Control of interpenetration and gas-sorption properties of metal-organic frameworks by a simple change in ligand design

Article abstract of DOI:10.1002/chem.201200456

In metal-organic framework (MOF) chemistry, interpenetration greatly affects the gas-sorption properties. However, there is a lack of a systematic study on how to control the interpenetration and whether the interpenetration enhances gas uptake capacities or not. Herein, we report an example of interpenetration that is simply controlled by the presence of a carbon-carbon double or single bond in identical organic building blocks, and provide a comparison of gas-sorption properties for these similar frameworks, which differ only in their degree of interpenetration. Noninterpenetrated (SNU-70) and doubly interpenetrated (SNU-71) cubic nets were prepared by a solvothermal reaction of [Zn(NO₃)₂]·6 H₂O in N,N-diethylformamide (DEF) with 4-(2-carboxyvinyl)benzoic acid and 4-(2-carboxyethyl)benzoic acid, respectively. They have almost-identical structures, but the noninterpenetrated framework has a much bigger pore size (ca. 9.0×9.0 A) than the interpenetrated framework (ca. 2.5×2.5 A). Activation of the MOFs by using supercritical CO ₂ gave SNU-70' and SNU-71'. The simulation of the PXRD pattern of SNU-71' indicates the rearrangement of the interpenetrated networks on guest removal, which increases pore size. SNU-70' has a Brunauer-Emmett-Teller (BET) surface area of 5290 m² g^-1, which is the highest value reported to date for a MOF with a cubic-net structure, whereas SNU-71' has a BET surface area of 1770 m² g^-1. In general, noninterpenetrated SNU-70' exhibits much higher gas-adsorption capacities than interpenetrated SNU-71' at high pressures, regardless of the temperature. However, at P<1 atm, the gas-adsorption capacities for N₂ at 77 K and CO₂ at 195 K are higher for noninterpenetrated SNU-70' than for interpenetrated SNU-71', but the capacities for H₂ and CH₄ are the opposite; SNU-71' has higher uptake capacities than SNU-70' due to the higher isosteric heat of gas adsorption that results from the smaller pores. In particular, SNU-70' has exceptionally high H₂ and CO₂ uptake capacities. By using a post-synthetic method, the C=C double bond in SNU-70 was quantitatively brominated at room temperature, and the MOF still showed very high porosity (BET surface area of 2285 m² g ^-1). Copyright

Full text of DOI:10.1002/chem.201200456

FULL PAPER
DOI: 10.1002/chem.201200456
Control of Interpenetration and Gas-Sorption Properties of Metal–Organic
Frameworks by a Simple Change in Ligand Design
Thazhe Kootteri Prasad and Myunghyun Paik Suh*[a]
Abstract: In metal–organic framework
(MOF) chemistry, interpenetration
greatly affects the gas-sorption proper-
ties. However, there is a lack of a sys-
tematic study on how to control the in-
terpenetration and whether the inter-
penetration enhances gas uptake ca-
pacities or not. Herein, we report an
example of interpenetration that is
simply controlled by the presence of
a carbon–carbon double or single bond
in identical organic building blocks,
and provide a comparison of gas-sorp-
tion properties for these similar frame-
works, which differ only in their degree
of interpenetration. Noninterpenetrat-
ed (SNU-70) and doubly interpenetrat-
ed (SNU-71) cubic nets were prepared
by a solvothermal reaction of [Zn-
benzoic acid, respectively. They have
almost-identical structures, but the
noninterpenetrated framework has
a much bigger pore size (ca. 9.0ꢀ
9.0 ꢁ) than the interpenetrated frame-
work (ca. 2.5ꢀ2.5 ꢁ). Activation of the
MOFs by using supercritical CO2 gave
SNU-70’ and SNU-71’. The simulation
of the PXRD pattern of SNU-71’ indi-
cates the rearrangement of the inter-
penetrated networks on guest removal,
which increases pore size. SNU-70’ has
a Brunauer–Emmett–Teller (BET) sur-
face area of 5290 m2 gÀ1, which is the
highest value reported to date for
area of 1770 m2 gÀ1. In general, nonin-
terpenetrated SNU-70’ exhibits much
higher gas-adsorption capacities than
interpenetrated SNU-71’ at high pres-
sures, regardless of the temperature.
