Complexation and extractability studies of lanthanide elements by 2,2′-[1,2-phenylenebis(oxy)]-bis(N-methyl-N-phenyl(acetamide))

Article abstract of DOI:10.1016/S0277-5387(03)00329-2

Solid complexes of lanthanide picrates with 2,2′-[1,2-phenylenebis(oxy)]-bis(N-methyl-N-phenyl(acetamide)) (L) have been prepared and characterized by elemental analysis, conductivity measurements, IR, electronic and ¹H NMR spectroscopies. The crystal structure of terbium complex shows a nona-coordination polyhedron in the form of a distorted mono-capped square antiprism. The extractability of lanthanide ions by L has been investigated using multitracer technology.

Full text of DOI:10.1016/S0277-5387(03)00329-2

Polyhedron 22 (2003) 1695ꢀ1699
/
www.elsevier.com/locate/poly
Complexation and extractability studies of lanthanide elements by
2,2?-[1,2-phenylenebis(oxy)]-bis(N-methyl-N-phenyl(acetamide))
Yu-Liang Zhang a, Wei-Hua Jiang a, Wei-Sheng Liu a,*, Yong-Hong Wen a,
Kai-Bei Yu b
a College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China
b Chengdu Center of Analysis and Measurement, Academia Sinica, Chengdu 610041, China
Received 3 March 2003; accepted 25 April 2003
Abstract
Solid complexes of lanthanide picrates with 2,2?-[1,2-phenylenebis(oxy)]-bis(N-methyl-N-phenyl(acetamide)) (
L) have been
1
prepared and characterized by elemental analysis, conductivity measurements, IR, electronic and H NMR spectroscopies. The
crystal structure of terbium complex shows a nona-coordination polyhedron in the form of a distorted mono-capped square anti-
prism. The extractability of lanthanide ions by L has been investigated using multitracer technology.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Lanthanide picrates complexes; X-ray structures; Solvent extraction
1. Introduction
consideration with the crystal structure
Acyclic polyethers offer many advantages over the use
of crown ethers in the extraction and analysis (ion-
selective electrodes) of rare earth metals. Their ring-like
coordination structures and terminal group effects on
the extractability have been widely studied [1ꢀ5]. Ding
/
et al. have reported that an amide acyclic polyether
N,N,N?,N?-tetraphenyl-3,6-dioxaoctanediamide has a
larger separation factor and distribution ratio to lighter
lanthanide ions than that of dicyclohexyl-18-crown-6
ether. The picrate ion (picꢁ) is often used as accom-
panying ion and enters the organic phase in the
extraction. To investigate the effects of the skeleton
and terminal group on the coordination property and
extractability of lanthanide ions, we prepared another
amide acyclic polyether 2,2?-[1,2-phenylenebis(oxy)]-
2. Experimental
bis(N-methyl-N-phenyl(acetamide)) (
earth metal picrate complexes. The extractability by
for rare earth metal ions has also been discussed in
L) and its rare
L
2.1. Materials
Lanthanide picrates [6] and
L [7] were prepared
according to literature methods. All commercially
available chemicals were of A.R. grade and were used
without further purification.
* Corresponding author. Tel.: ꢂ
891-2582.
E-mail address: liuws@lzu.edu.cn (W.-S. Liu).
/
86-931-891-2552; fax: ꢂ86-931-
/
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00329-2

1696
Y.-L. Zhang et al. / Polyhedron 22 (2003) 1695ꢀ1699
/
2.2. Preparation of the ligand (L)
Table 1
Crystal data and structure refinement for the complex [Tb(pic)3L]
Anhydrous K2CO3 (5.6 g, 41 mmol) was added into
the 20 ml DMF solution of pyrocatechol (2.20 g, 20
mmol) at 100 8C. After 0.5 h, a solution of N-methyl-N-
phenylchloroacetamide in 10 ml DMF was added
dropwise to the mixture and maintained at 110 8C for
7 h. When cooled, 60 ml distilled water was poured and
the turbid solution was extracted by 40 ml chloroform
three times. Organic phase was washed with water and
dried with anhydrous Na2SO4. Solvent removed, the
residue was chromatographed to afford white solid (L)
(yield: 82%).
