Two isostructural URJC-4 materials: From hydrogen physisorption to heterogeneous reductive amination through hydrogen molecule activation at low pressure

Article abstract of DOI:10.1021/acs.inorgchem.0c02127

Herein, two novel isostructural metal-organic frameworks (MOFs) M-URJC-4 (M = Co, Ni; URJC = "Universidad Rey Juan Carlos") with open metal sites, permanent microposity, and large surface areas and pore volumes have been developed. These novel MOFs, with polyhedral morphology, crystallize in the monoclinic P21/c space group, exhibiting a three-dimensional structure with microporous channels along the c axis. Initially, they were fully characterized and tested in hydrogen (H2) adsorption at different conditions of temperature and pressure. The physisorption capacities of both materials surpassed the gravimetric H2 uptake shown by most MOF materials under the same conditions. On the basis of the outstanding adsorption properties, the Ni-URJC-4 material was used as a catalyst in a one-pot reductive amination reaction using various carbonyl compounds and primary amines. A possible chemical pathway to obtain secondary amines was proposed via imine formation, and remarkable performances were accomplished. This work evidences the dual ability of M-URJC-4 materials to be used as a H2 adsorbent and a catalyst in reductive amination reactions, activating molecular H2 at low pressures for the reduction of C=N double bonds and providing reference structural features for the design of new versatile heterogeneous materials for industrial application.

Full text of DOI:10.1021/acs.inorgchem.0c02127

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Article
Two Isostructural URJC‑4 Materials: From Hydrogen Physisorption
to Heterogeneous Reductive Amination through Hydrogen
Molecule Activation at Low Pressure
†
†
́
́
Helena Montes-Andres, Pedro Leo, Antonio Munoz, Antonio Rodríguez-Dieguez, Gisela Orcajo,
̃
Duane Choquesillo-Lazarte, Carmen Martos,† Fernando Martínez, Juan A. Botas,†
and Guillermo Calleja*,†
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ABSTRACT: Herein, two novel isostructural metal−organic frame-
works (MOFs) M-URJC-4 (M = Co, Ni; URJC = “Universidad Rey
Juan Carlos”) with open metal sites, permanent microposity, and
large surface areas and pore volumes have been developed. These
novel MOFs, with polyhedral morphology, crystallize in the
monoclinic P21/c space group, exhibiting a three-dimensional
structure with microporous channels along the c axis. Initially, they
were fully characterized and tested in hydrogen (H2) adsorption at
different conditions of temperature and pressure. The physisorption
capacities of both materials surpassed the gravimetric H2 uptake
shown by most MOF materials under the same conditions. On the
basis of the outstanding adsorption properties, the Ni-URJC-4
material was used as a catalyst in a one-pot reductive amination
reaction using various carbonyl compounds and primary amines. A possible chemical pathway to obtain secondary amines was
proposed via imine formation, and remarkable performances were accomplished. This work evidences the dual ability of M-URJC-4
materials to be used as a H2 adsorbent and a catalyst in reductive amination reactions, activating molecular H2 at low pressures for
the reduction of CN double bonds and providing reference structural features for the design of new versatile heterogeneous
materials for industrial application.
ment of active and selective catalysts for effective utilization of
different hydrogen sources, especially for its insertion in
advanced and complex molecules, is highly demanded and
challenging. Hydrogenation reactions are widely used in the
pharmaceutical,7 fragrance,8 food,9 dye,10 and energy and
environmental sciences industries,11 being of particular interest
in hydrogenation procedures for the formation of secondary
amines, like reductive amination,12 where aldehydes or ketones
with primary or secondary amine groups give secondary or
tertiary amines, respectively, in a one-pot reaction. In fact, an
analysis of drug candidate synthesis published by three
pharmaceutical companies revealed that reductive amination
is among the six most frequently used transformations in
medicinal chemistry.13 The production of amines by reductive
INTRODUCTION
■
Metal−organic frameworks (MOFs) materials are a new class
of porous and crystalline polymers built up from metallic
clusters connected through organic linkers through coordina-
tion chemistry.1 The multiple combinations of metal sites and
organic linkers allow for the design of MOFs with diverse
structures, rich functionalities, and tunable pore systems,
achieving excellent properties for a wide range of applications,
such as drug or biomolecule release,2 gas separation and
purification,3 heterogeneous catalysis,4 and gas storage.5
Concerning the last one, MOF materials with high surface
areas can store hydrogen (H2) through a physisorption
mechanism, which presents many advantages in comparison
with chemisorption, such as total reversibility, fast adsorption−
desorption kinetics, and minor heat-transfer requirements in
desorption.6 Additionally, MOF materials with enhanced H2
physisorption properties might also be potential catalysts in
hydrogenation reactions. These materials may take advantage
of physisorbed H2 to be transferred to other substrates,
presumably through a hydrogenolysis mechanism in a
transition-metal-mediated redox process. Hence, the develop-
Received: July 17, 2020
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(λ = 1.54178 Å). Details of the structure determination are
summarized in section 3 of the SI. Crystallographic data (excluding
structure factors) of the Co-URJC-4 structure reported in this paper
have been deposited at Cambridge Crystallographic Data Centre
(CCDC 1992000). Powder XRD analysis was carried out with a
Philips X’PERT MPD diffractometer using Cu Kα monochromatic
radiation (1.542 Å) with a 0.01 step, 10 s of accumulation time
between steps, and a nonproportional X’Celerator detector. Le Bail
fitting was performed for Ni-URJC-4, from the data of the
isostructural Co-URJC-4, replacing Co by Ni, so the coordination
of Ni ions was just refined (Figure S4.1). In addition, the lattice
parameters were refined using TOPAS software (version 5, Bruker
AXS, Karlsruhe, Germany). Ar adsorption−desorption measurements
at 87 K were performed in an AutoSorb equipment (Quantachrome
Instruments). The specific surface area was calculated by the
Brunauer−Emmett−Teller (BET) equation,22 while the micropore
volume and pore-size distribution of materials were estimated by
nonlocal density functional theory (NL-DFT) applied for an Ar−C
kernel at 87 K based on a slit pore model.23 The skeletal density was
determined through He pycnometry in an AccuPyc II 1340 apparatus.
