Solvent effect on the luminescent properties of new europium and terbium nitrate complexes with 3,3,7,7-tetra[N-methyl-N-phenyl(acetamide)-2-oxymethyl]-5-oxanonane

Article abstract of DOI:10.1016/j.saa.2006.03.041

The multipodal ligand 3,3,7,7-tetra[N-methyl-N-phenyl(acetamide)-2-oxymethyl]-5-oxanonane (L) and its europium and terbium nitrate complexes were synthesized. The complexes were characterized by elemental analysis, IR, fluorescence spectroscopy and conduc

Full text of DOI:10.1016/j.saa.2006.03.041

Spectrochimica Acta Part A 66 (2007) 590–593
Solvent effect on the luminescent properties of new europium
and terbium nitrate complexes with
3
,3,7,7-tetra[N-methyl-N-phenyl(acetamide)-2-oxymethyl]-5-oxanonane
∗
Ke-Wei Lei, Wei-Sheng Liu , Min-Yu Tan
Department of Chemistry and State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou
30000, China
7
Received 19 October 2005; received in revised form 13 March 2006; accepted 30 March 2006
Abstract
The multipodal ligand 3,3,7,7-tetra[N-methyl-N-phenyl(acetamide)-2-oxymethyl]-5-oxanonane (L) and its europium and terbium nitrate com-
plexes were synthesized. The complexes were characterized by elemental analysis, IR, fluorescence spectroscopy and conductivity. The lanthanide
atoms are coordinated by O atoms from C O, C O C. With the difference of the solvent, the fluorescence properties of solvent effect for the
complexes were investigated. Some factors that influencing the fluorescent intensity were discussed.
©
2006 Elsevier B.V. All rights reserved.
Keywords: Ether-amide type multipodal ligand; Lanthanide; Fluorescence; Solvent effect
1
. Introduction
groups suitable for energy transfer, i.e. the coordinating groups
with cavities for lanthanide ions and amide-based crown ethers.
With several suitably designed arms, the multipodal ligands
could shield the encapsulated lanthanide ions from interaction
with the surroundings, and by deliberate incorporation of appro-
priate multiple absorption groups suitable for energy transfer,
they could be used to develop strong luminescent lanthanide
complexes (Scheme 1).
In this work, we first obtained a new open-chain crown
ether ligand 3,3,7,7-tetra[N-methyl-N-phenyl(acetamide)-2-
oxymethyl]-5-oxanonane (L) (Scheme 1) and its lanthanide
nitrate [Ln Eu(III), Tb(III)] complexes. The solvent effects on
fluorescence properties of the complexes were investigated.
Luminescent lanthanide complexes [1–4] are finding use as
labels and sensors for natural and medical science [5,6], which
is attributable to their large Stokes shifts, narrow emission pro-
files, etc. [7]. They have attracted more and more chemists to
design the organized molecular architectures containing triva-
lent lanthanide ions [Eu(III), Tb(III)] working as efficient light
conversion devices [1,8].
Amide-based crown ethers offer many advantages in extrac-
tion and analysis of the rare earth ions [9,10] because of
their ring-like coordination structure and terminal group effects.
The open-chain crown ethers containing amide groups possess
suitable molecular structure: a chain with inflexible terminal
groups. Therefore, they are excellent reagents for activating
ion-selective electrodes and extracts of rare earth ions [11].
However, luminescent properties on open-chain crown ethers
with lanthanide complexes have been rarely reported [12]. So
we have designed a series of multi-functional ligands having
both selective ability to enhance luminescence of lanthanide
complexes by providing some of proper conjugate absorption
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
Corresponding author. Tel.: +86 931 8912552; fax: +86 931 8912582.
E-mail address: liuws@lzu.edu.cn (W.-S. Liu).
xylenal orange as indicator. C, H and N were determined
1
386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.03.041

