Cd-MOF@PVDF Mixed-Matrix Membrane with Good Catalytic Activity and Recyclability for the Production of Benzimidazole and Amino Acid Derivatives

Article abstract of DOI:10.1021/acs.inorgchem.1c00084

Mixed-matrix membranes (MMMs) incorporating metal-organic framework crystalline fillers as heterogeneous catalysts for organic transformation reactions have attracted more attention in catalysis science. Herein, a new 3D cadmium metal-organic framework (H3O)·[Cd(dppa)] (1) was first synthesized using the rigid 4-(3,5-dicarboxylphenyl)picolinic acid (H3dppa) as an organic ligand under solvothermal conditions, exhibiting a novel 6,6-connected network and good tolerance to various solvents. After activation, 1 showed good catalytic reactivity and selectivity for the synthesis of benzimidazole derivatives, affording solvent-dependent catalytic activity. Then, using the microcrystals of 1 and poly(vinylidene fluoride) (PVDF) as raw materials, 1@PVDF MMMs were successfully prepared by polymer solution casting. Notably, the integration of MOF and PVDF endows the mixed-matrix membrane 1@PVDF with great advantages in terms of more dispersive Lewis acid catalytic sites and recyclability. As expected, 1@PVDF not only displays good catalytic activity comparable to that of activated 1 but also exhibits remarkable recyclability and continuous usability for the production of benzimidazole and α-or β-amino acid derivatives. To the best of our knowledge, this is the first time that a Cd-based MOF and MMMs have been applied as a catalyst for the production of a β-amino acid. The combination of catalytic MOF and PVDF provides a way to simplify the design of a flow reactor and reduce the costs of manufacturing.

Full text of DOI:10.1021/acs.inorgchem.1c00084

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Article
Cd-MOF@PVDF Mixed-Matrix Membrane with Good Catalytic
Activity and Recyclability for the Production of Benzimidazole and
Amino Acid Derivatives
Yansong Jiang, Jing Sun, Xiaona Yang, Jieyu Shen, Yu Fu, Yong Fan, Jianing Xu,* and Li Wang*
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ABSTRACT: Mixed-matrix membranes (MMMs) incorporating metal−organic
framework crystalline fillers as heterogeneous catalysts for organic transformation
reactions have attracted more attention in catalysis science. Herein, a new 3D
cadmium metal−organic framework (H3O)·[Cd(dppa)] (1) was first synthesized
using the rigid 4-(3,5-dicarboxylphenyl)picolinic acid (H3dppa) as an organic
ligand under solvothermal conditions, exhibiting a novel 6,6-connected network
and good tolerance to various solvents. After activation, 1 showed good catalytic
reactivity and selectivity for the synthesis of benzimidazole derivatives, affording
solvent-dependent catalytic activity. Then, using the microcrystals of 1 and
poly(vinylidene fluoride) (PVDF) as raw materials, 1@PVDF MMMs were
successfully prepared by polymer solution casting. Notably, the integration of MOF
and PVDF endows the mixed-matrix membrane 1@PVDF with great advantages in
terms of more dispersive Lewis acid catalytic sites and recyclability. As expected,
1@PVDF not only displays good catalytic activity comparable to that of activated 1 but also exhibits remarkable recyclability and
continuous usability for the production of benzimidazole and α- or β-amino acid derivatives. To the best of our knowledge, this is
the first time that a Cd-based MOF and MMMs have been applied as a catalyst for the production of a β-amino acid. The
combination of catalytic MOF and PVDF provides a way to simplify the design of a flow reactor and reduce the costs of
manufacturing.
MOFs. Thus, the open active sites and the size selectivity for
catalysis will remain. Meanwhile, the excellent dispersion of
MOF particles in the matrix causes a good flux of the reactant,
which enables more effective contact between the reactants
and the MOF catalyst, thereby enhancing the catalytic
performance in comparison to powder samples of MOF
catalysts.10
More recently, the synthesis of heterocyclic compounds,
especially benzimidazole derivatives with five-membered-ring
structures, has aroused great interest owing to their various
biological activities, including antifungal, antibacterial, anti-
cancer, and antiulcer activities.11,12 Catalysis by MOFs for the
synthesis of these compounds has emerged as a new green
route with high efficiency. Maji et al. introduced additional
Lewis acidic Cu(II) into an MOF via postsynthetic metalation
for the synthesis of benzimidazole derivatives.11 Neppolian et
al. tested NH2-MIL-125(Ti) (MIL = Materials of Institute
INTRODUCTION
■
As an important part of the polymeric membrane family,
mixed-matrix membranes (MMMs) with light weight, tunable
morphologies (fibers, porous spheres, and thin films), high
mechanical strength, and good chemical resistance have been
widely prepared and applied in chemical sensing, adsorption,
and separation.1−6 Currently, introducing metal−organic
framework (MOF) particles into a polymer matrix has become
an effective strategy to fabricate MMMs with multiple
functionalities. For example, Zhang et al. reported a MOF-
based MMM by a blending approach which exhibited good
flexibility and remarkable detection selectivity and sensitivity
for H2S with a quite low detection limit.7 Prasetya and co-
workers fabricated two MMMs with JUC-62 (JUC = Jilin
University China) and PCN-250 (PCN = porous coordination
network). These two light-responsive MMMs displayed gas
separation and beneficial aging characteristics for CO2/N2
separation under light irradiation.8 Moreover, a few MOF-
based MMMs have been applied in catalysis. Lei et al. reported
a series of MOF-polymer MMMs for the Knoevenagel
condensation of benzaldehyde with malononitrile.9 On the
basis of the larger pore size of polymer molecules in
comparison to that of the MOFs, the coupling is only limited
to the exposed surface ligands, preserving the porosity of
Received: January 10, 2021
Published: January 20, 2021
https://dx.doi.org/10.1021/acs.inorgchem.1c00084
© 2021 American Chemical Society
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photoelectron spectroscopy (XPS) was carried out with a ESCALAB
250 X-ray electron spectrometer equipped with Al Kα radiation.
Inductively coupled plasma optical emission spectrometer (ICP-OES)
analysis was performed on an Agilent 725 instrument. A fluorescence
spectrum was obtained on an Edinburgh Instrument FLS920
fluorescence spectrometer. The contact angle was determined with
a KRUSS GmbH DSA-25 instrument. N2 adsorption isotherms were
measured using a Micromeritics ASAP 2020 surface area analyzer at
77 K.
Synthesis of 1. Cd(NO3)2·4H2O (0.015 g, 0.10 mmol) and
H3dppa (0.015 g, 0.05 mmol) were dissolved in a mixture of
acetonitrile (CH3CN, 1.0 mL), ethanol (EtOH, 1.0 mL), and
deionized water (5.5 mL). Then, NaOH (70 μL, 1 M) was added to
adjust the pH value. After it was stirred for 10 min, the mixture was
transferred into a 25 mL Teflon-lined vessel, sealed in an autoclave
reactor, and heated for 4 days at 180 °C. Subsequently, light yellow
hexagonal block crystals could be obtained. The samples were washed
three times with CH3CN and dried in air. Yield: 64% based on Cd.
