Isostructural metal-organic frameworks assembled from functionalized diisophthalate ligands through a ligand-truncation strategy

Article abstract of DOI:10.1002/chem.201203297

Four isostructural metal-organic frameworks (MOFs) with various functionalized pore surfaces were synthesized from a series of diisophthalate ligands. These MOFs exhibit a new network topology of {4.6⁴.8} ₂{4².6⁴}{6⁴.8²} ₂{6⁶}. Hydrogen uptake as high as 2.67wt % at 77K/1bar and CO₂ uptake of 15.4wt % at 297K/1bar have been observed for PCN-308, which contains -CF₃ groups. The isostructural series of MOFs also showed reasonable adsorption selectivity of CO₂ over CH₄ and N₂. Gas station: Four isostructural metal-organic frameworks have been synthesized from functionalized ligands through a ligand-truncation strategy (see figure). The frameworks adopt a new topology. They are good adsorbent materials for both CO₂ capture and H₂ storage.

Full text of DOI:10.1002/chem.201203297

FULL PAPER
DOI: 10.1002/chem.201203297
Isostructural Metal–Organic Frameworks Assembled from Functionalized
Diisophthalate Ligands through a Ligand-Truncation Strategy
Yangyang Liu, Jian-Rong Li, Wolfgang M. Verdegaal, Tian-Fu Liu, and
Hong-Cai Zhou*[a]
Abstract: Four isostructural metal–organic frameworks (MOFs) with various func-
tionalized pore surfaces were synthesized from a series of diisophthalate ligands.
Keywords: adsorption · carbon di-
These MOFs exhibit a new network topology of {4.64.8} {42.64}{64.82}2{66}. Hydrogen
2ACHTNUTRGENNUG HCATUNGTRENNGUN
oxide · hydrogen storage · metal–or-
ganic frameworks · porous materi-
als
uptake as high as 2.67 wt% at 77 K/1 bar and CO2 uptake of 15.4 wt% at 297 K/
À
1 bar have been observed for PCN-308, which contains CF3 groups. The isostruc-
tural series of MOFs also showed reasonable adsorption selectivity of CO2 over
CH4 and N2.
Introduction
its extremely low volumetric energy density, the lack of an
efficient means of storage is the major huddle that limits the
practical use of hydrogen as a new energy carrier.[5] As new
adsorbent materials with high porosity, MOFs are also
promising storage media for hydrogen.[6]
Rapid growth of CO2 emission is considered one of the
main causes of global climate change. CO2 capture from
flue-gas streams in fossil-fuel-fired power plants is becoming
an urgent goal in environmental protection. Metal–organic
frameworks (MOFs), which have emerged as a new class of
porous materials, have great potential in this regard.[1] They
are highly crystalline inorganic–organic hybrid materials
that combine organic linkers and metal ions or metal-con-
taining units.[2] Through the judicious selection of the inor-
ganic and organic components, the structure and properties
of MOFs can be systematically tuned on the atomic level.
This endows the material with great advantages over other
porous materials with large surface area, adjustable compo-
sition, and modifiable pore surfaces, size, and shape. For in-
stance, coordinatively unsaturated metal centers (UMCs),
which are often generated from the removal of terminally
coordinated solvent molecules to the metal centers, can en-
hance gas adsorption and can also be utilized as Lewis acids
for catalysis.[3] Moreover, the pore size and properties of the
MOFs can be tailored by the choice of appropriate linkers
with various functionalities as well as by postsynthetic modi-
fications.[4] Another strategy to reduce CO2 emission is to
utilize clean-energy carriers such as hydrogen, which gener-
ates water as the only byproduct after energy is released.