K.-W. Lei et al. / Spectrochimica Acta Part A 66 (2007) 590–593
591
CDCl3): δ = 7.13–7.38 (m, 20H); 3.73(s, 8H; 4O CH2 C(O));
3.22 (s, 12H; 4N CH3); 3.21(s, 8H; 4C CH2 O); 2.98 (s,
4H; 2C CH2 O); 1.23 (q, 4H; 2R CH2 C); 0.70(t, 6H;
2CH3 R C). IR:ν 1674s (C O), 1112s (Ar O C). Formula
weight of L: 839.45. Analytical data, C 68.67(Calc. 68.71); H
7.39(7.45); N 6.56(6.68)%.
2.4. Synthesis of complexes
An ethyl acetate solution of Ln(NO3)3·6H2O [Ln = Eu(III),
Tb(III), 0.2 mmol] was added dropwise to a solution of the lig-
and L (0.1 mmol) in the ethyl acetate (30 ml). The mixture was
stirred for 4 h and white precipitate formed. The precipitate was
collected and washed three times with ethyl acetate. Further
drying in vacuum afforded a pale white powder, yield: 75–80%.
3. Result and discussion
Scheme 1. The ligand.
3
.1. Properties of the complexes
using an Elementar Vario EL. Conductivity measurements were
carried out with a DDS-307 type conductivity bridge using
Analytical data for the complexes listed in Table 1
−3
−3
◦
1
0
mol dm solutions in acetone at 25 C. IR spectra were
conform to an 2:6:1 metal-to-nitrate-to-L stoichiometry
recorded on Nicolet FT-170SX instrument using KBr discs in
[LnL]·[Ln(NO ) ]·(NO ). All complexes are soluble in DMF,
3
5
3
−
1
1
the 400–4000 cm region, H NMR spectra were measured
on a Varian Mercury plus 300 M spectrometer in CDCl3 solu-
tion with TMS as internal standard. Fluorescence measurements
were made on a Hitachi F-4500 spectrophotometer equipped
with quartz curettes of 1 cm path length at room temperature.
The excitation and emission slit widths were 10 nm.
acetonitrile, THF, MeOH, acetone, and dioxane, but sparingly
soluble in water and ethyl acetate. The molar conductances of the
complexes in acetone (see Table 1) indicate that all complexes
act as 1:1 electrolytes [13].
3.2. IR spectra
2
.3. Synthesis of the ligand
The main infrared bands of the ligand and its complexes are
presented in Table 2. The IR spectrum of free ligand shows
−
1
A solution of 3,3,7,7-tetrahydroxymethyl-5-oxanonane
2.5 g, 10 mmol) in THF was added dropwise into a THF solu-
bands at 1675 and 1112 cm , which may be assigned to ν(C O)
and ν(C O C), respectively. In the IR spectra of all the lan-
(
−1
tion that was suspended with NaH (1.6 g, 60%, 40 mmol), and
the mixture was stirred under nitrogen at room temperature
until no gas appeared. Then a solution of N-methyl-N-
phenylchloroacetamide (44 mmol) in THF was added dropwise
into the mixture. After the mixture was refluxed for 6 h, the
THF was evaporated and the residue was chromatographed on
silica gel (CHCl3/CH3CO2Et, 2:1) to afford ligand as a pale
thanide complexes, these bands shift by about 52 and 22 cm
towardlowerwavenumbers, thusindicatingthatthecarbonyland
ethereal oxygen atoms take part in coordination to the metal ion.
The absorption bands assigned to the coordinated nitrates
were observed at about 1492 cm (ν1), 1310 cm (ν4) and
816 cm (ν3) for the complexes, respectively, implying that
−
1
−1
−
1
coordinated nitrate groups in the complexes are bidentate lig-
ands [14]; The absorption band of about 1384 cm suggests
1
−1
yellow oil (4.3 g). Yield: 50%. L, H NMR spectrum (300 M,
Table 1
Analytical and molar conductance data for the complexes (calculated values in parentheses)
2
−1
)
Complexes
C
H
N
Ln
ꢀm(s·cm ·mol
[
[
EuL]·[Eu(NO3)5]·(NO3)
TbL]·[Tb(NO3)5]·(NO3)
38.14(38.05)
38.12(37.71)
4.23(4.12)
4.12(4.09)
9.16(9.25)
9.08(9.16)
20.89(20.06)
20.65(20.79)
180
176
Table 2
IR spectral data of the free ligands and their complexes (cm 1)
−
−
−
−
ν4(NO3 )
Compound
ν(C O)
ν(C
O
C)
ν1(NO3
)
ν3(NO3
)
ν(free)
L
1675
1623
1624
1112
1090
1091
[
EuL]·[Ln(NO3)5]·(NO3)
TbL]·[Ln(NO3)5]·(NO3)
1490
1492
816
816
1309
1310
1384
1384
[

