Synthesis of multifunctional metal-organic frameworks and tuning the functionalities with pendant ligands

Article abstract of DOI:10.1039/d0dt03012k

A series of multifunctional metal-organic frameworks (MOFs), SNU-170-SNU-176, has been synthesized using ligands, in which various functional pendants such as -NH2, -SMe, -OMe, -OEt, -OPr, and -OBu are attached to the phenyl ring of 4-(2-carboxyvinyl)benz

Full text of DOI:10.1039/d0dt03012k

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DOI: 10.1039/D0DT03012K
ARTICLE
Synthesis of Multifunctional Metal-Organic Frameworks and
Tuning the Functionalities by Organic Pendant of Ligand†
Thazhe Kootteri Prasada,b and Myunghyun Paik Suh*a
Received 00th January 20xx,
Accepted 00th January 20xx
A series of multifunctional metal-organic frameworks (MOFs), SNU-170 ~ SNU-176, have been synthesized by using the
ligands, in which various functional pendant such as -NH2, -SMe, -OMe, -OEt, -OPr, and –OBu is attached to the phenyl ring
of 4-(2-carboxyvinyl)benzoic acid. The MOFs are isostructural but the interpenetration depends on the pendant group of the
ligand. The MOFs exhibit high adsorption capacities of H2, CO2, and CH4 gases, ligand-based photoluminescence, and
chemical sensing abilities, all being affected by the pendant group. All of the as-synthesized MOFs can sense nitro-aromatics
by the luminescence quenching, and some of the activated MOFs can sense the type of solvents by the altered emission
maxima with enhanced intensity. In particular, SNU-176 synthesized from a mixture of two different ligands with –SMe and
-OMe pendants shows higher gas adsorption capacities than the MOFs synthesized from the individual ligands (SNU-171
and SNU-172). It also shows the ability to differentiate nitrobenzene (NB) and 2,4-dinitrotoluene (DNT) unlike the MOFs
constructed of the single ligands.
DOI: 10.1039/x0xx00000x
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Introduction
properties in the visible region, and chemical sensing abilities for
nitro-organics.
The design and synthesis of metal-organic frameworks (MOFs)
have attracted great attention due to the potential applications
of MOFs in gas storage,1-6 gas separation,7,8 catalysis,9-11 and
chemical sensing.12-14 It has been well known that the function
of the MOFs can be tuned by the choice of metal and organic
building blocks, but the strategy to generate the multi-
functionality in MOFs has been less explored.15,16 Furthermore,
despite numerous reports for the luminescent MOFs, the
application of them in chemical sensing is rather limited.12,17,18
Here, we report the synthesis of multifunctional MOFs by using
the aromatic carboxylate ligands having the functional organic
pendants on the aryl ring. We previously reported versatile MOFs
that have high surface areas and high gas uptake capacities.6,19-22 One
of which was SNU-70 that was constructed from 4-(2-
carboxyvinyl)benzoic acid (H2CVB) and Zn2+ salt.22 SNU-70’ had
unusually high BET surface area (5290 m2g-1) and high H2 and CO2 gas-
sorption capacities. To provide additional light-emitting and sensing
properties to the MOF, we have synthesized a series of ligands,
H2CVB-XR, where the phenyl ring of H2CVB is functionalized with
various electron-rich substituents such as -NH2, -SMe, -OMe, -OEt, -
OPr, and –OBu, and constructed new zinc(II) MOFs by using the
ligands (Scheme 1). The resulting MOFs show multifunctional
properties including high gas adsorption capacities, light-emitting
Scheme 1 Synthesis of MOFs from the functionalized 4-(2-carboxyvinyl)benzoic
acids (H2CVB-XR).
