Structure and luminescent investigation of the Ln(III)-β-diketonate complexes containing tertiary amides

Article abstract of DOI:10.1016/j.poly.2012.02.010

The synthesis and photoluminescent properties of Ln(III)- thenoyltrifluoroacetonate and dibenzoylmethanate complexes (Ln = Eu(III) and Gd(III) ions) containing tertiary amides such as dimethylacetamide (DMA), dimethylformamide (DMF), and dimethylbenzamide

Full text of DOI:10.1016/j.poly.2012.02.010

Polyhedron 38 (2012) 58–67
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Structure and luminescent investigation of the Ln(III)–b-diketonate complexes
containing tertiary amides
b
c
d
Ercules E.S. Teotonio a, , Hermi F. Brito , Gilberto F. de Sá , Maria Cláudia F.C. Felinto ,
Regina Helena A. Santos e, Rodolfo Moreno Fuquen e, Israel F. Costa a, Alan R. Kennedy f,
Denise Gilmore f, Wagner M. Faustino a
⇑
a Departamento de Química, Universidade Federal da Paraíba, 58051-900 João Pessoa, PB, Brazil
b Departamento de Química Fundamental, Instituto de Química da Universidade de São Paulo, 05508-900 São Paulo, SP, Brazil
c Departamento de Química Fundamental, CCEN, Universidade Federal de Pernambuco, 50670-90 Recife, PE, Brazil
d Instituto de Pesquisas Energéticas e Nucleares, Travessa R, 400 Cidade Universitária, 05508-970 São Paulo, SP, Brazil
e Instituto de Química de São Carlos, USP, C.P. 780, 13560-970 São Carlos, SP, Brazil
f WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, Scotland, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and photoluminescent properties of Ln(III)–thenoyltrifluoroacetonate and dibenzoylmeth-
anate complexes (Ln = Eu(III) and Gd(III) ions) containing tertiary amides such as dimethylacetamide
(DMA), dimethylformamide (DMF), and dimethylbenzamide (DMB) as neutral ligands are reported. The
Ln complexes were characterized by elemental analysis, complexometric titration with EDTA, and
infrared spectroscopy. Single-crystal X-ray structure data of the [Eu(DBM)3ꢀ(DMA)] compound indicates
Received 21 November 2011
Accepted 7 February 2012
Available online 25 February 2012
Keywords:
Europium
b-Diketonate
Tertiary amides
Crystalline structure
Luminescence quantum yield
ꢀ
that this complex crystallizes in the triclinic system, space group P1 with the following cell parameters:
a = 10.2580(3) Å, b = 10.3843(2) Å, c = 22.3517(5) Å,
a = 78.906(2)°, b = 78.049(2)°, k = 63.239(2)°, V =
2066.41(9) Å3, and Z = 2. The coordination polyhedron for the Eu(III) complex may be described as an
approximate C2v distorted monocapped trigonal prism. The optical properties of the Eu(III) complexes
were studied based on the intensity parameters and luminescence quantum yield (q). The values of
the X2 parameter of the Eu–DBM complexes are larger than those for the Eu–TTA complexes, indicating
that the Eu(III) ion is in a more polarizable chemical environment in the former case. The geometries of
the complexes have been optimized by using the Sparkle Model, and the results have been used to per-
form theoretical predictions of the ligand-to-metal energy transfer via direct and exchange Coulomb
mechanisms.
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
lifetime with a magnitude around microseconds, making them
useful for biological applications. In this case, it is not surprising
Since a long time, trivalent lanthanides ions, Ln(III), are attrac-
tive in coordination chemistry. This interest is not only due their
chemical properties that differ from those presented by the transi-
tion metal ions, but also because of their unique magnetic and
spectroscopy properties [1–3]. When a lanthanide ion is in a com-
pound, many of their properties are preserved owing to the shield-
ing of 4f orbitals from the environment by outer 5s and 5p orbitals,
causing the minimal perturbation by the external field generated
by the ligands [4,5]. For example, lanthanide compounds are char-
acterized as exhibiting narrow emitting and absorption bands.
Another important characteristic of the Ln(III) ions is that their
emitting levels generally exhibit exceptionally long excited state
that these compounds are currently applied in different fields,
ranging from fluoroimmunoassay reagents to light-emitting diodes
to enable low-cost, full-color, and flat-panel displays [6–8].
Special attention has been devoted to the Eu(III) compounds, as
their chelates generally exhibit red emission with higher intensity.
Besides, the luminescent properties of the Eu(III) ion present some
peculiarities, which reflect the internal structure of the energy lev-
els for this metal ion perturbed by the ligand field. The emission
bands arising from emitting non-degenerate level 5D0 give infor-
mation about the degenerescence loss of the 7FJ states in different
chemical environments. In addition, the emission intensity rate of
the 5D0 ? 7F1 transition is allowed by magnetic-dipole mechanism
and almost insensitive to the changes in the chemical environment
around the europium ion [1]. Based on these characteristics, more
detailed theoretical and experimental studies can be performed on
the Eu(III) complexes than on other lanthanide ions. In this case, it
⇑
Corresponding author. Tel.: +55 83 3216 7591; fax: +55 83 3216 7437.
E-mail address: teotonioees@quimica.ufpb.br (E.E.S. Teotonio).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.02.010

E.E.S. Teotonio et al. / Polyhedron 38 (2012) 58–67
59
is possible to obtain information about the coordination number,
symmetry site around the metal ion, and intensity parameters up
to the number of water molecules in the first coordination sphere
of the Eu(III) ion [4,5].
DMA, DMF, and DMBZ were purchased from Merck and used with-
out any previous treatment.
