Microporous-structural rare-earth coordination polymers constructed by 2-bromoterephthalate

Article abstract of DOI:10.1016/j.molstruc.2003.09.024

The two novel microporous rare-earth coordination polymers: La ₂(C₈H₃BrO₄)₃2H ₂O (1) and Pr₂(C₈H₃BrO ₄)₃2H₂O (2) are yielde

Full text of DOI:10.1016/j.molstruc.2003.09.024

Journal of Molecular Structure 689 (2004) 177–181
www.elsevier.com/locate/molstruc
Microporous-structural rare-earth coordination polymers constructed
by 2-bromoterephthalate
*
Haitao Xu, Jiahe Liang, Jing Zhuang, Huizhong Kou, Ruji Wang, Yadong Li
Department of Chemistry and The Key Laboratory of Atomic and Molecular Nanosciences (China Ministry of Education), Tsinghua University,
Haidian District, Beijing 100084, China
Received 28 July 2003; revised 11 September 2003; accepted 25 September 2003
Abstract
The two novel microporous rare-earth coordination polymers: La2(C8H3BrO4)32H2O (1) and Pr2(C8H3BrO4)32H2O (2) are yielded by the
hydrothermal synthesis. Complex 1 and 2 are isomorphous. The Ln3þ ion center is located in the nine-coordinated environment, and both
carboxyl groups of each ligand coordinate with the metal ion in the same coordination fashion. The ligands, whose carboxyl group chelates
Ln3þ ion center in m1 or m3 fashion, alternately link Ln3þ ions to get the 1D chain, then the carboxyl group chelating Ln3þ ion center in m3
fashion bridges another two Ln3þ ion centers from the other two chains to form metal-organic layer. The layers are connected by the ligands
in m4 fashion to furnish 1D channel-structures through b-axis. The microporous structure is well characterized by the nitrogen gas sorption
and desorption. TGA and X-ray powder diffraction pattern reveal that the thermal stability of complexes is high and the open frameworks are
retained upon removal of coordinated water molecules.
q 2003 Elsevier B.V. All rights reserved.
Keywords: Crystal structure; Coordination polymers; Microporous; Gas sorption
1. Introduction
[5] of the modifying dicarboxylate cluster. Compared with
the reports of d-block transition metal coordination poly-
mers [6–10], lanthanide coordination polymers are less
common. In fact, lanthanide ion possesses diverse coordi-
nation-mode and variable coordination number, which
would be used to furnish high-dimension coordination
polymer as nodes. However, the high coordination number
of lanthanide ion would be difficult for open frameworks’
formation of lanthanide coordination polymer in synthesis,
successful examples [11,12] of lanthanide coordination
polymers are less reported. In our mind, based on the
numerous condensed structures of lanthanide coordination
polymers reported, the modifying ligands would make
coordination structure change and construct the open
frameworks due to modifying group’s steric effect. On the
other hand, according to the literature reported, MOFs
constructed by 2-bromoterephthalate (o-Br-BDC) are rarely
studied. As mentioned above, 2-bromoterephthalic acid and
Ln3þ are chosen to construct two novel 1D channel-
structures dicarboxylate–lanthanide coordination polymers
with pendant groups by hydrothermal synthesis. In this
paper, two novel coordination polymers of lanthanide ions
Design and synthesis of metal-organic open frameworks
(MOFs) with large pores have rapidly developed in recent
years, owing to their interesting structural topologies and
crystal-packing motif with potential applications in absorp-
tion, separation, catalysis [1]. So far enormous effort is still
made in synthesizing extra-large porous coordination
polymer, and some excellent examples are achieved in
d-block transition metal carboxylate cluster such as Zn4O
(BDC)3·(DMF)8(C6H5Cl) [2a], Zn(BDC)·(DMF)(H2O)
[2b], Zn3(BDC)3·6CH3OH [2c] (BDC ¼ 1,4-benzenedicar-
boxylate), Zn4O(tpdc)3·(DMF)8 [2d] (tpdc ¼ p-Terphenyl-
dicarboxylate), and [Co3(bpdc)3bpy]·4DMF·H2O [3]
(bpdc ¼ biphenyldicarboxylate) of the dicarboxylate clus-
ter, Cu3(BTB)3·(H2O)3(DMF)8(H2O)2 [4] (BTB ¼ 4,40,400-
benzene-1,3,5-triyl-tribenzoic acid) of the tricarboxylate
cluster and Cu2[o-Br-C6H3(CO2)2]2(H2O)2·(DMF)8(H2O)2
*
Corresponding author. Tel.: þ86-1062772350; fax: þ86-1062788765.
E-mail address: ydli@mail.tsinghua.edu.cn (Y. Li).
0022-2860/$ - see front matter q 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2003.09.024

