Selective gas adsorption in the flexible metal-organic frameworks Cu(BDTri)L (L = DMF, DEF)

Article abstract of DOI:10.1002/chem.201000053

Use of the ditopic ligand 1,4benzenedi(1H-1,2,3-triazole) (H ₂BDTri) enabled isolation of two new three-dimensional metal-organic frameworks of formulae Cu(BDTri)L in which L = DMF (1) and diethylformamide (DEF; 2). These compounds have the same primary structure, featuring one-dimensional channels with the bridging DMF or DEF molecules pointing into the cavity. Upon exposure to solvent vapors, both display a reversible flexibility, as characterized by single-crystal to single-crystal phase transitions in 1. The O₂ adsorption isotherms for the compounds show a twostep adsorption behavior associated with a permanent microporosity and a pore-opening process. In the case of N₂ adsorption, only 1 exhibits a two-step adsorption isotherm, whereas 2 does not present any pore opening, demonstrating that design of a flexible framework cavity can control the pore opening and thereby possibly enhance O₂/ N₂ separation.

Full text of DOI:10.1002/chem.201000053

DOI: 10.1002/chem.201000053
Selective Gas Adsorption in the Flexible Metal–Organic Frameworks
CuACTHNUTRGNEUGN(BDTri)L (L=DMF, DEF)
Aude Demessence and Jeffrey R. Long*[a]
Abstract: Use of the ditopic ligand 1,4-
benzenedi(1H-1,2,3-triazole)
(H2BDTri) enabled isolation of two
new three-dimensional metal–organic
frameworks of formulae CuACTHNUTRGNEU(GN BDTri)L
in which L=DMF (1) and diethylfor-
mamide (DEF; 2). These compounds
have the same primary structure, fea-
turing one-dimensional channels with
the bridging DMF or DEF molecules
pointing into the cavity. Upon exposure
to solvent vapors, both display a rever-
sible flexibility, as characterized by
single-crystal to single-crystal phase
transitions in 1. The O2 adsorption iso-
therms for the compounds show a two-
step adsorption behavior associated
with a permanent microporosity and a
pore-opening process. In the case of N2
adsorption, only 1 exhibits a two-step
adsorption isotherm, whereas 2 does
not present any pore opening, demon-
strating that design of a flexible frame-
work cavity can control the pore open-
ing and thereby possibly enhance O2/
N2 separation.
Keywords: adsorption
·
metal–
organic frameworks · porous mate-
rials · triazoles
Introduction
ration, but also because of scientific interest as a result of
their simple structures and small differences in physical
properties.[7] To selectively adsorb gas molecules with very
similar kinetic diameters in a flexible framework, the ap-
proach is to modulate the pressure of the pore opening by
tuning the internal surface of the host. The conventional
ways to modulate pore surfaces is to chemically elaborate
the frameworks through incorporation of functional ligands,
inclusion of metal salts, adjustment of the charge, or addi-
tion of water molecules.[2a,8] Removing or changing the coor-
dinated solvent molecules through a postsynthetic approach
is also a common strategy used to control the gas adsorption
selectivity in rigid metal–organic frameworks.[9] Recognizing
the promise of effects induced by coordinated solvent mole-
cules, we have attempted to apply this strategy within a
series of flexible frameworks to modulate the gate opening
for O2/N2 gas separation.
In the design and synthesis of flexible porous materials
with new structural topologies and high thermal and chemi-
cal stabilities, carboxylate- and pyridine-based ligands have
been used extensively. Azolate-based bridging ligands, how-
ever, have recently attracted interest as a means of generat-
ing frameworks with surfaces featuring solvated metal
sites.[10] To obtain a high symmetry bridging ligand and new
triazolate-based frameworks, we developed the synthesis of
a ditopic ligand with a 1H-1,2,3-triazole function, namely
1,4-benzenedi(1H-1,2,3-triazole) (H2BDTri).[11] Herein, we
report two new flexible microporous metal–organic frame-
Flexible metal–organic frameworks have attracted much at-
tention for their “breathing” structures and unusual proper-
ties in response to guest adsorption.[1] This structural dyna-
mism has led to studies of selective gas adsorption,[2] molec-
ular accommodation,[3] sensing,[4] and the kinetics of (multi)-
ACHTUNGTRENNUNG
stepwise gas adsorption.[5] Associated with the flexibility of
the framework, such materials often exhibit gas selectivity
by a stepwise adsorption caused by a guest-induced frame-
work transition. Besides size or shape exclusion and adsor-
bate–surface interaction characteristics of rigid frameworks,
dynamic frameworks show structural rearrangements during
adsorption–desorption processes. These structural transfor-
mations are guest dependant and, interestingly, can lead to
control of the selectivity over several adsorbates.[6] In partic-
ular, small gaseous adsorbates, such as O2 and N2, are attrac-
tive targets for research, first because the differences in
sorption behavior between such similar gas molecules have
attracted commercial interest for processes such as air sepa-
[a] Dr. A. Demessence, Prof. J. R. Long
Department of Chemistry, University of California
Berkeley, Berkeley CA, 94720-1460 (USA)
Fax : (+1)510-643-3546
E-mail: jrlong@berkeley.edu
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000053.