Results and discussion
Syntheses and X-ray crystal structures of SNU-170 ~ SNU-176
We synthesized a series of ligands, H2CVB-XR, where XR is -
NH2, -SMe, -OMe, -OEt, -OPr, and –OBu (see ESI†). By heating
these ligands and Zn(NO3)2·6H2O at 105 oC in N,N-
dimethylformamide (DMF) for 24 h, we have obtained the MOF
crystals
of
[Zn4O(CVB-NH2)3]·18DMF·H2O
(SNU-171),
(SNU-170),
[Zn4O(CVB-
[Zn4O(CVB-SMe)3]·7DMF·3H2O
OMe)3]·7DMF·3H2O (SNU-172), [Zn4O(CVB-OEt)3]·7DMF·2H2O
(SNU-173), [Zn4O(CVB-OPr)3]·16DMF·3H2O (SNU-174), and
[Zn4O(CVB-OBu)3]·15DMF·3H2O (SNU-175). Also, we have
prepared [Zn4O(CVB-SMe)(CVB-OMe)2]·7DMF·3H2O (SNU-176)
by using a mixture of H2CVB-SMe and H2CVB-OMe (ESI†).
Single crystal X-ray diffraction studies reveal that SNU-170 ~
SNU-174 have similar cubic-net structures consisting of [Zn4O]6+
octahedral building units and linear dicarboxylate linkers (Fig. 1
and Table S1, ESI†). In the crystal structures, the ligands were
not well resolved due to the severe structural disorders and
thus their average conformations are presented. The
connections of the carboxylate groups of the ligand between
the [Zn4O] units indicate that the phenyl ring and the vinyl group
a. Department of Chemistry, Seoul National University
1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
E-mail: mpsuh@snu.ac.kr
Dr. Prasad’s current address: Centre for Chemical Biology and Therapeutics,
Institute for Stem Cell Science and Regenerative Medicine, Bellary Road,
Bangalore 560 065, India.
† Electronic Supplementary Information (ESI) available: CCDC 1440326-1440330.
For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/x0xx00000x
b.
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DOI: 10.1039/D0DT03012K
Fig. 1 X-ray crystal structures: (a) non-interpenetrated SNU-170; (b) doubly
interpenetrated SNU-171. The disordered parts and pendant functional groups
were modeled for clarity.
linked by a C-C single bond are located on the same plane. For
SNU-175 and SNU-176, the single crystals with the quality for X-
ray diffraction analysis could not be obtained, and their
structures were confirmed by the PXRD patterns. SNU-170 and
SNU-174 have non-interpenetrated structures, and SNU-171
~SNU-173 have doubly interpenetrated frameworks. Based on
the PXRD patterns, SNU-175 with –OBu pendant has a similar
structure to that of SNU-174 with -OPr pendant, and SNU-176
incorporating both –SMe and -OMe pedants has a similar
structure to SNU-171 and SNU-172 (Fig. S8, ESI†). The NMR
spectrum of SNU-176, measured in DMSO-d6/DCl, indicates that
it contains about 33% –SMe and 66% –OMe pendant groups
(Fig. S10, ESI†). The results reveal that the linker with a rigid
group (-NH2) produces a non-interpenetrated framework (SNU-
170), whereas the linkers with the rather small and flexible
functional groups such as -SMe, -OMe, and -OEt yield doubly
interpenetrated frameworks. The linkers with flexible but
bulkier substituents such as –OPr and -OBu result in non-
interpenetrated structures to accommodate the bulky groups in
the pores.
Fig. 2 Gas adsorption isotherms, (a) N2 at 77 K, (b) H2 at 77 K, (c) CO2 at 298 K,
and (d) CH4 at 298 K. SNU-170’ (red, square), SNU-171’ (blue, circle), SNU-172’
(green, triangle), SNU-173’ (pink, inverted triangle), SNU-174’ (violet, diamond),
and SNU-175’ (orange, rotated triangle). Filled shapes: adsorption; open shapes:
desorption. For SNU-176’, see Fig. S11, ESI†.
