Adjusting the structures of lanthanide(III) complexes by variation of the metal sources: From a 2D (32.4)(34.43.5 2.65.7) layer to an unusual 3D (412.6 3)(49.66) nia network

Article abstract of DOI:10.1016/j.inoche.2011.12.025

A novel coordination polymer [La(L)(H₂O)]_n (1) has been prepared by hydrothermal reaction of 5-hydroxyisophthalic acid (H ₃L) with La(NO₃)₃?6H₂O, which exhibits an unusual three-dimensional (3D) (6,6)-connected nia net with Point (Schlaefli) symbol of (4¹².6³)(4⁹.6 ⁶). Meanwhile, a two-dimensional (2D) (3,6)-connected (3 ².4)(3⁴.4³.5².6⁵.7) coordination network {[Ho₂(HL)₃(H₂O) ₂]?H₂O}_n (S1) was also obtained with partially deprotonated HL^2- ligand. Comparison of the structural differences between 1 and S1 suggests that the different metal sources play an important role in the construction of such coordination networks.

Full text of DOI:10.1016/j.inoche.2011.12.025

Inorganic Chemistry Communications 17 (2012) 104–107
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Adjusting the structures of lanthanide(III) complexes by variation of the metal
sources: From a 2D (32.4)(34.43.52.65.7) layer to an unusual 3D (412.63)(49.66)
nia network
⁎
Min Chen, Cong Wang, Min Hu, Chun-Sen Liu
Zhengzhou University of Light Industry, Henan Provincial Key Lab of Surface & Interface Science, Zhengzhou, Henan 450002, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel coordination polymer [La(L)(H2O)]n (1) has been prepared by hydrothermal reaction of 5-
hydroxyisophthalic acid (H3L) with La(NO3)3·6H2O, which exhibits an unusual three-dimensional (3D)
(6,6)-connected nia net with Point (Schläfli) symbol of (412.63)(49.66). Meanwhile, a two-dimensional
(2D) (3,6)-connected (32.4)(34.43.52.65.7) coordination network {[Ho2(HL)3(H2O)2]·H2O}n (S1) was also
obtained with partially deprotonated HL2– ligand. Comparison of the structural differences between 1 and
S1 suggests that the different metal sources play an important role in the construction of such coordination
networks.
Received 13 November 2011
Accepted 16 December 2011
Available online 24 December 2011
Keywords:
Lanthanide complexes
Crystal structures
Topology
© 2011 Elsevier B.V. All rights reserved.
Properties
The construction of coordination polymers based on assembly of
metal atoms and multifunctional organic ligands has been extensively
studied in recent years owing to their intriguing topologies and po-
tential applications as functional materials [1,2]. In comparison with
the d-block transition metal (TM) ions, lanthanide atoms have higher
coordination numbers and more flexible coordination spheres, which
make it even more difficult to control the structures. In addition,
according to the hard–soft acid–base theory, the lanthanide atoms
have high affinity for oxygen donor atoms [3]. In general, multicar-
boxylate ligands are usually employed in the construction of lantha-
nide polymeric complexes [4]. Among them, 5-hydroxyisophthalic
acid (H3L), as a carboxylate derivative, has attracted much interest
based on the following considerations: (1) it has two carboxyl groups
which may exhibit diverse coordination modes; (2) the hydroxyl
group may provide the additional binding site and connect metal
atoms to generate more complicated structures incorporation with
the carboxyl groups; and (3) the carboxyl and hydroxyl groups are
good candidates for hydrogen bonds to construct supramolecular
structures with higher dimensionality. Thus far, several lanthanide
coordination polymers constructed by using H3L have been reported
[5–9]. For example, Li and co-workers have hydrothermally synthe-
sized a series of 2D lanthanide layered structures, {[Ln(HL)(H2-
O)5]·0.5HL·H2O}n (Ln=Eu, Gd, Tb, Dy, and Er), which exhibited the
helical cation chains with organic ligands as templates [5]. Also, Yan, et
al. [6,7] and Huang, et al. [8] have successfully obtained a series of another
2D lanthanide networks, namely {[Ln(HL)(H2L)(H2O)2]·2H2O}n.(Ln=La,
Tb, Er, Sm for Yan, et al. and Nd for Huang, et al.), which comprise 1D
Ln–O–C–O–Ln chains. By the reaction of La(ClO4)3·6H2O with H3L in
the presence of NaOH and K2C2O4·6H2O, Si, et al. isolated a compli-
cated 3D structure with coordinated oxalic ions, {[La2(ox)(HL)2(H2-
O)4]·2H2O}n (ox=oxalate) [9]. Thus, further efforts are required to
provide more information on the coordination behavior of H3L, in
order to design and prepare new crystalline materials with such
types of organic ligands.
In this work,
a 3D (6,6)-connected nia lanthanide network
[La(L)(H2O)]n (1) was obtained by the reaction of H3L with La(NO3)3·6-
H2O under hydrothermal condition. Moreover, a 2D (3,6)-connected
(32.4)(34.43.52.65.7) coordination polymer {[Ho2(HL)3(H2O)2]·H2O}n
(S1) was synthesized in this research by changing the metal source.
Herein, we report the syntheses, crystal/topological structures, and
properties of 1 and S1.
Complexes 1 and S1 were obtained by the hydrothermal reaction
of H3L with Ln(NO3)3·6H2O (Ln=La for 1 and Ho for S1) in the pres-
ence of NaOH [10]. The compositions were confirmed by elementary
analysis and IR spectra, and the phase purities of the bulk samples
for luminescent/thermal measurements were identified by powder
X-ray diffraction (PXRD) (please see Fig. S6 in the Supplementary
material).
The structure of 1 has a very complicated 3D coordination frame-
work [11]. The asymmetric unit consists of one La(III) atom, one L3–
ligand, and one coordinated water molecule. Each La(III) atom is
nine-coordinated and shows a distorted tricapped trigonal prism co-
ordination geometry (see Fig. 1) finished by eight carboxylate O
atoms (O1, O2, O2A, O5B, O4C, O3D, O4D, and O5E) from six distinct
L3– ligands and one Owater atom (here O6). The La−O bond distances
and the bond angles around each La(III) atom are in the ranges from
⁎
Corresponding author. Fax: +86 371 63556510.
E-mail address: chunsenliu@zzuli.edu.cn (C.-S. Liu).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.12.025