Anal. Calcd: C, 40.43; H, 2.17; N, 3.97. Found: C, 40.66; H, 2.24; N,
3.85. IR (KBr, cm−1): 3249(m), 3168(m), 2965(m), 2814(m),
2478(w), 2162(w), 1959(w), 1903(w), 1832(m), 1576(s), 1435(s),
1397(s), 1354(s), 1270(m), 1104(w), 1072(w), 905(m), 850(s),
812(s), 769(s), 646(s), 562(m), 486(w), 429(w).
Lavoisier) for the synthesis of benzimidazole and benzothia-
zole derivatives, and the results showed that it was an efficient
oxidant-free heterogeneous catalyst with good yield.12
However, the reported MOF powder also has limited efficiency
in large-scale syntheses because of the long reaction time,
tedious workup procedure, and lower recyclability. Addition-
ally, as another member of carbon−carbon bond formation
reactions, the syntheses of amino acids and their derivatives are
of current interest due to their indispensable application in
organic transformations and biology.13,14 Especially, the
synthesis of unnatural β-amino acids is becoming an important
and urgent need of modern synthetic chemistry.15 The
reactions for the syntheses of amino acid derivatives include
the Strecker type reaction for α-amino acid derivatives and the
Mannich type reaction for β-amino acid derivatives. Since our
group reported an In-MOF catalyst for the synthesis of amino
acid derivatives in 2014, many MOFs have been used for the
Strecker reaction to achieve α-amino acid derivatives; however,
only a few focused on the synthesis of Mannich type reactions
for β-amino acid derivative production.16−19
̈
The creation and modification of the framework with
remarkable catalytic performance can be precisely tuned at a
molecular level by rationally designing inorganic or organic
building blocks.20 In order to obtain a highly efficient MOF-
based mixed-matrix membrane catalyst for the production of
benzimidazole and amino acid derivatives, we first designed
and prepared a novel three-dimensional cadmium MOF,
(H3O)·[Cd(dppa)] (1), by rational selection of Cd(II) as
the metal center and 4-(3,5-dicarboxylphenyl)picolinic acid
(H3dppa) with three carboxylate groups and a pyridine ring as
an organic linker under solvothermal conditions. 1 exhibits
excellent solvent stability and can provide additional
coordinated unsaturated sites (CUS) in addition to intrinsic
Lewis acidic Cd2+ centers after activation.21−23 As expected,
activated 1 has excellent catalytic properties for the syntheses
of benzimidazole derivatives and amino acid derivatives under
mild conditions at room temperature. Then the activated 1 as a
filler is introduced in a poly(vinylidene fluoride) (PVDF)
membrane matrix to form MMMs, 1@PVDF, which shows
catalytic properties comparable with those of the activated 1
and excellent recyclability for the syntheses of benzimidazole
and amino acid derivatives. Herein, we report the synthesis,
crystal structure, and characterization of 1 as well as the 1@
PVDF mixed-matrix membrane and their catalytic perform-
ances for the syntheses of benzimidazole and amino acid
derivatives.
Determination of Crystal Structure. A suitable regular single
crystal of 1 with dimensions 0.8 × 0.4 × 0.1 mm3 was carefully picked
out under an optical microscope for single-crystal XRD analysis. The
intensity data were collected on a Bruker D8 Quest diffractometer
with Mo Kα (λ = 0.71073 Å) radiation at a temperature of 293(2) K.
The structure was solved using direct methods and refined by full-
matrix least squares on F2 using the SHELXTL-2014 crystallographic
software packages.24 All of the Cd atoms were located first, and then
oxygen, nitrogen, and carbon atoms were subsequently found in
difference Fourier maps. All of the hydrogen atoms were placed
geometrically and refined in a riding model. All of the non-hydrogen
atoms were refined anisotropically. The contribution of the electron
density associated with disordered solvent molecules was removed by
the SQUEEZE method as implemented in PLATON.25,26 The crystal
data and structure refinement details for 1 are summarized in Table
S1 in the Supporting Information, and selected bond lengths and
angles are given in Tables S2 and S3.
Preparation of MMMs. A 0.15 g portion of PVDF was dissolved
in 1 mL of N,N-dimethylformamide (DMF), MOF particles (0, 10,
30, 50, and 70 wt %) were added to the solution, and the mixture was
stirred for 30 min. Then, the mixture was dropped onto glass a
substrate and allowed to stand for 24 h. A flexible membrane was
achieved, and it was washed several times with deionized water. Then
the membrane sample was dried under vacuum at room temperature
overnight.
Activation of MOFs. The as-synthesized sample of 1 was washed
three times with CH3CN and hexane and heated at 120 °C under
vacuum overnight.27,28
Catalytic Experiment. For the synthesis of benzimidazole
derivatives, the activated 1 (0.025 mmol) or 1@PVDF (size 1 cm
× 1 cm), o-phenylenediamine (1 mmol), aldehydic substrates (1
mmol), and solvent (1 mL) were placed in a reactor and stirred at
room temperature.
EXPERIMENTAL SECTION
■
Materials and Methods. All analytical reagents and chemical
materials were obtained from commercial sources and directly used
without any further purification. Powder X-ray diffraction (PXRD)
data were acquired via a Shimadzu XRD-6000 diffractometer with Cu
Kα radiation (λ = 1.5418 Å), in the 2θ range of 4−40°. Elemental
analysis (C, H, and N) was conducted on an Elementar Vario EL cube
CHNOS elemental analyzer. Fourier transform infrared (FT-IR)
spectra (KBr pellets) were recorded in the range 4000−400 cm−1 on a
IFS-66 V/S instrument using the KBr pellet method. Thermogravi-
metric analysis (TGA) was carried out using a PerkinElmer TGA7
thermogravimetric analyzer from 40 to 800 °C at a ramp heating rate
of 10 °C min−1 in an air atmosphere. 1H NMR spectra were measured
using a Bruker Avance III 400 console at a frequency of 400 MHz.
