Post-synthetic reversible incorporation of organic linkers into porous metal-organic frameworks through single-crystal-to-single-crystal transformations and modification of gas-sorption properties

Article abstract of DOI:10.1002/chem.201001549

The porous metal-organic framework (MOF) {[Zn₂(TCPBDA)-(H ₂O)₂]·30DMF·6H₂O}_n (SNU-30; DMF=N,N-dimethylformamide) has been prepared by the solvothermal reaction of N,N,N′,N′-tetrakis(4-carboxyphenyl)biphenyl-4,4′- diamine (H₄TCPBDA) and Zn(NO₃)₂·6H ₂O in DMF/tBuOH. The post-synthetic modification of SNU-30 by the insertion of 3,6-di(4-pyridyl)-1,2,4,5-tetrazine (bpta) affords single-crystalline {[Zn₂-(TCPBDA)(bpta)]·23DMF·4H ₂O}_n (SNU-31SC), in which channels are divided by the bpta linkers. Interestingly, unlike its pristine form, the bridging bpta ligand in the MOF is bent due to steric constraints. SNU-31 can be also prepared through a one-pot solvothermal synthesis from Zn^II, TCPBDA^4-, and bpta. The bpta linker can be liberated from this MOF by immersion in N,N-diethylformamide (DEF) to afford the single-crystalline SNU-30 SC, which is structurally similar to SNU-30. This phenomenon of reversible insertion and removal of the bridging ligand while preserving the single crystallinity is unprecedented in MOFs. Desolvated solid SNU-30' adsorbs N₂, O ₂, H₂, CO₂, and CH₄ gases, whereas desolvated SNU-31' exhibits selective adsorption of CO₂ over N ₂, O₂, H₂, and CH₄, thus demonstrating that the gas adsorption properties of MOF can be modified by post-synthetic insertion/removal of a bridging ligand.

Full text of DOI:10.1002/chem.201001549

DOI: 10.1002/chem.201001549
Post-Synthetic Reversible Incorporation of Organic Linkers into Porous
Metal–Organic Frameworks through Single-Crystal-to-Single-Crystal
Transformations and Modification of Gas-Sorption Properties
Hye Jeong Park, Young Eun Cheon, and Myunghyun Paik Suh*[a]
Abstract: The porous metal–organic
framework (MOF) {[Zn2A(TCPBDA)-
ACHTUNGTRENNUNG(H2O)2]·30DMF·6H2O}n (SNU-30;
DMF=N,N-dimethylformamide) has
been prepared by the solvothermal re-
action of N,N,N’,N’-tetrakis(4-carboxy-
phenyl)biphenyl-4,4’-diamine
unlike its pristine form, the bridging
bpta ligand in the MOF is bent due to
steric constraints. SNU-31 can be also
prepared through a one-pot solvother-
mal synthesis from ZnII, TCPBDA4ꢀ,
and bpta. The bpta linker can be liber-
ated from this MOF by immersion in
N,N-diethylformamide (DEF) to afford
the single-crystalline SNU-30SC, which
is structurally similar to SNU-30. This
phenomenon of reversible insertion
and removal of the bridging ligand
while preserving the single crystallinity
is unprecedented in MOFs. Desolvated
solid SNU-30’ adsorbs N2, O2, H2, CO2,
and CH4 gases, whereas desolvated
SNU-31’ exhibits selective adsorption
of CO2 over N2, O2, H2, and CH4, thus
demonstrating that the gas adsorption
properties of MOF can be modified by
post-synthetic insertion/removal of a
bridging ligand.
CTHUNGTRENNUNG
(H4TCPBDA) and ZnACHTNUGTRNEUNG(NO3)2·6H2O in
DMF/tBuOH. The post-synthetic modi-
fication of SNU-30 by the insertion of
3,6-di(4-pyridyl)-1,2,4,5-tetrazine (bpta)
Keywords: bridging ligands · crystal
engineering · gas sorption · metal–
affords single-crystalline
{[Zn2-
E
organic frameworks
methods
·
synthetic
(SNU-31SC), in which channels are di-
vided by the bpta linkers. Interestingly,
Introduction
pore size and pore shape of a MOF can be controlled by
post-synthetic methods, for example, by the insertion or re-
moval of organic linkers, the selectivity of adsorbed gases
and the gas uptake capacities could be easily modified. In
addition, the MOFs that transform their structures in re-
sponse to external stimuli by single-crystal-to-single-crystal
(SCSC) transformations are important for the development
of new and technologically useful devices and sensors. Even
though a considerable number of studies have been reported
on SCSC transformations of MOFs,[6,8–11] to the best of our
knowledge, there has been no report of SCSC transforma-
tions on the insertion or removal of the organic framework
component in a 3D MOF crystal, which alters the gas-sorp-
tion properties of the MOF.
Porous metal–organic frameworks (MOFs) have attracted
great attention because they can be applied in gas storage[1,2]
and separation,[3] catalysis,[4] and fabrication of metal nano-
particles.[2a,5,6] The gas-sorption properties of a MOF, such as
the type of adsorbed gases and the adsorption capacities,
depend on the pore size and pore shape of the MOF, gas
framework interactions, and gas–gas interactions. To change
the pore size and pore shape, in general, new MOFs should
be prepared by using a solvothermal reaction with different
metal and/or organic building blocks. Recently, post-synthe-
ses have been developed to functionalize MOFs.[7] If the
Herein, we report the unprecedented post-synthetic rever-
sible incorporation of bridging ligands in a MOF through
SCSC transformations. Interestingly, the bridging ligand 3,6-
di(4-pyridyl)-1,2,4,5-tetrazine (bpta), which is linear in the
pristine form, is significantly bent in the present MOF due
to steric constraints. The insertion of the organic linker
alters the pore size and pore shape, thus significantly chang-
ing the gas-sorption properties of the MOF.