M. Chen et al. / Inorganic Chemistry Communications 17 (2012) 104–107
105
Fig. 1. View of the local coordination environment of La(III) in 1. The atoms labeled with the suffixes A, B, C, D, and E are generated by the symmetry operations (x, −y+1/2, z+1/2),
(−x+2, y+1/2, −z+3/2), (x+1, −y+1/2, z+1/2), (x+1, y, z), and (−x +2, −y, −z+2), respectively.
2.458(3) to 2.754(3) Å and 49.12(11) to 153.72(12)°, respectively
(see Table S1 in the Supplementary material). In 1, the carboxylate
and hydroxyl groups of H3L ligand are fully deprotonated. The L3– li-
gand shows the μ6-bridging mode (see Scheme 1), which connect six
La(III) atoms through one μ2-hydroxyl and two μ2-η1:η2 chelating/
bridging carboxylate groups. Remarkably, the examples with the hy-
droxyl group involving in the metal coordination in different forms
of H3L ligands are still rare even though there are a few of coordina-
tion polymers constructed by H3L ligands [12–15]. To the best of
our knowledge, only four such polymeric complexes were reported,
namely [Ni(HL)(C10H14N4O)(H2O)]n [C10H14N4O=2,2'-bis(1H-imi-
dazolyl)ether] [12], {[CuZn(HL)2(bipy)(H2O)]·1.5H2O}n [bipy=4,4'-
bipyridyl] [13], {18-crown[6]·Cs[HL]}n [14] and {(Me2NH2)
[PbSr(HL)(L)]}n [15]. Significantly, complex 1 exhibits the first lan-
thanide example in which the hydroxyl group of H3L ligand takes
part in the coordination with the metal atoms. Based on the linkage
of carboxylater groups in L3– ligands, La(III) atoms are connected to
generate an infinite 2D layered motif (see Fig. 2). Moreover, the con-
nections of μ2-hydroxyl groups in L3– ligands bridge the 2D motifs
mentioned above to lead to the formation of the final 3D network
(see Fig. 3). In addition, in 1, the benzene π planes of L3– ligands do
not interact obviously with each other [the closest centroid–centroid
separation is 5.223 Å checked and calculated by PLATON procedure,
which is very longer than 3.8 Å].
well as Figs. S1–S3; brief description and discussion of S1 were
shown in the Supplementary material). The results indicate that the
more complicated structures can be obtained due to the increase of
coordination number of metal atoms with highly connected ligands.
Comparison of the structural differences between 1 and S1 suggests
that the different metal sources play an important role in their struc-
tural assemblies.
In addition, the solid-state photoluminescent properties of 1 and
S1 were investigated at room temperature, as shown in Fig. S4 in
the Supplementary material. The luminescence emission bands with
the peak maxima (λmax) were observed at 371 nm (λex =341 nm)
for 1 and 350 nm (λex =280 nm) for S1, respectively. To further
From the viewpoint of topology, both L3– ligand and La(III) atom
can be regarded as isolated 6-connectors due to each of them linking
six of the other ones. Thus, the overall net of 1 can be reduced as a
binodal (6,6)-connected network with the Point (Schläfli) symbol of
(49.66)(412.63) calculated by TOPOS program (see Fig. 4) [16],
which has been referred by O′Keeffe as an nia notation [17].
When we used Ho(NO3)3·6H2O instead of La(NO3)3·6H2O in this
research, a 2D (3,6)-connected (32.4)(34.43.52.65.7) topological net
(S1) was obtained under the same condition (see Figs. 5 and 6 as
Fig. 2. View of the 2D layered motif in 1.
Fig. 3. View of the 3D network in 1. The different layers are highlighted in different
colors.
Scheme 1. Coordination mode of L3– ligand in 1.

