Synthesis and structural characterization of new lanthanide coordination polymers with nitrilotriacetic acid

Article abstract of DOI:10.1016/j.molstruc.2004.01.019

Reported herein are the hydrothermal synthesis and crystal structures of four lanthanide coordination polymers with nitrilotriacetic acid (H ₃NTA) [Ln(NTA)(H₂O)]_n (Ln=La, 1; Pr, 2; Nd, 3; Eu, 4). Despite similar syntheses, compounds 1 to 4 show transformation in coordination mode of NTA and coordination number of Ln³⁺ duo to lanthanide contraction. The Ln(III) ions in 1 and 2 are nine-coordinated and connected through octadentate bridging ligands (NTA) to form a three-dimensional network. The Ln(III) ions in 3 and 4 are eight-coordinated and bridged by heptadentate bridging ligands (NTA) to form an extended two-dimensional layer structure, which further construct a three-dimensional supramolecular structure via coordination bond and three-centered hydrogen bonding between adjacent layers.

Full text of DOI:10.1016/j.molstruc.2004.01.019

Journal of Molecular Structure 692 (2004) 121–126
www.elsevier.com/locate/molstruc
Synthesis and structural characterization of new lanthanide
coordination polymers with nitrilotriacetic acid
a
Liang Huang , Li-Ping Zhang , Lin-Pei Jin
a,
b
*
aDepartment of Chemistry, Anyang Teacher College, Anyang, Henan Province, 455000, China
bDepartment of Chemistry, Beijing Normal University, Beijing, 100875, China
Received 30 October 2003; revised 30 October 2003; accepted 14 January 2004
Abstract
Reported herein are the hydrothermal synthesis and crystal structures of four lanthanide coordination polymers with nitrilotriacetic acid
(H3NTA) [Ln(NTA)(H2O)]n (Ln ¼ La, 1; Pr, 2; Nd, 3; Eu, 4). Despite similar syntheses, compounds 1 to 4 show transformation in
coordination mode of NTA and coordination number of Ln3þ duo to lanthanide contraction. The Ln(III) ions in 1 and 2 are nine-coordinated
and connected through octadentate bridging ligands (NTA) to form a three-dimensional network. The Ln(III) ions in 3 and 4 are eight-
coordinated and bridged by heptadentate bridging ligands (NTA) to form an extended two-dimensional layer structure, which further
construct a three-dimensional supramolecular structure via coordination bond and three-centered hydrogen bonding between adjacent layers.
q 2004 Elsevier B.V. All rights reserved.
Keywords: Lanthanide; Coordination polymer; Hydrothermal synthesis; Crystal structure; Hydrogen bond
1. Introduction
this paper presents the crystal structures of the four new
coordination polymers [Ln(NTA)(H2O)]n (Ln ¼ La, Pr, Nd
and Eu) which were synthesized by hydrothermal reaction.
The research on coordination polymers is an area of
substantial interest because of their fascinating structural
diversity and potential applications as functional materials
[1–3]. The single crystals of coordination polymers can be
obtained by several routes such as slow evaporation of
filtrate [4], recrystallization [5], diffusion [6], sol–gel
method [7] and hydrothermal reaction [8]. However,
different methods for preparing same material are open to
question. Nitrilotriacetic acid (H3NTA) is one of the
important derivatives of glycine and used in biochemistry
and medicine. Lanthanide complexes with nitrilotriacetate
have been studied for a long time. And the crystal structures
of five complexes obtained by conventional solution
synthesis were previously reported: [Nd(NTA)(H2O)2]
H2O [9], [Pr(NTA)(H2O)2] H2O [10], [Dy2(NTA)2(H2O)4]
4H2O [11], [Sm(NTA)(H2O)2] H2O [12], and
[Tm(NTA)(H2O)2] 2H2O [13]. In order to compare with
structures of lanthanide nitrilotriacetate complexes reported
and observe structural transformation in lanthanide series,
2. Experimental
2.1. Materials and apparatus
LnCl3·nH2O (Ln ¼ La and Pr, n ¼ 7; Ln ¼ Nd and Eu,
n ¼ 6) were prepared by dissolving their oxides in dilute
hydrochloric acid, respectively and then dried. All other
chemicals were purchased and used as received without
further purification. C, H and N data were obtained using an
American PE 2400 II CHNS/O elemental analyzer. Infrared
spectra were recorded with an American Nicolet Avatar 360
FT-IR spectrometer.
