Experimental, Structural, and Computational Investigation of Mixed Metal-Organic Frameworks from Regioisomeric Ligands for Porosity Control

Article abstract of DOI:10.1021/acs.cgd.0c00562

Porosity control and structural analysis of metal-organic frameworks (MOFs) can be achieved using regioisomeric ligand mixtures. While ortho-dimethoxy-functionalized MOFs yielded highly porous structures and para-dimethoxy-functionalized MOFs displayed almost nonporous properties in their N2 isotherms after evacuation, regioisomeric ligand-mixed MOFs showed variable N2 uptake amount and surface area depending on the ligand-mixing ratio. The quantity of N2 absorbed was tuned between 20 and 300 cm3/g by adjusting the ligand-mixing ratio. Both experimental analysis and computational modeling were performed to understand the porosity differences between ortho- A nd para-dimethoxy-functionalized MOFs. Detailed structural analysis using X-ray crystallographic data revealed significant differences in the coordination environments of DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2] (DMOF = dabco MOF, dabco = 1,4-diazabicyclo[2.2.0]octane). The coordination bond between Zn2+ and carboxylate in the ortho-functionalized DMOF-[2,3-(OMe)2] was more rigid than that in the para-functionalized DMOF-[2,5-(OMe)2]. Quantum-chemical simulation also showed differences in the coordination environments of Zn secondary building unit surrounded by methoxy-functionalized ligands and pillar ligands. In addition, the binding energy differences between Zn2+ and regioisomeric ligands (ortho- A nd para-dimethoxy-functionalized benzene-1,4-dicarboxylates) explained the rigidity and porosity changes of the mixed MOFs upon evacuation and perfectly matched with experimental N2 adsorption and X-ray crystallography data.

Full text of DOI:10.1021/acs.cgd.0c00562

Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE
Article
Experimental, Structural, and Computational Investigation of Mixed Metal-
Organic Frameworks from Regioisomeric Ligands for Porosity Control
Dopil Kim, Hyeonbin Ha, Youngik Kim, Younghu Son, Jiyoon Choi, Myung Hwan
Park, Youngjo Kim, Minyoung Yoon, Hyungjun Kim, Dongwook Kim, and Min Kim
Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.0c00562 • Publication Date (Web): 23 Jun 2020
Downloaded from pubs.acs.org on June 28, 2020
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Experimental, Structural, and Computational
Investigation of Mixed Metal-Organic Frameworks
from Regioisomeric Ligands for Porosity Control
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Dopil Kim,†,# Hyeonbin Ha,†,# Youngik Kim,† Younghu Son,‡ Jiyoon Choi,§,∥ Myung Hwan Park,¶
Youngjo Kim,† Minyoung Yoon,*,‡ Hyungjun Kim,*,§,∥ Dongwook Kim,*, and Min Kim*,†
†Department of Chemistry, Chungbuk National University, Cheongju, 28644, Republic of Korea
‡Department of Chemistry, Kyungpook National University, Daegu, 41566, Republic of Korea
§Department of Chemistry, Incheon National University, Incheon, 22012, Republic of Korea
∥Research Institute of Basic Sciences, Incheon National University, Incheon, 22012, Republic of
Korea
¶Department of Chemistry Education, Chungbuk National University, Cheongju, 28644,
Republic of Korea
ACS Paragon Plus Environment
1

Crystal Growth & Design
Page 2 of 31
1
2
3
4
5
6
Center for Catalytic Hydrocarbon Functionalization, Institute for Basic Science (IBS), Daejeon,
34141, Republic of Korea
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
KEYWORDS: metal-organic frameworks; regioisomer; functional groups; porosity; dimethoxy
ABSTRACT: Porosity control and structural analysis of metal-organic frameworks (MOFs) can
be achieved using regioisomeric ligand mixtures. While ortho-dimethoxy-functionalized MOFs
yielded highly porous structures and para-dimethoxy-functionalized MOFs displayed almost non-
porous properties in their N2 isotherms after evacuation, regioisomeric ligand-mixed MOFs
showed variable N2 uptake amount and surface area depending on the ligand-mixing ratio. The
quantity of N2 absorbed was tuned between 20 and 300 cm3/g by adjusting the ligand-mixing ratio.
Both experimental analysis and computational modeling were performed to understand the
porosity differences between ortho- and para-dimethoxy-functionalized MOFs. Detailed
structural analysis using X-ray crystallographic data revealed significant differences in the
coordination environments of DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2] (DMOF = dabco
MOF, dabco = 1,4-diazabicyclo[2.2.0]octane). The coordination bond between Zn2+ and
carboxylate in the ortho-functionalized DMOF-[2,3-(OMe)2] was more rigid than that in the para-
functionalized DMOF-[2,5-(OMe)2]. Quantum chemical simulation also showed differences in the
coordination environments of Zn-SBU (secondary building unit) surrounded by methoxy-
functionalized ligands and pillar ligands. In addition, the binding energy differences between Zn2+
and regioisomeric ligands (ortho- and para-dimethoxy-functionalized BDCs, BDC = benzene-1,4-
ACS Paragon Plus Environment
2

Page 3 of 31
Crystal Growth & Design
1
2
3
4
5
6
dicarboxylate) explained the rigidity and porosity changes of the mixed MOFs upon evacuation,
and perfectly matched with experimental N2 adsorption and X-ray crystallography data.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
INTRODUCTION
Metal-organic frameworks (MOFs) are emerging porous materials composed of infinitely
repeating coordination bonds between metal clusters (or ions) and multivalent ligands. Although
MOFs are generally synthesized under solvothermal conditions, empty pores can be generated by
solvent evacuation under vacuum. The permanent porosity of MOFs, which has been utilized in
various fields such as gas separation and molecular storage, has been intensively studied over the
past two decades.1–5 Because MOFs can be tuned at their metal cluster or ligands, porosity changes
have been investigated in non-porous and highly porous materials as a function of structural
changes. Isoreticular synthesis allows for the preparation of a series of MOFs with the same (or
similar) topology but different porosities.6
Functionalization is also a key strategy for achieving porosity changes. When a bulky
substituent is introduced at the ligand portion of the MOFs, decreased porosity is generally
observed. For example, bromo-functionalized and naphthyl-functionalized zirconium-based UiO-
66 (UiO-O = University of Oslo) showed a much lower porosity than pristine, non-functionalized
UiO-66.7 Although the functionalization method provides a series of MOFs with the same
framework but different porosities, the extent of the change is not directly predictable. In addition,
the synthesis and properties of MOFs can be altered by additional functionality on the ligand.8
The third approach for the porosity control of MOFs is structural flexibility. The MOF
framework can be flexible under some conditions, such as in pillared MOFs, and the structure of
ACS Paragon Plus Environment
3

