A novel 3D MOF with rich lewis basic sites as a base catalysis toward knoevenagel condensation reaction

Article abstract of DOI:10.1016/j.molstruc.2018.04.078

A novel 3D MOF with high stability, {[Eu(TATMA)(H₂O)·2H₂O}_n (namely 1), was solvothermally synthesized by a semi-rigid organic ligand 4,4,4″-s-triazine-1,3,5-triyltri-m-aminobenzoic acid (denoted as H₃TATMA) and

Full text of DOI:10.1016/j.molstruc.2018.04.078

Journal of Molecular Structure 1167 (2018) 11e15
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
A novel 3D MOF with rich lewis basic sites as a base catalysis toward
knoevenagel condensation reaction
Shixia Zhao
Department of Chemical Engineering, ZiBo Vocational Institute, Zibo, 255314, Shandong, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel 3D MOF with high stability, {[Eu(TATMA)(H2O)$2H2O}n (namely 1), was solvothermally syn-
thesized by a semi-rigid organic ligand 4,4,400-s-triazine-1,3,5-triyltri-m-aminobenzoic acid (denoted as
H3TATMA) and Eu(III) ion. The high stability is mainly attributed to 1D Eu(III) chains as inorganic nodes in
1. Furthermore, 1 has been characterized in detail by single crystal X-ray diffraction, powder X-ray
diffraction, elemental analysis (C, H and N) and thermogravimetric analysis. Thanks to its large number of
Lewis basic sites and high stability in 1, it can be considered as an excellent heterogeneous base catalysis
for Knoevenagel condensation reaction. In addition, the recycle sample can reuse at least four times
without any loss of activity.
Received 14 March 2018
Received in revised form
24 April 2018
Accepted 24 April 2018
Available online 26 April 2018
Keywords:
Metal-organic framework
H3TATMA
© 2018 Published by Elsevier B.V.
Lewis basic sites
Catalysis
Knoevenagel reaction
1. Introduction
catalysis to catalyse Knoevenagel condensation reaction [36e44].
Among all the common Lewis basic groups, many researches have
Metal-organic frameworks (MOFs) [1e6] are considered as
novel crystalline materials to attract large number of interests in
recent years, which is mainly ascribed to their abundant structures
and numerous potential application values, including gas adsorp-
tion and separation [7e13], carrier [14e16], sensor [17e24], optical
material [25e27], and catalysis [28e31]. So far, lots of novel
structures have been obtained by a variety of methods, including
organic ligands, metal ions/clusters, and synthetic conditions.
There into, organic ligands always play a decisive role to regulate
structure and function. Most of the ligands used to form MOFs are
rigid multicarboxylic acids. However, semi-rigid organic ligands
with multicarboxylic acids also become one class of the organic
ligands to assemble with many different metal ions to generate
novel structures in MOFs, particularly semi-rigid tritopic ligands
[32e35], because these ligands can generate MOFs with intriguing
architectures and interesting properties.
been focused on 1,3,5-triazine functional group, because it is rigid
and easily introduced into organic ligands [30,34,35,45]. For
example, Eddaoudi's group successfully incorporated 1,3,5-triazine
functional groups in an organic ligand to generate MOF materials
(namely rht-MOF-7) with high performance for small gases capture
and separation [45]. Therefore, it is also interesting to use such li-
gands to design and prepare such MOFs with Lewis basic sites to
catalyse Knoevenagel condensation reaction.
In this work, we selected a semi-rigid organic ligand 4,4,400-s-
triazine-1,3,5-triyltri-m-aminobenzoic acid (denoted as H3TATMA)
[46], because it both contains high density of Lewis basic sites and
multiple coordination sites. This ligand can assemble with Eu(III)
ions to generate
a
novel three-dimensional (3D) MOF,
{[Eu(TATMA)(H2O)$2H2O}n (namely 1). As we predicted, the
resultant crystals, as basic catalysts, can be employed to catalysis
Knoevenagel condensation reaction.
MOFs have been applied in catalysis fields, especially as het-
erogeneous base catalysts. The functional basic MOFs can be syn-
thesized by introducing Lewis basic sites in the organic ligands to
catalyse basic reaction, including Knoevenagel condensation reac-
tion. Up to now, some basic MOFs have been used as Lewis basic
2. Experimental
2.1. Materials and general methods
All chemical reagents in this work were purchased from com-
mercial sources without further purification. Powder X-ray
diffraction (PXRD) data were collected on a Riguku D/MAX2550
E-mail addresses: zbliyc@126.com, zbliyc@126.com.
https://doi.org/10.1016/j.molstruc.2018.04.078
0022-2860/© 2018 Published by Elsevier B.V.

