Synthesis, characterization and fluorescence properties of Eu(III) and Tb(III) complexes with novel mono-substituted β-diketone ligands and 1,10-phenanthroline

Article abstract of DOI:10.1016/j.saa.2008.10.059

Two novel pyridine-2,6-dicarboxylic acid derivatives of mono-β-diketone, methyl 6-benzoylacetyl-2-pyridinecarboxylate (MBAP) and 6-benzoylacetyl-2-pyridinecarboxylic acid (BAPA) and their Eu(III) and Tb(III) complexes were synthesized and characterized by elemental analysis, FT-IR, ¹H NMR and TG-DTG. Moreover, their Eu(III) and Tb(III) complexes using 1,10-phenanthroline as a secondary ligand were prepared and characterized. The luminescence properties of these complexes in solid state were investigated in detail. The results suggested that Tb(III) complexes exhibit more efficient luminescence than Eu(III) complexes, the fluorescence intensity of Ln(III) complexes with BAPA is about twice as strong as that of Ln(III) complexes with MBAP, the fluorescence of mono-β-diketone complexes using 1,10-phenanthroline as a secondary ligand was prominently higher than that of complexes without adding 1,10-phenanthroline, and the ligand BAPA is an excellent sensitizer to Eu(III) and Tb(III) ion.

Full text of DOI:10.1016/j.saa.2008.10.059

Spectrochimica Acta Part A 72 (2009) 703–708
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization and fluorescence properties of Eu(III) and Tb(III)
complexes with novel mono-substituted ␤-diketone ligands and
1,10-phenanthroline
Yi-Ming Luo∗, Jun Li, Lin-Xiang Xiao, Rui-Ren Tang, Xin-Cun Tang
College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 June 2008
Received in revised form 30 October 2008
Accepted 31 October 2008
Two novel pyridine-2,6-dicarboxylic acid derivatives of mono-␤-diketone, methyl 6-benzoylacetyl-2-
pyridinecarboxylate (MBAP) and 6-benzoylacetyl-2-pyridinecarboxylic acid (BAPA) and their Eu(III) and
Tb(III) complexes were synthesized and characterized by elemental analysis, FT-IR, 1H NMR and TG–DTG.
Moreover, their Eu(III) and Tb(III) complexes using 1,10-phenanthroline as a secondary ligand were
prepared and characterized. The luminescence properties of these complexes in solid state were inves-
tigated in detail. The results suggested that Tb(III) complexes exhibit more efficient luminescence than
Eu(III) complexes, the fluorescence intensity of Ln(III) complexes with BAPA is about twice as strong
as that of Ln(III) complexes with MBAP, the fluorescence of mono-␤-diketone complexes using 1,10-
phenanthroline as a secondary ligand was prominently higher than that of complexes without adding
1,10-phenanthroline, and the ligand BAPA is an excellent sensitizer to Eu(III) and Tb(III) ion.
© 2008 Elsevier B.V. All rights reserved.
Keywords:
Mono-␤-diketone
1,10-Phenanthroline
Eu(III) and Tb(III) complexes
Synthesis
Fluorescence
1. Introduction
pyridine-2,6-dicarboxylic acid (DPA) [13]. Our group has designed
and prepared two pyridine-2,6-dicarboxylic acid derivative lig-
Rare earth complexes with ␤-diketone ligands have attracted
considerable attention because of their high and sharply spiked
fluorescence emission efficiency, long lifetime, large Stoke’s shift
caused by the high absorption coefficient of ␤-diketone structure
[1]. This kind of complexes have promising applications in material
science such as luminescent probes [2], sensory materials [3] and
organic light-emitting devices (OLEDs) [4–6]. Many ␤-diketone-
type ligands and their lanthanide complexes have been reported
and investigated such as butyl methoxy-dibenzoyl-methane,
N-(2-amino-6-methyl-pyridinyl)ketoacetamide (BMDM),3-[3-5-
bis(phenylmeth-oxy)phenyl]-1-(9-phenanthryl-1)propane-1,3-
dione (PPD),1-phenyl-3-methyl-4(4-butylbenzoyl)-5-pyrazo-lone
(HPMBBP) and thenoyltrifluoroacetone (HTTA) [7–11], however,
either their absorption coefficients of the optical transitions
for these ions are low, or the thermal stability and mechanical
properties of the complexes are poor, which limits their practical
application considerably.