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works, CuACHTUNGTRENNUNG(BDTri)L, of the same structure type, but with dif-
ferent coordinated solvent molecules, L=DMF and diethyl-
formamide (DEF), directed toward the cavity interiors. Due
to the high stability of the triazolate-bridged framework, the
structural transformations through single-crystal to single-
crystal conversions can be fully characterized. We then ex-
amine how the cavity modifications affect the gate opening
and consequently the ability of the material to adsorb N2
and O2. The two-step isotherms associated with the breath-
ing of the framework reveals a high gas selectivity, depend-
ing on the coordinated solvent.
Results and Discussion
The reaction between CuCl2·2H2O and H2BDTri in an
acidic mixture of DMF at 1208C affords the porous metal–
organic framework CuACHTNUGTRENNUG(BDTri)ACHTUNGTNER(NUGN DMF)·1.2H2O (1a). X-ray
analysis of the green block-shaped crystals showed that the
compound crystallizes in the orthorhombic system, adopting
space group Imma with cell parameters of a=22.538(1), b=
7.044(3), c=13.772(6) ꢁ, and V=2186.5(2) ꢁ3. The com-
(DMF) (BDT2À =1,4-ben-
pound is isostructural to CuACTHNUGTRENNUG(BDT)HCATUNGTRENNGUN
zeneditetrazolate),[10a] exhibiting a framework wherein octa-
hedral CuII centers are bridged through a combination of
two triazolate groups and a DMF molecule to form one-di-
mensional chains (Figure 1). Neighboring chains are con-
nected through BDTri2À ligands to form an extended three-
dimensional network with one-dimensional channels run-
ning along the [010] direction (Figure 2).
Upon exposure of a single crystal of 1a to ambient atmos-
phere, its color changed from green to blue (1b) after
10 days, and then after 1 month to gray (1c). Remarkably,
the crystal remained intact throughout these changes, ena-
bling the structures of 1b and 1c to be determined. X-ray
Figure 2. Views of the crystal structures of 1a, 1b and 1c (from up to
down) showing the one-dimensional channels along the [010] direction.
Light blue, blue, and gray spheres represent Cu, N, and C atoms, while
purple spheres represent positions that are either a N or a C atom of a
triazolate ring; H atoms and bridging DMF molecules are omitted for
clarity.
analyses revealed two new crystallographic forms, wherein
the framework connectivity and space group are maintained,
with unit cell parameters of a=23.739(4), b=7.0724(1), c=
11.5405(2) ꢁ and V=1937.5(5) ꢁ3 for 1b, and a=24.561(3),
b=6.9860(9), c=9.1333(1) ꢁ and V=1567.1(4) ꢁ3 for 1c
(Figure 2 and Table 1). The change from 1a to 1c implies an
increase of more than 2 ꢁ of the a axis and a drastic de-
crease of the c parameter by more than 4.5 ꢁ (while the b
parameter remains almost unchanged) and is accompanied
by a reduction in the cell volume of 11 and 28% for 1b and
1c, respectively. The shrinkage of the framework is due to
the release of uncoordinated guest solvent molecules from
Figure 1. A portion of the crystal structure of 1a, showing part of a one-
dimensional chain. Light blue, red, blue, and gray spheres represent Cu,
O, N, and C atoms, while purple spheres represent positions that are
either a N or a C atom of a triazolate ring; H atoms are omitted for
clarity.
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J. R. Long and A. Demessence
Table 1. Unit cell parameters, cell volume, and angles, a and b, between
the phenyl and the triazolate rings and between the phenyl ring and the
plane formed by two copper ions (Cu1) and two bridging nitrogen atoms
(N1) from a triazolate function, respectively.
formed by aromatic rings is planar, but upon desolvation
and reduction in the unit cell volume, two phenomena occur
to minimize the lattice energy and explain the large shrink-
age. First, both triazolate rings of one ligand are bending,
one up and one down, to make an angle of 8.491(2)8 with
the benzene ring in 1c (Table 1 and Figure 3). Since the tria-
zolate and phenyl rings are planar, this angle is mostly ex-
plained by bending at the C2 carbon atoms of the triazolate
groups which produce an angle strain, similar to the curved
graphene sheets forming fullerenes, for example.[16] This
case represents the first characterization of the bending of a
sp2 carbon atom in a small cyclic organic molecule induced
by a framework. In addition to this deformation, the bridg-
ing nitrogen atoms of the triazolate rings act as a “kneecap”
around the Cu···Cu axis, with the angle b varying from
0.3(1)8 in 1a to 20.2(2)8 in 1c (Figure 3). Thus, these struc-
tural deformations explain the movement of the copper
atoms by a distance of 2.319 ꢁ along the [001] axis between
the structures of 1a and 1c. Presumably, the steric repulsion
between the methyl groups of the coordinated DMF mole-
cules and the C2 carbon atoms of the triazolate rings
(C2···C6=3.4(4) ꢁ) prevent the collapsing of the framework
and any further shrinkage. In addition, the strong bond be-
tween the triazolate rings and the metal ions is likely to
enable the observation of multiple single-crystal transforma-
tions,[15b] allowing us to identify a new example of frame-
work flexibility associated primarily with bending of the
bridging rigid ligands. Moreover, the coordinated DMF mol-
ecules extending into the pores act as pillars between the
copper chains to maintain a permanent microporosity.