However, at P<1 atm, the gas-adsorp-
tion capacities for N2 at 77 K and CO2
at 195 K are higher for noninterpene-
trated SNU-70’ than for interpenetrat-
ed SNU-71’, but the capacities for H2
and CH4 are the opposite; SNU-71’ has
higher uptake capacities than SNU-70’
due to the higher isosteric heat of gas
adsorption that results from the smaller
pores. In particular, SNU-70’ has ex-
ceptionally high H2 and CO2 uptake ca-
a MOF with
a cubic-net structure,
whereas SNU-71’ has a BET surface
pacities. By using a post-synthetic
method, the C=C double bond in SNU-
70 was quantitatively brominated at
room temperature, and the MOF still
showed very high porosity (BET sur-
face area of 2285 m2 gÀ1).
Keywords: carbon dioxide · adsorp-
tion · hydrogen · interpenetration ·
metal–organic frameworks
ACHTUNGTRENNUNG(NO3)2]·6H2O in N,N-diethylforma-
mide (DEF) with 4-(2-carboxyvinyl)-
benzoic acid and 4-(2-carboxyethyl)-
Introduction
However, when using ligands with similar length it is diffi-
cult to predict which framework will be interpenetrated and
which will be noninterpenetrated. Previously, it was report-
ed that interpenetrated structures showed higher gas-sorp-
tion capacities for N2 and H2 gases at 77 K under both low
and high pressures, and at 298 K under high pressure.[4,7a] In
contrast, theoretical calculations have predicted that nonin-
terpenetrated structures should have better gas-sorption ca-
pacities than interpenetrated structures.[9] Despite these con-
tradictory arguments, it is difficult to prove which is the
more general case because gas-sorption properties should be
compared between frameworks with similar structures that
only differ in their degree of interpenetration. However,
such cases are difficult to find.[4,7]
Herein, we report an example of interpenetration and
consequent gas-sorption properties of MOFs, which is
simply controlled by the presence of a carbon–carbon
double or single bond in identical organic building blocks
(Scheme 1). This is significant in several respects: 1) reports
of the systematic comparison of gas sorption properties for
similar frameworks that differ only in the degree of inter-
penetration are very rare; 2) highly porous SNU-70’ is pre-
sented, which has an extraordinary high surface area and ex-
Porous metal–organic frameworks (MOFs) have received
considerable attention due to their high surface areas and
excellent gas-sorption properties.[1–3] In MOF chemistry, con-
trol of the interpenetration is of high importance because
the degree of interpenetration significantly affects the gas-
sorption properties of the material.[2] There have been a few
reports of methods to control the interpenetration of MOFs.
Some reported methods include the addition of a template
during the synthesis,[4,5] rational design of ligands,[6,7] and ad-
justment of the reaction conditions, such as the concentra-
tion of building blocks and temperature.[8] In particular, if
the length of the ligand is elongated then the MOF has
a better tendency to form an interpenetrated structure.
[a] Dr. T. K. Prasad, Prof. M. P. Suh
Department of Chemistry, Seoul National University
Seoul 151-747 (Republic of Korea)
Fax : (+82)28868516
E-mail: mpsuh@snu.ac.kr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200456.
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directions, which is much larger than those of interpenetrat-
ed SNU-71 (ca. 2.5ꢀ2.5 ꢁ). The guest solvent molecules in
SNU-70 and SNU-71 could not be located from the differ-
ence map due to significant thermal disorder, and were de-
termined by elemental analyses and thermogravimetric anal-
ysis (TGA) data. As expected, the amount of guest solvent
molecules per formula unit in doubly interpenetrated SNU-
71 is nearly half that in SNU-70.