Elemental analyses for C, H, and N were carried out in a PerkinElmer
240C elemental analyzer. Fourier transform infrared (FT-IR) spectra
were recorded in a FT-IR Varian Excalibur Series 3100 UMA 600
spectrophotometer with a resolution of up to 4 cm−1. Thermogravi-
metric analysis (TGA) was performed in a Mettler-Toledo DSC-TGA
Star System device in an air atmosphere by heating samples at a rate
of 5 °C min−1 (characterization results are shown in Figure S5.2).
Physisorption Test. Cryogenic H2 (99.999%) adsorption
isotherms up to 16 bar were obtained in a Hiden Analytical
Intelligent gravimetric analyzer (IGA-003) equipped with an ultra-
high-vacuum system. The buoyancy correction was achieved by
employing He (99.99999%) adsorption isotherms at 273 K. For H2
adsorption−desorption isotherms at high pressure (170 bar) and near
room temperature conditions, a volumetric Quantachrome iSorbHP1
equipment was used. According to the National Institute of Standards
and Technology reference values [isothermal properties for H2;
http://webbook.nist.gov/], the H2 density was calculated by a
Helmholtz real-gas equation of state.24 The virial 2 equation was
selected as the adsorption isotherm model for fitting the experimental
adsorption data.25
Catalytic Test. The experimental setup for the catalytic runs is
described in section 7 of the SI. Typically, 1 equiv of the carbonyl
compound (60 mg, 0.56 mmol, for benzaldehyde and 0.33 mol for
acetophenone) and 1.4 equiv of the corresponding primary amine
were added to a suspension of Ni-URJC-4 (15 mg) in dry toluene (15
mL). The stirred system was sealed, purged with H2, and pressurized
up to 5 bar. Then, it was heated using a sand bath at 115 °C for 18 h.
Afterward, the reactor was depressurized and cooled to ambient
temperature. The catalyst was retaken through vacuum filtration with
nylon membranes (pore size 0.45 μm), and the products were
separated through a chromatographic column (5 g of silica gel and
mixtures of n-hexane and ethanol ethylacetate as the eluent).
Spectroscopic characterization of each product can be found in
section 8 of the SI. The reusability of the catalyst in successive cycles
was also evaluated. Details of the procedure followed for catalyst
recovery and reusability tests are included in section 9 of the SI.
amination using a soft hydride transfer agent such as
NaBH3CN is a standard methodology, which has a poor
atomic economy. Besides, the agent reducer is expensive,
generates byproducts, and takes place in a homogeneous
process. The use of H2 as a reducing agent and a
heterogeneous catalyst has obvious advantages with respect
to previous processes, such as the absence of byproducts,
scalable and greener process characteristics, easy purification,
and catalyst recovery. Thus, the development of not
complicated and easily available catalysts for reductive
aminations is crucial in industrial processes to allow the cost-
efficient production of amines. Generally, homogeneous and
heterogeneous catalysts compete for a gap in these hydro-
genation reactions, with most of these catalytic systems being
based on Pd,14 Ru,15 Rh,16 and Pt,17 which implies the use of
precious metal derivatives that increase production costs.
These costs are even higher in homogeneous systems because
of the extra cost of the separation process and the difficulty of
reusing the catalyst.
To our knowledge, although catalytic reduction method-
ologies have been recently developed by hydrogenation or H-
atom transfer using Co18 and Ni19 catalytic centers, there is no
transition-metal-based MOF in the literature that catalyzes this
process without the need for additives and nonprecious
metallic nanoparticles and without resorting to binary systems
with frustrated Lewis pairs.20
In this work, we describe the synthesis of two novel
isostructural MOFs, M-URJC-4 (M = Co, Ni), constructed
from transition-metal ions and an isophthalate-based linker
with the formula {[M16(EBTC)8(H2O)7(DMF)17]·25-
(DMF)}n. These materials exhibit permanent porosity and a
high number of active metal sites per unit volume, providing an
ideal scaffold suitable for H2 physisorption and potential
hydrogenation pathways that enable the synthesis of secondary
amines through a reductive amination reaction.
EXPERIMENTAL SECTION
■
Synthesis of H4EBTC. 5,5′-(Etine-1,2-diyl)diisophthalic acid
(H4EBTC) was used as the organic ligand for the preparation of
novel URJC-4 materials. Because H4EBTC is not commercially
available, it was prepared following a synthetic route in five steps,
based on a Sonogashira C−C coupling reaction21 (see sections 1 and
2 of the Supporting Information, SI).
Synthesis of M-URJC-4 (M = Co, Ni). H4EBTC (0.0352 g, 0.01
mmol) and 0.01 mmol of M(NO3)2·6H2O (M = Co, Ni) were
dissolved in a mixture of N,N-dimethylformamide (DMF; 5 mL) and
300 μL of nitric acid. The solution was then added to a 20 mL
scintillation vial and placed in a preheated oven at 100 or 120 °C for
the synthesis of Co-URJC-4 and Ni-URJC-4, respectively, during 72
h. After cooling to room temperature, high-quality crystals for single-
crystal X-ray diffraction (XRD) were obtained. MOF crystals were
isolated by decanting the mother liquid and washed several times with
DMF. Yield: ca. 55% (based on a linker).
FT-IR (Co-URJC-4): 1667 (s), 1645 (s), 1625 (s), 1588 (s), 1498
(m), 1426 (s), 1362 (s), 1301 (m), 1254 (m), 1092 (m), 1059 (m),
918 (w), 867 (w), 815 (w), 777 (m), 734 (m), 719 (m), 676 (m),
656 (m) cm−1. Anal. Calcd for C270H356N42O113Co16: C, 46.72; N,
8.48; H, 5.16. Found: C, 46.70; N, 8.51; H, 5.18.
FT-IR (Ni-URJC-4): 1661 (f), 1625 (f), 1588 (f), 1547 (m), 1498
(m), 1426 (f), 1362 (f), 1301 (m), 1254 (m), 1092 (m), 1059 (m),
918 (d), 867 (d), 815 (d), 777 (m), 734 (m), 719 (m), 676 (m), 656
(m) cm−1. Anal. Calcd for C270H356N42O113Ni16: C, 46.72; N, 8.47; H,
5.13. Found: C, 46.76; N, 8.49; H, 5.11.
RESULTS AND DISCUSSION
■
Prior to the preparation of MOFs, an organic synthetic route
with five reaction steps was used to obtain the organic linker
H4EBTC with excellent yields. The complete description of the
organic synthesis and NMR spectra of intermediate and final
products are shown in sections 1 and 2 of the SI, respectively.