Hydrogen can be produced from renewable energy sources
and has the highest gravimetric energy density of common
fuels owing to its low molecular weight. However, owing to
Some MOFs have shown impressive CO2-adsorption ca-
pacity and selectivity by incorporating specific functional
groups or unsaturated open metal sites into the robust 3D
framework. In particular, owing to the acidity of CO2, some
basic functional groups such as amine or amide groups in
the organic ligands can help enhance CO2 adsorption.[7]
A
pyridyl group is another basic functional group, but its effect
on CO2 adsorption in MOFs has rarely been studied. Polar
À
functional groups such as the CF3 group were postsyntheti-
cally introduced to a zinc MOF and the modified MOF was
found to have higher CO2/N2 selectivity, although postsyn-
thetic modification decreased the surface area.[8] [Cu
ACHTUNGTRENNUNG
1)2ACHTGNUTRENNUNG
uptake and highest CO2/CH4 selectivity at 298 K and 1 atm
among porous coordination polymers (PCPs) that do not
contain open metal sites, although more studies are needed
2À
to address the effect of SiF6 moieties.[9] Another MOF
with a perfluorinated pore surface was found to be a promis-
ing material for hydrogen storage.[10] Functional groups,
however, do not always have obvious effects on the gas-
sorption properties of MOFs.[11] To systematically study the
effects of various functional groups on gas-sorption proper-
ties of MOFs, ligands with pyridyl, methyl, and perfluoro-
methyl groups have been prepared in this work.
In MOF synthesis, symmetrically substituted organic link-
ers are usually preferred because MOFs based on these li-
gands tend to crystallize in space groups with high symme-
try, which often facilitate crystallization and the subsequent
crystallographic studies.[12] In addition, the synthesis of a
symmetrical ligand tends to proceed with less complica-
tion.[13] Indeed, symmetrical linker extension is a general
method to synthesize new MOFs that bear the same net-
[a] Y. Liu, Dr. J.-R. Li, W. M. Verdegaal, T.-F. Liu, Prof. H.-C. Zhou
Department of Chemistry, Texas A&M University
College Station, TX 77843 (USA)
Fax: (+1)979-845-1595
E-mail: zhou@tamu.edu
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203297.
Chem. Eur. J. 2013, 19, 5637 – 5643
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5637

work topology[13,14] as the nonextended frameworks, and oc-
casionally even entirely new structures.[12,15] Robust non-in-
terpenetrated frameworks with extended ligands usually
possess higher surface area[13] but extended linkers might
also result in framework interpenetration[16] or collapse[17]
during activation. The reverse of linker extension is ligand
truncation (Scheme 1). This proposed strategy provides a
method to introduce new types of building blocks with re-
duced symmetry, and the obtained frameworks might pos-
sess new topologies and interesting properties.
tetrafluoroboric acid (HBF4; 48% w/w aqueous solution) af-
forded green crystals of PCN-305 (PCN stands for “porous
coordination network”). PCN-305 crystallizes in the ortho-
rhombic Cmcm space group with a=24.650(7), b=
33.494(9), c=18.529(5) ꢁ. Unlike most MOFs that consist
of isophthalate moieties, PCN-305 does not contain cubocta-
hedral supramolecular building units in the structure.[18] In-
stead, there are one-dimensional channels along the c axis
and the uncoordinated free pyridyl functional groups point
to the pores of the framework (Figure 1a). The free volume
Scheme 1. Reduced symmetry ligand derived from the “ligand trunca-
tion” strategy.
Results and Discussion
Syntheses and structural characterizations: A series of C2-
symmetric ligands with different functional groups have
been designed based on the “ligand truncation” strategy and
synthesized by means of a Suzuki reaction. [1,1’:3’,1’’-ter-
phenyl]-3,3’’,5,5’’-tetracarboxylic acid (H4TPTA) was ob-
tained through the reaction between 1,3-dibromobenzene
and diethyl 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
ACHTUNGTRENNUNGisoACHTUNGTRENNUNGphthalate followed by hydrolysis (for details on ligand
synthesis, see the Experimental Section). 5,5’-(Pyridine-3,5-
diyl)diisophthalic acid (H4PDDA), 5’-(trifluoromethyl)-[1,1’:
3’,1’’-terphenyl]-3,3’’,5,5’’-tetracarboxylic acid (H4FTPTA),
and 5’-methyl-[1,1’:3’,1’’-terphenyl]-3,3’’,5,5’’-tetracarboxylic
acid (H4MTPTA) were synthesized through the same
method by simply changing the starting materials in the
Suzuki reaction.
