Luminescent properties of solvent effect for europium and terbium nitrate complexes with 3,3,7,7-tetra[N-benzyl-N-phenyl(acetamide)-2-oxymethyl]-5-oxanonane

Article abstract of DOI:10.1016/j.saa.2006.03.012

The multipodal ligand 3,3,7,7-tetra[N-benzyl-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.2006.03.012

Spectrochimica Acta Part A 66 (2007) 377–380
Luminescent properties of solvent effect for europium and
terbium nitrate complexes with
3,3,7,7-tetra[N-benzyl-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 730000, China
Received 29 September 2005; accepted 3 March 2006
Abstract
The multipodal ligand 3,3,7,7-tetra[N-benzyl-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 0 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
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 surround-
ings, and by deliberate incorporation of appropriate multiple
absorption groups suitable for energy transfer, they could be
used to develop strong luminescent lanthanide complexes.
In this work, we obtained a open-chain crown ether ligand
3,3,7,7-tetra[N-benzyl-N-phenyl(acetamide)-2-oxymethyl]-5-
oxanonane (L) (Scheme 1) and its lanthanide nitrate
[Ln = Eu(III) and 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) and 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 suit-
able molecular structure: a chain with inflexible terminal groups.
Therefore, theyareexcellentreagentsforactivatingion-selective
electrodes and extracts of rare earth ions [11]. However, lumi-
nescent properties on open-chain crown ethers with lanthanide
complexes have been rarely reported [12]. So we have designed
a series of multifunctional ligands having both selective ability
to enhance luminescence of lanthanide complexes by provid-
ing some of proper conjugate absorption groups suitable for
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
xylenal orange as indicator. C, H and N were determined
using an Elementar Vario EL. Conductivity measurements were
∗
Corresponding author. Tel.: +86 931 8912552; fax: +86 931 8912582.
E-mail address: liuws@lzu.edu.cn (W.-S. Liu).
1
386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.03.012

3
78
K.-W. Lei et al. / Spectrochimica Acta Part A 66 (2007) 377–380
THF was evaporated and the residue was washed by column
chromatography (silica gel, 2:1, CHCl3/CH3CO2Et) and evap-
orated in vacuum resulted a yellow oil (4.3 g), yield: 50%. L,
1
H NMR spectrum (300 M, CDCl3): δ = 6.92–7.26 (m, 40H),
4.84 (s, 8H; 4N–CH2–R), 3.75 (s, 8H; 4O–CH2–C(O)), 3.23
(s, 8H; 4C–CH2–O), 3.11 (s, 4H; 2C–CH2–O), 1.27 (q, 4H;
2
1
R–CH2–C), 0.76 (t, 6H; 2CH3–R–C). IR: ν 1675s (C O),
108s (Ar–O–C). Formula weight of L : 1142.58. Analyti-
c
cal data, C 75.77 (calc. 75.63%); H 7.02 (6.88%); N 5.06
4.90%).
(
2.4. Synthesis of complexes
An ethyl acetate solution of Ln(NO3)3·6H2O [Ln = Eu(III)
and Tb(III), 0.2 mmol] was added dropwise to a solution of the
ligand 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%.
Scheme 1.
3. Result and discussion
carried out with a DDS-307 type conductivity bridge using
−3
−3
◦
1
0
mol dm solutions in acetone at 25 C. IR spectra were
3.1. Properties of the complexes
recorded on Nicolet FT-170SX instrument using KBr discs in
−
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.
Analytical data for the complexes listed in Table 1
conform to an 2:6:1 metal-to-nitrate-to-L stoichiometry
[LnL]·[Ln(NO3)5]·(NO3). All complexes are soluble in DMF,
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 com-
plexes act as 1:2 electrolytes [13].
2
.3. Synthesis of the ligand
3.2. IR spectra
A solution of 3,3,7,7-tetrahydroxymethyl-5-oxanonane
(
2.5 g, 10 mmol) in THF was added dropwise into a THF solu-
The main infrared bands of the ligand and its complexes are
tion that was suspended with NaH (1.6 g, 60%, 40 mmol),
and the mixture was stirred under nitrogen at room temper-
ature until no gas appeared. Then, a solution of N-benzyl-N-
phenylchloroacetamide (44 mmol) in THF was added dropwise
into the mixture. After the mixture was refluxed for 6 h, the
presented in Table 2. The IR spectrum of free ligand shows bands
−
1
at 1676 and 1108 cm , which may be assigned to ν(C O) and
ν(C O C), respectively. In the IR spectra of all the lanthanide
−1
complexes, these bands shift by about 60 and 25 cm toward
lower wave numbers, thus indicating that the carbonyl and ethe-
Table 1
Analytical and molar conductance data for the complexes (calculated values in parentheses)
2
−1
)
Complexes
C
H
N
Ln
Am (s cm mol
[
[
EuL]·[Eu(NO3)5]·(NO3)
TbL]·[Tb(NO3)5]·(NO3)
48.01 (47.53)
47.06 (47.17)
4.39 (4.32)
4.20 (4.29)
7.85 (7.70)
7.52 (7.64)
16.58 (16.71)
17.69 (17.34)
167
171
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
1676
1616
1621
1108
1093
1076
[
EuL]·[Ln(NO3)5]·(NO3)
TbL]·[Ln(NO3)5]·(NO3)
1492
1495
816
826
1310
1306
1384
1384
[

