Two lanthanide-natrium pillared-layer frameworks constructed from 4,4′-oxybis(benzoic acid) and oxalate

Article abstract of DOI:10.1016/j.inoche.2011.08.012

Two new heterometallic lanthanide(III)-natrium(I) coordination polymers [LnNa(4,4′-oba)(ox)(H₂O)] (Ln = Nd 1, Sm 2) have been synthesized by hydrothermal reactions of 4,4′-Oxybis(benzoic acid) (4,4′-H₂oba) and Na₂C₂O₄ with corresponding lanthanide nitrate. Both compounds are isostructural and possess three-dimensional (3D) pillared-layer frameworks comprising Ln-Na-oxalate layers and 4,4′-oba pillars. The magnetic properties reveal that the two compounds have anti-ferromagnetic behaviors. Furthermore, the IR, PXRD, elemental and TG analyses are also investigated.

Full text of DOI:10.1016/j.inoche.2011.08.012

Inorganic Chemistry Communications 14 (2011) 1794–1797
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Two lanthanide-natrium pillared-layer frameworks constructed from
4,4′-oxybis(benzoic acid) and oxalate
⁎
Jing Xu, Weiping Su , Maochun Hong
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new heterometallic lanthanide(III)–natrium(I) coordination polymers [LnNa(4,4′-oba)(ox)(H2O)]
(Ln=Nd 1, Sm 2) have been synthesized by hydrothermal reactions of 4,4′-Oxybis(benzoic acid) (4,4′-
H2oba) and Na2C2O4 with corresponding lanthanide nitrate. Both compounds are isostructural and possess
three-dimensional (3D) pillared-layer frameworks comprising Ln–Na-oxalate layers and 4,4′-oba pillars.
The magnetic properties reveal that the two compounds have anti-ferromagnetic behaviors. Furthermore,
the IR, PXRD, elemental and TG analyses are also investigated.
Received 11 July 2011
Accepted 16 August 2011
Available online 25 August 2011
Keywords:
Lanthanide(III)–natrium(I)
Pillared-layer frameworks
Hydrothermal reaction
Anti-ferromagnetic property
© 2011 Elsevier B.V. All rights reserved.
The design and construction of metal–organic frameworks
(MOFs) have provoked increasing interest not only from their fasci-
nating topological networks [1] but also from their potential applica-
tions in gas storage and separation [2], magnetism [3], luminescence
[4], and catalysis [5]. To design and construct MOFs, the reasonable
selection of metal ion and organic ligand is very important. Recently,
lanthanides as metal centers, with high coordination number and
variable coordination environments [6] together with the special lu-
minescent [4b] and magnetic [3a,4a] properties deriving from 4f
electrons, have drawn considerable attention. As is well known, Ln
ions have high affinity and prefer to bind to oxygen donor atoms,
thus polycarboxylate ligands, such as pyridinecarboxylate [7],
imidazoledicarboxylate [8], and benzenepolycarboxylate [9], have
been widely employed in the construction of lanthanide-based
MOFs (LnMOFs). Furthermore, due to the potential applications of
