Selective Gas Uptake and Rotational Dynamics in a (3,24)-Connected Metal-Organic Framework Material

Article abstract of DOI:10.1021/jacs.0c11202

The desolvated (3,24)-connected metal-organic framework (MOF) material, MFM-160a, [Cu3(L)(H2O)3] [H6L = 1,3,5-triazine-2,4,6-tris(aminophenyl-4-isophthalic acid)], exhibits excellent high-pressure uptake of CO2 (110 wt% at 20 bar, 298 K) and highly selective separation of C2 hydrocarbons from CH4 at 1 bar pressure. Henry's law selectivities of 79:1 for C2H2:CH4 and 70:1 for C2H4:CH4 at 298 K are observed, consistent with ideal adsorption solution theory (IAST) predictions. Significantly, MFM-160a shows a selectivity of 16:1 for C2H2:CO2. Solid-state 2H NMR spectroscopic studies on partially deuterated MFM-160-d12 confirm an ultra-low barrier (～2 kJ mol-1) to rotation of the phenyl group in the activated MOF and a rotation rate 5 orders of magnitude slower than usually observed for solid-state materials (1.4 × 106 Hz cf. 1011-1013 Hz). Upon introduction of CO2 or C2H2 into desolvated MFM-160a, this rate of rotation was found to increase with increasing gas pressure, a phenomenon attributed to the weakening of an intramolecular hydrogen bond in the triazine-containing linker upon gas binding. DFT calculations of binding energies and interactions of CO2 and C2H2 around the triazine core are entirely consistent with the 2H NMR spectroscopic observations.

Full text of DOI:10.1021/jacs.0c11202

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Article
Selective Gas Uptake and Rotational Dynamics in a (3,24)-
Connected Metal−Organic Framework Material
William J. F. Trenholme, Daniil I. Kolokolov,* Michelle Bound, Stephen P. Argent, Jamie A. Gould,
Jiangnan Li, Sarah A. Barnett, Alexander J. Blake, Alexander G. Stepanov, Elena Besley,
Timothy L. Easun,* Sihai Yang,* and Martin Schröder*
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ABSTRACT: The desolvated (3,24)-connected metal−organic framework (MOF) material,
MFM-160a, [Cu3(L)(H2O)3] [H6L = 1,3,5-triazine-2,4,6-tris(aminophenyl-4-isophthalic
acid)], exhibits excellent high-pressure uptake of CO2 (110 wt% at 20 bar, 298 K) and
highly selective separation of C2 hydrocarbons from CH4 at 1 bar pressure. Henry’s law
selectivities of 79:1 for C2H2:CH4 and 70:1 for C2H4:CH4 at 298 K are observed, consistent
with ideal adsorption solution theory (IAST) predictions. Significantly, MFM-160a shows a
2
selectivity of 16:1 for C2H2:CO2. Solid-state H NMR spectroscopic studies on partially
deuterated MFM-160-d12 confirm an ultra-low barrier (∼2 kJ mol−1) to rotation of the phenyl
group in the activated MOF and a rotation rate 5 orders of magnitude slower than usually
observed for solid-state materials (1.4 × 106 Hz cf. 1011−1013 Hz). Upon introduction of CO2
or C2H2 into desolvated MFM-160a, this rate of rotation was found to increase with increasing
gas pressure, a phenomenon attributed to the weakening of an intramolecular hydrogen bond
in the triazine-containing linker upon gas binding. DFT calculations of binding energies and
2
interactions of CO2 and C2H2 around the triazine core are entirely consistent with the H NMR spectroscopic observations.
We report herein the synthesis of the hexacarboxylate linker
H6L, which has been used to prepare a (3,24)-connected
Cu(II) material (denoted MFM-160; MFM = Manchester
Framework Material) designed for both high CO2 uptake and
selective sorption of C2 hydrocarbons over CH4. With this in
mind, our ligand design was based around a triazine
core,11,23−26 coupled with a triangular arrangement of three
pendant isophthalic acid moieties, which can combine with a
Cu(II) paddlewheel motif to give a framework of rht topology,
used by us27−32 and others33−35 to prepare MOFs with
exceptional gas storage capacity. We show here that MFM-160
has the potential for extremely high CO2 uptake at higher
pressures, while at lower pressures it is capable of highly
selective sorption of C2 hydrocarbons over CH4 and CO2.
INTRODUCTION
■
Over the past two decades there has been a great deal of
interest in metal−organic framework (MOF) materials capable
of selectively storing and separating gases. Two areas of
1−8
significant interest are the capture of CO2
and the
separation of C2 hydrocarbons from methane.9−15 CO2 is
well-established as a leading contributor to climate change, and
over 85% of the world’s energy demand involves the burning of
fossil fuels.16,17 Materials capable of storing CO2 from flue gas
and automobiles are therefore in high demand. The use of
MOFs containing polar functional groups such as amines and
amides has proven to be effective for the uptake of CO2 at low
pressure, while MOFs with very large surface areas have shown
exceptional storage capacity for CO2 at higher pressures.5,18−21
Natural gas is a vitally important fuel and is also a feedstock
for the production of a variety of chemicals.22 Comprised
mainly of CH4, it is also increasingly being utilized in vehicles,
as its high H:C ratio results in lowered emissions of CO and
CO2 compared to normal hydrocarbon fuels.22 The main
sources of impurity in natural gas are the C2 hydrocarbons,
C2H2, C2H4, and C2H6.11 Removing these hydrocarbons
increases the purity of natural gas and provides a source of
C2 hydrocarbons for further use.23,24 Purification and
separation of C2 hydrocarbons are usually achieved by
cryogenic distillation, a very energy-intensive process, and
the use of selective adsorbents to separate different
components at room temperature is a potential alternative.23,24
EXPERIMENTAL SECTION
■
Synthesis of H6L (Scheme 1). Cyanuric chloride (736 mg, 3.99
mmol) was added to a mixture of 4-bromoaniline (2.20 g, 12.8 mmol,
3.2 equiv) and NaHCO3 (1.08 g, 12.8 mmol, 3.2 equiv) in 1,4-
dioxane/DMF (3:1, 30 mL) and the mixture heated at 120 °C in a
Received: October 24, 2020
Published: February 24, 2021
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microwave reactor for 1 h. The solvent was removed under vacuum
and the remaining solid washed with water (2 × 20 mL) and extracted
into Et2O. The organic layer was separated and the solvent removed
under vacuum. The resulting white solid was recrystallized from warm
hexane:EtOAc (5:1), filtered, and dried to give 2,4,6-tris(4-
bromophenylamino)-1,3,5-triazine (yield: 1.95 g, 83%). 1H NMR
spectroscopy (400 MHz, dmso-d6) δ = 9.54 (s, 3H), 7.80 (d, 6H, J =
6.8 Hz), 7.46 (d, 6H, J = 8.8 Hz); 13C{1H} NMR (100 MHz, dmso-
d6) δ = 164.3, 139.7, 131.6, 122.7, 114.2 ppm.
20 h. The crystalline product was removed by filtration, washed with
copious hot DMF, and dried to yield a green powder (yield: 210 mg,
82%) Anal. Calcd (Found) for C84H135N19O35Cu3: C, 46.67 (46.28);
H, 6.29 (6.23); N, 12.31 (12.42)%. Single crystals of MFM-160 were
prepared on a small scale using 20 mg of H6L and 4 equiv of
Cu(NO3)2·3H2O dissolved in DMF (1.5 mL). Addition of 3 M
HNO3 in DMF (0.6 mL) followed by heating in a sealed vial at 80 °C
for 20 h produced green octahedral crystals suitable for single-crystal
X-ray diffraction. The syntheses of H6L-d12 and MFM-160-d12
(Scheme 2) are described in the Supporting Information.