ands of bis-␤-diketone, and found that their Eu(III) and
Tb(III) complexes display relatively weak fluorescence intensity
[14,15], in an attempt to increase the fluorescence intensity of
the lanthanide complexes, in this paper, two novel pyridine-
2,6-dicarboxylic acid derivatives of mono-␤-diketone named
methyl 6-benzoylacetyl-2-pyridinecarboxylate (MBAP) and 6-
benzoylacetyl-2-pyridinecarboxylic acid (BAPA) and their Eu(III)
and Tb(III) complexes were synthesized. Both of the two novel
mono-␤-diketone ligands have rigid conjugated planar struc-
ture, carboxylate group or carboxyl group, which would be of
potential applications in time-resolved fluoroimmunoassay and
DNA probe. In addition, we prepared Eu(III) and Tb(III) mono-
␤-diketone complexes using 1,10-phenanthroline as a secondary
ligand since 1,10-phenanthroline is widely used as assistant
antenna groups for photosensitising lanthanide ion. The lumi-
nescence properties of all these complexes in solid state were
investigated in detail. The synthetic route of ligands is listed in
Scheme 1.
With an aim to develop novel optical materials, in recent
years, some rare earth complexes with ␤-diketone, aromatic
carboxylic acid and heterocyclic carboxylic acid group were
under development, such as benzoyl acetone (BA) [12] and
2. Experimental
2.1. Materials
∗
All starting materials were of AR grade and used without further
purification except that rare earth chlorides and dimethyl 2,6-
Corresponding author. Fax: +86 731 8879616.
E-mail address: ymluo@mail.csu.edu.cn (Y.-M. Luo).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.10.059

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Y.-M. Luo et al. / Spectrochimica Acta Part A 72 (2009) 703–708
Scheme 1. Synthesis of the ligands (MBAP and BAPA).
pyridinedicarboxylate were prepared according to the literature
methods [16–18]. Solvents were purified with conventional meth-
ods.
(10 ml) was added dropwise under stirring at 60 ◦C for 4 h [19],
the red precipitate was filtered and a yellow solid obtained was
washed with petroleum ether to remove unreacted starting mate-
rial. Addition of aqueous HCl (15 ml, 2 mol/l) led to precipitation of
yellow powder which was washed well with water. Recrystaliza-
tion from ethyl acetate gave a yellow crystal, which was dried in
a vacuum. Yield: (6.3 g, 73.7%). m.p. 116–118 ◦C. Elemental analyti-
cal (calc.) C% 67.53 (67.84), H% 4.62 (4.59), N% 4.88 (4.94). IR (KBr,
2.2. Instrumentation
Melting points were determined on a XR-4 apparatus (ther-
mometer uncorrected). Elemental analysis (C, H, N) was performed
on a Elemental vario EL elemental analyzer. The lanthanide content
was determined by EDTA titration. Infrared spectra were recorded
on a Nicolet NEXUS 670 FTIR spectrometer between KBr plates in
pellet): ꢀmax (cm−1); 3424 (C
C OH), 3065 (Ar H), 2947 (CH2),
1753 (CH3OC O), 1720 (diketone C O), 1601, 1570 (C C, C N)Ar,
1448, 1433 (C C, C N)Ar; 1H NMR (400 MHz, CDCl3): 16.5 (s, 1H,
C
C OH), 8.04–8.32 (m, 3H, C5H3N), 7.25–7.75 (m, 5H, C6H5), 7.14
the range of 4000–400 cm−1 1H NMR spectra were measured with
.