This organic linker was used for the synthesis of the two M-
URJC-4 materials. Although the synthesis and application of
new H4EBTC-based MOFs have been increased in recent
years, these MOFs are still scarce.26 First, a heuristic method
was carried out to determine the best conditions for obtaining
Materials and Methods. XRD data collection of suitable single
crystals of compounds M-URJC-4 was performed at 100(2) K on a
Bruker D8 VENTURE diffractometer equipped with Cu Kα radiation
B
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a pure crystalline MOF material using Co, named Co-URJC-4.
Its crystalline structure was solved by single-crystal XRD,
attaining a monoclinic P21/c space group and the following
unit cell parameters: a = 19.1972(8) Å, b = 38.1664(17) Å, c =
47.308(2) Å, α = γ = 90°, and β = 90.105(2)°. The asymmetric
unit is comprised of 16 crystallographically independent Co
ions and eight molecules of the EBTC4− ligand (Figure S3.1).
In the Co-URJC-4 structure, eight different metallic clusters
are formed by two different Co ions (Figure S3.2). Thus, all
Co ions show a distorted octahedral coordination geometry,
with various carboxylate groups belonging to different organic
ligands, showing different modes of coordination and DMF
coordination molecules. Seven of these eight dinuclear clusters
also show one water coordination molecule. Concerning the
linker coordination mode, EBTC4− exhibits three different
coordination modes (Figure S3.3). In the first one, two
carboxylate groups are coordinated to the metallic Co centers,
showing a syn−syn bidentate bridge mode, while the other two
carboxylate groups are connected to the Co centers, featuring
bidentate chelate modes (μ2-η1:η1 and μ3-η1:η2). In the second
mode, the ligand is connected to eight Co atoms showing bis-
bidentate bridge coordination. Finally, in the third coordina-
tion mode, the ligand is coordinated to six Co atoms. Here,
two carboxylate groups are connected to the organic molecule
by a bidentate chelate mode and the other two by tridentate
bridge chelate coordination. The Co−O distances are in the
range of 1.85(2)−2.324(18) Å. Figure 1 shows a three-
from the porous system. Thus, the theoretical accessible
volume Vvoid is 47% of the total crystal volume, as calculated
using the PLATON program28 (Figure S3.7).
The presence of the characteristic crystalline phase of the
new material in the bulk sample was confirmed by the high
similarity between the experimental XRD pattern and the
simulated pattern obtained from its crystallographic data
(Figure 2). As observed, the location and intensity of the main
reflections match well in both patterns, endorsing the
crystalline structure resolved by single-crystal XRD.
Figure 2. Powder and single-crystal XRD patterns of the Co-URJC-4
material.
To check the phase purity, the Le Bail fitting was carried out
using the unit cell parameters of the Co structure (Figure
S3.8). As observed, not even a trace of any other impurity
phase is present in the pristine sample. Similar conditions were
used to synthesize the isostructural Ni-URJC-4 material, as
indicated in the Experimental Section. The obtained solid was
highly crystalline, as demonstrated by the presence of intense
reflections in its XRD pattern (Figure S4.1). Because the
powder XRD pattern shows good matching with that of Co-
URJC-4, they were considered to be isostructural materials.
Similarly, Le Bail fitting was carried out to obtain Ni-URJC-4
unit cell information (Table S4).
On the other hand, although the URJC-4 compounds were
isostructural materials, the morphologies of both greatly differ.
The scanning electron microscopy (SEM) micrographs for the
Co-URJC-4 material revealed that it crystallizes, forming large
polyhedral crystals, whereas Ni-URJC-4 is formed by spherical
aggregates of small crystals (Figure S5.1). The thermal stability
in an air atmosphere of the crystalline URJC-4 materials was
evaluated using TGA, as shown in Figure S5.2. Three evident
weight losses for each material can be observed. The first one
takes place at roughly 80 °C, and it is attributed to the
elimination of the water molecules retained in the pores of the
materials because of the humidity of the environment. The
second weight loss, centered at ca. 150 °C, is due to
evaporation of the DMF molecules that are coordinated to
the structure and that come from the synthesis media. Finally,
the last weight loss corresponds to the decomposition of the
organic ligand, resulting in the collapse of the crystalline
structure and forming subsequent metal oxides as CoO and
NiO, respectively. A comparison of the theoretical weight loss
of the two URJC-4 materials (considering its empirical
formula) and the experimental weight loss (calculated from
their TGA profiles) is reported in Table S5. The results prove
that weight loss values agree reasonably well for each material,
indicating that the assignment made for thermal decom-
position of the species is correct. The porosity of the new
materials was measured by Ar adsorption/desorption iso-
therms at 87 K (Figure 3). Both URJC-4 materials displayed
Figure 1. 3D structure of guest-free Co-URJC-4 along the a axis.
Color code: dark blue, Co; gray, C; red, O; light blue, N. H atoms are
omitted for clarity.
dimensional (3D) view of the Co-URJC-4 structure along the
a axis. Coordination of the metallic clusters with the organic
ligand leads to a very complex 3D network,26,27 differentiating
two types of rhomboidal cavities along the a axis with pore-
limiting windows of 17 Å × 12.54 Å and 9.73 Å × 12.73 Å
(Figure S3.4). Views along the b and c axes are depicted in
Figures S3.5 and S3.6, respectively. Removal of the solvent
molecules might generate unsaturated metal sites accessible
C
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the characteristic type I adsorption−desorption isotherm of a
microporous material, according to the IUPAC classification.29
Figure 4. Experimental H2 adsorption isotherms of URJC-4 at 77 K.
Figure 3. Ar adsorption−desorption isotherms at 87 K. Closed
symbols: adsorption data. Open symbols: desorption data.
Additionally, regarding the pore-size distribution of both
materials, there are two narrow contributions centered at 9 and
13 Å (Figure S5.3), which is in agreement with the
crystallographic data, particularly for the 3D view of the
structure along the a axis (Figure S3.4). The skeletal density of
the materials was measured by He pycnometry, from which the
crystal density was estimated. The textural properties and
crystal density of both materials appear in Table 1.
