Terminal group effects on the fluorescence spectra of Eu(III) nitrate complexes with a family of amide-based 1,10-phenanthroline derivatives

Article abstract of DOI:10.1016/j.saa.2005.03.010

Four ligands 1,10-phenanthroline-5,6-bis(N,N-dibenzyl-1′- oxopropylamide) (L^a) 1,10-phenanthroline-5,6-bis(N-methyl-N-benzyl- 1′-oxopropylamide) (L^b) 1,10-phenanthroline-5,6-bis(N-benzyl- 1′-oxopropylamide) (L^c) and 1,10-phenanthroline-5,6-bis(N,N- diethyl-1′-oxopropylamide) (L^d), and their lanthanide(III) (La and Eu) complexes 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, Ar-O -C and N atoms from phen With the difference of the ligands, the fluorescent intensities of the Eu(III) complexes vary regularly in the THF solution. Some factors that influence the fluorescent intensity were discussed.

Full text of DOI:10.1016/j.saa.2005.03.010

Spectrochimica Acta Part A 62 (2005) 826–830
Terminal group effects on the fluorescence spectra of Eu(III)
nitrate complexes with a family of amide-based
1,10-phenanthroline derivatives
Su-Wen Chen, Yu-Liang Zhang, Wei Dou, Ya-Wen Wang, Wei-Sheng Liu∗
Department of Chemistry and State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering,
Lanzhou University, Lanzhou 730000, China
Received 29 January 2005; received in revised form 23 March 2005; accepted 23 March 2005
Abstract
Four ligands 1,10-phenanthroline-5,6-bis(N,N-dibenzyl-1ꢀ-oxopropylamide) (La) 1,10-phenanthroline-5,6-bis(N-methyl-N-benzyl-1ꢀ-
oxopropylamide) (Lb) 1,10-phenanthroline-5,6-bis(N-benzyl-1ꢀ-oxopropylamide) (Lc) and 1,10-phenanthroline-5,6-bis(N,N-diethyl-1ꢀ-
oxopropylamide) (Ld), and their lanthanide(III) (La and Eu) complexes 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, Ar–O –C and N atoms
from phen With the difference of the ligands, the fluorescent intensities of the Eu(III) complexes vary regularly in the THF solution. Some
factors that influence the fluorescent intensity were discussed.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Amide-based 1,10-phenanthroline derivative; Synthesis; Complexes; Fluorescent property
1. Introduction
[6,7] because of their ring-like coordination structure and
terminal group effects [7,8]. So, we have designed a series
of multi-functional ligands having selective ability to coor-
dinate more than one lanthanides ions. The luminescence
of these lanthanide complexes were enhanced by providing
some of the proper conjugate absorption groups suitable for
energy transfer, i.e. phen, and the other coordinating groups
with cavities for lanthanide ions, i.e. amide-based open-chain
crown ethers. In the present work, we designed and synthe-
sized four ligands and their europium(III) nitrate complexes.
The terminal group effects on fluorescence properties of the
complexes were investigated.
The development of luminescent probes and sensors [1] is
the subject of intensive research, both in natural and medical
science [2,3]. Probes based on europium and terbium ions are
of special interest because of the particularly suitable spec-
troscopic properties of these ions [2,4]. The main advantages
of lanthanide chelates in the fluorescence spectrometry are
their large stokes shifts, narrow emission profiles and long
fluorescence lifetimes [5]. These have led to use lanthanides
as fluorescent probes for highly sensitive time-resolved flu-
orimetric immunoassays, metal ion coordination in proteins
and structural studies of biological macromolecule [2]. And
these properties have also been used to improve the sensitivity
for lanthanide estimation by conventional spectrofluorimetry
and laser-induced spectrofluorimetry [5].
2. Experimental
Amide-based open-chain crown ethers offer many advan-
tages in the extraction and analysis of the rare earth ions
2.1. Materials
All commercially available chemicals were of A.R.
grade and all the solvents used were purified by standard
methods.
∗
Corresponding author. Tel.: +86 931 8912552; fax: +86 931 8912582.
E-mail address: liuws@lzu.edu.cn (W.-S. Liu).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.03.010

S.-W. Chen et al. / Spectrochimica Acta Part A 62 (2005) 826–830
827
2.2. Methods
ppm): δ 8.99–8.97 (m, 2H; phen: 2H and 9H); 8.69–8.65 (m,
2H; phen: 4H and 7H); 7.76–7.68 (m, 2H; phen: 3H and 8H);
7.19–7.16 (s, 20H; 2Ar H); 5.14 (s, 4H; 2O–CH2–C(O)); 4.42
(s, 8H; 4N–CH2–Ar).
