Design and coordination behavior of the first selective recognition ligand of 147Pm(III).

Article abstract of DOI:10.1039/b312381b

A new amide tripodal ligand, 6-[2-(2-diethylamino-2-oxoethoxy)ethyl]-N,N,12-triethyl-11-oxo-3,9-dioxa-6,12-diazatetradecanamide (4) has been designed and synthesized for the recognition of rare earth ions. Three representative complexes of trivalent lighter (La), middle (Gd), and heavier (Er) rare earth ions with 4 were synthesized and characterized by X-ray crystallography. In the complex, the heptadentate forms a cup-like coordination cavity encapsulating the central ion. Different supramolecular complex dimers are constructed by pi-pi interaction and van der Waals forces in accordance with the lanthanide contraction. The differences of the cavity and dimer structures were investigated further by assessing the separation efficiency of in multitrace solvent extraction of rare earth ions from picrate acid solution and the ligand has the best separation factor for 147Pm(III).

Full text of DOI:10.1039/b312381b

View Article Online / Journal Homepage / Table of Contents for this issue
Design and coordination behavior of the first selective recognition
ligand of 147Pm(III)†
Weisheng Liu,* Xiaofeng Li, Yonghong Wen‡ and Minyu Tan
Department of Chemistry and National Laboratory of Applied Organic Chemistry,
Lanzhou University, Lanzhou 730000, P. R. China. E-mail: liuws@lzu.edu.cn;
Fax: 86 931 8912582; Tel: 86 931 8912552
Received 6th October 2003, Accepted 23rd December 2003
First published as an Advance Article on the web 16th January 2004
A new amide tripodal ligand, 6-[2-(2-diethylamino-2-oxoethoxy)ethyl]-N,N,12-triethyl-11-oxo-3,9-dioxa-6,12-
diazatetradecanamide (4) has been designed and synthesized for the recognition of rare earth ions. Three
representative complexes of trivalent lighter (La), middle (Gd), and heavier (Er) rare earth ions with 4 were
synthesized and characterized by X-ray crystallography. In the complex, the heptadentate 4 forms a cup-like
coordination cavity encapsulating the central ion. Different supramolecular complex dimers are constructed by π–π
interaction and van der Waals forces in accordance with the lanthanide contraction. The differences of the cavity and
dimer structures were investigated further by assessing the separation efficiency of 4 in multitrace solvent extraction
of rare earth ions from picrate acid solution and the ligand has the best separation factor for 147Pm().
elements by tripodal ligands have been reported. Herein is
1
Introduction
reported a new amide tripodal ligand 4 designed by referring to
tripod 2 and the efficient extractant 1. The result of multitrace
solvent extraction of rare earths indicates it has the highest
recognition towards 147Pm(). Additionally, we also give a
detailed explanation on how the cup-like coordination structure
of 4 recognizes the guest metal ions through the matching of
the cup-like structure to the metal radii.
Crown ethers and cryptands have been widely studied in the
extraction of rare earth and actinide elements for their excellent
selectivity towards metal ions.1–4 Open chain polyethers offer
many advantages over traditional crown ethers, they are less
toxic, easily prepared, and can form a ring-like coordination
cavity and recognize rare earth cation whose size matches the
cavity.5–9 Ding et al.7 reported the extraction of lighter lan-
thanide ions with five derivatives of glycol-O,OЈ-diacetamide,
among which N,N,NЈ,NЈ-tetraphenyl-3,6-dioxaoctanediamide
(1) (Scheme 1) has the largest separation factor, and both the
factor and distribution ratio of light lanthanide ions for 1 are
larger than those for dicyclohexyl-18-crown-6 ether.10
147Pm (T 1/2 = 17.7 y) is the only man-made radioactive
element in rare earths. It is one of the most important fission
materials and a useful X-ray source for bone mineral determin-
ation in vivo and in vitro. However, no efficacious extractant
of this isotope has been reported.17,18 4 is the first selective
recognition ligand for 147Pm().