Scanning electron microscopy (SEM) images were obtained with a
JEOL JSM-IT500A instrument. Energy-dispersive X-ray spectroscopy
(EDS) was conducted on a Thermo FEI instrument. X-ray
Aldimines were synthesized by aldehydes and amines, which has
been reported before.29
For the Strecker reaction, 1@PVDF (size 1 cm × 1 cm), 0.5 mmol
of aldimines, 1.5 mmol of TMSCN, and 1 mL of CDCl3 were placed
in the reactor at room temperature.
For the Mukaiyama aldol reaction, 1@PVDF (size 1 cm × 1 cm),
0.5 mmol of p-nitrobenzaldehyde, 1.5 mmol of silyl ketene acetal, and
1 mL CD3CN were placed in the reactor at room temperature.
For the Mannich reaction, 1@PVDF (size 1 cm × 1 cm), 0.5 mmol
of aldimine, 1.5 mmol of silyl ketene acetal, and 1 mL of CD3CN were
placed in the reactor at room temperature.
The reactions were monitored by 1H NMR spectra, and the
conversion yield was determined to be the sum of integrals of all
signals (substrate and product).
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Figure 1. (a) 1D chain, (b) 2D layer, and (c) 3D framework of 1 along the c axis. (d) Simplification of the metal center and ligand and schematic
representation of the topology for 1.
Figure 2. (a) PXRD patterns of 1 and 1@PVDF along with a simulated pattern. (b) PXRD pattern of the powder of 1 treated with various solvents.
(c) FT-IR spectra of 1 and 1@PVDF. (d) Effect of time on the yield.
Recycling Catalysis Experiments. To test the recyclability of
the catalyst, five runs were carried out under the same reaction
conditions as described previously, except for using the recycled
catalyst in the last run. After each run of the reaction, 1 was separated
from the reaction system by centrifugation. Then, the catalyst was
washed several times with CH2Cl2 and hexane and dried at 100 °C
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Scheme 1. Schematic Illustration of the Preparation of MOFs@PVDF Mixed-Matrix Membranes
under vacuum before the next run. For 1@PVDF, the membrane was
pulled out from the reaction system and washed several times with
CH3CN. Then the membrane was dried under vacuum for the next
run of catalysis.
molecule in the channel. Moreover, in order to further
understand the framework of 1 clearly, a topological analysis
has been carried out with TOPOS 4.0 software. Topologically,
the Cd atom can be viewed as a 6-connected node, and the
ligand can be seen as a 6-connected node (Figure 1d). Thus,
the overall structure of 1 can be reduced into a novel 6,6-
connected framework with an extending point symbol of {38·
412·5}.
Characterization. The PXRD pattern for 1 is consistent
with the simulated pattern from the single-crystal XRD data,
confirming the phase purity of the samples (Figure 2a). The
difference between them is due to the different orientations of
the powder samples. The thermogravimetric analysis for 1 was
acquired in an air atmosphere from 40 to 800 °C with a
heating rate of 10 °C min−1. There are two steps of weight loss
of 1 (Figure S1). The first step from 75 to 155 °C corresponds
to the loss of the protonated water guest (found, 2.07%;
calculated, 2.17%) The second step of weight loss above 165
°C corresponds to the decomposition of the framework.
To examine the stability of 1, the powder sample was
immersed in various solvents (water (H2O), methanol
(MeOH), alcohol (EtOH), N,N-dimethylformamide (DMF),
dimethyl sulfoxide (DMSO), dichloromethane (DCM),
acetone, and hexane) for 7 days. The PXRD patterns reveal
that 1 exhibits good stability after treatment with these solvents
(Figure 2b). Furthermore, 1 can be exposed to the air for over
6 months with retainment of the structure.
RESULTS AND DISCUSSION
■
Crystal Structure of 1. 1 crystallized in the monoclinic
system and P21/c (No. 14) space group, and the asymmetric
unit only contains one crystallographically independent Cd
atom and one ligand molecule. As shown in Figure S1, the Cd
atom is coordinated with five carboxyl oxygen atoms and one
nitrogen atom, forming a distorted-octahedral coordination
geometry. The Cd−O bond lengths range from 2.197(2) to
2.356(2) Å, and the Cd−N bond length is 2.364(2) Å. The
average N−Cd−O and O−Cd−O angles are 97.08 and
107.72°, respectively, which are quite in accord with those of
other Cd-MOFs.30−35 The three carboxylate oxygen atoms of
the organic ligand are completely deprotonated. The dppa3−
anion links five Cd(II) cations in μ2-η2 and μ3-η1:η2 fashions
through its three carboxylate groups. The N atom from the
pyridine unit coordinates to one Cd(II) cation. It is noted that
adjacent COO−(C1) and N atoms coordinate with an identical
Cd(II) cation in a chelation mode.
Two Cd(II) cations are connected by two carboxylates,
forming a zigzag chain along the c axis (Figure 1a). The
adjacent zigzag chains run parallel to each other and are
interconnected by dppa3− ligands to generate a 2D layer in the
ac plane (Figure 1b). Then, the neighboring layers are
connected by the carboxylate groups in benzene rings to
form a pseudo-2D network. These pseudo-2D networks are
connected with each other by the pyridine motif, forming 3D
frameworks (Figure 1c). Notably, the negative charge of the
host framework was balanced by one guest protonated water
Scheme 1 illustrates the detailed procedures for the
preparation of MMMs. In brief, a suspension of 1 and
poly(vinylidene fluoride) (PVDF) was magnetically stirred for
30 min at room temperature to yield a mixture. Thereafter, the
mixture was dropped to uniformly deposit it upon the entire
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Figure 3. (a) Tyndall effect of a 1 fine suspension in solution. (b, c) images of 1@PVDF (d, e) SEM images of 1@PVDF. (f) cross-section SEM
image. (g−i) EDS mapping images (g, Cd; h, O; i, N). The scale bars are 20, 5, and 40 μm for (d−f), respectively.
surface of glass. The particles of 1 are well dispersed in the
polymer solution, which can be verified by the Tyndall effect.
As shown in Figure 3a, the light goes through the solution
from right to left. In the polymer solution containing 1
particles, a bright light path in the solution can be found, while
the polymer solution without 1 has no light path. The XRD
pattern of 1@PVDF also displays good agreement with the
simulated pattern, in which some broad peaks originate from
the weak diffraction of the PVDF matrix (Figure 2a). Notably,
the top of the MMM has strong diffraction intensity, while the
bottom of the MMM has very weak diffraction intensity, which
could be due to the dispersion of the MOF filler being more
concentrated on the upper surface of the membrane. The
mechanical behavior of 1@PVDF with different loadings of the
fillers has been tested. As shown in Figure S3, we have not
obtained a pure PVDF membrane by a polymer solution
casting method; the product on the glass sheet has obvious
cracks, whereas the 1@PVDF samples were quite continuous.