pillared-layer MOFs in adsorption, separation and catalysis [10], it
is necessary to further research the construction of pillared-layer
MOFs.
Up to now, much work is centered on using one type of ligand. If an
auxiliary ligand was to be introduced, the cooperativity of both ligands
may offer possibilities for the formation of unforeseen LnMOFs with
useful properties [11]. Inspired by our previous experience [12], in
this contribution, we chose two types of 4,4′-Oxybis(benzoic acid)
(4,4′-H2oba) and oxalate as mixed ligands to construct lanthanide coor-
dination frameworks, based on the following considerations: (1) 4,4′-
H2oba, as a V-shaped, flexible and long spacer with two carboxylate
groups, shows versatile coordination modes, which makes it a useful
bridge to construct coordination polymers [13]; (2) oxalate, as one of
the simplest bis-bidentate connectors, can facilitate the formation of ex-
tended structures by bridging metal centers [14]. Accordingly, our aim
is to synthesize new LnMOFs based on mixed ligands with useful
properties.
Herein, we report the syntheses and characterization of two new
isostructural 3D Ln–Na pillared-layer coordination polymers: [LnNa
(4,4′-oba)(ox)(H2O)] (Ln=Nd 1, Sm 2), in which 4,4′-oba ligands
work as pillars and link the Ln–Na-oxalate layers, resulting in
pillared-layer heterometallic frameworks. The as-synthesized sam-
ples of two compounds have also been measured by IR, PXRD, ele-
mental and TG analyses.
Compounds 1 and 2 were successfully synthesized in the same
conditions by the hydrothermal reactions of Ln(NO3)3 (Ln=Nd,
Sm), 4,4′-H2oba and Na2C2O4 in a molar ratio of 1:1:2 at 170 °C
[15]. X-ray structural analyses [16] reveal that compounds 1 and 2
are isostructural and crystallize in the monoclinic P21/c space group.
Therefore, only the crystal structure of 1 is described in detail. The se-
lected bond lengths and angles are given in Table S1. The hydrogen
bond parameters are listed in Table S2.
As shown in Fig. 1, the asymmetric unit of 1 contains one Nd3+ ion,
one Na+ ion, one 4,4′-oba ligand, one oxalate ligand and one coordinat-
ed water molecule. Nd atom is nine-coordinated and has distorted
tricapped trigonal prism geometry: four OC−OO atoms from three 4,4′-
oba ligands, and five OC−OO atoms from three oxalate ligands (Fig. S2).
The Nd―O bond lengths vary from 2.395(3) to 2.545(3) Å and the
O―Nd―O angles range from 64.37(9) to 103.50(11)° (Table S1).
Owing to the effect of lanthanide constriction, the Sm―O bond
lengths in 2 are slightly shorter than the corresponding Nd―O bond
lengths in 1 (Table S1). Na atom is six-coordinated and surrounded by
three OC−OO atoms from three oxalate ligands, two OC−OO atoms from
⁎
Corresponding author. Tel./fax: +86 591 8377 1575.
E-mail address: wpsu@fjirsm.ac.cn (W. Su).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.08.012

