Synthesis, structure, and catalytic properties of a copper(II) coordination polymer material constructed from 5-nitro-1,2,3-benzenetricarboxylic acid and bis(4-pyridylformyl)piperazine mixed ligands

Article abstract of DOI:10.1016/j.jssc.2019.120908

One three-dimensional coordination polymer material, {[Cu₃(nbta)₂(bpfp)₂(H₂O)₂](H₂O)₂}_n (H₃nbta = 5-nitro-1,2,3-benzenetricarboxylic acid, bpfp = bis(4-pyri

Full text of DOI:10.1016/j.jssc.2019.120908

Journal of Solid State Chemistry 278 (2019) 120908
Contents lists available at ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Synthesis, structure, and catalytic properties of a copper(II) coordination
polymer material constructed from 5-nitro-1,2,3-benzenetricarboxylic acid
and bis(4-pyridylformyl)piperazine mixed ligands
,b,
Zhao-Hao Li a, Li-Ping Xue a *, Qiu-Pei Qin a, Yi-Jing Zhao a
a College of Chemistry and Chemical Engineering, And Henan Key Laboratory of Function-Oriented Porous Materials, Luoyang Normal University, Luoyang, Henan,
471934, PR China
b College of Food and Drug, Luoyang Normal University, Luoyang, Henan, 471934, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
One three-dimensional coordination polymer material, {[Cu3(nbta)2(bpfp)2(H2O)2](H2O)2}n (H3nbta ¼ 5-nitro-
1,2,3-benzenetricarboxylic acid, bpfp ¼ bis(4-pyridylformyl)piperazine), is synthesized and structurally charac-
terized. X-Ray structural analysis shows that the compound exhibits a three-dimensional structure featuring an
unusual 3-nodal 4-connected topology. The compound is further characterized by elemental analysis, infrared
spectrum, thermogravimetric analysis, and UV–vis absorption spectrum. Importantly, the compound exhibits
efficient heterogeneous catalytic activity to the Knoevenagel reaction at room temperature. Moreover, the recy-
clability and heterogeneity of the reaction were also explored.
5-Nitro-1,2,3-benzenetricarboxylic acid
Bis(4-pyridylformyl)piperazine
Crystal structure
Coordination polymer
Heterogeneous catalysis
1. Introduction
topologies because it has multiple binding ability at its pyridyl rings and
its formyl groups. During the self-assembly of CPs, it could adopt
Rational design and construction of coordination polymers (CPs) as
multifunctional materials have stayed on the focus of materials research
in terms of structural chemistry, catalysis, gas storage and separation,
chemical sensing, and other functions [1–7]. At present, the knowledge
about how to precisely assembly and predict the structure of CPs on the
molecular level is still in its infancy. As is well known, many factors
affected the structural assembly process of these CPs including organic
ligands, central metal ions, counter ion, material ratio, temperatures, pH
values, solvents and so on [8–13]. In this regard, organic ligands are
crucial for the assembly of CPs with structural architectures and func-
tionalities. And it is found that the use of organic multicarboxylate li-
gands and auxiliary N-donor ligands as mixed multifunctional connectors
is an effective synthetic strategy for the construction of such materials
[14–16].
On the other hand, the organic groups incorporating on CPs, such as
free amide, carboxylate, and pyridyl groups, act as guest-accessible
functional sites where organic substrates could bind via various non-
covalent interactions leading to their activation in heterogeneous catal-
ysis [17–21]. The bis(4-pyridylformyl)piperazine (bpfp) ligand is a good
candidate for the construction of CPs with attractive structures and
different conformations depending upon the synthesis conditions [22].
Recently, we have successfully synthesized two CPs based on methyl-
3-hydroxy-5-carboxy-2-thiophenecarboxylate and bpfp mixed ligands,
where heterogeneous catalytic activities to the Knoevenagel reaction are
observed [23]. Noted, the Knoevenagel reaction of aldehydes with active
methylene compounds is well known, not only as a weak base-catalyzed
model reaction but also as a reaction that generates a C–C bond having
wide applications for the synthesis of some important and valuable
organic molecules [24,25]. Over the last few years, various catalysts have
been investigated for this reaction. However, several of these catalysts
suffer from several drawbacks including long reaction times, high reac-
tion temperatures and some of the reagents employed are expensive [26].
Our recent research interest focuses on the combination of bpfp and
cheap and commercially available multicarboxylate ligands to construct
new CPs with catalytic activities. In this work, one three-dimensional
compound, namely {[Cu3(nbta)2(bpfp)3(H2O)2](H2O)2}n (1), was suc-
cessfully synthesized based on 5-nitro-1,2,3-benzenetricarboxylic acid
(H3nbta) and bpfp mixed ligands. Detailed characterizations of 1 are
discussed. Moreover, catalytic studies revealed that 1 shows efficient
heterogeneous catalytic activity for the Knoevenagel reaction.
* Corresponding author. College of Chemistry and Chemical Engineering, and Henan Key Laboratory of Function-Oriented Porous Materials, Luoyang Normal
University, Luoyang, Henan, 471934, PR China.
E-mail address: lpxue@163.com (L.-P. Xue).
https://doi.org/10.1016/j.jssc.2019.120908
Received 7 July 2019; Received in revised form 1 August 2019; Accepted 9 August 2019
Available online 10 August 2019
0022-4596/© 2019 Elsevier Inc. All rights reserved.