Density functional theory (DFT) calculations were performed as
implemented in the Q-Chem quantum chemistry package.36 The
strength of adsorption sites was analyzed using a fragment of the
linker formed by the central triazine ring and three phenyl rings
(Figure S33). The binding energies (BE) between the guest molecule
and the linker were calculated in addition to their relative positions
corresponding to the strongest binding. These calculations were
performed in two stages. Geometry optimization was carried out using
dispersion-corrected DFT calculations at the B3LYP/6-31+G** level
of theory, and the binding energies were subsequently calculated at
the higher B3LYP/6-311+G** level, with BE = Eopt(complex) −
Scheme 1. Synthesis of H6L
E
opt(linker) − Eopt(guest molecule). Binding energies were corrected
for basis set superposition error (BSSE).
RESULTS AND DISCUSSION
■
The preparation of H6L was achieved via microwave-assisted
nucleophilic substitution between 4-bromoaniline and cyanuric
chloride to give the tribromo intermediate (Scheme 1).37
A
microwave-assisted Pd(II)-catalyzed Suzuki cross-coupling of
this intermediate with 3,5-di(ethoxycarbonyl)phenylboronic
acid gave the hexa-ester product, which was then hydrolyzed in
aqueous NaOH followed by acidification with HCl to give H6L
in good yield. It is worth noting that the short reaction times of
1 h for each of the substitution and cross-coupling reactions
provide a facile and energy-efficient route to this linker.
Solvothermal reaction of H6L and Cu(NO3)2·3H2O in
acidified DMF at 80 °C for 24 h yielded green octahedral
single crystals of MFM-160, [Cu3(L)(H2O)3]·13DMF·7H2O.
MFM-160 crystallizes in the tetragonal space group I4/m
with unit cell dimensions a = 32.6838(3) Å, c = 48.0624(7) Å,
and V = 51341(1) Å3 and shows a (3,24)-connected
framework structure of rht topology containing three distinct
cages, A, B, and C (Figure 1). Cage A is a truncated
cuboctahedron formed from 12 [Cu2(O2CR)4] paddlewheel
units connected to 24 different linkers, with the spacing
between cuboctahedra determined by the distance between
isophthalate moieties on the arms of the linker. This results in
the formation of larger cages B (truncated tetrahedron) and C
(truncated cube). With the aqua ligands removed from the
axial positions of the paddlewheel, the accessible internal
diameter of cage A is 13.0 Å, and that of cage B is 13.8 Å, with
a cage length of 22.7 Å and the accessible windows between
these cages measuring 6.5−8.2 Å. The largest cage, C, has an
accessible diameter of 19.6 Å and a cage length of 35.2 Å, with
windows of 6.4−8.4 Å. All internal diameters were calculated
by fitting a sphere from the center of the cage to its walls,
taking into account van der Waals radii. Window diameters
were calculated from the largest sphere able to fit through the
aperture. The potential accessible volume of desolvated MFM-
160a (“a” denotes the desolvated form) is 77%, as calculated
by the VOID algorithm within the software PLATON38 (after
removal of all guest solvates and coordinated water molecules),
2,4,6-Tris(4-bromophenylamino)-1,3,5-triazine (1.32 g, 2.23
mmol), diethylisophthalate-5-boronic acid (2.14 g, 8.05 mmol, 3.6
equiv), and K3PO4 (8.50 g, 40.1 mmol, 18 equiv) were added to a
degassed mixture of 1,4-dioxane/water (10:1, 110 mL). [Pd(dppf)-
Cl2] (40 mg, 0.055 mmol, 2.4% equiv) was added and the reaction
heated in a microwave reactor at 85 °C for 1 h. The solvent was
removed under vacuum and the product extracted into CHCl3. The
combined organic phase was then washed with water and brine and
dried over MgSO4. Upon evaporation of CHCl3, the crude product
was dissolved in CH2Cl2 and purified by passing through a plug of
silica gel to give the pure ester product 1,3,5-triazine-2,4,6-
tris(aminophenyl-4-isophthalic ethyl ester) as a white solid (yield:
1
1.86 g, 82%). H NMR spectroscopy (300 MHz, dmso-d6) δ = 9.58
(s, 3H), 8.42 (t, 3H, J = 1.5 Hz), 8.39 (d, 6H, J = 1.5 Hz), 8.04 (d,
6H, J = 6.0 Hz), 7.71 (d, 6H, J = 8.7 Hz), 4.37 (q, 12H, J = 7.1 Hz),
1.35 (t, 18H, J = 7.1 Hz); 13C{1H} NMR (100 MHz, dmso-d6) δ =
165.8, 165.1, 139.6, 138.6, 131.9, 131.5, 130.1, 129.8, 127.5, 121.4,
61.6, 14.6 ppm.
The hexa-ester (1.70 g, 1.67 mmol) was dissolved in a mixture of
THF (30 mL) and 2 M NaOH (30 mL) and heated at 75 °C for 16 h.
Upon cooling, THF (30 mL) was added, the aqueous layer was
separated, and concentrated HCl was added dropwise to the solution
until pH ∼1. The resulting precipitate was filtered and recrystallized
from a mixture of hot DMF/water (5:1) to give the H6L [1,3,5-
triazine-2,4,6-tris(aminophenyl-4-isophthalic acid)] as a white solid
(yield: 1.36 g, 96%). 1H NMR (400 MHz, dmso-d6) δ = 9.59 (s, 3H),
8.44 (t, 3H, J = 1.6 Hz), 8.39 (d, 6H, J = 1.6 Hz), 8.04 (d, 6H, J = 8.0
Hz), 7.73 (d, 6H, J = 8.8 Hz); 13C{1H} NMR (100 MHz, dmso-d6) δ
= 167.1, 164.5, 141.4, 140.8, 132.6, 132.4, 131.3, 128.7, 127.5, 121.2
ppm. Anal. Calcd (Found) for C45H30N6O12: C, 63.83 (63.39); H,
3.57 (3.45); N, 9.93 (9.80)%.
Synthesis of MFM-160·13DMF·7H2O. H6L (100 mg, 0.118
mmol) and Cu(NO3)2·3H2O (114 mg, 0.472 mmol, 4 equiv) were
added to DMF/H2O (8 mL; 15:1, v/v) and sonicated until
dissolution. A solution of 3 M HNO3 in DMF (3 mL) was then
added and the solution heated in a 50 mL Schott bottle at 80 °C for
with a calculated crystal density of 0.540 g cm−3
.
Thermogravimetric analysis of the as-synthesized sample of
MFM-160 in air showed loss of DMF and H2O solvent below
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Figure 1. View of cages A, B, and C in MFM-160. The large colored spheres in the center of the cages represent the solvent-accessible volume.
Color code for atoms: Cu, cyan; O, red; N, blue, C, gray. Hydrogen atoms are omitted for clarity.
170 °C, with the material stable up to 290 °C, above which a
mass loss corresponding to framework decomposition is
observed (Figure S2).
To prepare activated MFM-160a for gas sorption experi-
ments, the DMF of the as-synthesized sample was exchanged
with analytical-grade acetone by decanting the mother liquor
and replacing it with analytical-grade acetone. This process was
repeated twice daily for 5 days. The sample was then activated
by heating at 100 °C under reduced pressure for 20 h,
whereupon a color change from dark green to purple was
observed; this is a typical indicator of the removal of
coordinated solvent from the Cu(II) paddlewheel node. The
permanent porosity of the framework was confirmed via a N2
sorption isotherm measured volumetrically at 77 K, which
showed reversible type-I behavior and an uptake of 983 cm3
g−1 (123 wt%) at 1 bar (Figure S5). The slight changes in
gradient in the range 30−120 mbar are assigned to the
sequential filling of the micropores and mesopores. The
estimated Brunauer−Emmett−Teller (BET) surface area of
MFM-160a as calculated from this isotherm was 3847 m2 g−1,
with a total pore volume of 1.52 cm3 g−1.