(s, 1H, CH ), 4.03 (s, 3H, OCH3).
a Bruker-400 MHz nuclear magnetic resonance instrument using
CDCl3 as solvent and TMS as internal reference. Thermogravimet-
ric (TG) and differential thermal gravimetry (DTG) were performed
in the nitrogen atmosphere using a Shimadzu DTG 40 system at
a heating rate of 10 ◦C min−1 from 30 ◦C to 700 ◦C. Fluorescence
measurements were made on a Hitich F-4500 spectrometer, the
excitation and emission slit widths were 5 nm and 2.5 nm, respec-
tively with PMT voltage at 400 V.
2.4. Synthesis of 6-benzoylacetyl-2-pyridinecarboxylic acid
To a solution of methyl 6-benzoylacetyl-2-pyridinecarboxylate
(0.50 g, 1.75 mmol)in acetone (10 ml) was added 30% aqueous NaOH
(0.28 g, 7 mmol) under stirring at r.t. for 5 h, the precipitate was
filtered and a yellow solid afforded was washed with acetone.
Addition of aqueous HCl (15 ml, 2 mol/l) led to precipitation of a
yellowish powder which was washed well with water. Recrystal-
ization from ethanol gave a yellowish crystal, which was dried in a
vacuum. Yield: (0.45 g, 98%). m.p. 142–144 ◦C. Elemental analytical
(calc.) C% 66.62 (66.91), H% 4.15 (4.09), N% 5.11 (5.20). IR (KBr, pel-
2.3. Synthesis of methyl 6-benzoylacetyl-2-pyridinecarboxylate
Flaky sodium (0.69 g, 0.03 mol) was added to a solution of
dimethyl 2,6-pyridinedicarboxylate (5.9 g, 0.03 mol) in dry toluene
(70 ml), and then acetophenone (0.36 g, 0.03 mol) in dry toluene
let): ꢀmax (cm−1); 3467 (C
(COOH), 1693 (diketone C O), 1605, 1574 (C C, C N)Ar, 1464, 1429
C OH), 3060 (Ar H), 2884 (CH2), 1717

Y.-M. Luo et al. / Spectrochimica Acta Part A 72 (2009) 703–708
705
Table 1
Elemental analytical data for the complexes.
Complex
C (%) found(calc.)
50.79(51.11)
H (%) found(calc.)
N (%) found(calc.)
Ln (%) found(calc.)
Eu(MBAP)3·7H2O
4.81(4.70)
4.37(4.57)
4.49(4.33)
4.34(4.29)
4.53(4.67)
4.32(4.54)
4.12(4.30)
4.09(4.26)
3.57(3.72)
5.71(5.57)
3.71(3.87)
5.52(5.72)
3.81(3.70)
5.70(5.53)
3.71(3.85)
5.56(5.68)
13.22(13.48)
15.20(15.11)
14.17(14.01)
15.28(15.54)
14.19(14.02)
15.51(15.69)
14.63(14.56)
16.28(16.14)
Eu(MBAP)2(Phen)·6H2O
Eu(BAPA)3·7H2O
52.13(52.48)
50.01(49.76)
51.67(51.53)
50.35(50.79)
52.40(52.12)
49.82(49.45)
51.39(51.17)
Eu(BAPA)2(Phen)·6H2O
Tb(MBAP)3·7H2O
Tb(MBAP)2(Phen)·6H2O
Tb(BAPA)3·7H2O
Tb(BAPA)2(Phen)·6H2O
(C C, C N)Ar; 1H NMR (400 MHz, CDCl3): 16.46 (s, 1H, C
C OH),
3.2. Infrared spectra
10.7 (s, 1H, COOH), 8.15–8.45 (m, 3H, C5H3N), 7.42–8.06 (m, 5H,
C6H5), 7.26 (s, 1H, CH ).