2.2. Preparation of complexes
LnCl3·nH2O (0.3 mmol; La, n ¼ 7; 0.1114 g; Pr, n ¼ 7;
0.1120 g; Nd, n ¼ 6; 0.1076 g; Eu, n ¼ 6; 0.1099 g) and
H3NTA (0.3 mmol, 0.0573 g) were dissolved in 10 ml
deionized water, respectively and the pH value was adjusted
to about 5.5 with NaOH aqueous solution. The mixture was
*
Corresponding author. Tel.: þ86-1306-443-3577; fax: þ86-0372-290-
2048.
E-mail address: lpzhang@aytc.edu.cn (L.-P. Zhang).
0022-2860/$ - see front matter q 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.01.019

122
L. Huang et al. / Journal of Molecular Structure 692 (2004) 121–126
Table 1
Crystallographic data for complexes 1,2,3 and 4
1
2
3
4
Formula
LaC6H8NO7
345.04
PrC6H8NO7
347.04
NdC6H8NO7
350.37
EuC6H8NO7
358.09
Formula weight
Crystal system
Space group
˚
a(A)
˚
b(A)
˚
c(A)
Orthorhombic
Orthorhombic
Monoclinic
Monoclinic
P2(1)2(1)2(1)
7.068(3)
10.251(4)
12.120(4)
90
P2(1)2(1)2(1)
7.016(2)
10.162(4)
12.054(4)
90
P2(1)/n
P2(1)/n
6.856(3)
6.692(3)
20.102(8)
90
6.872(5)
6.708(5)
20.029(14)
90
a(deg)
b(deg)
g(deg)
Z
90
90
92.472(12)
90
92.880(6)
90
90
90
4
4
4
4
3
˚
V(A )
878.1(5)
2.610
859.3(5)
2.683
922.4(11)
2.523
921.0(6)
2.582
dcalcdðg=cm3Þ
Temperature(K)
F(000)
293(2)
656
293(2)
664
293(2)
668
293(2)
680
m(mm21
)
4.884
0.0235
0.0466
5.689
0.0207
0.0402
5.646
0.0548
0.1210
6.827
0.0227
0.0503
R½I . 2sðIÞꢀ R1
wR2
placed in a Teflon-lined stainless steel vessel (23 ml). The
vessel was sealed and heated (La and Pr, at 140 8C for 5 d;
Nd and Eu, at 150 8C for 3 d) under autogeneous pressure
and then cooled to room temperature. After filtered, the
product was washed with ethanol and then dried under
ambient. Block crystals were collected (yield: 38.5% for 1,
34.7% for 2, 29.4% for 3, 32.1% for 4).
2.3. Single-crystal X-ray diffraction
Single-crystal X-ray data were collected on a Bruker
SMART 1000 CCD diffractometer equipped with graphite
˚
monochromatized Mo Ka radiation ðl ¼ 0:71073 A).
Semiempirical absorption corrections were applied using
the SADABS program. All calculations were carried out
with use of SHELXS-97 and SHELXL-97 programs [14]. The
structures were solved by the direct methods. All structures
were refined on F[2] by full-matrix least-squares methods.
The crystallographic data of the complexes are summarized
in Table 1 and the selected bond distances in Table 2.
[La(NTA)(H2O)]n (1) Found(%): C, 20.88; H, 2.21; N,
4.21. Calcd(%): C, 20.88; H, 2.34; N, 4.06. IR(KBr pellet,
cm21): 3406(s, br), 3005(w), 2928(w), 2899(w), 1602(vs),
1561(s), 1458(m), 1411(s), 1337(w), 1257(w), 1124(w),
1009(w), 992(w), 929(w), 907(w), 745(w), 670(w), 592(w),
540(w).
[Pr(NTA)(H2O)]n (2) Found(%): C, 20.71; H, 2.15; N,
4.17. Calcd(%): C, 20.76; H, 2.32; N, 4.04. IR(KBr pellet,
cm21): 3356(s, br), 3009(w), 2933(w), 2898(w), 1602(vs),
1561(s), 1458(m), 1407(s), 1334(w), 1255(w), 1123(w),
1008(w), 993(w), 930(w), 907(w), 729(w), 686(w), 597(w),
542(w).