CO2, H2, and Hydrocarbon Gas Adsorption Isotherms.
In order to probe the effectiveness of MFM-160a to adsorb
different gases, we performed gas adsorption isotherm
experiments between 0 and 20 bar using CO2 and CH4 (at
298 and 273 K, Figure 2) and H2 (at 77 and 87 K, Figure S6).
Low-pressure (0−1 bar) isotherms of C2 hydrocarbons were
run at 298 and 273 K for comparison with the data obtained
for CH4 (Figure 3).
Figure 2. Adsorption isotherms for CO2 and CH4 in MFM-160a from
0 to 20 bar (filled triangles, adsorption; open triangles, desorption).
77 K and 5.3 wt% at 87 K, whereas the uptake at 1 bar was
2.14 wt% at 77 K and 1.40 wt% at 87 K (Figure S6).
As shown in Figure 3, the uptakes of C2H2, C2H4, and C2H6
at 273 K are 212 cm3 g−1 (24.7 wt%), 175 cm3 g−1 (21.9 wt%),
and 201 cm3 g−1 (27.0 wt%) at 1 bar, respectively. At 298 K,
these values become 128 cm3 g−1 (14.9 wt%), 115 cm3 g−1
(14.4 wt%), and 110 cm3 g−1 (14.8 wt%). This comparatively
low uptake of CH4 at 1 bar (15.3 cm3 g−1 at 298 K, 27.1 cm3
g−1 at 273 K) in MFM-160a makes the material of great
interest for selective separation of C2 hydrocarbons over CH4.
To estimate the selectivity of each hydrocarbon over CH4, we
employed Henry’s law, in which constants KH were determined
using a virial fit of the measured isotherm data (Figures S7−
S16).
MFM-160a shows exceptional capacity for CO2 storage at 20
bar, with uptakes of 558 cm3 g−1 (110 wt%) and 719 cm3 g−1
(141 wt%) at 298 and 273 K, respectively. At 195 K and 1 bar,
MFM-160a nears saturation at 881 cm3 g−1 (173 wt%). This
uptake of CO2 up to 20 bar at 298 K is one of the highest
reported to date: to the best of our knowledge the current
record uptake under these conditions is 627 cm3 g−1 (123 wt%,
19.8 bar) in MOF-177.5,20 The CH4 uptake of MFM-160a at
20 bar was 199 cm3 g−1 (14.2 wt%) at 298 K and 274 cm3 g−1
(19.6 wt%) at 273 K. The H2 uptake at 20 bar was 6.4 wt% at
Using these constants, the selectivity (S) of one gas, i, over
the second gas, j, was determined from the following equation:
Sij = KHi/KHj
The selectivities for C2H2:CH4, C2H4:CH4, and C2H6:CH4
at 273 K were calculated to be 104:1, 130:1, and 10:1,
respectively. While lower than current benchmark materials
such as NKMOF-1-Ni39 and ZJU-74a,40 the C2H2:CH4
separation of 79:1 at 298 K is comparable to those of other
Cu(II) triazine-based MOFs, such as [Cu3(TDPAT)]11
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of C2H2 over CO2 in porous formates.43 The separation of
CO2 from C2H2 is notoriously difficult as a result of their
similar sizes and sublimation points;44 the current high
selectivity for C2H2 over CO2 is promising and represents
one of the highest selectivities for a MOF for this
separation.45,46 It should be noted that repeating the
desorption−adsorption cycles of these isotherms gives
identical results, confirming the stability of MFM-160 to
repeated activation and reuse.
In addition to Henry’s law, the gas selectivities for
C2H2:CH4, C2H4:CH4, C2H6:CH4, and C2H2:CO2 in binary
mixtures were analyzed using the ideal adsorption solution
theory (IAST) model.47 Each isotherm was fitted using a dual-
site or single-site Langmuir−Freundlich model, with the
chosen model based on the accuracy of the resulting fitting
(Figures S17−S26). The selectivities for each mixture (Figures
3c and S27) are in agreement with the Henry’s law calculations
at 273 K, as the order of selectivity over CH4 is shown to be
C2H4 > C2H2 ≫ C2H6. At very low pressures (∼20 mbar) the
C2H4:CH4 selectivity is predicted to be 110:1, which decreases
rapidly with increasing pressure before reaching 26:1 at 1 bar.
The C2H2:CH4 selectivity is 97:1 below 30 mbar and decreases
to 28:1 at 1 bar. At 298 K, the IAST predictions show that the
selectivity for C2H4 over CH4 is much greater than that of
C2H2 between 20 and 200 mbar (111:1 versus 51:1 at 20
mbar), although the selectivities are approximately equal at 1
bar.
The isosteric heats of adsorption (Qst) for each gas were
calculated using a virial method to fit the sorption isotherms at
273 and 298 K. The heats of adsorption at zero loading for
CO2, C2H2, C2H4, and C2H6 are 30, 37, 36, and 24 kJ mol−1,
respectively. Each has a higher Qst at zero loading than CH4
(23 kJ mol−1). The values of Qst follow the same pattern as the
selectivities at 298 K (C2H2 > C2H4 ≫ C2H6), although at
273 K the C2H4:CH4 selectivity is greater than the C2H2:CH4
selectivity (130:1 versus 104:1).
2
Solid-State H NMR Spectroscopic Studies of Acti-
vated and Gas-Loaded MFM-160. In order to gain a greater
understanding of the C2H2:CO2 separation and of the behavior
of both gases within the porous material, 2H NMR
spectroscopic studies were carried out on a partially deuterated
analogue of MFM-160, denoted MFM-160-d12 (Scheme 2).
The dynamics of the phenyl ring can affect the adsorption
properties in two ways: first, the phenyl rings themselves
Figure 3. Adsorption isotherms for CH4, C2H6, C2H4, and C2H2 in
MFM-160a from 0 to 1 bar at (a) 273 and (b) 298 K (filled triangles,
adsorption; open triangles, desorption). (c) Calculated IAST
selectivities for MFM-160a at 298 K.
Scheme 2. Synthesis of H6L-d12
(TDPAT6− = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-tri-
azine) and [Cu3(TDPAH)]23 (TDPAH6− = 2,5,8-tris(3,5-
dicarboxylphenylamino)-s-heptazine), which have selectivities
of 127:1 and 81:1, respectively. However, the calculated
selectivities are higher than those reported for smaller-pore
Cu(II) MOFs such as UTSA-50a13 and UTSA-15a41 (68:1 and
56:1, respectively).
The selectivity for C2H2 over CO2 (15:1 at 298 K; 16:1 at
273 K) demonstrates the potential of MFM-160a for the
purification of acetylene, in which CO2 is a common impurity.
A study by Li et al.42 strongly suggested that the presence of N-
centers within pores does not improve the selectivity for C2H2
over CO2. Thus, in the case of MFM-160a, we tentatively
attribute this selectivity to the greater van der Waals
interactions between the framework and C2H2 molecules, as
described by Samsonenko and co-workers for selective uptake
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provide an accessible adsorption site as a result of the aromatic
π-system; second, the phenyl rotation directly affects the
effective size and geometry of the pore. Probing the framework
dynamics is also of interest for comparison with other known
MOFs, thus improving understanding of structure−property
relationships. The rotational dynamics in MFM-160-d12 were
probed in the activated, desolvated material (Figures 4 and
pressure uptake of C2H2 is significantly higher than that of
CO2, respective pressures of 0.32 and 1 bar were chosen for
comparison of the two gases at the same concentrations. The
loadings of 0.32 bar of C2H2 and 1 bar of CO2 each correspond
to ∼3.1 gas molecules per linker, where the empirical formula
of MFM-160-d12 gives a density of 1043.43 g mol−1. The
higher loadings of 1 bar of C2H2 and 5 bar of CO2 correspond
to 5.9 and 10.8 molecules per linker, respectively.