2
Experimental
2.1 Materials
The lanthanide picrates19 and α-chloride-N,N-diethyl-
acetamide20 were prepared following the literature methods.
THF and triethanolamine were dried using 4Å molecule sieves.
The radiotracer 152Eu was purchased from the China National
Nuclear Corporation. The other chemicals were of A. R. grade
and used without further purification.
2.2 Instrumentation
IR spectra were recorded on a Nicolet 170SXFT-IR instrument
using KBr discs in the 220–4000 cmϪ1 region. 1H NMR spectra
were measured on a FT-80A spectrometer in CDCl3 solution
with TMS as an internal standard. The metal ions were deter-
mined by EDTA titration using xylenal orange as an indicator.
C, N and H were determined using an Elementar Vario EL.
HRMS were determined on a Bruker Dalton APEXII 47e
Fourier transform spectrometer with EI ionization method.
X-Ray diffraction data were collected at room temperature
on a R3M/E four-circle diffractometer with graphite-mono-
chromated Mo-Kα-radiation (λ = 0.71073 Å). The unit-cell
parameters were determined by least-squares refinement of
24–25 reflections. The data sets were corrected for Lorentz and
polarization effects.
Scheme 1 Molecular structures of different selective ligands of rare
earth elements.
A suitably designed tripodal ligand is regarded as a potential
recognition reagent towards small molecules or ions.11–14 Kim
and Ahn developed a benzene-based tripodal oxazoline as an
efficient recognition system for some alkylammonium ions
which is valuable in clinical application.15 Wietzke et al. investi-
gated the complexation structures and Ln/An selectivities of
tripodal N-donor ligands 2 and 3 (Scheme 1).16 However, so far,
no systematic research on the recognition towards lanthanide
† Electronic supplementary information (ESI) available: Table S1: Ana-
lytical data for the complexes (%). Table S2: Selected bond lengths (Å)
and angles (Њ) for the complexes. See http://www.rsc.org/suppdata/dt/
b3/b312381b/
‡ Present address: College of Chemistry and Molecule Engineering,
Qingdao University of Science & Technology, Qingdao, 266042, P. R.
China.
2.3 Preparation of the ligand (4)
A solution of triethanolamine (1.5 g, 10 mmol) in THF was
added dropwise to a THF solution containing a suspension of
D a l t o n T r a n s . , 2 0 0 4 , 6 4 0 – 6 4 4
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
640

View Article Online
NaH (1.2 g, 60%, 30 mmol) and the mixture was stirred under
nitrogen at room temperature until gas evolution ceased.
Then, a solution of α-chloride-N,N-diethyl acetamide (4.9 g,
33 mmol) in THF was added dropwise to the mixture. After
refluxing for 6 h, the THF was evaporated and the residue
was washed by column chromatography (silica gel, CHCl3–
CH3CO2Et = 2 : 1) resulting in a yellow oil (4.3 g, yield = 56%).
1H NMR (CDCl3, δ/ppm): 1.08 (m, 18H, CH3), 2.82 (t, 6H,
NCH2), 3.33 (m, 12H, CONCH2), 3.59 (t, 6H, CH2O), 4.13 (s,
square prism for Gd and a monocapped square antiprism for
Er.
In the three complexes, 4 forms a cup-like coordination struc-
ture, which can be regarded as a distorted pseudo-monocapped
trigonal prism with N1 as the cap (Fig. 2). One triangle base
(∆1) comprises three carbonyl O atoms (O2, O4, O6), another
(∆2) consists of three ether O atoms (O1, O3, O5). The two
planes are almost parallel forming a dihedral angle of 5.8, 3.5
and 4.2Њ for the La, Gd and Er complexes, respectively. Within
three cup-like structures, La is the closest to ∆1 (1.0615, 1.1878
and 1.1975 Å from ∆1 for La, Gd and Er, respectively), while Er
is the closest to ∆2 (1.2359, 1.0568 and 0.985 Å from ∆2 for La,
Gd and Er, respectively). Simplified polyhedrons formed by
coordinated oxygen atoms are shown to clarify the differences
of three cup-like structures (see Fig. 2(aЈ), (bЈ) and (cЈ)).