1a
1b
1c
a [ꢁ]
b [ꢁ]
c [ꢁ]
V [ꢁ3]
a [8]
22.538(1)
7.044(3)
13.772(6)
2186.5(2)
0.671(2)
0.262(1)
23.739(4)
7.0724(1)
11.5405(2)
1937.5(5)
2.481(2)
24.561(3)
6.9860(9)
9.1333(1)
1567.1(4)
8.491(2)
b [8]
9.223(2)
20.162(2)
the pores of the structure, as observed previously for rever-
sible expanding/shrinking frameworks.[12]
Two explanations have been proposed to describe such
breathing behavior.[13] The first is related to the host–guest
interactions and the second to the intrinsic flexibility of the
framework itself, which is induced by the existence of weak
points within the skeleton, allowing the deformation of the
network under the action of a stimulus. Such a deformation
of the framework structure is usually associated with the
modifications of the bridging ligands[14] and/or metal coordi-
nation sphere (solvent removal, elongation of bonds).[15] In
1a–c, however, the position of the atoms around the CuII
centers remains geometrically almost invariant (bond
lengths and angles vary by just 0.04 ꢁ and 28, respectively)
and consequently is not responsible for the structural defor-
mations. Instead, the deformation of the framework is
mostly explained by the geometry changes associated with
flexing of the bridging ligand (Figure 3). In 1a, the ligand
Powder X-ray diffraction patterns allowed a study of the
structural dynamics associated with the flexibility of the
framework to be performed. In Figure 4a the diffraction pat-
tern for a freshly prepared sample of 1c upon drying under
vacuum is displayed. Addition of water to the sample indu-
ces an immediate change in the pattern, corresponding to
the regeneration of the structure of 1a upon incorporation
of guest water molecules. Leaving the framework in air at
room temperature for only a few minutes then leads to a re-
verse to the closed structure of 1c through release of the
water molecules. A similar breathing effect was observed
when the sample was treated with methanol instead of
water (Figure 4e). During the reversible transformations, the
peaks of the powder diffraction patterns exhibit drastic but
continuous displacements that are characteristic of a breath-
ing effect, without loss of crystallinity after several desolva-
tion-resolvation cycles. These tests demonstrate the chemical
stability of the framework in solvents such as water and
methanol, as well as structural stability through the course
of multiple breathing events.
Figure 3. View of the structural deformations upon desolvation of the
pores from 1a (light colors) to 1c (dark colors). Light blue, red, dark
blue, and gray spheres represent Cu, O, N, and C atoms, while blue
spheres represent positions that are either a N or a C atom of a triazolate
ring; H atoms are omitted for clarity. The projection is along the [010] di-
rection with an edge-on view of the BDTri2À ligands bridging between
CuII centers. The angles a and b are the angles between the benzene and
triazolate rings and the benzene ring and the plane formed by two
copper atoms (Cu1) and two coordinated nitrogen atoms (N1) from a tri-
azolate group, respectively.
To investigate the flexible nature of the compound, we
measured the H2, N2, and O2 adsorption isotherms at 77 K
(Figure 5). The H2 isotherm reveals a reversible excess
uptake of 3.6 mmolgÀ1 (0.77 wt%), which did not increase
significantly at higher pressures of up to 100 bar. The N2 and
O2 isotherms are characterized by two distinct adsorption
steps and marked hysteresis, which is related to the flexibili-
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Selective Gas Adsorption
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1b (0.337 mLgÀ1) than to that of 1a (0.458 mLgÀ1), suggest-
ing that the framework is not completely opened at this
pressure. The Langmuir surface area obtained by fitting the
linear part of the isotherm in the high-pressure range is
1160 m2 g.[17] Therefore, the first step of this two-step N2 ad-
sorption isotherm is related to the structure of 1c in which
the DMF molecules act as pillars to leave a permanent mi-
croporosity, whereas the second step apparently originates
from the pore opening of the framework. Although many
metal–organic frameworks exhibiting a structural change
prompted by external stimuli display multi-stepwise gas ad-
sorption isotherms,[5a] the phenomena are usually related to
a “blocking effect”[18] or to a “breathing effect”.[19] To the
best of our knowledge, the present case represents only the
second example in which this kind of gas adsorption is asso-
ciated with the presence of rigid micropores due to the pil-
laring role of anions or solvent molecules, followed by a
pore opening process.[20]
The two-step O2 adsorption isotherm at 77 K, compared
with the N2 adsorption isotherm, shows a larger amount of
adsorbed gas and a lower pressure for the pore opening.