In the activated, desolvated MFM-160-d12, the temperature-
dependent behavior of the line shapes in the 2H NMR spectra
confirms that the deuterated phenyl rings are mobile, with a
dynamic process gradually developing between ∼120 and 300
K (Figures 4 and 5). Below 123 K the line shape is mainly
composed of a Pake-powder pattern with quadrupolar coupling
parameters (Q0 = 176 kHz, η0 ≈ 0) typical for a static C−D
2
group on the H NMR spectroscopic time scale. At ∼300 K,
the spectrum is dominated by the narrowed line shape
expected for an axial rotation around the phenyl C2 axis (Q1 ≈
20 kHz ≈ Q0/8).48 At the same time, over the whole
temperature range studied, these two components co-exist.
Such a phenomenon has been reported for UiO-6649 and
indicates that the phenyl motion at each given temperature is
characterized by a distribution of rotation rates, which suggests
that the rotational potential fluctuates to a certain degree
across the framework. In common with work by Schmidt et
al.,50 the rate constant is assumed to obey a log-normal
distribution, with k1 being the mean value of the rotation rate
at each given temperature and σ being the width of the
distribution. By considering the C2 symmetry of the phenyl
fragment, the uniaxial rotation around the C2 axis can be
modeled by either a 4-site or a 6-site jump rotation model
(Figure 6). Notably, in most cases the 6-site jump model can
also efficiently describe more complex axial rotations.51
Figure 4. Temperature dependence of the line shape of resonances
due to the phenyl groups in guest-free MFM-160-d12 as measured by
2H NMR spectroscopy (experimental, black; simulation, red).
2
Numerical fitting of the experimentally observed H NMR
spectroscopic patterns shows that only the 6-site jump rotation
gives an agreement with our data.
Although the distribution of the jump sites has to obey C2
symmetry, the initial position of the phenyl orientation might
be distorted from a fully symmetric case. This distortion is
S28) in the presence of CO2 at 1 and 5 bar loadings (Figures
S29 and S30, respectively) and in the presence of C2H2 at 0.32
and 1 bar (Figures S31 and 32, respectively). As the low-
Figure 5. Comparison of the experimental line shapes and rotation rates for phenyl groups in guest-loaded MFM-160-d12 at 123 and 223 K.
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inhomogeneity is considerably lower than that observed in
UiO-66 and may be attributed to the flexible nature of MFM-
160.
2
The most striking features of the H NMR spectra for
MFM-160-d12 are the kinetic parameters of the deuterated
phenyl motion. The Arrhenius plot (Figure 7a) is linear and
Figure 6. View of stable orientation sites for the phenyl rings
depending on the jump rotation model. (a) The starting position of
the plane of the mobile phenyl ring is tilted by an angle φi. The axial
jump rotation about the C2 symmetry axis of the phenyl group is then
realized by either (b) an n = 4 site exchange motion or (c) an n = 6
site exchange. The distribution of the orientation sites is governed
only by the value of the first position, φ1 = φi. All elementary jumps
are assumed to be governed by the same rate constant, k = k1/n. Even
in the case of the same value of φi in the intermediate jump rate, the
two models give qualitatively distinct patterns.
readily introduced into the re-orientation model as an angular
parameter φi (Figure 6). For a 6-site jump rotation mechanism,
the jump positions are given as follows: φ1 = φi, φ2 = π/2, φ3 =
π − φ1, φ4 = π + φ1, φ5 = π/2, φ6 = π + φ2. Within such a
model, we assume that all positions have equal probability. In
our model, the angle φi = 45°, where φi is the angle between
the plane of the mobile phenyl ring and the plane of the
aromatic ring fixed to the Cu(II) node. Thus, it follows that
the value Δφ1 = 2φi can be directly compared with the crystal
structure. Despite the model being able to give distinct rate
constants for each elementary jump, we have found that a
simple kinetic matrix defined by one rate constant is sufficient
to provide good agreement with the experimental observations.
Thus, this 6-site jump rotation model accurately simulates the
experimental temperature dependence of the 2H NMR spectral
line shapes. The model Δφ1 = 2φi ≈ 90° is consistent with the
crystallographic data and underscores that the orientation of
the phenyl rings is not homogeneously distributed. The log-
normal distribution width is almost constant over the
temperature range: σ ≈ 1.3−1.4. Thus, the present
Figure 7. Arrhenius plots of the rotation rate constants k1: (a) of all
gas-loaded samples, (b) of CO2-loaded MFM-160, and (c) of C2H2-
■
○
loaded MFM-160. ( ) Guest-free MFM-160-d12; (blue ) 1 bar CO2
●
loading; (red Δ) 5 bar CO2 loading; (pink ) 0.32 bar C2H2 loading;
(dark green ) 1 bar C2H2 loading. All gas loadings were performed
▼
at 298 K.
shows an activation barrier, E0 = 2.1 kJ mol−1, and collision
factor, k00/2π = 1.4 × 106 Hz. This activation barrier is so low
that it is comparable to the torsional barrier for methyl groups
in xylenes or 2-methylimidazole, i.e., aromatic systems where
the internal steric interactions are minimized. The torsional
barrier for methyl groups in such compounds has been
measured experimentally by neutron scattering techniques and
2H NMR spectroscopy, which confirm in both cases that E0
does not exceed 1.5 kJ mol−1.52,53 Such low values have not
been reported previously for solid-state materials based upon
carboxylate ligands but have been confirmed for many different
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samples of MFM-160-d12. However, similar low barriers have
been reported recently for MOFs incorporating metal−amine
linkers, such as 2-methylimidazole in ZIF-852 and dabco in
[Zn2(bdc)2(dabco)].54
It is interesting to consider the possible sources of steric
interaction hindering phenyl rotation in MFM-160-d12. The
electrostatic interactions are maximized when all aromatic rings
are in the same plane, in which case the closest interatomic
distances can be given as d1 ≈ 2.2 Å, d2 ≈ 3.1 Å, and d3 ≈ 2.0 Å
(Figure 8). The main interaction is likely governed by sites III
of the extremely low starting value for the guest-free material,
i.e., k00/2π = 1.4 × 106 Hz, while normal pre-exponential
factors for an elementary rotation are typically in the range of
1011−13 Hz.
For the C2H2-loaded material, the situation is different: at
the intermediate concentration (∼0.32 bar at room temper-
ature), conditions in which the C2H2 concentration is
equimolar to that of CO2 at 1 bar, no effect on the phenyl
dynamics is observed (Figure 7c), and the rotation is
characterized by the same parameters as for the activated,
desolvated MFM-160-d12, with E3 = 1.9 kJ mol−1 and k30 = 1.2
× 106 Hz. Upon increasing the C2H2 concentration to 1 bar,
the rate of phenyl ring rotation clearly increases; however, the
activation barrier remains the same, E4 = 1.9 kJ mol−1, but the
collision factor rises to k40 = 1.8 × 106 Hz. This is shown on
the corresponding Arrhenius plots (Figure 7c).
This behavior can be interpreted in terms of host−guest
interactions. At the lower loading the phenyl rings do not
interact with C2H2, and only at higher loadings is there a subtle
increase of the collision factor. This shows that the occupancy
of C2H2 sites around the mobile phenyl rings is low, even at
higher concentrations. Thus, C2H2 coordinates predominantly
to the Cu(II) paddlewheel sites and interacts with the phenyl
rings only through random collisions, most likely when most of
the metal sites are occupied. At 0.32 bar of C2H2 (3.1 gas
molecules per formula unit), the Cu(II) sites are very likely
saturated, with C2H2 bound strongly and not able to influence
Figure 8. View of the deuterated (green) mobile phenyl ring in
MFM-160-d12. The scheme shows the possible hydrogen-bonding
sites (I, II, and III) that will influence the rotational potential for
rotation of the phenyl group.
2
phenyl rotation, as shown by H NMR spectroscopy.