H4PDDA contains two isophthalate groups and one pyrid-
yl group. Solvothermal reaction between H4PDDA and Cu-
ACHTUNGTRENNUNG(NO3)2·2.5H2O in dimethylacetamide (DMA) solvent with
Figure 1. a) Structure of PCN-305 viewed along the c axis with the pyrid-
yl groups pointing towards the pores. b) Topology of PCN-305.
in fully desolvated PCN-305 is 69.8% as calculated by
PLATON.[19] From the viewpoint of topology, the dicop-
AHCTUNGTREGpNNNU er(II) paddlewheel secondary building units (SBUs) and
PDDA ligands both serve as four-connected (4-c) nodes. As
a result, PCN-305 adopts the very rare 4- 4-nodal net (Fig-
2ACHTUNGTRENNUNG
ure 1b) with a topological point symbol of {4.64.8} {42.64}-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
with H4TPTA, H4MTPTA, and H4FTPTA, respectively, in
N,N-dimethylformamide (DMF) solvent in the presence of
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Isostructural Metal–Organic Frameworks
FULL PAPER
which is typical for dicopper(II) paddlewheel frameworks.[20]
The N2 sorption for these isostructural MOFs at 77 K exhib-
its reversible type I isotherms, thus indicating their micropo-
rous nature. The calculated Brunauer–Emmett–Teller
(BET) and Langmuir surface areas as well as pore volumes
are listed in Table 1. Among them, PCN-306 with no func-
Table 1. Surface areas and pore volume of the isostructural MOFs.
MOF
SBET [m2 gÀ1
]
SLangmuir [m2 gÀ1
]
Vpore [cm3 gÀ1
]
À
PCN-306 ( H)
1927
1720
1418
1376
2929
2599
2234
2235
1.043
0.926
0.810
0.808
À
PCN-305 ( N)
À
PCN-308 ( CF3)
À
PCN-307 ( CH3)
tional groups has the highest surface area (BET:
1927 m2 gÀ1 Langmuir: 2929 m2 gÀ1) and pore volume
(1.043 cm3 gÀ1). The surface area of PCN-305 is smaller than
;
Figure 2. PXRD of isostructural MOFs PCN-305, -306, -307, and -308.
À
À
that of PCN-306. When adding CH3 or CF3 functional
groups into the ligands, the surface areas and pore volumes
of the MOFs understandably further decreased.
HBF4. Powder X-ray diffractions (PXRD) shown in Figure 2
confirm they are isostructural. Thermal gravimetric analyses
showed these four MOFs have similar thermal stability and
decompose at around 3008C (Figure S1 in the Supporting
Information).
CO2/CH4/N2 gas adsorption: The CO2, CH4, and N2 adsorp-
tions at 273 K were measured for isostructural MOFs PCN-
305, -306, -307, and -308 as shown in Figure 4. They exhibit-
ed impressive CO2-adsorption capacity, particularly for
N2 adsorption: The permanent porosity of the isostructural
MOFs was confirmed by N2 adsorption measurements at
77 K (Figure 3). PCN-305, -306, -307, and -308 were activat-
ed through the same procedure in which they were degassed
under dynamic vacuum at 508C for 8 h after solvent ex-
Figure 4. Sorption isotherms for CO2, CH4, and N2 at 273 K of the iso-
structural MOFs.
PCN-308 with polar functional groups, among the highest
reported so far. The CO2 capacities for the isostructural
MOFs at 273 and 297 K are listed in Table 2. Table 3 lists all
the MOFs that have higher CO2 adsorption capacities than
PCN-308. From this we can see that PCN-308 has the same
CO2 capacity as the N,N’-dimethylethylenediamine (mmen)-
incorporated MOF, mmen–CuBTTri (BTTri=1,3,5-tris(1H-
1,2,3-triazol-4-yl)benzene),[7f] although mmen–CuBTTri has
a much higher heat of adsorption (96 kJmolÀ1). This can be
attributed to the higher surface area of PCN-308 (BET sur-
Figure 3. N2-sorption isotherms of PCN-305, -306, -307, and -308 at 77 K.
change with methanol and then dichloromethane for two
days each. Crystallinity of the MOFs is retained after the re-
moval of solvent guest molecules, as indicated by the
powder X-ray diffraction patterns (Figures S2–S5 in the Sup-
porting Information).