The first step, similar to that of N2, is characterized by a
steep rise at low pressure, related to the microporosity of
1c. The number of gas molecules adsorbed at the plateau is
approximately 1.6 times the number of N2 molecules ad-
sorbed, in line perhaps with the smaller kinetic diameter of
O2 (3.46 ꢁ) relative to N2 (3.64 ꢁ).[21] The second O2 ad-
sorption step, governed by the pore-opening process, arises
at a lower pressure than for N2, which correlates with the
expected strength of interactions with a surface, as reflected
in the different boiling points of the molecules (N2 =77 K,
O2 =90 K).[5b] The much larger amount of adsorbed O2 gas
associated with the second step (17.8 mLgÀ1 at 195 mbar)
seems to correspond to the available pore volume of struc-
ture 1a instead of 1b. Thus, the interaction/repulsion of
guest gas molecules with the surfaces of the framework, and
their gate-opening ability, cannot be excluded as a determin-
ing factor for the adsorption selectivity. In considering other
possible reasons for the larger amount of O2 adsorbed, fac-
tors such as the paramagnetism of O2 and the greater quad-
rupole moment of N2 could also potentially play a role.[6,22]
At 168 mbar, O2 molecules are adsorbed more favorably
(17.0 mLgÀ1) than N2 molecules (2.9 mLgÀ1) with a selectivi-
ty of 5.9:1. To the best of our knowledge, only a few other
metal–organic frameworks have been shown to exhibit a
similar effect with these gases at low pressure.[10,23] While
this ratio is not the highest reported, it represents a good
compromise between the selectivity ratio and the quantity
Figure 4. Powder X-ray diffraction patterns of different phases observed
for CuACHTUNGTRENNUNG(BDTri)ACHTUNGTRENNUNG(DMF). a) Structure 1c upon drying under vacuum, b) at
t=1 min after adding a drop of H2O, c) at t=15 min (1a), d) at t=40 min
(1c), e) at t=45 min after adding a drop of MeOH (1a), and f) at t=
75 min (1c). The orange and green dotted lines correspond to the evolu-
tion of the positions of the 101 and 200 reflections, respectively.
Figure 5. Gas adsorption isotherms for the uptake of N2, H2, and O2 in
CuACHTUNGTRENNUNG(BDT)ACHTUNGTRENNUNG(DMF) at 77 K.
ty of the framework. After a steep rise at low pressure, the
N2 isotherm reaches a plateau. The amount of adsorbed gas
at this first step (0.100 mLgÀ1 at 168 mbar) is in good agree-
ment with the void volume of 1c calculated from the crystal
structure (0.108 mLgÀ1) and can be attributed to the perma-
nent porosity of the phase. A Langmuir fit to the first step
of the N2 adsorption data gives an apparent surface area of
330 m2 gÀ1. At higher pressure, the amount of N2 adsorbed in
the second step reaches 3.5 times that of the first step. At
77 K and 960 mbar, the adsorbed amount of N2 of
0.357 mLgÀ1 corresponds more closely to the void volume of
of adsorbed gas. For example, Yb4CAHTUNGTRNE(NUGN m4-H2O)(4,4’,4’’-S-tria-
zine-2,4,6-triyl-tribenzoate)8/3A(SO4)2·3H2O·10DMSO has the
CTHUNGTRENNUNG
highest selectivity ratio ꢀ9.4:1, but a low quantity of ad-
sorbed O2 (9.4 mLgÀ1 of adsorbed O2 at 201 mbar and
77 K)[24] and {Ag
2ACTHNUTRGENN[UG Ag4-ACHTUGNTREN(NGUN 3,5-bis(trifluoromethyl)-1,2,4-triazo-
late)6]}n exhibits a large capacity for O2 uptake (21 mmolgÀ1
at 30 mbar and 77 K), but a relatively poor O2/N2 selectivity
of 1.2:1.[25] Both N2 and O2 isotherms show hysteresis loops
associated with a two-step desorption process. Indeed, the
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J. R. Long and A. Demessence
open phase is maintained until the pressure drops to 50 and
30 mbar for N2 and O2, respectively. The low-pressure pla-
teau in the desorption curves can be attributed to adsorb-
ent–adsorbate or adsorbate–adsorbate interactions through
van der Waals forces until the framework releases sufficient
gas molecules to allow pore closing, after which the amount
of gas adsorbed drops precipitously.[17] This second desorp-
tion step is due to the permanent microporosity of 1c, simi-
lar to what is observed for rigid frameworks. Adsorption
measurements of N2 and O2 gas molecules at 87 K show that
the pressure needed to open the pores increases as the tem-
perature increases (Figure S3 in the Supporting Informa-
tion). For N2 adsorption the pressure of pore opening is
shifted from 170 to 570 mbar for experiments at 77 and
87 K, respectively, while for O2 adsorption, the shift is from
30 to 180 mbar at the same temperatures. Such behavior has
been previously observed with different gases in several
flexible metal–organic frameworks, and has been explained
as relating to the rate at which the gas molecules strike the
solid surface under supercritical conditions.[5]
duced surface area can also be explained by the presence of
the larger DEF solvent molecules within the closed frame-
work structure. As for Cu
(DMF), the O2 adsorption isotherm measured at 77 K for
Cu(BDTri)(DEF) reveals a two-step adsorption process. A
ACHTUNGTREN(GNUN BDT)ACHTUNREGTNNUNG ACHTUNGTRENNUNG(BDTri)-
(DMF)[10a] and Cu
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Langmuir fit to the low-pressure step of the isotherm gives
an estimated surface area of 240 m2 gÀ1. The second step,
much more significant, occurs at 50 mbar and corresponds
to adsorption of 15.9 mmolgÀ1 of O2 at 200 mbar. At this
pressure the selectivity of O2 over N2 reaches 13.5, by far
surpassing the value of the isostructural compounds Cu-
AHCTUNGTERNNG(UN BDT)ACHUTNTGERNNUG(DMF) and CuACHTUNREGTG(NNUN BDTri)ACHTNUGTRENN(UGN DMF) and representing the
highest value yet observed for a microporous material under
similar conditions. It also represents an initial demonstration
of how changing the molecules bound at the surface within
a flexible metal–organic framework can dramatically affect
the gas adsorption selectivity.