178
H. Xu et al. / Journal of Molecular Structure 689 (2004) 177–181
and 2-bromoterephthlic acid: [La2(C8H3BrO4)3·(H2O)2] 1,
and [Pr2(C8H3BrO4)3·(H2O)2] 2 are reported and the
properties are characterized.
1519 (vs), 1409 (vs), 1375 (vs), 1282 (w), 1037 (m), 844
(s), 773 (s).
Crystal 2 was synthesized following the procedure
above: Pr(NO3)3 (0.081 g) was added to a mixture of 2-
bromoterephthalic acid (0.049 g), NaOH (0.011 g). Light-
green needle crystals of 2 were suitable for X-ray
diffraction. IR (KBr pellet cm21): 3430 (s), 1560 (s), 1409
(s), 1376 (vs), 1280 (w), 1037 (m), 1037 (m), 846 (s), 775 (s).
2. Experimental section
All starting regents are as purchased without further
purification. IR spectra are recorded on a NICOLET 560
FT-IR spectrophotometer as KBr pellets. TGA exper-
iment is performed on a TGA-2050 thermal analyzer
under 80-ml/min N2 atmosphere. The final temperature is
950 8C at a heating rate of 10 8C/min. The single-crystal
structure data is collected on Bruker SMART CCD
diffractometer with graphite-monochromated Mo Ka
3. Results and discussion
Two kinds of crystals are all stable in air and insoluble in
water and common organic solvent. Infrared spectroscopies
of the complexes 1 and 2 distilled by KBr pellets are
determined within the frequency range 4000–400 cm21
.
˚
(l ¼ 0:7173 A) radiation at room temperature. The
Due to the symmetric and asymmetric stretching–vibration
of carboxyl groups, the infrared spectra showed the expected
structures are solved by using Bruker SHELXTL.
These little crystals were obtained by hydrothermal
technique: A mixture of 2-bromoterephthalic acid
(0.047 g), NaOH (0.010 g) and distillated water (20 ml)
was heated till boiling. When it was cooled, the solution
was put into a 40 ml bomb added La(NO3)3 (0.072 g).
The bomb was sealed and heated at 160 8C for 72 h, and
then it was cooled to room temperature. White needle
crystals of 1 were yielded and suitable for X-ray
diffraction. IR (KBr pellet cm21): 3415 (m), 1558 (vs),
Table 2
Selected bonds and angles for 1 and 2
La1–O5
2.468(5)
2.478(5)
Pr1–O5
2.419(9)
2.424(9)
2.459(9)
2.482(10)
2.504(10)
2.507(8)
2.527(8)
2.642(7)
2.663(7)
La1–O9B
Pr1–O9B
La1–O3A
2.495(5)
Pr1–O3A
La1–O4A
2.523(5)
Pr1–O4A
La1–O8
2.540(6)
Pr1–O8
La1–O6B
2.551(5)
Pr1–O6B
La1–O7C
2.566(5)
Pr1–O7C
La1–O7
2.678(4)
Pr1–O7
La1–O6
2.699(4)
Pr1–O6
Table 1
O5–La1–O9B
O5–La1–O3A
O9B–La1–O3A
O5–La1–O4A
O9B–La1–O4A
O3A–La1–O4A
O5–La1–O8
O9B–La1–O8
O3A–La1–O8
O4A–La1–O8
O5–La1–O6B
O9B–La1–O6B
O3A–La1–O6B
O4A–La1–O6B
O8–La1–O6B
O5–La1–O7C
O9B–La1–O7C
O3A–La1–O7C
O4A–La1–O7C
O8–La1–O7C
O6B–La1–O7C
O5–La1–O7
O9B–La1–O7
O3A–La1–O7
O8–La1–O7
O6B–La1–O7
O7C–La1–O7
O5–La1–O6
O9B–La1–O6
O3A–La1–O6
O4A–La1–O6
O8–La1–O6
137.80(17)
78.47(17)
127.09(18)
129.52(17)
80.35(18)
51.57(19)
134.97(18)
70.5(2)
O5–Pr1–O9B
O5–Pr1–O3A
O9B–Pr1–O3A
O5–Pr1–O4A
O9B–Pr1–O4A
O3A–Pr1–O4A
O5–Pr1–O8
O9B–Pr1–O8
O3A–Pr1–O8
O4A–Pr1–O8
O5–Pr1–O6B
O9B–Pr1–O6B
O3A–Pr1–O6B
O4A–Pr1–O6B
O8–Pr1–O6B
O5–Pr1–O7C
O9B–Pr1–O7C
O3A–Pr1–O7C
O4A–Pr1–O7C
O8–Pr1–O7C
O6B–Pr1–O7C
O5–Pr1–O7
O9B–Pr1–O7
O3A–Pr1–O7
O8–Pr1–O7
O6B–Pr1–O7
O7C–Pr1–O7
O5–Pr1–O6
O9B–Pr1–O6
O3A–Pr1–O6
O4A–Pr1–O6
O8–Pr1–O6
138.4(3)
Crystal structure data for 1 (deposited in CCDC-210051) and 2 (deposited
in CCDC-209644)
77.5(3)
127.6(3)
129.3(3)
79.8(3)
52.5(3)
135.9(3)
69.6(3)
114.3(4)
79.6(4)
76.6(3)
76.2(3)
80.8(3)
87.1(3)
144.9(3)
72.7(3)
137.6(3)
78.6(3)
101.2(3)
69.0(3)
146.0(3)
72.5(3)
68.6(3)
141.3(3)
104.2(3)
69.1(2)
113.87(19)
74.2(3)
90.7(3)
141.5(3)
151.8(3)
72.2(3)
Compound
1
2
Empirical formula
Formula weight
Temperature
C
24H13Br3La2O14
C24H13Br3O14Pr2
1046.89
1042.89
293(2) K
293(2) K
˚
l (Mo Ka) A
0.71073
0.71073
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
Monoclinic
P2ð1Þ=n
Monoclinic
P2ð1Þ=n
114.1(2)
80.0(2)
12.236(1)
7.0490(14)
18.767(1)
95.73(1)
12.295(3)
6.9780(14)
18.598(4)
95.26(3)
76.65(16)
75.85(16)
80.85(16)
87.54(18)
145.63(18)
72.03(17)
138.00(17)
79.54(16)
101.67(17)
68.61(19)
145.70(16)
71.89(16)
68.60(16)
141.42(17)
104.3(2)
b
3
˚
Volume A
1610.6(6)
2
1588.9(6)
2
Z
rcal (g/cm3)
2.150
6.400 mm21
2.188
6.865 mm21
Absorption coefficient
Fð000Þ
976
984
Theta range data collection
Limiting indices
3.09–25.998
15 # h # 13;
28 # k # 7;
23 # l # 23
9191/3150
2714
2.08–26.008
215 # h # 13;
28 # k # 8;
222 # l # 21
9038/3124
2396
Reflections collected/unique
Reflections with I . 2sðIÞ
Data/restraints/parameters
Goodness-of-fit on F2
3150/0/208
1.028
3124/0/208
1.080
68.84(14)
112.88(11)
73.42(15)
90.50(16)
142.31(16)
152.43(17)
72.39(19)
Final R indices ½I . 2sðIÞꢀ
R1 ¼ 0:0483;
wR2 ¼ 0:1211
R1 ¼ 0:0559;
wR2 ¼ 0:1259
2.297 and 21.097
R1 ¼ 0:0788;
wR2 ¼ 0:1929
R1 ¼ 0:1012;
wR2 ¼ 0:2073
4.660 and 24.001
R indices (all data)
Largest diff. peak and hole