Empirical formula
Temperature (K)
Formula weight
Crystal size (mm)
Crystal system
Space group
C48H39N14O25Tb
285(2)
1370.85
0.56ꢃ
/
0.48ꢃ0.20
/
triclinic
¯
P1
/
˚
a (A)
14.273(2)
14.955(2)
16.572(2)
97.898(9)
111.386(8)
113.090(7)
2862.9(7)
2
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
V (A )
˚
Z
Dcalc (g cmꢁ3
F(0 0 0)
)
1.590
1380
2.3. General preparation of the complexes
˚
L (A)
0.71073
10578
9683
Reflections collected
Independent reflections
u Range for data collection
Range of h, k, l
A solution of 0.1 mmol lanthanide picrate in 5 ml
anhydrous ethanol was added dropwise to a solution of
L in 10 ml anhydrous ethanol. The mixture was stirred
at room temperature for 5 h. The precipitated solid
complex was filtered, washed with ethanol and dried in
vacuo over P4O10 for 2 days.
1.57ꢀ
05h 5
165k 5
195l 518
0.794
R1ꢄ0.0363, wR2ꢄ
R1ꢄ0.0638, wR2ꢄ
0.362, ꢁ0.419
/25.01
/
/16
ꢁ/
/
/15
ꢁ/
/
/
Gooding-of-fit on F2
Final R indices [I ꢀ
R indices (all data)
˚
Largest difference peak hole (e A
/
2s(I)] a
/
/
0.0563
0.0603
All the complexes are yellow powers and stable in air.
Single crystals of the solvated terbium complex
/
/
ꢁ3
)
/
[Tb(pic)3L]×
/
3MeCN were grown and recrystallized
a
wꢄ
/
1/[s2(Fo2)ꢂ
/
(0.0337P)2]; Pꢄ
/
(Fo2ꢂFc2)/3.
/
from MeCN with slow evaporation at room tempera-
ture. About a month later, transparent yellow crystals
formed from the solution.
2.6. Solvent extraction
The multitracer solution was prepared by using gold
foil as the target material irradiated with 60 MeV
nucleonꢁ1 18O8ꢂ ion beam at the Heavy Ion Research
Facility in Lanzhou, China. The chemical separation
procedure was similar to that described in the literature
[8]. The multitracer solution obtained contained nine
radioactive rare earth nuclides: 141Ce, 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. Ion
strength was adjusted to be 0.1 by a lithium chloride
solution. An aqueous picric acid solution (2.0 cm3)
containing the required multitracer at pH 2.50 was
vigorously shaken with an equal volume of the nitro-
benzene solution of L in 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 g-
activities were assayed using of a calibrated HPGe g-
ray spectrometer. The detector has an efficiency of 40%
and resolution of 2.3 keV at 1322 keV. The g-ray spectra
recorded on 4096 channels were analyzed and the peak
areas were computed with the SAMPO [9] program.
Assignment of the nuclides to each peak of the g-ray
spectra was made on the basis of its energy and half-life.
The distribution ratio (D) was determined as a ratio of
2.4. Chemical and physical measurements
The metal ions were determined by EDTA titration
N analysis
using xylenal orange as an indicator. CÃ
/
HÃ
/
was determined by using a Vario-EL analyzer. Con-
ductivity was determined using a conductivity bridge
with 10ꢁ3 mol cmꢁ3 in MeOH at 25 8C. IR spectra were
recorded on a Nicolet AVATAR 360 FT-IR instrument
using KBr discs in the 400ꢀ
4000 cmꢁ1 region. 1H NMR
/
spectra were measured on a Brucker AM200 spectro-
meter in CD3COCD3 solution with TMS as internal
standard.
2.5. X-ray crystallography
For the terbium complex, X-ray measurements were
performed on a Siemens P4 four-circle diffractometer
with graphite monochromatized Mo Ka radiation at
285(2) K. A summary of crystallographic data and
details of the structure refinements are listed in Table 1.
The structure was solved by direct methods and refined
by full matrix least-squares techniques with all non-
hydrogen atoms treated anisotropically. All calculations
were performed with the program package SHELXTL
.