[a] H. J. Park, Y. E. Cheon, 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.201001549.
11662
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Chem. Eur. J. 2010, 16, 11662 – 11669

FULL PAPER
low as 0.381 gcmꢀ3 after removal of the guest and coordinat-
ed solvent molecules. Thermogravimetric analysis (TGA)
suggests that the framework is thermally stable up to 3008C
(Figure S2 in the Supporting Information).
SCSC transformation of SNU-30 on insertion of bpta linkers
to afford [Zn2ACHTNUGTRNENUG(TCPBDA)CAHTUNGTREN(NUNG bpta)]·23DMF·4H2O (SNU-
31SC): When the yellow crystal of SNU-30 was immersed in
a solution of bpta in DMF (0.033m) at 808C for 3 hours, two
coordinated water molecules in SNU-30 were quantitatively
substituted with a bpta ligand, thus resulting in a red crystal
of {[Zn2ACHTNUTRGENNUG(TCPBDA)ACHTUNTGREN(NGUN bpta)]·23DMF·4H2O}n (SNU-31SC) by
a SCSC transformation. Retention of the single crystallinity
during the insertion of bpta was proven by photographs
taken under a microscope (Figure 2).
Results and Discussion
Preparation and X-ray crystal structure studies of {[Zn2-
ACHTUNGTRENNUNG(TCPBDA)ACHTUNGTRENNUNG(H2O)2]·30DMF·6H2O}n ACHTNGUTREN(NUGN SNU-30): We have
prepared porous MOF SNU-30 from the solvothermal reac-
tion of N,N,N’,N’-tetrakis(4-carboxyphenyl)biphenyl-4,4’-di-
ACHTUNGTRENNUNGamine (H4TCPBDA) and ZnACHTUGNTREN(NGUN NO3)2·6H2O in N,N-dimethyl-
formamide (DMF)/tBuOH (5:1 v/v, 6 mL) at 808C for 24 h.
The X-ray crystal structure studies of SNU-30 reveal that
the connectivity of square-shaped {Zn2ACHTNUGTRENUNG(O2CR)4} secondary
building units and the rectangular TCPBDA4ꢀ ion gives rise
to an NbO-type 3D framework, in which a water molecule
is coordinated at the axial site of every ZnII ion (Figure 1
and Table S1 in the Supporting Information). The phenyl
rings around the nitrogen atoms in the TCPBDA4ꢀ ion are
twisted to each other with an average dihedral angle of
66.80(7)8. The framework generates 3D channels. Rhombic-
and honeycomblike channels are generated on the bc and ac
planes, respectively. Their effective aperture sizes are 10.7ꢁ
17.4 and 13.8ꢁ17.5 ꢂ2, respec-
Figure 2. Photos of the SNU-30 crystal a) before and b) after immersion
in the solution of bpta (0.033m) in DMF at 808C for 3 hours, which af-
fords SNU-31SC.
The synchrotron X-ray crystal structure of SNU-31SC in-
dicates that the bpta ligand connects ZnII paddle-wheel units
by maintaining the main framework structure of SNU-30
(Figure 3). Interestingly, the bpta unit in SNU-31SC is sig-
tively. On the ab plane, two dif-
ferent channels with rhombic-
and honeycomblike apertures
of effective sizes 2.7ꢁ3.8 and
5.1ꢁ10.5 ꢂ2, respectively, are
formed. The void volume of
SNU-30 is 82.1% (2.15 cm3 gꢀ1)
and
becomes
82.6%
(2.17 cm3 gꢀ1) without the coor-
dinated aqua ligands, as esti-
mated by PLATON.[12] The cal-
culated density of SNU-30 is as
Figure 3. The X-ray crystal structure of SNU-31SC. Views seen on the a) bc, b) ac, c) ab planes. Color scheme:
Zn=green, C=gray, O=red, N=blue, bpta linker=pink.
nificantly bent to fit into the
{Zn2} paddle-wheel units, con-
trary to the completely planar
structure in a pristine bpta crys-
tal (Figures S5 and S6 in the
Supporting Information). The
dihedral angle between the two
pyridyl rings is 19.53(23)8 and
that between the pyridine and
tetrazine rings is 11.10(22)8.
Rhombic cavities (effective
Figure 1. X-ray crystal structure of SNU-30. Views of the 3D framework seen on the a) bc, b) ac, and c) ab
planes. Color scheme: Zn=green, C=gray, O=red, N=blue.
Chem. Eur. J. 2010, 16, 11662 – 11669
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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11663

M. P. Suh et al.
aperture size: 18ꢁ12 ꢂ2) are formed, which are similar in
size to those of SNU-30, on the bc plane. Due to the bent
bpta ligand, dumbbell- and rectangular-shaped channels (ef-
fective aperture size: 2.5ꢁ14.6 and 2.6ꢁ6.6 ꢂ2, respectively)
are generated, the aperture sizes of which are significantly
decreased relative to those of SNU-30, on the ac plane. The
honeycomblike channels are divided into smaller rectangu-
lar channels (effective aperture size: 1.1ꢁ8.6 ꢂ2) on the ab
plane. The solvent-accessible volume of SNU-31SC is
76.1%, as estimated by PLATON.[12] The TGA data of
SNU-31SC reveal 62.6% weight loss at 25–2008C, which
corresponds to the loss of all the guest solvent molecules
(calcd: 63.0% for 23DMF and 4H2O molecules), and the
additional weight loss of 8.8% at 230–3808C, which corre-
sponds to the loss of the bpta linker (calcd: 8.5%; Figure S8
in the Supporting Information).