H. Xu et al. / Journal of Molecular Structure 689 (2004) 177–181
179
Fig. 1. (a) ORTEP plot of 1 showing local coordination environment of La (III). (b) Metal-organic layer.
strong characteristic absorption peaks at 1558, 1519, 1409,
1375 for crystal 1; and 1560, 1517,1409 and 1376 cm21 for
crystal 2, respectively. No absorptions of any protonated
2-bromoterephthalate (1715–1680 cm21) confirm that
o-Br-BDC is completely deprotonated by NaOH. The
absorption peaks at 3415 cm21 for 1 and 3430 cm21 for 2
are depicted to nO–H of coordination water.
H2O, the rest of O atoms are provided by carboxyl groups of
the ligands. Both carboxyl groups of each ligand link La3þ
ion in the same coordination fashion. Two carboxyl groups
chelate the La3þ ion center in m1 and m3 fashions, and two
chelating angles are 51.57(19)8 (O3A–La1–O4A) and
68.84(14)8 (O6B–La1–O7), respectively. The other four
carboxyl groups bridge the La3þ ion center in m3 or m2
fashion. All carboxyl groups of o-Br-BDC are deprotonated,
in agreement with the IR data in which there is no strong
absorption peak around 1700 cm21 for –COOH. The La–O
Single-crystal X-ray diffraction analyses reveal that two
crystals of [La2(C8H3BrO4)3·(H2O)2] 1 and [Pr2(C8H3
BrO4)3·(H2O)2] 2 are isomorphic. The crystallographic
data of complexes are listed in Tables 1 and 2. The
coordination structure of coordination polymer 1 is chosen
to study as an example in this paper.
˚
bond length is in the range of 2.468(5)–2.699(4) A, and the
˚
mean bond length is 2.537 A.
Three kinds of coordination modes of o-Br-BDC ligands
are present in the structure: (1) each carboxyl group of o-Br-
BDC ligand chelate the La3þ ion center in m1 fashion. (2)
Each carboxyl group of o-Br-BDC ligand chelates the La3þ
ion center and bridges the other two in m3 fashion. (3) Each
Complex 1 is a novel 1D channel-structural coordination
polymer with pendant groups. Only one crystallographically
independent lanthanide ion is located in nine-member
coordination environment (Fig. 1a). Except for O8 from