Z.-H. Li et al.
Journal of Solid State Chemistry 278 (2019) 120908
Table 1
Crystallographic data and structure refinement summary for 1.
1
Empirical formula
Formula mass
Crystal system
space group
a/Å
C50H44Cu3N10O24
1359.57
Triclinic
P-1
5.73679(16)
15.2047(4)
15.7581(4)
98.823(2)
97.360(2)
95.912(2)
1336.48(6), 1
1.689
b/Å
c/Å
Fig. 1. View of the coordination environment of Cu(II) ions in compound 1.
Symmetry codes: (#1) 1 ꢁ x, 1 ꢁ y, 1 ꢁ z; (#2) x ꢁ1, y, z; (#3) 1 ꢁ x, 1 ꢁ y, ꢁ z.
o
α
/
β/o
γ/o
V/Å3, Z
Dc (g cmꢁ3
)
μ
/mmꢁ1
1.281
F(000)
693
Reflections collected/unique
Data/restraints/parameters
GOF(F2)
24485/4588
4588/0/398
1.055
0.0334/0.0794
0.0379/0.0814
Ra1/wRb2 [I > 2
σ
(I)]
Ra1/wRb2 (all data)
2. Experimental
2.1. Materials and methods
All reagents were of analytical grade and used without further puri-
fication. Elemental analyses for C, H, and N were carried out on a Flash
2000 elemental analyzer. The infrared (IR) spectra were recorded as KBr
pellets on
diffraction (PXRD) patterns were obtained on a Bruker D8-ADVANCE X-
ray diffractometer with Cu K
formed usingꢁa1SDTQ600 thermogravimetric analyzer with a heating rate
of 10 ꢀC min under flowing air. The morphology was investigated by
SEM (Hitachi SU8220). 1H NMR spectra was measured with a Bruker
AVANCE-400 NMR spectrometer. The Solid UV–vis diffuse reflectance
spectra were measured with a 1901 UV–vis Spectrometer (Puxi, China),
and a BaSO4 plate was employed as the reflectance standard.
a Nicolet Avatar-360 spectrometer. The powder X-ray
Fig. 2. Perspective view of the 2D layer structure.
α
radiation (λ ¼ 1.5418 Å). TGA was per-
2.2. Synthesis of {[Cu3(nbta)2(bpfp)3(H2O)2](H2O)2}n (1)
Blue block crystals of 1 were synthesized by the following procedure:
a mixture of H3nbta (0.1 mmol, 0.026 g), Cu(OAc)2⋅H2O (0.1 mmol,
0.020 g), bpfp (0.05 mmol, 0.0148 g) and deionized water (6 mL) was
sealed in a 25 mL Teflon-lined stainless steel vessel and heated at 413 K
for three days and then cooling to room temperature. Crystals of 1 were
collected by filtration and washed with distilled water in 56% yield
(based on Cu). Anal. Cal for C50H44Cu3N10O24: C, 44.13; H, 3.24; N,
10.30; Found: C, 44.11; H, 3.26; N, 10.28. IR data (KBr, cmꢁ1): 3671(w),
3525(w), 3406(w), 3098(w), 3081(w), 2920(w), 2868(w), 1636(s),
1597(s), 1573(m), 1516(m), 1456(m), 1419(s), 1338(s), 1279(m),
1250(m), 1167(m), 1153(m), 1063(m), 1001(s), 908(m), 841(s),
827(m), 763(m), 746(m), 717(s), 655(w), 651(w).
Fig. 3. View of the 3D net connected by 2D layer and 4-bpfp.
3. Results and discussion
3.1. Structural description
Compound 1 shows an unusual trinodal 4-connected 3D network. The
details of single-crystal data and structure refinement are summarized in
Table 1. The asymmetric unit of 1 consists of one and half Cu(II) centers,
one nbta ligand, two halves of bpfp ligands, one coordinated water
molecule and one lattice water molecule (Fig. 1). The four-coordinated
Cu1 atom is in a square-planar environment with the CuO2N2 chromo-
phore satisfied by two identical monodentate carboxylate oxygen atoms
from two nbta ligands and two identical pyridyl nitrogen atoms from two
bpfp ligands. The Cu2 is in a distorted square-pyramidal environment
coordinated by three carboxylate oxygen atom from three nbta ligands,
and one pyridyl nitrogen atom from one bpfp ligand and one coordinated
2.3. Single-crystal structure determination
The X-ray data of compound 1 was collected on a Rigaku Oxford
Diffraction SuperNova diffractometer using Mo Kα radiation. The struc-
ture was solved by direct methods based on the Olex2 program as an
interface together with the SHELXT and SHELXL programs, in order to
solve and refine the structure respectively [27–29]. All non-hydrogen
atoms were refined anisotropically and hydrogen atoms were placed at
the calculation positions. The details of crystal data and structure
refinement are summarized in Table 1 and the selected bond lengths and
bond angles are listed in Table S1.
water molecule. The addison parameter τ for Cu2 atom is 0.13, indicating
2

