Synthesis, characterization of the luminescent lanthanide complexes with (Z)-4-(4-methoxyphenoxy)-4-oxobut-2-enoic acid

Article abstract of DOI:10.1016/j.saa.2007.04.017

(Z)-4-(4-Methoxyphenoxy)-4-oxobut-2-enoic acid and its solid rare earth complexes LnL₃·2H₂O (Ln = La, Eu, Tb) were synthesized and characterized by means of MS, elemental analysis, FTIR, ¹³C NMR and TG-DTA. The IR and

Full text of DOI:10.1016/j.saa.2007.04.017

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Spectrochimica Acta Part A 69 (2008) 427–431
Synthesis, characterization of the luminescent lanthanide complexes
with (Z)-4-(4-methoxyphenoxy)-4-oxobut-2-enoic acid
Guo-Jian Duan, Ying Yang∗, Tong-Huan Liu, Ya-Ping Gao
College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China
Received 4 January 2007; received in revised form 20 March 2007; accepted 17 April 2007
Abstract
(Z)-4-(4-Methoxyphenoxy)-4-oxobut-2-enoic acid and its solid rare earth complexes LnL3·2H2O (Ln = La, Eu, Tb) were synthesized and cha-
racterized by means of MS, elemental analysis, FTIR, 13C NMR and TG–DTA. The IR and 13C NMR results show that the carboxylic groups
in the complexes coordinated to the rare earth ions in the form of a bidentate ligand, but the ester carboxylic groups have not taken part in the
coordination. The luminescence spectra of Eu(III) and Tb(III) complexes in solid state were also studied. The strong luminescence emitting peaks
at 616 nm for Eu(III) and 547 nm for Tb(III) can be observed, which could be attributed to the ligand has an enhanced effect to the luminescence
intensity of the Eu and Tb.
© 2007 Published by Elsevier B.V.
Keywords: (Z)-4-(4-Methoxyphenoxy)-4-oxobut-2-enoic acid; Synthesis; Complexes; Luminescence properties
1. Introduction
with La(III), Eu(III), Tb(III). The results indicate that the car-
boxlic group acting as a bidentate chelate coordinated to the
lanthanide ions, and the Eu(III) and Tb(III) complexes exhibit
characteristic luminescence with comparatively high brightness
and good monochromatic.
Derivatives of 2-butenedioic acid, such as its alkyl esters
[1–3], possess a conjugated structure and have been widely
applied as potential catalysts, semiconductors, photoresist
devices, and can improve the stability of polymers. Some
2-butenedioic acid monoalkyl esters form quite strong coor-
dination bonds with alkali and alkaline earth metals, such as
Li+, Ca2+ and Mg2+, etc., giving excellent antibacterial and
a static action. And luminescent lanthanide complexes [4–6]
have attracted intense research interest from both material and
biological science [7] mainly due to their strong fluorescence
emission, large stokes’ shifts, narrow emission profiles and
long fluorescence lifetime [8], they have been widely used in
many aspects, such as fluorescence mark, fluorescence ana-
lysis, environmental sciences, and cell biology [9–12]. Their
use has opened up a lot of opportunities in growing fields of
large social and economical impact. As part of our continuing
investigation into the preparation of lanthanide and actinide
compounds with the derivatives of 2-butenedioic acid, we
report here the synthesis and spectroscopic study of the (Z)-4-
(4-methoxyphenoxy)-4-oxobut-2-enoic acid and its complexes
2. Experimental
2.1. Materials
All commercially available chemicals were of A.R. grade and
all solvents used were purified by standard methods.
2.2. Methods
The metal ions were determined by EDTA titration using
xylenol orange as an indicator. Nitrogen, carbon and hydro-
gen analyses were determined using a Vario EL elemental
analyzer. IR spectra were recorded on a Nicolet Avatar 360
FTIR instrument using KBr discs in the 400–4000 cm−1 region.
Thermal analysis (TG–DTA) was carried out on a PCT-2A ther-
mal balance; 13C NMR spectra were measured on a Varian
Mercury-400BB NMR spectrometer. MS were performed on
a HP-5988A spectrometer (EI at 70 eV). Luminescence mea-
surements were made on a Hitachi F-4500 spectrophotometer
equipped with quartz curettes of 1 cm path length at room
∗
Corresponding author. Tel.: +86 931 8912552; fax: +86 931 8912582.
E-mail address: yangying@lzu.edu.cn (Y. Yang).
1386-1425/$ – see front matter © 2007 Published by Elsevier B.V.
doi:10.1016/j.saa.2007.04.017