Activation of the MOFs by using supercritical CO2 gives
completely desolvated materials, [Zn4OACHTUNGRTEN(NUNG CVB)3] (SNU-70’)
and [Zn4O(CEB)3] (SNU-71’). The powder X-ray diffraction
AHCTUNGTRENNUNG
(PXRD) patterns indicate that SNU-70 retains its structure
but SNU-71 undergoes a structural rearrangement upon re-
moval of the guest solvent molecules (Figure 2).[10] The pos-
Scheme 1. Ligands used in SNU-70 and SNU-71.
ceptionally high H2, CO2, and CH4 gas-sorption capacities;
3) the rearrangement of the interpenetrated networks upon
guest removal, which leads to expansion of pore size, is re-
vealed; 4) the post-synthetic bromination of the C=C double
bonds in the MOF is reported, in particular quantitatively
and at room temperature.
Results and Discussion
Syntheses and X-ray crystal structures of SNU-70 and SNU-
71:
ACHTUNGTRENNUNG
Pale-yellow
cubic
crystals
of
and
[Zn4O-
[Zn4O-
(SNU-70)
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
(H2CVB) or 4-(2-carboxyethyl)benzoic acid (H2CEB), re-
spectively, at 1058C for 12 h in N,N-diethylformamide
(DEF). X-ray crystal structures (Figure 1) of SNU-70 and
Figure 2. PXRD patterns: a) as-synthesized SNU-70, b) pattern of SNU-
70 simulated based on X-ray crystallographic data, c) SNU-70’ resulting
from supercritical CO2 treatment of SNU-70, d) as-synthesized SNU-71,
e) pattern of SNU-71 simulated based on X-ray crystallographic data,
f) SNU-71’ resulting from supercritical CO2 treatment of SNU-71, and
g) simulated pattern of the modeled structure of SNU-71’, which is de-
scribed in Figure 3.
Figure 1. X-ray crystal structures of: a) noninterpenetrated SNU-70, and
b) doubly interpenetrated SNU-71. The interpenetrated two independent
frameworks are represented in red and blue.
SNU-71 indicate that they have similar cubic-net structures
that are constructed from [Zn4O]6+ octahedral secondary
building units (SBUs) and linear dicarboxylate linkers, simi-
larly to MOF-5.[7b] In both frameworks, the distances be-
tween the nearest [Zn4O] clusters in a cubic net is 15 ꢁ.
sible structure of SNU-71’ was simulated from the PXRD
pattern by using the Materials Studio program.[11] Upon
guest removal, the two interpenetrated frameworks move
However, SNU-70 has
a noninterpenetrated structure
À
whereas SNU-71 has a doubly interpenetrated structure.
Noninterpenetrated SNU-70 generates square channels with
dimensions of approximately 9.0ꢀ9.0 ꢁ in three orthogonal
closer due to the hydrogen-bonding interactions of C H···O,
which enlarges the pore size from 2.5ꢀ2.5 ꢁ to 6.0ꢀ5.8 ꢁ,
as shown in Figures 3 and 4.
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Gas Sorption Properties of Metal–Organic Frameworks
FULL PAPER
amount of N2 due to the increase in pore size on desolva-
tion, as discussed earlier. The SNU-71’ sample has a pore
volume of 0.709 cm3 gÀ1 and
a BET surface area of
1770 m2 gÀ1 (Langmuir 1923 m2 gÀ1).
The H2 adsorption isotherms of SNU-70’ and SNU-71’
were measured at 77 and 87 K (Figure 5b), and the isosteric
heats (Qst) of the H2 adsorption were estimated from the
data by using the virial equation.[13] In contrast to the N2 ad-
sorption, SNU-71’ adsorbs a higher amount of H2 gas than
SNU-70’ at 77 and 87 K below P<1 atm. This might be re-
lated to the isosteric heat of H2 adsorption in SNU-71’,
which is approximately 2 kJmolÀ1 higher than that of SNU-
70’. The smaller pore size of SNU-71’ increases the overlap
potential between the framework and hydrogen.[14] Howev-
er, at 77 K and high pressure, the H2 uptake capacity of
SNU-70’ becomes greater than that of SNU-71’ (Figure 6).
The excess H2 uptake capacity of SNU-70’ is greater than
SNU-71’ by a factor of 1.85 at 77 K and 1.54 at 298 K. The
total H2 uptake capacity of SNU-70’ is 2.1 times greater
than that of SNU-71’ at 77 K and 2.4 times greater at 298 K.