2.2. Syntheses of Ln(III) complexes
One of the most important kinds of lanthanide compounds is
that based on b-diketonate ligands as luminescent sensitizers
(such as TTA, DBM, ACAC, and DPM) [1,9–12]. According to the ‘‘an-
tenna effect’’, the most important sensitization pathway of the
europium excitation in the coordination compound has an excita-
tion of the organic ligand as the first process. This sensitization oc-
curs via its singlet state (S), intersystem crossing from singlet to
triplet state, and energy transfer from the ligand triplet state (T)
to the 4f excited levels belonging to Ln(III) ions. The ligand-to-me-
tal energy transfer is dependent on the energy gap between the do-
nor state and the receptor one. The highest energy transfer rates to
the Eu(III) ion have been found when the organic ligands (anten-
nas) have the T state position around 23000 cmꢁ1 [1]. In this case,
the TTA and DBM ligands, presenting their triplet energy around
20300 and 20600 cmꢁ1, respectively, are considered excellent
luminescent sensitizers for the europium ion. Several works have
reported the structural, photo, and electroluminescent properties
of the TTA [1,13] and DBM [14–16] complexes. When these com-
plexes present water molecules in the first coordination sphere
of the Eu(III) ion, the luminescence intensity is significantly
quenched by the multiphonon decay process involving O–H oscil-
lators. On the other hand, when a second kind of ligands such as
heterocyclic, sulfoxide, phosphine oxide, and amide replace the
water molecules in the first coordination sphere of the metal, the
[Ln(TTA)3(H2O)2] and [Ln(DBM)3(H2O)] precursor complexes
(Ln(III) = Eu and Gd) were synthesized according to the literature
[9,23]. Considering that Eu and Gd complexes containing amide li-
gands were prepared in the same general way, the preparations of
the [Eu(TTA)3(DMA)2] and [Eu(DBM)3(DMA)] compounds are given
as representative.
2.2.1. [Eu(TTA)3(DMA)2]
DMA (0.26 g, 2.94 mmol) was added drop wise to a stirred solu-
tion of [Eu(TTA)3(H2O)2] (1.00 g, 1.17 mmol) in acetone (30 mL).
The reaction mixture was kept as a standby at room temperature
overnight, yielding a solid product that was washed with water
to remove the excess of dimethylacetamide ligand, filtered, and
then vacuum dried. Yield: 1.10 g (94.8%). Anal. Calc. for C32H30EuF9-
N2O8S3: C, 38.83; H, 3.03; N, 2.83; Eu, 15.35. Found: C, 38.90; H,
3.12; N, 2.73; Eu, 15.25%. IR (cmꢁ1, Nujol):
m = 1643 (m), 1610
(s), 1535 (s), 1502 (s), 1434 (s), 1412 (s), 1354 (m), 1307 (s),
1232 (m), 1180 (s), 1130 (s), 1059 (w), 933 (w), 854 (w), 781
(m), 717 (m), 679 (m), 640 (m), 579 (m), 480 (w).
2.2.2. [Eu(TTA)3(DMF)(H2O)]
Yield: 1.03 g (96.74%). Anal. Calc. for C27H21EuF9NO8S3: C, 35.77;
H, 2.11; N, 1.55; Eu, 16.76. Found: C, 36.25; H, 2.36; N, 1.97; Eu,
emission quantum efficiency (g) increases, as well as the volatility,
thermal stability, and carrier transport to electroluminescence de-
vices [17,18].
16.68%. IR (cmꢁ1, Nujol):
m = 3626 (w), 1674 (m), 1649 (s), 1599
(s), 1537 (s), 1506 (s), 1462 (s), 1412 (s), 1379 (m), 1356 (m),
1305 (s), 1250 (m), 1229 (m), 1180 (s), 1140 (s), 1063 (m), 932
(m), 858 (m), 787 (m), 720 (m), 679 (m), 640 (m), 580 (m), 492
(m), 461 (w).
Tertiary amides such as DMA and DMF are generally used as
solvents; however, their high donor ability makes it possible for
them to coordinate with metal ions in many complexes. For exam-
ple, several works in literature report the coordination of these
molecules to Ln(III) ions, acting as primary and secondary ligands
[19–22]. Although a great number of studies have been concerned
with ternary b-diketonate complexes, up to now, to the best of our
knowledge, no work has reported the structural or spectroscopic
properties of lanthanide diketonate complexes containing tertiary
amides.
Our goal in this work is to describe the synthesis, characteriza-
tion, and luminescent properties of Eu(III) and Gd(III) complexes
with TTA and DBM, along with tertiary amides such as DMA,
DMF, and DMB as secondary ligands. The photoluminescent
investigations of the complexes were discussed in terms of the
experimental intensity parameters X2 and X4, Einstein’s emission
2.2.3. [Eu(TTA)3(DMBZ)2]
Yield: 1.25 g (95.56%). Anal. Calc. for C42H34EuF9N2O8S3: C,
45.29; H, 3.08; N, 2.51; Eu, 13.64. Found: C, 45.50; H, 3.04; N,
2.70; Eu, 13.54%. IR (cmꢁ1, Nujol):
m = 1643 (m), 1606 (s), 1576
(m), 1535 (m), 1462 (s), 1412 (m), 1377 (w), 1354 (w), 1304 (s),
1234 (m), 1186 (s), 1059 (w), 1030 (w), 932 (w), 856 (w), 785
(s), 745 (m), 717 (s), 642 (m), 606 (w), 581 (m), 523 (w), 488(w),
388 (w).