revealed by the PXRD patterns showing the altered peak
positions and peak heights compared with those of the as-
synthesized (Fig. S2-S8, ESI†). On activation, non-
interpenetrated SNU-170’ and SNU-175’ become amorphous
but regain the crystallinity by immersion in DMF for 1 h (Fig. S9,
ESI†). The N2 adsorption isotherms of SNU-170’ ~ SNU-176’
indicate that non-interpenetrated SNU-170’ has the highest BET
(Langmuir) surface area, 3200 (3970) m2 g-1, among the present
MOFs. The BET surface areas of doubly interpenetrated SNU-
171’ ~ SNU-173’ are significantly lower than that of SNU-170’,
but higher than SNU-174’ and SNU-175’ that incorporate bulky
pendants, –OPr and –OBu, respectively. Doubly interpenetrated
Gas sorption properties of SNU-170’ ~ SNU-176’
We measured adsorption isotherms of N2, H2, CO2, and CH4
gases after activating the crystals of SNU-170 ~ SNU-176 with
supercritical CO2 (Fig. 2 and Fig. S11, ESI†). The data are
summarized in Table 1. The activated MOFs, SNU-171’ ~ SNU-
174’, and SNU-176’ undergo structural transformations as
Table 1 The gas adsorption properties of MOFs
SNU-176’
SNU-170’
SNU-171’
SNU-172’
SNU-173’
SNU-174’
SNU-175’
SNU-70’
BET S.A. [m2 g-1]
3200
1.24
154
81
5.40
361
39
21
20.9
36
1610
0.67
199
131
7.40
374
96
45
27
189
20
12
1600
0.64
207
132
7.41
363
91
1510
0.61
201
135
8.43
353
97
548
0.27
91
16
-
8
7
-
62
13
10
1780
0.74
235
141
7.63
413
101
48
26.3
186
21
12
17.4
5290
2.17
134
78
5.12
1127
31
18
17.2
54
Vpore [cm3 g-1]
H2, 77 K [cm3 g-1]a
H2, 87 K [cm3 g-1]a
Qst (H2) [kJ mol-1]b
CO2, 195 K [cm3 g-1]a
CO2, 273 K [cm3 g-1]a
CO2, 298 K [cm3 g-1]a
Qst (CO2) [kJ mol-1]c
CH4, 195 K [cm3 g-1]a
CH4, 273 K [cm3 g-1]a
CH4, 298 K [cm3 g-1]a
Qst (CH4) [kJ mol-1]c
59
6.75
244
29
14
26.2
54
8
4
-
46
51
30.9
166
19
11
16.6
30.5
175
22
12
23.1
31.8
-
-
-
-
11
6
-
11
7
9.4
18.7
a At 1 atm. b Isosteric heat of adsorption at zero coverage. c Isosteric heat of adsorption at low loading.
2 | J. Name., 2012, 00, 1-3
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Fig. 3 Photoluminescence spectra of MOFs. (a) As synthesized samples,
View Article Online
SNU-171’ ~ SNU-173’, despite the smaller surface areas, show
higher uptake capacities of H2 gas at 77 K and 1 atm and CO2 gas
excitation at 400 nm for SNU-170, 390 nm for SNU-171, 350 nm for SNU-176,
DOI: 10.1039/D0DT03012K
and 330 nm for the rest of the samples. (b) After supercritical CO2 activation,
excitation at 400 nm for SNU-170’, 390 nm for SNU-171’, 350 nm for SNU-176’,
and 330 nm for the rest of the samples.