The metal ions were determined by EDTA titration
using xylenol orange as an indicator. Carbon, nitrogen
and hydrogen analyses were determined using a Vario EL
elemental analyzer. Conductivity measurements were car-
ried out with a DDSJ-308 type conductivity bridge using
1.0 × 10−3 mol dm−3 solution in MeOH at 25 ◦C. IR spec-
tra were recorded on a Nicolet Avatar 360 FT-IR instrument
2.3.3. 1,10-Phenanthroline-5,6-bis(N-methyl-N-benzyl-
1ꢀ-oxopropylamide) (Lb, R1 = methyl, R2 = benzyl)
Yield, 80%. IR (cm−1, KBr): 1662 (C=O), 1613 (phen,
1
C=N), 1114 (Ar–O), 1492 (phen ring). H NMR (CDCl3,
using KBr discs in the 400–4000 cm−1 region. H NMR
1
ppm): δ 9.15–9.11 (m, 2H; phen: 2H and 9H); 8.87–8.70 (m,
2H; phen: 4H and 7H); 7.73–7.58 (m, 2H; phen: 3H and 8H);
7.30 (s, 10H; 2Ar H); 5.11 (s, 4H; 2CH2); 4.65–4.48 (s, 4H;
2O–CH2–C(O)); 3.00–2.86 (s, 6H; 2CH3).
spectra were measured on a FT-80A spectrometer in CDCl3
solution, with TMS as the internal standard. Fluorescence
measurements were made on a Hitachi F-4500 spectropho-
tometer equipped with quartz curettes of 1 cm path length at
room temperature. The excitation and emission slit widths
were 10 nm.
2.3.4. 1,10-Phenanthroline-5,6-bis(N-benzyl-1ꢀ-
oxopropylamide) (Lc, R1 = H, R2 = benzyl)
Yield, 78%. IR (cm−1, KBr): 1667 (C=O), 1616 (phen,
1
2.3. Synthesis of the ligand
C=N), 1117 (Ar–O), 1497 (phen ring). H NMR (CDCl3,
ppm): δ 9.14–9.12 (m, 2H; phen: 2H and 9H); 8.41–8.38 (m,
2H; phen: 4H and 7H); 7.65–7.61 (m, 2H; phen: 3H and 8H);
7.36–7.32 (m, 10H; 2Ar H); 7.31–7.29 (m, 2H; 2C(O)–N–H);
4.73 (s, 4H; 2O–CH2–C(O)); 4.59–4.52 (m, 4H; 2CH2).
Compounds 1, 2 and 3 (Fig. 1) were prepared according
to the literature methods [9–12].
2.3.1. General procedure for ligand synthesis
2.3.5. 1,10-Phenanthroline-5,6-bis(N,N-diethyl-1ꢀ-
oxopropylamide) (Ld, R1 = R2 = ethyl)
The four ligands were prepared by the same procedure.
Anhydrous K2CO3 (4.0 g) was added slowly to the DMF
solution of 2 (1.5 g, 6.04 mmol) at 110 ◦C. An hour later, a
DMF solution containing 3 (18.0 mmol) was added dropwise
and slowly to the mixture. The reaction mixture was stirred
for 24 h. Fifty milliliters water was poured and extracted
by CHCl3 (3 × 40 ml). Organic phase combined was evap-
orated in vacuum. The crude product was chromatographed
on silica gel (EtOAc/MeOH, 95:5) to afford 4 as pale yellow
solids.
Yield, 70%. IR (cm−1, KBr): 1657 (C=O), 1614 (phen,
1
C=N), 1117 (Ar–O), 1492 (phen ring). H NMR (CDCl3,
ppm): δ 9.13–9.09 (m, 2H; phen: 2H and 9H); 8.34–8.30
(m, 2H; phen: 4H and 7H); 7.67–7.62 (m, 2H; phen: 3H and
8H); 7.35 (m, 10H; 2Ar H); 3.73 (s, 4H; 2O–CH2–C(O));
3.43–3.41 (m, 8H; 4CH2); 1.25–1.13 (m, 12H; CH3).
