Exceptional thermal stability in a supramolecular organic framework: Porosity and gas storage

Article abstract of DOI:10.1021/ja1042935

Reaction of β-amino-β-(pyrid-4-yl)acrylonitrile with the aromatic dicarboxaldehydes 9,10-bis(4-formylphenyl)anthracene and terephthalaldehyde affords the dihydropyridyl products 9,10-bis(4-((3,5-dicyano-2,6-dipyridyl) dihydropyridyl)phenyl)anthracene (L¹) and 1,4-bis(4-(3,5-dicyano-2,6- dipyridyl)dihydropyridyl)benzene (L²), respectively. In the solid state [L¹]?2.5DMF?3MeOH (SOF-1) crystallizes in the monoclinic space group P2₁/c and forms a 3D stable supramolecular organic framework via strong N-H...N_py hydrogen bonds and π-π interactions. The material incorporates pyridyl-decorated channels and shows permanent porosity in the solid state. The pore volumes of the desolvated framework SOF-1a calculated from the N₂ isotherm at 125 K and the CO₂ isotherm at 195 K are 0.227 and 0.244 cm³ g ^-1, respectively. The N₂ absorption capacity of SOF-1a at 77 K is very low, with an uptake of 0.63 mmol g^-1 at 1 bar, although saturation N₂ adsorption at 125 K is 6.55 mmol g^-1 (or 143 cm³ g^-1). At ambient temperature, SOF-1a shows significant CO₂ adsorption with approximately 3 mol of CO₂ absorbed per mole of host at 16 bar and 298 K, corresponding to 69 cm ³ g^-1 at STP. SOF-1a also adsorbs significant amounts of C₂H₂, with an uptake of 124 cm³ (STP) g ^-1 (5.52 mmol g^-1) at 1 bar at 195 K. Methane uptake at 195 K and 1 bar is 69 cm³ (STP) g^-1. Overall, gas adsorption measurements on desolvated framework SOF-1a reveal not only high capacity uptakes for C₂H₂ and CO₂, compared to other crystalline molecular organic solids, but also an adsorption selectivity in the order C₂H₂ > CO₂ > CH₄ > N₂. Overall, C₂H₂(270 K)/CH ₄(273 K) selectivity is 33.7 based on Henry's Law constant, while the C₂H₂(270 K)/CO₂(273 K) ratio of uptake at 1 bar is 2.05. The less bulky analogue L² crystallizes in the triclinic space group P1 as two different solvates [L²] ?2DMF?5C₆H₆ (S2A) and [L²] ?2DMF?4MeOH (S2B) as pale yellow tablets and blocks, respectively. Each L² molecule in S2A participates in two N-H...O hydrogen bonds between dihydropyridyl rings and solvent DMF molecules. Packing of these layers generates 1D nanochannels along the crystallographic a and b axes which host DMF and benzene molecules. In S2B, each L² ligand participates in hydrogen bonding via an N-H...O interaction between the N-H of the dihydropyridyl ring and the O of a MeOH and also via an N...H-O interaction between the N center of a pyridine ring and the H-O of a second MeOH molecule. The presence of the L²-HOMe hydrogen bonds prevents ligand-ligand hydrogen bonding. As a result, S2B crystallizes as one-dimensional chains rather than as an extended 3D network. Thermal removal of solvents from S2A results in conversion to denser phase S2C which shows no effective permanent porosity.