The π–π stacking of the picrate anions in the supramolecular
complex dimers is illustrated schematically in Fig. 3. In the La
complex, the π–π stacking occurs between only two bidentated
picrate anions from two complex molecules. For the Gd com-
plex, four uncoordinated picrate anions from two [Gd(Pic)-
(4)](Pic)2 moieties form a two-layer π–π stacking. For the Er
complex, four free picrate anions and two bidentate ones from
two complex molecules form a linear π–π stacking.
6H, CH2CO); IR: ν/cmϪ1 1464 (C᎐O), 1121 (C–O–C), 1087
᎐
cmϪ1 (C–N). MS (FAB): m/z 489.4 ([M ϩ H]ϩ).
2.4 Synthesis of the complexes
Reactions of equal mol equiv. of lanthanide picrates and 4 in
absolute C2H5OH give the complexes [Ln(4)(Pic)3] (Ln = La,
Nd, Gd, Tb, Er) which were verified by analytical data (Table
S1†). Crystals suitable for single-crystal X-ray studies were
obtained by recrystallization from C2H5OH–CHCl3 (1 : 1).
CCDC reference numbers 196838–196840.
See http://www.rsc.org/suppdata/dt/b3/b312381b/ for crystal-
lographic data in CIF or other electronic format.
2.5 Solvent extraction
3.2 Extraction principle
The multitracer solution was prepared by use of UO2(NO3)2 as
the target material irradiated with a 60 MeV/nucleon 18O8ϩ ion
beam at the Heavy Ion Research Facility in Lanzhou, China.
The chemical separation procedure was similar to the liter-
ature.21 The obtained multitracer solution contained 12 radio-
active rare earth nuclides: 140La, 141Ce, 147Nd, 148Pm, 147Eu,
149Gd, 153Tb, 160Er, 167Tm, 166Yb, 177Lu and 87Y. The solvents
were saturated with each other prior to use to prevent volume
changes of the phases during extraction. The ionic strength was
adjusted to be 0.1 by a lithium chloride solution. An aqueous
picric acid solution (2.0 cm3) containing the required multi-
tracer at pH 2.50 was vigorously shaken with an equal volume
of a nitrobenzene solution of 4 at a test tube with a ground
stopper at room temperature for 5 min. After phase separation
by centrifugation (1 min, 3000 rpm), 1.0 cm3 samples were
taken from each phase and their γ-activities were assayed by use
of a calibrated HPGe γ-ray spectrometer. The detector has an
efficiency of 40% and a resolution of 2.3 keV at 1322 keV. The
γ-ray spectra recorded on 4096 channels were analyzed and
the peak areas of the spectra were computed with the code
SAMPO22 on a PII computer. Assignment of the nuclides to
each peak of the γ-ray spectra was made on the basis of its
energy and half-life. The distribution ratio (D) was determined
as a ratio of the radioactivity of the organic and aqueous
phases.
The overall extraction equilibrium between an aqueous solu-
tion of a trivalent metal cation (M3ϩ) and picrate anion (PicϪ)
and an organic solution of ligand (L) can be expressed as in
eqn. (1). The extraction equilibrium constant (Kex) can be
written by eqn. (2). In view of the tracer amount of mental
ions extracted, the distribution ratio, D, is given by eqn. (3).
Modification of eqn. (2) leads to eqn. (4). The complexation
stoichiometry (n) and the extraction equilibrium constant (Kex)
can be determined by use of the slope method according to eqn.
(4). The total ligand concentration in the organic phase is much
higher than that of the metal ion in the aqueous phase and the
distribution of free ligand can be neglected, so the total ligand
concentration was used here.