In particular, the H2 uptake capacity of SNU-70’ at 77 K and
high pressure is extraordinarily high, with an excess of
73.8 mggÀ1 (total 117.4 mggÀ1) at 77 K and 70 bar. This is
comparable to the highest reported H2 uptake capacities,
such as 99.5 mggÀ1 excess at 56 bar (total 164 mggÀ1 at
70 bar) for NU-100,[12] 86 mggÀ1 excess (total 176 mggÀ1 at
80 bar) for MOF-210,[1] 74.0 mggÀ1 excess (total 163 mggÀ1
at 80 bar) for MOF-200,[1] and 81.0 mggÀ1 excess (total
110.6 mggÀ1 at 90 bar) for SNU-77H.[15]
The CO2 gas sorption isotherms of SNU-70’ and SNU-71’
were measured at various temperatures (Figure 7). At 195 K
and 1 atm, SNU-70’ shows a S-shaped isotherm similar to
MOF-5, due to the attractive electrostatic interactions be-
tween the CO2 molecules.[16] SNU-70’ exhibits a CO2 adsorp-
tion capacity of 2214 mggÀ1 at 195 K and 1 atm, which is
about four times greater than that of SNU-71’, in accord-
ance with the fact that N2 adsorption is higher for SNU-70’
than SNU-71’ at 77 K and P<1 atm. The CO2 uptake ca-
pacity of SNU-70’ is higher than the reported value for
MOF-5 (1500 mggÀ1) and pmg-MOF-5 (2000 mggÀ1) under
Figure 3. Simulated structural transformation of SNU-71 on removal of
guest molecules. a) X-ray crystal structure of SNU-71, and b) simulated
structure of desolvated SNU-71’ based on its PXRD pattern.
Figure 4. Simulated structure of SNU-71’. a) View along the ac or bc
plane, and b) view along the ab plane.
Gas-sorption properties: Gas-sorption isotherms of SNU-70’
and SNU-71’ were measured for N2, H2, CO2, and CH4, and
the data are summarized in Table 1 together with the data
for other MOFs for comparison. Noninterpenetrated SNU-
70’ has a pore volume of 2.17 cm3 gÀ1 and a BET surface
area of 5290 m2 gÀ1 (Langmuir 6100 m2 gÀ1), which is the
highest of all MOFs with cubic-net structures and is compa-
rable to the highest values reported so far for MOFs such as
MOF-210[1] (BET 6240 m2 gÀ1) and NU-100 (BET
6143 m2 gÀ1).[12] Although the pore size of as-synthesized
SNU-71 is much smaller than the kinetic diameter of N2
(3.64 ꢁ), the desolvated SNU-71’ sample adsorbs a large
Table 1. Gas adsorption properties of SNU-70’ and SNU-71’, with comparisons to other MOFs.
SNU-70’
SNU-71’
SNU-77H[15]
MOF-5[1,2a]
MOF-177[1]
MOF-210[1]
NU-100[12]
PCN-68[24]
BET S.A. [m2 gÀ1
]
5290
2.17
12.4
73.8/117.4/70
4.0/14.5/70
5.12
2210
35
1420/1640/45
17.2
39
4.9
168/224/45
9.4
1770
0.709
14.4
39.9/54.6/70
2.6/6.1/70
7.22
580
46
493/564/45
17.8
49
3670
1.52
17.9
81.0/110/90
5.0/11.9/90
7.05
1690
39
933/1030/40
19.9
87
6.2
142/173/35
14.3
4400
1.55
1.32
53/82/80
–
4500
6240
3.60
–
86/176/80
–
–
–
6143
2.82
18.2
99.5/164/70
–
6.1
–
–
5109
2.13
18.7
73.2/135/50
10.1/29/90
6.09
–
–
1338/1804/100
21.2
–
–
186/465/100
15.2
Vpore [cm3 gÀ1
]
1.89
H2, 77 K [mggÀ1
H2, 77 K [mggÀ1
]
]
1.25[27]
[a]
[b]
73/116/80
–
H2, 298 K [mggÀ1
]
]
[b]
Qst (H2) [kJmolÀ1
4.8
–
–
[c]
CO2, 195 K [mggÀ1
CO2, 298 K [mggÀ1
CO2, 298 K [mggÀ1
]
]
]
1500[17]
46[21]
[a]
35[21]
–
[a]
[b]
[c]
864/1030/50
16.5[25]
–
1356/1550/80
2396/2870/50
–
–
–
264/475/80
–
2043/2315/40
Qst (CO2) [kJmolÀ1
]
14[28]
–
–
–
–
–
CH4, 195 K [mggÀ1
CH4, 298 K [mggÀ1
CH4, 298 K [mggÀ1
]
]
]
–
–
[a]
[a]
[b]
[c]
5.2
101/121/45
14.6
–
165/250/80
243/345/80
–
Qst (CH4) [kJmolÀ1
]
12.2[26]
[a] At 1 atm. [b] At high pressure. Excess/total capacity/pressure in bar. [c] Isosteric heat of adsorption at zero coverage.