3. Results and discussion
3.1. Structures of [Ln(NTA)(H2O)]n(Ln ¼ La, 1; Pr, 2)
Single-crystal X-ray diffraction studies reveal that
complexes 1 and 2 are isostructural. The asymmetric
unit of 2 is shown in Fig. 1. There is one type of Pr(III)
ion environment in the asymmetric unit of 2. As shown in
Fig. 1, Pr(1) is nine-coordinated and surrounded by eight
oxygen atoms and one nitrogen atom, one nitrogen and
three oxygen atoms of which come from one NTA ligand
and four oxygen atoms from four different NTA ligands
and one oxygen from a water molecule. The Pr–O bond
[Nd(NTA)(H2O)]n (3) Found(%): C, 20.65; H, 2.42; N,
3.82. Calcd(%): C, 20.57; H, 2.30; N, 4.00. IR(KBr pellet,
cm21): 3423(s, br), 2961(w), 2927(w), 1637(vs), 1578(vs),
1459(w), 1425(s), 1402(m), 1336(w), 1307(w), 1270(w),
1232(w), 1125(w), 1016(w), 990(w), 930(w), 914(w),
769(w), 737(w), 603(w), 575(w), 497(w), 419(w).
[Eu(NTA)(H2O)]n (4) Found(%): C, 20.26; H, 2.30; N,
3.75. Calcd(%): C, 20.12; H, 2.25; N, 3.91. IR(KBr pellet,
cm21): 3406(s, br), 2961(w), 2933(w), 1642(vs), 1595(vs),
1578(vs), 1466(w), 1427(s), 1399(w), 1339(w), 1316(w),
1275(w), 1232(w), 1130(w), 1117(w), 1019(w), 990(w),
933(w), 915(w), 770(w), 740(w), 670(w), 604(w), 576(w),
419(w).
˚
distances range from 2.441 to 2.613 A. The average
˚
˚
distance is 2.535 A. The Pr-N bond length is 2.797 A. In
the reference [5], Pr(III) is also nine-coordinated and
surrounded by eight oxygen atoms and one nitrogen, two
oxygen atoms of which are from two coordinated water
molecules but only one coordinated water molecule in the

L. Huang et al. / Journal of Molecular Structure 692 (2004) 121–126
123
Table 2
˚
Selected bond distances (A) for complexes 1,2,3 and 4
Bond distances in 1
La(1)–O(2)#1
La(1)–O(1)
La(1)–O(3)
La(1)–O(6)#2
La(1)–O(7)
2.489(4)
2.497(4)
2.550(4)
2.557(4)
2.558(4)
La(1)–O(5)
2.585(4)
2.606(4)
2.636(4)
2.827(5)
La(1)–O(4)#3
La(1)–O(5)#4
La(1)–N(1)
Bond distances in 2
Pr(1)–O(2)#1
Pr(1)–O(1)
2.441(4)
2.469(4)
2.505(4)
2.507(3)
2.520(4)
Pr(1)–O(5)
2.572(4)
2.599(4)
2.613(4)
2.797(4)
Pr(1)–O(4)#3
Pr(1)–O(5)#4
Pr(1)–N(1)
Pr(1)–O(7)
Pr(1)–O(3)
Pr(1)–O(6)#2
Bond distances in 3
Nd(1)–O(2)#1
Nd(1)–O(1)
2.393(8)
2.404(9)
2.406(9)
2.414(10)
Nd(1)–O(6)#3
Nd(1)–O(3)
Nd(1)–O(7)
Nd(1)–N(1)
2.440(9)
2.469(8)
2.483(8)
2.679(10)
Nd(1)–O(4)#2
Nd(1)–O(5)
Bond distances in 4
Eu1–O(2)#1
Eu1–O(1)
2.381(3)
2.384(3)
2.385(3)
2.406(3)
Eu1–O(6)#3
Eu1–O(7)
Eu1–O(3)
Eu1–N(1)
2.417(3)
2.439(4)
2.442(3)
2.655(4)
Eu1–O(4)#2
Eu1–O(5)
Symmetry transformations used to generate equivalent atoms: 1: #1
2x þ 2; y þ 1=2; 2z þ 3=2; #2 x þ 1; y; z; #3 2x þ 3=2; 2y; z 2 1=2; #4