12
S. Zhao / Journal of Molecular Structure 1167 (2018) 11e15
diffractometer with Cu-K
a
(
l
¼ 1.5418 Å) with a 2
q
range of 4e40ꢀ
days. Yellow block-shaped crystals were generated directly after it
was cooled to room temperature. The obtained samples were
washed with distilled H2O and dried in air. Yield: 67% (based on
H3TATMA). FT-IR (KBr): 3432 (br), 1625 (s), 1577 (s), 1550 (s), 1525
(s), 1413 (s), 1352 (s), 1306 (s), 1240 (s), 1127 (s), 758 (s), 601 (s), 522
(s) (Fig. S1). Anal. calcd for C24H21O9N6Eu: C 41.81, H 3.07, N 12.19%;
found: C 41.78, H 3.05, N 12.17%.
at room temperature. Elemental analysis (C, H and N) were ach-
ieved on a Perkin-Elmer 240 analyzer. Thermogravimetric analysis
(TGA) were carried on a TGA Q500 thermal analyzer in air from
30 ꢀC to 800 ꢀC at a heating rate of 10 ꢀC/min. Fourier-transform
infrared (FT-IR) spectra were performed by IFS 66 V/S Fourier-
transform infrared spectrometer from 4000 to 400 cmꢁ1 by pre-
paring a pellet. The gas chromatograph data were obtained from
Agilent 7890 A gas chromatograph machine.
2.3. X-ray structure determination and structure refinement
The single crystal data of 1 was performed on a Bruker SMART
2.2. Synthesis of 1
CCD diffractometer with graphite-monochromated Mo
Ka
(
l
¼ 0.71073 Å) radiation at 293(2) K. The structures were solved by
A mixture of Eu(NO3)3$6H2O (40.0 mg, 0.088 mmol), H3TATMA
(25 mg, 0.05 mmol), H2O (3 mL) and NaOH aqueous solution
direct methods and refined by the full-matrix least-squares on F2 of
all data using the Shelxl-97 program [47]. All non-hydrogen atoms
were refined with anisotropic displacement parameters. Crystal
data of 1 is listed in Table 1 and the selected bond lengths and bond
angles are summarized in Table S1.
(0.05 M, 30
mL) was added in a 23.0 mL Teflon-lined autoclave,
which was further sonicated about 15 min and put into 180 ꢀC for 3
Table 1
Crystal data and structure refinement for 1.
3. Results and discussion
Compound
1
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C24H21O9N6Eu
689.44
Triclinic
P-1
8.2205(3)
11.3539(5)
14.1196(7)
113.473(5)
103.573(4)
92.256(3)
1161.92(10)
2
1.971
2.771
4097
0.044
1.034
0.0306, 0.0666
0.0345, 0.0697
3.1. Structural description for 1
From the single-crystal X-ray diffraction analysis, it shows that 1
crystallizes in the triclinic P-1 space group with three-dimensional
(3D) coordinated structure. As illustrated in Fig. S2, the asymmetric
unit of 1 has one independent Eu(III) ion, one coordinated H2O
molecule, a fully deprotonated TATMA3ꢁ ligand and two guest H2O
molecules. The TATMA3ꢁ ligand has only one coordinated mode as
b (Å)
c (Å)
a
b
g
(º)
(º)
(º)
V (Å3)
m5- : : : : :
h1 h1 h1 h2 h1 h2 to link with five Eu(III) ions (Fig. 1a). As
Z
r
shown in Fig. 1b, the Eu(III) ion is coordinated with nine oxygen
atoms from four carboxylate groups from ligands and one coordi-
nated H2O molecule. Each Eu(III) ion can be further connected by
the oxygen atoms to generate 1D Eu(III) inorganic chains
(EuꢁO ¼ 2.415(3)ꢁ2.618(3)Å). The Eu,,,,Eu distance in the 1D
chain is in the range of 4.169 through 4.171 Å. The 1D inorganic
Eu(II) chains are linked by fully deprotonated TATMA3ꢁ ligands,
(calc g cmꢁ3
(mmꢁ1
)
m
)
Nref
R(int)
Goodness-of-fit on F2
R1, wR2 [I > 2
s(I)]
R1, wR2 (all data)
Fig. 1. (a) Coordination mode of TATMA3ꢁ ligand; (b) one-dimensional inorganic Eu(III) chain; (c, d) viewing the 3D framework from entirely different views (The hydrogen atoms
are removed for clarity, and C, gray; N, blue; O, red; Eu, green). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this
article.)