Crystal Growth & Design
Page 4 of 31
1
2
3
4
5
6
7
8
9
MOFs and porosity can also be changed upon application of external stimuli.9,10 Gas pressure is a
common stimuli for MOF flexibility control. Therefore, porosity control of flexible MOFs under
standard conditions (e.g., 1 atm) remains quite difficult. Recently, the correlation between
functional group regioisomerism and MOF structural flexibility has been revealed using various
combinations of chemical tags within pillared DMOFs (DMOF = dabco MOFs; DABCO = 1,4-
diazabicyclo[2.2.0]octane).11–13 DMOF contains a dimeric paddle-wheel-type SBU (secondary
building unit) as a MOF node14 and can exhibit structural flexibility. Recently, the flexibility of
DMOFs was altered by the position of the functional group (i.e., regioisomerism).11 From
comparison experiments with various functional group combinations, the electron density of the
MOF ligand was shown to be correlated with the flexibility of DMOFs by Hammett plots.12,13
Electron-rich combinations such as NH2-OMe, NH2-X, and OMe-OMe at the para-positions
yielded flexible DMOFs upon evacuation, while ortho-NH2-OMe, NH2-X, and OMe-OMe along
with other electron-deficient combinations resulted in an inflexible framework. In other words,
although both DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2] contain identical frameworks from
solvothermal synthesis (i.e., as-synthesized status), as indicated by powder X-ray diffraction
patterns (PXRD), the porosities of the two DMOFs differ after evacuation. While ortho-
functionalized, electron-rich, DMOF-[2,3-(OMe)2] showed a pore volume of 0.329 cm3/g after
evacuation (inflexible framework to evacuation), para-functionalized DMOF-[2,5-(OMe)2]
displayed an almost non-porous value of 0.085 cm3/g after evacuation (flexible framework to
evacuation).13 Although these extreme differences between the ortho- and para-regioisomers
within electron-rich ligands are unique and interesting, the fine-control of MOF flexibility to
evacuation remains a difficult task.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment
4

Page 5 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Herein, a mixed ligand strategy between para-dimethoxy and ortho-dimethoxy-functionalized
ligands was implemented to control MOF porosity using the same topology and framework. By
judicious choice of ligand ratio, the quantity of adsorption (N2), surface area, and calculated pore
volume were controlled after evacuation (i.e., activation of the MOFs). Detailed structural analyses
of DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2] were performed to determine differences in
specific properties. In addition, quantum chemical simulation allowed for estimation of the energy
differences between the coordination bonds of DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2].
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
EXPERIMENTAL SECTION
2.1. Preparation of regioisomeric ligands
Dimethy-2,3-dimethoxyterephthalate and diethy-2,5-dimethoxyterephthalate were prepared
following literature procedures (Scheme S1).11,15
Dimethyl-2,3-dimethoxyterephthalate (1a): Dimethyl-2,3-dihydroxyterephthalate (1.27 g, 5
mmol), potassium carbonate (830 mg, 16 mmol) were dissolved in acetone. Iodomethane (1 mL,
16 mmol) were added to solution, and solution mixture was stirred for overnight under reflux
condition. When the reaction was finished (monitored by TLC), organic solvent was evaporated,
and then water and EtOAc were added to dissolve all organic molecules and inorganic salts. The
solution was three times extracted with EtOAc. The organic layer was dried using anhydrous
MgSO4. After filtered off the solid, the solution was evaporated and dried under vacuum. Further
purification on flash column chromatograph with n-hexane/EtOAc was performed to obtain
colorless solid.
Diethyl-2,5-dimethoxyterephthalate (1b): Diethyl-2,5-dimethoxyterephthalate was obtained in
comparable yield from a similar procedure for 1a; using diethyl-2,5-dihydroxyterephthalate than
ACS Paragon Plus Environment
5

Crystal Growth & Design
Page 6 of 31
1
2
3
4
5
6
dimethyl-2,3-dihydroxyterephthalate. The colorless solid were obtained after column
chromatography.
7
8
9
2,3-Dimethoxyterephthalic acid (2a): Dimethyl-2,3-dihydroxyterephthalate (1.02 g, 4 mmol)
was dissolved in 20 mL of THF. And 20 mL of a 4% potassium hydroxide aqueous solution was
added to THF solution. The solution mixture was stirred overnight under reflux condition. Once
conversion was complete (monitored by TLC), THF was removed by evaporation, and the solution
was acidified with a 1.0 M HCl aqueous solution to pH 2. The precipitate was collected by filtration
and washed with water. The desired compound was obtained colorless solid.
2,5-Dimethoxyterephthalic acid (2b): 2,5-Dimethoxyterephthalic acid was obtained in
comparable yield from a similar procedure for 2a; using diethyl-2,5-dimethoxyterephthalate (1b)
as a starting material. The desired compound was obtained colorless solid.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2.2. Preparation of mixed MOFs
The DMOF series was prepared and activated using a modified method from what has been
previously described (Scheme S2).13,16
DMOF-[2,3-(OMe)2]: 2a (89.6 mg, 0.4 mmol) and Zn(NO3)2·6H2O (119 mg, 0.4 mmol) were
dissolved in 10 mL of DMF (N,N-dimethylformamide). To this mixture, DABCO (90 mg, 0.8
mmol) was added and the white precipitate was filtered out with fine porosity disc filter. Then, the
clear solution was moved to a scintillation vial (20 mL size) and heated from room temperature to
100 °C (increasing rate = 2.5 °C/min). The temperature was held for 24 h at 100 °C, and then
cooled to room temperature (decreasing rate = 2.5 °C/min). The resulting crystals were washed
with DMF (5 mL X 3) and chloroform (5 mL X 3). The chloroform solution was replaced with
fresh chloroform (5 mL) per 24 h for three cycles. The colorless crystals were obtained after
washing and soaked in CHCl3 until usage.
ACS Paragon Plus Environment
6

Page 7 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
DMOF-[2,5-(OMe)2]: 2b (89.6 mg, 0.4 mmol) and Zn(NO3)2·6H2O (119 mg, 0.4 mmol) were
dissolved in 10 mL of DMF. To this mixture, DABCO (90 mg, 0.8 mmol) was added and the white
precipitate was filtered out with fine porosity disc filter. Then, the clear solution was moved to a
scintillation vial (20 mL size) and heated from room temperature to 100 °C (increasing rate = 2.5
°C/min). The temperature was held for 24 h at 100 °C, and then cooled to room temperature
(decreasing rate = 2.5 °C/min). The resulting crystals were washed with DMF (5 mL X 3) and
chloroform (5 mL X 3). The chloroform solution was replaced with fresh chloroform (5 mL) per
24 h for three cycles. The colorless crystals were obtained after washing and soaked in CHCl3 until
usage.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
DMOF-[2,3-(OMe)2]x[2,5-(OMe)2]y: The mixed DMOFs were obtained by following similar
procedure of [DMOF-2,3-(OMe)2] and DMOF-[2,5-(OMe)2] with ligand mixtures. 2a and 2b were
mixed with various mole fractions (3:1, 1:1, and 1:3), and then Zn(NO3)2·6H2O (119 mg, 0.4
mmol) was added, and the solid mixtures were dissolved in 10 mL of DMF. To this mixture,
DABCO (90 mg, 0.8 mmol) was added and the white precipitate was filtered out with fine porosity
disc filter. Then, the clear solution was moved to a scintillation vial (20 mL size) and heated from
room temperature to 100 °C (increasing rate = 2.5 °C/min). The temperature was held for 24 h at
100 °C, and then cooled to room temperature (decreasing rate = 2.5 °C/min). The resulting crystals
were washed with DMF (5 mL X 3) and chloroform (5 mL X 3). The chloroform solution was
replaced with fresh chloroform (5 mL) per 24 h for three cycles. The colorless crystals were
obtained after washing and soaked in CHCl3 until usage.
RESULTS AND DISCUSSION
Synthesis of mixed DMOFs with different ligand ratios and associated porosity changes
ACS Paragon Plus Environment
7