2.4. Synthesis of complexes
2.3.2. 1,10-Phenanthroline-5,6-bis(N,N-dibenzyl-1ꢀ-
oxopropylamide) (La, R1 = R2 = benzyl)
Anethyl acetatesolution ofLn(NO3)3·6H2O[Ln = Eu(III)
or La(III), 0.15 mmol] was added dropwise to a solution of
ligand L (0.1 mmol) in the ethyl acetate (20 ml). The mix-
ture was stirred for 24 h and white precipitate was formed.
Yield, 85%. IR (cm−1, KBr): 1663 (C=O), 1613 (phen,
1
C=N), 1116 (Ar–O), 1495 (phen ring). H NMR (CDCl3,
Fig. 1. Scheme of the synthesis of the ligands. (i) KBr, H2SO4, HNO3, −15 ◦C; (ii) NH2NH2·HCl, 100 ◦C; (iii) K2CO3, DMF, 110 ◦C (La: R1 = benzyl,
R2 = benzyl; Lb: R1 = methyl, R2 = benzyl; Lc: R1 = H, R2 = benzyl; Ld: R1 = ethyl, R2 = ethyl).

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S.-W. Chen et al. / Spectrochimica Acta Part A 62 (2005) 826–830
and 6–27 cm-1, respectively; thus indicating that carbonyl,
ethereal oxygen atom and phen nitrogen atom take part in
coordination to the metal ion.
The precipitate was collected and washed three times with
ethyl acetate. Further drying in vacuum afforded a pale white
powder, yield: 80%.
The absorption bands assigned to the coordinated nitrates
were observed as two bands at about 1470 cm−1 (ν1) and
1310 cm−1 (ν4), for the complexes, respectively. The differ-
ences between the strongest absorption band ν1 and ν4 of
nitrate group lie in 182–189 cm−1 and 115–122 cm−1, indi-
cating that coordinated nitrate groups in the complexes are
bidentate and unibentate ligands [15], respectively. The ν3
(E) of free nitrate group appears at approximately 1384 cm−1
in the spectra of the complexes [16], in agreement with the
results of the conductivity experiments.
3. Results and discussion
3.1. Properties of the complexes
Analytical data for the complexes are listed in Table 1,
conformed to [Eu4(NO3)10L3]·(NO3)2 and [La4(NO3)10L3]·
(NO3)2.
All complexes are soluble in DMF, acetonitrile, THF,
methanolandethanol, butsparinglysolubleinwaterandethyl
acetate. Conductivity measurement for these complexes in
methanol solution (in Table 1) indicates that both complexes
are 2:1 ionic complexes [13].
3.3. Fluorescence studies
Under identical experimental, the fluorescence char-
acteristics of the complexes in THF, dioxance, MeCN
and DMF solution are studied. In THF solution, the
europium complexes have the strongest fluorescence [17].
The fluorescence characteristics of the europium com-
plexes in THF solution are listed in Table 3 (concentration:
5.5 × 10−4). The maximum excitation wave lengths of the
THF solution are observed at 366, 351, 350 and 314 nm
for [Eu4(NO3)10La ]·(NO3)2, [Eu4(NO3)10Lb ]·(NO3)2,
3.2. IR spectra
IR spectra of the complexes are similar to each other. The
main infrared bands of the ligands and their complexes are
presented in Table 2. Table 2 shows main infrared data of
the four Eu(III) and La(III) complexes. The IR spectrum
of the free ligands show strong band at 1657–1667 cm−1
,
3
3
which is attributable to stretch vibrations of the ca−rb1onyl
group of amide (ν(C=O)). The peak at 1613–1617 cm can
be assigned to ν(C=N), and the peak at 1114–1117 cm−1
to ν(Ar–O) [14]. In the IR spectra of the lanthanum com-
plexes, the ν(C=O), ν(C=N) and ν(Ar–O) shift by 8–30, 6–12
[Eu4(NO3)10Lc ]·(NO3)2 and [Eu4(NO3)10Ld ]·(NO3)2,
3
3
respectively. As shown in Fig. 2, The emission spectra of
the four complexes at the room temperature in THF solution
are similar to each other, and show characteristic emission
bands of an Eu(III) ion at about 595 and 619 nm, assigned
Table 1
Elemental analytical and molar conductance data for the complexes
Complexes
C (%) found (calc.)
H (%) found (calc.)
N (%) found (calc.)
Ln (%) found (calc.)