Table 1. Textural Properties of URJC-4 Materials
a
b
material
SBET (m2 g−1
)
Vp (cm3 g−1
)
ρcrystal (g cm−3
)
Co-URJC-4
Ni-URJC-4
862
829
0.297
0.293
1.12
1.15
Figure 5. Experimental H2 adsorption isotherms of URJC-4 at 298 K.
a
b
Specific surface area using the BET equation. Total pore volume at
P/P0 = 0.98.
Table 2. H2 Adsorption Capacity of the URJC-4 Materials
a
a
b
b
H2 excess
(wt %)
H2 total (g
L−1
H2 excess
(wt %)
H2 total (g
L−1
material
)
)
H2 Adsorption Measurements. H2 adsorption tests were
performed at different conditions of pressure and temperature
in order to study the H2 adsorption properties of the MOF
materials. Thus, the URJC-4 samples were activated under
high vacuum at 10−5 mbar and 423 K during 8 h. Then, the
gravimetric H2 uptake at 77 K and up to 16 bar was recorded
(Figure 4). A type I profile regarding the IUPAC29 was
identified for both materials, which is roughly saturated at 16
bar with a gravimetric H2 excess uptake of about 3.50 and 3.73
wt % for Co and Ni materials, respectively. Moreover, no
hysteresis cycle is observed, with the adsorption−desorption
process being completely reversible.
Because the H2 adsorption capacity of the novel MOFs at 77
K is relatively high compared to those of several well-known
MOF materials reported in the literature,30 the URJC-4
materials were further tested in H2 adsorption at higher
temperature and pressure (298 K and 170 bar). These results
are depicted in Figure 5, observing that the URJC-4 materials
are able to reach gravimetric values of 0.54 and 0.61 wt %,
which correspond to the total volumetric values of 10.19 and
11.28 g L−1 for the Co and Ni structures, respectively (Table
2). In this case, the H2 adsorption process is also reversible,
confirming the physisorption mechanism.
Ni-URJC-4
Co-URJC-4
3.73
3.50
45.49
43.16
0.61
0.54
11.28
10.19
a
b
Measurements performed at 77 K and 16 bar. Measurements
performed at 298 K and 170 bar.
Likely, the values of the H2 adsorption capacity at room
temperature are comparable to those recorded for some MOF
structures like the well-known Ni-MOF-74.30 This could be
attributed to the presence of a high density of open metal sites
in the structure of URJC-4 materials, which are able to interact
directly with the H2 molecule, promoting a high energetic
adsorption and thus, high H2 retention capacity.
Catalytic Tests. Because the URJC-4 materials have porous
crystalline structures with Ni and Co metal sites, being able to
perform efficiently H2 adsorption at room temperature through
a physisorption mechanism, these compounds could be
potential candidates for heterogeneously catalyzed hydro-
genation reactions.
Taking into account that the structural stability of MOF
materials in different chemical media is a crucial issue for their
application as heterogeneous catalysts, the chemical stability of
URJC-4 materials was tested in methanol and toluene, usually
D
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used as solvents in heterogeneous hydrogenation reactions.
The crystalline structure of both materials collapses in
methanol. However, the Ni-URJC-4 material was stable in
toluene, keeping the characteristic XRD pattern of the pristine
crystalline framework (Figure S6). Toluene is considered to be
a good solvent because it promotes the H2O elimination that is
produced in the reaction, stimulating a shift balance toward
imine formation. By this reason, toluene has been used as the
solvent of the reductive amination reactions tested in this
work.
Table 3. One-Pot Amination Reactions between Different
Carbonyl and Amine Substrates (or Directly from Imines)
Using a Ni-URJC-4 Catalyst
The catalytic activity of the Ni-URJC-4 material was studied
in the synthesis of secondary amines through a reductive
amination reaction in a one-pot process (see the reaction
scheme in Table 3). The dual function of Ni sites to adsorb
and activate H2 for the reaction with carbonyl-based substrates
makes the porous metal−organic scaffold of the Ni-URJC-4
material work as a nanostructured reactor. As described in the
Experimental Section, a slight stoichiometric excess of the
primary amine (1.4 equiv of amine per 1 equiv of the carbonyl
compound) was used to avoid subsequent condensation
reactions between substituted amines and unreacted carbonyl
compounds. All of the resulting products were isolated using
flash chromatography on silica gel and characterized with the
usual spectroscopic techniques (see section 8 in the SI). As can
be seen in Table 3, the hydrogenation reaction of several
primary amines and carbonyl compounds allows one to obtain
the substituted secondary amine in a one-pot reaction with
remarkable yields (between 76% and 91%; entries 1−6) under
selected operation conditions.
With the purpose of elucidating a possible reaction
mechanism, the test was carried out in two steps. First, the
reaction was performed in the absence of H2, forming the
imine intermediates exclusively. Then, in a second step,
hydrogenation of these imines in the presence of Ni-URJC-4
and H2 (Table 3, entries 7 and 8) leads to the substituted
secondary amines in entries 6 and 4, respectively. These results
evidenced that the Ni-URJC-4 material can activate carbonyl
compounds and amines, acting as Lewis acid transition-metal
catalysts, as well as the H2 molecule to reduce double bonds in
a one-pot procedure.
It must be noted that the catalytic activity of the Ni
precursor [Ni(NO3)2·6H2O] used for the preparation of the
Ni-URJC-4 material was tested under the same conditions of
entry 4 in Table 3. This experiment showed no conversion of
the initial reactants. The crude of the reaction was analyzed by
1H NMR, observing that the characteristic −CH− and −NH−
signals at 5.58 and 4.28 ppm of the N-benzydrylaniline
compound were not detected (Figure S8.17), unlike the signals
of the starting materials, which were clearly identified. Thus,
these results evidenced that the homogeneous Ni(II) precursor
is not active in these specific conditions, while Ni(II) as a part
of a MOF like URJC-4 is active in the reaction with very good
yields.
The catalytic activity of Ni-URJC-4 for the formation of
imines was confirmed by their isolation in catalytic tests
performed in the absence of a H2-reducing atmosphere.