2.2.4. [Eu(DBM)3(DMA)]
Single crystals of this compound were obtained from a reaction
of [Eu(DBM)3(H2O)] (1.00 g, 1.19 mmol) in acetone (20 mL) with
the dimethylacetamide ligand (0.2594 g, 2.98 mmol). After evapo-
ration of the solvent, yellow single crystals were obtained, which
were washed with distillated water and dried in vacuum desicca-
tors. Yield: 1.04 g (96.09%). Anal. Calc. for C49H42EuNO7: C, 64.76;
H, 4.66; N, 1.54; Eu, 16.72. Found: C, 64.86; H, 4.86; N, 1.53; Eu,
coefficient (A), quantum emission efficiency (g), and quantum
yield (q). Based on the single crystal X-ray data, the structure of
the [Eu(DBM)3ꢀDMA] complex has also been discussed. Theoretical
structures of the complexes were also calculated and optimized
using semiempirical Sparkle Model for the Calculation of Lanthanide
Complexes (SMLC). With the help of these data, a theoretical inves-
tigation of the ligand-to-metal energy transfer mechanism has
been performed.
16.68%. IR (cmꢁ1, Nujol):
m = 1624 (s), 1595 (s), 1547 (s), 1518
(s), 1460 (s), 1381 (s), 1307 (s), 1219 (m), 1182 (m), 1067 (m),
1024 (m), 972 (w), 935 (w), 845 (w), 812 (w), 783 (m), 754 (m),
723 (s), 689 (s), 606 (m), 513 (m), 480 (m), 447 (m), 428 (m).
2. Experimental
2.1. Reagents and syntheses
2.2.5. [Eu(DBM)3(DMF)]
Yield: 1.00 g (93.84%). Anal. Calc. for C48H40EuNO7: C, 64.43; H,
5.29; N, 1.57; Eu, 16.98. Found: C, 64.54; H, 4.99; N, 1.81; Eu,
Lanthanide oxides (Eu2O3 and Gd2O3), thenoyltrifluoroacetone
(HTTA), and dibenzoylmethane (HDBM) ligands were purchased
from Aldrich Co. and used as they had been received. The Ln2O3
were converted to their chlorides by treatment with concentrated
hydrochloride acid as described by Teotonio et al. [9]. The amides
16.84%. IR (cmꢁ1, Nujol):
m = 1661 (m), 1595 (s), 1546 (s), 1516
(s), 1458 (s), 1377 (s), 1308 (m), 1221 (m), 1178 (w), 1107 (w),
1065 (m), 1022 (m), 1000 (w), 937 (w), 783 (w), 756 (m), 721
(s), 787 (m), 608 (m), 515 (m), 449 (w), 420 (w), 382 (w).

60
E.E.S. Teotonio et al. / Polyhedron 38 (2012) 58–67
2.2.6. [Eu(DBM)3(DMBZ)]
coordinated amide ligands shows a downward shift of the amide
Yield: 1.11 g (96.00%). Anal. Calc. for C54H44EuNO7: C, 66.80; H,
I band
m
(C@O) from a higher (ꢂ1676 cmꢁ1) to lower wave number
4.57; N, 1.44; Eu, 15.65. Found: C, 64.54; H, 4.99; N, 1.81; Eu,
(ꢂ1600 cmꢁ1). These results suggest that the bonding of the amide
16.84%. IR (cmꢁ1, Nujol):
m
= 1678 (w), 1595 (s), 1547 (s), 1519
ligands to the Ln(III) ions occurs through the oxygen atoms.
(s), 1456 (s), 1377 (s), 1308 (s), 1284 (m), 1211 (m), 1176 (m),
1066 (m), 1022 (m), 999 (w), 941 (w), 860 (w), 812 (w), 783 (m),
756 (m), 721 (s), 690 (s), 647 (w), 607 (w), 511 (w), 446 (w).
3.2. Description of structure of the [Eu(DBM)3ꢀ(DMA)] complex
Single crystals of the [Eu(DBM)3ꢀ(DMA)] complex acceptable for
the X-ray diffraction analysis were growing up via slow evapora-
tion of a mixture of the starting materials, [Eu(DBM)3ꢀ(H2O)]
complex, and DMA, using acetone as a solvent. The intensity data
were taken using 123 K as temperature. Details of the data
collection and refinement parameters of the structure are pre-
sented in Table 1.
2.3. Apparatus
The carbon, hydrogen, and nitrogen percentages in the
complexes were determined from elemental analyses, using a
Perkin-Elmer model 240 microanalyzer, while the Eu(III) content
was performed by complexometric titration with EDTA [23].
The infrared absorption spectra were recorded in KBr pellets in
a Bomen model MB-102 spectrophotometer using the range of 400
up to 4000 cmꢁ1. Thermogravimetric analyses (TGA) were per-
formed by using a thermobalance TGA-50 Shimadzu under a uni-
form air flow rate of 50 mL minꢁ1 from room temperature to
The crystal structure (Fig. 1a) shows that the Eu3+ ion is seven
coordinate to six oxygen atoms from three chelating DBM ligands,
O(1–6), and one from the DMA ligand, O(7). The DMBA ligand is
disordered in the crystal structure, they are in two positions with
0.5 of occupation factors. A similar structural DMA disorder has
been observed in the lanthanide complexes by Yan and Chen
[21]. The crystal structure presents non conventional intermolecu-
lar hydrogen bonds type C–H. . .O, between C(43)–H(43)...O(4)
[1 ꢁ x, 1 + y, z (symmetry operation)] with dC...O = 3.420(4) Å,
and angle equal to 157°. This non conventional interaction pro-
duces an infinite two dimensional chain, in the (100) plane. In
the b-diketone chelate rings, the mean bond for the carbon–carbon
(C–C) is 1.38 Å, and the C–C–C mean bond angle of 121°, respec-
900 °C, with a heating rate of 5 °C minꢁ1
X-ray crystallography data were collected on an Oxford Diffrac-
tion Gemini S Kappa CCD diffractometer with a graphite-mono-
.
chromated Mo K
a radiation (k = 0.71073 Å) at 123(2) K. Data
were processed using the WinGX system [24]. The structure of
the [Eu(DBM)3ꢀ(DMA)] complex was solved by SIR2002 [25]. The
structure refinement was carried out with the SHELXL-97 [26]. The
molecular representation was made using ORTEP3 [27], and the geo-
metrical parameters were calculated using a PLATON system [28,29].