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G.-J. Duan et al. / Spectrochimica Acta Part A 69 (2008) 427–431
Fig. 1. The MS spectrum of HL.
Table 1
temperature. The excitation and emission slit widths were
2.5 nm.
Elemental analyses of the ligand and complexes
Complexes
C (%)
H (%)
RE (%)
2.3. Synthesis of the ligand
HL
59.42 (59.46)
47.62 (47.26)
46.41 (46.53)
45.73 (46.15)
4.511 (4.505)
3.453 (3.699)
3.536 (3.642)
3.606 (3.613)
0
LaL3·2H2O
EuL3·2H2O
TbL3·2H2O
16.66 (16.59)
18.09 (17.86)
18.63 (18.53)
Maleic anhydride 2.94 g (30 mmol) and p-hydroxyanisole
3.72 g (30 mmol) was added to a three-neck flask equipped with
a condenser, heated it to 95 ◦C, then anhydrous pyridine (0.4 ml)
was added dropwise to the mixture under stirring, 0.2 ml pyri-
dine was added in the same way after 15 min again. The reaction
mixture was stirred at the temperature of 95–100 ◦C for 1.5 h.
After cooling to the room temperature, the crude product was
chromatographedonsiliagel[5:1, v:vpetroleumether/ethylace-
tate] to afford ligand as a white solid, yield: 45%. MS (EI, 70ev):
m/z (%) 222 (M+, 8.99), 124 (100), 109 (27.41), 99 (19.74), 81
(10.50), 45 (15.25), as in Fig. 1. And the structure is shown in
Fig. 2.
containing Ln(NO3)3·6H2O (Ln = La, Eu, Tb) (0.5 mmol) was
added dropwise to the solution a. The mixture was stirred for 2
days and white precipitate formed. The precipitate was collected
and washed three times with the mixture of acetone/water (v:v,
2:1). Further drying in a vacuum afforded a pale white powder,
yield: 70–80%.
3. Results and discussion
2.4. Synthesis of the complexes
3.1. Properties of the complexes
The solution of the ligand (1.5 mmol) in the acetone (15.0 ml)
was adjusted with the solution of NaOH (3.0 ml) to neutralize all
of the carboxylic groups, this is solution a. A solution (7.0 ml)
Analytical data for the complexes are listed in Table 1. The
results show that the formulas of the complexes are LnL3·2H2O.
All complexes are soluble in DMSO and DMF.
Fig. 2. Scheme of the synthesis of the ligand.

G.-J. Duan et al. / Spectrochimica Acta Part A 69 (2008) 427–431
429
Table 2
IR spectra data of the free ligand and its complexes (cm−1
)
Complexes
V O–H
V COO−
Vs CH3
Vas C–O–C
Vs C–O–C
Vas COO−
Vs COO−
ꢀVas-s
V Ln–O
HL
NaL
LaL3·2H2O
EuL3·2H2O
TbL3·2H2O
3440
3448
3438
3420
3422
1743
1737
1734
1736
1737
1685
2838
2836
2837
2837
2834
1235
1251
1248
1248
1249
1143
1144
1147
1147
1148
1596
1555
1548
1547
1400
1430
1435
1440
196
125
113
107
455
457
456
3.2. IR spectra
There are two resonance peaks at 165.928 and 164.399 ppm,
which can be assigned to C1 and C4, respectively. It is worthy of
note that chemical shift of C1 undergo about 5.965 ppm down-
field shift in the complex, but the change of C4 is not significant,
these results indicate that the oxygen atom attached to C1 takes
part in coordination, and the oxygen atom attached to C4 does
not.
The IR spectra of the complexes are obviously different from
the ligand, but they resemble with each other. The characteristic
bands of the ligand and complexes are listed in Table 2.
The infrared spectrum of ligand shows strong bands at
1743 cm−1 and 1685 cm−1, which are assigned to v(C O) of
ester carbonyl group and carboxylic group, respectively. In the
complexes, the band for v(C O) of ester carbonyl group is shif-
ted by 6–9 cm–1 towards lower wave numbers, compared with
NaL, it is clear that the ester carbonyl group does not take part in
coordination. At the same time, the band for v(C O) of carboxy-
lic group is disappeared completely, thus indicates that all the
carboxylic groups take part in coordination. This is correspon-
ding with the results of 13C NMR. The peaks at ca. 2837 cm−1
and 1248 cm−1 are assigned to the νas(CH3) and ν(C–O–C)
[13], the two bands indicated that there has Ar–O–CH3 group in
the ligand and complexes. Two strong absorption bands lying
at 1430–1440 cm−1 and 1547–1555 cm−1 were observed in
complexes, which were attributed to the symmetric vibration
absorption vs (COO−) and asymmetric vibration absorption vas
(COO−) of the carboxylic groups. The determined ꢀVas-s for
the Ln(III) complexes is far smaller than that of NaL (196 cm−1),
which shows that the symmetry of the carboxylic group in the
complexes is C2v, the same to the free ion. This state clearly that
the carboxlic group acting as a bidentate chelate coordinated to
the lanthanide ions in the complexes [14,15]. The two absorption
approximately at 788 and 560 cm−1 are assigned to in-plane and
out-of-plane bending vibration of coordination water, respecti-
From the results of 13C NMR of ligand and La(III) complex.
We can see that the change of chemical shifts of C2 and C3 are
obvious. This is because C2 and C3 were affected by C1 and C4
at the same time in the ligand, so the chemical surroundings of
C2 and C3 are similar with each other, and the chemical shifts are
similar, too. In the La(III) complex, the oxygen atom attached
to C1 was coordinated with La(III), so C2 and C3 were affected
by C4 only, so the chemical shifts of C2 and C3 undergo about
7.620 and 6.292 ppm downfield and upfield shifts, respectively.
For the La(III) complex, the 13C chemical shifts for C5–C11
areallfoundatrathernormalpositions, whicharesimilartothose
observed in ligand. These results indicate that all oxygen atoms
attached to these carbons do not take part in the coordination.
On the basis of above evidence and analyses, the possible
structure of the complexes is shown in Fig. 4.
3.4. TG–DTA analysis
Thermal behaviors of the ligand and the La(III) complexes
have been studied. Samples of about 10 mg were placed in a
crucible, and heated up to 800 ◦C at the rate of 10 ◦C/min in an
air atmosphere at ambient pressure, using ␣-Al2O3 as reference
material.
The DTA curve of free ligand has an endothermic peak at
153 ◦C, but there is no weight loss on the corresponding TG
curve, showing that this is a phase transition process, which is
the same as the melting point of the ligand (148 ◦C). In the range
of 273–285 ◦C, the free ligand has an obvious weight loss, excee-
ded 85%, but there has a small endothermic peak on the DTA
curve, this is because it has a decomposition process in the range
of the temperature, and a large part of produces of decomposi-
tion have volatilized in a form of gas. There is an endothermic
vely [16]. The broad continuous absorption (ca. 3400 cm−1
indicates that crystal water is simultaneously present [16,17].
)
3.3. 13C NMR spectra
The 13C NMR of free ligand and the La(III) complex were
measured in CD3COCD3, CD3SOCD3 at room temperature, res-
pectively. The 13C NMR data were shown in Table 3, and Fig. 3
is the 13C NMR spectra of the HL and the La(III) complex.
Table 3
13C NMR (100 MHz) data of HL and LaL3·2H2O
1
2
3
4
5
6, 10
7, 9
8
11
HL(CD3COCD3)
LaL3·2H2O(CD3SOCD3)
ꢀδa
165.928
171.893
−5.965
135.992
143.612
−7.620
133.448
127.156
6.292
164.399
164.772
−0.373
144.855
143.675
1.180
123.104
122.421
0.683
115.171
114.378
0.793
158.475
156.91
1.565
55.836
55.374
0.462
a
ꢀδ = δHL − δLaL3·2H2O.