However, with an equimolar loading of CO2, where the
Cu(II) sites were also expected to be saturated, the phenyl ring
rotation is much more affected by the guest CO2 molecules
than for C2H2, strongly suggesting that CO2 occupies binding
sites on the linker, while open Cu(II) sites are still available.
These observations, therefore, provide a good insight into the
selectivity for C2H2 over CO2, as the stronger binding of C2H2
at the open Cu(II) sites very likely accounts for the greater
uptake of C2H2 at low pressures. Interestingly, the C2H2:CO2
selectivity in [Cu2(pzdc)2(pyz)] (pzdc2− = pyrazine-2,3-
dicarboxylate; pyz = pyrazine), a MOF without open Cu(II)
sites, was assigned to the binding of C2H2 with free carboxylate
oxygen atoms lining the pores.56
and I, but these distances do not offer an obvious explanation
for the ultra-low value of k00 (usually ∼1011−13 Hz in MOF
materials). However, this may be explained by the short
intramolecular hydrogen bond (1.91 Å) between the phenyl
protons and the triazine N atoms observed in the crystal
structure, thus restricting the rotation of the ring by affecting
its pre-exponential factor.
Although the effect of gas loading is not very strong in terms
of absolute values, it is an unexpected one (Figure 5). With
CO2 as the guest species, the concentration dependence at 123
K is as expected, with a higher gas loading resulting in a slower
rate of phenyl rotation. At the higher loading of ∼5 bar (at 298
K), the decrease in rotation rate is also more evident, even
without detailed numerical analysis of the observed line shape.
However, at 223 K this effect is inverted: with increased
loading of CO2, the rate of phenyl rotation actually increases, a
phenomenon previously unobserved in a MOF or any other
solid-state material.55 On a quantitative level, the effect is
clearly seen on an Arrhenius plot (Figure 7b) for the
corresponding rotational rate constants: the slope for the
CO2-loaded material is notably steeper in comparison to that
of the guest-free material. While not very pronounced for the
intermediate loading (1 bar), with E1 = 2.6 kJ mol−1 and k10/
2π = 2.3 × 106 Hz, the effect becomes more evident at higher
concentration (5 bar), with E2 = 4.2 kJ mol−1 and k20/2π = 7.6
× 106 Hz. In the latter case the barrier is approximately
doubled compared with that of the desolvated material, but the
collision factor is increased by 6-fold, so even though the
barrier has increased, the collision factor overrides this,
suggesting that CO2 blocks or breaks the internal H-bonding,
thus allowing more rapid rotation of the phenyl groups. It is
possible to readily observe the collision factor behavior because
Computational Modeling of Gas Binding Sites in
2
MFM-160. To understand further the observations from H
NMR spectroscopy and to help explain the hydrocarbon
selectivity demonstrated by MFM-160a, DFT calculations were
performed using the Q-Chem quantum chemistry package.36
An extensive search for binding sites between all guest
molecules and the linker fragment was performed, with
configurations showing the strongest binding and binding
energy ranges summarized in Table 1; Table S2 shows the full
range of binding configurations. The strongest binding of CO2
to the linker fragment was found to be at site A1 (Table 1), in
which the CO2 molecule interacts above the linker, with a
binding energy of −19.5 kJ mol−1. The interaction is
dominated by a strong electrostatic interaction between the
carbon of CO2 and the N-center of the central ring. This
interaction is enhanced by two weak hydrogen bonds between
the other oxygen of CO2 and nearby protons of the
neighboring phenyl ring and the bridging − NH group.
These interactions have a significant cooperative effect on the
binding of CO2 to the linker fragment. The slow rotation of the
phenyl ring, as observed by 2H NMR spectroscopy, was
attributed to a hydrogen bond between a phenyl proton and a
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Table 1. Optimized B3LYP/B3LYP/6-31+G* and B3LYP/6-311+G* Binding Energies and Structural Details of C21H18N6−
Guest Molecule Complexes Corresponding to These Strongest Binding Energies
N atom of the triazine core. Therefore, the increased rotation
upon CO2 loading may be explained by the weakening or
removal of this hydrogen bond upon CO2 binding at site A1.
Increased occupancy at this site at higher CO2 loading would
also explain the increased rate of rotation from the 1 bar- to the
5 bar-loaded sample. Overall, CO2 interacts more strongly with
the linker fragment than C2H2, giving a range of binding
energies from −19.5 to −12.4 kJ mol−1.
The strongest binding site for C2H2 is over the bridging
amine nitrogen between the triazine ring and the outer phenyl
rings, with a binding energy of −18.2 kJ mol−1 (site C1, Table
1). There is a cooperative binding effect, with the hydrogens of
C2H2 interacting with the triazine ring and the neighboring
phenyl ring, but the binding is dominated by an interaction
between the π-bonds of the C2H2 and the bridging nitrogen.
As with CO2, this interaction is likely to affect the hydrogen
bond between the phenyl proton and the triazine core, leading
2
to the increased phenyl rotation rate observed by H NMR
spectroscopy upon addition of 1 bar C2H2. At lower pressures
(0−0.32 bar), this site is unoccupied, as confirmed by the
values of E0 and k00 at 0.32 bar remaining the same as those
observed in the guest-free material. Between 0.32 and 1 bar,
where the Cu(II) paddlewheel sites are expected to be
saturated, the increased occupancy of this site disrupts the
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intramolecular hydrogen bond of the linker, and the rotation of
the phenyl group increases. It would have been interesting to
observe the effect of a higher loading of C2H2 on the rotational
dynamics, but there are well-established safety concerns with
the use of C2H2 above 1 bar.
The π-bond interaction of C2H2 with the linker leads to
stronger interactions overall compared to other hydrocarbons,
and as a result the C2H2 molecule interacts with a similar range
of binding energies to O2 (−13.3 to −18.2 kJ mol−1). These
comparable binding energies strongly suggest that the triazine
functionality is not responsible for the selectivity for C2H2 over
CO2. As stated earlier, it is likely that increased van der Waals
interactions between C2H2 and the framework in comparison
to those with CO2, as well as the higher affinity of the former
for the open Cu(II) sites, are responsible for the selective
uptake.
The ranges of interactions between the hydrocarbons C2H4
and C2H6 and the linker were also investigated and found to be
very similar: −11.7 to −16.2 kJ mol−1 and −10.2 to −16.3
kJ mol−1, respectively. The strongest interaction, between
C2H4 and the linker and also C2H6 and the linker, occurs
over the central triazine ring. This is an interaction between
the central carbon−carbon bond of the two hydrocarbons,
C2H4 and C2H6, and the delocalized π-system of the central
ring. On average, the binding of C2H4 is stronger than that of
C2H6 due to the strength of the interaction between the alkene
double bond and the linker.
To complete the computational investigation, we found that
the strongest binding of CH4 to the linker was in complex B
(Table 1), where the CH4 molecule interacts above the central
triazine ring to give a binding energy of −10.3 kJ mol−1. There
is a weak hydrogen bond between a CH4 hydrogen atom and a
nitrogen atom of the triazine ring. There are also additional
weak electrostatic interactions between other CH4 hydrogen
atoms and the central ring. The binding energy interactions
between CH4 and the linker are the weakest of all those
studied, consistent with the experimental isotherm data.
