical atomic coordinates for the Sparkle/AM1 coordination polyhe-
dron of the Eu(fod)3 Æ diphenbipy complex
˚
Atom
R (A)
h (ꢂ)
0.00
/ (ꢂ)
0.00
1.97
63.90
279.21
215.27
141.53
293.34
136.92
23.36
Eu3+
0.00
2.39
2.39
2.39
2.38
2.39
2.38
2.51
2.51
O (fod) (1.918, 3.36)
O (fod) (1.918, 3.36)
O (fod) (1.918, 3.36)
O (fod) (1.918, 0.03)
O (fod) (1.918, 3.36)
O (fod) (1.918, 0.03)
N (diphenbipy)(3.188, 0.03)
N (diphenbipy) (3.188, 0.03)
87.70
91.03
71.19
80.42
143.99
150.87
60.86
11.94
Acknowledgments
We appreciate the financial support from CNPq and
CAPES (Brazilian agencies), FAP-SE and also Grants
from the Instituto do Mileˆnio de Materiais Complexos.
We also thank CENAPAD (Centro Nacional de Processa-
mento de Alto Desempenho) at Campinas, Brazil.
The charge factors and the polarizability appear beside the ion (g, a in
3
10ꢀ24 A ).
˚
References
´
´
´
[1] C. de Mello Donega, S.A. Junior, G.F. de Sa, J. Chem. Soc. Chem.
Comm. 10 (1996) 1199.
Table 4
[2] N. Sabbatini, M. Guardigli, J.-M. Lehn, Coord. Chem. Rev. 123
(1993) 201.
[3] N. Sabbatini, M. Guardigli, I. Manet, R. Ungaro, A. Casti, R.
Ziessel, G. Ulrich, Z. Asfari, J.-M. Lehn, Pure Appl. Chem. 67 (1995)
135.
Experimental and theoretical values of the intensity parameters X2 and X4
in 10ꢀ20 cm2, the splitting of the 7F1 manifold, DE0–1 in the Eu(fo-
d)3 Æ 2H2O and in the Eu(fod)3 Æ diphenbipy complexes
Eu(fod)3 Æ 2H2O
Eu(fod)3 Æ diphenbipy
[4] R.O. Freire, R.Q. Albuquerque, S. Alves Jr., G.B. Rocha, M.E. de
Mesquita, J. Chem. Phys. Lett. 405 (2005) 123.
[5] R.O. Freire, M.O. Rodrigues, F.R. Gonc¸alves e Silva, N.B. da Costa
Ju´nior, M.E. de Mesquita, J. Molecul. Model. (2005), doi:10.1007/
s00894-005-0280-7.
Experimental Theoretical Experimental Theoretical
X2
X4
10.9 · 10ꢀ20
2.1 · 10ꢀ20
190.4
10.9 · 10ꢀ20 17.9 · 10ꢀ20
17.9 · 10ꢀ20
2.6 · 10ꢀ20
184.5
2.1 · 10ꢀ20
2.6 · 10ꢀ20
DEmax (cmꢀ1
)
190.3
184.5
[6] R.O. Freire, G.B. Rocha, A.M. Simas, Inorg. Chem. 44 (9) (2005)
3299.
[7] R.O. Freire, N.B. da Costa Jr., G.B. Rocha, A.M. Simas, J.
Organomet. Chem. 690 (2005) 4099.
[8] N.B. da Costa Jr., R.O. Freire, G.B. Rocha, A.M. Simas, Inorg.
Chem. Comm. 8 (2005) 831.
[9] R.O. Freire, G.B. Rocha, A.M. Simas, Chem. Phys. Lett. 411 (2005)
61.
[10] R.O. Freire, G.B. Rocha, A.M. Simas, J. Comput. Chem. 26 (14)
(2005) 1524.
has a very well-established analytical expression. The theo-
retical calculations have reproduced the experimental val-
ues of the 7F1 manifold in both complexes using the
charge factors appearing in Tables 2 and 3. The very high
value of the X2 for Eu(fod)3 Æ diphenbipy reflects the hyper-
sensitive behavior of the D0 ! F2 transition. In our cal-
culations, it was possible to distinguish between the
forced electric dipole and the dynamic coupling mecha-
nism. We found that this latter largely dominates because
it was not possible to fit theoretically the experimental
intensity parameters data without entering this contribu-
tion into the Xk equation [23]. This can be seen by means
of the polarizability values achieved for the ligating oxygen
and nitrogen ions (see Tables 2 and 3).
5
7
[11] M.E. de Mesquita, S. Alves Jr., F.C. Oliveira, R.O. Freire, N.B.C.
´
Ju´nior, G.F. de Sa, Inorg. Chem. Comm. 5 (2002) 292.
[12] M.E. de Mesquita, F.R.G. e Silva, R.Q. Albuquerque, R.O. Freire,
E.C. da Conceic¸ao, J.E.C. da Silva, N.B.C. Ju´nior, G.F. de Sa´, J.
˜
Alloy. Comp. 366 (2004) 124.
[13] M.E. de Mesquita, S.A. Ju´nior, F.R.G. e Silva, M.A. Couto dos
´
Santos, R.O. Freire, N.B.C. Ju´nior, G.F. de Sa, J. Alloy. Comp. 374
(2004) 320.
[14] O.L. Malta, Chem. Phys. Lett. 88 (1982) 353.

E.R. dos Santos et al. / Chemical Physics Letters 418 (2006) 337–341
341
[15] J.J.P. Stewart, In MOPAC 93.00 Manual, Fujitsu Limited, Tokyo,
Japan, 1993.
Lanthanides in LaF3, Report – Argonne National Laboratory,
1977.
[16] J.E. Ridley, M.C. Zerner, Theor. Chim. Acta 42 (1976) 223.
[17] M.C. Zerner, G.H. Loew, R.F. Kirchner, U.T. Mueller-Westerhoff, J.
Am. Chem. Soc. 102 (1980) 589.
[18] M.C. Zerner, In ZINDO Manual, QTP, University of Florida,
Gainesville, FL. 32611, 1990.
[20] O.L. Malta, S.J.L. Ribeiro, M. Faucher, P. Porcher, J. Phys. Chem.
Solids 52 (1991) 587.
[21] H.F. Brito, O.L. Malta, J.F.S. Menezes, J. Alloy. Comp. 303 (2000)
336.
[22] N.B. da Costa, R.O. Freire, M.A. Couto dos Santos, M.E. de
Mesquita, J. Mol. Struct. – Theochem 545 (2001) 131.
[23] R.D. Peacock, Struct. Bond. 22 (1975) 83.
[19] W.T, Carnall, H. Crosswhite, H.M Crosswhite, Energy
Level Structure and Transition Probabilities of the Trivalent