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G.-J. Duan et al. / Spectrochimica Acta Part A 69 (2008) 427–431
Fig. 3. 13C NMR of HL and lanthanum complex ((a) HL and (b) La(III) complex).
peak at 170–189 ◦C for the La(III) complex, the corresponding
TG curve shows that the weight loss is equal to two water mole-
cules, it indicates that the presence of two coordinating water
molecules in the La(III) complex. The result is accord with the
elemental analyses study. Two strong exothermic peaks on DTA
curve can be observed in the range of 338–420 ◦C. Although the
discontinuous changes on TG curves indicate that the decompo-
sition have taken place in steps, but the changes are so nearly to
deduce the detailed decomposition processes.
3.5. Luminescence studies
The excitation and emission spectra, as well as the lumines-
cence intensity, were measured on dried and finely powdered
samples at room temperature. The major luminescence spec-
tral data are summarized in Table 4. Fig. 5 is the luminescence
spectral of the complexes of Eu(III) and Tb(III).
The europium and terbium complexes exhibited strong cha-
racteristic luminescence of europium and terbium ions. The
emission spectrum of the europium complex is shown in Fig. 5a.
Two visible bright emission peaks, which centered at 592.0 nm
and615.6 nmwereobserved[18]andassignedto5D0 → F1 and
7
Fig. 4. Suggest structure of the complexes.

G.-J. Duan et al. / Spectrochimica Acta Part A 69 (2008) 427–431
431
the 5D4 → FJ transition [20]. As we know luminescence inten-
sity of solid Ln (Ln = Eu, Tb) nitrate is quite weak, but from the
date of Table 4 we know that the luminescence intensity of Ln
(Ln = Eu, Tb) complex is far stronger than that of Ln (Ln = Eu,
Tb) nitrate, respectively. So we can say that the ligand has an
enhanced effect to the luminescence intensity of the Eu and Tb.
Further work has to be undertaken in order to investigate the
effect.
7
Table 4
Fluorescence data of the solid complexes
Complexes
Slit (nm)
2.5
λex (nm)
λem (nm)
RFIa
Assignment
7
EuL3·2H2O
466.0
592.0
615.6
678
1365
5D0 → F1
7
5D0 → F2
7
TbL3·2H2O
2.5
370.0
492.4
546.6
585.2
621.0
242
6790
499
5D4 → F6
5D4 → F5
7
7
5D4 → F4
7
189
5D4 → F3
a
4. Conclusion
RFI: relative fluorescence intensity.
According to the data and discussions above, it is obvious that
the ligand form complexes with lanthanide(III) ions. The Eu(III)
and Tb(III) complexes exhibited characteristic luminescence of
Eu(III) and Tb(III) ions. Obvious changes in IR spectra and 13
C
NMR were observed when the ligand formed the lanthanide
complexes, these results indicate that the Eu(III) and Tb(III)
ions were coordinated to the oxygen atoms of the carboxylic
group.
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