Z.-H. Li et al.
Journal of Solid State Chemistry 278 (2019) 120908
Fig. 5. PXRD patterns of as-synthesized and simulated compound 1.
Fig. 4. Topological view of the 4-connected network, where the cyan, green and
red balls represent the Cu2, Cu1 and nbta3ꢁ anion nodes, respectively. (For
interpretation of the references to colour in this figure legend, the reader is
referred to the Web version of this article.
that the coordination environment of Cu2 atom is closer to square-
pyramidal geometry than a trigonal–bipyramidal configuration [30].
The Cu–O/N distances associated with central Cu atoms in the range of
1.9353(18)–2.2433(18) Å, which are within the normal ranges [31]. In
1, all three carboxyl groups of the H3nbta are deprotonated and the
resulted nbta3ꢁ anion exhibit the μ4 η1 η0 η1 η0 η1 η1 coordination mode
- : : : : :
to connect adjacent Cu atoms, generating a 2D layered network along the
ac crystal plane (Fig. 2). Moreover, the adjacent 2D layers are linked into
a 3D architecture via the anti conformation tethering of 4-bpfp ligand
(Fig. 3). Topological approach can help us to better understand the 3D
structure. The nbta3ꢁ anion linking four Cu atoms can be considered a
4-connected node. The Cu1 atom connected by two 4-bpfp ligands and
two nbta3ꢁ anions can be viewed as a 4-connected node, and the Cu2
atom connected by one bpfp ligand and three nbta3ꢁ anions are also
4-connected. All bpfp ligands serve as 2-connected linkers. So the
structure could be simplified a new 3-nodal 4-connected network with
Fig. 6. TGA curve for compound 1.
2
2
2
3
4
€
the Schlafli symbol of {4 .6.8 .10}2{4 .6 .8}2{8.10 .12} analyzed by the
TOPOS program (Fig. 4) [32]. To the best of our knowledge, the present
structure represented the first example of 3-nodal 4-connected network.
Moreover, the coordinated carboxylates participated in hydrogen
bonding with the coordinated water molecule (O10–H1W⋯O2 and
O10–H2W⋯O3(x ꢁ 1, y, z)) (Table S1). The uncoordinated carbonyl
groups of bpfp and nitro groups also participated in hydrogen bonding
with
the
lattice
water
molecule
(O12–H3W⋯O11
and
O12–H4W⋯O7(x ꢁ 2, y þ 1, z)). Meanwhile, the structure also contains
C–H⋯O supramolecular interactions between the pyridyl ring and
carbonyl moiety of bpfp (C10–H10⋯O9(ꢁx, ꢁ y þ 1, ꢁ z þ 1)), pyridyl
rings of bpfp and carboxylates of nbta (C15–H15⋯O5(x ꢁ 1, y, z);
C15–H15⋯O6(ꢁx, ꢁ y þ 1, ꢁ z); C19–H19⋯O1(x ꢁ 1, y, z) and
C22–H22⋯O9(x þ 1, y, z)), piperazine rings of bpfp and carboxylates of
nbta(C17–H17B⋯O8(–x þ 1, ꢁ y þ 1, ꢁ z) and C18–H18⋯O8(– x þ 1, ꢁ
y þ 1, ꢁ z), and these interactions further stabilize the supramolecular
network.
Fig. 7. UV–vis absorption spectra of the free H3nbta, bpfp, and compound 1.
3.2. PXRD, TGA and UV–vis absorbance properties
corresponding simulated pattern obtained from the single-crystal struc-
ture data, which confirms the phase purity of the as-synthesized sample
(Fig. 5). The slight differences in intensity may be owing to the preferred
The phase purity of compound 1 was recorded by PXRD pattern of the
bulk sample. The experimental PXRD curve is consistent with the
3

