First examples of ternary lanthanide 5-aminoisophthalate complexes: Hydrothermal syntheses and structures of lanthanide coordination polymers with 5-aminoisophthalate and oxalate

Article abstract of DOI:10.1016/j.molstruc.2007.08.007

Two new lanthanide coordination polymers with mixed-carboxylates, [Ln(OX)(HAPA)(H₂O)]_n[Ln = Eu (1), Ho (2); H₂APA = 5-aminoisophthalic acid; OX = oxalate] were obtained by hydrothermal reactions, and characterized by singl

Full text of DOI:10.1016/j.molstruc.2007.08.007

Available online at www.sciencedirect.com
Journal of Molecular Structure 879 (2008) 25–29
www.elsevier.com/locate/molstruc
First examples of ternary lanthanide 5-aminoisophthalate
complexes: Hydrothermal syntheses and structures of
lanthanide coordination polymers with 5-aminoisophthalate and oxalate
a,
b
c
c
Chong-Bo Liu *, Hui-Liang Wen , Sheng-Shui Tan , Xiu-Guang Yi
a
College of Environmental and Chemical Engineering, Nanchang University of Aeronautics, Nanchang 330063, People’s Republic of China
b
State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang 330047, People’s Republic of China
c
Department of Chemistry, Nanchang University, Nanchang 330047, People’s Republic of China
Received 20 July 2007; received in revised form 9 August 2007; accepted 10 August 2007
Available online 21 August 2007
Abstract
Two new lanthanide coordination polymers with mixed-carboxylates, [Ln(OX)(HAPA)(H2O)]n[Ln = Eu (1), Ho (2); H2APA =
5-aminoisophthalic acid; OX = oxalate] were obtained by hydrothermal reactions, and characterized by single crystal X-ray diffraction,
elemental analysis and IR spectra. Complexes 1 and 2 are both 3-D supramolecular structure, in which lanthanide ions are bridged by
oxalate and 5-aminoisophthalate ligands forming 2-D metal–organic framework, and 2-D networks are further architectured to form
3-D supramolecular structures by hydrogen bonds. The two carboxylate groups of H2APA ligand are all deprotonated and exhibit che-
þ
lating and bridging bidentate coordination modes, respectively, and the amino group in HAPA presents –NH3 in the titled complexes.
The thermogravimetric analysis was carried out to examine the thermal stability of the titled complexes. And the photoluminescence
property of 1 was investigated.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Lanthanide; Oxalate; 5-Aminoisophthalate; Supramolecular complex; Photoluminescence; Hydrothermal reaction
1. Introduction
much less work has been carried out to investigate coor-
dination polymers of aminoisophthalic acid, for example,
5-aminoisophthalic acid (H2APA). The introduction of
one amino group to isophthalic acid will contribute to
rich hydrogen bonds and the architecture of supramolec-
ular structure. Compared with its transition metal coor-
dination polymers [22–26], lanthanide coordination
polymers of 5-aminoisophthalate were less investigated.
Up to now, although several binary lanthanide coordina-
tion polymers with H2APA have been reported [27–29],
ternary lanthanide coordination polymers have never
been reported before.
In recent years the chemistry of novel metal–organic
coordination polymers exploiting non-covalent interac-
tion such as coordination bonds, hydrogen bonding
and/or p–p stacks etc. [1–3] has received much attention
due to enormous variety of intriguing structural topolo-
gies and the potential application in catalysis, adsorption
and photoelectronics [4–6]. In construction of metal–
organic frameworks, plentiful bridging ligands especially
multidentate ones are used. Isophthalic acid as an asym-
metrical dicarboxylic acid ligand has been widely used to
construct metal–organic frameworks [7–21]. However,
In the present case, we report two new lanthanide coor-
dination polymers with mixed-carboxylates, in which lan-
thanide ions are bridged by two types of dicarboxylate
ligands, 5-aminoisophthalate and oxalate ligands.
*
Corresponding author. Tel./fax: +86 791 830 5786.
E-mail address: cbliu2002@163.com (C.-B. Liu).
0022-2860/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.08.007