Experimental details, Scheme S1, Figures S1−S33, and
Tables S1−S3 (PDF)
Accession Codes
CCDC 1522524 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
Sihai Yang − School of Chemistry, University of Manchester,
Manchester M13 9PL, U.K.; orcid.org/0000-0002-1111-
9272; Email: sihai.yang@nottingham.ac.uk
Martin Schröder − School of Chemistry, University of
Manchester, Manchester M13 9PL, U.K.; orcid.org/0000-
0001-6992-0700; Email: m.schroder@nottingham.ac.uk
Daniil I. Kolokolov − Boreskov Institute of Catalysis, Siberian
Branch of Russian Academy of Sciences, Novosibirsk 630090,
Russia; Novosibirsk State University, Novosibirsk 630090,
Russia; Email: daniil.kolokolov@gmail.com
Timothy L. Easun − School of Chemistry, University of
Nottingham, Nottingham NG7 2RD, U.K.; School of
Chemistry, Cardiff University, Cardiff CF10 3AT, U.K.;
orcid.org/0000-0002-0713-2642; Email: EasunTL@
cardiff.ac.uk
Authors
William J. F. Trenholme − School of Chemistry, University of
Manchester, Manchester M13 9PL, U.K.; School of
Chemistry, University of Nottingham, Nottingham NG7
2RD, U.K.
Michelle Bound − School of Chemistry, University of
Nottingham, Nottingham NG7 2RD, U.K.
Stephen P. Argent − School of Chemistry, University of
Nottingham, Nottingham NG7 2RD, U.K.
Jamie A. Gould − School of Chemistry, University of
Nottingham, Nottingham NG7 2RD, U.K.; Faculty of
Science, Agriculture and Engineering, Newcastle University,
Newcastle upon Tyne NE1 7RU, U.K.
Jiangnan Li − School of Chemistry, University of Manchester,
Manchester M13 9PL, U.K.
Sarah A. Barnett − Diamond Light Source, Harwell Science
and Innovation Campus, Didcot, Oxfordshire OX11 0DE,
U.K.
CONCLUSIONS
■
We have demonstrated an energy- and cost-efficient route to a
large hexacarboxylate linker through microwave-assisted syn-
thesis. This has led to the synthesis of a new, highly porous
(3,24)-connected Cu(II) MOF, designated MFM-160. We
have shown that its activated form, MFM-160a, exhibits an
exceptional capacity for uptake of CO2 at 20 bar and 298 K
(110 wt%). We have also shown that the relatively poor uptake
of CO2 and CH4 at lower pressures (≤1 bar) makes MFM-
160a a material of interest for the purification of natural gas
and of acetylene, as confirmed by Henry’s law and IAST
calculations. A 2H NMR spectroscopic study of phenyl rotation
dynamics confirmed an ultra-low rotation barrier but very slow
phenyl rotation. The rotation was shown to increase upon gas
loading, a unique phenomenon not previously observed in a
solid-state material, which is attributed to the weakening of an
intramolecular hydrogen bond upon gas binding, leading to an
increased rate of rotation. The results of DFT calculations are
consistent with this, as both gases show clear binding
interactions near this hydrogen bond.
Alexander J. Blake − School of Chemistry, University of
Nottingham, Nottingham NG7 2RD, U.K.
Alexander G. Stepanov − Boreskov Institute of Catalysis,
Siberian Branch of Russian Academy of Sciences, Novosibirsk
630090, Russia; Novosibirsk State University, Novosibirsk
630090, Russia; orcid.org/0000-0003-2754-5273
Elena Besley − School of Chemistry, University of Nottingham,
Nottingham NG7 2RD, U.K.; orcid.org/0000-0002-
9910-7603
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.0c11202
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.0c11202.
■
sı
Notes
The authors declare no competing financial interest.
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(11) Liu, K.; Ma, D.; Li, B.; Li, Y.; Yao, K.; Zhang, Z.; Han, Y.; Shi,
Z. High storage capacity and separation selectivity for C2 hydro-
carbons over methane in the metal−organic framework Cu−TDPAT.
J. Mater. Chem. A 2014, 2, 15823−15828.
(12) Li, Q.; Wu, N.; Li, J.; Wu, D.; Li, Y. Amino-functionalized
water-stable metal−organic framework for enhanced C2H2/CH4
separation performance. Inorg. Chem. 2020, 59, 2631−2635.
(13) Xu, H.; Cai, J.; Xiang, S.; Zhang, Z.; Wu, C.; Rao, X.; Cui, Y.;
Yang, Y.; Krishna, R.; Chen, B.; Qian, G. A cationic microporous
metal−organic framework for highly selective separation of small
hydrocarbons at room temperature. J. Mater. Chem. A 2013, 1, 9916−
9921.
(14) He, Y.; Song, C.; Ling, Y.; Wu, C.; Krishna, R.; Chen, B. A new
MOF-5 homologue for selective separation of methane from C2
hydrocarbons at room temperature. APL Mater. 2014, 2, 124102−
124106.
(15) Barnett, B. R.; Gonzalez, M. I.; Long, J. R. Recent progress
towards light hydrocarbon separations using metal−organic frame-
works. Trends Chem. 2019, 1, 159−171.
(16) Rackley, S. A. Carbon capture and storage; Butterworth-
Heinemann, 2010.
ACKNOWLEDGMENTS
■
We thank the EPSRC, the University of Nottingham, and the
University of Manchester for funding. This project has received
funding to M.S. from the European Research Council (ERC)
under the European Union’s Horizon 2020 research and
innovation programme (grant agreement no. 742401, NANO-
CHEM). We are very grateful to Diamond Light Source for
access to Beamline I19. W.J.F.T. thanks Johnson Matthey for
funding and Dr. Hugh Hamilton and Dr. Ian Casely for
valuable discussions. T.L.E. gratefully acknowledges the Royal
Society for the award of a University Research Fellowship. M.S.
and D.I.K. gratefully acknowledge receipt of the Royal Society
International Exchanges Scheme grant ref IE150114. D.I.K.
also acknowledges the support from the Russian Science
Foundation, project 17-73-10135. D.I.K. and A.G.S. also
acknowledge the support of Ministry of Science and High
Education of the Russian Federation (project AAAA-A21-
121011390053-4, Boreskov Institute of Catalysis). E.B. and
M.B. acknowledge the High Performance Computing (HPC)
Facility at the University of Nottingham for providing
computational time. J.L. also thanks the China Scholarship
Council (CSC) for funding.
(17) Li, J.-R.; Ma, Y.; McCarthy, M. C.; Sculley, J.; Yu, J.; Jeong, H.-
K.; Balbuena, P. B.; Zhou, H.-C. Carbon dioxide capture-related gas
adsorption and separation in metal−organic frameworks. Coord.
Chem. Rev. 2011, 255, 1791−1823.
(18) Zheng, B.; Bai, J.; Duan, J.; Wojtas, L.; Zaworotko, M. J.
Enhanced CO2 binding affinity of a high-uptake rht-type metal−
organic framework decorated with acylamide groups. J. Am. Chem.
Soc. 2011, 133, 748−751.
(19) Yuan, D.; Zhao, D.; Sun, D.; Zhou, H.-C. An isoreticular series
of metal−organic frameworks with dendritic hexacarboxylate ligands
and exceptionally high gas-uptake capacity. Angew. Chem., Int. Ed.
2010, 49, 5357−5361.
(20) Furukawa, H.; Ko, N.; Go, Y. B.; Aratani, N.; Choi, S. B.; Choi,
E.; Yazaydin, A. O.; Snurr, R. Q.; O’Keeffe, M.; Kim, J.; Yaghi, O. M.
Ultrahigh porosity in metal−organic frameworks. Science 2010, 329,
424−428.
REFERENCES
■
(1) Chen, K. J.; Scott, H. S.; Madden, D. G.; Pham, T.; Kumar, A.;
Bajpai, A.; Lusi, M.; Forrest, K. A.; Space, B.; Perry, J. J.; Zaworotko,
M. J. Benchmark C2H2/CO2 and CO2/C2H2 separation by two
closely related hybrid ultramicroporous materials. Chem 2016, 1,
753−765.
(2) Ding, M.; Flaig, R. W.; Jiang, H. L.; Yaghi, O. M. Carbon capture
and conversion using metal−organic frameworks and MOF-based
materials. Chem. Soc. Rev. 2019, 48, 2783−2828.