The excitation and emission spectra at room (ꢂ298 K) and li-
quid nitrogen temperature were collected at an angle of 22.5°
(front face) in a spectrofluorimeter (SPEX-Fluorolog 2) with a dou-
ble-grating 0.22 m monochromator (SPEX 1680) and a 450 W Xe-
non lamp as an excitation source. In order to eliminate the
second-order diffraction of the source radiation, a cut-off filter
was used in the measurements. All spectra were recorded by using
a detector mode correction. The luminescence decay curves of the
emitting levels were measured using a phosphorimeter SPEX
1934D accessory coupled to the spectrofluorometer. The lumines-
cence instruments were fully controlled by a DM3000F spectro-
scopic computer program, and the spectral intensities were
automatically corrected for the photomultiplier response.
tively, is consistent with the delocalization of the
p-electrons in
the chelate ring system in b-diketonates [28–31]. It is interesting
to notice that phenyl rings are twisted from the plane defined by
the chelating rings, but the twist angles are noticeably different,
as can be seen in Fig. 1a. In order to better demonstrate the twist
effect, the DBM ligands in the [Eu(DBM)3ꢀ(DMA)] complex are la-
beled as A, B, and C (Fig. 1a). The phenyl rings in the molecules
A, B, and C are twisted from the chelating ring of 9.5° and 23.9°,
22.3° and 47.1°, and 24.2° and 20.9°, respectively. It is important
to note that the twist effect observed in the [Eu(DBM)3ꢀ(DMA)]
complex is more pronounced than that presented in the hydrated
complex reported by Zalkin and Templeton [32] and Lennartson
et al. [33]. This behavior indicates that the tertiary amide DMA pro-
vides a higher steric hindrance onto the coordinated DBM ligands
than the coordinated water molecules; therefore, the phenyl
groups are orientated in order to minimize steric repulsion among
3. Results and discussion
3.1. Characterization of the complexes
Table 1
Crystal Data and Details of the Structure Determination for the [Eu(DMB)3(DMA)]
complex.
The percentages of the Ln(III) ions were determined by com-
plexometric titration with EDTA, where the Ln-complexes were
dissolved in methanol using xylenol orange as an indicator. These
data together with the results of the elemental analysis of C, H, and
N reveal the general formulas [Ln(TTA)3ꢀL2] and [Ln(DBM)3ꢀL] for
the complexes. Although the same synthetic route had been ap-
plied to obtain the complexes, the Ln–TTA-complexes with DMF
were only obtained as a monohydrated one, presenting the formula
[Ln(TTA)3ꢀDMFꢀH2O]. Similar quaternary complexes presenting
formula [Ln(Nic)3ꢀDMFꢀH2O], where Nic is the ligand pyridine-3-
carboxylate, were synthesized by Yan and Xie [19].
Formula
C49H42EuNO7
908.80
Formula weight
Crystal system
Space group
a, b, c (Å)
triclinic
ꢀ
P1
10.2580(3), 10.3843(2), 22.3517(5)
a
, b,
V (Å3)
Z, Dcalc (g/cm3)
(Mo K
) (mmꢁ1
F(000)
c
(°)
78.906(2), 78.049(2), 63.239(2)
2066.41(9)
2, 1.461
1.571
924
l
a
)
Crystal size (mm)
T (K)
0.18 ꢃ 0.20 ꢃ 0.24
123
k (Mo K
h (°) min:max
hkl max:min
Total, Unique Data, R(int)
Observed data [I > 2.0
Nref, Npar
a
) (Å)
0.71073
2.7:30.3
The infrared spectral data of the Ln–b-diketonate complexes
with the tertiary amide ligands (except those of the [Ln(TTA)3ꢀ
DMFꢀH2O] complexes) as compared with those of the hydrated pre-
cursors (figures not shown) do not present a broad band around
3500 cmꢁ1 assigned to the O–H stretching of the H2O molecules,
indicating a complete substitution of the water molecules by the
tertiary amide ligands in the first coordination sphere of the Ln(III)
ion. The comparison between the infrared spectra of the free and
ꢁ14:13; ꢁ14:14; ꢁ29:31
26471, 10963, 0.035
8929
10963, 544
0.0295, 0.0514, 0.92
0.00, 0.00
r(I)]
R, wR2, S
Max. and Avg. shift/error
Min. and Max. Resd. Dens. (e/Å3)
ꢁ0.66, 0.64

E.E.S. Teotonio et al. / Polyhedron 38 (2012) 58–67
61
Fig. 1. (a) ORTEP3 drawing (50% of probability) displaying the X-ray structure of the [Eu(DBM)3(DMA)] complex, the H atoms and the DMA disorder are omitted for clarifying
and (b) coordination polyhedron of Eu3+ ion in the [Eu(DBM)3(DMA)].
the ligands. Twists of the DBM anion were also reported in
Refs. [34,35]. Another significant structural difference between
[Eu(DBM)3ꢀ(DMA)] and the hydrated complexes is the weak inter-
molecular interactions.
O(x)–Eu(1)–O(x0) (where x = 1, 2, 3, 4, 5, and 6) in the first coordi-
nation sphere. The interatomic distances Eu(1)–O(x) have an aver-
age value of 2.3 Å.