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M. P. Suh and T. K. Prasad
*
,
*
) and
Figure 5. The N2 and H2 adsorption isotherms of SNU-70’ (
&
SNU-71’ ( , &). a) N2 at 77 K, and b) H2 at 77 and 87 K. Filled shapes:
adsorption; open shapes: desorption.
*
,
*
) and
Figure 6. High-pressure gas-adsorption isotherms of SNU-70’ (
&
SNU-71’ ( , &) for H2 at a) 77, and b) 298 K. c: excess uptake; a:
total uptake; filled shapes: adsorption; open shapes: desorption.
similar conditions.[17] However, at 298 K and 1 atm, the CO2
uptake capacity of SNU-71’ becomes 1.3 times greater than
that of SNU-70’ (35 mggÀ1 in SNU-70’ and 46 mggÀ1 in
SNU-71’). There have been some MOFs that adsorb CO2
with high uptake capacity and high selectivity, such as SNU-
and 40 bar for NU-100.[12] The isosteric heats of CO2 adsorp-
tion in SNU-70’ and SNU-71’ are 17.2 and 17.8 kJmolÀ1, re-
spectively, as calculated from the isotherms measured at
195, 273, and 298 K up to 1 atm by using the Clausius–Cla-
peyron equation.
The CH4 adsorption isotherms show relatively high ad-
sorption capacities. At 195 and at 298 K and up to 1 atm,
SNU-71’ shows slightly higher CH4 uptake than SNU-70’
(Figure 8), similar to the results for H2 adsorption at 77 K
and P<1 atm. The zero coverage isosteric heats of CH4 ad-
sorption in SNU-70’ and SNU-71’ are 9.4 and 14.6 kJmolÀ1,
M10 (9.2 wt%),[18] SNU-21S (11.1 wt%),[19] and Mg
2ACTHNUTRGNE(NUG dobdc)
(35.2 wt%).[20] At 298 K and 45 bar, SNU-70’ adsorbs CO2
with an excess 1420 mggÀ1 (total 1640 mggÀ1; Figure S3 in
the Supporting Information), which is comparable to that of
MOF-177 (excess 1493 mggÀ1, total 1656 mggÀ1 at 298 K
and 42 bar).[21] The reported highest excess CO2 uptake ca-
pacities at 298 K and high pressures are 2400 mggÀ1 at
50 bar for MOF-200 and MOF-210,[1] 2043 mggÀ1 at 298 K
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Gas Sorption Properties of Metal–Organic Frameworks
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*
*
) and SNU-71’
Figure 7. The gas-adsorption isotherms of SNU-70’ (
,
*
*
) and SNU-71’
Figure 8. The gas-adsorption isotherms of SNU-70’ (
&
,
&
( , &) for CO2 at: a) 195, and b) 273 and 298 K. Filled shapes: adsorp-
( , &) for CH4 at: a) 195, and b) 273 and 298 K. Filled shapes: adsorp-
tion; open shapes: desorption.
tion; open shapes: desorption.
respectively. However, at 298 K and 45 bar, the CH4 uptake
capacity of SNU-70’ (excess 168 mggÀ1, total 224 mggÀ1) are
much higher than those of SNU-71’ (excess 101 mggÀ1, total
121 mggÀ1; Figure S4 in the Supporting Information).