(3) Alsmail, N. H.; Suyetin, M.; Yan, Y.; Cabot, R.; Krap, C. P.; Lu,
̈
J.; Easun, T. L.; Bichoutskaia, E.; Lewis, W.; Blake, A. J.; Schröder, M.
Analysis of high and selective uptake of CO2 in an oxamide-containing
{Cu2(OOCR)4}-based metal−organic framework. Chem. - Eur. J.
2014, 20, 7317−7324.
(21) Llewellyn, P. L.; Bourrelly, S.; Serre, C.; Vimont, A.; Daturi, M.;
Hamon, L.; De Weireld, G.; Chang, J.-S.; Hong, D.-Y.; Kyu Hwang,
Y.; Hwa Jhung, S.; Férey, G. High uptakes of CO2 and CH4 in
mesoporous metal−organic frameworks MIL-100 and MIL-101.
Langmuir 2008, 24, 7245−7250.
(4) An, J.; Geib, S. J.; Rosi, N. L. High and selective CO2 uptake in a
cobalt adeninate metal−organic framework exhibiting pyrimidine- and
amino-decorated pores. J. Am. Chem. Soc. 2010, 132, 38−39.
(5) Millward, A. R.; Yaghi, O. M. Metal−organic frameworks with
exceptionally high capacity for storage of carbon dioxide at room
temperature. J. Am. Chem. Soc. 2005, 127, 17998−17999.
(6) Forse, A. C.; Milner, P. J.; Lee, J. H.; Redfearn, H. N.; Oktawiec,
J.; Siegelman, R. L.; Martell, J. D.; Dinakar, B.; Porter-Zasada, L. B.;
Gonzalez, M. I.; Neaton, J. B.; Long, J. R.; Reimer, J. A. Elucidating
CO2 chemisorption in diamine-appended metal−organic frameworks.
J. Am. Chem. Soc. 2018, 140, 18016−18031.
(7) Yang, S.; Sun, J.; Ramirez-Cuesta, A. J.; Callear, S. K.; David, W.
I. F.; Anderson, D. P.; Newby, R.; Blake, A. J.; Parker, J. E.; Tang, C.
C.; Schröder, M. Selectivity and direct visualization of carbon dioxide
and sulfur dioxide in a decorated porous host. Nat. Chem. 2012, 4,
887−894.
(8) Carrington, E. J.; McAnally, C. A.; Fletcher, A. J.; Thompson, S.
P.; Warren, M.; Brammer, L. Solvent-switchable continuous-breathing
behaviour in a diamondoid metal−organic framework and its
influence on CO2 versus CH4 selectivity. Nat. Chem. 2017, 9, 882−
889.
(9) Yang, L.; Qian, S.; Wang, X.; Cui, X.; Chen, B.; Xing, H. Energy-
efficient separation alternatives: metal−organic frameworks and
membranes for hydrocarbon separation. Chem. Soc. Rev. 2020, 49,
5359−5406.
(10) Hu, F.; Di, Z.; Wu, M.; Li, J. Building a robust 3D Ca-MOF by
a new square Ca4O SBU for purification of natural gas. Dalt. Trans.
2020, 49, 8836−8840.
(22) Czaja, A. U.; Trukhan, N.; Muller, U. Industrial applications of
̈
metal−organic frameworks. Chem. Soc. Rev. 2009, 38, 1284−1293.
(23) Liu, K.; Li, B.; Li, Y.; Li, X.; Yang, F.; Zeng, G.; Peng, Y.;
Zhang, Z.; Li, G.; Shi, Z.; Feng, S.; Song, D. An N-rich metal−organic
framework with an rht topology: high CO2 and C2 hydrocarbons
uptake and selective capture from CH4. Chem. Commun. 2014, 50,
5031−5033.
(24) Yang, S.; Ramirez-Cuesta, A. J.; Newby, R.; Garcia-Sakai, V.;
Manuel, P.; Callear, S. K.; Campbell, S. I.; Tang, C. C.; Schröder, M.
Supramolecular binding and separation of hydrocarbons within a
functionalized porous metal−organic framework. Nat. Chem. 2015, 7,
121−129.
(25) Li, B.; Zhang, Z.; Li, Y.; Yao, K.; Zhu, Y.; Deng, Z.; Yang, F.;
Zhou, X.; Li, G.; Wu, H.; Nijem, N.; Chabal, Y. J.; Lai, Z.; Han, Y.;
Shi, Z.; Feng, S.; Li, J. Enhanced binding affinity, remarkable
selectivity, and high capacity of CO2 by dual functionalization of a rht-
type metal-organic framework. Angew. Chem., Int. Ed. 2012, 51,
1412−1415.
(26) Luebke, R.; Eubank, J. F.; Cairns, A. J.; Belmabkhout, Y.;
Wojtas, L.; Eddaoudi, M. The unique rht-mof platform, ideal for
pinpointing the functionalization and CO2 adsorption relationship.
Chem. Commun. 2012, 48, 1455−1457.
(27) Yan, Y.; Lin, X.; Yang, S.; Blake, A. J.; Dailly, A.; Champness, N.
R.; Hubberstey, P.; Schröder, M. Exceptionally high H2 storage by a
metal−organic polyhedral framework. Chem. Commun. 2009, 1025−
1027.
3357
https://dx.doi.org/10.1021/jacs.0c11202
J. Am. Chem. Soc. 2021, 143, 3348−3358

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
(28) Yan, Y.; Telepeni, I.; Yang, S.; Lin, X.; Kockelmann, W.; Dailly,
A.; Blake, A. J.; Lewis, W.; Walker, G. S.; Allan, D. R.; Barnett, S. A.;
Champness, N. R.; Schröder, M. Metal-organic polyhedral frame-
works: high H2 adsorption capacities and neutron powder diffraction
studies. J. Am. Chem. Soc. 2010, 132, 4092−4094.
(29) Yan, Y.; Blake, A. J.; Lewis, W.; Barnett, S. A.; Dailly, A.;
Champness, N. R.; Schröder, M. Modifying cage structures in metal-
organic polyhedral frameworks for H2 storage. Chem. - Eur. J. 2011,
17, 11162−11170.
(30) Yan, Y.; Yang, S.; Blake, A. J.; Lewis, W.; Poirier, E.; Barnett, S.
A.; Champness, N. R.; Schröder, M. A mesoporous metal−organic
framework constructed from a nanosized C3-symmetric linker and
[Cu24(isophthalate)24] cuboctahedra. Chem. Commun. 2011, 47,
9995−9997.
(31) Yan, Y.; Suyetin, M.; Bichoutskaia, E.; Blake, A. J.; Allan, D. R.;
Barnett, S. A.; Schröder, M. Modulating the packing of
[Cu24(isophthalate)24] cuboctahedra in a triazole-containing metal−
organic polyhedral framework. Chem. Sci. 2013, 4, 1731−1736.
(32) Yan, Y.; Yang, S.; Blake, A. J.; Schröder, M. Studies on metal−
organic frameworks of Cu(II) with isophthalate linkers for hydrogen
surfaces for highly selective CO2/CH4 and C2H2/CH4 gas sorption at
room temperature. Inorg. Chem. 2011, 50, 3442−3446.
(42) Li, J.-R.; Tao, Y.; Yu, Q.; Bu, X.-H.; Sakamoto, H.; Kitagawa, S.
Selective gas adsorption and unique structural topology of a highly
stable guest-free zeolite-type MOF material with N-rich chiral open
channels. Chem. - Eur. J. 2008, 14, 2771−2776.
(43) Samsonenko, D. G.; Kim, H.; Sun, Y.; Kim, G.-H.; Lee, H.-S.;
Kim, K. Microporous magnesium and manganese formates for
acetylene storage and separation. Chem. - Asian J. 2007, 2, 484−488.