When the content of the filler was increased, the agglomeration
of 1 particles occurred owing to the particle−particle
interactions. The dispersion of the filler in the membrane is
poor, and the mechanical behavior of membrane becomes hard
and fragile. The morphology of 1@PVDF was characterized by
scanning electron microscopy (SEM) (Figure 3d,e). It is noted
that 1 adheres to the surface of the PVDF matrix and the
PVDF substrate stacked up with the evaporation of the solvent
to form a hierarchical structure. The strong electrostatic
interactions among the frameworks of 1 and −F groups of
PVDF resulted in good affinity of the crystalline fillers in the
synthesized MMM. The cross-section image reveals that the
thickness of 1@PVDF is about 120 μm (Figure 3f). 1@PVDF
not only exhibits extra hierarchical structures but also displays
good flexibility, making it highly adaptable for a variety of
practical applications. Moreover, the energy-dispersive X-ray
spectroscopy (EDS) elemental mapping suggested that the Cd,
C, N, O, and F atoms are homogeneously dispersed in 1@
PVDF (Figure 3g−i). Among these elements, Cd, N, and O
originate from Cd2+ and organic ligands in 1, which is in
agreement with the results of the PXRD analysis. Furthermore,
the valences of Cd in 1 and 1@PVDF were studied by X-ray
photoelectron spectroscopy (XPS). As shown in Figure S5, the
3d peaks of Cd can be observed at 405.1 eV in both 1 and 1@
PVDF, which indicated that the valence of Cd was +2 and also
proves the successful integration of 1 and the PVDF matrix.
The FT-IR spectra further proves the successful incorporation
of the PVDF matrix and 1. As shown in Figure 2c, the strong
bands at 1695, 1576, and 1435 cm−1 correspond to the
vibration of the CO bond and the benzene ring from the
organic ligands, and the bands at 3031 and 2984 cm−1
correspond to the vibration of the C−H bond in the PVDF
sample. 1@PVDF contains the bands of both 1 and PVDF.
These results not only reveal the existence of organic ligands in
the structure of 1 but also indicate the integration PVDF with
1.
Catalytic Properties. The six-coordinated Cd(II) center in
1 has CUS and performs as the Lewis acid active site for
catalysis. Thus, the capability of 1 as a Lewis acid catalyst was
first measured in the synthesis of benzimidazole derivatives.
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The catalytic experiments were carried out at room temper-
ature with the mole ratio of selected o-phenylenediamine and
aromatic aldehydes being 1:1. First, solvent screening experi-
ments were performed. A kinetics experiment indicated that
2.5 mol % of catalyst gave 94% conversion of benzaldehydes in
CD3CN after 3 h (Table 1). With CDCl3 and DMSO as the
products could be detected, which might be due to the poor
solubility of the reactant and the product in D2O. Therefore,
we chose CD3CN or DMSO as the solvent for this reaction. It
is noted that after removal of the catalyst by filtration after 1 h,
the reaction nearly shut down, affording 60% conversion yield
upon standing for another 2 h. Meanwhile, ICP-OES results
also demonstrated that there is no obvious Cd2+ leaching in the
reaction system. These results indicated that no homogeneous
catalyst exists in this catalytic system and proved the
heterogeneous feature of activated 1. In contrast, we utilized
Cd(NO3)2·4H2O, H3dppa, and a physical mixture of Cd-
(NO3)2·4H2O and H3dppa as homogeneous catalysts in this
reaction; the conversion yields were 85%, 50%, and 90%,
respectively. Unfortunately, these homogeneous catalysts are
difficult to separate from the reaction system for recycling.
In order to examine the general catalytic properties and the
chemical selectivity of 1 with varied reactants, different
substituent groups of aromatic aldehyde substrates for this
reaction under the same conditiosn were investigated. As
illustrated in Table 1, when o-fluorobenzaldehyde and o-
methoxybenadehyde are the substrates in DMSO, the
conversion yields are 68% and 94%, which suggested that a
electron-donating group has a positive effect in comparison
with an electron-withdrawing group. The position of a group
such as −CN has obvious effects on this reaction. The
conversion yields of o- and p-cyanobenzaldehyde are over 99%
which is much higher than that of m-cyanobenzaldehyde
(44%). When the substrate aldehyde is replaced by substrates
of larger size such as 1-naphthaldehyde and cinnamaldehyde,
the conversion yields decrease to 85% and 75%, respectively.
With he heterocyclic aldehyde 4-pyridinecarboxaldehyde as the
substrate, the conversion yield can also reach 99%. In addition,
when the substrate is aliphatic valeraldehyde, the conversion
yield decreased to 30%. Moreover, when CD3CN was the
solvent, the conversion yields of these substrates all increase in
Table 1. Catalytic Reactions and Results of Reactions of a
Series of Benzaldehyde Derivatives with o-
a
Phenylenediamine
yield (%)
entry
substrate
benzaldehyde
catalyst
CD3CN
DMSO-d6
1
2
3
4
5
6
7
8
9
10
1
1
1
1
1
1
1
1
1
1
94
95
98
96
96
99
90
83
99
83
88
68
94
>99
44
>99
85
75
99
30
p-fluorobenzaldehyde
p-methoxybenzaldehyde
p-cyanobenzaldehyde
m-cyanobenzaldehyde
o-cyanobenzaldehyde
1-naphthaldehyde
cinnamaldehyde
pyridine-4-carboxaldehyde
pentanal
a
Reaction conditions: o-phenylenediamine (1 mmol), aldehydic
substrates (1 mmol), solvent (1 mL), catalyst (0.025 mmol), room
temperature, 3 h.
solvents, the conversions decreased to 86% and 88%,
respectively (Table S4). The influence of these solvents on
the reaction can be attributed to the different polarities of these
solvents. When D2O was used as the solvent, only trace
Figure 4. Schematic representation of conversion yields of different substrates catalyzed by 1.