at 298
K and 1 atm, compared with those of non-
interpenetrated SNU-170’ and SNU-174’. They adsorb 45 ~ 51
cm3 g-1 (2.0 ~ 2.3 mmol g-1) of CO2 at 298 K and 1 atm, about a
half, compared with the top 20 MOFs with high CO2 adsorption
capacity.7 Interestingly, SNU-176’ constructed of two different
ligands with –SMe and -OMe pendants shows higher adsorption
capacities for H2, CO2, and CH4 gases as well as higher BET
surface area and DR pore volume than the MOFs composed of
the respective individual ligands, SNU-171’ and SNU-172’. In
particular, the isosteric heats (Qst) of H2, CO2, and CH4
adsorption in SNU-170’ ~ SNU-176’, which contain functional
organic pendants, are significantly higher than those in SNU-70’
having no pendant (Table 1). This indicates stronger interaction
between the gases and the organic functional pedants of the
MOFs. Furthermore, interpenetrated frameworks (SNU-171’ ~
SNU-173’) exhibit higher Qst (H2, CO2, CH4) values than non-
interpenetrated ones (SNU-170’ and SNU-174’), similar to the
other cases.4,22
emission maxima that appear at significantly longer
wavelengths, by 74 ~ 87 nm, than those with XR = OMe, OEt,
OPr, and OBu. In the absence of an electron-donating group at
the benzene ring of the ligand, the emission would be weak and
takes place at a shorter wavelength (UV region), and hence is
not shown in the visible region. For the ligands with electron-
donating substituents -XR, however, there exists more electron
density in the benzene ring, and the emission takes place in the
longer wavelength, visible region. The stronger the electron-
donating nature of -XR, the longer the wavelength of the
emission spectrum, XR = -NH2> -SMe> -OR. The relative intensity
of the emission spectrum of H2CVB-NH2 is about eight times
stronger than that of H2CVB-SMe and nearly twice stronger than
those of H2CVB-OR (R = Me, Et, Pr, Bu). The quantum yield of
H2CVB-NH2 in DMF is 0.38, compared with 0.54 of quinine
sulphate. For the other ligands, the quantum yields are too low
to calculate with reliability. The solid-state PL spectra of the
ligands show broader and red-shifted emission bands compared
with those of the DMF solutions (Table 2), like the previous
report.24
The as-synthesized MOFs are photo-luminescent due to their
luminescent ligands. The MOFs show red-shifted emission
bands compared with those of the DMF solutions of the ligands,
but blue-shifted emission bands compared with the
corresponding solid ligands (Table 2). The emission shifts of the
MOFs compared to the ligands may be related to the metal-
ligand coordination that offers an electron-withdrawing effect
on the ligand and/or the increased distance between the
ligands in the MOF crystals, which affect the intra-ligand
HOMO–LUMO energy gap.25,26
To evaluate the CO2 separation and capture ability of
present MOFs, the separation parameters23 for the vacuum
swing adsorption (VSA) process are calculated for the gas
mixtures similar to flue gas (1:9 CO2/N2) and landfill gas (1:1
CO2/CH4) and summarized in Table S2, ESI†. The results indicate
that SNU-176’ is the best material among the present MOFs for
ads
flue gas separation by the VSA process (12 = 15.34 and S =
25.0). The characteristic pore properties generated from the
two different functional groups (-SMe and -OMe) in SNU-176’
might give rise to the phenomena.
Photoluminescence properties of ligands and MOFs
The DMF solution of H2CVB-NH2 exhibits characteristic
fluorescence in the visible region, which can be seen even by
the naked eyes, contrary to the non-emissive H2CVB.
Therefore, the photoluminescence (PL) properties of the
H2CVB-XR ligands and the MOFs are investigated. The PL
emission spectra of the ligands (1 x 10-4 M) in the DMF
solutions are significantly affected by the functional groups
(Table 2 and Fig. S12, ESI†). The solutions of H2CVB-XR with XR
Upon the removal of DMF and H2O guest solvent molecules
from SNU-170 ~ SNU-176 by using supercritical CO2, the
resulting activated MOFs exhibit significantly decreased
luminescence intensities with the red-shifted emission by 11 nm
~ 30 nm, compared with the PL spectra of the as-synthesized
MOFs (Table 2, Fig. 3, and Fig. S13, ESI†). A similar significant
=
N H
a n d
S M e
s h o w
t h e
2
Table 2. Photo-luminescent properties of ligands and MOFs
Ligands, nm MOFs, nm
DMF soln. a Solid b
As-syn c
512
Dried d
536
CVB-NH2
493
478
404
405
406
405
525
499
460
432
430
420
-
SNU-170
SNU-171
SNU-172
SNU-173
SNU-174
SNU-175
SNU-176
CVB-SMe
CVB-OMe
CVB-OEt
471
482
412
442
413
440
CVB-OPr
412
442
CVB-OBu
CVB-SMe-OMe
414
440
-
472
470
a 1x 10-4 M; Excitation at 395 nm for H2CVB-NH2, 362 nm for H2CVB-SMe, and 350
nm for the rest of the samples. b Excitation at 360 nm for H2CVB-NH2 and H2CVB-
SMe, and 320 nm for the rest of the samples. c, d Excitation at 400 nm for SNU-170,
390 nm for SNU-171, and 330 nm for the rest of the samples.