(44) Matsuda, R.; Kitaura, R.; Kitagawa, S.; Kubota, Y.; Belosludov,
R. V.; Kobayashi, T. C.; Sakamoto, H.; Chiba, T.; Takata, M.;
Kawazoe, Y.; Mita, Y. Highly controlled acetylene accommodation in
a metal−organic microporous material. Nature 2005, 436, 238−241.
(45) Mukherjee, S.; Sensharma, D.; Chen, K.-J.; Zaworotko, M. J.
Crystal engineering of porous coordination networks to enable
separation of C2 hydrocarbons. Chem. Commun. 2020, 56, 10419−
10441.
(46) Lin, R. B.; Li, L.; Wu, H.; Arman, H.; Li, B.; Lin, R. G.; Zhou,
W.; Chen, B. Optimized separation of acetylene from carbon dioxide
and ethylene in a microporous material. J. Am. Chem. Soc. 2017, 139,
8022−8028.
(47) Myers, A. L.; Prausnitz, J. M. Thermodynamics of mixed-gas
adsorption. AIChE J. 1965, 11, 121−127.
(48) Komoroski, R. A. High resolution NMR spectroscopy of synthetic
polymers in bulk; VCH Publishers: New York, 1986.
storage. Acc. Chem. Res. 2014, 47, 296−307.
̈
(33) Farha, O. K.; Ozgu
̈
r Yazaydın, A.; Eryazici, I.; Malliakas, C. D.;
Hauser, B. G.; Kanatzidis, M. G.; Nguyen, S. T.; Snurr, R. Q.; Hupp, J.
T. De novo synthesis of a metal−organic framework material featuring
ultrahigh surface area and gas storage capacities. Nat. Chem. 2010, 2,
944−948.
(49) Kolokolov, D. I.; Stepanov, A. G.; Guillerm, V.; Serre, C.; Frick,
B.; Jobic, H. Probing the dynamics of the porous Zr terephthalate
(34) Farha, O. K.; Eryazici, I.; Jeong, N. C.; Hauser, B. G.; Wilmer,
2
UiO-66 framework using H NMR and neutron scattering. J. Phys.
̈
C. E.; Sarjeant, A. A.; Snurr, R. Q.; Nguyen, S. T.; Yazaydın, A. O.;
Chem. C 2012, 116, 12131−12136.
Hupp, J. T. Metal−organic framework materials with ultrahigh surface
areas: is the sky the limit? J. Am. Chem. Soc. 2012, 134, 15016−15021.
(35) Farha, O. K.; Wilmer, C. E.; Eryazici, I.; Hauser, B. G.; Parilla,
P. A.; O’Neill, K.; Sarjeant, A. A.; Nguyen, S. T.; Snurr, R. Q.; Hupp,
J. T. Designing higher surface area metal−organic frameworks: are
triple bonds better than phenyls? J. Am. Chem. Soc. 2012, 134, 9860−
9863.
(50) Schmidt, C.; Kuhn, K. J.; Spiess, H. W. Distribution of
correlation times in glassy polymers from pulsed deuteron NMR.
Frontiers in Polymer Science; Steinkopff: Darmstadt, 1985; Vol. 71, pp
71−76.
(51) Macho, V.; Brombacher, L.; Spiess, H. W. The NMR-
WEBLAB: An internet approach to NMR lineshape analysis. Appl.
Magn. Reson. 2001, 20, 405−432.
(52) Kolokolov, D. I.; Stepanov, A. G.; Jobic, H. Mobility of the 2-
methylimidazolate linkers in ZIF-8 probed by 2H NMR: saloon doors
for the guests. J. Phys. Chem. C 2015, 119, 27512−27520.
(53) Kirstein, O.; Prager, M.; Dimeo, R. M.; Desmedt, A. Rotational
dynamics of methyl groups in m-xylene. J. Chem. Phys. 2005, 122,
No. 014502.
(54) Gabuda, S. P.; Kozlova, S. G.; Samsonenko, D. G.; Dybtsev, D.
N.; Fedin, V. P. Quantum rotations and chiral polarization of qubit
prototype molecules in a highly porous metal−organic framework: 1H
NMR T1 study. J. Phys. Chem. C 2011, 115, 20460−20465.
(55) Khudozhitkov, A. E.; Arzumanov, S. S.; Kolokolov, D. I.;
Kholdeeva, O. A.; Freude, D.; Stepanov, A. G. Guests like gear levers:
donor binding to coordinatively unsaturated metal sites in MIL-101
controls the linker′s rotation. Chem. - Eur. J. 2019, 25, 5163−5168.
(56) Zhang, Z.; Xiang, S.; Chen, B. Microporous metal−organic
frameworks for acetylene storage and separation. CrystEngComm
2011, 13, 5983−5992.
(36) Shao, Y.; Molnar, L. F.; Jung, Y.; Kussmann, J.; Ochsenfeld, C.;
Brown, S. T.; Gilbert, A. T. B.; Slipchenko, L. V.; Levchenko, S. V.;
O’Neill, D. P.; DiStasio, R. A., Jr; Lochan, R. C.; Wang, T.; Beran, G.
J. O.; Besley, N. A.; Herbert, J. M.; Yeh Lin, C.; Van Voorhis, T.;
Hung Chien, S.; Sodt, A.; Steele, R. P.; Rassolov, V. A.; Maslen, P. E.;
Korambath, P. P.; Adamson, R. D.; Austin, B.; Baker, J.; Byrd, E. F.
C.; Dachsel, H.; Doerksen, R. J.; Dreuw, A.; Dunietz, B. D.; Dutoi, A.
D.; Furlani, T. R.; Gwaltney, S. R.; Heyden, A.; Hirata, S.; Hsu, C.-P.;
Kedziora, G.; Khalliulin, R. Z.; Klunzinger, P.; Lee, A. M.; Lee, M. S.;
Liang, W.; Lotan, I.; Nair, N.; Peters, B.; Proynov, E. I.; Pieniazek, P.
A.; Min Rhee, Y.; Ritchie, J.; Rosta, E.; David Sherrill, C.; Simmonett,
A. C.; Subotnik, J. E.; Woodcock, L. H., III; Zhang, W.; Bell, A. T.;
Chakraborty, A. K.; Chipman, D. M.; Keil, F. J.; Warshel, A.; Hehre,
W. J.; Schaefer, H. F., III; Kong, J.; Krylov, A. I.; Gill, P. M. W.; Head-
Gordon, M. Advances in methods and algorithms in a modern
quantum chemistry program package. Phys. Chem. Chem. Phys. 2006,
8, 3172−3191.
(37) Sha, Y.; Dong, Y. Microwave assisted synthesis of 2,4,6-
triarylamino-1,3,5-triazines as potential UV absorbent. Synth.
Commun. 2003, 33, 2599−2604.
(38) Spek, A. L. PLATON SQUEEZE: A tool for the calculation of
the disordered solvent contribution to the calculated structure factors.
Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 9−18.
(39) Peng, Y. L.; Pham, T.; Li, P.; Wang, T.; Chen, Y.; Chen, K. J.;
Forrest, K. A.; Space, B.; Cheng, P.; Zaworotko, M. J.; Zhang, Z.
Robust ultramicroporous metal−organic frameworks with benchmark
affinity for acetylene. Angew. Chem., Int. Ed. 2018, 57, 10971−10975.
(40) Pei, J.; Shao, K.; Wang, J. X.; Wen, H. M.; Yang, Y.; Cui, Y.;
Krishna, R.; Li, B.; Qian, G. A chemically stable Hofmann-type
metal−organic framework with sandwich-like binding sites for
benchmark acetylene capture. Adv. Mater. 2020, 32, 1908275.
(41) Chen, Z.; Xiang, S.; Arman, H. D.; Mondal, J. U.; Li, P.; Zhao,
D.; Chen, B. Three-dimensional pillar-layered copper(II) metal−
organic framework with immobilized functional OH groups on pore
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J. Am. Chem. Soc. 2021, 143, 3348−3358