A color change from green to deep purple-blue was ob-
served, thus indicating the generation of open copper sites,
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5639

H.-C. Zhou et al.
Table 2. CO2-uptake capacity at 1 bar, heat of adsorption (Qst), and gas selectivities at 273 K for the isostruc-
tural MOFs.
ference in the heat of adsorp-
tion for the isostructural MOFs.
It demonstrates that different
functional groups in this struc-
ture do not affect the CO2 af-
finity of the framework signifi-
cantly.
CO2 uptake [wt%] at
Qst
Selectivity
CO2/N2 0.15:0.85 v/v
273 K
297 K
N
]
CO2/CH4 1:1 v/v
À
PCN-305 ( N)
23.2
22.9
23.2
24.8
14.5
13.8
14.4
15.4
23.847
23.997
22.836
22.215
52
40
50
37
7.2
7.5
8.8
7.8
À
PCN-306 ( H)
À
PCN-307 ( CH3)
À
PCN-308 ( CF3)
The selectivities of CO2/N2
and CO2/CH4 were calculated
from the experimental single-component isotherms by using
the ideal adsorbed solution theory (IAST) method[34] (for
details, see the Supporting Information). The CO2/N2 selec-
tivity calculation was based on a CO2/N2 mixture with CO2
concentration of 15% (partial pressure of 0.15 atm) at a
total pressure of 1 atm, whereas the CO2/CH4 selectivity cal-
culation was based on a CO2/CH4 mixture with CO2 concen-
tration of 50% (partial pressure of 0.50 atm) at a total pres-
sure of 1 atm (Figure 5). The selectivities suggested by IAST
Table 3. CO2-uptake capacities for MOFs at 1 bar.[a]
MOF
Capacity [wt%][b]
T [K]
Ref.
[22]
[23]
[24]
[25]
[26]
[7d]
[27]
[27]
[9]
SNU-5
Cu2ACHTUNGTRENNUNG(EBTC)ACHTUNGTRENNUNG(H2O)2·xG
Mg–MOF-74
HKUST-1 (4 wt% H2O)
Cu(Me-4py-trz-ia)
Cu–TDPAT
Co–MOF-74
Ni–MOF-74
38.5
25.9
35.2
27
273
273
296
298
298
298
298
298
298
298
296
293
298
295
298
298
298
298
26.8
25.8
24.9
23.9
23.1
22.01
19.8
19.8
19.8
18.3
17.6
17.4
15.9
15.4
Cu
ACHTUNGTRENNUNG(bpy-1)2ACHTUNGTRENNUNG(SiF6)
[28]
[27]
[29]
[30]
[31]
[32]
[25]
[33]
[7f]
ACHTUNGTRENNUNG{[CuL]uLLERLI2O}n
Zn–MOF-74
HKUST-1
MMPF-2
PCN-124
PCN-26-ac
HKUST-1 (8 wt% H2O)
PCN-6
mmen–Cu–BTTri
[a] EBTC=1,1’-ethynebenzene-3,3’,5,5’-tetracarboxylate; G=guest mole-
cule. [b] Capacities listed are the highest reported CO2 capacities for
each MOF.
face area: 1418 m2 gÀ1) than mmen–CuBTTri (BET surface
area: 870 m2 gÀ1). The combined high surface area, open di-
copper paddlewheel metal sites, and polar functional groups
make PCN-308 a good sorbent candidate for CO2 capture
and storage.
From the adsorption isotherms, the isostructural MOFs do
not show a large difference in CO2-adsorption capacity at
À
1 bar. PCN-308 with polar CF3 functional groups has
slightly higher CO2 uptake than the other three MOFs, even
though it has reduced surface area. This demonstrated that
polar groups could enhance CO2 adsorption.[8] The insignifi-
cant increase might be attributable to the decreased surface
area of the framework by the addition of the functional
groups. The combined effect of surface area and polar
groups resulted in the slight increase in the CO2 adsorption.