This journal is © The Royal Society of Chemistry 20xx
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and Fig. S14, ESI†). Furthermore, the emission maxima of the
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MOFs depend on the type of solvents, suDggOeI:s1t0in.1g03t9h/eDi0rDsTo0lv30e1n2tK-
sensing capability. The non-polar aromatic solvents like
benzene and toluene show the most red-shifted emissions, in
particular for SNU-172’ and SNU-173’ by 6 ~ 10 nm, compared
with other solvents, which accords with the previous
reports.26,27 The shifts of the emission maxima depending on
the solvents are attributed to the interaction between the
ligands of the MOFs and the solvents. The solvents with
different polarities and shapes interact differently with the
ligands in the MOF pores, leading to the change in the intra-
ligand HOMO–LUMO energy gap.
The development of sensing materials to detect nitro
derivatives of organic compounds, which are strong explosives,
is important.18 When a drop of 0.5 M DMF solution of
nitrobenzene (NB) or that of 2,4-dinitrotoluene (DNT) is added
to the as-synthesized MOFs, the PL emission spectra of SNU-170
~ SNU-176 are quenched (Fig. S15, ESI†), implying that the
MOFs can sense nitro-organics. The PL quenching must be
attributed to the photo-induced electron transfer from
electron-donating ligand to the electron-deficient nitro-
aromatics upon excitation, which is a deactivation process of
PL.18, 29 While the quenched PL spectra of SN170 ~ SNU-175
upon the addition of NB and DNT solutions show no noticeable
difference, those of SNU-176 display a small difference
between NB and DNT in the peak positions, max = 469 nm for
NB and 467 nm for DNT (Fig. S16, ESI†). This suggests that the
judicious selection and introduction of multiple ligands to a
MOF may be a good strategy for developing MOF materials that
not only detect the general nitro-organics but also pinpoint the
target compounds.
Fig. 4 Time-dependent regeneration of photoluminescence spectra of activated
SNU-170’ on the addition of a few drops of DMF. Excitation at 380 nm. A black
line corresponds to the activated sample of SNU-170’.
decrease in the emission intensity and the red-shift emission
were previously observed for other activated MOFs, and they
were explained by the solvent effect of the guest molecules.27
As shown in Fig. 4, the PL emission intensity and the
emission wavelength of the activated MOF restore upon re-
solvation. On the addition of a few drops of DMF to the
activated SNU-170’, the emission band undergoes a blue-shift
from 536 nm to 510 nm, and its relative intensity increases to
reach the saturation stage in ca. 60 min, suggesting a slow
structural rearrangement on re-solvation. As described in the X-
ray structures of MOFs, the phenyl ring and the vinyl group of
H2CVB-XR, which are linked by a C-C single bond, are located on
the same plane. The planar arrangement leads to the
conjugation of the -electron cloud of a benzene ring with a
double bond of the vinyl group, which is necessary for
luminescence. The planar ligand arrangement is further
stabilized in the MOF when the solvent molecules fill the void
space. On removal of the guest solvent, the C-C single bond is
prone to the rotation, which leads to an irregular structure and
reduces the degree of -conjugation in the bulk sample, even
though the MOF retains the connectivity of metal and ligand.
These are reflected in the PXRD patterns exhibiting the loss of
crystallinity (Fig. S9, ESI†) as well as the emission spectra with a
remarkable reduction of intensity. The structural changes
together with the guest-solvent effect influence the
excitation/emission mechanism in the activated MOFs, leading
to the dramatic decrease in the emission intensity and the red-
shifted emission band. Interestingly, upon re-solvation, both
the crystallinity as well as photoluminescence is restored, which
supports the recovery of the MOF structure and the degree of
-conjugation.