Table 1. Gas sorption data of SNU-30’ and SNU-31’.
Gas
T
P
Adsorption capacity
[K]
G
SNU-31’
wt%
mmol gas
wt% mmol gas
per gram of host
per gram of host
N2
H2
77
77
0.9
1.0
27.0
1.42
9.67
7.04
<0.1
0.51
0.20
2.75[a] 13.6[a]
61
3.27[b] 16.2[b]
87
77
87
195 1.0
273 1.0
1.0
0.20
0.61
0.72
39.2
39.1
46.2
11.5
5.12
21.9
6.82
1.32
0.38
4.79
3.57
12.3
12.2
10.5
2.62
1.16
4.98
4.25
0.82
0.23
2.99
<0.1
O2
17.2
5.29
2.62
9.41
0.62
3.90
1.20
0.60
2.14
0.38
CO2
1.0
50
298
195 1.0
273 1.0
CH4
1.0
50
298
The same compound as SNU-31SC, {[Zn
2ACHTUNGTRENN(UNG TCPBDA)-
1.52
0.95
ACHTUNGTRENNUNG(bpta)]·20DMF·4H2O}n (SNU-31), was also synthesized
[a] Excess H2 adsorption. [b] Total H2 adsorption.
from the solvothermal reactions of ZnII, H4TCPBDA, and
bpta in DMF at 858C for 24 h (Scheme S2 in the Supporting
Information). However, instead of the bpta ligand, when
4,4’-dipyridine (bpy), 1,2-bis(4-pyridyl)ethane (bpea), or
trans-1,2-bis(4-pyridyl)ethylene (bpee) linkers were added
to the reaction mixture, only SNU-30 was formed because
the lengths of bpy, bpea, and bpee (6.98, 9.21, and 9.19 ꢂ,
respectively) are too short to fit the two mutually parallel
paddle-wheel units of the framework (Figure S3 in the Sup-
porting Information). The X-ray crystal structure of SNU-31
is very similar to that of SNU-31SC, and the bpta ligand is
also significantly bent, although the space groups are differ-
ent from each other, that is, Imma and Pmnb, respectively,
as a result of the differences in the measurement tempera-
ture and the type of radiation. The TGA data of SNU-31 in-
dicate that the main framework is thermally stable up to
4008C, although the bpta linkers are liberated at higher tem-
peratures than 2508C (Figure S11 in the Supporting Infor-
mation).
formed (Table 1 and Table S3 in the Supporting Informa-
tion). The solvent-accessible volume of SNU-30SC is
82.7%, as estimated by PLATON,[12] similar to that of SNU-
30 (82.1%).
To the best of our knowledge, the present result is the
first report of a SCSC transformation in which an organic
linker is quantitatively and reversibly inserted to and re-
moved from a 3D MOF without changing the main frame-
work structure, although there are a few reports on the in-
sertion of organic linker into a 2D layer or a polyhedron
that led to a 3D MOF.[13,14]
Gas-sorption properties of SNU-30’ and SNU-31’: Desolvat-
ed solids [Zn
2ACHUTGTNRENNGU(TCPBDA)]n (SNU-30’) and [Zn2ACHTUTGNREN(NUGN TCPBDA)-
AHCTUNGTRENNUNG
method to examine their gas-sorption properties (see the
Experimental Section). SNU-30’ and SNU-31’ lost their
transparency and single crystallinity. The powder X-ray dif-
fraction (PXRD) patterns of SNU-30’ and SNU-31’ indicate
that some structural changes occur on the removal of guest
solvent molecules (Figures S18 and S19 in the Supporting
Information). The supercritical CO2 drying method also of-
fered similar PXRD patterns.
SCSC transformation of SNU-31 on removal of bpta linkers
to afford SNU-30SC: When the crystals of SNU-31 or SNU-
31SC were immersed in dried N,N-diethylformamide (DEF)
for seven days at room temperature, the color of the crystals
changed from red (lmax =340, 526 nm) to yellow (lmax
=
379 nm), and {[Zn2A(TCPBDA)(H2O)2]·23DEF}n (SNU-
G
E
The gas-adsorption isotherms of SNU-30’ and SNU-31’
were measured for N2, O2, H2, CH4, and CO2 (adsorption
data are compared in Table 1). SNU-30’ adsorbs N2, showing
a type-I isotherm that is characteristic for a microporous
material (Figure 5a). The Langmuir and BET surface areas
estimated from the N2 gas-sorp-
30SC) was obtained with retention of the single crystallinity,
as evidenced by photographs taken during the reaction
(Figure 4). The X-ray crystal structure of SNU-30SC is very
similar to that of SNU-31, from which SNU-30SC was
tion data are 770 and
704 m2 gꢀ1, respectively. The
pore volume estimated by using
the
Dubinin–Radushkevich
(DR) equation is 0.28 cm3 gꢀ1.
This surface area is significantly
low relative to the theoretical
values: 3924 m2 gꢀ1 of Connolly
Figure 4. Photographs showing the SCSC transformation of SNU-31 to SNU-30SC on removal of bpta linkers
by immersion of SNU-31 in DEF.