However, adding methyl or pyridyl functional groups into
the MOF does not change the adsorption amount. In sum-
mary, functional groups present in this structure do not have
noticeable effect on the CO2-adsorption capacity.
To better understand the adsorption properties of differ-
ent functionalized MOFs, the isosteric heats of adsorption
(Qst) were calculated from the CO2-adsorption isotherms at
three different temperatures (273, 283, and 297 K) by using
the Clausius–Clapeyron equation[21] Qst =ÀRd
ACHUTGTNREN(NUG lnP)/dACHTUNGTNER(NUGN 1/T)
Figure 5. IAST selectivities of a) CO2 over N2 for 15% CO2, 85% N2
binary mixtures and b) CO2 over CH4 for equimolar binary mixtures in
PCN-305, -306, -307, and -308.
(R=gas constant, P=pressure, T=temperature; for details,
see the Supporting Information). There is no significant dif-
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Isostructural Metal–Organic Frameworks
FULL PAPER
only six reported MOFs that have higher hydrogen uptake
than PCN-308 at 1 bar and 77 K as listed in Table 4. As
shown, although PCN-308 has a lower surface area than
PCN-14,[35] the hydrogen uptake does not drop significantly,
which might be attributed to the high density of unsaturated
open metal sites after activation. PCN-12, which was report-
ed by the same group, has the second-highest hydrogen
uptake so far. It was also constructed from ligands with two
isophthlate moieties (methylenediisophthalate (mdip)). But
unlike the 1D channel structure in the isostructural MOFs
reported in this work, the isophthalate moieties in the mdip
ligand formed cuboctahedral cages. This was because in the
mdip ligand, the two isophthalate groups are linked by a
bent bridge (methylene) instead of the rigid benzene ring in
this work. Their structural difference results in the differ-
ence in gas-sorption properties.
The isosteric heats of adsorption were calculated on the
basis of the H2-adsorption isotherms at 77 and 87 K for each
compound (Figure 6b). The functional groups did not show
significant influence in either the H2 uptake or the heat of
adsorption. It demonstrated that for these isostructural
MOFs the capacity of hydrogen is basically related to the
structures. Different functional groups have little effect on
the H2 uptake.
Conclusion
A series of robust, porous, isostructural MOFs with different
functional groups have been synthesized from diisophthalate
ligands on the basis of a ligand-truncation strategy. The
frameworks adopt a unique 4-c 4-nodal net topology with
the Schlafli symbol of {4.64.8} {42.64}{64.82}2{66}. The isostruc-
2ACHTNUTRGENNUG HCATUNGTRENNGUN
Figure 6. a) H2 uptake and b) isosteric heats of H2 adsorption (Qst) for
the isostructural MOFs.
Table 4. H2 uptake and heat of adsorption for selected MOFs and PCN-305, -306, -307, and -308.
are listed in Table 2. The iso-
structural MOFs showed no-
ticeable selectivity of CO2 over
CH4 and N2 at 273 K. PCN-305
with pyridyl functional groups
has the highest selectivity of
CO2 over N2, whereas PCN-307
with methyl groups has the
highest selectivity of CO2 over
CH4. There is no apparent rela-
tionship between the selectivi-
ties and different functional
SBET [m2 gÀ1
]
SLangmuir [m2 gÀ1
]
H2 uptake [wt%]
Qst [kJmolÀ1
]
Ref.
[26]
PCN-12
UTSA-20
SNU-5
1943
1156
2425
3.05
2.9
2.84
2.8
[27]
[28]
2850
2745
[29]
Cu
4A
2506
[25]
PCN-14
1753
2.7
8.6
PCN-308
PCN-307
PCN-306
PCN-305
1418.66
1376.68
1927.44
1650.75
2234.21
2235.89
2929.19
2550.25
2.67
2.62
2.50
2.20
6.48
6.24
6.37
6.47
this work
this work
this work
this work
groups in these isostructural MOFs.
tural MOFs showed not only high CO2-adsorption capacities
but also noticeable selectivities of CO2 over CH4 and N2.