Conclusions
We have synthesized multifunctional MOFs that exhibit high gas
uptake capacities, photoluminescence, and chemical sensing
abilities by utilizing asymmetric dicarboxylic acids having
various organic functional pedants on the aryl moiety. The
pendant functional groups of the ligands affect the
interpenetration of the MOFs. They increase the gas-sorption
capacities and the isosteric heats of adsorption for H2, CO2, and
CH4 gases. They provide ligand-based photoluminescence and
chemical sensing abilities to the MOFs: all as-synthesized MOFs
can sense nitro-aromatics by the luminescence quenching and
some activated MOFs can sense solvents by the altered
emission maxima with enhanced intensity. Interestingly, the
MOF (SNU-176) composed of two different ligands shows the
highest gas uptake capacities among the present MOFs. It also
shows the ability to differentiate nitrobenzene (NB) and 2,4-
dinitrotoluene (DNT), unlike the MOFs constructed of single
ligands. This work shows a strategy to generate and fine-tune
the multi-functionality of MOFs by the judicious introduction of
functional groups in the ligand. It also suggests that the MOFs
synthesized from the multiple ligands having selected
functional pendants would provide the enhanced
functionalities that the MOFs prepared from the single ligand
cannot.
The sensing ability of the MOFs
To see if the present luminescent MOFs can be applied in
sensing the type of solvents, we measured the PL spectra of the
activated MOFs at room temperature after adding a few drops
of DEF, DMA, acetone, benzene, and toluene. With any of these
solvents, the luminescence intensities of the activated MOFs
increase, and the emission bands display blue shifts (Table S3
4 | J. Name., 2012, 00, 1-3
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molecules could not be located from the difference maps, and the
Experimental
View Article Online
residual electron density corresponding to thDeOsoI:l1v0e.n10t3m9/oDle0cDuTl0e3s0w12aKs
ignored by using the SQUEEZE33 option of PLATON.34 The pendant
groups and the central benzene ring in the dicarboxylic acids have a
high thermal disorder as the structures were solved by using the data
collected at 293 K. The X-ray diffraction analysis at 100 K could not
be performed due to poor diffraction profiles. The positions of the
carbon atoms of the ligand were fixed and refined isotropically and
the exact positions of the pendent groups could not be located from
the difference map particularly due to the asymmetric dicarboxylate
ligand and the flexibility of the pendant groups. Therefore, the
numbers of the guest solvent molecules were calculated from the
elemental and thermogravimetric analyses data. The X-ray
crystallographic data are presented in Table S1, ESI†.
General methods
All chemicals were commercially available reagent grade and used
without further purification. IR spectra were recorded on a Perkin-
Elmer Spectrum One FTIR spectrophotometer. UV-Visible and
diffuse reflectance spectra were measured on a Perkin-Elmer
Lambda 35 UV/Vis spectrometer. Photoluminescence spectra were
measured on a Perkin-Elmer LS-55 luminescence spectrometer.
Elemental analyses were performed with a Perkin-Elmer 2400
Series II CHN analyzer. Thermogravimetric analysis (TGA) was
performed on TGA Q50 TA instruments under an N2 atmosphere at
a scan rate of 5 oC/min (Fig. S17-S23, ESI†). NMR spectra were
measured on a Bruker Spectrospin 300 spectrometer. Powder X-ray
diffraction (PXRD) data were recorded on a Bruker D8 Advance
diffractometer operating at 40 kV and 40 mA and employing Cu-
Ka (λ = 1.54050 Å) with a scan speed of 0.2 s per step and a step
size of 0.02 in 2θ.
Methods
Activation of MOFs with supercritical CO2. The crystals of as-
synthesized MOFs (ca. 0.1 g) were placed in the supercritical dryer
together with DMF, and the drying chamber was sealed. The
o
temperature and pressure of the chamber were increased to 40 C
Synthesis of ligands
and 200 bar with CO2. The chamber was vented at a rate of 10 mL
min-1 and then filled with CO2 again. The cycle of refilling with CO2,
pressurizing, and then venting was repeated for 24 h. After drying,
the closed container was transferred to a glove bag filled with argon
and transferred to a gas sorption cell. The gas sorption isotherms
were measured after samples were evacuated under high vacuum.
SNU-170’: Anal. Calcd for [Zn4O(CVB-NH2)3] (C30H21N3O13Zn4):ꢀ C,
40.35; H, 2.37; N, 4.71. Found:ꢀ C, 39.54; H, 2.83; N, 4.55. SNU-171’:
Anal. Calcd for [Zn4O(CVB-SMe)3] (C33H24O13S3Zn4):ꢀ C, 40.19; H, 2.45.