This work shows a rare example of selective two-step gas
adsorption at low pressure associated with the flexibility of
the framework and coupled with a guest-dependent gate-
opening pressure.[26]
To study the effect of the solvent molecules pointing into
the channel-like pores of the structure on the pore opening
for O2/N2 gas adsorption, the compound was synthesized in
DEF instead of DMF. The powder X-ray diffraction pattern
of the resulting framework, corresponding to a formula of
Conclusion
Cu
(BDTri)
E
These results demonstrate the successful incorporation of
the new bridging ligand BDTri2À in the flexible metal–organ-
phase of Cu
N
ACHTUNGTRENNUNG
works of these two materials are identical, but with different
bridging solvent molecules (Figure S4 in the Supporting In-
formation). Prior to measuring H2, N2, and O2 gas adsorp-
tion isotherms, this compound was degassed by heating at
1208C under dynamic vacuum. As shown in Figure 6, the H2
adsorption isotherm at 77 K reveals a reversible uptake of
2.3 mmolgÀ1 (0.46 wt%) at 1.2 bar. This represents a lower
ic frameworks CuACTHNGUTERN(UNG BDTri)(L) (L=DMF, DEF). Due to the
strong bonds between the triazolate rings and the CuII cen-
ters, the initial and final stages of breathing could be charac-
terized, together with an intermediate state, leading to a de-
tailed understanding of the structural deformations associat-
ed with framework breathing. Here, deformation of the
ligand coupled with the ability of the triazolate ring to act
as a kneecap is responsible for the reversible flexibility. The
bending at an sp2 carbon atom in triazolate function has no
analogue in carboxylate-based frameworks. Hence, it ap-
pears that the use of triazolate-based ligands can provide a
new way of generating flexible frameworks.
value than the DMF-based CuACTHNUTRGENUGN(BDTri) framework, consis-
tent with the greater volume occupied by the bridging DEF
molecules, which reduces the pore volume of the closed
phase (analogous to 1c). Interestingly, the N2 adsorption iso-
therm at 77 K does not display two steps, but rather a type I
curve indicating a BET surface area of 100 m2 gÀ1. This re-
The CuACTHNUGRTNENUG(BDTri)ACHTUNGTNER(NUGN DMF) framework also shows two-step
isotherms at 77 K for the adsorption of O2 and N2, which is
associated with the permanent microporosity of the closed
phase and a pore-opening process. Moreover compared with
the isostructural tetrazolate-based framework Cu
(DMF),[10a] a significant improvement in the amount of gas
taken up is observed. With larger DEF bridging molecules,
the analogous framework Cu(BDTri)(DEF) exhibits a selec-
ACHTUNGTRENNUNG(BDT)-
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
tive pore opening with O2 but not with N2 gas. This observa-
tion points to the importance of how adjusting the nature of
coordinated solvent molecules on a framework surface can
lead to control over selectivity and the pressure required to
induce pore opening. This selective breathing has implica-
tions for a range of potential applications, including stereo-
specific chemical catalysis, molecular separations, and chem-
ical sensing. It is important to emphasize, however, that
while these materials are of significant interest for under-
standing selective gas interactions within metal–organic
Figure 6. Gas adsorption isotherms for the uptake of N2, H2, and O2 in
CuACHTUNGTRENNUNG(BDTri)ACHTUNGTRENNUNG(DEF) at 77 K.
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Selective Gas Adsorption
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tubes containing the degassed samples were transferred to an electronic
balance and weighed again to determine the mass of sample (94.7 and
41.3 mg for L=DMF and DEF, respectively). The tube was then trans-
ferred back to the analysis port of the gas adsorption instrument. The
outgas rate was again confirmed to be less than 2 mtorrminÀ1
(0.27 PaminÀ1). For all isotherms, warm and cold free-space correction
measurements were performed by using ultra-high purity He gas (UHP
grade 5.0, 99.999% purity). The N2, O2, and H2 isotherms at 77 K were
measured in a liquid nitrogen bath, using UHP-grade gas sources. The N2
and O2 gas adsorption experiments were paused after 50 h to refill the
liquid nitrogen bath (time of full experiment around 4 d). Oil-free
vacuum pumps and oil-free pressure regulators were used for all meas-
urements to prevent contamination of the samples during the evacuation
process, or of the feed gases during the isotherm measurement.
frameworks, they are unlikely to find utility in performing
O2/N2 separations owing to 1) the low temperatures required
(at 298 K and 1.2 bar, the O2 adsorbed in CuACTHUNTGRENNUG(BDTri)AHCTUNGTRNE(NUGN DMF)
drops to 0.03 mmolgÀ1 (Figure S5 in the Supporting Infor-
mation)) and 2) the fact that pore opening induced by one
component of a mixture of gases is also likely to enable
entry for other components of similar size.