Crystal Growth & Design
Page 8 of 31
1
2
3
4
5
6
7
8
9
In the previous study focusing on the flexibility control of MOFs with functional group
regioisomerism,11–13 the possibility of porosity control of MOFs with a combination of ligands was
raised. Electron-rich, dimethoxy functionalization was selected, and Zn-based DMOFs were
studied as the main MOF system as it showed a significant flexibility changes based on the
regioisomerism.17 Two main ligands, BDC-2,3-(OMe)2 and BDC-2,5-(OMe)2, were prepared by
following previously reported procedures through methylation of dihydroxy ligands (Scheme
S1).13
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Mixed ligand strategies for MOFs are commonly used to introduce multi-functionalities. Various
combinations of ligands have been studied for the preparation of mixed MOFs.18,19 Among them,
ligand combinations with the same coordinating ligands but different chemical tags have been
extensively studied because they allow for the generation of isoreticular structures from pristine,
non-functionalized, or single-functionalized MOFs. For example, mixed UiO-66-(NH2)x(Br)y (x+y
=1) were simply prepared using a mixed ligand solution of BDC-NH2 and BDC-Br, exhibiting the
same framework as those of UiO-66, UiO-66-NH2, and UiO-66-Br.20 Therefore, a series of ratio-
controlled mixtures of BDC-2,3-(OMe)2 and BDC-2,5-(OMe)2 allowed for identical MOF
structures with completely different porosities.
ACS Paragon Plus Environment
8

Page 9 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Synthesis of mixed DMOFs with BDC-2,3-(OMe)2 and BDC-2,5-(OMe)2 and their
associated PXRD patterns (as-synthesized) and simulated PXRD patterns (for DMOF-[2,3-(OMe)2]
and DMOF-[2,5-(OMe)2].
Using a series of dimethoxy-functionalized ligands, Zn(II)-based DMOFs were synthesized
(Figure 1 and Scheme S2). DMOF-[2,3-(OMe)2], DMOF-[2,3-(OMe)2]3[2,5-(OMe)2]1, DMOF-
[2,3-(OMe)2]1[2,5-(OMe)2]1, DMOF-[2,3-(OMe)2]1[2,5-(OMe)2]3, and DMOF-[2,5-(OMe)2] were
prepared by combining the appropriate ligand mixture with DABCO in DMF, and heating the
mixture to 100 °C for 24 h. Crystalline ratio-controlled DMOFs exhibited the framework that was
1
identical to that of the parent DMOF-1, as evidenced by the PXRD pattern (Figure 1). The H
ACS Paragon Plus Environment
9

Crystal Growth & Design
Page 10 of 31
1
2
3
4
5
6
7
8
9
NMR spectra after acid digestion (with DCl in D2O) of the DMOFs showed that the ratio of BDC-
2,3-(OMe)2 and BDC-2,5-(OMe)2 from the solution mixture was completely retained in all
DMOFs. In addition, for the 2:1 ratio between the BDCs and Zn(NO3)2, the DABCO ligands were
confirmed for all samples (Figure S1). Although the ratios between the two regioisomers were well
matched at the bulk level, a detailed NMR analysis was additionally performed to confirm the
homogeneity of MOF crystals with two different ligands. A large single crystal of DMOF-[2,3-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
(OMe)2]1[2,5-(OMe)2]1 (<2 mm in size) was selected, and the H NMR spectra (from overnight
measurement) after acid digestion clearly showed two significant signals arising simultaneously
from two regioisomeric ligands (Figure S2). Therefore, it was clearly confirmed that the
combinations of regioisomeric ligands with different functional group positions were compatible
with the proposed DMOF synthesis.
Figure 2. N2 full isotherms (77 K) of the obtained mixed DMOFs from the regioisomeric ligand
mixtures.
ACS Paragon Plus Environment
10

Page 11 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Gas adsorption experiments with N2 (at 77 K) were performed to confirm the porosity of the
mixed DMOFs. Previously, electron-rich DMOF with a para-position group such as DMOF-[2,5-
(OMe)2] showed almost non-porous properties after evacuation, indicating a flexible framework.
The Brunauer-Emmett-Teller (BET) surface area of DMOF-[2,5-(OMe)2] was 73 m2/g, while the
ortho-regioisomer DMOF-[2,3-(OMe)2] was highly porous after evacuation, indicating an
inflexible framework (BET surface area = 1554 m2/g; Figure S3).13 Although both DMOF-[2,3-
(OMe)2] and DMOF-[2,5-(OMe)2] contained identical frameworks in the as-synthesized state,
their porosity was totally changed from highly porous to non-porous by moving the relative
position of the functional group.13 Interestingly, the DMOF porosity was generally controllable by
mixing of the two regioisomeric ligands. The equivalent-proportioned DMOF-[2,3-(OMe)2]1[2,5-
(OMe)2]1 obtained using a 1:1 ligand mixture of BDC-2,3-(OMe)2 and BDC-2,5-(OMe)2 showed
moderate porosity (~120 cm3/g adsorbed at STP), micropore volume (329 cm3/g), and BET surface
area (437 m2/g; Figures 2 and S3–S6). In addition, the sample prepared using a 3:1 ratio of BDC-
2,3-(OMe)2 to BDC-2,5-(OMe)2 showed a highly porous structure (1057 m2/g BET surface area),
but lower porosity than that of pure DMOF-[2,3-(OMe)2] (Figures 2 and S4). Finally, the sample
prepared using a 1:3 ratio of BDC-2,3-(OMe)2 to BDC-2,5-(OMe)2 displayed almost non-porous
properties; however, it was slightly more porous than pure DMOF-[2,5-(OMe)2] (Figures 2 and
S6). All ratio-controlled DMOFs showed identical frameworks as the as-synthesized form (as
indicated by the PXRD patterns; Figure 1), but showed completely different porosities, as indicated
by N2 adsorption after evacuation (Table S1; micropore volume). Moreover, gas adsorption
experiments with CO2 (at 298 K) were performed to confirm the porosity changes of the mixed
DMOFs and determine the flexibility of the molecular interactions (Figure S7). Not surprisingly,
DMOF-[2,3-(OMe)2] showed the highest CO2 uptake, while DMOF-[2,5-(OMe)2] displayed the
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment
11