partially brominated at room temperature in 24 h, and quan-
titative bromination was possible only at 1008C.[22] In the
present case, the diffusion of Br2 into the pores must be
much easier due to the very large pore size of SNU-70,
which leads to more efficient bromination even at room
temperature. For SNU-70Br, the BET surface area is
2285 m2 gÀ1 (Langmuir 2550 m2 gÀ1) and the pore volume is
0.908 cm3 gÀ1, which indicates that it still retains high porosi-
ty, although its porosity is reduced compared with that of
SNU-70’. SNU-70Br has H2 uptake capacities of 7.3 mggÀ1
at 77 K and 1 atm and 4.2 mggÀ1 at 87 K and 1 atm
(Figure 9). The isosteric heat of the H2 adsorption is 6.14 to
4.41 kJmolÀ1, which is slightly higher than that of SNU-70’.
Post-synthetic bromination of SNU-70: The C=C double
bond in the ligand of SNU-70 was brominated at room tem-
perature, then dried by using supercritical CO2 to give SNU-
70Br. The elemental analysis data and the NMR spectra
measured in [D6]DMSO for the crystals that were digested
in DCl indicated that all C=C bonds in SNU-70 were bromi-
nated (see Figure S5 in the Supporting Information). Previ-
ously, it was reported that the C=C bonds in a MOF were
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M. P. Suh and T. K. Prasad
In particular, the SNU-70’ sample shows an extraordinarily
high surface area and exceptionally high H2 and CO2 gas-
sorption capacities. However, it should be noted here that
gas-sorption properties cannot be easily predicted from the
interpenetration. As seen in Figures 5 and 8, at P<1 atm,
the gas-adsorption capacities for N2 at 77 K and CO2 at
195 K are higher for noninterpenetrated SNU-70’ than inter-
penetrated SNU-71’, but H2 and CH4 adsorptions are the re-
verse, that is, SNU-71’ has higher uptake capacities than
SNU-70’. By a post-synthetic method, the C=C bonds in
SNU-70 were quantitatively brominated at room tempera-
À
ture and a noninterpenetrated MOF with a C C bond in the
ligand, which still shows a high porosity (BET 2285 m2 gÀ1
;
pore volume 0.908 cm3 gÀ1), was also successfully construct-
ed. The present results might be useful for future construc-
tion of highly porous MOFs with interpenetration that may
be controlled by a small change in the ligand to fine-tune
the gas-sorption properties.
Experimental Section
Synthesis of ligands: 4-(2-Carboxyvinyl)benzoic acid (H2CVB) and 4-(2-
carboxyethyl)benzoic acid (H2CEB) were synthesized by using previously
reported procedures (see the Supporting Information).[23]
ACHNUTERTG[NGUNN Zn4OAHCTNUTRGENG(UNN CVB)3]·13DEF·2H2O (SNU-70): [ZnACTHUNGTREN(NUGN NO3)2]·6H2O (0.030 g,
0.101 mmol) and H2CVB (0.015 g, 0.075 mmol) were dissolved in DEF
(5 mL) in a glass bottle, which was sealed and heated at 1058C for 12 h
in a programmable furnace. Pale-yellow cubic crystals were formed,
which were filtered and washed with DEF (yield: 0.030 g, 55%). FTIR
(KBr pellet): n˜ =1667 (DEF), 1607 cmÀ1 (carboxylate); elemental analy-
sis calcd (%) for C95H165N13O28Zn4: C 51.89, H 7.56. N 8.28; found: C
52.26, H 8.10, N 8.87.
A
N
(SNU-71):
[Zn
N
(0.030 g,
0.101 mmol) and H2CEB (0.015 g, 0.075 mmol) were dissolved in DEF
(5 mL) in a glass bottle, which was sealed and heated at 1058C for 12 h
in a programmable furnace. Pale-yellow cubic crystals were formed,
which were filtered and washed with DEF (yield: 0.020 g, 55%). FTIR
(KBr pellet): n˜ =1670 (DEF), 1609 cmÀ1 (carboxylate); elemental analy-
sis calcd (%) for C60H92N6O20Zn4: C 48.72, H 6.27, N 5.68; found: C
49.83, H 6.05, N 5.63.