The recovery of the heterogeneous catalyst after the reaction
was practically complete (above 95%). Moreover, the Ni
leached-off was almost negligible with concentrations below
0.1 mg L−1 in the reaction medium for all cases (results from
inductively coupled plasma optical emission spectrometry
measurements). Thus, the Ni-URJC-4 material seems to be
very stable. In addition, the reusability of this catalyst was also
a
b
Isolated yields. Isolated yield in the second catalytic cycle after
c
d
catalyst recovery. Catalyst: Ni(NO3)2·6H2O. Catalytic hydro-
genation of an imine previously synthesized under the same reaction
conditions in the absence of a H2-reducing atmosphere.
evaluated in consecutive reaction cycles (entries 1 and 4 of
Table 3), demonstrating the robustness of Ni-URJC-4, in
terms of the catalytic activity and crystalline structure (see
section 9 of the SI). All of these results confirm the relevant
heterogeneous activity, chemical stability, and potential
E
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reusability of the Ni-URJC-4 material in successive reaction
cycles.
Considering the catalytic results, a possible chemical
mechanism of the process via imine formation is proposed in
Figure 6. Presumably, activation of the O atom from the
the material was not doped with any external additive and that
it acts as a 100% functional material in the catalytic process of
adsorption/activation. Moreover, Ni-URJC-4 was easily
recovered after reaction, maintaining its crystalline structure
and catalytic activity in successive reaction cycles. This
methodology could serve as a starting platform for the
development of new heterogeneous catalysis methodologies
based on MOF-type materials using common components as
transition metals. These results make Ni-URJC-4 a promising
new catalyst, becoming a greener and cheaper alternative to
other known catalysts for one-pot reductive amination
reactions.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c02127.
■
sı
1
Synthesis and H and 13C NMR spectra of the organic
ligand H4EBTC, XRD data and structure refinement of
Co-URJC-4, Le Bail fitting of Ni-URJC-4, SEM images,
TGA, pore-size distribution, chemical stability of
1
materials, H and 13C NMR spectra of amine products,
and reusability test (PDF)
Accession Codes
CCDC 1992000 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.
Figure 6. Proposed mechanism for the reductive amination reaction
using Ni-URJC-4.
AUTHOR INFORMATION
Corresponding Author
■
carbonyl group through coordination with the Ni center of the
MOF material (Ni···OC−) takes place in a first stage,
following the subsequent nucleophilic attack of the amine over
the activated carbonyl. Thereafter, the removal of a water
molecule leads to the corresponding imine.31 The final
hydrogenation process possibly occurs through a mediated
hydrogenolysis process between the metal-coordinated sub-
strate and H to obtain the secondary amine.
Guillermo Calleja − Department of Chemical, Energy and
Mechanical Technology, Rey Juan Carlos University, 28933
Mostoles, Spain; orcid.org/0000-0002-4932-7149;
Email: guillermo.calleja@urjc.es
Authors
́
Helena Montes-Andres − Department of Chemical, Energy and
Mechanical Technology, Rey Juan Carlos University, 28933
Mostoles, Spain
CONCLUSIONS
■
In this work, the synthesis and structural characterization of
two isostructural MOFs, named M-URJC-4 (M = Co, Ni),
based on the coordination of transition-metal ions and a non-
commercially available isophtalate-type linker are reported.
Both materials exhibit 3D structures crystallizing in a
monoclinic system and a P21/c space group and providing a
permanent microporosity with 9 and 13 Å channels along the c
axis. Both materials have exhibited the ability to physisorb H2
with uptake values among the highest recorded for MOF
structures at room temperature. The Ni-URJC-4 material was
evaluated as a heterogeneous catalyst in a reductive amination
reaction with different carbonyls and primary amines as
substrates. Remarkable performances have been achieved with
product yields between 76 and 91% under low H2 pressure
conditions. These results show a significant advance in
heterogeneous catalysis, where the same material has three
notable intrinsic properties: (1) the ability to adsorb H2, (2)
activation of carbonyl compounds and amines, acting as Lewis
acid transition metal catalysts, and (3) activation of a H2
molecule to reduce double bonds. It is important to note that
Pedro Leo − Department of Chemical and Environmental
Technology, Rey Juan Carlos University, 28933 Mostoles,
Spain; orcid.org/0000-0002-6888-4215
Antonio Munoz − Department of Chemical and Environmental
̃
Technology, Rey Juan Carlos University, 28933 Mostoles, Spain
́
Antonio Rodríguez-Dieguez − Department of Inorganic
Chemistry, University of Granada, Granada, Spain;
orcid.org/0000-0003-3198-5378
Gisela Orcajo − Department of Chemical, Energy and
Mechanical Technology, Rey Juan Carlos University, 28933
Mostoles, Spain; orcid.org/0000-0001-8880-748X
Duane Choquesillo-Lazarte − Laboratorio de Estudios
́
Cristalograficos, IACT, CSIC, Universidad de Granada, 18100
Armilla, Granada, Spain; orcid.org/0000-0002-7077-8972
Carmen Martos − Department of Chemical, Energy and
Mechanical Technology, Rey Juan Carlos University, 28933
Mostoles, Spain
Fernando Martínez − Department of Chemical and
Environmental Technology, Rey Juan Carlos University, 28933
Mostoles, Spain; orcid.org/0000-0002-9684-7630
F
https://dx.doi.org/10.1021/acs.inorgchem.0c02127
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
(10) Zhou, X.; Jiang, Y.-F.; Guo, H.-L.; Wang, X.; Liu, Y.-N.; Imran,
M.; Xu, A.-W. Hydrogenation/oxidation triggered highly efficient
reversible color switching of organic molecules. Catal. Sci. Technol.
2017, 7, 1379−1385.
Juan A. Botas − Department of Chemical, Energy and
Mechanical Technology, Rey Juan Carlos University, 28933
Mostoles, Spain
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c02127
́
(11) Kondratenko, E. V.; Mul, G.; Baltrusaitis, J.; Larrazabal, G. O.;
́
Perez-Ramírez, J. Status and perspectives of CO 2 conversion into
fuels and chemicals by catalytic, photocatalytic and electrocatalytic
processes. Energy Environ. Sci. 2013, 6, 3112−3135.
Author Contributions
†These authors contributed equally to this work. The
manuscript was written through the contributions of all
authors. All authors have given approval to the final version
of the manuscript.
(12) (a) Niu, Z.; Bhagya Gunatilleke, W. D. C.; Sun, Q.; Lan, P. C.;
Perman, J.; Ma, J.-G.; Cheng, Y.; Aguila, B.; Ma, S. Metal-organic
framework anchored with a Lewis pair as a new paradigm for catalysis.