Crystal Growth & Design
Page 12 of 31
1
2
3
4
5
6
7
8
9
lowest uptake for CO2 at 298 K. Thus, no differences between DMOF-N2 and DMOF-CO2
interactions were observed owing to structural changes induced by regioisomerism. Furthermore,
the CO2 uptake was controlled by mixed-regioisomeric DMOFs (0.25–3.75 mmol/g; Figure S7).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. Pore size distribution of the mixed-regioisomeric DMOFs using the H-K method for
micropore analysis.
The porous properties of the DMOFs were evaluated using BET surface area, total pore volume,
and pore size distribution (PSD; Table S1). The BET surface area is a good measure of the size of
accessible empty space. However, PSD provides insight into the pore size, shape, and population
changes within the DMOFs. The PSD differ depending on the calculation method. Therefore, the
PSD calculated by the NLDFT (Non-Linear Density Function Theory) method assuming
cylindrical pore geometry incorporated in an ASAP2020 gas sorption instrument was first
plotted21,22 to provide information regarding the pore size distribution over a wide range—from
micro- to macropores (Figure S8). The PSD determined using the NLDFT method demonstrated
ACS Paragon Plus Environment
12

Page 13 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
that no meso- and macropores were present in the prepared DMOF, indicating that a PSD method
for micropores should be used, such as the Horváth-Kawazoe (H-K) model.23 The PSD of the
DMOF calculated using the H-K model assuming a narrow cylindrical pore geometry is presented
in Figure 3 focusing on the micropore range (0–20 Å).24 The average pore size was ~ 5.4 Å
regardless of the 2,3- and 2,5-OMe ligand ratio. However, the pore volume corresponding to the
largest pore occupying size decreased with increasing 2,5-OMe ligand ratio. The PSD results
clearly indicate that the decreased surface area is not derived from pore size and shape changes in
the DMOFs, but originates from the decrease in the number (or volume) of the accessible pores.
Therefore, increasing the 2,5-OMe ligand content allows for the generation of a greater amount of
non-accessible small pores in the DMOF, resulting in an accessible pore volume decrease without
a significant pore size change.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Because the gas adsorption experiments were conducted with fully evacuated samples (i.e.,
activated samples with empty pores), the structural changes caused by evacuation were monitored
by PXRD after vacuum drying. Interestingly, only the most non-porous DMOF-[2,5-(OMe)2]
showed a significant peak shift to a higher angle, indicating structural changes from large pores
(lp) to narrow pores (np). This structural change was not reversible as the as-synthesized status
was not recovered after re-solvation with either CHCl3 or DMF. Other mixed DMOFs and porous
DMOF-[2,3-(OMe)2] exhibited no peak shift in the PXRD data upon evacuation (Figure S9). The
mixed-regioisomeric DMOFs were instantly decomposed during the PXRD measurements.
Therefore, only several broad peaks at low angles were confirmed; however, detailed structural
information of the fully dried DMOFs was not obtained by PXRD and single X-ray diffraction
data (SXRD). For the flexible-irreversible DMOF-[2,5-(OMe)2], similar PXRD peak shifts upon
evacuation were observed in a previous study with other flexible DMOFs, DMOF-2,5-NH2Cl, and
ACS Paragon Plus Environment
13

Crystal Growth & Design
Page 14 of 31
1
2
3
4
5
6
7
8
9
DMOF-2,5-NH2Br.11 In addition, the PXRD peak shifts upon evacuation from the lp to np phases
(~1° in 2θ) are very similar for three electron-rich DMOFs with para-functionalizations (evacuated
DMOF-[2,5-(OMe)2] vs. evacuated DMOF-2,5-NH2Cl and DMOF-2,5-NH2Br; Figure S9).11
This structural transformation from lp to np is likely the main factor for porosity control. The
additional inclusion of electron-rich ligands (e.g., BDC-2,5-(OMe)2) could induce a more
collapsed framework compared to the pristine electron-deficient MOFs (e.g., DMOF-[2,3-
(OMe)2]), with the related porosity changes upon evacuation. These structural transformations of
mixed-regioisomeric DMOFs can occur simultaneously for a whole crystal or during the partial
collapse of specific crystal domains. Since detailed structural evaluation after evacuation is rather
challenging, high-level computational approaches must be performed to understand the structural
transformation mechanisms in infinite frameworks. Not surprisingly, thermogravimetry analysis
(TGA) showed no significant changes as a function of regioisomeric ligand ratios for a series of
DMOF-[2,3-(OMe)2]x[2,5-(OMe)2]y (x or y = 0, 1, and 3; Figure S10).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Structural differences between DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2]
To determine the porosity changes of a series of mixed DMOFs prepared using different
regioisomeric ligands, the structural differences between the DMOF regioisomers, DMOF-[2,3-
(OMe)2] and DMOF-[2,5-(OMe)2], were carefully evaluated via SXRD (Figures 4, S11, Tables
S2–S10, and Cambridge Crystallographic Data Centre Deposit# 1994998-1995002). Generally,
both DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2] adopted similar structures over the entire
framework. Dinuclear zinc units formed paddle-wheel type nodes, and this SBU was bridged by
BDC-(OMe)2 ligands to form a distorted 2-dimensional square-grid (i.e., Zn2(BDC-(OMe)2)2).
Two axial positions of Zn2 SBU were contained two DABCO molecules as pillar ligands to
ACS Paragon Plus Environment
14

Page 15 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
configure 3-dimensional frameworks from 2-dimensional sheets. The overall structure of both
DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2] were identical to the previously reported DMOF-
1 structure prepared from the non-functionalized BDC ligand,14 but the detailed coordination
environments between the dimeric paddle-wheel SBU and BDC ligands differed significantly in
terms of methoxy group position. First, the disorder of dimethoxy functional groups displayed
different behaviors for regioisomeric DMOFs. For the ortho-functionalized DMOF-[2,3-(OMe)2],
the position of the dimethoxy group was fixed, and two methoxy groups were directed into the
inside of the square. Simultaneously, the other two methoxy groups pointed toward the outside of
the 2-dimensional square (Figure 4a). In contrast, all methoxy groups were disordered in the para-
functionalized DMOF-[2,5-(OMe)2] (Figure 4b).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. Structural differences observed in the SXRD data of DMOF-[2,3-(OMe)2] (a, left) and
DMOF-[2,5-(OMe)2] (b, right). Because of the disorder of the substituents on the BDC-2,5-
(OMe)2 ligand, the methoxy groups were refined as disordered over the 2, 3, 5, and 6 positions of
the benzene ring. Color scheme: Zn (cyan), O (red), C (gray), and N (blue).
In addition, the overall balances of the whole structures were distinguished by the relative
positions of the methoxy groups. While the 2-dimensional sheet from the top view formed exact
ACS Paragon Plus Environment
15