The IR spectral data of the ligands and their lanthanide(III) com-
plexes were listed in Table 2. In the ligands of MBAP and BAPA, we
observed broad weak bands with fine structure at 3424 cm−1 and
2.5. Synthesis of complexes
3467 cm−1 which can be attributed to the C
C OH. In addition,
high intensity sharp bands are observed at 1753 cm−1, 1720 cm−1
in MBAP and 1717 cm−1, 1693 cm−1 in BAPA which are attributed
to the ROC O and ␤-diketone C O, respectively. The high inten-
sity bands at 1601 cm−1 in MBAP and 1605 cm−1 in BAPA were
assigned to C C. These bands confirm the presence of the aromatic
ring. Medium intensity bands in the 1574–1491 cm−1 region were
regarded as a combination of C N of the pyridine ring and aro-
matic C C stretching vibrations. High intensity bands appearing at
1304 cm−1 in MBAP and 1318 cm−1 in BAPA were assigned to the
The complex Eu(MBAP)3·7H2O was prepared in the following
steps. A solution of methyl 6-benzoylacetyl-2-pyridinecarboxylate
(0.59 g, 2.1 mmol) in ethanol (10 ml) was added dropwise to a
solution of Eu(Cl)3·6H2O (0.26 g, 0.7 mmol) in ethanol (10 ml)
under stirring at 60 ◦C for 24 h. Then the pH value of the mix-
ture was adjusted to 6 by adding an aqueous solution of sodium
hydroxide (5%), the green precipitate obtained was separated by
filtration, washed three times with ethanol and dried in vac-
uum for 48 h. The yield was about 61% based on the amount of
EuCl3 used.
The complex Eu(MBAP)2(Phen)·6H2O was prepared as follows:
1,10-phenanthroline (0.13 g, 0.7 mmol) in ethanol (10 ml) was added
to a solution prepared as described for Eu(MBAP)3·7H2O above. The
mixture was heated under stirring at 60 ◦C for 24 h. Then the pH
value of the mixture was adjusted to 6 by adding an aqueous solu-
tion of sodium hydroxide (5%). The green precipitate obtained was
filtered, washed three times with ethanol and dried in vacuum for
48 h, yield: 69%.
C
O vibration from C
C O.
In the case of Ln(III) complexes we observed the following
changes. All the complexes exhibited broad medium intensity
bands at about 3364 cm−1, which were assigned to the coordi-
nated water molecule. The high intensity bands appearing around
1753 cm−1 in MBAP and 1717 cm−1 in BAPA, which were ascribed
to ROC O, downshifted to 1608 cm−1 in the Ln(III) complexes,
this confirms that the oxygen atoms of ROC O coordinated to
Ln(III) ions successfully. The high intensity bands appearing around
1572 cm−1 in MBAP and 1574 cm−1 in BAPA, due to C N in pyri-
dine ring, downshifted to about 1522 cm−1 and 1524 cm−1 in
Similarly, the other six complexes Eu(BAPA)3·7H2O, Eu(BAPA)2
(Phen)·6H2O, Tb(MBAP)3·7H2O, Tb(MBAP)2(Phen)·6H2O, Tb
(BAPA)3·7H2O, and Tb(BAPA)2(Phen)·6H2O were prepared.
All complexes are soluble in DMF, DMSO and methanol, a little
soluble in ethanol, ethyl acetate and acetone, insoluble in benzene,
diethyl ether and THF.
these Ln(III) complexes. The obvious shifts indicated that the C
N
groups of the ligands coordinated to the Ln(III) ions through nitro-
gen atoms. The high intensity bands due to C O vibration from
C
C
O appearing at 1304 cm−1 in MBAP and 1318 cm−1 in BAPA
downshifted to around 1287 cm−1 and 1285 cm−1 in the Ln(III)
complexes, which confirms that the enol hydroxyl groups reacted
with Ln(III) ions via deprotonation. The complexes showed medium
intensity bands in the region 562–594 cm−1 which was assigned
to Ln–N [20,21] and 423–437 cm−1 assigned to Ln–O modes
[22].