Moreover, they exhibited high H2 uptake, particularly for
H2 uptake: Low-pressure H2-sorption isotherms at 77 K
were collected for the isostructural MOFs to evaluate their
H2-adsorption performances. They exhibited high H2-ad-
sorption capacity at low pressure (1 bar; Figure 6a). Among
À
PCN-308 with CF3 functional group (2.67 wt% at 77 K/
1 bar). For the series of isostructural MOFs, the capacities
of CO2 and H2 are basically related to the textural proper-
ties rather than the functional groups of the MOFs.
À
them, PCN-308 with CF3 functional groups exhibits a hy-
drogen uptake of 2.67 wt% at 1 bar and 77 K, which is
among the highest for MOFs at low pressure. There are
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5641

H.-C. Zhou et al.
1606 (w), 1408 (m), 1356 (m), 1321 (m), 1269 (s), 1219 (w), 1188 (w),
1112 (s), 1093 (w), 914 (w), 887 (m), 758 (m), 694 (m), 665 cmÀ1 (w).
Experimental Section
Synthesis of 5’-methyl-[1,1’:3’,1’’-terphenyl]-3,3’’,5,5’’-tetracarboxylic acid
(H4MTPTA): This was synthesized by following a similar procedure to
the synthesis of ligand H4PDDA. Except for changing the starting materi-
als of 1,3-dibromobenzene to 1,3-dibromo-5-methylbenzene, the molar
ratio of the reactants remained the same. Tetraethyl 5’-methyl-[1,1’:3’,1’’-
terphenyl]-3,3’’,5,5’’-tetracarboxylate: 1H NMR (300 MHz, CD3Cl): d=
1.41 (t, 12H), 2.50 (s, 3H), 4.42 (q, 8H), 7.47 (s, 2H), 7.64 (s, 1H), 8.44
Materials and methods: All the general reagents were commercially
available and used as received. CuACTHUNTRGNE(UNG NO3)2·2.5H2O was purchased from
VWR; 1,3-dibromobenzene from Alfa Aesar; 3,5-dibromotoluene from
TCI America; 3,5-dibromopyridine from Frontier Scientific; and 3,5-di-
bromobenzotrifluoride from AOBChem. Dimethyl 5-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)isophthalate and diethyl 5-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)isophthalate[36] were synthesized according to re-
ported procedures. 1H NMR spectroscopic data was collected using a
Mercury 300 spectrometer. Elemental microanalyses (EA) were per-
formed by Atlantic Microlab, Inc. FTIR data were recorded using an
IRAffinity-1 instrument. TGA data were obtained using a TGA-50 (Shi-
madzu) thermogravimetric analyzer with a heating rate of 28CminÀ1
under an N2 atmosphere. The PXRD patterns were recorded using a
Bruker D8-Focus Bragg–Brentano X-ray powder diffractometer equip-
ped with a Cu sealed tube (l=1.54178 ꢁ) at room temperature. Simula-
tion of the PXRD spectrum was carried out by the single-crystal data
and the diffraction-crystal module of the Mercury program available free
of charge on the Internet.
1
(d, 4H), 8.71 ppm (t, 2H). H4MTPTA: H NMR (300 MHz, [D6]DMSO):
d=2.30 (s, 3H), 7.64 (d, 2H), 7.84 (s, 1H), 8.46 (q, 6H); FTIR (KBr):
n˜ =2989 (w), 2650 (w), 2579 (w), 1728 (s), 1595 (w), 1450 (m), 1359 (m),
1288 (m), 1213 (s), 1143 (w), 1085 (w), 920 (w), 862 (w), 760 (s), 705 (m),
673 cmÀ1 (m).
Synthesis of PCN-305:
0.20 mmol), Cu(NO3)2·2.5H2O (160 mg, 0.85 mmol), and tetrafluoroboric
acid (HBF4; 0.2 mL, 48% w/w aqueous solution) in N,N-dimethylacet-
amide (DMA; 17 mL) was sealed in a 20 mL glass vial and placed in an
A solution of ligand H4PDDA (80 mg,
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
oven at 758C. Blue block crystals that were suitable for X-ray analysis
formed within 72 h. FTIR (KBr): n˜ =3446 (w), 2934 (w), 1664 (s), 1507
(w), 1395 (s), 1250 (w), 1103 (m), 1024 (m), 958 (w), 859 (w), 773 (m),
729 (s), 662 cmÀ1 (m).