M3ϩaq ϩ 3PicϪaq ϩ nLorg ↔ [M(L)n(Pic)3]org
(1)
(2)
(3)
(4)
Kex = ([M(L)n(Pic)3]org)/([M3ϩ]aq[PicϪ]3aq[L]n
)
org
D = ([M(L)n(Pic)3]org)/[M3ϩ
]
aq
log(D/[PicϪ]3aq) = nlog[L]org ϩ logKex
3.3 Extraction of 152Eu
In order to establish the optimum extraction condition and
obtain the comparative distribution ratios of rare earth ions,
quantitative extraction experiments on 152Eu (single tracer)
were carried out at various pH values (Table 2) and concen-
trations of 4 (Table 3) using nitrobenzene as the diluent. The
experiment demonstrated that the extraction reaction could
reach equilibrium within 2 min.
3
Results and discussion
3.1 Crystal structures of the complexes
The structures of the La, Gd and Er complexes were deter-
mined by X-ray crystallography, and selected crystal data are
listed in Table 1. Selected bond lengths (Å) and angles are listed
in Table S2.† As we can see from Fig. 1(a), when coordinated to
La, 4 acts as a heptadentate ligand, three chains of it stretch
around and form a cup-like cavity to encapsulate the metal ion.
Two picrate anions (one unidentate and one bidentate) bind to
the cation through the spaces between the three chains. The
third picrate anion is linked to the complex cation by electro-
static forces. The coordination geometry around La is best
described as a bicapped distorted dodecahedron. The co-
ordination modes of Gd and Er with 4 are similar to that of the
La complex (see Fig. 1(b) and (c)), while only one bidentate
picrate is coordinated to the central ion and the other two
picrates lie outside of the coordination sphere. The metal
environment can be described as a monocapped distorted
It can be seen from Table 2 that the distribution ratio of 152Eu
reached a maximum at pH 2.5. The 4 concentration variation
experiment (Table 3) showed that the extraction of 152Eu was
quantitative with about 1.0 × 10Ϫ3 mol LϪ1 4 solution, and even
at the lowest 4 concentrations, the extractabilities were repro-
ducible. The data in Table 3 were analyzed by eqn. (4); the
log(D/[PicϪ]3aq) value when plotted as a function of log[4]org
gave a straight line of slope 1 (Fig. 4), indicating that the com-
plexation stiochiometry is 1 : 1. This is in agreement with the
crystal structures of the La, Gd and Er complexes determined
by X-ray crystallography. The value of logKex obtained from
the intercept of the straight line is 10.40. In addition, 0.5–1.0
mol LϪ1 perchloric acid, nitric acid and hydrochloric acid could
strip 152Eu3ϩ quantitatively, so 4 is a fine extrant.
D a l t o n T r a n s . , 2 0 0 4 , 6 4 0 – 6 4 4
641

View Article Online
Table 1 Selected crystal data for La, Gd and Er complexes with 4
Complex
[La(Pic)2(4)]Pic
[Gd(Pic)(4)](Pic)2
[Er(Pic)(4)](Pic)2
Formula
Mr
Crystal system
Space group
a/Å
b/Å
c/Å
C42H54N13O27La
1311.89
C42H54N13O27Gd
1330.23
C42H54N13O27Er
1340.24
Monoclinic
P21/n
12.337(2)
11.270(2)
38.712(6)
90
94.15(1)
90
5368.3(15)
4
Triclinic
Triclinic
¯
¯
P1
P1
13.600(2)
14.492(2)
15.816(3)
76.71(1)
85.20(1)
65.16(1)
2752.8(8)
2
12.184(2)
12.905(2)
18.305(2)
105.26(1)
91.22(1)
93.22(1)
2770.4(7)
2
α/Њ
β/Њ
γ/Њ
V/Å3
Z
Dc/g cmϪ3
θ Range/Њ
T /K
1.583
1.59–25.00
298
1.595
2.24–25.00
298
1.658
1.70–25.00
298
Crystal form
Crystal size/mm
Crystal color
Total data collected
Unique data
Range of h, k, l
Prismatic
0.56 × 0.54 × 0.48
Yellow
10364
9573
Prismatic
0.52 × 0.52 × 0.42
Yellow
10504
9666
Plate
0.68 × 0.40 × 0.16
Yellow
10831
7995
0 to 14
0 to 13
Ϫ46 to 45
0.0347
0.0839
0 to 15
0 to 14
Ϫ15 to 16
Ϫ18 to 18
0.0263
0.0577
0.586, Ϫ0.399
Ϫ14 to 14
Ϫ21 to 21
0.0274
0.0644
0.993, Ϫ0.591
R=Σ(||Fo| Ϫ |Fc||)/Σ|Fo|
Rw=Σ(w1/2||Fo| Ϫ |Fc||)/Σw1/2|Fo|
Largest diff. peak, hole/e ÅϪ3
0.701, Ϫ0.690
Fig. 1 Molecular structures of (a) [La(Pic)2(4)]Pic, (b) [Gd(Pic)(4)](Pic)2 and (c) [Er(Pic)(4)](Pic)2 with thermal ellipsoids at 50% probability. The
O13 in [Er(Pic)(4)]ؒ(Pic)2 is disordered.