Y.-L. Zhang et al. / Polyhedron 22 (2003) 1695ꢀ
/
1699
1697
Table 2
Analytical data and molar conductance values for [Ln(pic)3L] (Lnꢄ
/Gd, Tb, Er, Y)
Complex
C (%) found (calc.)
H (%) found (calc.)
N (%) found (calc.)
Ln (%) found (calc.)
Lm (s cm2 molꢁ1
)
Gd(pic)3L
Tb(pic)3L
Er(pic)3L
Y(pic)3L
40.52(40.48)
40.45(40.43)
40.19(40.16)
42.82(42.83)
2.71(2.43)
2.57(2.43)
2.36(2.41)
3.23(2.57)
12.42(12.37)
12.32(12.45)
12.52(12.27)
13.08(13.09)
12.62(12.52)
12.74(12.70)
13.32(13.02)
7.55(7.70)
19.27
16.58
18.33
16.52
the radioactive strengths of the organic and aqueous
phases.
to 6.94 ppm). This is probably due to the inductive effect
of LnÃO (L) bands and a change in the conformation of
the ligand in the complexes. The larger shift for ÃC(O)Ã
CHÃ protons than for ÃC6H4Ã protons indicates that
the LnÃO (CÄO) bond is stronger than the LnÃO (ArÃ
OÃC) bond [11].
/
/
/
/
/
/
/
/
/
/
3. Result and discussion
/
1
The H NMR signal of the OH group in free HPic
disappears in the complexes, indicating that the H-atom
of the OH group is replaced by Ln(III). The benzene ring
protons of the free HPic exhibit a singlet at 9.12 ppm.
Upon coordination, the signal moves to higher field,
respectively, at 9.02 ppm. Only one singlet is observed
for the benzene ring protons of the three coordination
picrate groups indicating fast exchange among the
group in solution [12].
Analytical data for the complexes (presented in Table
2) conform to a 1:3:1 metal-to-picrate-to-L stoichiome-
try. All complexes are soluble in DMSO, DMF, MeCN,
methanol and acetone, and are slightly soluble in
ethanol, chloroform and ethyl acetate. They are spar-
ingly soluble in benzene, Et2O and cyclohexane. The
molar conductance values of the complexes in methanol
(Table 2) indicate the presence of a non-electrolyte [10].
3.1. IR spectra
3.3. X-ray crystal structure
The IR spectrum of free L shows bands at 1677 and
1117 cmꢁ1 assigned to n(CÄ
complexes, the bands shift by approximately 45 and 35
/
O) and n(ArÃ
/
OÃ
/
C). In the
Fig. 1 shows the structure and the atomic numbering
schemes for the Tb(III) complex in [Tb(pic)3L]×
Selected bond lengths and angles are given in Table 3.
/
3MeCN.
cmꢁ1 towards lower wavenumbers, indicating that the
CÄ
metal ions. The different shifts of the wavenumbers
indicate that the LnÃO (carbonyl) bond is stronger than
the LnÃO (ether) bond.
/O and ether O-atoms take part in coordination to the
Table 3
/
˚
Selected bond lengths (A) and angles (8) for the Tb complex
/
Bond lengths
The OH out-of-plane bending vibration of free HPic
at 1151 cmꢁ1 disappears in the spectra of the complex,
indicating that the H-atom of the OH group is replaced
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
/
O(1)
O(3)
2.331(3)
2.545(2)
2.264(3)
2.562(3)
2.606(3)
TbÃ
TbÃ
TbÃ
TbÃ
/
O(2)
O(4)
2.567(2)
2.352(3)
2.279(3)
2.240(3)
/
/
/
O(5)
O(18)
O(25)
/
O(12)
O(19)
by Ln(III). The vibration n(CÃ
/
O) at 1265 cmꢁ1 is shifted
/
/
toward higher frequency by approximately 10 cmꢁ1 in
the complex. This is due to the following different
/
Bond angles
O(1)Ã
O(1)Ã
O(1)Ã
O(1)Ã
O(1)Ã
O(1)Ã
O(1)Ã
O(1)Ã
O(2)Ã
O(2)Ã
O(2)Ã
O(2)Ã
O(2)Ã
O(2)Ã
O(2)Ã
O(3)Ã
O(3)Ã
O(3)Ã
/
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
/
O(2)
63.60(9)
124.19(9)
158.41(9)
80.8(1)
O(3)Ã
O(3)Ã
O(3)Ã
O(4)Ã
O(4)Ã
O(4)Ã
O(4)Ã
O(4)Ã
O(5)Ã
O(5)Ã
O(5)Ã
O(5)Ã
O(12)Ã
O(12)Ã
O(12)Ã
O(18)Ã
O(18)Ã
O(19)Ã
/
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
TbÃ
/
O(18)
O(19)
O(25)
O(5)
90.6(1)
142.48(9)
143.84(9)
80.5(1)
effects. First, after forming the LnÃ
/
O bond, the p-bond
/
/O(3)
/
/
character in the CÃO bond increases. Secondly, coordi-
/
/
/O(4)
/
/
nation of the oxygen atom of L to Ln(III) causes the p-
character to be weakened. The free HPic has ns(NO2) at
1342 cmꢁ1, which splits into two band at approximately
1362 and 1329 cmꢁ1, respectively, in the complexes.
