JOURNAL OF CHEMICAL RESEARCH 2011
RESEARCH PAPER 187
MARCH, 187–189
Synthesis and fluorescent properties of Eu and Tb complexes of a
new aryl amide ligand
Yanhua Zhang, Xiang Chen and Damin Tian*
Department of Chemistry and Chemical Engineering, Henan University of Urban Construction, Pingdingshan, Henan 467036, P. R. China
A new ligand, 1,2-bis[(2-benzyloxy)benzoylamino]ethane, and its complexes of europium and terbium have been
synthesised and characterised. Under UV light, the europium and terbium complexes exhibited characteristic
emissions and measurement of the lowest triplet state energy level of the ligand indicates that it matches better to
the lowest resonance energy level of the Tb(III) ion than to that of the Eu(III) ion.
Keywords: aryl amide ligand, rare earth, complexes, fluorescence
obtained on a Hitachi F-4500 spectrofluorometer. The excitation and
emission slit widths were 2.5 nm and the PMT voltage was 700 V.
Preparation of ligand 1: The synthetic route for 1 is shown in
Scheme 1. 1,2-bis(2-hydroxybenzoylamino)ethane (10 mmol), potas-
sium carbonate (24 mmol) and DMF (100 mL) were warmed to ca
92 °C. After half an hour, benzyl bromide (20 mmol) was added. The
reaction mixture was stirred at 92–95 °C for 15 h. After cooling down,
the mixture was poured into pure water (200 mL). The resulted solid
was filtered and washed by pure water several times, then dried to
get the white ligand 1, yield 90%, m. p. 172–174 °C; 1H NMR
(CDCl3, 400 MHz): 3.55 (d, 4H, –CH2–N), 5.15 (s, 4H, –CH2–O),
6.95–7.95 (m, 18H, ArH), 8.29 (s, 2H, N–H); IR (KBr): 1642 (s,
C=O), 1594 (m), 1531 (m), 1486 (m), 1450 (m), 1299 (m), 1218 (m,
ArO), 1100 (m, C–O–C), 810 (w), 750 (s), 698 (m). Anal. (Calcd) C,
74.96 (74.98); H, 5.94 (5.87); N, 5.69 (5.83); O, 13.29 (13.32)%.
Preparation of the complexes: An ethyl acetate solution (5 mL) of
Ln(NO3)3·6H2O (Ln = Eu or Tb) (0.1 mmol) was added dropwise to
a solution of 0.1 mmol of 1 in chloroform (5 mL). The mixture was
stirred at room temperature for 5 h, then the precipitated complex was
filtered, washed with ethyl acetate and chloroform and dried in vacuo
over P4O10 for 48 h. Both complexes were obtained as white powders,
yield 70–78 %.
Compounds containing lanthanide(III) ions have widely been
used as probes and labels in a variety of biological and chemi-
cal applications1,2 because of their unique luminescence
properties, such as long fluorescent decay time3 and narrow
emission bands.4,5 Since f–f transitions are spin- and parity-
forbidden, the exited state of the lanthanide ion is populated
through intramolecular energy transfer from the ligand to the
lanthanide ion (antenna effect).6 It is generally accepted that
the energy transfer from ligand to lanthanide(III) ion occurs
from the lowest triplet state energy level T1 of the ligand to the
resonance level of the lanthanide(III) ion.7 This energy transfer
process is one of the most important processes influencing
the luminescence properties of lanthanide complexes, so it is
essential to design the ligand to optimise the luminescent pro-
perties of these lanthanide ion by facilitating the well-known
light conversion process and forming strongly luminescent
lanthanide ion complexes.8 We have designed and prepared a
new aryl amide ligand 1,2-bis[(2-benzyloxy)benzoylamino]et
hane (1, Scheme 1) and its europium(III) and terbium(III)
complexes, and studied the fluorescent properties of the com-
plexes in detail. The lowest triplet state energy level T1 of 1
matches the lowest resonance level of the Tb(III) ion better
than that of the Eu(III) ion.
Results and discussion
Analytical data for the complexes listed in Table 1 show a 1:1 metal-
to-1 stoichiometry. Both complexes are soluble in DMF, DMSO,
acetonitrile and acetone, and slightly soluble in methanol, ethanol,
chloroform and ethyl acetate. Conductivity measurement results in
acetone (Table 1) indicate that both complexes act as nonelectrolytes11,
implying that all nitrate groups are in the coordination sphere.
The most important IR peaks of the ligand and its complexes are
presented in Table 2. The IR spectra of the complexes are similar
to each other, which indicates that their structures are similar.
The IR spectrum of the free ligand shows strong bands at 1642 and
1100 cm−1, which are attributable to [ν(C=O)] of the amide group and
ν(C-O-C), respectively. In the synthesised complexes, the low-energy
band remains unchanged, but the high-energy band red shifts to about
1615 cm−1 (Δ ν = 27 cm−1) as compared to its counterpart for the free
ligand, thus indicating that only the oxygen atom of C=O takes part in
Experimental
1,2-bis(2-hydroxybenzoylamino)ethane9 and rare earth nitrates10 were
prepared according to the literature methods. All commercially
available chemicals were of A.R. grade and were used without further
purification. The metal ions were determined by EDTA titration using
xylenol orange as an indicator. Carbon, hydrogen and nitrogen analy-
ses were determined using a PE-2400(II) Elementar instrument. IR
spectra were recorded on a Perkin-Elmer Spectrum One instrument
using KBr pellets in the 4000–400 cm−1 region. Conductivity mea-
surements were carried out with a DDS-11A conductivity bridge
using 1.0×10−4 mol·L−1 solution in acetone at 25 °C. 1H NMR spectra
were measured on a Bruker Avance 400 spectrometer in CDCl3 solu-
tion with TMS as internal standard. Luminescence spectra were
Scheme 1 The synthetic route for the ligand 1.
* Correspondent: E-mail: tiandamin2009@163.com