Crystal Growth & Design
Page 16 of 31
1
2
3
4
5
6
7
8
9
square-type pores in the net structure of DMOF-[2,5-(OMe)2], the 2-dimensional squares from the
top view of DMOF-[2,3-(OMe)2] were slightly squeezed, and the two-crossed vertically
enlarged/horizontally enlarged squares repeated over the entire 2-dimensional sheet. Moreover,
coordination between the zinc cation and carboxylate was also distinct for the two regioisomeric
DMOFs. The coordination bonds in the para-functionalized DMOF-[2,5-(OMe)2] showed
fluctuating characteristics, especially the Zn–O bonds that were completely disordered. In contrast,
DMOF-[2,3-(OMe)2] displayed a single position for the Zn–O bond for all coordination bonds in
the framework. Therefore, to maintain balance over the entire framework, the ligand was bent to
an arrow type to the inside and outside of the pore (Figures 4 and S11). The Zn-BDC-Zn angle in
the ortho-DMOF was 164°, while the para-functionalized DMOF-2,5-(OMe)2 showed a perfectly
flat 180° angle (Figure S12). We assumed that this discrepancy originated from differences in the
coordination bond strengths of the DMOFs. The coordination bonds between Zn2+ and BDC-2,3-
(OMe)2 are much stronger than the coordination bond between Zn2+ and BDC-2,5-(OMe)2.
Therefore, the Zn-O coordination bonds in DMOF-[2,3-(OMe)2] were completely maintained in a
single position of the X-ray structure, retaining the original pore size of DMOF-[2,3-(OMe)2] (i.e.,
porosity to N2 after evacuation). In contrast, the weaker coordination bonds of DMOF-[2,5-
(OMe)2] were disordered in the associated X-ray structures, and adopted a narrow pore size upon
evacuation. Finally, the crystal structures of the regiomixtures, DMOF-[2,3-(OMe)2]3[2,5-
(OMe)2]1, DMOF-[2,3-(OMe)2]1[2,5-(OMe)2]1, and DMOF-[2,3-(OMe)2]1[2,5-(OMe)2]3 were
analyzed using SXRD data. Interestingly, all three mixtures displayed almost identical structures
to that of DMOF-[2,5-(OMe)2] (Figure S13). The structural rigidity of DMOF-[2,3-(OMe)2] was
only observed for the pure DMOF from BDC-2,3-(OMe)2, strongly suggesting that the disorder
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment
16

Page 17 of 31
Crystal Growth & Design
1
2
3
4
5
6
characteristics of coordination bonds from the para-functionalized BDC-2,5-(OMe)2 were
dominant over the ortho-functionalized ligand.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Quantum chemical simulations to examine differences in coordination between
regioisomeric mixtures
Quantum chemical simulations were performed to examine the coordination environment
differences between regioisomeric MOFs with dimethoxy-functionalities. It is not appropriate to
use quantum chemistry to investigate entire MOF particles with a nearly infinite 3D matrix-like
structure. As discussed previously,17 rationally truncated cluster model structures can instead be
used to generally understand and describe the electronic and geometric features of entire MOFs.
The cluster model has been widely used to investigate MOF properties such as spin property,25
hydrogen gas adsorption,26 and photophysical properties.27 The cluster model structures
incorporated two Zn divalent ions coordinated by four BDC-(OMe)2 anion ligands (ortho- and
para-functionalized BDCs), which were capped by two neutral DABCOs (e.g., Zn2(BDC-2,3-
(OMe)2)4(DABCO)2 and Zn2(BDC-2,5-(OMe)2)4(DABCO)2). The formula of these clusters are
identical to the well-known molecular formula of Zn-based MOFs (e.g., Zn2(BDC)2(DABCO)).
Four conformers are possible depending on the relative orientation of the methoxy groups in
neighboring BDCs for each model, and all possible conformers were considered in the simulations.
This simplified cluster model is useful for obtaining insight into the chemical interactions between
the BDC-(OMe)2 ligands and two divalent Zn ions. The lowest-energy structures were determined
by density functional theory (DFT) with the ωB97X-D functional. The double-zeta with
polarization functions, 6-31G* basis sets were employed for describing light atoms (H, C, N, and
ACS Paragon Plus Environment
17

Crystal Growth & Design
Page 18 of 31
1
2
3
4
5
6
O), whereas LANL2DZ ECP and its corresponding basis sets were used to compute the Zn atoms.
All quantum chemical simulations were performed using Q-Chem 5.2.28
7
8
9
We predicted four energetic minima for each model structure using the DFT approach. Two of
the four model structures of Zn2(BDC-2,5-(OMe)2)4(DABCO)2 were excluded from the analysis
because of strong π-π interactions between two adjacent BDCs that are not present over the entire
MOF framework. Because of truncation and use of simplified models, which include only one
SBU, BDC ligands gain artificial freedom to rearrange, which is not possible in the real MOF
structures. This implies that caution must be exercised when the approximate simplified model is
used to represent nearly infinite 3D framework-type structures. The global minimum-energy
geometry of Zn2(BDC-2,3-(OMe)2)4(DABCO)2 does not include such unrealistic interactions. The
ground state geometries of the two model structures, the third lowest-energy structure of Zn2(BDC-
2,3-(OMe)2)4(DABCO)2 and lowest-energy structure of Zn2(BDC-2,5-(OMe)2)4(DABCO)2,
determined by DFT geometry optimizations are shown in Figure 5 (Figures S14 and S15).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Isomer
Side view
Top view
2,3-(OMe)2
2,5-(OMe)2
ACS Paragon Plus Environment
18

Page 19 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Figure 5. The predicted ground state geometries of the model systems, Zn2(BDC-2,3-
(OMe)2)4(DABCO)2 and Zn2(BDC-2,5-(OMe)2)4(DABCO)2. The atoms directly connected to the
metal ions are described with a ball-and-stick model, while other atoms are described with a simple
line model. Hydrogen atoms were removed for clarity. Color scheme: Zn (cyan), O (red), C (gray),
and N (blue).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The general shape of the optimized models includes two square pyramids with Zn2+ placed at
the center. Deviation from an octahedral-like structure for a zinc central atom has also been
reported in previously,17 and a similar geometric distortion was observed for the two model
structures studied herein. In the optimized model structures, the ortho-functionalized BDC-2,3-
(OMe)2 ligands have two methoxy groups placed at the same side causing severe steric hindrance,
resulting in methoxy groups perpendicular to a benzene ring on BDC. However, the methoxy
groups in the para-functionalized BDC-2,5-(OMe)2 ligands do experience such crowdedness and
retain planar structures. This difference in methoxy orientation affects the relative arrangement
and position of the two square pyramid structures.
The dominant interaction between zinc cations and carboxylic anions is the electrostatic term.
This indicates that other interactions could be adjusted to maximize Coulombic attraction. The
methoxy groups perpendicular to an ortho-functionalized BDC-2,3-(OMe)2 ring induced an
asymmetric CBDC-OBDC-Zn angle to relieve the steric hindrance between the methoxy groups and
DABCO while maintaining sizable electrostatic attractions (XBDC is an X atom in the BDC ligand).
This asymmetric carboxyl coordination was appreciably observed where the two CBDC-OBDC-Zn
angles are 167° and 96° in one BDC ligand, and 153° and 104° for the other BDC ligand in the
cluster (Figure S16). Therefore, the centers of the two square pyramids deviated significantly from
each other, as quantified using the two angles formed by NDABCO-Zn1-Zn2 (152° and 160°,
ACS Paragon Plus Environment
19