5
92
K.-W. Lei et al. / Spectrochimica Acta Part A 66 (2007) 590–593
Table 3
Fluorescence data for the complexes
−
Complexes
Concentration (mol l 1)
Solvent
λex (nm)
λem (nm)
RFI
413
Assignment
−4
−4
−4
−4
−4
−4
5
5
5
5
5
5
5
5
5
5
5
5
7
[
TbL]·[Ln(NO3)5]·(NO3)
10
Dioxane
327
491
D4– F6
7
5
46
492
46
492
46
492
46
489
47
492
47
268
232
261
351
356
231
134
1028
542
268
330
D4– F5
7
10
10
10
10
10
Acetone
MeCN
THF
353
328
354
335
338
D4– F6
7
5
D4– F5
7
D4– F6
7
5
D4– F5
7
D4– F6
7
5
D4– F5
7
DMF
D4– F6
7
5
D4– F5
7
MeOH
D4– F6
7
5
D4– F5
−
−
−
−
−
−
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
5
5
7
[
EuL]·[Ln(NO3)5]·(NO3)
10
Acetone
MeCN
DMF
332
398
396
397
398
397
592
17
592
17
592
17
592
17
592
16
592
17
33
129
23
84
31
47
14
43
13
26
8
D0– F1
7
6
D0– F2
7
1
1
1
1
1
0
0
0
0
0
D0– F1
7
6
D0– F2
7
D0– F1
7
6
D0– F2
7
Dioxane
THF
D0– F1
7
6
D0– F2
7
D0– F1
7
6
D0– F2
7
MeOH
D0– F1
7
6
14
D0– F2
RFI is relative fluorescence intensity.
that there is free nitrate in the complexes, which is in agreement
with the results of the conductivity experiments.
paring Figs. 1 and 2, we can observe that the fluorescence
intensities of terbium complex at 546 nm are stronger than those
of europium complex at 617 nm in all sorts of solutions. Based
3
+
3
.3. Fluorescence studies
on the theory of antenna effect [16,17], the luminescence of Ln
chelates is related to the efficiency of the intramolecular energy
transfer between the triple level of the ligand and the emitting
level of the ions, which depends on the energy gap between the
two levels. In organic solution, the energy gap between the lig-
Under identical experimental, the fluorescence characteris-
tics of the complexes in dioxane, acetone, MeCN, THF, DMF
and MeOH solutions are listed in Table 3. The ligand having
multiple aromatic rings has a strong antenna effect. So its ter-
bium and europium complexes have strong fluorescence. The
fluorescence characteristic emission wavelengths of the terbium
and europium ions were observed. In DMF solution, the ter-
bium complex has the strongest fluorescence, and then in MeCN,
MeOH, dioxane and acetone, THF solutions (Fig. 1). We also
can see the fluorescence intensities for the europium complex
become weaker from acetone, MeCN, DMF, dioxane, THF, to
MeOH solution (Fig. 2). This is due to the coordinating effects
of solvents, which is solvate effect [15]. The amide-based por-
tion of the ligand forms a caverned conformation suitable for the
uptake of a lanthanide ion, but this ajar cavity could not prevent
absolutely the solvent molecules from entering. Together with
the raising coordination abilities of solutions for the lanthanide
ions, the oscillatory motions of the entering molecules consume
more energy which the ligand triple level transfer to the emitting
level of the lanthanide ion. Thus, the energy transfer could not
be carried out perfectly.
In the emission spectra of the terbium complex, due to the
present of a scattering signal near 491 nm, the peak height at
Fig. 1. Emission spectra of the terbium complex in different solutions at room
temperature concentration (10 mol l ): (1) in DMF; (2) in MeCN; (3) in
MeOH; (4) in dioxane; (5) in acetone; and (6) in THF solution.
−4
−1
5
46 nm was used to measure the fluorescence intensities. Com-

K.-W. Lei et al. / Spectrochimica Acta Part A 66 (2007) 590–593
593
4. Conclusion
According to the data and discussion above, the amide-based
multipodal ligand could form complexes with lanthanide ions
and exhibit a caverned conformation. The complexes exhib-
ited characteristic fluorescence of europium and terbium ion,
respectively. The different solvents may affect the fluorescence
ofeuropiumandterbiumions. Theotherapplicationoftheligand
such as lanthanide-ion extraction is in studying deeply. Based on
those results, a series of new amide-based multipodal derivatives
could be designed and synthesized to optimize the luminescent
properties of these lanthanide ions.
Acknowledgements
We are grateful to the NSFC (Grants 20371022, 20431010
and 20021001), the Specialized Research Fund for the Doctoral
Program of Higher Education (200307300015), and the Key
Project of the Ministry of Education of China (Grant 01170)
for financial support.
Fig. 2. Emission spectra of the europium complex in different solutions at room
temperature concentration (10 mol l ): (1) in acetone; (2) in MeCN; (3) in
DMF; (4) in dioxane; (5) in THF; and (6) in MeOH solution.
−4
−1
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−4
−1
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−
4
−1
temperature (10 mol l ) (λex: 325 nm; λem: 460 nm) is
2
(1995) 995.
showed in Fig. 3.