3. Results and discussion
3.1. Elemental analysis
Analytical data for the complexes were presented in Table 1. The
results of elemental analysis indicated that the composition of the
complexes conforms to Ln(MBAP)3·7H2O, Ln(MBAP)2(Phen)·6H2O,
Ln (BAPA)3·7H2O, and Ln(BAPA)2(Phen)·6H2O.
According to the results above, we reached the conclusion that
the ligands coordinated to the Ln(III) ions via the oxygen atoms
of the carbonyl, enol hydroxyl groups and the nitrogen atoms of
the pyridine ring and 1,10-phenanthroline. The elemental analysis
Table 2
The most important IR bands of the ligands and their complexes (cm−1).
Compound
ꢀ(C OH)
ꢀ(ROC O)
ꢀ(C C)
ꢀ(C N)
ꢀ(C O)
ꢀ(Ln N)
ꢀ(Ln O)
MBAP
BAPA
3424
3467
3338
3364
3398
3364
3363
3371
3386
3396
1753
1717
1609
1608
1608
1608
1610
1610
1612
1615
1601
1605
1570
1571
1568
1568
1572
1573
1569
1571
1572
1574
1521
1523
1523
1521
1523
1522
1524
1523
1304
1318
1287
1287
1290
1291
1288
1287
1285
1283
Eu(MBAP)3·7H2O
Eu(MBAP)2(Phen)·6H2O
Eu(BAPA)3·7H2O
Eu(BAPA)2(Phen)·6H2O
Tb(MBAP)3·7H2O
Tb(MBAP)2(Phen)·6H2O
Tb(BAPA)3·7H2O
Tb(BAPA)2(Phen)·6H2O
594
562
562
562
589
596
594
593
428
437
430
423
439
437
436
436

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Y.-M. Luo et al. / Spectrochimica Acta Part A 72 (2009) 703–708
Fig. 1. Chemical structures of the complexes.
Table 3
Fluorescence data for the complexes.
Complex
Slit (nm)
5
ꢁex (nm)
ꢁem (nm)
RFI
Assignment
Eu(MBAP)3·7H2O
281
592
619
287
775
5D0
5D0
→
→
7F1
7F2
Eu(MBAP)2(Phen)·6H2O
Eu(BAPA)3·7H2O
5
282
292
312
284
293
301
285
592
619
673
1916
5D0
5D0
→
→
7F1
7F2
2.5
2.5
2.5
2.5
2.5
2.5
592
619
3894
736
5D0
5D0
→
→
7F1
7F2
Eu(BAPA)2(Phen)·6H2O
Tb(MBAP)3·7H2O
592
619
2143
6581
5D0
5D0
→
→
7F1
7F2
493
545
2144
4102
5D4
5D4
→
→
7F6
7F5
Tb(MBAP)2(Phen)·6H2O
Tb(BAPA)3·7H2O
493
545
3218
5795
5D4
5D4
→
→
7F6
7F5
493
545
5519
9369
5D4
5D4
→
→
7F6
7F5
Tb(BAPA)2(Phen)·6H2O
493
545
8124
>10,000
5D4
5D4
→
→
7F6
7F5
and IR spectra results put together lead us to propose the general
structures shown in Fig. 1.
3.3. Fluorescence studies
The fluorescence characteristics of Eu(III) and Tb(III) complexes
in solid state were measured at room temperature under PMT
voltage 400 V. Under identical experimental conditions, the fluo-
rescence characteristics of all complexes in solid state were listed
in Table 3. The fluorescence spectra of the complexes were shown
in Figs. 2–5. In the Eu(III) complexes, we could see that the emission
7
band 5D0 → F2 is obviously higher than the other emission band
7
5D0 → F1 (Figs. 2 and 3), and in the Tb(III) complexes the emission
band 5D4 → F5 is distinctly stronger than the other emission bands
7
7
7
7
5D4 → F6, 5D4 → F4 and 5D4 → F3 (Figs. 4 and 5).