J. Xu et al. / Inorganic Chemistry Communications 14 (2011) 1794–1797
1795
Fig. 1. The asymmetric unit of 1 with 30% thermal ellipsoids. All hydrogen atoms are
omitted for clarity. Symmetry codes for the generated atoms are the same as Table S1.
two 4,4′-oba ligands and one coordinated water molecule, exhibiting a
distorted octahedral geometry (Fig. S3), with the Na―O bond lengths
being 2.291(4)–2.719(4) Å and the O―Na―O angles being 70.33
(11)–112.40(13)° (Table S1).
Owing to the high cooperativity between 4,4′-oba and oxalate ligands,
the 4,4′-oba ligand only adopts a single μ6-η2, η2, η1, η1 coordination
mode by connecting two Na+ ions and three Nd3+ ions (Scheme 1a)
and the oxalate ligand links three Na+ ions and three Nd3+ ions adopting
a single μ8-η2, η2, η2, η2 coordination mode (Scheme 1b). As shown in
Fig. 2a, Nd and its neighboring Nd#3 (symmetry #3: 2−x, −y, −z)
are linked together through two μ2–O atoms of two oxalate ligands to
form an edge-sharing metallic dimer with a Nd⋯Nd distance about
4.079(2) Å.
The Nd2 dimer further connects two neighboring Na atoms through
six OC−OO atoms forming a {Nd2Na2} second building units (SBUs), in
which the Nd⋯Na distance is 3.672(3) Å. Then the oxalate ligands bridge
these {Nd2Na2} SBUs into two dimensional (2D) heterometallic layers
in the bc plane (Fig. 2b). Finally, 4,4′-oba ligands act as pillars to link
the Ln–Na-oxalate layers into a 3D pillared-layer network along the b
axis (Fig. 3). PLATON calculated a total potential solvent-accessible vol-
ume of about 86.4 Å3 (approximately 4.7% of unit cell).
The synthesized products of compounds 1 and 2 have been charac-
terized by powder X-ray diffraction (PXRD) (Fig. S4). The experimental
PXRD patterns correspond well with the results simulated from the sin-
gle crystal data, indicating the high purity of the synthesized samples.
The difference in reflection intensities between the simulated and ex-
perimental patterns was due to the variation in preferred orientation
of the powder samples during the collection of the experimental
PXRD data.
The thermal stabilities of 1 and 2 were examined by the thermo-
gravimetric analysis (TGA) in N2 atmosphere with a heating rate of
15 °C/min from 30 to 1000 °C. These two compounds both undergo
two steps of weight loss (Fig. S5). TG curves of 1 and 2 show that
from 90 to 285 °C one coordinated water molecule was gradually
Fig. 2. (a) View of {Nd2Na2} SBUs in 1. Symmetry codes for the generated atoms (ex-
cept O7#7: x, −0.5−y, −0.5+z) are the same as Table S1. (b) The 2D layer with
Nd(III)–Na(I) bridged by oxalate.
and 2 are given in Fig. 4. As shown in Fig. 4a, at 300 K, the experimental
χMT value of 1 is 1.63 cm3 K mol−1, which is close to the expected value
4
of 1.64 cm3 K mol−1 for one single Nd3+ ion with a I9/2 ground state
[3a]. As the temperature is lowered, χMT decreases to a minimum at
about 4.5 K and then increases rapidly to reach 0.72 cm3 K mol−1 at
2 K. The plot of χM−1 vs. T over the temperature range 30–300 K obeys
the Curie–Weiss law [χM=C/(T−θ)] with C=1.92 cm3 K mol−1 and
θ=−67.99 K. The decrease of χMT and the negative value of θ may be
due to the depopulations of the Stark levels and/or possible anti-
ferromagnetic interactions between Nd3+ ions [17], and the increase
at low temperature reveals dominant ferromagnetic interaction be-
tween Nd3+ ions. As shown in Fig. 4b, for 2, the observed χMT value is
0.48 cm3 K mol−1, which is slightly higher than the expected value of
0.32 cm3 K mol−1 for one single Sm3+ ion. As the temperature cools
down, the χMT value monotonously decreases, which is obviously at-
tributed to the thermal depopulation of the stark component of lantha-
nide ion at low temperature [3a,18]. At 2 K, χMT is 0.03 cm3 K mol−1
,
which is slightly lower than the expected value of 0.09 cm3 K mol−1
6
for one Sm3+ ion with a H5/2 ground state [3a]. The decrease of χMT
value on cooling indicates the anti-ferromagnetic interactions between
Sm3+ ions within 2.
In summary, we have successfully synthesized two 3D Ln(III)–Na(I)
heterometallic coordination polymers, each with a pillared-layer net-
work based on Ln–Na-oxalate layers pillared by 4,4′-oba ligands. Both
compounds show anti-ferromagnetic properties. This work opens new
lost for
1 (calcd/found: 3.4/3.8%), and for 2 (calcd/found:
3.36/3.79%), respectively. Above 420 °C, the frameworks began to col-
lapse accompanying with the decomposition of the organic ligands.
Temperature dependence of magnetic susceptibilities of compounds
1 and 2 have been performed on the polycrystalline samples in the tem-
perature range 2–300 K. The plots of χMT and χM vs. T for compounds 1
Fig. 3. View of the 3D pillared-layer network along the b axis for 1.
Scheme 1. Coordination modes of the 4,4′-oba and oxalate ligands observed in 1.

1796
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This work is financially supported by 973 Program (2011CB932404,
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H2oba (0.25 mmol, 0.0646 g), Na2C2O4 (0.5 mmol, 0.0670 g), and H2O (6 mL) was
sealed in a 25 mL Teflon-lined autoclave at 170 °C for 4 days, then cooled to room tem-
X-ray crystallographic data for compounds 1 and 2 in cif format,
general characterizations (IR, PXRD and TGA), crystallographic data
and additional structure figures. Supplementary data to this article
can be found online at doi:10.1016/j.inoche.2011.08.012.
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