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Gas Sorption of Post-Synthetically Modified Metal–Organic Frameworks
FULL PAPER
11.5 wt% (58.63 cm3 gꢀ1 at STP)
at 273 K and 1 atm. SNU-30’
adsorbs 22.3 wt% of CO2 at
298 K
and
45 bar
(total:
25.5 wt%; Figure S24 in the
Supporting Information). These
values are similar to the CO2
adsorption
capacity
of
43.0 wt% at 195 K and 1 atm
for SNU-9,[18] but lower than
the highest value, namely,
149 wt% in MOF-5 at 195 K
and 1 atm.[23] The CH4 uptake
capacities of SNU-30’ are
6.82 wt% (95.18 cm3 gꢀ1 at STP)
at 195 K and 1 atm (3.4 CH4
molecules per formula unit)
and 1.32 wt% (18.40 cm3 gꢀ1 at
STP) at 273 K and 1 atm. SNU-
~
&
*
Figure 5. Gas-sorption isotherms of SNU-30’. a) N2 ( ) at 77 K, O2 ( ) and H2 ( ) at 77 (red) and 87 K (blue);
~
*
b) CO2
( ) and CH4 ( ) at 195 (black), 273 (red), and 298 K (blue). Filled shapes: adsorption; open shapes:
desorption.
surface area estimated by using the Materials Studio pro-
gram[15] and 5390 m2 gꢀ1 of the accessible surface area calcu-
lated from a simple Monte Carlo integration,[16] thus indicat-
ing that the framework is shrunken on desolvation. The plot
of the pore-size distribution estimated by the Saito–Foley
model[17] offers pore diameters of 10.5 and 11.8 ꢂ (Fig-
ure S20 in the Supporting Information).
30’ adsorbs an excess amount of CH4 up to 4.79 wt% at
298 K and 50 bar (total 6.21 wt%; Figure S24 in the Sup-
porting Information). These CH4 capacities are relatively
low compared with 21.8 wt% at 303 K and 60 bar for MIL-
101[24] and 15.5 wt% at 298 K and 35 bar for MOF-5.[25]
Contrary to SNU-30’, SNU-31’ hardly adsorbs N2, H2, O2,
and CH4 gases (Figure 6a). The X-ray structure of SNU-31
indicates that the channel sizes are big enough for these
gases to enter (kinetic diameters: 3.64, 2.89, and 3.8 ꢂ for
N2, H2, and CH4, respectively), but the channels seem to be
contracted on guest removal. Interestingly, however, SNU-
31’ adsorbs CO2, which has a kinetic diameter of 3.3 ꢂ, up
to 12.9 wt% (65.7 cm3 gꢀ1 at STP) at 195 K and 1 atm (Fig-
ure 6a). This finding must be attributed to the quadrupole
moment of CO2 (ꢀ1.34ꢁ10ꢀ39 Cm2),[26] which induces stron-
ger interaction with the framework than other gases. The de-
sorption isotherm at 195 K shows a large hysteresis. The sur-
face area and pore volume of SNU-31’, estimated from the
CO2 adsorption isotherm by applying the DR equation, are
308 m2 gꢀ1 and 0.14 cm3 gꢀ1, respectively. Relative to the the-
oretical values of the surface area (i.e., 3921 m2 gꢀ1 of Con-
nolly surface area estimated by using the Materials Studio
program[15] and 4809 m2 gꢀ1 of the accessible surface area
calculated from a simple Monte Carlo integration),[16] this
surface area is remarkably lower, thus indicating that the
framework is shrunken on desolvation. The CO2 sorption
isotherms at 298 K exhibit adsorption capacities of
2.62 wt% at 1 atm and 9.83 wt% at 40 bar (Figure S25 in
the Supporting Information). The MOF that selectively ad-
sorbs CO2 over other gases can be applied in a CO2-capture
material from industrial flue gas.[2b] To verify the selective
and reversible CO2 adsorption in SNU-31’, a gas-cycling ex-
periment was performed in a TG pan with a flow of 15%
CO2 in N2 (v/v) at 258C, which approximately mimics indus-
trial flue gas, followed by a stream of pure N2 gas (Fig-
ure 6b). A reversible change of 0.32 wt% was observed
over repeated cycles, and the material was regenerated by
switching the gas stream to a N2 gas flow.
SNU-30’ adsorbs 39.2 wt% O2 (275 cm3 gꢀ1 at STP) at
77 K and 0.20 atm and 39.1 wt% O2 (274 cm3 gꢀ1 at STP) at
87 K and 0.61 atm (Figure 5a). This O2 adsorption capacity
at 77 K and 0.20 atm is comparable to those of SNU-9
(51.4 wt%,
336 cm3 gꢀ1),[19] but lower than the highest data (618 cm3 gꢀ1)
for [Co
(BDP)] (BDP=1,4-benzene di(4’pyrazolyl).[20] The
360 cm3 gꢀ1)[18]
and
FMOF-1
(48 wt%,
ACHTUNGTRENNUNG
O2 adsorption densities in SNU-30’, estimated by using the
pore volume derived from the N2 adsorption data, are
1400 kgmꢀ3 at 77 K and 0.20 atm and 1397 kgmꢀ3 at 87 K
and 0.61 atm. This outcome suggests that O2 gas is highly
compressed within the pores, given that the density of liquid
O2 is 1142 kgmꢀ3.