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M. Chen et al. / Inorganic Chemistry Communications 17 (2012) 104–107
Fig. 4. A schematic representation of the 3D nia topology (blue spheres: La(III) atoms;
orange spheres: L3− ligands).
Fig. 6. A schematic representation of the 2D network in S1 with (32.4)(34.43.52.65.7) to-
pology (blue spheres: [Ho2] binuclear units; orange spheres: HL2− ligands with hy-
droxyl O10).
analyze the nature of these emission bands, the photoluminescent
properties of the free H3L have also been investigated under the
same experimental conditions. The emission band for free H3L ligand
is attributable to the π*→n transitions. The fluorescent behaviors of 1
and S1 are very similar to that observed for the free H3L ligand (see
Fig. S4 in the Supplementary material), which displays the maximal
emission at 364 nm upon excitation at 345 nm. Moreover, the emis-
sion mechanism for 1 and S1 can be properly ascribed to charge–
transfer transition between the H3L ligand and the central Ln(III)
ion [18].
Thermogravimetric (TG) analyses were performed to explore the
thermal stability of 1 and S1 under a nitrogen atmosphere by heating
the corresponding complexes from room temperature to at least
800 °C with a heating rate of 10 °C min−1 (see Fig. S5 in the Supple-
mentary material). The TGA curve exhibits that 1 features two stages
of weight loss, the first weight loss of 5.36% between 274 and 324 °C
(peaking at 303 °C), corresponding to the loss of one water molecule
(calcd: 5.54%). Then, the sample remains largely unchanged until the
decomposition occurs at the temperature of ca. 620 °C. Finally, com-
plex 1 starts to quickly decompose with one sharp step of weight
loss (peaking at 731 °C). The final residue is not characterized be-
cause its weight loss does not stop until heating ends at 900 °C. The
TGA curve for S1 shows a first weight loss of 5.85% in the range of
130–174 °C (peaking at 154 °C), corresponding to the loss of coordi-
nated free water molecules (calcd: 5.91%). The residue keeps ther-
mally stable from 157 to 428 °C, and then shows a continuous
weight loss of 39.41% from 430 to 900 °C (peaking at 447 and
593 °C), revealing the decomposition of the coordination framework.
In summary, two new lanthanide coordination polymers have
been prepared under hydrothermal conditions by employing 5-
hydroxyisophthalic acid (H3L) ligand, which exhibited (6,6)-con-
nected 3D nia net with Point (Schläfli) symbol of (412.63)(49.66) (1)
and (3,6)-connected 2D (32.4)(34.43.52.65.7) net (S1), respectively.
Especially, the La(III) complex 1 provides the first example of lantha-
nide architecture which the hydroxyl group of H3L involving in the
coordination. The present finding promotes us to make a further sys-
temic study on the coordination chemistry of 5-hydroxyisophthalic
acid, which may enrich the design and synthesis of crystalline mate-
rials based on such versatile multidentate building blocks.
Acknowledgements
This work was supported by the National Natural Science Fund of
China (21171151), Plan For Scientific Innovation Talent of Henan
Province (114100510017), and Program for New Century Excellent
Talents in University (NCET-10-0143).
Appendix A. Supplementary material
CCDC 853405 and 853406 contain the supplementary crystallo-
graphic data for [La(L)(H2O)]n (1) and {[Ho2(HL)3(H2O)2]·H2O}n
(S1), respectively. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from The Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.
uk. Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.inoche.2011.12.025.
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