X-ray crystallography: X-ray data were collected by using an Enraf
Nonius Kappa CCD diffractometer with graphite-monochromated MoKa
radiation (l=0.71073 ꢁ) at 298 K. The respective crystals were sealed in
a glass capillary together with the mother liquor. Preliminary orientation
matrixes and unit cell parameters were obtained from the peaks of the
first ten frames and then refined by using the whole data set. Frames
were integrated and corrected for Lorentz and polarization effects by
using DENZO.[29] The scaling and global refinement of crystal parame-
ters were performed by SCALEPACK.[29] The structure was solved by
using SHELXS-97[30] and full-matrix least-squares refinement against F2
was carried out by using SHELXL-97.[30] All ring hydrogen atoms were
assigned on the basis of geometrical considerations and allowed to ride
upon the respective carbon atoms. The unsymmetrical dicarboxylate link-
ers are randomly oriented and the long and short parts cannot be differ-
entiated from the benzene ring; the structures were refined by providing
the appropriate occupancy factors. The solvent molecules could not be
located from the difference maps, and the residual electron density corre-
sponding to the solvent molecules was removed by using SQUEEZE[31]
in the PLATON software.[32] The formulae of both SNU-70 and SNU-71
were determined from elemental analyses and TGA data.
Figure 9. The adsorption isotherms of SNU-70Br’ for: a) N2 at 77 K, and
b) H2 at 77 and 87 K. Filled shapes: adsorption; open shapes: desorption.
Conclusion
The present study demonstrates that the interpenetration of
MOFs with almost-identical network structures can be con-
trolled by a simple change in the ligand, that is, the presence
À
of a C=C or a C C bond. Comparison of the gas-sorption
properties indicate that the noninterpenetrated structure
(SNU-70’) exhibits generally much higher gas adsorption ca-
pacities than the interpenetrated structure (SNU-71’) at high
pressures regardless of the temperature, whereas the oppo-
site is observed at low pressures due to the higher isosteric
heats of the gas adsorption resulting from the smaller pores.
Crystal data for SNU-70: C95H165N13O28Zn4; pale-yellow cubic crystal
3
¯
(0.2ꢀ0.2ꢀ0.2 mm); Fm3m; a=30.234(4) ꢁ; V=27637(6) ꢁ ; Z=8; T=
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Gas Sorption Properties of Metal–Organic Frameworks
FULL PAPER
298(2) K; 1calcd =0.411 gcmÀ3; m=0.701 cmÀ1; F
214 reflections were collected, of which 214 were unique. Final R
0.0869(0.2640) with GOF=1.203.
ACHTUNGTRENNUNG
Acknowledgements
CTHUNGTRENNUNG
ACHTUNGTRENNUNG
This work was supported by a National Research Foundation of Korea
(NRF) Grant funded by the Korean Government (MEST; nos.: 2011-
0031432 and 2012-0000651).
Crystal data for SNU-71: C60H92N6O20Zn4; pale-yellow cubic crystals
3
¯
(0.3ꢀ0.3ꢀ0.3 mm); I43m; a=15.031(1) ꢁ; V=3396.0(5) ꢁ ; Z=8; T=
298(2) K; 1calcd =0.835 gcmÀ3; m=1.427 cmÀ1; F
A
A
ACHTUNGTRENNUNG
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CCDC-846935 (SNU-70) and -846936 (SNU-71) contain the supplemen-
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Received: February 12, 2012
Published online: && &&, 0000
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Gas Sorption Properties of Metal–Organic Frameworks
FULL PAPER
Flexible by design: By a slight change
in the ligand flexibility, almost-identi-
cal frameworks that differ only in their
interpenetration were constructed (see
figure). The noninterpenetrated frame-
work shows significantly higher gas-
sorption capacities at high pressures
compared with the interpenetrated
structure, which only adsorbs more gas
at low pressures (P<1 atm).
Supramolecular Chemistry
T. K. Prasad, M. P. Suh* .... &&&& — &&&&
Control of Interpenetration and Gas-
Sorption Properties of Metal–Organic
Frameworks by a Simple Change in
Ligand Design
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