S. Zhao / Journal of Molecular Structure 1167 (2018) 11e15
13
Fig. 2. (a) The PXRD patterns of simulated (black) and experimental (red) samples; (b) the TGA data of the experimental sample. (For interpretation of the references to colour in
this figure legend, the reader is referred to the Web version of this article.)
resulting in a 3D structure (Fig. 1c and 1d).
yields of aldehyde with electron donor groups (one eOMe group,
entry 5 and two eOMe groups, entry 6) reduced 89 and 77,
respectively.
3.2. PXRD and thermal analysis
Furthermore, it is very important for catalysis to easily
The powder X-ray diffraction (PXRD) pattern of as-synthesized 1
was carried out at room temperature. The corresponding charac-
teristic peaks of the experimental 1 are matched very well with the
simulated ones from single crystal structure (Fig. 2a), which indi-
cated that the phase purity of a lot of synthetic crystalline materials.
As illustrated Fig. 2b, the thermogravimetric analyses (TGA) anal-
ysis of 1 exhibited a weight loss of 8.02% before 180 ꢀC, belonging to
loss of coordinated and guest H2O molecules (calculated 7.83%).
With the increasing temperature, the origin structure began to
collapse and decompose completely. The final product of thermal
decomposition was Eu2O3.
Table 2
Knoevenagel condensation reaction based on different aldehyde substrates was
catalyzed by 1.
Entry
1
Substrate
Product
Yield (%)
98
3.3. Catalysis properties
Thanks to lots of Lewis basic sites in 1, the resultant sample was
further investigated as a basic catalyst. We selected Knoevenagel
condensation reaction as study model (Table 2). Firstly, the as-
synthesized 1 was soaked into toluene overnight and dried in the
air. In a prototype experiment, substrate (1 mmol), malononitrile
(1.2 mmol), catalyst (1, 100 mg) and toluene (5 mL) were all added
into a glass reactor. The reacting mixture was heated and stirred at
80 ꢀC for 3 h. The yields were easily confirmed and analysed by gas
chromatography. As shown in Table 2, it contains all the catalytic
results of Knoevenagel condensation reaction based on different
aldehyde substrates. Catalyst 1 was considered as a heterogeneous
base catalysis for this reaction. As illustrated in entry 1, the catalytic
yield of 2-benzylidenemalononitrile product was about 98%, which
was selected as a model to further discuss and investigate the ki-
netic catalytic effect in detail (Fig. 3a). The kinetic catalytic data
illustrated that the reaction almost completely reacted within 3 h.
To prove the importance of the catalyst, the reaction stopped
immediately after removing the catalysis 1. Furthermore, the cat-
alytic yield of 2-benzylidenemalononitrile was only about 4%
without the catalyst 1, which also confirmed the important of 1 for
this reaction (entry 2). Various substituted aldehyde reactants were
applied to study the difference in the presence of catalysis 1. The
corresponding results demonstrated that the outstanding yields
(>99%) were discovered for the withdrawing groups, including eF
and eNO2 groups (entries 3 and 4). Nevertheless, the reaction
2
3
4
>99
4
5
6
>99
89
77

14
S. Zhao / Journal of Molecular Structure 1167 (2018) 11e15
Fig. 3. (a) The kinetics analysis of the Knovenagel condensation reaction; (b) The recycle ability of catalysis 1.
9463e9466.
recollected and recycle after the catalytic reaction. In this reaction,1
was easily separated after such reactions via centrifuging at 7000
r,minꢁ1 for 2 min, which can be reused after washing several times
with fresh toluene. As illustrated in Fig. 3b, the catalytic effect of
recycle catalysis 1 was nearly no any decrease after reusing four
catalytic cycles, which is mainly attributed to the high stability of 1.
The PXRD patterns of reused sample demonstrated that the
framework can keep well (Fig. S3). Additionally, the inductively
coupled plasma data showed that it did not have Eu(III) ion in the
reaction solution after filtrating catalysis, confirming the hetero-
geneous catalysis nature of 1.
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venagel condensation reaction. The sample can be separated and
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Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.molstruc.2018.04.078.
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