The seven-coordinated {EuO7} polyhedron can be described as a
C2v distorted monocapped trigonal prism, in which the C2 axis
crosses the oxygen atom from DMA (Fig. 2b), being the capping
ligand for the amide oxygen atom. Table 2 presents the distances
from the Eu(1) center to oxygen atoms and the angles
3.3. Thermogravimetric data
Thermogravimetric (TG) curves of the TTA and DBM-complexes
recorded from 25 to 900 °C are presented in Fig. 2a and b, respec-
tively. As can be seen in Fig. 2a, the TG curve for the hydrated

62
E.E.S. Teotonio et al. / Polyhedron 38 (2012) 58–67
(a) 100
90
80
70
60
50
40
30
20
[Eu(TTA)3(H2O)2]
[Eu(TTA)3(DMA)2]
[Eu(TTA)3(DMF)(H2O)]
[Eu(TTA)3(DMB)2]
200
400
600
800
Temperature / oC
(b) 100
[Eu(DBM)(H2O)]
[Eu(DBM)3(DMA)]
[Eu(DBM)3(DMF)]
[Eu(DBM)3(DMB)]
90
80
70
60
50
40
30
20
10
200
400
600
800
Temperature / oC
Fig. 2. TG curves of the complexes (a) [Gd(TTA)3L2] and (b) [Gd(DBM)3L] (where L = H2O, DMA, DMF, and DMB). The complex containing TTA and DMF ligands presents the
formula [Gd(TTA)3(DMF)(H2O)].
[Eu(TTA)3ꢀ(H2O)2] complex displays the first weight loss event up
Table 2
to 120 °C that corresponds to 4.3% of the initial weight. These data
Selected bond lengths (Å) and angles (°) around the europium ion for the
[Eu(DMB)3(DMA)] complex.
agree with the loss of the two water molecules. The TG curve of the
[Eu(TTA)3ꢀDMFꢀH2O] complex presents a weight loss (2%) in the
Bond lengths
Eu–O1
Eu–O3
Eu–O5
Eu–O7(DMA)
temperature range of 25–120 °C, which is attributed to the dehy-
dration process. All of the TTA-amide complexes show weight
losses starting around 120 up to 250 °C, which can be assigned to
the release of amide ligands. This event is followed by an abrupt
weight loss until a temperature of about 400 °C, which might be
attributed to the decomposition of the Eu(TTA)3 system. The
decomposition process was completed around 850 °C, resulting
in a white Eu2O3 as the final product (approximately 20% of the
original weight).
2.337(2)
2.343(1)
2.343 (2)
2.341(2)
Eu–O2
Eu–O4
Eu–O6
2.313(2)
2.349(2)
2.342(1)
Bond angles
O1–Eu–O2
O1–Eu–O4
O1–Eu–O6
O2–Eu–O3
O2–Eu–O5
O2–Eu–O7
O3–Eu–O5
O3–Eu–O7
O4–Eu–O6
O5–Eu–O6
O6–Eu–O7
73.50(6)
149.13(6)
88.43(5)
82.24(6)
76.78(6)
155.66(6)
128.07(5)
85.49(6)
111.32(5)
72.08(5)
74.71(6)
O1–Eu–O3
O1–Eu–O5
O1–Eu–O7
O2–Eu–O4
O2–Eu–O6
O3–Eu–O4
O3–Eu–O6
O4–Eu–O5
O4–Eu–O7
O5–Eu–O7
81.13(5)
134.28(6)
83.91(6)
116.40(6)
112.82(6)
72.04(5)
158.51(6)
75.91(6)
79.13(6)
126.87(6)
The TG curves of the Eu-DBM complexes (Fig. 2b) with amide
ligands do not show any weight loss until further heating to
150 °C, which suggests that these compounds are anhydrous. The
weight losses that occur in the range from 150 to 260 °C can be
attributed to losses of amide ligands. After three consecutive
weight losses until 850 °C, Eu2O3 was obtained as the final product.

E.E.S. Teotonio et al. / Polyhedron 38 (2012) 58–67
63
3.4. Theoretical geometries of the complexes
of the Eu–TTA-amide systems are better described as distorted
dodecahedrons.
The geometries of the europium complexes were obtained by
using an improved version of the semiempirical Sparkle Model for
the Calculation of Lanthanide complexes (SMLC), implemented into
the MOPAC6 package, according to the procedure described in Refs.
[36]. The theoretical geometries of the [Eu(DBM)3L] complexes
were optimized using the experimental structural data of the
[Eu(DBM)3(DMA)] complex as starting geometry. Thus, the input
geometries of the [Eu(DBM)3(DMF)] and [Eu(DBM)3(DMB)] com-
plexes where obtained by substitution of the methyl in the acetyl
amide moiety by H and phenyl groups, respectively. Since X-ray
structural data were not obtained for the [Eu(TTA)3L2] complexes,
the input geometries for this kind of compounds were obtained by
using the HYPERCHEM program [37].
3.5. Luminescence study of the lanthanide complexes
The excitation spectra of the Eu(III) TTA and DBM complexes in
the solid state were recorded from 250 to 590 nm at a liquid nitro-
gen temperature, on monitoring the emission intensity of the
5D0 ? 7F2 transition (Fig. 3). These spectra are dominated by the
broad bands in the spectral interval from 250 to 500 nm that are
assigned to the centered singlet–singlet b-diketonate ligand
transitions. This result indicates that the luminescence from
Eu(III)–b-diketonate-amide complexes is a consequence of the sen-
sitization of the europium excited state by energy transfer from the
ligands. Besides, the spectra show narrow bands due to excitation
from the 7F0 ground state to 5L6 (overlapped by the centered ligand
transitions), 5D3 (ꢂ448 nm), 5D2 (ꢂ464 nm), 5D1 (ꢂ525 nm), and
5D0 (ꢂ579 nm) excited states. The spectrum of the complex con-
taining the DMB amide is quite different from the spectra of the
other complexes, indicating a higher disturbance caused by this
ligand in comparison with the otherwise complexes, probably
because of its steric effects.