SNU-30’ adsorbs H2 gas up to 1.42 wt% (158 cm3 gꢀ1 at
STP) at 77 K and 1 atm and 0.72 wt% of H2 (80 cm3 gꢀ1 at
STP) at 87 K and 1 atm (Figure 5a). The isosteric heat of H2
adsorption for SNU-30’ is 8.12-7.27 kJmolꢀ1 depending on
the degree of H2 loading, as estimated from the data at 77
and 87 K by using the virial equation (Figures S21 and S22
in the Supporting Information).[21] This isosteric heat of H2
adsorption is significantly higher than those of common
MOFs, such as MOF-5 (4.8 kJmolꢀ1),[22] due to the vacant
coordination sites in SNU-30’. The excess and total H2 ad-
sorption capacities at 77 K and 61 bar are 2.75 and
3.27 wt%, respectively (Figure S23 in the Supporting Infor-
mation). However, the H2 adsorption capacity at 298 K and
71 bar becomes 0.16 wt%, similar to all other MOFs that
show very low room-temperature H2 storage capacities.
The CO2 and CH4 adsorption isotherms of SNU-30’ are
presented in Figure 5b. SNU-30’ adsorbs CO2 up to
46.2 wt% (235.19 cm3 gꢀ1 at STP) at 195 K and 1 atm and
Chem. Eur. J. 2010, 16, 11662 – 11669
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M. P. Suh et al.
Preparation of N,N,N’,N’-tetrakis(4-bromophenyl)biphenyl-4,4’-diamine:
N,N,N’,N’-tetraphenylbiphenyl-4,4’-diamine (2.0 g, 4.0ꢁ10ꢀ3 mol) was dis-
solved in CHCl3 (80 mL), and the solution in CHCl3 (20 mL) of Br2
(0.6 mL) was slowly added in an ice bath. After stirring at 08C for
45 min, the mixture was added to hot EtOH (ca. 500 mL) and cooled to
08C until a microcrystalline white precipitate of N,N,N’,N’-tetrakis(4-bro-
mophenyl)biphenyl-4,4’-diamine formed, which was filtered, washed with
EtOH, and dried under reduced pressure (1.86 g, 58%). 1H NMR
(300 MHz, CDCl3): d=7.5 (d, 4H), 7.4 (d, 8H), 7.1 (d, 4H), 7.0 ppm (d,
8H).
Preparation of N,N,N’,N’-tetrakis(4-carboxyphenyl)biphenyl-4,4’-diamine
(H4TCPBDA): N,N,N’,N’-tetrakis(4-bromophenyl)biphenyl-4,4’-diamine
(1.86 g, 2.3ꢁ10ꢀ3 mol) was dissolved in freshly distilled THF (80 mL),
and n-butyllithium in hexane (20 mL, 1.6m) was slowly added at ꢀ788C.
After the mixture was stirred for 1 h, crushed dry ice was added to the
solution from which a green precipitate immediately formed. Acetic acid
was added to the greenish suspension for acidification until the precipi-
tate disappeared. The resulting solution was added to mixture of water
(ca. 500 mL) and MeOH (ca. 10 mL), from which a green–white precipi-
tate was formed. The precipitate was recrystallized in MeOH/water,
washed with water, and dried in a drying pistol (1.25 g, 80%). 1H NMR,
(300 MHz, [D6]DMSO): d=7.8 (d, 8H), 7.7 (d, 4H), 7.4 (d, 4H), 7.1 ppm
(d, 8H); elemental analysis calcd (%) for [H4TCPBDA]·2H2O
(C40H32N2O10): C 68.57, H 4.60, N 4.00; found: C 68.25, H 4.44, N 3.80;
FTIR (KBr pellet): n˜ =1688 (O-C=O), 1594 cmꢀ1; UV/Vis (0.1m NaOH):
lmax =347 nm; UV/Vis (diffuse reflectance): lmax =280 nm; luminescence
(0.1m NaOH): lmax =452 nm; solid luminescence: lmax =471 nm.
Solvothermal synthesis of {[Zn
(SNU-30): A solution of H4TCPBDA (32.2 mg, 0.05 mmol) in DMF
(5 mL) and a solution of Zn(NO3)2·6H2O (30.0 mg, 0.1 mmol) in tBuOH
2ACHTUNGTRNENUG(TCPBDA)AHCTUNGTRENN(UNG H2O)2]·30DMF·6H2O}n
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(1 mL) were mixed in a glass serum bottle, which was tightly capped with
a silicon stopper and aluminum seal, and heated at 808C for 24 h. The so-
lution was cooled to room temperature, and the resulting yellow rod-
shaped crystals were filtered and washed briefly with DMF (29.8 mg,
25%). Solid SNU-30 is insoluble in water and common organic solvents
such as DMF, DEF, N,N-dimethylacetamide (DMA), EtOH, MeOH,
^
Figure 6. Selective CO2 sorption isotherms of SNU-31’. a) CO2
( ) mea-
sured up to 1 atm at 195 (black), 273 (blue), and 298 K (pink) relative to
~
*
adsorption isotherms for N2
( ) and H2 ( ) measured at 77 K and CH4
&
( ) measured at 195 K. Filled shapes: adsorption; open shapes: desorp-
tion. b) Gas-cycling experiment for SNU-31’ at 258C with a flow of 15%
CO2 in N2 (v/v) followed by a flow of pure N2.
tBuOH, and MeCN. Elemental analysis calcd (%) for Zn2C120H216N26O36
:
C 50.98, H 8.23, N 14.63; found: C 51.12, H 8.01, N 14.73; FTIR (KBr
pellet): n˜ =3432 (O H), 1662 (C=O (DMF)), 1595 cmꢀ1 (O-C=O
(TCPBDA)); UV/Vis (diffuse reflectance) lmax =350 nm; solid lumines-
cence: lmax =472 nm.