Table 2 Effect of pH on the extraction of 152Eu3ϩ with a 2.0 × 10Ϫ4
mol LϪ1 nitrobenzene solution of 4 from a 0.02 mol LϪ1 aqueous picric
acid solution
pH
DEu
2.0
2.0
3.0
3.5
4.0
4.56
12.50
11.76
7.93
7.62
These values are plotted as a function of the reciprocal ionic
radius (rϪ1) of the rare earth in Fig. 5.
Fig. 2 The cup-like structures (a, b and c) and the corresponding
polyhedrons formed by coordinated oxygen atoms (aЈ, bЈ and cЈ) in the
La3ϩ, Gd3ϩ and Er3ϩ complexes.
It can be seen from Table 4 and Fig. 5 that the ligand 4
exhibits the highest extractability for promethium. Studies on
solvent extraction of rare earths with the common crown ethers
showed that 15-crown-5 exhibits the highest extractability for
samarium, and 18-crown-6 for praseodymium.3 The extract-
ability sequence observed is also in agreement with the crystal
structure determinations (see crystal structure section). This
sequence resulting from the extractabilities of rare earth ions
are determined not only by the cation–cavity size relationship
but by the hydration energy of the cation extracted as well. The
logKex values decrease from Pm to Lu with decreasing ionic
3.4 Rare earth ion selectivity
The results of extraction by the multitracer method were
analyzed according to eqn. (4). As exemplified with 152Eu3ϩ in
Fig. 4, 4 forms a 1 : 1 complex over the entire ligand concen-
tration range employed (1.0–5.0 × 10Ϫ4 mol LϪ1). The logKex
values are given as the intercepts of the log[4]org vs. log(D/
[PicϪ]3aq) plots, like that in Fig. 4, and are listed in Table 4.
D a l t o n T r a n s . , 2 0 0 4 , 6 4 0 – 6 4 4
642

View Article Online
Table 3 Effect of the concentration of 4 on extraction of 152Eu3ϩ from
Table 4 Extraction equilibrium constants (logKex) of complexes of 4
with rare earth picrates for the water–nitrobenzene system
0.02 mol LϪ1 picric acid solution at pH 2.5
104[4]/mol LϪ1
DEu
Eu (%)
RE
logKex
0.2
0.4
0.6
0.8
1
2
4
6
8
10
0.92
47.92
59.84
78.40
80.84
84.78
92.59
96.26
97.71
100
La3ϩ
Ce3ϩ
Nd3ϩ
Pm3ϩ
Eu3ϩ
Gd3ϩ
Tb3ϩ
Er3ϩ
Tm3ϩ
Yb3ϩ
Lu3ϩ
Y3ϩ
9.57
10.16
10.20
10.65
10.25
10.12
9.83
9.66
9.26
9.33
8.89
1.49
3.63
4.22
5.57
12.5
25.71
42.68
a
∞
∞
a
100
a ∞: Mo radioactivies were determined in the organic phase.