The theoretical geometry obtained for the complex Eu
(DBM)3(DMA)] agrees with the experimental one. The coordination
polyhedra obtained via the SMLC method for all of the Eu–DBM-
amide complexes might be described as distorted monocapped tri-
gonal prisms, while the eight-coordinate {EuO8} polyhedra for all
Fig. 4 shows the emission spectra of the TTA and DBM
Eu-complexes, under excitation at 350 nm. These spectra consist
of sharp bands assigned to the intraconfigurational 5D0 ? 7FJ tran-
sitions (J = 0–4), being the band attributed to the hypersensitive
5D0 ? 7F2 dominating. Several less intense bands are also observed
in the range of 500–570 nm, which correspond to the transitions:
5D1 ? 7F0 (526 nm), 5D1 ? 7F1 (536 nm), and 5D1 ? 7F2 (557 nm).
The emission spectra of the Eu–TTA-amide complexes (Fig. 4a)
present similar profiles, indicating that the DMA and DMF ligands
distort the structure of the diketonate ligands in a similar way con-
ducting very close site symmetry around the Eu3+ ion. On the other
hand, the steric hindrance due the DMB ligand is higher than those
from the other amide ligands, which cause a more pronounced dis-
tortion in the complexes, lowering the symmetry around the metal
ion, which is in agreement with the excitation spectra features just
discussed. The phosphorescence broad band from diketonate
ligands is not present in any spectra, which suggests that the intra-
molecular ligand-to-metal energy transfer is very efficient.
Analysis of the emission bands corresponding to the 5D0 ? 7FJ
transitions for the [Eu(TTA)3(amide)] complexes shows that these
bands split in a number of components expected by both the coor-
dination polyhedral obtained via X-ray diffraction and theoretical
structural data. In this case, 5D0 ? 7F1 transitions exhibit two more
closely spaced higher-energy components, which are compatible
with a pseudo-C3v symmetry around the Eu3+ ion.
(a)
[Eu(TTA)3(H2O)2]
[Eu(TTA)3(DMA)2]
[Eu(TTA)3(DMF)(H2O)]
[Eu(TTA)3(DMB)2]
250
300
350
400
λ (nm)
450
500
550
[Eu(DBM)3(H2O)]
[Eu(DBM)3(DMA)]
[Eu(DBM)3(DMF)]
[Eu(DBM)3(DMB)]
(b)
Emission spectra of the [Eu(DBM)3(amide)] complexes display
a
nearly identical pattern, but more splitting than in the
precursor hydrated complex, reflecting the distortion of the amide
coordination.
In order to evaluate the efficiency of luminescence of the euro-
pium complexes, the luminescence quantum yield (q) and the
intrinsic quantum efficiency (
tally determined [1,38,39].
g
) of the Eu3+ ion were experimen-
The values of
g were calculated from the ratio Arad/Atotal, where
Arad and Atotal are radiative and total rates assigned to the decay
processes of the 5D0 emitting level, respectively. In this case, the
Arad values were obtained by summing the radiative spontaneous
coefficients due to the 5D0 ? 7FJ transitions, while Atotal ones were
250
300
350
400
λ (nm)
450
500
550
determined from the lifetime values of the 5D0 emitting level (
s
) by
considering the reciprocal relation between these properties
(Atotal = 1/ ). Further specific details about these parameters are
Fig. 3. Excitation spectra of the europium complexes recorded at nitrogen liquid
temperature with emission monitored on the hypersensitive 5D0 7F2 transition:
(a) [Eu(TTA)3L2] and (b) [Eu(DBM)3L] (where L = H2O, DMA, DMF, and DMB).
The complex containing TTA and DMF ligands presents the formula
[Eu(TTA)3(DMF)(H2O)].
s
?
reported in the literature [1].
The quantum efficiency of the 5D0 emitting level (
g) for the
b-diketonate complexes are presented in Table 3. The data reveal

64
E.E.S. Teotonio et al. / Polyhedron 38 (2012) 58–67
(a)
[Eu(TTA)3(DMB)2]
[Eu(TTA)3(DMF)(H2O)]
[Eu(TTA)3(DMA)2]
[Eu(TTA)3(H2O)]
450
500
550
600
650
700
(b)
[Eu(DBM)3(DMB)]
[Eu(DBM)3(DMF)]
[Eu(DBM)3(DMA)2]
[Eu(DBM)3(H2O)]
45 0 50 0 55 0 600 65 0 70 0
λ (nm)
Fig. 4. Emission spectra of the europium complexes recorded at nitrogen liquid temperature with excitation monitored at 350 nm: (a) [Eu(TTA)3L2] and (b) [Eu(DBM)3L]
(where L = H2O, DMA, DMF and DMB). The complex containing TTA and DMF ligands presents the formula [Eu(TTA)3(DMF)(H2O)].
Table 3
Experimental intensity parameters for the [Eu(TTA)3L2] and [Eu(DBM)3L] complexes, where L = H2O, DMA, DMF, and DMB.
Complexes
X2
X4
Arad
Anrad
Atot
g
(%)
qexp (%)
qcalc (%)
[Eu(TTA)3(H2O)2]a
[Eu(TTA)3(DMA)2]
[Eu(TTA)3(DMF)(H2O)]
[Eu(TTA)3(DMB)2]
[Eu(DBM)3(H2O)]
[Eu(DBM)3(DMA)]
[Eu(DBM)3(DMF)]
[Eu(DBM)3(DMB)]
33.0
36.9
23.8
36.4
19.9
51.0
44.3
46.5
4.6
9.3
9.1
7.6
4.4
6.7
6.8
8.6
1110
1295
904
1255
716
1752
1491
1488
2730
498
651
3846
1793
1555
1524
2845
2941
2438
3930
29
72
58
82
25
60
61
38
23
78
45
81
–
45
43
–
28
71
57
81
25
59
60
–
269
2129
1189
947
2442
a
Ref. [1].