ꢀ
Conclusion
We have demonstrated that a proper organic linker can be
quantitatively and reversibly inserted into a MOF while
maintaining single crystallinity to change the gas-sorption
properties of the MOF. This type of post-synthetic modifica-
tion could afford various new MOFs that could be applied
in selective gas storage or gas separation.
Preparation of {[Zn2ACTHNUTRGENN(UG TCPBDA)CAHTUNGTERN(NUGN bpta)]·23DMF·4H2O}n (SNU-31SC)
through the SCSC transformation of SNU-30 by the post-synthetic inser-
tion of a bpta linker: Single crystals of SNU-30 (36.2 mg, 0.012 mmol)
were immersed in a solution of bpta (7.7 mg) in DMF (0.033m, 1 mL) at
808C for 3 h. The crystals changed from yellow to red with retention of
single
crystallinity,
and
crystals
of
{[Zn2ACTHNGUTERNN(UG TCPBDA)-
AHCTUNGTRENNUNG
and washed briefly with anhydrous DMF. If SNU-30 was immersed for
longer period of time, bpta precipitated out and the crystallinity of SNU-
31SC became poor. Interestingly, when the same reaction was carried out
under different conditions, such as at room temperature with the same
concentration of bpta or at 808C with much more dilute solution of bpta
(1.2ꢁ10ꢀ3 m), the bpta ligand was not introduced into SNU-30 probably
due to slow diffusion of bpta. To prove the maintenance of single crystal-
linity and exclude the possibility of dissolution and recrystallization
during the bpta insertion, photographs of a single crystal were taken
before and after immersion in the solution of bpta (7.7 mg) in DMF
(0.033m, 1 mL) at 808C for 3 h. Elemental analysis calcd (%) for
Zn2C121H201N31O31: C 52.26, H 7.29, N 15.61; found: C 52.36, H 7.14, N
Experimental Section
General methods: All the chemicals and solvents used in the syntheses
were of reagent grade and used without further purification. MeCN was
dried by distillation over P2O5 in a N2 atmosphere prior to use. DEF was
dried over activated molecular sieves. H4TCPBDA was prepared by mod-
ifying previously reported methods.[27] IR spectra were recorded on a
Perkin–Elmer Spectrum One FTIR spectrophotometer. UV/Vis diffuse
reflectance spectra were recorded on a Perkin–Elmer Lambda 35 UV/Vis
spectrophotometer. Emission spectra were recorded on a Perkin–Elmer
LS55 luminescence spectrophotometer. Elemental analyses were per-
formed on a Perkin–Elmer 2400 series II CHN analyzer. TGA and differ-
ential scanning calorimetry (DSC) were performed in a N2 atmosphere at
a scan rate of 58C minꢀ1 on TGA Q50 and DSC Q10 instruments (TA in-
struments), respectively. PXRD data were recorded on a Bruker D5005
diffractometer at 40 kV and 40 mA for CuKa radiation (l=1.54050 ꢂ) at
a scan speed of 58minꢀ1 and a step size of 0.028 in 2q.
ꢀ
ꢀ
15.64; FTIR (KBr pellet): n˜ =3435 (O H), 2927 (C H), 1667 (C=O
(DMF)), 1595 cmꢀ1 (O-C=O (TCPBDA)); UV/Vis (diffuse reflectance):
lmax =527 nm.
Solvothermal synthesis of {[Zn
(SNU-31): H4TCPBDA (32.2 mg, 0.05 mmol) and bpta (13.0 mg,
0.05 mmol) were dissolved in DMF (2 mL), and Zn(NO3)2·6H2O
2ACHUTNGTREN(GUN TCPBDA)AHCUTNGTREN(NUNG bpta)]·20DMF·4H2O}n
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
(30.0 mg, 0.1 mmol) was dissolved in DMF (1 mL). The solutions were
mixed and placed in a glass serum bottle, which was tightly capped with
11666
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 11662 – 11669

Gas Sorption of Post-Synthetically Modified Metal–Organic Frameworks
FULL PAPER
a silicon stopper and aluminum seal, and heated at 858C for 24 h. The so-
lution was cooled to room temperature, and the resulting red rod-shaped
crystals were filtered and washed briefly with mother liquor. The forma-
tion of SNU-31 is independent of the stoichiometry of the reactants
(28.6 mg, 22.3%). Solid SNU-31 is insoluble and stable in MeCN, n-
hexane, n-dodecane, and toluene. Elemental analysis calcd (%) for
Zn2C112H180N28O32: C 52.52, H 7.08, N 15.31; found: C 52.17, H 7.43, N
were collected at 298 K on an Enraf Nonius Kappa CCD diffractometer
using graphite-monochromated MoKa radiation (l=0.71073 ꢂ). Prelimi-
nary orientation matrices and unit-cell parameters were obtained from
the peaks of the first ten frames and refined by using the complete data
set. The frames were integrated and corrected for Lorentz and polariza-
tion effects by using DENZO.[29] Scaling and global refinement of the
crystal parameters were performed using SCALEPACK.[29] The absorp-
tion corrections were made. The crystal structures were solved by the
direct method[30] and refined by full-matrix least-squares refinement with
the computer program SHELXL-97.[31] The positions of the non-hydro-
gen atoms were refined with anisotropic displacement factors. The hydro-
gen atoms were positioned geometrically by using a riding model. For all
the samples, the guest molecules that occupy the channels could not be
refined in the X-ray structure due to the severe disorder, and they were
determined based on the IR spectra, elemental analysis, and TGA data.