Chem. 2018, 4, 2587−2599. (b) Chatterjee, M.; Ishizaka, T. T.;
Kawanami, H. Reductive amination of furfural to furfurylamine using
aqueous ammonia solution and molecular hydrogen: an environ-
mentally friendly approach. Green Chem. 2016, 18, 487−496.
(c) Komanoya, T.; Kinemura, T.; Kita, Y.; Kamata, Y. K.; Hara, M.
Electronic effect of ruthenium nanoparticles on efficient reductive
amination of carbonyl compounds. J. Am. Chem. Soc. 2017, 139,
11493−11499. (d) Gallardo-Donaire, J.; Ernst, M.; Trapp, O.;
Schaub, T. Direct Synthesis of Primary Amines via Ruthenium-
Catalysed Amination of Ketones with Ammonia and Hydrogen. Adv.
Synth. Catal. 2016, 358, 358−363.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work has been supported by the Regional Government of
Madrid (Projects ACES2030-CM and S2018/EMT-4319), the
Spanish Ministry of Science and Innovation, and the Spanish
State Research Agency [Projects PGC2018-099296-B-I00,
PGC2018-102052-B-C21, and PGC2018-102047-B-I00 and
Grant FPI BES-2016-076433 (to H.M.-A.)].
(13) Roughley, S. D.; Jordan, A. M. J. The medicinal chemist’s
toolbox: an analysis of reactions used in the pursuit of drug
candidates. J. Med. Chem. 2011, 54, 3451−3479.
REFERENCES
(14) (a) Heinen, A. W.; Peters, J. A.; Van Bekkum, H. The reductive
amination of benzaldehyde over Pd/C catalysts: Mechanism and
effect of carbon modifications on the selectivity. Eur. J. Org. Chem.
2000, 13, 2501−2506. (b) Chen, X.; Shen, K.; Ding, D.; Chen, J.;
Fan, T.; Wu, R.; Li, Y. Solvent-driven selectivity control to either
anilines or dicyclohexylamines in hydrogenation of nitroarenes over a
bifunctional Pd/MIL-101 catalyst. ACS Catal. 2018, 8, 10641−10648.
(c) Postma, R. S.; Brunet Espinosa, R.; Lefferts, L. Competitive
adsorption of nitrite and hydrogen on palladium during nitrite
hydrogenation. ChemCatChem 2018, 10, 3770−3776. (d) Lu, Y.-M.;
Zhu, H.-Z.; Li, W.-G.; Hu, B.; Yu, S.-H. Size-controllable palladium
nanoparticles immobilized on carbon nanospheres for nitroaromatic
hydrogenation. J. Mater. Chem. A 2013, 1, 3783−3788.
■
(1) (a) Stock, N.; Biswas, S. Synthesis of metal-organic frameworks
(MOFs): routes to various MOF topologies, morphologies, and
composites. Chem. Rev. 2012, 112, 933−969. (b) Bai, Y.; Dou, Y.; Xie,
L. H.; Rutledge, W.; Li, J. R.; Zhou, H. C. Zr-based metal−organic
frameworks: design, synthesis, structure, and applications. Chem. Soc.
Rev. 2016, 45, 2327−2367. (c) Salunkhe, R. R.; Kaneti, Y. V.; Kim, J.;
Kim, J. H.; Yamauchi, Y. Nanoarchitectures for metal−organic
framework-derived nanoporous carbons toward supercapacitor
applications. Acc. Chem. Res. 2016, 49, 2796−2806. (d) Li, B.; Wen,
H. M.; Cui, Y.; Zhou, W.; Qian, G.; Chen, B. Emerging
multifunctional metal−organic framework materials. Adv. Mater.
2016, 28, 8819−8860.
(2) Horcajada, P.; Gref, R.; Baati, T.; Allan, P. K.; Maurin, G.;
(15) (a) Leng, F.; Gerber, I. C.; Lecante, P.; Bentaleb, A.; Munoz,
̃
́
Couvreur, P.; Ferey, G.; Morris, R.; Serre, C. Metal−organic
A.; Illescas, B. M.; Martín, N.; Melinte, G.; Ersen, O.; Martinez, H.;
Axet, M. R.; Serp, p. Hexakis [60] Fullerene Adduct-Mediated
Covalent Assembly of Ruthenium Nanoparticles and Their Catalytic
Properties. Chem. - Eur. J. 2017, 23, 13379−13386. (b) Wu, Y.; Yu,
H.; Guo, Y.; Jiang, X.; Qi, Y.; Sun, B.; Li, H.; Zheng, J.; Li, X. A rare
earth hydride supported ruthenium catalyst for the hydrogenation of
N-heterocycles: boosting the activity via a new hydrogen transfer path
and controlling the stereoselectivity. Chem. Sci. 2019, 10, 10459−
10465. (c) Veerakumar, P.; Dhenadhayalan, N.; Lin, K.-C.; Liu, S.-B.
Highly stable ruthenium nanoparticles on 3D mesoporous carbon: an
excellent opportunity for reduction reactions. J. Mater. Chem. A 2015,
3, 23448−23457. (d) Zhu, L.; Shan, S.; Petkov, V.; Hu, W.; Kroner,
A.; Zheng, J.; Yu, C.; Zhang, N.; Li, Y.; Luque, R.; Zhong, C.-J.; Ye,
H.; Yang, Z.; Chen, B.H. Ruthenium−nickel−nickel hydroxide
nanoparticles for room temperature catalytic hydrogenation. J.
Mater. Chem. A 2017, 5, 7869−7875.
frameworks in biomedicine. Chem. Rev. 2012, 112, 1232−1268.
(3) Li, J. R.; Sculley, J.; Zhou, H. C. Metal−organic frameworks for
separations. Chem. Rev. 2012, 112, 869−932.
(4) Dhakshinamoorthy, A.; Li, Z.; Garcia, H. Catalysis and
photocatalysis by metal organic frameworks. Chem. Soc. Rev. 2018,
47, 8134−8172.
́
́
(5) Montes-Andres, H.; Leo, P.; Orcajo, G.; Rodríguez-Dieguez, A.;
Choquesillo-Lazarte, D.; Martos, C.; Botas, J. A.; Martínez, F.; Calleja,
G. Novel and Versatile Cobalt Azobenzene-Based Metal-Organic
Framework as Hydrogen Adsorbent. ChemPhysChem 2019, 20, 1334−
1339.