x þ 1=2; 2y þ 1=2; 2z þ 2:, 2: #1 2x; y þ 1=2; 2z þ 1=2; #2 x 2 1; y, z; #3
2x þ 1=2; 2y; z 2 1=2; #4x 2 1=2; 2y þ 1=2; 2z þ 1:, 3: #1 x; y þ 1; z; #2
2x þ 1=2; y þ 1=2; 2z þ 1=2; #3 x 2 1; y; z; 4: #1 x; y þ 1; z; #2 2x þ 1=2;
y þ 1=2; 2z þ 1=2; #3 x 2 1; y; z:
asymmetric unit of 2. Different syntheses methods result
in different structures of the two Pr(III) complexes. NTA
is heptadentate ligand (Fig. 2a) in [Pr(NTA)(H2O)2] H2O
[5], while it is octa-dentate ligand (Fig. 2b) in 2. In 2, the
nitrogen atom of NTA ligand coordinates to Pr(III) ion in
Fig. 2. The coordination modes of NTA ligands in [Pr(NTA)(H2O)2] H2O 5
(a), [Pr(NTA)(H2O)]n 2 (b) and [Nd(NTA)(H2O)]n 3 (c). All hydrogen
atoms are omitted for clarity.
monodentate mode and three carboxylate groups coordi-
nate to Pr(III) ions in three different modes (Fig. 2b). (i)
syn-anti-bridging bidentate [O(1#)–C–O(2#)]. (ii) anti–
anti-bridging bidentate [O(3#)–C–O(4#)]. (iii) m3-brid-
ging tridentate [O(5#)–C–O(6#)]. Three carboxylate
groups of NTA ligand bridge Pr(III) ions along three
different directions and form 3-D network (Fig. 3). Two
types of hydrogen bonds exist between coordinated water
molecules and carboxylate group oxygen atoms. The
related parameters are listed in Table 3.
3.2. Structures of [Ln(NTA)(H2O)]n(Ln ¼ Nd, 3; Eu, 4)
Single-crystal X-ray diffraction results reveal that
complexes 3 and 4 are isostructural. The complex 3
possesses an asymmetric unit containing one Nd(III) ion
(Fig. 4). Nd(III) ion is eight-coordinated and possesses an
NO7 environment composed of one N atom and three O
atoms from one NTA ligand, three O atoms from other
Fig. 1. The asymmetric unit of [Pr(NTA)(H2O)]n 2 showing 50% thermal
ellipsoids. All hydrogen atoms are omitted for clarity.

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L. Huang et al. / Journal of Molecular Structure 692 (2004) 121–126
Fig. 3. Packing diagram of [Pr(NTA)(H2O)]n 2 viewed along a-axis. All hydrogen atoms are omitted for clarity.
Table 3
˚
Hydrogen bonds parameters(A,8) for complexes 1,2,3 and 4
Complex
D–H
d(D–H)
d(H· · ·A)
angleDHA
d(D· · ·A)
Position of A
1
2
3
4
O(7)–H(1)
O(7)–H(2)
O(7)–H(1)
O(7)–H(2)
O(7)–H(7B)
O(7)–H(7B)
O(7)–H(7B)
O(7)–H(7B)
0.879
0.944
0.893
0.898
0.850
0.850
0.847
0.847
1.950
1.875
1.922
1.914
2.222
2.298
2.236
2.335
155.6
155.5
156.5
155.9
137.6
130.1
139.0
131.3
2.775
2.762
2.764
2.758
2.906
2.919
2.928
2.963
Oð3Þ½21=2 þ x; 1=2 2 y; 2 2 zꢀ
Oð1Þ½2 2 x; 1=2 þ y; 3=2 2 zꢀ
Oð3Þ½1=2 þ x; 1=2 2 y; 1 2 zꢀ
Oð1Þ½2x; 1=2 þ y; 1=2 2 zꢀ
Oð2Þ½2x; 2y; 2zꢀ
Oð6Þ½1 2 x; 1 2 y; 2zꢀ
Oð2Þ½2x; 2y; 2zꢀ
Oð6Þ½1 2 x; 1 2 y; 2zꢀ
three NTA ligands and one O atom from water molecule.