The electron densities of the disordered guest molecules were flattened
by using the SQUEEZE option of PLATON.[12] The crystallographic data
for SNU-30, SNU-30SC, SNU-31, SNU-31SC, SNU-31MeCN, and the
bpta crystal are summarized in Table 2 (also Tables S1 and S2 in the Sup-
porting Information). CCDC-769073 (SNU-30), CCDC-769074 (SNU-
30SC), CCDC-769075 (SNU-31), CCDC-769076 (SNU-31SC), CCDC-
769077 (SNU-31MeCN), and CCDC-769078 (bpta) contain the supple-
mentary crystallographic data of this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
ꢀ
ꢀ
15.16; FTIR (KBr pellet): n˜ =3430 (O H), 2931 (C H), 1660 (C=O
(DMF)), 1595 cmꢀ1 (O-C=O (TCPBDA);. UV/Vis (diffuse reflectance):
lmax =340, 526 nm.
Preparation of {[Zn2ACHTUNGTRENNUNG(TCPBDA)ACHUTNTGREN(NUNG H2O)2]·23DEF}n (SNU-30SC) by the
SCSC transformation of SNU-31 on removal of bpta: Crystals of SNU-31
were immersed in dried DEF at room temperature for 7 days. The crys-
tals changed from red to yellow with retention of single crystallinity,
which resulted the crystals of {[Zn2ACHTNUGTRENN(UG TCPBDA)AHCUTGNTRNE(NUGN H2O)2]·23DEF}n (SNU-
30SC). However, when SNU-31 was immersed for 7 days in another sol-
vent, such as DMF or DMA, the single crystallinity was lost with the lib-
eration of the bpta linkers. When the crystal was immersed in MeOH,
EtOH, or tBuOH the whole framework dissociated. Elemental analysis
calcd (%) for Zn2C155H281N25O33: C 59.03, H 8.98, N 11.10; found: C
ꢀ
58.97, H 8.76, N 11.12; FTIR (KBr pellet): n˜ =3467 (O H), 1661 (C=O
(DEF)), 1595 cmꢀ1 (O-C=O (TCPBDA)); UV/Vis (diffuse reflectance):
lmax =379 nm; solid luminescence: lmax =462 nm.
Preparation of [Zn2ACHTUNGTRENNUNG(TCPBDA)]n ACHTUNGTNER(NUGN SNU-30’): Compound SNU-30 was
heated in a Schlenk tube at 1508C under vacuum for 24 h. Elemental
Low-pressure gas-sorption measurements: The gas-sorption experiments
were performed by using an automated micropore gas analyzer Auto-
sorb-1 and Autosorb-3B (Quantachrome Instruments). The crystals of
SNU-30 and SNU-31MeCN as-synthesized were directly introduced to
the gas-sorption apparatus and activated at 150 and 808C, respectively,
under vacuum for 24 h to protect the desolvated solids from exposure to
air. All the gases used were of 99.999% purity. The H2 and O2 gas-sorp-
tion isotherms were monitored at 77 and 87 K, and the CO2 and CH4
gas-sorption isotherms were measured at 195, 273, and 298 K at each
equilibrium pressure by the static volumetric method. The weight of the
sample was measured precisely after each gas-sorption measurement.
The surface area and total pore volume for SNU-30’ were determined
from the N2 gas isotherm at 77 K. Multipoint BET and the Langmuir sur-
face area were estimated by using the data recorded at P/P0 =0.00057–
analysis calcd (%) for Zn2C40H24N2O8: C 60.70, H 3.06, N 3.54; found: C
59.16,
(TCPBDA)); UV/Vis (diffuse reflectance): lmax =405 nm; solid lumines-
cence: lmax =523 nm.
H 3.16, N
3.47; FTIR (KBr pellet): n˜ =1598 cmꢀ1 (O-C=O
Preparation
of
{[Zn
(TCPBDA)
G
(SNU-
31MeCN): Crystals of SNU-31 were immersed in anhydrous MeCN for
one day, and then the solvent was replenished with fresh anhydrous
MeCN. The crystals were immersed for another two days until all the
DMF guest molecules were exchanged with MeCN. Elemental analysis
calcd (%) for Zn2C92H102N28O13: C 56.99, H 5.30, N 20.23; found: C
ꢁ
56.85, H 5.27, N 20.30; FTIR (KBr pellet): n˜ =2250 (C N (MeCN)),
1595 cmꢀ1 (O-C=O (TCPBDA)).
Preparation of [Zn
N
ACHTUGTNREN(NUG bpta)]n ACHTUNTGREN(NUGN SNU-31’): Compound SNU-
31MeCN was heated in
a
Schlenk
tube at 708C under vacuum for 6 h.