180
H. Xu et al. / Journal of Molecular Structure 689 (2004) 177–181
Fig. 2. Packing diagram along the b axis of 1 and 2.
group of o- Br-BDC ligand bridges two La3þ ion center in
m2 fashion. Substitute group Br of o- Br-BDC in the
structure existes in two kinds of disordered state: Br
disorderly presenting in one of two adjacent carbons in
benzene ring of one-carboxyl group (Br1 and Br10 shown in
Fig. 1a) and in two equal positions of two-carboxyl groups’
adjacent carbon in benzene ring (Br2 and Br20 shown in Fig.
1a). The disorderly modifying groups would possess steric
effect and be advantaged to form the open frameworks. Two
kinds of coordination modes of o-Br-BDC, whose carboxyl
group chelates La3þ ion center in m1 or m3 fashion,
alternately linked La3þ ions to get 1D chains. The carboxyl
group chelates La3þ ion center and bridges the two La3þ
ions center from the other two chains in m3 fashion to form
metal-organic layer (Fig. 1b). The adjacent benzene rings
were parallel to each other in a layer. The layers are bridged
by the carboxyl groups in m2 fashion to furnish 1D channel-
structures. The 1D channels along b-axis is about
weight loss from 500 to 950 8C less to ligands loss
(calculated: 62.04%) due to not to decompose completely
to La2O3. The result of 2 is similar to that of 1. 3.55% weight
loss at 160 8C equivalent to the removal of coordination
water (calculated: 3.28%) and 66.68% from 500 to 950 8C
due to ligands loss (calculated: 64.95%). From 160 to
500 8C no weight loss is observed and it means to get a new
stable compound formulated as [Pr2(C8H3BrO4)3], up to
950 8C the product is completely decomposed and weight is
28% (calculated: 31.5%). Comparing with the X-ray powder
diffraction pattern (XRPD) of the two original compounds 1
and 2, respectively, XRPD of the dehydrated solids are very
similar to that of original compounds except for a few
different position and intensity of diffraction lines indicating
no change in the open frameworks after evacuating small
2
˚
6.0 £ 9.0 A (Fig. 2). The channels with coordination
waters are hydrophilic microporous structure.
To evaluate the microporous volume and the apparent
surface area of rare-earth coordination polymers, the N2 gas
sorption desorption isotherms for compound 2 is deter-
mined. It reveals microporous absorbed nitrogen at low
˚
pressure (Fig. 3). Maximum pore volume is 5.363 A. BET
surface area is 300(3) m2/g.
Thermogravimetric analysis of compound 1 and 2
performed in nitrogen. The results show two weight loss
steps in 1: 3.47% weight loss at 169 8C equivalent to the
removal of coordination water (calculated: 3.28%), 52.70%
Fig. 3. Nitrogen gas sorption and desorption isotherm at 77.35 K for
complex 1.

H. Xu et al. / Journal of Molecular Structure 689 (2004) 177–181
181
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earth dicarboxylate coordination polymers are achieved and
their properties are well characterized.
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This work is financially supported by the NSFC
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