26
C.-B. Liu et al. / Journal of Molecular Structure 879 (2008) 25–29
Table 2
2. Experimental
2.1. General
˚
Selected bond lengths (A) for 1 and 2
1
Eu(1)–O(1)
Eu(1)–O(3)#2
Eu(1)–O(5)
Eu(1)–O(7)#3
Eu(1)–O(9)
2.391(3)
2.564(3)
2.499(3)
2.463(3)
2.469(3)
Eu(1)–O(2)#1
Eu(1)–O(4)#2
Eu(1)–O(6)
2.371(3)
2.454(3)
2.552(3)
2.492(3)
All reagents were Analytical grade and used as received
without further purification. Elemental analyses (C, H, N)
were carried out with a Vario EL elemental analyzer, and
FT-IR spectra were recorded on a Nicolet Avatar 360
FT-IR spectrometer in the range of 4000–400 cmꢀ1. Ther-
mogravimetric analyses were performed with a ZRY-2P
Thermal Analyzer. The excitation spectrum and emission
spectrum of 1 were recorded with Shimadzu RF-5301 PC
spectrophotofluorometer.
Eu(1)–O(8)#3
2
Ho(1)–O(1)
Ho(1)–O(3)#1
Ho(1)–O(5)
Ho(1)–O(7)
Ho(1)–O(9)
2.410(3)
2.312(2)
2.410(2)
2.440(3)
2.416(3)
Ho(1)–O(2)
2.494(2)
2.334(3)
2.555(3)
2.455(2)
Ho(1)–O(4)#2
Ho(1)–O(6)#3
Ho(1)–O(8)#3
1: #1 ꢀx + 1,ꢀy + 2,ꢀz + 2; #2 ꢀx + 1,ꢀy + 1,ꢀz + 2; #3 ꢀx + 1/
2,y + 1/2,ꢀz + 3/2; 2: #1x,y ꢀ 1,z; #2 ꢀx,ꢀy + 1,ꢀz; #3 ꢀx + 1/2,y + 1/
2,ꢀz + 1/2.
2.2. Synthesis of complexes 1 and 2
[Eu(OX)(HAPA)(H2O)]n (1). Complex 1 was first
prepared by mixing europium chloride, 5-aminoisophthalic
acid, oxalic acid, sodium hydroxide and deionized water in
the following ratio: 1:1:1:2:5556. The resulting gel was aged
at 120 ꢁC for 72 h in a 25-ml Teflon-lined stainless reactor
under autogeneous pressure, then cooled at 10 ꢁC /2 h to
100 ꢁC, followed by slow cooling to room temperature.
Upon cooling to RT, the desired product appeared as
brown blocks in ca. 20% yield. Anal. Calcd for
C10H8NO9Eu (438.13): C, 27.39; H, 1.83; N, 3.20%.
Found: C, 26.94; H, 1.90; N, 3.04%. IR data (KBr pellet,
m[cmꢀ1]): 3431 m, 1623 s, 1560 vs, 1458 m, 1384 m, 1134
m, 784 m.
crystals of 2 were obtained with a yield of ca. 41%. Anal.
Calcd for C10H8NO9Ho (451.1): C, 26.67; H, 1.78; N,
3.11%. Found: C, 26.59; H, 2.20; N, 2.68%. IR data
(KBr pellet, m[cmꢀ1]): 3422 m, 1637 s, 1560 vs, 1458 m,
1420 m, 1137 m, 625 m.
2.3. X-ray crystallography
The single-crystal X-ray data of 1 and 2 were collected
using a Bruker SMART 1000 CCD area detector diffrac-
tometer with graphite-monochromated Mo-Ka radiation
˚
(k = 0.71073 A). Semi-empirical absorption corrections
were applied to the two complexes using the SADABS pro-
gram. The structures were solved by direct methods using
the program SHELXS 97 [30] and refined by full-matrix
least squares on F2 using SHELXL 97 [31]. All non-hydro-
gen atoms were refined anisotropically. Hydrogen atoms
were placed in geometrically calculated positions. Experi-
mental details for X-ray data collection of 1 and 2 are pre-
sented in Table 1, and the selected bond lengths are listed in
Table 2.
[Ho(OX)(HAPA)(H2O)]n (2). The synthesis of
complex 2 followed by the similar procedure as for 1. Wine
Table 1
Crystal data for 1 and 2
Complex
1
2
Empirical formula
Formula weight
T (K)
C
438.13
294(2)
10H8NO9Eu
C10H8NO9Ho
451.1
113(2)
Crystal system
Space group
Monoclinic
C2/c
20.030(3)
9.5082(14)
13.6444(15)
90
118.060(8)
90
2293.1(5)
8
Monoclinic
C2/c
19.9307(16)
9.3985(8)
13.5264(12)
90
118.321(3)
90
2230.5(3)
8
3. Results and discussion
˚
a (A)
˚
b (A)
3.1. Structural descriptions
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
X-ray single crystal diffraction studies reveal that 1 and
2 are isostructural. So only the structure of 1 will be dis-
cussed in detail.
3
˚
V (A )
Z
In complex 1, there is one crystallographically indepen-
dent Eu3+ ion, one HAPA ligand, one oxalate and one
coordinated water molecule in asymmetric unit as shown
in Fig. 1. The Eu3+ ion is coordinated to nine oxygen
atoms, among which one oxygen atom (O9) is from one
water molecule, four oxygen atoms (O1, O2A, O3B,
O4B) are from three HAPA ions, and the other four oxy-
gen atoms (O5, O6, O7A, O8A) are from two oxalate ions.
The two carboxylate groups of H2APA ligands are
both completely deprotonated and exhibit chelating and
h range (ꢁ)
2.30–26.43
5.523
1680
2.538
0.998
6347
2351
0.0351
0.0230, 0.0535
0.0284, 0.0555
1.146, ꢀ1.567
2.32–27.88
7.149
1712
2.687
1.038
10,020
2653
0.0498
0.0222, 0.0534
0.0250, 0.0539
1.550, ꢀ1.420
l (mmꢀ1
F (000)
)
Dc (mg mꢀ3
)
Goodness-of-fit on F2 (e A
No. data collected
No. unique data
Rint
)
ꢀ3
˚
R1, wR2 [I > 2r(I)]
R1, wR2 (all data)
Largest diff. peak and hole (e A
ꢀ3
˚
)