Table 2. Crystallographic data for SNU-30, SNU-31SC, SNU-31, SNU-30SC, and SNU-31MeCN (squeezed).[a]
Elemental analysis calcd (%) for
Zn2C52H32N8O8: C 60.77,
H 3.14, N
SNU-30
SNU-31SC
SNU-31
SNU-30SC
SNU-31MeCN
10.90; found: C 60.82, H 3.14, N 9.87;
FTIR (nujol): n˜ =1597 cmꢀ1 (O-C=O
(TCPBDA)); UV/Vis (diffuse reflec-
tance): lmax =336, 545 nm.
formula
space group
Mr
a [ꢂ]
b [ꢂ]
Zn2C40H28N2O10 Zn2C52H32N8O8
Zn2C52H32N8O8
Imma
Zn2C40H28N2O10 Zn2C52H32N8O8
Imma
Pmnb
1027.63
34.103(7)
23.758(5)
17.033(3)
13800(5)
4
Imma
827.43
34.583(7)
22.915(5)
18.833(4)
14925(5)
4
Imma
827.43
35.965(7)
23.273(5)
17.219(3)
14412.5(11)
4
1027.63
34.158(7)
22.850(5)
19.049(4)
14868(5)
4
1027.63
34.277(7)
23.356(5)
18.400(4)
14730 (5)
4
X-ray crystallography: The diffraction
data of SNU-31SC and the bpta crys-
tal were measured at 100 K with syn-
chrotron radiation (l=0.9000 ꢂ) on a
6B MX-I ADSC Quantum-210 detec-
tor with a silicon (111) double-crystal
monochromator at the Pohang Accel-
erator Laboratory (PAL), Korea. The
crystals were coated with paraton oil
to prevent the loss of guest molecules.
The diffraction data were collected by
using the omega scan method through
a total rotation of 3608. The ADSC
Quantum-210 ADX program (Ver.
1.96)[28] was used for data collection,
and HKL2000 (Ver. 0.98.699)[29] was
used for cell refinement, reduction,
and absorption correction. For SNU-
30, SNU-31, SNU-30SC, and SNU-
31MeCN, each crystal was sealed in a
glass capillary together with the
mother liquor and the diffraction data
c [ꢂ]
V [ꢂ3]
Z
1calcd [gcmꢀ3
T [K]
]
0.381
0.495
0.459
298
0.368
0.463
298
100
298
298
l [ꢂ]
0.71073
0.349
0.985
0.9000
0.370
0.918
0.71073
0.343
0.766
0.71073
0.337
0.776
0.71073
0.346
0.922
m [mmꢀ1
]
GOF (F2)
R1, Wr2
[I>2s(I)]
R1, wR2
0.0693[b]
0.1973[c]
0.1121[b]
0.2045[c]
,
,
0.0702[b]
0.1816[d]
0.0917[b]
0.1897[d]
,
,
0.0522[b]
0.1177[e]
0.1422[b]
0.1332[e]
,
,
0.0678[b]
0.1864[f]
0.1254[b]
0.1967[f]
,
,
0.0742[b]
0.1917[g]
0.1001[b]
0.2020[g]
,
,
AHCTUNGTRENN(GUN all data)
[a] As a result of the severe disorder of the guest molecules only the coordinating H2O molecules and bpta
linkers were refined for SNU-30/SNU-30SC and SNU-31/SNU-31SC, respectively. [b] R=SjjFo jꢀjFc jj/SjFo j.
1
[c] wR(F2)=[Sw(F2oꢀFc2)2/Sw(F2o)2] = where w=1/[s2(Fo2)+(0.0952P)2 +(0.0000)P], P=(Fo2 +2F2c)/3 for SNU-
2
1
30. [d] wR(F2)=[Sw(F2oꢀFc2)2/Sw(Fo2)2] = where w=1/[s2(Fo2)+(0.1295P)2 +(0.0000)P], P=(Fo2 +2F2c)/3 for
2
1
SNU-31SC. [e] wR(F2)=[Sw(Fo2ꢀF2c)2/Sw(Fo2)2] = where w=1/[s2(F2o)+(0.0579P)2 +(0.0000)P], P=(Fo2 +2F2c)/3
2
1
for SNU-31. [f] wR(F2)=[Sw(Fo2ꢀF2o)2/Sw(Fo2)2] = where w=1/[s2(F2o)+(0.0994P)2 +(0.0000)P], P=(Fo2 +2F2c)/
2
1
2
3 for SNU-30SC. [g] wR(F2)=[Sw(Fo2ꢀFc2) /Sw(Fo2)2] = , where w=1/[s2(Fo2)+(0.1315P)2 +(0.0000)P], P=(Fo2 +
2
2F2c)/3 for SNU-31MeCN.
Chem. Eur. J. 2010, 16, 11662 – 11669
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11667

M. P. Suh et al.
0.093 atm and 0.00057–0.11 atm, respectively. The surface area and pore
volume for SNU-31’ were estimated from the CO2 gas isotherm at 195 K
by applying the DR equation.
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High-pressure gas-sorption measurements: High-pressure gas-sorption
isotherms for H2, CO2, and CH4 were measured on a Rubotherm magnet-
ic suspension balance (MSB) apparatus by using the gravimetric method.
All the gases used were of 99.999% purity and the impurity trace water
was removed by passing the gases through the drying trap (model 500)
filled with molecular sieves (5 ꢂ), which were purchased from Chroma-
tography Research Supplies (CRS). SNU-30’ and SNU-31’ were prepared
by heating crystals of SNU-30 and SNU-31MeCN at 150 and 808C, re-
spectively, under vacuum for 24 h by using a Schlenk line, and they were
activated again in the apparatus by evacuation at 1508C and 808C, re-
spectively. The H2 sorption isotherms were measured at 77 and 298 K.
The CO2 and CH4 sorption isotherms were measured at 298 K. To obtain
the excess adsorption isotherm, all the data were corrected for buoyancy
of the system and the sample. The sample density used for buoyancy cor-
rection was determined from the He displacement isotherm (up to
100 bar) measured at 298 K. The total amount of gas adsorbed was calcu-
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Ctotal ¼ Cexcess þ ðVpore ꢂ dgas ꢂ 100Þ
ð1Þ
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