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comparison with those for DMSO as the solvent. The electron
effect has a slight impact on this reaction, and the the position
of the substituent group also has a slight impact on this
reaction. It is noted that the conversion yields of 1-
naphthaldehyde, cinnamaldehyde, and valeraldehyde are also
lower than for others; however, they are still higher than those
of the reactions performed in DMSO. As far as we know, most
MOF-catalyzed syntheses of benzimidazole derivative reactions
are longer than 6 h. 1 can reduce the reaction time to within 3
h with good conversion yield, which reveals that it is a new,
efficient Lewis acid catalyst for this reaction. Furthermore, in
order to show these results clearly, the conversion yield
changes of different substrates with o-phenylenediamine are
illustrated in Figure 4.
Table 2. Catalytic Reactions Catalyzed by Different
Membrane Catalysts
entry
substrate
catalyst
solvent
yield (%)
1
2
3
4
5
6
benzaldehyde
benzaldehyde
benzaldehyde
benzaldehyde
benzaldehyde
benzaldehyde
CD3CN
CD3CN
CD3CN
CD3CN
CD3CN
CD3CN
trace
94
73
83
82
1@PVDF
ZIF-8@PVDF
HKUST-1@PVDF
MIL-68(In)@PVDF
UiO-66@PVDF
47
HKUST-1 is higher than the others and HKUST-1@PVDF
also has a higher conversion yield. However, the conversion
yield of UiO-66 only reached 43%, and its corresponding
MMM also had a slightly higher yield of 47%. These results
demonstrated that this method is a universal, facile, and
effective way to construct MOF-based MMMs with remarkable
catalytic performance and recyclability. More importantly, the
conversion yield of 1@PVDF is higher than those of other
MOFs@PVDF, indicating that 1@PVDF is an excellent solid
Lewis acid catalyst for the production of benzimidazole
derivatives. For 1@PVDF, the Cd(II) centers do not
coordinate to solvent molecules; thus, the active sites in 1
will remain for catalysis. Moreover, the better catalytic
performance of MMMs in comparison to powders may result
from the reaction mixture simply passing through the active
MMM and the product being recovered from the eluent.10
Furthermore, as shown in Figure 3d, the intrinsic hierarchical
pores of the composite had advantages over the traditional
catalysts reported by Feng et al.36
Although coordination unsaturated sites are widely regarded
as Lewis acid sites in catalysis, most of them lack direct
evidence to prove their Lewis acid sites in MOFs. Thus, to
prove that an MOF-based catalyst is a Lewis or Brønsted acid
catalyst is a very important issue in catalysis.37−41 As reported
by Lin et al., the Lewis acidity of a catalyst can be probed by N-
methylacridone (NMA) fluorescence.38 NMA is a fluorescent
dye and has lone pairs that can bind to unsaturated sites in
MOFs. In this process, the maximum emission peak shifts
significantly upon binding to the metal sites in MOFs. As seen
in Figure S13, the maximum emission peak shifts from 433 to
441 nm (for 1) and 467 nm (for activated 1). This result
indicated that activated 1 is indeed a Lewis acid catalyst.
With the good catalytic performance for the synthesis of
benzimidazole derivatives as inspiration, 1@PVDF as an
effective heterogeneous catalyst for amino acid derivatives
has also been carried out (Scheme 2). For the Strecker type
reaction, the aldimine substrates have been synthesized by the
reported method.29 As shown in Table 3, the conversion yield
of the N-Ph-phenylaldimine substrate is 88%, that with the
electron-withdrawing group −CH3 is over 99%, and with the
electron-donating group −NO2 is only 31%, which demon-
strated that the electron effect of the functional group had a
great impact on the product.42,43 Moreover, when heterocyclic
substrates were employed, the conversion yield was only 52%,
and when the protecting group was n-propyl, a greater than
99% conversion yield could be achieved, which indicated that
the protecting group has a slight effect on the reaction
catalyzed by 1@PVDF.
To test the recyclability of the catalyst, 1 can be recovered
by centrifugal separation and reused for at least five cycles with
a slight loss of catalytic activity (Figure S6). Although 1 can be
reused for at least five runs, there is still some loss due to
electrostatic attraction and inevitable losses during transfer.
Therefore, 1@PVDF can offer a facile way to recycle the
catalyst and is convenient for applications in further industrial
production. 1@PVDF (10 wt %) has both good dispersion and
flexible features; thus it was selected as the catalyst for further
catalytic experiments. Since 1 binds to PVDF, 1@PVDF only
needs to be pulled out from the reaction system rather than
centrifugal separation. In this process, there is no catalyst loss.
Thus, 1@PVDF can be regarded as an ideal candidate for
catalysis. As shown in Figure 2d, the catalytic reaction rate of
1@PVDF is higher than that of the activated 1, and their final
yields are both 94%. Notably, the better catalytic performance
may be related to the morphology of the MMM. The
hierarchical structure facilitates more efficient mass transport,
and the large surface area provides more active sites and mass
transport for catalysis. These qualities may improve the rate of
the catalysis reaction catalyzed by 1@PVDF in comparison to
1. Additionally, in order to understand the stability of the
catalyst, FT-IR and PXRD have been measured. As illustrated
in Figure 2c, the FT-IR spectra have no obvious difference
between that before catalysis and that after catalysis for five
runs. In addition, the structure of 1 does not change before and
after catalysis, which can be confirmed by PXRD analysis
(Figure S7). Hence, to investigate the application of 1@PVDF
in an actual continuous reaction, the reactants and products
were removed from the catalysis system and fresh reactants
were placed in the reactor, while 1@PVDF without any change
was still located in the reactor. After 5 runs, the conversion
yield of the product was 84%, and after 10 runs, the conversion
yield slightly decreased to 76%, which suggested that the
membrane catalyst can be continuously reused at least 10
times.
To verify that this approach is a universal strategy to
fabricate catalytic MOF MMMs, we choose the four well-
known MOFs ZIF-8, HKUST-1, MIL-68(In), and UiO-66 as
the MOF fillers to construct MMMs (Figures S8−S11). All of
these MMMs are flexible and have hierarchical structures. The
MOF particles are well dispersed in the polymer matrix and
adhered to the PVDF (Figure S12). Their catalytic perform-
ances were also examined by the synthesis of benzimidazole
derivatives. As shown in Table 2, when we used MMMs
instead of the powder samples to carry out the catalytic
reaction, most of the MMMs improved the conversion yield
about 10% in comparison to the reactions catalyzed by pure
powder samples. Among them, the conversion yield of
Furthermore, as the other amino acid derivative production
reaction, the Mannich reaction catalyzed by 1@PVDF has also
been evaluated.44−47 Before this reaction, the Mukaiyama aldol
reaction was tested (Scheme 3). For this reaction, 0.5 mmol of
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Scheme 2. Strecker and Mannich Reactions Catalyzed by 1@PVDF
of yield (Figure S16). The structure of 1 is also retained after
catalysis, as proven by PXRD analysis (Figure S17). Notably,
this is the first example of the Mannich reaction for the
production of β-amino acid derivatives catalyzed with high
efficiency by a Cd-based MOF. This provided a new type of
catalytic center of MOFs for the Mannich reaction and
enriched the catalytic chemistry of Cd-MOF catalysts.