It is shown in Figs. 2–5 that the complexes show the character-
istic emissions of Eu(III) and Tb(III). Among these eight complexes,
it is clearly observed that the fluorescence intensity of Tb(III)
complexes with MBAP and BAPA is much stronger than that of
corresponding Eu(III) complexes. This is mostly because that the
luminescence of Ln(III) complexes is related to the efficiency of
the intramolecular energy transfer between the triplet level of
the ligands and the emitting level of the ions, which depends on
the energy gap between the two levels, probably the energy gap
between the ligand triplet levels and the emitting level of Tb(III)
Fig. 2. Fluorescence spectrum of the Eu(MBAP)2(Phen)·6H2O (b) and
Eu(MBAP)3·7H2O (a) in solid. The excitation and emission slit widths were
5 nm and the PMT voltage was 400 V.

Y.-M. Luo et al. / Spectrochimica Acta Part A 72 (2009) 703–708
707
Fig. 3. Fluorescence spectrum of Eu(BAPA)2(Phen)·6H2O(b) and Eu(BAPA)3·7H2O (a)
in solid. The excitation and emission slit widths were 2.5 nm and the PMT voltage
was 400 V.
Fig. 5. Fluorescence spectrum of the Tb(BAPA)2(Phen)·6H2O (b) and Tb(BAPA)3·
7H2O (a) in solid. The excitation and emission slit widths were 2.5 nm and the PMT
voltage was 400 V.
favors to the energy transfer process compared with Eu(III) com-
plexes.
In addition, the fluorescence emission of Eu(III) and Tb(III) com-
plexes using 1,10-phenanthroline as a secondary ligand is at least
40% higher than corresponding complexes without adding 1,10-
phenanthroline in each case (Figs. 2–5).
It is also observed that the fluorescence intensity of Ln(III)
complexes with BAPA is about twice as strong as that of Ln(III)
complexes with MBAP. Compared with previously reported Tb(III)
complexes with bis-␤-diketone-type ligands that we have synthe-
sized [15], Tb(III) complexes with BAPA and 1,10-phenanthroline in
this paper have slightly higher fluorescence, this could mainly be
attributed to the introduction of carboxyl functional group which
is beneficial to the energy transfer from the ligands to Tb(III) ion.
Figs. 6 and 7 show the thermogravimetric and differential ther-
mal gravimetry curves obtained by heating Tb(BAPA)3·7H2O and
Tb(BAPA)2(Phen)·6H2O in nitrogen atmosphere with the heating
rate of 10 ◦C min−1. The decomposition takes place between 30 ◦C
and 700 ◦C. The thermal analytical data are listed in Table 4. In the
TG–DTG curves, there are two main successive mass loss stages
from 30 ◦C to 700 ◦C for the two complexes. The first mass loss stage
of Tb(MBAP)3·7H2O starts at 111 ◦C, ends at 145 ◦C and reaches the
largest rate at 123 ◦C with mass loss percentage of 11.24%, this stage
roughly coincides with the value of 11.11%, calculated for the loss of
seven water molecules from the complex. Similarly, the first mass
loss stage of Tb(MBAP)2(Phen)·6H2O starts at 105 ◦C, ends at 145 ◦C
and reaches the largest rate at 124 ◦C with mass loss percentage
of 10.45%, this stage roughly coincides with the value of 10.66%,
calculated for the loss of six water molecules from the complex.
The second stage of Tb(MBAP)3·7H2O with 72.61% mass loss
starts at 445 ◦C, finishes at 610 ◦C and reaches the largest rate at
498 ◦C. The mass loss percentage is near the loss of three MBAP
molecules from the complex (calc. 72.39%). And the second stage
of Tb(MBAP)2(Phen)·6H2O with 70.49% mass loss starts at 450 ◦C,
3.4. Thermogravimetric analysis
The two complexes Tb(BAPA)3·7H2O and Tb(BAPA)2(Phen)·
6H2O were selected to perform thermal decomposition analysis.