ꢀm (s cm2 mol−1
)
[Eu4(NO3)10La3]·(NO3)2
[La4(NO3)10La3]·(NO3)2
[Eu4(NO3)10Lb3]·(NO3)2
[La4(NO3)10Lb3]·(NO3)2
[Eu4(NO3)10Lc3]·(NO3)2
[La4(NO3)10Lc3]·(NO3)2
[Eu4(NO3)10Ld3]·(NO3)2
[La4(NO3)10Ld3]·(NO3)2
46.52 (46.46)
47.31 (47.18)
39.44 (39.01)
37.93 (39.71)
38.09 (37.64)
38.52 (38.34)
34.20 (34.42)
32.83 (33.07)
3.49 (3.37)
3.36 (3.12)
2.59 (3.07)
2.85 (3.12)
2.56 (2.74)
2.34 (2.79)
3.05 (3.40)
3.04 (3.47)
9.39 (9.85)
9.69 (10.00)
11.25 (11.37)
11.19 (11.58)
11.55 (11.71)
11.57 (11.92)
12.28 (12.60)
12.35 (12.85)
17.90 (17.60)
16.71 (16.54)
20.45 (20.57)
19.00 (19.14)
20.81 (21.17)
19.28 (19.71)
22.67 (22.79)
21.03 (21.25)
202
208
200
196
200
201
207
204
Table 2
IR spectral data of the free ligands and their complexes (cm−1
)
−
−
−
Compound
ν (C=O)
ν (Ar–O)
ν (C=N)
ν1 (NO3
)
ν4 (NO3
)
ν3 (NO3
)
La
1663
1655
1653
1662
1645
1651
1667
1637
1637
1657
1630
1630
1116
1127
1126
1114
1120
1121
1117
1130
1127
1117
1129
1144
1613
1620
1619
1613
1619
1623
1616
1626
1625
1614
1626
1624
[Eu4(NO3)10La3]·(NO3)2
[La4(NO3)10La3]·(NO3)2
Lb
1482, 1430
1495, 1454
1300, 1314
1300, 1308
1384
1384
[Eu4(NO3)10Lb3]·(NO3)2
[La4(NO3)10Lb3]·(NO3)2
Lc
1470, 1429
1461, 1432
1286, 1307
1302, 1319
1384
1384
[Eu4(NO3)10Lc3]·(NO3)2
[La4(NO3)10Lc3]·(NO3)2
Ld
1489, 1429
1470, 1428
1300, 1314
1300, 1317
1384
1384
[Eu4(NO3)10Ld3]·(NO3)2
1496, 1431
1477, 1422
1310, 1302
1300, 1294
1384
1384
[La4(NO3)10Ld3]·(NO3)2

S.-W. Chen et al. / Spectrochimica Acta Part A 62 (2005) 826–830
829
Table 3
Fluorescence data for the complexes
Complex
Concentration (mol dm−3
)
Solve
THF
λex (nm)
λem (nm)
RFI
Assignment
[Eu4(NO3)10La3]·(NO3)2
5.5 × 10−4
366
619
595
619
595
619
595
619
595
7130
1750
4330
1312
2658
746
5D0 → F2
7
5D0 → F1
7
[Eu4(NO3)10Lb3]·(NO3)2
[Eu4(NO3)10Lc3]·(NO3)2
[Eu4(NO3)10Ld3]·(NO3)2
5.5 × 10−4
5.5×10-4
5.5 × 10-4
THF
THF
THF
351
350
314
5D0 → F2
7
7
5D0 → F1
7
5D0 → F2
5D0 → F1
7
7
1475
42
5D0 → F2
5D0 → F1
7
7
5
7
5
7
4. Conclusion
to D0 → F1, and D0 → F2. The D0 → F3 emission
peaks are too weak to be observed at about 645–660 nm
range [2]. The emission at 619 nm from 5D0 → F2 electronic
7
According to the data and discussion above, obvious
changes in IR spectra were observed, after the ligands formed
complexes with Eu(III) and La(III) ions. In the complexes,
europium ions were coordinated to the C=O oxygen atoms
and phen nitrogen atoms. The complexes exhibited charac-
teristic fluorescence of europium ions. The terminal group
may affect the fluorescence of europium ions. Based on
those results, a series of new amide-based phenanthroline
derivatives could be synthesized to optimize the luminescent
properties of these lanthanide ions.