C.-B. Liu et al. / Journal of Molecular Structure 879 (2008) 25–29
27
bonds that the 2-D layer structures are constructed to a sta-
ble 3-D supramolecular architecture, as shown in Fig. 2b.
To the best of our knowledge, six coordination modes of
5-aminoisophthalate ligand have been reported (Scheme
1b–g), the coordination mode of 5-aminoisophthalate
ligand (Scheme 1a) in the titled complexes has not been
appeared before. Based on ‘‘soft-hard acidꢀbase theory’’,
it is found that the nitrogen atom of amino group is coor-
dinated to transition metal ions in all the transition metal
coordination polymers [22–26], as shown in Scheme 1c–g;
while the nitrogen atom of amino group is not coordinated
to lanthanide ions in the binary lanthanide coordination
polymers with H2APA and the titled compound, as shown
in Scheme 1a and b. In the reported binary lanthanide
coordination polymers with H2APA, one carboxylate
group adopts bridging bidentate mode, the other carboxyl-
ate group adopts bridging–chelating mode and one APA
ligand joins four lanthanide ions, while in the titled com-
plexes every HAPA ligand employs chelating and bridging
bidentate coordination modes and joins three lanthanide
ions, which may be contributed to the introduction of oxa-
late. All the reported binary lanthanide complexes with
APA are 3-D networks sustained by coordination bonds;
while the titled complexes are 2-D lanthanide–organic
frameworks which are further constructed to a 3-D supra-
molecular structure via hydrogen bonds. It is shown that
the oxalate ions have important impact on the self-assem-
bly of the titled lanthanide coordination polymers.
Fig. 1. Asymmetric unit of [Eu(OX)(HAPA)(H2O)]n with 20% thermal
ellipsoids. All the hydrogen atoms are omitted for clarity.
bridging bidentate coordination modes, respectivelyþ(as
shown in Scheme 1a), and the amino group as –NH3 in
the titled complexes [32]. So, each HAPA ligand links three
europium atoms with EuÆÆÆEu distances of 9.880, 9.508 and
˚
5.469 A, each oxalate ligand chelates two Eu(III) ions with
˚
a EuÆÆÆEu distance of 6.327 A, forming a 2-D infinite
network containing regular parallelograms with
2
˚
10.86 · 6.33 A based on the Eu–Eu distance (see
Fig. 2a), in which oxalate ligands join Eu(III) ions from
two directions with the dihedral angles of 63ꢁ. Every paral-
lelogram contains two HAPA ligands with the dihedral
angles of 12.5ꢁ.
3.2. Fluorescent property of 1
There are rich hydrogen bonds in 1, such as O–HÆÆÆO
hydrogen bonds of coordinated water molecules with car-
boxylate oxygen atoms of HAPA ligands (OÆÆÆO distance
from 2.771–2.826 A), N–HÆÆÆO hydrogen bonds of the
amino group of HAPA ligands with carboxylate oxygen
The europium complex emits red light when excited by
ultraviolet light. Fig. 3 shows the luminescence spectrum
of complex 1 excited with 300 nm light at 293 K. The five
peaks in Fig. 3 correspond to 5D0 fi 7F0, 5D0 fi 7F1,
5D0 fi 7F2, 5D0 fi 7F3 and 5D0 fi 7F4 transitions of the
Eu3+ ion, respectively. It is well-known that the
˚
atoms of oxalate ligands (NÆÆÆO distance from 2.803–
˚
2.868 A), as shown in Table 3. It is via these rich hydrogen
a
b
c
O
O
O
O
M
M
NH2
NH2
M
O
O
O
O
M
M
M
M
O
O
O
O
NH2
M
M
M
M
d
e
f
g
M
O
O
O
M
M
O
O
O
O
M
NH
NH2
2
O
M
M
O
O
O
O
M
O
O
NH
M
2
NH
M
2
M
HOOC
M
Scheme 1. Coordination modes of 5-aminoisophthalate ligand.