Table 3. Strecker Reaction between Aldimines and
TMSCN
a
CONCLUSION
■
In summary, a new stable 3D Cd-based MOF (1) was
synthesized and characterized under solvothermal conditions.
After activation, 1 acts as a Lewis acid and exhibits good
reactivity and selectivity for the synthesis of benzimidazole
derivatives from aldehydes and o-phenylenediamine at room
temperature. Meanwhile, a 1@PVDF mixed-matrix membrane
was prepared by a polymer solution casting approach which
can easily operate in the catalytic reaction system and exhibits
remarkable recyclability. Moreover, this marriage of 1 and a
PVDF mixed-matrix membrane also exhibits excellent catalytic
performance and recyclability in the production of two amino
acid derivatives by the Strecker reaction and the Mannich
reaction. We believe that this successful preparation of a
catalytic MOF@PVDF MMM provides not only a simple way
for continuous flow production and reduction of the cost but
also excellent recyclability. Our future studies will focus on the
synthesis of new multivariate MOFs with both Lewis acid and
Lewis base sites and their composites as well as their catalytic
properties for organic transformations.
a
Reaction conditions: 1@PVDF (size 1 cm × 1 cm), 0.5 mmol of
aldimine, 1.5 mmol of TMSCN, 1 mL of CDCl3, room temperature,
24 h.
p-nitrobenzaldehyde and 1.5 mmol of silyl ketene acetal were
dissolved in 1 mL of CD3CN at room temperature. The final
product was obtained gradually, and after 96 h, the conversion
yield was 82% and there was no further increase after that.48−50
Subsequently, the Mannich reaction with 0.5 mmol of N-Ph-
phenylaldimine and 1.5 mmol of silyl ketene acetal were added
to 1 mL of CD3CN. This reaction proceeded smoothly; the
conversion yield was 72% after 48 h and no longer increased
with a longer reaction time. Additionally, the 1@PVDF catalyst
can be easily separated from the reaction system and recycled
at least five times for amino acid production with a slight loss
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c00084.
TG curve, PXRD, EDS mapping, fluorescence spectrum,
contact angle, N2 adsorption isotherms, proposed
catalysis mechanism, crystal data and structure refine-
ment details, selected bond lengths and angles, and other
catalytic reactions (PDF)
Scheme 3. Mukaiyama Aldol Reaction Catalyzed by 1@PVDF
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Solution processable metal-organic frameworks for mixed matrix
membranes using porous liquids. Nat. Mater. 2020, 19, 1346−1353.
(4) Wu, T.; Prasetya, N.; Li, K. Recent advances in aluminium-based
metal-organic frameworks (MOF) and its membrane applications. J.
Membr. Sci. 2020, 615, 118493.
(5) Wang, H.; Zhao, S.; Liu, Y.; Yao, R.; Wang, X.; Cao, Y.; Ma, D.;
Zou, M.; Cao, A.; Feng, X.; Wang, B. Membrane adsorbers with
ultrahigh metal-organic framework loading for high flux separations.
Nat. Commun. 2019, 10, 4204.
(6) Shu, L.; Xie, L.-H.; Meng, Y.; Liu, T.; Zhao, C.; Li, J.-R. A thin
and high loading two-dimensional MOF nanosheet based mixed-
matrix membrane for high permeance nanofiltration. J. Membr. Sci.
2020, 603, 118049.
(7) Zhang, X.; Zhang, Q.; Yue, D.; Zhang, J.; Wang, J.; Li, B.; Yang,
Y.; Cui, Y.; Qian, G. Flexible Metal-Organic Framework-Based Mixed-
Matrix Membranes: A New Platform for H2S Sensors. Small 2018, 14,
1801563.
(8) Prasetya, N.; Teck, A. A.; Ladewig, B. P. Matrimid-JUC-62 and
Matrimid-PCN-250 mixed matrix membranes displaying light-
responsive gas separation and beneficial ageing characteristics for
CO2/N2 separation. Sci. Rep. 2018, 8, 2944.
(9) Lei, Z.; Deng, Y.; Wang, C. Multiphase surface growth of
hydrophobic ZIF-8 on melamine sponge for excellent oil/water
separation and effective catalysis in a Knoevenagel reaction. J. Mater.
Chem. A 2018, 6, 3258−3263.
Accession Codes
CCDC 2025521 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
Jianing Xu − College of Chemistry, Jilin University, Changchun
130012, Jilin, People’s Republic of China; Email: xujn@
jlu.edu.cn
Li Wang − College of Chemistry, Jilin University, Changchun
130012, Jilin, People’s Republic of China; orcid.org/
0000-0003-3923-4384; Email: lwang99@jlu.edu.cn
Authors
Yansong Jiang − College of Chemistry, Jilin University,
Changchun 130012, Jilin, People’s Republic of China
Jing Sun − College of Chemistry, Jilin University, Changchun
130012, Jilin, People’s Republic of China; Jiangsu Provincial
Engineering Research Center for Biomedical Materials and
Advanced Medical Devices, Huaiyin Institute of Technology,
Huai’an 223003, Jiangsu, People’s Republic of China
Xiaona Yang − College of Chemistry, Jilin University,
Changchun 130012, Jilin, People’s Republic of China
Jieyu Shen − College of Chemistry, Jilin University, Changchun
130012, Jilin, People’s Republic of China
(10) Denny, M. S., Jr.; Kalaj, M.; Bentz, K. C.; Cohen, S. M.
Multicomponent metal-organic framework membranes for advanced
functional composites. Chem. Sci. 2018, 9, 8842−8849.
(11) Chakraborty, A.; Bhattacharyya, S.; Hazra, A.; Ghosh, A. C.;
Maji, T. K. Post-synthetic metalation in an anionic MOF for efficient
catalytic activity and removal of heavy metal ions from aqueous
solution. Chem. Commun. (Cambridge, U. K.) 2016, 52, 2831−4.
(12) Sankar, V.; Karthik, P.; Neppolian, B.; Sivakumar, B. Metal−
organic framework mediated expeditious synthesis of benzimidazole
and benzothiazole derivatives through an oxidative cyclization
pathway. New J. Chem. 2020, 44, 1021−1027.