9.44
Fig. 3 Dimeric structures constructed by π–π stacking in the complexes of (a) La, (b) Gd and (c) Er. The disorder in the Er complex is not shown.
Fig. 4 Plot of log(D/[picϪ]3aq) vs. log[L]org for the extraction of 152Eu3ϩ
Fig. 5 Extraction equilibrium constants as a function of the reciprocal
from 0.02 mol LϪ1 picric acid solution at pH 2.5.
ionic radius of the rare earth.
radius because the extraction of aqueous heavier rare earths is
4
Conclusion
highly discouraged by the increased hydration energy.3 This
order suggests also that rare earth ions extracted are not com-
pletely dehydrated and the extraction process involves hydrated
species. The same models have been proposed by Mohapatra
and Manchanda23 and Inoue aqnd co-workers.3,4 The latter
studied in detail the participation of water of hydration in the
rare earth picrate complexes extracted by 18-crown-6 with
NMR spectroscopy and demonstrated that three water mole-
cules bound in the first solvation shell are brought into
the organic phase through extraction of the rare earth picrate.3
The mutual cation selectivities for each rare earth element
are listed in Table 5. It can be seen from Table 5 that it is
possible to separate promethium from other rare earth elements
by use of 4.
The new amide tripodal ligand 4 has been designed and syn-
thesized. The ligand as a new extractant has not only high
extractability but also excellent cation selectivity towards 147Pm.
To the best of our knowledge, 4 is the first selective recognition
ligand of 147Pm(). The coordination structures of its rare
earth complexes have been studied systematically in order to
explain its selectivity to lanthanide ions and to search for new
high-effective extracting agents for lanthanide separation. The
La, Gd and Er complexes differ in crystal system, space group
and supramolecular structure. The coordination number, cup-
like structure and supramolecular dimer display a systematic
change consistent with lanthanide contraction. This may be a
main reason why 4 has a coordination selectivity to different
D a l t o n T r a n s . , 2 0 0 4 , 6 4 0 – 6 4 4
643

View Article Online
Table 5 Relative cation selectivity as measured by Kex ratios
RE
RE/La
RE/Ce
RE/Nd
RE/Pm
RE/Eu
RE/Gd
RE/Tb
RE/Er
RE/Tm
RE/Yb
RE/Lu
RE/Y
La
Ce
Nd
Pm
Eu
Gd
Tb
Er
Tm
Yb
Lu
Y
–
0.26
–
0.23
0.91
–
0.17
0.65
0.71
–
0.79
0.59
0.30
0.20
0.08
0.10
0.03
0.12
0.21
0.81
0.89
1.26
–
0.74
0.38
0.26
0.10
0.12
0.04
0.15
0.28
1.10
1.20
1.70
1.35
–
0.51
0.35
0.14
0.16
0.06
0.21
0.55
2.14
2.34
3.31
2.63
1.95
–
0.68
0.27
0.32
0.11
0.41
0.81
3.16
3.47
4.90
3.89
2.88
1.48
–
0.40
0.47
0.17
0.60
2.04
7.94
8.71
12.30
9.77
7.24
3.72
2.51
–
1.74
6.76
7.41
10.47
8.32
6.17
3.16
2.14
0.85
–
4.79
18.62
20.42
28.84
22.91
16.98
8.71
5.89
2.34
2.75
–
1.35
5.25
5.75
8.13
6.46
4.79
2.45
1.66
0.66
0.78
0.28
–
3.89
4.27
6.03
4.79
3.55
1.82
1.23
0.49
0.58
0.21
0.74
1.10
1.55
1.23
0.91
0.47
0.32
0.13
0.15
0.05
0.19
1.41
1.12
0.83
0.43
0.29
0.11
0.13
0.05
0.17
1.17
0.43
1.51
0.36
1.29
3.55
6 Y.-S. Yang and Y.-Z. Ding, J. Nucl. Radiochem., 1982, 4, 21.
7 Y.-Z. Ding, J.-C. Lu, Y.-S. Yang, G.-Z. Tan and J.-Z. Xu, Huaxue
Shiji, 1986, 8, 201.