28
C.-B. Liu et al. / Journal of Molecular Structure 879 (2008) 25–29
Fig. 2. (a) The 2-D layer structure of complex 1 showing the linking of Eu(III) ions through 5-aminoisophthalate and oxalate ligands along the c-axis, all
the hydrogen atoms are omitted for clarity (b). The 3-D supramolecular network of complex 1 along the c-axis, dashes present hydrogen bonds.
Table 3
˚
Hydrogen bonding geometry (A and ꢁ) for 1 and 2
D–H
d(D–H)
d(HÆÆÆA)
<DHA
d(DÆÆÆA)
A
1
O(9)–H(9A)
O(9)–H(9B)
N(1)–H(1C)
N(1)–H(1B)
N(1)–H(1A)
N(1)–H(1A)
0.85
0.85
0.89
0.89
0.89
0.89
2.111
1.986
1.923
2.300
2.054
2.335
141.2
152.8
169.6
116.3
151.5
116.3
2.826
2.771
2.803
2.811
2.868
2.844
O1 [x,ꢀy + 2,z ꢀ 1/2]
O4 [x,ꢀy + 1, zꢀ1/2]
O8
O6 [ꢀx + 1/2,y ꢀ 1/2,ꢀz + 3/2]
O5 [ꢀx + 1/2,ꢀy + 3/2,ꢀz + 2]
O7 [x,ꢀy + 1,z + 1/2]
2
O(9)–H(9B)
O(9)–H(9A)
N(1)–H(1C)
N(1)–H(1A)
0.68
0.83
0.91
0.91
2.323
1.922
1.859
1.953
135.0
174.4
169.5
164.2
2.845
2.759
2.759
2.839
O(4) [ꢀx,y ꢀ 1,ꢀz + 1/2]
O(1) [ꢀx,y,ꢀz + 1/2]
O(7) [x ꢀ 1/2,ꢀy + 1/2,zꢀ1/2]
O(8) [ꢀx,y + 1,ꢀz + 1/2]
5D0
7F2
of
the
Eu(III)
ion.
The
intensity
ratio
I
(5D0 fi 7F2/5D0 fi 7F1) is ca. 1.55, which indicates that
the Eu(III) ion in 1 is not located at the center of inversion
and symmetry of Eu(III) ion site is low [33].
5D0
7F1
3.3. Thermogravimetric analysis
Considering the title complexes are isostructural, com-
plex 1 was taken as an example to carry out its TG analysis
to examine its thermal stability. TG curve of 1 shows that
the first weight loss of 4.4% from 220 to 350 ꢁC corre-
sponds to the loss of one coordinated water molecule per
[Eu(OX)(HAPA)(H2O)] (Calc. 4.1%). Increasing tempera-
ture led to the further decomposition of 1 at 390 ꢁC, and
the final pyrolysis was completed at 700 ꢁC, as indicated
by a significant weight loss of 72.6% with Eu2O3 (Calc.
73.1%).
5D0
5D0
7F4
7F0
5D0
7F3
400
450
500
550
600
650
700
750
Wavelength/nm
Fig. 3. Emission spectrum of 1 corresponding to the 5D0 fi 7FJ (J = 0–4)
transitions, kexc = 300 nm, T = 293 K.
4. Conclusions
5D0 fi 7F2 transition induced by the electric dipole is
hypersensitive to the coordination environment of the
Hydrothermal reactions of lanthanide chloride with two
kinds of dicarboxylates, HAPA and OX gave rise to two
new coordination polymers [Eu(OX)(HAPA)(H2O)]n (1)
5
Eu(III) ion, while the D0 fi 7F1 transition is a magnetic
dipole one which is fairly insensitive to the environment

C.-B. Liu et al. / Journal of Molecular Structure 879 (2008) 25–29
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The crystallographic data for the structures have been
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