This indicates that the nitronyl O-atoms take part in
coordination [6].
/
/O(5)
/
/
/
/
O(12)
O(18)
O(19)
O(25)
O(3)
87.8(1)
130.5(1)
85.0(1)
/
/
O(12)
O(18)
O(19)
O(25)
O(12)
O(18)
O(19)
O(25)
113.6(1)
64.9(1)
81.5(1)
/
/
/
/
/
/
/
/
/
/
66.2(1)
/
/
121.8(1)
142.51(9)
144.1(1)
80.8(1)
/
/
60.60(8)
119.77(9)
72.18(9)
70.77(9)
133.03(9)
140.97(9)
115.88(9)
63.07(9)
81.58(9)
75.60(9)
/
/
/
/O(4)
/
/
/
/O(5)
/
/
3.2. 1H NMR spectra
/
/
O(12)
O(18)
O(19)
O(25)
O(4)
/
/
133.68(9)
66.2(1)
/
/
/
/
O(18)
O(19)
O(25)
O(19)
O(25)
O(25)
1
The H NMR spectra of free L and its lanthanide
complexes were measured in CD3COCD3. Upon coor-
/
/
/
/
133.9(1)
70.09(9)
84.7(1)
/
/
/
/
/
/
/
/
dination, the signals of Ã
lower field by 0.42 ppm (from 4.46 to 4.88 ppm) and
those of ÃC6H4Ã protons by only 0.09 ppm (from 6.85
/
C(O)Ã
/
CHÃ
/
are shifted towards
/
/O(5)
/
/
65.5(1)
/
/O(12)
/
/
65.4(1)
/
/

1698
Y.-L. Zhang et al. / Polyhedron 22 (2003) 1695ꢀ1699
/
Fig. 1. Molecular structure of [Tb(pic)3L] with atom labeling scheme.
The crystal structure is composed of [Tb(Pic)3L] and
on the oxygen anion of the picrate and the smaller steric
3CH3CN linked by van der Waals’ forces. Tb(III) ion is
nona-coordinated by four oxygen atoms of L and five
O-atoms of two bidentate and one unidentate picrates.
The coordination polyhedron is a distorted mono-
capped square anti-prism. Four O-atoms of L (O(1),
˚
effect. The TbÃ
/
O (CÄ
/
O) distance (mean 2.342 A) are
O (ArÃOÃC) distance
(mean 2.556 A), which suggests that the TbÃO (CÄO)
C) bond, in
significantly shorter than the TbÃ
/
/
/
˚
/
/
bond is stronger than the TbÃ
/
O (ArÃ
/
OÃ
/
1
agreement with the H NMR and IR spectral data.