Crystal Growth & Design
Page 20 of 31
1
2
3
4
5
6
7
8
9
respectively; Figure S16). This structural feature indicates that the two square pyramids in the
cluster are slipped stacked in the ortho-functionalized BDC-2,3-(OMe)2. From this displacement,
the OBDC belonging to the other square pyramid is shifted closer to the Zn ions (2.40 Å and 2.66 Å
compared to the inoperative ones of 3.3 and 3.4 Å), and the coordination environment near Zn is
similar to a 5+1 configuration (four close OBDC, one NDABCO, and one distant OBDC). This provides
extra interaction between distant OBDC and Zn in addition to the four strongly bound in its square
pyramids (Sideview of cluster in Figure 5). However, in the Zn2(BDC-2,5-(OMe)2)4(DABCO)2
model structures, where BDC ligands experience much less steric hindrance, marginal impacts on
the interaction between Zn cations and carboxylic anions were observed. The centers of the two
square pyramids are nearly in line (i.e., NDABCO-Zn1-Zn2 = 165°; Figure S17), and no additional
distant OBDC coordination was observed in the para-functionalized Zn2(BDC-2,5-
(OMe)2)4(DABCO)2 model structures.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Using these optimized structures, the binding energy was defined as E[Zn2(BDC-2,n-
-
4+
(OMe)2)4(DABCO)2]–4×E[BDC-2,n-(OMe)2)4 ]–E[Zn2(DABCO)2 ], where n is either 3 or 5
(E[X] is the electronic energy of chemical species X). Electronic energy was obtained from DFT
geometry optimizations. This calculation yielded a binding energy of 133.7 kcal/mol for the ortho-
functionalized Zn2(BDC-2,3-(OMe)2)4(DABCO)2 model and 125.2 kcal/mol for the para-
functionalized Zn2(BDC-2,5-(OMe)2)4(DABCO)2 model. This indicated indicates that the ortho-
functionalized BDC-2,3-(OMe)2 ligands were more strongly bound to the Zn2+ ions than the para-
functionalized BDC-2,5-(OMe)2. This can be understood based on the structural features of the
extra interaction between the Zn2+ and distant ODBC (see above). The binding energy analysis
performed via quantum chemical simulations supported and explained the different porosities
observed for the mixed DMOFs after the blending of the two regioisomeric BDC-2,3-(OMe)2 and
ACS Paragon Plus Environment
20

Page 21 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
BDC-2,5-(OMe)2 ligands after evacuation under vacuum. The more strongly coordinated ortho-
functionalized BDC-2,3-(OMe)2 ligands were more resistant to external pressure and stimuli. The
small structural changes in the relative orientation of substituents at the molecular level could
affect the properties of the metal-ligand clusters and entire MOF framework, resulting in different
macroscopic behavior at the experimental level.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
CONCLUSION
Porosity control of pillared DMOFs was achieved using a ligand-blending strategy with BDC-
2,3-(OMe)2 and BDC-2,5-(OMe)2 regioisomers. The correlation between the functional group
position and structural flexibility has been revealed via electron-density-controlled BDC ligands
and DMOFs. For electron-rich BDC ligands, functional group regioisomerism allowed for
different degrees of flexibility. Pure DMOF-[2,3-(OMe)2] showed highly porous properties (~300
cm2/g absorbed N2) at 1 atm after evacuation, while pure DMOF-[2,5-(OMe)2] adopted an almost
non-porous structure toward N2. The ligand ratio of the ortho- and para-functionalized ligands
resulted in a moderate porosity of the resulting DMOFs. Although all the mixed DMOFs with
different ligand ratios showed identical structures in the as-synthesized state, as evidenced by
PXRD pattern analysis, the porosity of the mixed DMOFs varied with the ligand ratio from non-
porous to highly porous. When a 1:1 ratio of the two regioisomeric ligands was incorporated into
the DMOFs, the average porosity obtained fell in between the two pure DMOF-(OMe)2s. When
the ortho-functionalized BDC-2,3-(OMe)2 was more abundant that of the para-functionalized
ligand, the resulting DMOF-[2,3-(OMe)2]3[2,5-(OMe)2]1 displayed higher porosity than the 1:1
ligand mixture.
ACS Paragon Plus Environment
21

Crystal Growth & Design
Page 22 of 31
1
2
3
4
5
6
7
8
9
Detailed structural analysis was performed to examine differences between the regioisomeric
functional groups and associated porosity changes. Although the two regioisomeric DMOFs,
DMOF-[2,3-(OMe)2] and DMOF-[2,5-(OMe)2], are identical except for the ligand positions, the
coordination environments were slightly different in the X-ray structures. Interestingly, the ortho-
functionalized DMOF-[2,3-(OMe)2] showed more rigid coordination bonds between the Zn2+ and
carboxylate in BDC compared to those in DMOF-[2,5-(OMe)2]. Therefore, the overall structural
balance of the frameworks was modulated by the bending motion of the ligand in the ortho-
functionalized DMOF-[2,3-(OMe)2]. In contrast, the twisting motion of SBU adjusted the
structural balance of the frameworks in DMOF-[2,5-(OMe)2] because the coordination of DMOF-
[2,5-(OMe)2] is much weaker than that of DMOF-[2,3-(OMe)2]. These structural findings are well
correlated with the experimental N2 adsorption results. The coordination bond differences between
ortho- and para-functionalized dimethoxy ligands induced porosity changes upon evacuation.
Finally, quantum chemical simulations were performed to understand the binding differences
between ortho- and para-dimethoxy-functionalized ligands. While BDC ligands experience much
less steric hindrance in the Zn2(BDC-2,5-(OMe)2)4(DABCO)2 model structures, the methoxy
groups perpendicular to the BDC-2,3-(OMe)2 ring induced an asymmetric CBDC-OBDC-Zn angle
to relieve steric hindrance between the methoxy groups and DABCO while maintaining sizable
electrostatic attractions. Therefore, the center of the two square pyramids in the vertex of the
DMOF structure significantly deviated. Additionally, these differences in the optimized structures
were successfully utilized for binding energy comparisons. This calculation gave a binding energy
of 133.7 kcal/mol for the ortho-functionalized Zn2(BDC-2,3-(OMe)2)4(DABCO)2 model and
125.2 kcal/mol for the para-functionalized Zn2(BDC-2,5-(OMe)2)4(DABCO)2 model, indicating
that the ortho-functionalized BDC-2,3-(OMe)2 ligands are more strongly bound to Zn2+. The more
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment
22