Experimental Section
General: All reagents were obtained from commercial vendors and used
without further purification. The compound 1,4-diethynylbenzene was
synthesized according to a previously published procedure (see the Sup-
porting Information).[27]
X-ray structure determinations: Crystals, coated in Paratone-N oil and at-
tached to Kapton loops, were transferred to a Siemens SMART APEX
diffractometer (1a and 1b) or to a Bruker Platinum 200 Instrument at
the Advanced Light Source at the Lawrence Berkeley National Labora-
tory (1c), and cooled in a nitrogen stream. Lattice parameters were ini-
tially determined from a least-squares analysis of more than 100 centered
reflections; these parameters were later refined against all data. None of
the crystals showed significant decay during data collection. The raw in-
tensity data were converted (including corrections for background, Lor-
entz, and polarization effects) to structure factor amplitudes and their
esds by using the SAINT 7.07b program. An empirical absorption correc-
tion was applied to each data set by using SADABS. Space-group assign-
ment was based on systematic absences, E statistics, and successful refine-
ment of the structures. Structures were solved by direct methods with the
aid of difference Fourier maps and were refined against all data by using
the SHELXTL 5.0 software package. Hydrogen atoms were inserted at
idealized positions and refined by using a riding model with an isotropic
thermal parameter 1.2 times that of the attached carbon atom. The disor-
der evident in the electron-density map prevented the refinement of sol-
vent molecules within the pores of 1a and 1b. As such, all peaks with
electron densities larger than one electron were refined as partially occu-
pied O and C atoms. CCDC-755760, 755761, and 755762 contains the
supplementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
H2BDTri·2H2O: Trimethylsilyl azide (5.2 g, 45 mmol) was added to a so-
lution of DMF and MeOH (60 mL, 9:1) containing CuI (286 mg,
1.5 mmol) and 1,4-diethynylbenzene (1.9 g, 15 mmol) under a nitrogen at-
mosphere. The reaction mixture was stirred at 908C for 44 h. The mixture
was cooled to room temperature, filtered, and concentrated. Water
(30 mL) was added to the filtrate to obtain the product as a pale yellow
precipitate. The solid was washed with Et2O and dried under vacuum to
1
yield the product (2.6 g, 82%). H NMR (300 MHz, (CD3)2SO): d=15.03
(s, 1H), 8.31 (s, 1H), 7.95 ppm (s, 2H). IR (neat): n˜ =3155, 3115, 2960,
2865, 1655, 1460, 1430, 1370, 1355, 1335, 1310, 1225, 1200, 1135, 1080,
1005, 970, 875, 845, 730, 705, 650 cmÀ1; elemental analysis calcd (%) for
C10H8N6·2H2O: C 48.38, H 4.87, N 33.85; found: C 48.58, H 4.88, N
33.80.
CuACHTUNGTRENNUNG(BDTri)ACHTUNGTRENNUNG(DMF)·1.2H2O: A mixture of solutions of CuCl2·2H2O
(0.075m, 0.15 mmol) in DMF (200 mL) and H2BDTri·2H2O (0.075m,
0.15 mmol) in DMF (200 mL) was titrated with dilute HNO3 until the pH
of the solution reached 4. The mixture was heated in a 2 mL scintillation
vial sealed with a Teflon-lined cap at 808C for 48 h. The resulting green
crystals were collected by filtration and found to be suitable for single-
crystal X-ray analysis. For larger scales,
a mixture of solutions of
CuCl2·2H2O (0.10 mg, 0.59 mmol) in DMF (15 mL) and of H2BDTri·2H2O
(140 mg, 0.56 mmol) in DMF (15 mL) was titrated with dilute HNO3
until the pH of the solution reached 4. The mixture was heated in a
125 mL scintillation vial sealed with a Teflon-lined cap at 808C for 48 h.
The resulting powder was collected by filtration, washed with DMF, and
dried under reduced pressure to yield the product (150 mg, 73%). IR
(neat): n˜ =3335, 2925, 2855, 1660, 1490, 1475, 1435, 1415, 1390, 1235,
1215, 1155, 1100, 1060, 985, 825, 665 cmÀ1; elemental analysis calcd (%)
for C13H14.4CuN7O2.2: C: 42.11, H: 4.74, N: 26.44; found C:42.11, H: 3.69,
N: 26.69.
Other physical measurements: Infrared spectra were collected on a Nico-
let Avatar 360 FTIR spectrometer with an attenuated total reflectance
accessory. 1H NMR spectra were obtained by using a Bruker AVQ-400
instrument. Elemental analyses were obtained from the Microanalytical
Laboratory of the University of California, Berkeley. Powder X-ray dif-
fraction patterns were recorded using CuKa radiation (l=1.5406 ꢁ) on a
Bruker D8 Advance diffractometer. Thermogravimetric analyses were
carried out at a ramp rate of 18CminÀ1 in a nitrogen flow with a TA In-
struments TGA Q5000 V3.1 Build 246 instrument.