dipole transition is the strongest, suggesting low symmetry
around the Eu(III) ion [18]. Therefore, the peak height at
619 nm is used to measure the fluorescence intensities of
four europium complexes. From Fig. 2, the biggest fluo-
5
rescence intensities of D0–7F2 continually fall along with
the sterically hindered decrease of the terminal groups(from
dibenzylamide to N-methylbenzylamide, benzylamide and
diethylamide). Based on the antenna effect [19,20], the inten-
sity of the luminescence of Ln3+ complexes is related to the
efficiency of the intramolecular energy transfer between the
triplet energy level of the ligand and the emitting level of
the central ion, which depends on the gap between the two
levels. We consider that the positively effective group to the
fluorescence intensitiesof the Eu(III) complexesismainly the
phen, as can be deduced by the excited wave numbers. And
the terminal group is negatively effective to the fluorescence
intensity of the Eu(III) complex. The bridging ligand with
the smaller terminal group increases the coordinated ability
of O atoms of the C=O and Ar–O–C to lanthanide ions and
decreases the fluorescence intensity of the Eu(III) complexes,
respectively.
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.
References
[1] N. Sabbatini, M. Guardigli, J.-M. Lehn, Coord. Chem. Rev. 123
(1993) 201.
[2] F.S. Richardson, Chem. Rev. 82 (1982) 514.
[3] J.-C.G. Bu¨nzli, in: J.-C.G. Bu¨nzli, G.R. Choppin (Eds.), Lanthanide
Probes in Life, Chemical and Earth Sciences, Elsevier, Amsterdam,
1989 (Chapter 7).
[4] I. Hemmila, T. Stahlberg, P. Mottram, Bioanalytical Applications of
Labelling Techologies, Wallac Oy, Turku, 1995.
[5] B.S. Panigrahi, Spectrochim. Acta A 56 (2000) 1337.
[6] Y.-S. Yang, S.-H. Cai, Hua Xue Shi Ji 6 (1984) 133.
[7] Y.-Z. Ding, J.-Z. Lu, Y.-S. Yang, Hua Xue Shi Ji
201.
8 (1986)
[8] Y.-H. Wen, Z. Qin, W.-S. Liu, J. Radioanal. Nucl. Chem. 250 (2001)
285.
[9] M. Yamada, Y. Tanaka, Y. Yoshimoto, S. Kuroda, I. Shimao, Bull.
Chem. Soc. Jpn. 65 (1992) 1006.
[10] T.S. Eckert, T.C. Bruice, J. Am. Chem. Soc. 105 (1983) 4431.
[11] R.D. Gillard, R.E.E. Hill, J. Chem. Soc., Dalton Trans. (1974)
1217.
[12] L.-Y. Fan, W.-S. Liu, X.-M. Gan, N. Tang, M.-Y. Tan, W.-H. Jiang,
K.-B. Yu, Polyhedron 19 (2000) 779.
Fig. 2. Emission spectra of the europium complexes at room tem-
perature in THF solution concentration: 5.5 × 10−4 mol dm−3
. (1)
[Eu4(NO3)10La3]·(NO3)2 λex = 366 nm; (2) [Eu4(NO3)10Lb3]·(NO3)2
λex = 351 nm;
(3)
[Eu4(NO3)10Lc3]·(NO3)2
λex = 350 nm;
(4)
[Eu4(NO3)10Ld3]·(NO3)2 λex = 314 nm.
[13] W.J. Greary, Coord. Chem. Rev. 7 (1971) 81.

830
S.-W. Chen et al. / Spectrochimica Acta Part A 62 (2005) 826–830
[14] R.M. Silverstein, G.C. Bassler, T.C. Morrill, Spectrometric Identifi-
cation of Organic Compound, fifth ed., Wiley, New York, 1991.
[15] (a) N.F. Curtis, Y.M. Curtis, Inorg. Chem. 4 (1964) 804;
(b) K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, fifth ed., Wiley, New York, 1997.
[16] Y. Hirashima, K. Kanetsuki, I. Yonezu, Bull. Chem. Soc. Jpn. 56
(1983) 783.
[17] Y.-L. Zhang, W.-S. Liu, W. Dou, Spectrochim. Acta A. 60 (2004)
1707–1711.
[18] M. Albin, R.R. Wright Jr., W.D. Horrochs, Inorg. Chem. 24 (1985)
2491.
[19] J.-M. Lehn, Angew. Chem. Int. Ed. Engl. 29 (1990) 1304.
[20] M. Latva, H. Takalo, K. Simberg, J. Kankare, J. Chem. Soc., Perkin
Trans. 2 (1995) 995.