Page 23 of 31
Crystal Growth & Design
1
2
3
4
5
6
strongly coordinated ortho-functionalized BDC-2,3-(OMe)2 ligands were more resistant to
external pressure and stimuli.
7
8
9
In summary, MOF porosity could be controlled by a ligand-mixing strategy with regioisomeric
ligands. Although the chemical formula and as-synthesized structures are identical, the porosities
upon evacuation varied and were controllable by adjusting the ligand ratio. The detailed structural
analysis using X-ray crystallography and quantum chemical simulation revealed important
differences in the coordination environment between the zinc ion and carboxylate ligand for the
ortho- and para-regioisomers. The small structural change in the relative orientation of
substituents at the molecular level affected the properties of the metal-ligand clusters and the entire
MOF framework, resulting in different macroscopic behavior.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
AUTHOR INFORMATION
Corresponding Author
Minyoung Yoon, Department of Chemistry, Kyungbook National University, Daegu, 41566,
Korea, *E-mail: myyoon@knu.ac.kr (M. Yoon)
Hyungjun Kim, Department of Chemistry, Incheon National University, Incheon, 22012, Korea,
*E-mail: kim.hyungjun@inu.ac.kr (H. Kim)
Dongwook Kim, Center for Catalytic Hydrocarbon Functionalization, Institute of Basic Science,
*E-mail: dwkxtal@kaist.ac.kr (D. Kim)
Min Kim, Department of Chemistry, Chungbuk National University, Cheongju, 28644, Korea, *E-
mail: minkim@chungbuk.ac.kr (M. Kim)
ACS Paragon Plus Environment
23

Crystal Growth & Design
Page 24 of 31
1
2
3
4
Authors
5
6
7
8
9
Dopil Kim – Department of Chemistry, Chungbuk National University, Cheongju, 28644, Korea
Hyeonbin Ha –Department of Chemistry, Chungbuk National University, Cheongju, 28644, Korea
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Youngik Kim – Department of Chemistry, Chungbuk National University, Cheongju, 28644,
Korea
Younghu Son – Department of Chemistry, Kyungbook National University, Daegu, 41566, Korea
Jiyoon Choi – Department of Chemistry, Incheon National University, Incheon, 22012, Korea
Myung Hwan Park – Department of Chemistry Education, Chungbuk National University,
Cheongju, 28644, Korea
Youngjo Kim – Department of Chemistry, Chungbuk National University, Cheongju, 28644,
Korea
Author Contributions
#D. Kim and H. Ha contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This research was supported by the Basic Science Research Program (2019R1A2C4070584) and
the Science Research Center (2016R1A5A1009405) through the National Research Foundation of
ACS Paragon Plus Environment
24

Page 25 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Korea (NRF) funded by the Ministry of Science and ICT. Single crystal and powder X-ray
diffraction experiments at PLS-II, 2D-SMC beamlines were supported in part by MSIT and
POSTECH. H. Ha (Ph. D. Student) was supported by Basic Science Research Program
(2019R1A6A3A13095922) through the NRF funded by the Ministry of Education. Jiyoon Choi
and Hyungjun Kim was supported by the Basic Science Research Program
(2017R1A6A1A06015181) through the NRF funded by the Ministry of Educations.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ASSOCIATED CONTENT
Supporting Information.
Synthetic details; NMR spectra; single crystal data; full isotherm data; powder XRD data; TGA
data; additional images from computational approaches (PDF)
Accession Codes: CCDC 1994998-1995002 contain 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 e-mailing data_request@ccdc.cam.ac.kr, or by contacting The Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK; fax +44-1223-336033.
This information is available free of charge via the Internet at http://pubs.acs.org/
REFERENCES
(1) Zhou, H.-C.; Long, J. R.; Yaghi, O. M. Introduction to Metal–Organic Frameworks. Chem.
Rev. 2012, 112, 673–674.
ACS Paragon Plus Environment
25

Crystal Growth & Design
Page 26 of 31
1
2
3
4
5
6
(2) Murray, L. J.; Dincă, M.; Long, J. R. Hydrogen Storage in Metal–Organic Frameworks.
Chem. Soc. Rev. 2009, 38, 1294–1314.
7
8
9
(3) Li, J.-R.; Kuppler, R. J.; Zhou, H.-C. Selective Gas Adsorption and Separation in Metal–
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Organic Frameworks. Chem. Soc. Rev. 2009, 38, 1477–1504.
(4) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Metal–Organic
Framework Materials as Catalysts. Chem. Soc. Rev. 2009, 38, 1450–1459.
(5) MacGillivray, L. R.; Lukehart, C. M. Metal-Organic Framework Materials; Wiley;
Hoboken, NJ, USA, 2014.
(6) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Reticular
Synthesis and the Design of New Materials. Nature 2003, 423, 705–714.
(7) Nouar, F.; Devic, T.; Chevreau, H.; Guillou, N.; Gibson, E.; Clet, G.; Daturi, M.; Vimont,
A.; Grenèche, J. M.; Breeze, M. I.; Walton, R. I.; Llewellyn, P. L.; Serre, C. Tuning the Breathing
Behaviour of MIL-53 by Cation Mixing. Chem. Commun. 2012, 48, 10237–10239.
(8) Cohen, S. M. Postsynthetic Methods for the Functionalization of Metal-Organic
Frameworks. Chem. Rev. 2012, 112, 970–1000.
(9) Klein, N.; Hoffmann, H. C.; Cadiau, A.; Getzschmann, J.; Lohe, M. R.; Paasch, S.;
Heydenreich, T.; Adil, K.; Senkovska, I.; Brunner, E.; Kaskel, S. Structural Flexibility and
Intrinsic Dynamics in the M2(2,6-Ndc)2(Dabco) (M = Ni, Cu, Co, Zn) Metal-Organic Frameworks.
J. Mater. Chem. 2012, 22, 10303–10312.
(10) Schneemann, A.; Bon, V.; Schwedler, I.; Senkovska, I.; Kaskel, S.; Fischer, R. A. Flexible
Metal–Organic Frameworks. Chem. Soc. Rev. 2014, 43, 6062–6096.
ACS Paragon Plus Environment
26