CuACHTUNGTRENNUNG(BDTri)ACHTUNGTRENNUNG(DEF)·0.9H2O: A mixture of solutions of CuCl2·2H2O
(0.10 mg, 0.59 mmol) in DEF (15 mL) and of H2BDTri·2H2O (140 mg,
0.56 mmol) in DEF (15 mL), was titrated with dilute HNO3 until the pH
of the solution reached 4. The mixture was heated in a 125 mL scintilla-
tion vial sealed with a Teflon-lined cap at 808C for 48 h. The powder was
collected by filtration, washed with DEF, and dried under reduced pres-
sure to yield the product (135 mg, 62%). IR (neat): n˜ =3245, 2975, 2935
2880, 1650, 1495, 1475, 1435, 1415, 1385, 1250, 1210, 1150, 1105, 1060,
985, 835, 665 cmÀ1; elemental analysis calcd (%) for C15H17.8CuN7O1.9: C:
41.99, H: 3.48, N: 29.61; found C:42.01, H: 3.15, N: 29.89.
Acknowledgements
This research was supported by General Motors, Inc., and as part of the
Center for Gas Separations Relevant to Clean Energy Technologies, an
Energy Frontier Research Center funded by the U.S. Department of
Energy, Office of Science, Office of Basic Energy Sciences under Award
Number DE-SC0001015. We thank Dr. H. J. Choi, Dr. D. M. DꢂAlessan-
dro, and Dr. S. Horike for helpful discussions. A portion of this research
was conducted at the Advanced Light Source facility at the Lawrence
Berkeley National Laboratory, which is operated by the DoE under Con-
tract DE-AC03-76SF00098.
Gas adsorption measurements: Gas adsorption isotherms for pressures in
the range 0–1.2 bar were measured by using a Micromeritics ASAP2020
instrument. Powders of the compounds CuACTHNUTRGNEUNG(BDTri)(L) (L=DMF, DEF)
were transferred to a preweighed analysis tube, which was capped with a
Transeal and evacuated by heating at 1208C under dynamic vacuum until
an outgas rate of less than 2 mtorrminÀ1 (0.27 PaminÀ1) was achieved.
The powder X-ray diffraction patterns of the desolvated frameworks cor-
respond to the collapsed framework structure 1c. (Attempts to remove
the coordinating DMF molecules in 1c by heating at 0.28CminÀ1 to tem-
peratures between 120 and 2508C did not change the surface area, while
at 2708C the framework lost its crystallinity) The evacuated analysis
[1] a) S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. 2004, 116, 2388;
Angew. Chem. Int. Ed. 2004, 43, 2334; b) K. Uemura, R. Matsuda, S.
Kitagawa, J. Solid State Chem. 2005, 178, 2420; c) A. J. Fletcher,
K. M. Thomas, M. J. Rosseinsky, J. Solid State Chem. 2005, 178,
Chem. Eur. J. 2010, 16, 5902 – 5908
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5907

J. R. Long and A. Demessence
2491; d) D. Bradshaw, J. E. Warren, M. J. Rosseinsky, Science 2007,
315, 977; e) C. Serre, C. Mellot-Draznieks, S. Surblꢃ, N. Audebrand,
Y. Filinchuk, G. Fꢃrey, Science 2007, 315, 1828; f) G. Fꢃrey, C. Serre,
Chem. Soc. Rev. 2009, 38, 1380.
J. A. Ripmeester, D. T. Cramb, G. K. H. Shimizu, Nat. Mater. 2008,
7, 229.
[16] H. W. Kroto, J. R. Heath, S. C. OꢂBrien, R. F. Curl, R. E. Smalley,
Nature 1985, 318, 162.
[2] a) P. L. Llewellyn, S. Bourrelly, C. Serre, Y. Filinchuk, G. Fꢃrey,
Angew. Chem. 2006, 118, 7915; Angew. Chem. Int. Ed. 2006, 45,
7751; b) T. K. Maji, R. Matsuda, S. Kitagawa, Nat. Mater. 2007, 6,
142.
[3] Y. Kubota, M. Takata, R. Matsuda, R. Kitaura, S. Kitagawa, T. C.
Kobayashi, Angew. Chem. 2006, 118, 5054; Angew. Chem. Int. Ed.
2006, 45, 4932.
[17] R. Kitaura, K. Seki, G. Akiyama, S. Kitagawa, Angew. Chem. 2003,
115, 444; Angew. Chem. Int. Ed. 2003, 42, 428.
[18] E.-Y. Choi, K. Park, C.-M. Yang, H. Kim, J.-H. Son, S. W. Lee, Y. H.
Lee, D. Min, Y.-U. Kwon, Chem. Eur. J. 2004, 10, 5535.
[19] C. Serre, S. Bourrelly, A. Vimont, N. A. Ramsahye, G. Maurin, P. L.
Llewellyn, M. Daturi, Y. Filinchuk, O. Leynaud, P. Barnes, G. Fꢃrey,
Adv. Mater. 2007, 19, 2246.
[4] G. J. Halder, C. J. Kepert, B. Moubaraki, K. S. Murray, J. D. Cashion,
Science 2002, 298, 1762.