Z.-H. Li et al.
Journal of Solid State Chemistry 278 (2019) 120908
Fig. 8. SEM images of (a) fresh and (b) used compound 1.
orientation during collection of the experimental data. The TGA of
compound 1 was carried out under flowing air with a heating rate of
10 ꢀC minꢁ1. As shown in Fig. 6, the weight loss of 5.23% in the range
from 60 to about 200 ꢀC corresponds to the loss of all lattice and coor-
dinated water molecules in the product (calcd 5.30%). Then, there is no
mass change till to 243 ꢀC. Succeeding weight losses for them correspond
to the decomposition of the coordination network and complete de-
compositions are almost achieved about 485 ꢀC.
At ambient temperature, the optical absorption of solid 1 and the
H3nbta, bpfp ligands were measured. As seen in Fig. 7, the spectra of the
H3nbta ligand presented one maxima absorption at λmax ¼ 262 nm and
the free bpfp ligand itself exhibited two strong absorption at λmax ¼ 247,
313 nm, respectively. Compound 1 showed strong absorptions in the UV
region owing to the contribution of charge transfer transitions between
metal centers and organic ligands. Moreover, the absorptions are
observed at ca. 676 nm in the visible region, which is mainly assigned to
a metal-centred (MC) transition [33,34].
3.3. Catalytic properties
The as-prepared compound 1 is quite stable in air for a prolonged
period of time. To test the catalytic activty of compound 1, we focused on
the standard Knoevenagel reaction of 4-fluorobenzaldehyde with malo-
nonitrile in DMF. The reaction times were monitored by TLC, and the
product yields were determined by column chromatography. Under
aerobic conditions, we found that the reaction was practically accom-
plished (99% yield, isolated yields) within 1.5 h using a 1 mol% com-
pound 1 loading at room temperature. However, the reaction without
compound 1 proceeded for a longer time (3 h) and generated only 21%
yield under the same reaction conditions. Moreover, free bpfp ligand was
Table 2
The Knoevenagel condensation by catalyzed compound 1a.
4

Z.-H. Li et al.
Journal of Solid State Chemistry 278 (2019) 120908
added to test the catalytic effect, and a reaction yield of 49% was reached
after 3 h. From the viewpoint of structure, compound 1 do not have
effective pore and thus the catalytic efficiency mainly attributed to active
sites on the surface. The uncoordinated carbonyl moieties of bpfp as
reactive base sites may abstract the proton from the active methylene
group of malononitrile to produce the corresponding nucleophilic spe-
cies, as confirmed from a lower wavenumber shift and splitting of the
nitrile group in the IR spectrum (2202 and 2179 cmꢁ1) (Fig. S1) [35].
The Lewis acidic Cu(II) centre interacts with the carbonyl group of the
benzaldehyde, generating a polarization of this group and thus increasing
the electrophilic character of the carbonylic carbon atom, which is also
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://do
i.org/10.1016/j.jssc.2019.120908.
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4. Conclusion
In summary, a three-dimensional coordination polymer material
{[Cu3(nbta)2(bpfp)3(H2O)2](H2O)2}n based on 5-nitro-1,2,3-benzenetri-
carboxylic acid and bis(4-pyridylformyl)piperazine mixed ligands was
synthesized under hydrothermal conditions. The structural character-
ization demonstrates that the compound exhibits a 3D structure with an
unusual 4-connected topology. Importantly, the compound can acts as an
efficient catalyst for the Knoevenagel reaction.
Acknowledgments
This work was supported by the National Natural Science Foundation
of China (No. 21671094).
5