Found:ꢀ C, 38.84; H, 2.84. SNU-172’: Anal. Calcd for [Zn4O(CVB-
OMe)3] (C33H24O16Zn4):ꢀ C, 42.25; H, 2.58. Found:ꢀ C, 41.77; H, 2.68.
SNU-173’: Anal. Calcd for [Zn4O(CVB-OEt)3] (C36H30O16Zn4):ꢀ C, 44.11;
H, 3.08. Found:ꢀ C, 42.68; H, 3.55. SNU-174’: Anal. Calcd for
[Zn4O(CVB-OPr)3] (C39H36O16Zn4):ꢀ C, 45.82; H, 3.55. Found:ꢀ C, 44.84;
H, 3.97. SNU-175’: Anal. Calcd for [Zn4O(CVB-OBu)3] (C42H42O16Zn4):ꢀ
C, 47.40; H, 3.98. Found:ꢀ C, 44.98; H, 4.37. SNU-176’: Anal. Calcd for
[Zn4O(CVB-SMe)1(CVB-OMe)2] (C33H24O15SZn4): C, 41.54; H, 2.54.
Found:ꢀ C, 38.51; H, 2.97.
Series of substituted 4-(2-carboxyvinyl)benzoic acids with various
functional groups (-NH2, -SMe, -OMe, -OEt, -OPr, and -OBu) were
prepared by modifying the reported synthetic methods. (see the
Supporting Information for details of synthetic procedures and
characterization data). The ligands obtained were characterized by
elemental analyses, FTIR, and 1H NMR spectra.
Synthesis of MOFs
Synthesis of [Zn4O(CVB-NH2)3]•18DMF•H2O (SNU-170).
Zn(NO3)2·6H2O (0.060 g, 0.201 mmol), and H2CVB-NH2 (0.021 g, 0.101
mmol) were dissolved in N,N-dimethylformamide (5 mL) in a glass
serum bottle, which was capped with a silicon stopper and
aluminium seal, and then heated at 105oC for 24 h in a programmable
furnace. Yellow cubic shaped crystals formed, which were filtered,
washed with DMF, and stored in DMF. Yield: 0.040 g (54 %). Anal.
Calcd for C84H149N21O32Zn4: C, 45.31; H, 6.74; N, 13.21. Found: C,
44.50; H, 6.96; N, 13.78. FTIR (KBr pellet): ῦ = 2927 (amino), 1671
cm-1 (DMF).
Synthesis of SNU-171 ~ SNU-176. The MOFs were synthesized by
using the corresponding H2CVB-XR by the method similar to that for
the synthesis of [Zn4O(CVB-NH2)3]•18DMF•H2O (SNU-170). The data
for the characterization are presented in ESI†.
Measurements of gas sorption data. Gas adsorption-desorption
measurements were performed by using Autosorb-1 or Autosorb-3B
(Quantachrome Instruments) up to 1 atm. All gases used in the
studies were of 99.999 % purity. Before and after the gas sorption
measurement, the sample weight was measured precisely.
X-ray crystallography
Calculation of isosteric heat of H2 adsorption. The isosteric heat of
H2 adsorption was estimated from adsorption data measured at 77
and 87 K. These data were fit into a virial-type expression (1) by using
the R-Program.35 In which, ai and bi are temperature independent
parameters, P is pressure (atm), N is the amount adsorbed H2 gas (mg
g-1), T is temperature (K), and m and n represent the number of
coefficients required to adequately describe the isotherms. The
isosteric heat of H2 adsorption (Qst) was calculated using the Eqn. 2,
where R is the universal gas constant.