[20] A. Kondo, H. Noguchi, L. Carlucci, D. M. Proserpio, G. Ciani, H.
Kajiro, T. Ohba, H. Kanoh, K. Kaneko, J. Am. Chem. Soc. 2007,
129, 12362.
˘
[5] a) H. J. Choi, M. Dinca, J. R. Long, J. Am. Chem. Soc. 2008, 130,
7848; b) D. Tanaka, K. Nakagawa, M. Higuchi, S. Horike, Y.
Kubota, T. C. Kobayashi, M. Takata, S. Kitagawa, Angew. Chem.
2008, 120, 3978; Angew. Chem. Int. Ed. 2008, 47, 3914.
[21] D. W. Breck, Zeolite Molecular Sieves, Wiley, New York, 1984.
[22] S. S. Kaye, H. J. Choi, J. R. Long, J. Am. Chem. Soc. 2008, 130,
16921.
[6] J.-R. Li, R. J. Kuppler, H.-C. Zhou, Chem. Soc. Rev. 2009, 38, 1477.
[7] C. R. Reid, I. P. Oꢂkoye, K. M. Thomas, Langmuir 1998, 14, 2415.
[23] a) D. N. Dybtsev, H. Chun, S. H. Yoon, D. Kim, K. Kim, J. Am.
˘
Chem. Soc. 2004, 126, 32; b) M. Dinca, J. R. Long, J. Am. Chem.
˘
[8] a) M. Dinca, J. R. Long, J. Am. Chem. Soc. 2007, 129, 11172; b) B.
Soc. 2005, 127, 9376; c) S. M. Humphrey, J.-S. Chang, S. H. Jhung,
J. W. Yoon, P. T. Wood, Angew. Chem. 2007, 119, 276; Angew.
Chem. Int. Ed. 2007, 46, 272; d) S. Ma, X.-S. Wang, C. D. Collier,
E. S. Manis, H.-C. Zhou, Inorg. Chem. 2007, 46, 8499; e) J.-R. Li, Y.
Tao, Q. Yu, X.-H. Bu, H. Sakamoto, S. Kitagawa, Chem. Eur. J.
2008, 14, 2771; f) H.-S. Choi, M. P. Suh, Angew. Chem. 2009, 121,
6997; Angew. Chem. Int. Ed. 2009, 48, 6865; g) P. L. Llewellyn, P.
Horcajada, G. Maurin, T. Devic, N. Rosenbach, S. Bourrelly, C.
Serre, D. Vincent, S. Loera-Serna, Y. Filinchuk, G. Fꢃrey, J. Am.
Chem. Soc. 2009, 131, 13002.
Arstad, H. Fjellvꢄg, K. O. Kongshaug, O. Swang, R. Blom, Adsorp-
tion 2008, 14, 755; c) M. Dinca, A. Dailly, J. R. Long, Chem. Eur. J.
2008, 14, 10280.
˘
[9] a) O. K. Farha, K. L. Mulfort, J. T. Hupp, Inorg. Chem. 2008, 47,
10223; b) A. Demessence, D. M. DꢂAlessandro, M. L. Foo, J. R.
Long, J. Am. Chem. Soc. 2009, 131, 8784; c) Y.-S. Bae, O. K. Farha,
J. T. Hupp, R. Q. Snurr, J. Mater. Chem. 2009, 19, 2131.
˘
[10] a) M. Dinca, A. F. Yu, J. R. Long, J. Am. Chem. Soc. 2006, 128,
˘
8904; b) M. Dinca, A. Dailly, Y. Liu, C. M. Brown, D. A. Neumann,
J. R. Long, J. Am. Chem. Soc. 2006, 128, 16876.
[24] S. Ma, X.-S. Wang, D. Yuan, H.-C. Zhou, Angew. Chem. 2008, 120,
4198; Angew. Chem. Int. Ed. 2008, 47, 4130.
[25] C. Yang, X. Wang, M. A. Omary, J. Am. Chem. Soc. 2007, 129,
15454.
[11] T. Jin, S. Kamijo, Y. Yamamoto, Eur. J. Org. Chem. 2004, 3789.
[12] T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry,
T. Bataille, G. Fꢃrey, Chem. Eur. J. 2004, 10, 1373.
[13] a) S. Kitagawa, K. Uemura, Chem. Soc. Rev. 2005, 34, 109; b) G.
Fꢃrey, Chem. Soc. Rev. 2008, 37, 191.
[14] C. Serre, C. Mellot-Draznieks, S. Surblꢃ, N. Audebrand, Y. Fili-
nchuk, G. Fꢃrey, Science 2007, 315, 1828.
[26] Z. Wang, S. M. Cohen, J. Am. Chem. Soc. 2009, 131, 16675.
[27] E. Weber, M. Hecker, E. Koepp, W. Orlia, M. Czugler, I. Csçregh, J.
Chem. Soc. Perkin Trans. 2 1988, 1251.
[15] a) D. Bradshaw, J. E. Warren, M. J. Rosseinsky, Science 2007, 315,
977; b) B. D. Chandler, G. D. Enright, K. A. Udachin, S. Pawsey,
Received: January 9, 2010
Published online: April 15, 2010
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