˚
The Nd–O bond distances range from 2.393 to 2.483 A.
˚
The average distance is 2.452 A. The Nd-N bond length is
˚
2.679 A. In [Nd(NTA)(H2O)2] H2O [4], Nd(III) is nine-
coordinated and the coordination mode of NTA is similar
to that of NTA in [Pr(NTA)(H2O)2] H2O [5] (Fig. 2a).
However, in complex 3, NTA is heptadentate ligand
(Fig. 2c) and three carboxylate groups of NTA coordinate
to Nd(III) ion in anti–anti bridging bidentate mode. As
shown in Fig. 5, the carboxylate groups of NTA bridge
˚
Nd(III) ions along b-axis with the distance of 6.708 A
between two adjacent Nd(III) ions and the carboxylate
groups of NTA bridge Nd(III) ions along a-axis with the
˚
distance of 6.872 A between two adjacent Nd(III) ions.
The two types of carboxylate groups of NTA ligands link
Nd(III) ions into 2-D layer structure (Fig. 5). In the 2-D
structure, all Nd(III) ions are coplanar. Two adjacent
Nd(III) ions planes are bridged by the carboxylate groups
˚
of NTA ligands along c-axis with the distance of 5.9 A
between two Nd(III) ions planes and 3-D coordination
polymer is formed by bridging NTA ligands (Fig. 6).
Fig. 4. The asymmetric unit of [Nd(NTA)(H2O)]n 3 showing 50% thermal
ellipsoids. All hydrogen atoms are omitted for clarity.

L. Huang et al. / Journal of Molecular Structure 692 (2004) 121–126
125
4. Conclusion
The four lanthanide nitrilotriacetate complexes,
[Ln(NTA)(H2O)]n (Ln ¼ La, 1; Pr, 2; Nd, 3; Eu, 4) have
been obtained by hydrothermal synthesis and characterized
by single crystal X-ray analysis. From 1 to 4, the average
˚
distances of Ln–O bond are 2.560, 2.528,2.430, 2.408 A
and the distances of Ln–N bond are 2.827, 2.797, 2.679,
˚
2.655 A, respectively. Ln(III) ions are nine-coordinated in
1, 2 and eight-coordinated in 3, 4. The results mentioned
above prove the effect of lanthanide contraction. Compared
[Pr(NTA)(H2O)]n (2) with [Pr(NTA)(H2O)2] H2O [10]
synthesized by conventional method, the coordination
numbers of Pr(III) are identical, while the coordination
modes of NTA ligands and the numbers of coordinated
water molecules are different. In [Nd(NTA)(H2O)]n (3),
Nd(III) ions are eight-coordinated and there is only one
coordinated water molecule. But the Nd(III) ion is nine-
coordinated and there are two coordinated water molecules
in [Nd(NTA)(H2O)2] H2O [9] synthesized by conventional
Fig. 5. Projection down c-axis showing 2-D layer structure connected by the
two types of carboxylate groups of NTA ligands along a- and b-axis. The
carboxylate groups of NTA along c-axis and all hydrogen atoms are omitted
for clarity.
Fig. 6. Packing diagram of [Nd(NTA)(H2O)]n 3 viewed along b-axis. All hydrogen atoms attached to C atoms are omitted for clarity.
The coordinated water molecules protrude the polymeric
layer and hydrogen atoms bond to the oxygen atoms of
carboxylate groups from the neighboring layer. Interest-
ingly, three-center hydrogen bonds are formed in the
crystal (Fig. 6). The H donor O(7)–H(7B) comes from
aqua ligand and the hydrogen bond acceptors are O(2)
½2x; 2y; 2zꢀ and O(6) ½1 2 x; 1 2 y; 2zꢀ. The related
parameters are listed in Table 3. 3-D supramolecular
architecture is also formed by the three-center hydrogen
bonds (Fig. 6).
method. And the coordination modes of NTA ligands are
different in the two complexes either. The results indicate
that two methods of hydrothermal and conventional
syntheses can generate different complexes and structures.
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