where A0k are the coefficients of spontaneous emission,
v is the Lor-
that the substitution of water molecules by the tertiary amides
significantly increases the quantum efficiency of the europium
complexes. The Eu–TTA-complex with DMF was only obtained in
the monohydrated form [Eu(TTA)3ꢀ(DMF)(H2O)]. The lowest value
entz local field correction term that is given by
v
= n(n2 + 2)2/9 with
2
ðkÞ
7
5
the refractive index n = 1.5, and matrix elements h FkkU k D0i are
described in Ref. [41]. In this work, the X6 parameter was not
experimentally determined due to the low intensity of the
5D0 ? 7F6 transition.
of
g determined for this complex (g = 58%) is owing to the presence
of only one water molecule in the first coordinated sphere of the
Table 3 presents the experimental intensity parameters for the
TTA and DBM-complexes with the tertiary amide ligands. Among
the TTA and DBM complexes, the highest values of the intensity
parameter X2 are observed for those complexes with DMA and
DBM ligands. Since this parameter is usually related to the degree
of covalent character of the lanthanide metal ion-ligand bond [1],
the results can be explained in terms of the inductive effect of
Eu(III) ion [40].
Experimental Judd–Ofelt intensity parameters for the Eu(III)
ion in the complexes are determined by the following Eqs. (1)
and (2)
4e2
x
3A0k
ðkÞ
Xk
¼
ð1Þ
2
7
5
3ꢀhc3
v
h FkkU k D0i

E.E.S. Teotonio et al. / Polyhedron 38 (2012) 58–67
65
the substituting CH3 and phenyl in the DMA and DBM, respectively,
which increase the polarizability of the oxygen atom coordinated
to the europium ion. In addition, it is also seen that the complexes
with DBM present values of X2 parameters higher than those with
TTA. Based on the dynamic-coupling model, this behavior may be
also due to ligand polarizability, considering that the phenyl
groups make the DBM ligand more polarizable than the trifluorom-
etane substituent in the TTA anion.
The energy values (singlet; triplet states) for the Gd–diketonate
complexes are the following (in cmꢁ1): [Gd(TTA)3(H2O)2] (29498;
20325); [Gd(TTA)3(DMA)2] (29240; 20921); [Gd(TTA)3(DMF)-
(H2O)] (29498; 20747); [Gd(TTA)3(DMB)2] (29283; 20833);
[Gd(DBM)3ꢀH2O] (29718; 20534); [Gd(DBM)3DMA] (29718;
21186); [Gd(DBM)3DMF] (29762; 21186); [Gd(DBM)3DMB]
(29369; 21277).
3.6. Intramolecular b-diketonate-to-Eu3+ energy transfer
Experimental singlet and triplet energies of the ligands in the
complexes were applied to calculate the energy transfer processes
of the ligand-to-lanthanide ion and to investigate the luminescent
properties of Eu(III) compounds. In this case, the experimental sin-
glet energies were assumed as the energy corresponding to max-
In order to obtain information about intramolecular b-diketo-
nate to Eu(III) ion energy transfer in the complexes, the energy
transfer WET rates were calculated according to the theoretical
model previously described in the literature [1].
ima absorbance in the absorption spectra (assigned to the
p ?
p⁄
transitions). In contrast, triplet energies were estimated as the en-
ergy corresponding to the shortest wavelength (0–0 phonon tran-
sition) on the basis of the phosphorescence spectra of the
gadolinium complexes recorded at 77 K, under an excitation at
377 nm (Fig. 5) [1,9,23].
In this work, the following ligand-to-metal energy transfer
pathways are considered: S1 ? 5D4, T ? 5D1 and T ? 5D0, which
are based on the relative energy position of the donor ligand and
acceptor Eu3+ states. Table 4 shows the values of the energy trans-
fer and back-energy transfer rates of the complexes. According to
the selection rules for the ligand-to-europium ion energy transfer
process, the S1 ? 5D4 (Eu3+) pathway is dominated by the 2k-mul-
tipolar mechanism, while the T ? 5D1 and T ? 5D0 ones are mainly
due to the exchange mechanism.
Among the energy transfer rates (Tables 4 and 5), low values are
obtained for the S1 ? 5D4 channel (ꢂ9.1 ꢃ 106 sꢁ1), indicating that
the 2k-multipolar mechanism plays a few roles in the energy trans-
fer from the TTA or DBM ligands to Eu3+ ion. On the other hand, the
T ? 5D1 and T ? 5D0 pathways have energy transfer rates
(ꢂ1.0 ꢃ 1010 sꢁ1) around four orders of magnitude higher than
the latter, indicating that direct ligand-to-metal energy transfer
is dominated by the exchange mechanism. Although the T ? 5D1
(a)
[Gd(TTA)3(H2O)2]
[Gd(TTA)3(DMA)2]
[Gd(TTA)3(DMF)(H2O)]
[Gd(TTA)3(DMB)2]
Table 4
Energy transfer rates from ligand states (singlet and triplet) to europium levels 2S+1LJ
(Eu3+) in the [Eu(TTA)3(L)2] complexes, where L = H2O, DMA, DMF, and DMB ligands.