O(2), O(3), O(4)) are not quite coplanar. Their deviation
˚
0.16 A. The
from the mean plane is in the range of 0.09ꢀ
/
3.4. Extracting data
˚
Tb atom lies out of this plane by 0.40 A. The average
distance between the Tb(III) ion and the coordination
˚
O(19) is the
Table 4 shows the distribution ratios and separation
coefficients of the lanthanide ions for L. The data
indicate that the sequence of the extractability of the
oxygen atoms is 2.416 A, where the TbÃ
/
shortest, owing probably to the higher electron density
Table 4
The distribution ratios and separation coefficients of rare earth ions for L
Ce
Eu
Gd
Tb
Er
Tm
Yb
Lu
Y
a
b
b
b
b
b
a
b
b
b
b
b
b
a
b
b
b
b
b
b
b
a
b
b
b
b
b
b
b
b
D
1.88
1.21
0.64
0.91
0.48
0.75
0.52
0.28
0.43
0.57
0.21
0.11
0.17
0.23
0.40
RE/Ce
RE/Eu
RE/Gd
RE/Tb
RE/Er
RE/Tm
RE/Yb
RE/Lu
RE/Y
ꢀ/
1.55
2.07
3.62
ꢀ/
1.33
2.33
ꢀ/
1.75
4.33
ꢀ/
2.48
b
8.95
b
5.76
b
ꢀ
/
b
b
ꢀ
/
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
ꢀ
/
b
b
b
ꢀ
/
b
b
ꢀ
/
Aqueous phase: [Hpic]ꢄ
/
0.02 mol lꢁ1, pH 2.50; organic phase: [L]ꢄ
/
5.0ꢃ
/
10ꢁ4 mol lꢁ1; Tꢄ
18 8C.
/
a
Very low D or no extraction.
Unable to calculate.
b

Y.-L. Zhang et al. / Polyhedron 22 (2003) 1695ꢀ
/
1699
1699
rare earth ions for L is in an inversive order. This is
because the extraction of lanthanide ions from the
aqueous phase to the organic phase gets more difficult
with increasing atomic number.
In conclusion, L, acting as a tetradentate ligand, can
form stable solid complexes with lanthanide ions and
exhibits a caverned conformation, which is suitable for
the uptake of a cation. The internal cavity formed by the
coordination oxygen atoms is sensitive to the variation
of the lanthanide ions. In addition, the coordination
stability also depends heavily on the ligand’s terminal
group.
Acknowledgements
We are grateful to the National Natural Science
Foundation of China (projects 29571014 and
20071015), the Foundation for University Key Teachers
of the Ministry of Education, and a Key Project of the
Ministry of Education of China (01170) for financial
support.
References
[1] S.X. Liu, W.S. Liu, M.Y. Tan, K.B. Yu, G.Z. Tan, Helv. Chim.
Acta 80 (1997) 586.
[2] L.Y. Fan, W.S. Liu, X.M. Gan, N. Tang, M.Y. Tan, W.H. Jiang,
K.B. Yu, Polyhedron 19 (2000) 779.
[3] Y.S. Yang, Y.Z. Ding, G.Z. Tan, J.Z. Xu, Z.Q. Yiao, F.S. Zhang,
J. Nucl. Radiochem. 6 (1984) 196.
4. Supplementary material
[4] Y. Gao, J.Z. Ni, J. Nucl. Radiochem. 5 (1983) 146.
[5] Y. Yang, Y. Ding, J. Nucl. Radiochem. 4 (1982) 21.
[6] Y.C. Tian, Y.Q. Liang, J.Z. Ni, Chem. J. Chin. Univ. 9 (1988)
113.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Center, CCDC No. 200308. Copies of this
information may be obtained free of charge from the
director, CCDC, 12 Union Road, Cambridge CB2 IEZ,
[7] W. Zhang, H.W. Hu, Nanjing Daxue Xuebao 21 (1985) 662.
[8] X. Yin, J. Du, X. Zhang, X. Wang, X. Dai, T. Sun, Z. Tao, J.
Radioanal. Nucl. Chem. Lett. 214 (1996) 89.
[9] J.T. Routti, S.G. Prussin, Nucl. Instrum. Methods 72 (1969) 125.
[10] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[11] S.X. Liu, W.S. Liu, M.Y. Tan, K.B. Yu, J. Coord. Chem. 10
(1996) 391.
UK (fax: ꢂ
/
44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
[12] X. Mao, L.F. Shen, J.Z. Ni, Bopuxuezazhi 1 (1985) 201.