(6) (a) Dalebrook, A. F.; Gan, W.; Grasemann, M.; Moret, S.;
Laurenczy, G. Hydrogen storage: beyond conventional methods.
Chem. Commun. 2013, 49, 8735−8751. (b) Rosi, N. L.; Eckert, J.;
Eddaoudi, M.; Vodak, D. T.; Kim, J.; O’Keeffe, M.; Yaghi, O. M.
Hydrogen storage in microporous metal-organic frameworks. Science
2003, 300, 1127−1129. (c) Zhao, D.; Yuan, D.; Zhou, H. C. The
current status of hydrogen storage in metal−organic frameworks.
Energy Environ. Sci. 2008, 1, 222−235.
(7) Long, J.; Shen, K.; Li, Y. Bifunctional N-doped Co@ C catalysts
for base-free transfer hydrogenations of nitriles: controllable
selectivity to primary amines vs imines. ACS Catal. 2017, 7, 275−284.
(8) Linares, N.; Moreno-Marrodan, C.; Barbaro, P. PdNP@ Titanate
Nanotubes as Effective Catalyst for Continuous-Flow Partial Hydro-
genation Reactions. ChemCatChem 2016, 8, 1001−1011.
(16) (a) Chatterjee, M.; Ishizaka, T.; Kawanami, H. Reductive
amination of furfural to furfurylamine using aqueous ammonia
solution and molecular hydrogen: an environmentally friendly
approach. Green Chem. 2016, 18, 487−496. (b) Li, C.; Wan, F.;
Chen, Y.; Peng, H.; Tang, W.; Yu, S.; McWilliams, J. C.; Mustakis, J.;
Samp, L.; Maguire, R. J. Stereoelectronic Effects in Ligand Design:
Enantioselective Rhodium-Catalyzed Hydrogenation of Aliphatic
Cyclic Tetrasubstituted Enamides and Concise Synthesis of (R)-
Tofacitinib. Angew. Chem., Int. Ed. 2019, 58, 13573−13583.
(c) Nairoukh, Z.; Wollenburg, M.; Schlepphorst, C.; Bergander, K.;
Glorius, F. The formation of all-cis-(multi) fluorinated piperidines by
a dearomatization−hydrogenation process. Nat. Chem. 2019, 11,
264−270.
(9) Edwards, H. D.; Shelver, W. L.; Choi, S.; Nisbet, D. J.; Krueger,
N. A.; Anderson, R. C.; Smith, S. B. Immunogenic inhibition of
prominent ruminal bacteria as a means to reduce lipolysis and
biohydrogenation activity in vitro. Food Chem. 2017, 218, 372−377.
G
https://dx.doi.org/10.1021/acs.inorgchem.0c02127
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
(17) (a) Nakamura, Y.; Kon, K.; Touchy, A. S.; Shimizu, K.; Ueda,
W. Selective synthesis of primary amines by reductive amination of
ketones with ammonia over supported Pt catalysts. ChemCatChem
2015, 7, 921−924. (b) Dhiman, M.; Polshettiwar, V. Ultrasmall
nanoparticles and pseudo-single atoms of platinum supported on
fibrous nanosilica (KCC-1/Pt): engineering selectivity of hydro-
genation reactions. J. Mater. Chem. A 2016, 4, 12416−12424.
(18) (a) Thacker, N. C.; Lin, Z.; Zhang, T.; Gilhula, J. C.; Abney, C.
W.; Lin, W. Robust and porous β-diketiminate-functionalized metal−
organic frameworks for earth-abundant-metal-catalyzed C−H amina-
tion and hydrogenation. J. Am. Chem. Soc. 2016, 138, 3501−3509.
(b) Jagadeesh, R. V.; Murugesan, K.; Alshammari, A. S.; Neumann,
H.; Pohl, M.-M.; Radnik, J.; Beller, M. MOF-derived cobalt
nanoparticles catalyze a general synthesis of amines. Science 2017,
358, 326−332. (c) Murugesan, K.; Wei, Z.; Chandrashekhar, V. G.;
Neumann, H.; Spannenberg, A.; Jiao, H.; Beller, M.; Jagadeesh, R. V.
Homogeneous cobalt-catalyzed reductive amination for synthesis of
functionalized primary amines. Nat. Commun. 2019, 10, 5443. (d) Ai,
W.; Zhong, R.; Liu, X.; Liu, Q. Hydride transfer reactions catalyzed by
cobalt complexes. Chem. Rev. 2019, 119, 2876−2953.
(19) (a) Liu, Y.; Yi, Z.; Tan, X.; Dong, X.; Zhang, X. Nickel-
Catalyzed Asymmetric Hydrogenation of Cyclic Sulfamidate Imines:
Efficient Synthesis of Chiral Cyclic Sulfamidates. Science 2019, 19,
63−73. (b) Hoshimoto, Y.; Hayashi, Y.; Suzuki, H.; Ohashi, M.;
Ogoshi, S. One-Pot, Single-Step, and Gram-Scale Synthesis of
Mononuclear [(η6-arene)Ni(N-heterocyclic carbene)] Complexes:
Useful Precursors of the Ni0−NHC Unit. Organometallics 2014, 33,
1276−1282. (c) Lin, C. Y.; Power, P. P. Complexes of Ni (I): a “rare”
oxidation state of growing importance. Chem. Soc. Rev. 2017, 46,
An unusual case of symmetry-preserving isomerism. Chem. Commun.
2010, 46, 1329−1331. (d) Zhai, L.; Zhang, W.-W.; Zuo, J.-L.; Ren,
X.-M. Simultaneous observation of ligand-based fluorescence and
phosphorescence within a magnesium-based CP/MOF at room
temperature. Dalton Trans. 2016, 45, 11935−11938. (e) Hausdorf, S.;
Seichter, W.; Weber, E.; Mertens, F. O. R. L. Large pores generated by
the combination of different inorganic units in a zinc hydroxide
ethynylene diisophthalate MOF. Dalton Trans. 2009, 1107−1113.
(f) Zheng, B.; Sun, X.; Li, G.; Cairns, A. J.; Kravtsov, V. Ch.; Huo, Q.;
Liu, Y.; Eddaoudi, M. Solvent-Controlled Assembly of Ionic Metal−
Organic Frameworks Based on Indium and Tetracarboxylate Ligand:
Topology Variety and Gas Sorption Properties. Cryst. Growth Des.