Full text of DOI:10.1021/ja1042935

Published on Web 09/24/2010
Exceptional Thermal Stability in a Supramolecular Organic
Framework: Porosity and Gas Storage
Wenbin Yang,† Alex Greenaway,† Xiang Lin,† Ryotaro Matsuda,‡,§
Alexander J. Blake,† Claire Wilson,† William Lewis,† Peter Hubberstey,†
Susumu Kitagawa,‡,§ Neil R. Champness,*,† and Martin Schro¨der*,†
School of Chemistry, UniVersity of Nottingham, UniVersity Park, Nottingham, NG7 2RD, U.K.,
ERATO Kitagawa Integrated Pores Project, Science and Technology Agency (JST), Kyoto Research
Park Building No. 3, Shimogyo-ku, Kyoto 600-8815, Japan, and Institute for Integrated Cell-Material
Science (iCeMS), Kyoto UniVersity, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
Received May 18, 2010; E-mail: Neil.Champness@nottingham.ac.uk; M.Schroder@nottingham.ac.uk
Abstract: Reaction of ꢀ-amino-ꢀ-(pyrid-4-yl)acrylonitrile with the aromatic dicarboxaldehydes 9,10-bis(4-
formylphenyl)anthracene and terephthalaldehyde affords the dihydropyridyl products 9,10-bis(4-((3,5-
dicyano-2,6-dipyridyl)dihydropyridyl)phenyl)anthracene (L1) and 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihy-
dropyridyl)benzene (L2), respectively. In the solid state [L1]·2.5DMF·3MeOH (SOF-1) crystallizes in the
monoclinic space group P21/c and forms a 3D stable supramolecular organic framework via strong
N-H· · ·Npy hydrogen bonds and π-π interactions. The material incorporates pyridyl-decorated channels
and shows permanent porosity in the solid state. The pore volumes of the desolvated framework SOF-1a
calculated from the N2 isotherm at 125 K and the CO2 isotherm at 195 K are 0.227 and 0.244 cm3 g-1
,
respectively. The N2 absorption capacity of SOF-1a at 77 K is very low, with an uptake of 0.63 mmol g-1
at 1 bar, although saturation N2 adsorption at 125 K is 6.55 mmol g-1 (or 143 cm3 g-1). At ambient
temperature, SOF-1a shows significant CO2 adsorption with approximately 3 mol of CO2 absorbed per
mole of host at 16 bar and 298 K, corresponding to 69 cm3 g-1 at STP. SOF-1a also adsorbs significant
amounts of C2H2, with an uptake of 124 cm3 (STP) g-1 (5.52 mmol g-1) at 1 bar at 195 K. Methane uptake
at 195 K and 1 bar is 69 cm3 (STP) g-1. Overall, gas adsorption measurements on desolvated framework
SOF-1a reveal not only high capacity uptakes for C2H2 and CO2, compared to other crystalline molecular
organic solids, but also an adsorption selectivity in the order C2H2 > CO2 > CH4 > N2. Overall, C2H2(270
K)/CH4(273 K) selectivity is 33.7 based on Henry’s Law constant, while the C2H2(270 K)/CO2(273 K) ratio
2
j
of uptake at 1 bar is 2.05. The less bulky analogue L crystallizes in the triclinic space group P1 as two
different solvates [L2]·2DMF·5C6H6 (S2A) and [L2]·2DMF·4MeOH (S2B) as pale yellow tablets and blocks,
respectively. Each L2 molecule in S2A participates in two N-H· · ·O hydrogen bonds between dihydropyridyl
rings and solvent DMF molecules. Packing of these layers generates 1D nanochannels along the
crystallographic a and b axes which host DMF and benzene molecules. In S2B, each L2 ligand participates
in hydrogen bonding via an N-H· · ·O interaction between the N-H of the dihydropyridyl ring and the O of
a MeOH and also via an N · · ·H-O interaction between the N center of a pyridine ring and the H-O of a
second MeOH molecule. The presence of the L2-HOMe hydrogen bonds prevents ligand-ligand hydrogen
bonding. As a result, S2B crystallizes as one-dimensional chains rather than as an extended 3D network.
Thermal removal of solvents from S2A results in conversion to denser phase S2C which shows no effective
permanent porosity.
B, C, N, and O) via strong covalent bonds,1 amorphous porous
organic polymers,11 and supramolecular organic assemblies held
Introduction
Low-density porous organic crystalline materials (sometimes
termed as “organic zeolites”1d,e) have attracted significant
research efforts in recent years1-7 and can be compared to
porous analogues composed of metal-organic components.8 Of
particular interest is the ability of porous organic hosts to provide
accessible internal surface areas for capturing, storing, and
separating gases.9,10 Such systems include crystalline covalent
organic frameworks (COFs) constructed from light elements (H,
together via weak noncovalent interactions such as hydrogen
bonds and π-π stacking interactions.3c However, since the
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† University of Nottingham.