Complexes
Non-radiative
transitions
Energy transfer
rates (sꢁ1
Back-transfer
rates (sꢁ1
)
)
[Eu(TTA)3(H2O)2]
S ? 5D4
T ? 5D1
T ? 5D0
9.17 ꢃ 106
2.21 ꢃ 1010
1.15 ꢃ 1010
9.55 ꢃ 106
1.92 ꢃ 1010
8.43 ꢃ 109
8.99 ꢃ 106
2.01 ꢃ 1010
9.28 ꢃ 109
1.08 ꢃ 103
5.60 ꢃ 107
3.93 ꢃ 103
3.86 ꢃ 103
2.84 ꢃ 106
1.68 ꢃ 102
1.06 ꢃ 103
6.82 ꢃ 106
4.24 ꢃ 102
450
500
550
600
650
700
λ (nm)
[Eu(TTA)3(DMA)2]
[Eu(TTA)3(DMF)(H2O)]
[Eu(TTA)3(DMB)2]
S ? 5D4
T ? 5D1
T ? 5D0
S ? 5D4
T ? 5D1
T ? 5D0
[Gd(DBM)3H2O]
[Gd(DBM)3DMA]
[Gd(DBM)3DMF]
[Gd(DBM)3DMB]
(b)
S ? 5D4
T ? 5D1
T ? 5D0
9.54 ꢃ 106
1.97 ꢃ 1010
8.85 ꢃ 109
3.14 ꢃ 103
4.43 ꢃ 106
2.69 ꢃ 102
Table 5
Energy transfer rates from ligand states (singlet and triplet) to europium levels 2S+1LJ
(Eu3+) in the [Eu(DBM)3L] complexes, where L = H2O, DMA, and DMF ligands.
Complexes
Non-radiative
transition
Energy transfer
rates (sꢁ1
Back-transfer
rates (sꢁ1
)
)
[Eu(DBM)3(H2O)]
S?5D4
T?5D1
T?5D0
S?5D4
T?5D1
T?5D0
S?5D4
T?5D1
T?5D0
8.23 ꢃ 106
2.12 ꢃ 1010
1.04 ꢃ 1010
8.32 ꢃ 106
1.77 ꢃ 1010
7.20 ꢃ 109
8.65 ꢃ 106
1.77 ꢃ 1010
7.20 ꢃ 109
3.41 ꢃ 102
1.98 ꢃ 107
1.31 ꢃ 103
3.44 ꢃ 102
7.41 ꢃ 105
40.7
450
500
550
600
650
700
[Eu(DBM)3(DMA)]
[Eu(DBM)3(DMF)]
λ(nm)
2.90 ꢃ 102
7.41 ꢃ 105
40.7
Fig. 5. Phosphorescence spectra of the gadolinium complexes recorded at nitrogen
liquid temperature with excitation monitored at 350 nm: (a) [Gd(TTA)3L2] and (b)
[Gd(DBM)3L] (where L = H2O, DMA, DMF and DMB). The complex containing TTA
and DMF ligands presents the formula [Gd(TTA)3(DMF)(H2O)].

66
E.E.S. Teotonio et al. / Polyhedron 38 (2012) 58–67
channel presents the highest values of WET (Table 4), it also exhib-
its the highest values of back-energy transfer rates. This behavior
reflects the small difference (ꢂ1500 cmꢁ1) between donor triplet
and acceptor 5D1 states. The calculated values of WET and WBET re-
flect the optimum relative energy of the T and 5D0 states that pro-
vides high values of WET and minimizes the back-energy transfer
process. Consequently, this result suggests that the net excitation
of Eu3+ ion in the complexes is significantly dependent on the
T ? 5D0 channel.
The optical data in the Tables 4 and 5 suggest that no significant
difference between the energy transfer processes exists for the
complexes with TTA and DBM ligands. However, the WBET values
are higher in the complexes with the TTA ligand, which probably
reflects the relative position of the donor and acceptor states. It
is important to mention that the ligand-to-Eu3+ ion charge-transfer
states have been neglected in the present calculations. Although
this approximation could attribute more serious problems in some
Eu3+-complexes, it is considered less important in the diketonate
complexes with neutral ligands.
From the energy transfer rates presented in Tables 4 and 5 and
solving an appropriate set of rate equations in the stationary state,
including radiative and non-radiative processes, luminescence
quantum yields of the Eu3+–diketonate complexes with neutral
amide ligands have been calculated. The theoretical analysis was
performed for the normalized populations of the ligand and metal
ion states, according to the procedure described by de Sá et al. [1].
The calculated values of luminescence quantum yield are also
summarized in Tables 4 and 5. The experimental quantum yield
(qexp) of the complexes in the solid state are determined according
to the modified procedure developed by Bril and co-workers
[38,39] with some experimental modifications [42]. In this work,
magnesium oxide and sodium salicylate were used as reflectance
and luminescent standard materials, respectively. The value of qexp
for [Eu(DBM)3(DMB)] complex was not determined owing to the
hygroscopic behavior of the sample.
more polarizable chemical environment around the Eu(III) ion is
in this system than in the TTA-complexes. The complexes contain-
ing tertiary amides coordinated with europium present high values
of experimental quantum yield (q), which is similar to other Eu-
diketonate complexes reported in the literature.
Acknowledgments
This research is supported by grants from the Conselho Nacion-
al de Desenvolvimento Científico e Tecnológico (CNPq), Instituto
Nacional de Ciência e Tecnologia-Nanotecnologia para Marcadores
Integrados (INCT-INAMI), PRONEX, and Fundação de Amparo à Pes-
quisa do Estado de São Paulo (FAPESP).
Appendix A. Supplementary data
CCDC nꢄ 854223 contains the supplementary crystallographic
data for complex [Eu(DBM)3(DMA)]. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033;
or e-mail: deposit@ccdc.cam.ac.uk.
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Six Eu(III)-diketonate complexes containing tertiary amides
were synthesized and characterized. The characterization methods
indicate that the complexes present the general formulas
[Ln(TTA)3ꢀL2] and [Ln(DBM)3ꢀL], where L = H2O, DMA, DMF, and
DMB, except the TTA-complex with DMF presents the formula
[Eu(TTA)3ꢀ(DMF)(H2O)]. The site symmetry close to C2V or C3V
determined on the basis of the photoluminescent spectrum for
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SPARKLE theoretical method. The higher values of the intensity
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