K.-W. Lei et al. / Spectrochimica Acta Part A 66 (2007) 377–380
379
Table 3
Fluorescence data for the complexes
−
Complexes
Concentration (mol l 1)
Solvent
λex (nm)
λem (nm)
RFI
360
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
326
492
D4– F6
7
5
47
493
47
492
47
491
47
489
47
492
47
401
240
352
438
782
319
277
1108
547
459
773
D4– F5
7
10
10
10
10
10
Acetone
MeCN
THF
344
329
329
338
331
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
398
398
398
398
398
398
592
17
592
17
591
17
592
17
592
16
592
17
18
59
30
128
36
56
23
71
14
27
10
16
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
D0– F2
RFI is relative fluorescence intensity.
real oxygen atoms take part in coordination to the metal ion
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.
(Table 2).
The absorption bands assigned to the coordinated nitrates
−
1
−1
were observed at about 1492 cm (ν1), 1310 cm (ν4) and
8
In the emission spectra of the terbium complex, due to the
present of a scattering signal near 491 nm, the peak height at
547 nm was used to measure the fluorescence intensities. Com-
paring Figs. 1 and 2, we can observe that the fluorescence
intensities of terbium complex at 547 nm are stronger than those
of europium complex at 617 nm in all sorts of solutions. Based
−1
16 cm (ν3) for the complexes, respectively, implying that
coordinatednitrategroupsinthecomplexesarebidentateligands
−
1
[
14]. The absorption band of about 1384 cm suggests that
there is free nitrate in the complexes, which is in agreement
with the results of the conductivity experiments.
3
+
on the theory of antenna effect [16,17], the luminescence of Ln
3
.3. Fluorescence studies
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, acetone and THF solutions (Fig. 1). We can
also see the fluorescence intensities for the europium complex
become weaker from MeCN, dioxane, acetone, DMF, 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
Fig. 1. Emission spectra of the terbium complex in different solutions at room
temperature concentration: 10 mol l . In (1) DMF, (2) MeCN, (3) MeOH,
(4) dioxane, (5) acetone and (6) THF solution.
−4
−1

3
80
K.-W. Lei et al. / Spectrochimica Acta Part A 66 (2007) 377–380
of europium and terbium ions. 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 Doc-
toral Program of Higher Education (200307300015) and the Key
Project of the Ministry of Education of China (Grant 01170) for
financial support.
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Fig. 2. Emission spectra of the europium complex in different solutions at room
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−1
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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
[
[
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2