Fig. 4. Fluorescence spectrum of the Tb(MBAP)2(Phen)·6H2O (b) and Tb(MBAP)3·
7H2O (a) in solid. The excitation and emission slit widths were 2.5 nm and the PMT
voltage was 400 V.
Fig. 6. TG–DTG curves of Tb(MBAP)3·7H2O under N2 atmosphere with the heating
rate of 10 ◦C min−1
.

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Y.-M. Luo et al. / Spectrochimica Acta Part A 72 (2009) 703–708
Table 4
Thermal decomposition data for Tb(MBAP)3·7H2O and Tb(MBAP)2(Phen)·6H2O.
Complex
Stage
Temperature range (◦C)
DTG peak temperature (◦C)
Mass loss rate (%) found (calc.)
Probable lost molecules
Intermediate
Tb(MBAP)3·7H2O
I
II
111–145
445–610
123
498
11.24(11.11)
72.61(72.39)
7H2O
3MBAP
Tb(MBAP)3
Tb4O7
Tb(MBAP)2(Phen)·6H2O
I
II
105–145
450–620
124
472
10.45(10.66)
70.49(70.87)
6H2O
2MBAP 1Phen
Tb(MBAP)2(Phen)
Tb4O7
the ligands to Ln(III) ions was occurring at the oxygen atoms of the
carbonyl, enol hydroxyl groups and the nitrogen atoms of the pyri-
dine ring and 1,10-phenanthroline. The fluorescence data indicate
that Tb(III) complexes with MBAP and BAPA exhibit much higher
emission than corresponding Eu(III) complexes and the fluores-
cence intensity of Ln(III) complexes with BAPA is about twice as
strong as that of Ln(III) complexes with MBAP. It is worth noting that
addition of 1,10-phenanthroline to the Eu(III) and Tb(III) complexes
lead to the formation of complexes with over 40% higher fluo-
rescence emission, in addition, Tb(III) complexes with BAPA emit
stronger green emission than Tb(III) complexes with correspond-
ing bis-␤-diketone-type ligands we previously reported and would
be considered as promising candidates for applications in organic
light-emitting devices (OLEDs), sensory materials and luminescent
probes.
Acknowledgements
This work is financially supported by National Natural Science
Foundation of China (no. 20676152) and the Science Foundation of
Hunan Province (no. 05JT1022).
Fig. 7. TG–DTG curves of Tb(MBAP)2(Phen)·6H2O under N2 atmosphere with the
heating rate of 10 ◦C min−1
.
finishes at 620 ◦C and reaches the largest rate at 472 ◦C. The mass
loss percentage is near the loss of two MBAP molecules and one
1,10-phenanthroline molecule from the complex (calc. 70.87%). Fur-
ther heating the two complexes to higher temperatures results in
plateaus in TG curves corresponding to the formation of Tb4O7.
In conclusion, on the basis of the TG–DTG analysis, the
thermal decomposition processes of Tb(MBAP)3·7H2O and
Tb(MBAP)2(Phen)·6H2O are predicted as follows:
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◦
◦
Tb(MBAP)3 · 7H2O111 −–→145 CTb(MBAP)3445−−→610 CTb4O7
−7H
O
−3MBAP
2
◦
C
Tb(MBAP) (Phen) · 6H2O 105−–→145
Tb(MBAP)2(Phen)
Tb4O7
2
−6H
O
2
◦
C
450−–→620
−2MBAP,−1Phen
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4. Conclusions
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The synthesis and fluorescence properties of Eu(III) and
Tb(III) complexes with two novel mono-substituted ␤-diketone-
type ligands, methyl 6-benzoylacetyl-2-pyridinecarboxylate, 6-
benzoylacetyl-2-pyridinecarboxylic acid and 1,10-phenanthroline
were reported. According to the IR spectra data, coordination of