Yu Fu − College of Chemistry, Jilin University, Changchun
130012, Jilin, People’s Republic of China
Yong Fan − College of Chemistry, Jilin University, Changchun
130012, Jilin, People’s Republic of China
́
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.1c00084
(13) Najera, C.; Sansano, J. M. Catalytic Asymmetric Synthesis of α-
Amino Acids. Chem. Rev. 2007, 107, 4584−4671.
(14) Yoon, T. P.; Jacobsen, E. N. Privileged Chiral Catalysts. Science
2003, 299, 1691.
Author Contributions
(15) Wang, W.; Zhang, S.; Hu, S.; Wang, D.; Gao, W.; Cong, R.;
Yang, T. Octahedron-based redox molecular sieves M -PKU-1 (M =
Cr, Fe): A novel dual-centered solid acid catalyst for heterogeneously
catalyzed Strecker reaction. Appl. Catal., A 2017, 542, 240−251.
(16) Xia, J.; Xu, J.; Fan, Y.; Song, T.; Wang, L.; Zheng, J. Indium
metal-organic frameworks as high-performance heterogeneous cata-
lysts for the synthesis of amino acid derivatives. Inorg. Chem. 2014, 53,
10024−6.
(17) Verma, A.; Tomar, K.; Bharadwaj, P. K. Chiral Cadmium(II)
Metal-Organic Framework from an Achiral Ligand by Spontaneous
Resolution: An Efficient Heterogeneous Catalyst for the Strecker
Reaction of Ketones. Inorg. Chem. 2017, 56, 13629−13633.
(18) Chai, J.; Zhang, P.; Xu, J.; Qi, H.; Sun, J.; Jing, S.; Chen, X.;
Fan, Y.; Wang, L. An in-based 3D metal-organic framework as
heterogeneous Lewis acid catalyst for multi-component Strecker
reactions. Inorg. Chim. Acta 2018, 479, 165−171.
(19) Reinares-Fisac, D.; Aguirre-Diaz, L. M.; Iglesias, M.; Snejko, N.;
Gutierrez-Puebla, E.; Monge, M. A.; Gandara, F. A Mesoporous
Indium Metal-Organic Framework: Remarkable Advances in Catalytic
Activity for Strecker Reaction of Ketones. J. Am. Chem. Soc. 2016,
138, 9089−92.
(20) Bavykina, A.; Kolobov, N.; Khan, I. S.; Bau, J. A.; Ramirez, A.;
Gascon, J. Metal-Organic Frameworks in Heterogeneous Catalysis:
Recent Progress, New Trends, and Future Perspectives. Chem. Rev.
2020, 120, 8468−8535.
(21) Dhakshinamoorthy, A.; Asiri, A. M.; Garcia, H. Metal-organic
frameworks catalyzed C-C and C-heteroatom coupling reactions.
Chem. Soc. Rev. 2015, 44, 1922−47.
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors gratefully acknowledge financial support through
the National Science Foundation of China (No. 51803212,
U1601203, 51775232, 51505183), the Preresearch Projects in
the Equipment Field (No. 61400040404) and the Science and
Technology Development Plan Project of Jilin Province (No.
20190201155JC).
REFERENCES
■
(1) Fan, L.; Kang, Z.; Shen, Y.; Wang, S.; Zhao, H.; Sun, H.; Hu, X.;
Sun, H.; Wang, R.; Sun, D. Mixed Matrix Membranes Based on
Metal−Organic Frameworks with Tunable Pore Size for CO2
Separation. Cryst. Growth Des. 2018, 18, 4365−4371.
(2) Pastore, V. J.; Cook, T. R.; Rzayev, J. Polymer−MOF Hybrid
Composites with High Porosity and Stability through Surface-
Selective Ligand Exchange. Chem. Mater. 2018, 30, 8639−8649.
(3) Knebel, A.; Bavykina, A.; Datta, S. J.; Sundermann, L.; Garzon-
Tovar, L.; Lebedev, Y.; Durini, S.; Ahmad, R.; Kozlov, S. M.; Shterk,
G.; Karunakaran, M.; Carja, I. D.; Simic, D.; Weilert, I.; Kluppel, M.;
Giese, U.; Cavallo, L.; Rueping, M.; Eddaoudi, M.; Caro, J.; Gascon, J.
2095
https://dx.doi.org/10.1021/acs.inorgchem.1c00084
Inorg. Chem. 2021, 60, 2087−2096

Inorganic Chemistry
pubs.acs.org/IC
Article
(22) Gupta, V.; Mandal, S. K. Design and Construction of a Chiral
Cd(II)-MOF from Achiral Precursors: Synthesis, Crystal Structure
and Catalytic Activity toward C−C and C−N Bond Forming
Reactions. Inorg. Chem. 2019, 58, 3219−3226.
(41) Fu, G.; Cirujano, F. G.; Krajnc, A.; Mali, G.; Henrion, M.;
Smolders, S.; De Vos, D. E. Unexpected linker-dependent Brønsted
acidity in the (Zr)UiO-66 metal organic framework and application to
biomass valorization. Catal. Sci. Technol. 2020, 10, 4002−4009.
(42) Chai, J.; Wang, P.; Jia, J.; Ma, B.; Sun, J.; Tao, Y.; Zhang, P.;
Wang, L.; Fan, Y. In(III) and Sc(III) based coordination polymers
derived from rigid benzimidazole-5,6-dicarboxylic acid: Synthesis,
crystal structure and catalytic property. Polyhedron 2018, 141, 369−
376.
(43) Wang, P.; Zhang, L.; Zhu, Z.; Wu, S.; Shan, L.; Fan, Y.; Wang,
L.; Chen, X.; Xu, J. Two three-dimensional Sc(III)-MOFs: Synthesis,
crystal structure and catalytic property. Inorg. Chim. Acta 2020, 501,
119304.
(23) Kokcam-Demir, U.; Goldman, A.; Esrafili, L.; Gharib, M.;
Morsali, A.; Weingart, O.; Janiak, C. Coordinatively unsaturated metal
sites (open metal sites) in metal-organic frameworks: design and
applications. Chem. Soc. Rev. 2020, 49, 2751−2798.
(24) Sheldrick, G. M. SHELXL-2014: Program for Structure Solution;
̈
̈
University of Gottingen, Gottingen, Germany, 2014.
(25) Spek, A. L. As calculated by PLATON. Acta Crystallogr., Sect. A
1990, 46, C34.