‡ Science and Technology Agency (JST).
§ Kyoto University.
9
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J. AM. CHEM. SOC. 2010, 132, 14457–14469 14457

A R T I C L E S
Yang et al.
Scheme 1. Views of Some of the Ligands Previously Used To Prepare Crystalline Supramolecular Organic Frameworksa
a (a) C[4] ) calix[4]arene; (b) TBC[4] ) p-tert-butylcalix[4]arene; (c) TBC[4]DHQ ) 1,2-dimethoxy-p-tert-butylcalix[4]dihydroquinone; (d) DC[4]DHQ
) dimethoxy-p-H-calix[4]dihydroquinone; (e) C[4]HQ ) calix[4]hydroquinone; (f) AC[n] ) azacalix[n]arene (n ) 4, 6, 7); (g) CBDU ) cyclic bis(4,4′-oxybis(benzyl))diurea;
(h) TPP ) tris(o-phenylenedioxy)cyclotriphosphazene; (i) CB[6] ) cucurbit[6]uril; (j) TMSBP ) 3,3′,4,4′-tetrakis(trimethylsilylethynyl)biphenyl.
removal of included species typically favors conversion to a
denser phase to maximize attractive inter- and intramolecular
interactions, most supramolecular organic frameworks (SOFs)
are not sufficiently robust to retain microporosity upon guest
removal.2 Thus, relatively few types of SOF materials show
permanent porosity with reversible gas sorption properties;2b,3-7,10
examples of organic assemblies include anthracenebisresorcinol
derivatives,1d,e calix[n]arenes (n ) 4, 5, 6, 7),6 dipeptides,3
tris(o-phenylenedioxy)cyclotriphosphazene,2b,12 cucurbit[6]uril
(CB[6]),10b 3,3′,4,4′-tetra(trimethylsilylethynyl)biphenyl,10c and
bis-urea macrocycles (Scheme 1).10d A common feature of these
stable supramolecular organic frameworks is that they incor-
porate bulky building blocks with favorable molecular configu-
rations such as hemisphere-shaped,6c cone-shaped,6j and
cup-shaped,6e,i,m or hollowed pseudospherical shapes10b associ-
ated with suitable cooperative functional groups. Thus, a
favorable molecular configuration promotes the formation of
cavities or lattice voids, while cooperative functional groups
play key roles in stabilizing molecular configurations via
intramolecular1d,6j,n and intermolecular hydrogen bonds,3,6n,10b
π-π stacking interactions,7a and van der Waals forces.6j,n
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We report herein the synthesis and assembly of the bulky
dihydropyridyl tecton 9,10-bis(4-((3,5-dicyano-2,6-dipyridyl)dihy-
9
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Thermal Stability in a SOF
A R T I C L E S
Scheme 2. View of Structures of L1 and L2
on a Nicolet Avatar 360 FT-IR system over the 4000-400 cm-1
range. Thermal gravimetric analysis was performed on a Rheometric
Scientific STA 1500H thermal analyzer at a heating rate of 1 °C/
min-1. X-ray powder diffraction data were collected on a Philips
X’pert powder diffractometer with Cu KR radiation from samples
mounted on a flat glass plate sample holder. Scans of approximately
90 min were run for each sample over the range 5° e 2θ e 60°
with a step size of 0.02° in 2θ. Simulated powder patterns were
generated from the final single crystal refinement model using
MERCURY, version 1.4.2.13
dropyridyl)phenyl)anthracene (L1) to give a stable porous 3D
network. This system combines bulky polyaromatic groups
(Scheme 2), lateral nitrile, and pyridyl functional groups
cojoined by dihydropyridyl moieties to afford spatially orientated
hydrogen bond donor and acceptor groups. Assembly of L1 in
the solid state via hydrogen bonds and π-π stacking interactions
generates a porous organic framework [L1]·2.5DMF·3MeOH
(SOF-1), showing particularly impressive thermal stability.
Although MOFs can show high thermal stability and associated
permanent porosity, they incorporate metals leading to an
increase in the molecular weight and potential toxicity of the
material. COFs and related organic materials have the advantage
of light constituents but are often thermally sensitive. SOF-1
incorporates both low molecular weight and thermal stability
with permanent porosity and high gas uptake capacities and
selectivity.