X-ray single-crystal data were collected on an ADSC Quantum-
210 detector at 2D SMC with silicon (111) double crystal
monochromator at the Pohang Accelerator Laboratory, Korea. Each
crystal was sealed in a glass capillary together with the DMF and the
data were collected at 293 K. The ADSC Q210 ADX program30 was
used for data collection and HKL3000 sm31 was used for cell
refinement, reduction, and absorption corrections. The structure
was solved using SHELXS-201331 and full-matrix least-squares
refinement against F2 was carried out using SHELXL-2013.32 All
hydrogen atoms were assigned based on geometrical considerations
and allowed to ride on the respective carbon atoms. The solvent
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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ARTICLE
Journal Name
12 Y. M. Zhang, S. Yuan, G. Day, X. Wang, X. Y. Yang and H. C.
Calculation of isosteric heats of CO2 and CH4 adsorption. The CO2
and CH4 Gas adsorption isotherms at 195, 273, and 298 K were fitted
with a Langmuir-Freundlich equation (Eqn. 3). The isosteric heats of
CO2 and CH4 adsorption were calculated from the Langmuir-
Freundlich fitted isotherms by using the Clausius-Clapeyron
expression (4), in which, P is pressure (atm), N is the amount
adsorbed gas (mmol g-1), Nm is the amount adsorbed gas at
saturation, and b and c are constants.
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use of five parameters: (1) CO2 uptake under the adsorption
ads
ads
conditions, N1 (mol kg-1), (2) Working CO2 capacity, ΔN1 = N1
-
N1 (mol kg-1), (3) Regenerability, R = (ΔN1/ N1ads) x 100 (%), (4)
Selectivity under adsorption conditions, α12 = (N1ads/ N2ads)(y2/y1),
des
ads
(5) Sorbent selection parameter, S = (α12ads)2/(α12des)(ΔN1/ ΔN2). Here
N is the adsorbed amount and y is the mole fraction in the gas phase.
Subscripts 1 and 2 indicate the strongly adsorbed component (CO2)
and the weakly adsorbed component (CH4 or N2), respectively. The
selectivity parameters were extracted from the isotherms of CO2,
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equation (Eqn. 3). The results are presented in Table S2, ESI†.
Conflicts of interest
There are no conflicts to declare.
29 M. Pamei and A. Puzari, Nano-Structures & Nano-Objects,
2019, 19, 100364; T. K. Kim, J. H. Lee, D. Moon, and H. R.
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Acknowledgments
This work was supported by the National Research Foundation of
Korea (NRF) Grant funded by the Korean Government (MEST; No.
2005-0049412).
32 SHELX-2013-Programs for Crystal Structure Analysis.
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DOI: 10.1039/D0DT03012K
Fig. 1 X-ray crystal structures: (a) non-interpenetrated SNU-170; (b) doubly interpenetrated SNU-171. The
disordered parts and pendant functional groups were modeled for clarity.
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Fig. 2 Gas adsorption isotherms, (a) N2 at 77 K, (b) H2 at 77 K, (c) CO2 at 298 K, and (d) CH4 at 298 K.
SNU-170’ (red, square), SNU-171’ (blue, circle), SNU-172’ (green, triangle), SNU-173’ (pink, inverted
triangle), SNU-174’ (violet, diamond), and SNU-175’ (orange, rotated triangle). Filled shapes: adsorption;
open shapes: desorption. For SNU-176’, see Fig. S11, ESI†.
207x255mm (300 x 300 DPI)

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Fig. 3 Photoluminescence spectra of MOFs. (a) As synthesized samples, excitation at 400 nm for SNU-170,
390 nm for SNU-171, 350 nm for SNU-176, and 330 nm for the rest of the samples. (b) After supercritical
CO2 activation, excitation at 400 nm for SNU-170’, 390 nm for SNU-171’, 350 nm for SNU-176’, and 330
nm for the rest of the samples
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Fig. 4 Time-dependent regeneration of photoluminescence spectra of activated SNU-170’ on the addition of
a few drops of DMF. Excitation at 380 nm. A black line corresponds to the activated sample of SNU-170’.
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Scheme 1 Synthesis of MOFs from the functionalized 4-(2-carboxyvinyl)benzoic acids (H2CVB-XR).
248x41mm (149 x 149 DPI)

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Table of Content
Multifunctional metal-organic frameworks synthesized from the ligands with various
organic functional pendants show high gas adsorption, photoluminescence, and chemical
sensing properties, being tuned by the pendants.