Page 27 of 31
Crystal Growth & Design
1
2
3
4
(11) Kim, M.; Boissonnault, J. A.; Dau, P. V.; Cohen, S. M. Metal-Organic Framework
5
6
Regioisomers Based on Bifunctional Ligands. Angew. Chem., Int. Ed. 2011, 50, 12193–12196.
7
8
9
(12) Hahm, H.; Yoo, K.; Ha, H.; Kim, M. Aromatic Substituent Effects on the Flexibility of
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Metal–Organic Frameworks. Inorg. Chem. 2016, 55, 7576–7581.
(13) Ha, H.; Hahm, H.; Jwa, D. G.; Yoo, K.; Park, M. H.; Yoon, M.; Kim, Y.; Kim, M.
Flexibility in Metal–Organic Frameworks Derived from Positional and Electronic Effects of
Functional Groups. CrystEngComm 2017, 19, 5361–5368.
(14) Dybtsev, D. N.; Chun, H.; Kim, K. Rigid and Flexible: A Highly Porous Metal–Organic
Framework with Unusual Guest-Dependent Dynamic Behavior. Angew. Chem., Int. Ed. 2004, 43,
5033–5036.
(15) Heldmann, C.; Schulze, M.; Wegner, G. Rigid-Rod-like Main Chain Polymers with
Rigidly Attached Chromophores. A Novel Structural Concept for Electrooptical Materials. 1.
Synthesis and Characterization. Macromolecules 1996, 29, 4686–4696.
(16) Wang, Z.; Tanabe, K. K.; Cohen, S. M. Accessing Postsynthetic Modification in a Series
of Metal-Organic Frameworks and the Influence of Framework Topology on Reactivity. Inorg.
Chem. 2009, 48, 296–306.
(17) Ha, H.; Kim, Y.; Kim, D.; Lee, J.; Song, Y.; Kim, S.; Park, M. H.; Kim, Y.; Kim, H.; Yoon,
M.; Kim, M. Effect of the Metal within Regioisomeric Paddle‐Wheel‐Type Metal–Organic
Frameworks. Chem. Eur. J. 2019, 25, 14414–14420.
ACS Paragon Plus Environment
27

Crystal Growth & Design
Page 28 of 31
1
2
3
4
5
6
7
8
9
(18) Burrows, A. D. Mixed-Component Metal-Organic Frameworks (MC-MOFs): Enhancing
Functionality through Solid Solution Formation and Surface Modifications. CrystEngComm 2011,
13, 3623–3642.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(19) Abednatanzi, S.; Gohari Derakhshandeh, P.; Depauw, H.; Coudert, F. X.; Vrielinck, H.;
Van Der Voort, P.; Leus, K. Mixed-Metal Metal-Organic Frameworks. Chem. Soc. Rev. 2019, 48,
2535–2565.
(20) Kim, M.; Cahill, J. F.; Prather, K. A.; Cohen, S. M. Postsynthetic Modification at
Orthogonal Reactive Sites on Mixed, Bifunctional Metal-Organic Frameworks. Chem. Commun.
2011, 47, 7629–7631.
(21) Tarazona, P.; Marini Bettolo Marconi, U.; Evans, R. Phase Equilibria of Fluid Interfaces
and Confined Fluids: Non-Local Versus Local Density Functionals. Mol. Phys. 1987, 60, 573–
595.
(22) Lastoskie, C.; Gubbins, K. E.; Quirke, N. Pore Size Distribution Analysis of Microporous
Carbons: a Density Functional Theory Approach. J. Phys. Chem. 1993, 97, 4786–4796.
(23) Horváth, G.; Kawazoe, K. Method for the Calculation of Effective Pore Size Distribution
in Molecular Sieve Carbon. J. Chem. Eng. Jpn. 1983, 16, 470–475.
(24) Everett, D. H.; Powl, J. C. Adsorption in Slit-like and Cylindrical Micropores in the Henry’s
Law Region. J. Chem. Soc., Faraday Trans. 1, 1976, 72, 619–636.
(25) Schwalbe, S.; Trepte, K.; Seifert, G.; Kortus, J. Screening for High-Spin Metal Organic
Frameworks (MOFs): Density Functional Theory Study on DUT-8(M1,M2) (with Mi = V,...,Cu).
Phys. Chem. Chem. Phys. 2016, 18, 8075–8080.
ACS Paragon Plus Environment
28

Page 29 of 31
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
(26) Dangi, G. P.; Pillai, R. S.; Somani, R. S.; Bajaj, H. C.; Jasra, R. V. A Density Functional
Theory Study on the Interaction of Hydrogen Molecule with MOF-177. Mol. Simul. 2010, 36,
373–381.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(27) Wilbraham, L.; Coudert, F. X.; Ciofini, I. Modelling Photophysical Properties of Metal-
Organic Frameworks: A Density Functional Theory Based Approach. Phys. Chem. Chem. Phys.
2016, 18, 25176–25182.
(28) Shao, Y.; Gan, Z.; Epifanovsky, E.; Gilbert, A. T.; Wormit, M.; Kussmann, J.; Lange, A.
W.; Behn, A.; Deng, J.; Feng, X.; Ghosh, D.; Goldey, M.; Horn, P. R.; Jacobson, L. D.; Kaliman,
I.; Khaliullin, R. Z.; Ku_s, T.; Landau, A.; Liu, J.; Proynov, E. I.; Rhee, Y. M.; Richard, R. M.;
Rohrdanz, M. A.; Steele, R. P.; Sundstrom, E. J.; Woodcock, H. L.; Zimmerman, P. M.; Zuev, D.;
Albrecht, B.; Alguire, E.; Austin, B.; Beran, G. J.; Bernard, Y. A.; Berquist, E.; Brandhorst, K.;
Bravaya, K. B.; Brown, S. T.; Casanova, D.; Chang, C. M.; Chen, Y.; Chien, S. H.; Closser, K.
D.; Crittenden, D. L.; Diedenhofen, M.; Distasio, R. A.; Do, H.; Dutoi, A. D.; Edgar, R. G.; Fatehi,
S.; Fusti-Molnar, L.; Ghysels, A.; Golubeva-Zadorozhnaya, A.; Gomes, J.; Hanson-Heine, M. W.;
Harbach, P. H.; Hauser, A. W.; Hohenstein, E. G.; Holden, Z. C.; Jagau, T. C.; Ji, H.; Kaduk, B.;
Khistyaev, K.; Kim, J.; Kim, J.; King, R. A.; Klunzinger, P.; Kosenkov, D.; Kowalczyk, T.;
Krauter, C. M.; Lao, K. U.; Laurent, A. D.; Lawler, K. V.; Levchenko, S. V.; Lin, C. Y.; Liu, F.;
Livshits, E.; Lochan, R. C.; Luenser, A.; Manohar, P.; Manzer, S. F.; Mao, S. P.; Mardirossian,
N.; Marenich, A. V.; Maurer, S. A.; Mayhall, N. J.; Neuscamman, E.; Oana, C. M.; Olivares-
Amaya, R.; Oneill, D. P.; Parkhill, J. A.; Perrine, T. M.; Peverati, R.; Prociuk, A.; Rehn, D. R.;
Rosta, E.; Russ, N. J.; Sharada, S. M.; Sharma, S.; Small, D. W.; Sodt, A.; Stein, T.; Stuck, D.;
Su, Y. C.; Thom, A. J.; Tsuchimochi, T.; Vanovschi, V.; Vogt, L.; Vydrov, O.; Wang, T.; Watson,
M. A.; Wenzel, J.; White, A.; Williams, C. F.; Yang, J.; Yeganeh, S.; Yost, S. R.; You, Z. Q.;
ACS Paragon Plus Environment
29