Synthesis
of
[1,1’:3’,1’’-terphenyl]-3,3’’,5,5’’-tetracarboxylic
acid
(H4TPTA): 1,3-Dibromobenzene (1.00 g, 4.24 mmol), dimethyl 5-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)isophthalate (3.00 g, 9.33 mmol), CsF
(4.00 g), and [PdACHTUNGTRENNUNG(PPh3)4] (200 mg) were added to a 250 mL Schlenk flask.
Synthesis of PCN-306: A solution of ligand H4TPTA (80 mg, 0.20 mmol),
CuACHTUNTRGNEUNG(NO3)2·2.5H2O (160 mg, 0.85 mmol), and tetrafluoroboric acid (HBF4;
0.1 mL, 48% w/w aqueous solution) in DMF (17 mL) was sealed in a
20 mL glass vial and placed in an oven at 608C. Blue crystalline powder
was obtained within 72 h. FTIR (KBr): n˜ =3305 (w), 2603 (w), 1861 (w),
1718 (m), 1610 (m), 1550 (s), 1423 (m), 1366 (s), 1225 (m), 1151 (w), 1128
(w), 1072 (w), 922 (w), 896 (w), 773 (s), 719 (m), 702 cmÀ1 (w).
The flask was connected to Schlenk line, the air was evacuated, and then
refilled with nitrogen. 1,2-Dimethoxyethane (DME; 150 mL) was de-
gassed (2 h) and added to the flask through a cannula. The flask was
equipped with a water condenser and heated to reflux under nitrogen for
3 days. The solvent was removed on a rotary evaporator. H2O (100 mL)
was added and extracted with CH2Cl2. The organic phase was dried with
MgSO4. After the removal of CH2Cl2 solvent, the crude product was
washed with acetone to give pale yellow solid product tetraethyl
Synthesis of PCN-307: Carried out by following the same procedure as
that for PCN-306. A solution of ligand H4MTPTA (80 mg, 0.19 mmol),
CuACHTUNTRGNEUNG(NO3)2·2.5H2O (160 mg, 0.85 mmol), and tetrafluoroboric acid (HBF4;
0.1 mL, 48% w/w aqueous solution) in DMF (17 mL) was sealed in a
20 mL glass vial and placed in an oven at 608C. Blue crystalline powder
was obtained within 72 h. FTIR (KBr): n˜ =3063 (w), 2380 (w), 1715 (m),
1628 (m), 1562 (s), 1418 (s), 1375 (s), 1280 (m), 1219 (m), 1128 (w), 1082
(w), 885 (w), 775 (m), 732 (m), 683 (w), 669 cmÀ1 (w).
[1,1’:3’,1’’-terphenyl]-3,3’’,5,5’’-tetracarboxylate with
a yield of 70%
(1.54 g) based on 1,3-dibromobenzene. 1H NMR (300 MHz, CD3Cl): d=
3.98 (s, 12H), 7.61 (t, 1H), 7.67 (d, 2H), 7.86 (t, 1H), 8.50 (d, 4H),
8.69 ppm (t, 2H).
Tetraethyl [1,1’:3’,1’’-terphenyl]-3,3’’,5,5’’-tetracarboxylate (1.54 g) was dis-
solved in a mixed solvent of THF and MeOH (60 mL, 1:1 v/v), and
NaOH (20 mL, 2n) aqueous solution was added. The mixture was stirred
at room temperature overnight. After the organic phase was removed,
the aqueous phase was acidified with 20% hydrochloric acid to give a
white precipitate, which was filtered and washed with water several
times. Yield: 1.27 g, 94%. 1H NMR (300 MHz, [D6]DMSO): d=7.65 (t,
1H), 7.80 (d, 2H), 8.04 (s, 1H), 8.46 ppm (s, 6H); FTIR (KBr): n˜ =3017
(w), 2633 (w), 1717 (s), 1595 (w), 1454 (m), 1415 (m), 1364 (m), 1288 (s),
1213 (s), 1118 (w), 1078 (w), 923 (m), 796 (w), 756 (s), 691 cmÀ1 (m).