8 Y.-S. Yang and S.-H. Cai, Huaxue Shiji, 1985, 6, 133.
9 S.-X. Liu, W.-S. Liu, M.-Y. Tan, K.-B. Yu and G.-Z. Tan, Helv.
Chim. Acta, 1997, 80, 586.
10 Y. Gao and J.-Z. Ni, J. Nucl. Radiochem., 1983, 5, 146.
11 M. P. Lowe, P. Caravan, S. J. Rettig and C. Orvig, Inorg. Chem.,
1998, 37, 1637.
lanthanide ions. In addition, the complexes have an excellent
liposolubility, therefore the coordination selectivity and extract-
ability could be improved to some extent by adding picric acid
to the extraction system. Further studies on the amide tripodal
compounds as extractants must be of significance, and the data
harvested will be helpful to the predetermined synthesis of new
extractants.
12 C.-Y. Su, B.-S. Kang, H.-Q. Liu, Q.-G. Wang, Z.-N. Chen, Z.-L. Lu,
Y.-X. Tong and T. C. W. Mak, Inorg. Chem., 1999, 38, 1374.
13 Y. Bretonnière, M. Mazzanti, R. Wietzke and J. Pécaut, Chem.
Commun., 2000, 1543.
14 Y. Bretonnière, R. Wietzke, C. Lebrun, M. Mazzanti and J. Pécaut,
Inorg. Chem., 2000, 39, 3499.
15 S.-G. Kim and K. H. Ahn, Chem. Eur. J., 2000, 18, 3399.
16 R. Wietzke, M. Mazzanti, J.-M. Latour, J. Pécaut, P.-Y. Cordier and
C. Madic, Inorg. Chem., 1998, 37, 6697.
Acknowledgements
This work was supported by NSFC (Grants 20071015,
20371022 and QT project), University Doctoral Foundation of
the Ministry of Education (Grant 200307300015), and Key
project of the Ministry of Education of China (Grant 01170).
17 D. Nayak, S. Lahiri and N. R. Das, J. Radioanal. Nucl. Chem., 1999,
244, 555.
18 M. L. P. Reddy, M. S. Murali and J. N. Mathur, J. Radioanal. Nucl.
Chem., 1998, 230, 29.
19 Y.-C. Tian, Y.-Q. Liang and J.-Z. Ni, Chem. J. Chin. Univ., 1988, 9,
113.
References
1 F. D. Jong and D. N. Rdinhoudt, Stability and Reactivity of Crown
Ether Complexes, Academic, London, 1981, pp. 3–30.
2 R. D. Rogers, L. K. Kurihara and E. J. Voss, Inorg. Chem., 1987, 26,
2360.
3 K. Nakagawa, S. Okada, Y. Inoue, A. Tai and T. Hakushi,
Anal. Chem., 1988, 60, 2527.
4 Y. Inoue, K. Nakagawa and T. Hakushi, J. Chem. Soc.,
Dalton Trans., 1993, 15, 2279.
5 J.-C. G. Bünzli, Handbook on the Physics and Chemistry of Rare
Earths, ed. K. A. Gschneider Jr. and L. Eyring, Elsevier Science,
Amsterdam, 1987, vol. 9, p. 321.
20 H. Röhnert, Arch. Pharm., 1960, 293, 573.
21 X. Yin, J. Du, X. Zhang, X. Wang, X. Dai, T. Sun and Z. Tao,
J. Radioanal. Nucl. Chem. Lett., 1996, 214, 89.
22 J. T. Routti and S. G. Prussin, Nucl. Instrum. Methods, 1969, 72,
125.
23 P. K. Mohapatra and V. K. Manchanda, J. Radioanal. Nucl. Chem.,
1999, 241, 101.
D a l t o n T r a n s . , 2 0 0 4 , 6 4 0 – 6 4 4
644