(26) Spek, A. L. Single-crystal structure validation with the program
(44) Weiner, B.; Szymanski, W.; Janssen, D. B.; Minnaard, A. J.;
Feringa, B. L. Recent advances in the catalytic asymmetric synthesis of
beta-amino acids. Chem. Soc. Rev. 2010, 39, 1656−91.
(45) de Graaff, C.; Ruijter, E.; Orru, R. V. Recent developments in
asymmetric multicomponent reactions. Chem. Soc. Rev. 2012, 41,
3969−4009.
PLATON. J. Appl. Crystallogr. 2003, 36, 7−13.
(27) Jiang, Y.; Xu, J.; Zhu, Z.; Jiang, C.; Ma, L.; Wang, H.; Wang, L.;
Fan, Y., Manganese-organic framework assembled by 5-((4′-(tetrazol-
5″-yl)benzyl)oxy)isophthalic acid: A solvent-free catalyst for the
formation of carbon−carbon bond. Inorg. Chim. Acta 2020, 510,
119735.
(46) Shi, Y.; Wang, Q.; Gao, S. Recent advances in the
intramolecular Mannich reaction in natural products total synthesis.
Org. Chem. Front. 2018, 5, 1049−1066.
(28) Zhu, Z.; Tao, Y.; Jiang, Y.; Zhang, L.; Xu, J.; Wang, L.; Fan, Y.
Two scandium coordination polymers: rapid synthesis and catalytic
properties. CrystEngComm 2019, 21, 5261−5268.
(29) Liu, L.; Zhang, S.; Fu, X.; Yan, C. H. Metal-free aerobic
oxidative coupling of amines to imines. Chem. Commun. (Cambridge,
U. K.) 2011, 47, 10148−50.
(47) Bice
̧
r, A.; Kaya, R.; Yakalı, G.; Gu
̈
ltekin, M. S.; Cin, G. T.;
̇
Gulci̧ n, I. Synthesis of novel β-amino carbonyl derivatives and their
̈
inhibition effects on some metabolic enzymes. J. Mol. Struct. 2020,
1204, 127453.
(30) Das, P.; Mandal, S. K. Strategic Design and Functionalization of
an Amine-Decorated Luminescent Metal Organic Framework for
Selective Gas/Vapor Sorption and Nanomolar Sensing of 2,4,6-
Trinitrophenol in Water. ACS Appl. Mater. Interfaces 2018, 10,
25360−25371.
(48) Bae, H. Y.; List, B. Triflimide: An Overlooked High-
Performance Catalyst of the Mukaiyama Aldol Reaction of Silyl
Ketene Acetals with Ketones. Chem. - Eur. J. 2018, 24, 13767−13772.
(49) Woyciechowska, M.; Forcher, G.; Buda, S.; Mlynarski, J.
General switch in regioselectivity in the Mukaiyama aldol reaction of
silyloxyfuran with aldehydes in aqueous solvents. Chem. Commun.
(Cambridge, U. K.) 2012, 48, 11029−31.
(50) Simsek, S.; Kalesse, M. Enantioselective synthesis of polyketide
segments through vinylogous Mukaiyama aldol reactions. Tetrahedron
Lett. 2009, 50, 3485−3488.
(31) Wang, X.; Liu, Y.; Lin, H.; Xu, N.; Liu, G.; Wang, X.; Chang,
Z.; Li, J. A novel cadmium metal−organic framework-based
multiresponsive fluorescent sensor demonstrating outstanding sensi-
2−
tivities and selectivities for detecting NB, Fe3+ ions and Cr2O7
anions. CrystEngComm 2020, 22, 6626−6631.
(32) Yuan, F. L.; Yuan, Y. Q.; Chao, M. Y.; Young, D. J.; Zhang, W.
H.; Lang, J. P. Deciphering the Structural Relationships of Five Cd-
Based Metal-Organic Frameworks. Inorg. Chem. 2017, 56, 6522−
6531.
(33) Cao, H.-L.; Cai, F.-Y.; Yu, K.; Zhang, Y.-Q.; Lu, J.; Cao, R.
̈
Photocatalytic Degradation of Tetracycline Antibiotics over CdS/
Nitrogen-Doped−Carbon Composites Derived from in Situ Carbon-
ization of Metal−Organic Frameworks. ACS Sustainable Chem. Eng.
2019, 7, 10847−10854.
(34) Wang, Y.-N.; Wang, S.-D.; Yang, L.-L.; Zhao, Y.-F.; Yang, Q.-F.
A luminescent cadmium coordination polymer for highly sensitive
detection of Ascorbic Acid. J. Solid State Chem. 2020, 289, 121519.
(35) Guo, X.; Xu, J.; Sun, J.; Chen, X.; Wang, L.; Fan, Y. Three layer-
structured cadmium coordination polymers based on flexible 5-(4-
pyridyl)-methoxylisophthalic acid: rapid synthesis and luminescence
sensing. CrystEngComm 2019, 21, 1001−1008.
(36) Feng, L.; Wang, K.-Y.; Lv, X.-L.; Yan, T.-H.; Zhou, H.-C.
Hierarchically porous metal−organic frameworks: synthetic strategies
and applications. Nat. Sci.Rev. 2020, 7, 1743−1758.
(37) Hall, J. N.; Bollini, P. Metal−Organic Framework MIL-100
Catalyzed Acetalization of Benzaldehyde with Methanol: Lewis or
Brønsted Acid Catalysis? ACS Catal. 2020, 10, 3750−3763.
(38) Ji, P.; Drake, T.; Murakami, A.; Oliveres, P.; Skone, J. H.; Lin,
W. Tuning Lewis Acidity of Metal-Organic Frameworks via
Perfluorination of Bridging Ligands: Spectroscopic, Theoretical, and
Catalytic Studies. J. Am. Chem. Soc. 2018, 140, 10553−10561.
(39) Ji, P.; Feng, X.; Oliveres, P.; Li, Z.; Murakami, A.; Wang, C.;
Lin, W. Strongly Lewis Acidic Metal-Organic Frameworks for
Continuous Flow Catalysis. J. Am. Chem. Soc. 2019, 141, 14878−
14888.
(40) Quan, Y.; Lan, G.; Fan, Y.; Shi, W.; You, E.; Lin, W. Metal-
Organic Layers for Synergistic Lewis Acid and Photoredox Catalysis.
J. Am. Chem. Soc. 2020, 142, 1746−1751.
2096
https://dx.doi.org/10.1021/acs.inorgchem.1c00084
Inorg. Chem. 2021, 60, 2087−2096