Synthesis of PCN-308: Carried out by following the same procedure as
that for PCN-306. A solution of ligand H4FTPTA (80 mg, 0.17 mmol),
CuACHTUNTRGNEUNG(NO3)2·2.5H2O (160 mg, 0.85 mmol), and tetrafluoroboric acid (HBF4;
0.1 mL, 48% w/w aqueous solution) in DMF (17 mL) was sealed in a
20 mL glass vial and placed in an oven at 608C. Blue crystalline powder
was obtained within 72 h. FTIR (KBr): n˜ =3092 (w), 2374 (w), 1701 (w),
1618 (m), 1560 (s), 1413 (s), 1352 (s), 1276 (m), 1176 (w), 1116 (m), 1082
(w), 891 (m), 763 (m), 723 (m), 650 cmÀ1 (w).
Crystal data for PCN-305 [Cu2ACHTUNGTRENG(NU PDDA)]: C63H24Cu6N3O30; Mr =1684.15;
orthorhombic; a=24.650(7), b=33.494(9), c=18.529(5) ꢁ; V=
15298.04 ꢁ3; T=110(2) K; space group Cmcm; Z=4; Rint =0.1109; R1 =
0.1371; wR2 =0.4164; GoF=0.999.
Synthesis of 5,5’-(pyridine-3,5-diyl)diisophthalic acid (H4PDDA): This
was synthesized by following a similar procedure to the synthesis of
ligand H4PDDA. Except for changing the starting materials of 1,3-dibro-
mobenzene to 3,5-dibromopyridine, the molar ratio of the reactants re-
mained the same. Tetraethyl 5,5’-(pyridine-3,5-diyl)diisophthalate:
1H NMR (300 MHz, CD3Cl): d=1.45 (t, 12H), 4.76 (q, 6H), 8.19 (d,
1H), 8.52 (d, 4H), 8.77 (t, 2H), 8.96 ppm (s, 2H). H4PDDA: 1H NMR
(300 MHz, [D6]DMSO): d=8.55 (t, 2H), 8.61 (q, 4H), 8.79 (s, 1H),
9.12 ppm (s, 2H); FTIR (KBr): n˜ =3016 (w), 1741 (s), 1458(w), 1365 (m),
1219 (s), 1145 (w), 1066 (w), 958 (w), 894 (m), 812 (w), 758 (m), 669 cmÀ1
(w).
CCDC-900615 (PCN-305) contains the supplementary crystallographic
data for 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.
Acknowledgements
Synthesis of 5’-(trifluoromethyl)-[1,1’:3’,1’’-terphenyl]-3,3’’,5,5’’-tetracar-
boxylic acid (H4FTPTA): This was synthesized by following a similar pro-
cedure to the synthesis of ligand H4PDDA. Except for changing the start-
ing materials of 1,3-dibromobenzene to 1,3-dibromo-5-(trifluoromethyl)-
benzene, the molar ratio of the reactants remained the same. Tetraethyl
5’-(trifluoromethyl)-[1,1’:3’,1’’-terphenyl]-3,3’’,5,5’’-tetracarboxylate:
1H NMR (300 MHz, CD3Cl): d=1.42 (t, 12H), 4.44 (q, 8H), 7.88 (s, 2H),
8.01 (s, 1H), 8.45 (d, 4H), 8.71 ppm (t, 2H). H4FTPTA: 1H NMR
(300 MHz, [D6]DMSO): d=8.12 (s, 2H), 8.39 (s, 1H), 8.53 (s, 2H),
8.54 ppm (s, 4H); FTIR (KBr): n˜ =3014 (w), 2652 (w), 2558 (w), 1716 (s),
This work was supported as part of the Center for Gas Separations Rele-
vant to Clean Energy Technologies, an Energy Frontier Research Center
funded by the U.S. Department of Energy (DOE), Office of Science,
Office of Basic Energy Sciences under Award Number DE-SC0001015.
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Received: September 14, 2012
Revised: January 17, 2013
Published online: February 27, 2013
Chem. Eur. J. 2013, 19, 5637 – 5643
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www.chemeurj.org
5643