2016, 16 (9), 5554−5562.
(27) Bonneau, C.; O’Keeffe, M.; Proserpio, D. M.; Blatov, V. A.;
Batten, S. R.; Bourne, S. A.; Lah, M. S.; Eon, J. G.; Hyde, S. T.;
̈
̈
Wiggin, S. B.; Ohrstrom, L. Deconstruction of Crystalline Networks
into Underlying Nets: Relevance for Terminology Guidelines and
Crystallographic Databases. Cryst. Growth Des. 2018, 18 (6), 3411−
3418.
(28) Spek, A. L. Single-crystal structure validation with the program
PLATON. J. Appl. Crystallogr. 2003, 36, 7.
(29) Thommes, M.; Kaneko, K.; Neimark, A. V.; Olivier, J. P.;
Rodriguez-Reinoso, F.; Rouquerol, J.; Sing, K. S. W. Physisorption of
gases, with special reference to the evaluation of surface area and pore
size distribution (IUPAC Technical Report). Pure Appl. Chem. 2015,
87, 1051−1069.
(30) (a) Suh, M. P.; Park, H. J.; Prasad, T. K.; Lim, D. W. Hydrogen
storage in metal−organic frameworks. Chem. Rev. 2012, 112, 782−
́
́
835. (b) Berenguer-Murcia, A.; Marco-Lozar, J. P.; Cazorla-Amoros,
D. Hydrogen storage in porous materials: status, milestones, and
challenges. Chem. Rec. 2018, 18, 900−912.
́
5347−5399. (d) Leonard, N. G.; Chirik, P. J. Air-Stable α-diimine
nickel precatalysts for the hydrogenation of hindered, unactivated
alkenes. ACS Catal. 2018, 8, 342−348. (e) Eberhardt, N. A.; Guan, H.
Nickel hydride complexes. Chem. Rev. 2016, 116, 8373−8426.
(f) Heinz, C.; Lutz, J. P.; Simmons, E. M.; Miller, M. M.; Ewing,
W. R.; Doyle, A. G. Ni-catalyzed carbon−carbon bond-forming
reductive amination. J. Am. Chem. Soc. 2018, 140, 2292−2300.
(g) Hu, Y.; Chen, J.; Li, B.; Zhang, Z.; Gridnev, I. D.; Zhang, W.
Nickel-Catalyzed Asymmetric Hydrogenation of 2-Amidoacrylates.
Angew. Chem., Int. Ed. 2020, 59, 5371−5375. (h) Li, J.; Wang, B.; Qin,
Y.; Tao, Q.; Chen, L. MOF-derived Ni@ NC catalyst: synthesis,
characterization, and application in one-pot hydrogenation and
reductive amination. Catal. Sci. Technol. 2019, 9, 3726−3734.
(20) Niu, Z.; Zhang, W.; Lan, P. C.; Aguila, B.; Ma, S. Promoting
Frustrated Lewis Pairs for Heterogeneous Chemoselective Hydro-
genation via the Tailored Pore Environment within Metal−Organic
Frameworks. Angew. Chem., Int. Ed. 2019, 58, 7420−7424.
(21) Sonogashira, K.; Tohda, Y.; Hagihara, N. A convenient
synthesis of acetylenes: catalytic substitutions of acetylenic hydrogen
with bromoalkenes, iodoarenes and bromopyridines. Tetrahedron Lett.
1975, 16, 4467−4470.
(31) (a) Kumah, R. T.; Tsaulwayo, N.; Xulu, B. A.; Ojwach, S. O.
Structural, kinetics and mechanistic studies of transfer hydrogenation
of ketones catalyzed by chiral (pyridyl) imine nickel (ii) complexes.
Dalt. Trans. 2019, 48, 13630−13640. (b) Benitez-Medina, G. E.;
Garcia, J. J. Hydrogenation and N-alkylation of anilines and imines via
transfer hydrogenation with homogeneous nickel compounds. Dalt.
Trans. 2019, 48, 17579−17587. (c) Li, B.; Chen, J.; Zhang, Z.;
Gridnev, I. D.; Zhang, W. Nickel-Catalyzed Asymmetric Hydro-
genation of N-Sulfonyl Imines. Angew. Chem., Int. Ed. 2019, 58,
7329−7334. (d) Yue, H.; Guo, L.; Liu, X.; Rueping, M. Nickel-
catalyzed synthesis of primary aryl and heteroaryl amines via C−O
bond cleavage. Org. Lett. 2017, 19, 1788−1791.
(22) Brunauer, S.; Emmett, P. H.; Teller, E. Adsorption of gases in
multimolecular layers. J. Am. Chem. Soc. 1938, 60, 309−319.
(23) Ravikovitch, P. I.; Haller, G. L.; Neimark, A. V. Density
functional theory model for calculating pore size distributions: pore
structure of nanoporous catalysts. Adv. Colloid Interface Sci. 1998, 76−
77, 203−226.
(24) Leachman, J. W.; Jacobsen, R. T.; Penoncello, S. G.; Lemmon,
E. W. Fundamental equations of state for parahydrogen, normal
hydrogen, and orthohydrogen. J. Phys. Chem. Ref. Data 2009, 38,
721−748.
(25) Czepirski, L.; JagieŁŁo, L. Virial-type thermal equation of gas
solid adsorption. Chem. Eng. Sci. 1989, 44, 797−801.
(26) (a) Hu, Y.; Xiang, S.; Zhang, W.; Zhang, Z.; Wang, L.; Bai, J.;
Chen, B. A new MOF-505 analog exhibiting high acetylene storage.
Chem. Commun. 2009, 7551−7553. (b) Hu, Y. X.; Ma, H. B.; Zheng,
B.; Zhang, W. W.; Xiang, S.; Zhai, L.; Wang, L. F.; Chen, B.; Ren, X.
M.; Bai, J. Three Novel Isomeric Zinc Metal−Organic Frameworks
from a Tetracarboxylate Linker. Inorg. Chem. 2012, 51, 7066−7074.
(c) Sun, D.; Ma, S.; Simmons, J. M.; Li, J.-R.; Yuan, D.; Zhou, H.-C.
H
https://dx.doi.org/10.1021/acs.inorgchem.0c02127
Inorg. Chem. XXXX, XXX, XXX−XXX