Synthesis of Ligand L1. 4-Cyanopyridine, 4-formylphenylbo-
ronic acid, potassium tert-butoxide, 9,10-dibromoanthracene, potas-
sium carbonate, Pd(PPh3)4, anhydrous CH3CN, and ZnI2 were
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2009, 15, 4523. (f) Yang, W.; Lin, X.; Jia, J.; Blake, A. J.; Wilson,
C.; Hubberstey, P.; Champness, N. R.; Schro¨der, M. Chem. Commun.
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A. J.; Dailly, A.; Brown, C. M.; Simmons, J. M.; Zoppi, M.; Walker,
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Dailly, A.; Blake, A. J.; Champness, N. R.; Hubberstey, P.; Schro¨der,
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Champness, N. R.; Schro¨der, M. Nat. Chem. 2009, 1, 487. (m) Yan,
Y.; Telepeni, I.; Yang, S.; Lin, X.; Kockelmann, W.; Dailly, A.; Blake,
A. J.; Lewis, W.; Walker, G. S.; Allan, D. R.; Barnett, S. A.;
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Experimental Section
Elemental analyses of C, H, and N were performed by the
Elemental Analytical Service of the School of Chemistry, University
of Nottingham, U.K. Infrared spectra were measured as KBr disks
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2002, 298, 1000. (b) Ishii, Y.; Takenaka, Y.; Konishi, K. Angew.
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Yang et al.
purchased from the Aldrich Chemical Co. and used as received
without further purification. 9,10-Bis(4-((3,5-dicyano-2,6-dipy-
ridyl)dihydropyridyl)phenyl)anthracene (L1) was synthesized from
ꢀ-amino-ꢀ-(pyrid-4-yl)acrylonitrile and 9,10-bis(4-formylphenyl)-
anthracene in acetic acid, with these two precursors being prepared
according to previously described methods.14
ꢀ-Amino-ꢀ-(pyrid-4-yl)acrylonitrile (290.5 mg, 2.0 mmol) and
9,10-bis(4-formylphenyl)anthracene (193.3 mg, 0.5 mmol) were
mixed in acetic acid, deaerated using N2 for 10 min, and then heated
at 125 °C to give a clear orange-red solution. After 30 min a yellow
solid began to precipitate. The reaction mixture was refluxed for
48 h yielding a large amount of yellow solid, which was collected
by filtration, washed with hot acetic acid, and dissolved in aqueous
HCl solution (1 M, 100 mL) under heating and stirring. Basification
with KOH solution to pH ≈ 8 afforded the deep yellow solid L1
(yield: 348 mg, 78%).
6 months: 10.45 (s, 2H, NH), 8.81 (d, J ) 6.0 Hz, 8H, PyH), 7.96
(s, 2.5H, OdCH-DMF), 7.83 (d, 4H, J ) 8.1 Hz ArH), 7.77 (d, J
) 6.0 Hz, 8H, PyH), 7.65-7.61 (m, 8H, ArH), 7.50-7.46 (m, 4H,
ArH), 5.09 (s, 2H, CH), 2.89 (s, 7.5H, CH3-DMF), 2.73 (s, 7.5H,
CH3-DMF), corresponding to a composition of [L1]·2.5DMF. IR
(KBr, νmax, cm-1): 3422 (br), 3195 (s), 3079 (s), 2930 (m), 2837
(m), 2205 (s), 1660 (s), 1600 (s), 1548 (m), 1505 (s), 1438 (w),
1412 (s), 1385 (s), 1344 (m), 1291 (s), 1099 (w), 943 (w), 828 (s),
774 (m), 694 (m).
Synthesis of 1,4-Bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)-
benzene (L2 or S2C) and [L2]·2DMF ·5C6H6 (S2A). A solution of
ꢀ-amino-ꢀ-(pyrid-4-yl)acrylonitrile (0.58 g, 4 mmol) in glacial
acetic acid (15 mL) was treated with terephthalaldehyde (0.13 g, 1
mmol), and the reaction mixture was refluxed for 24 h. After the
mixture was cooled to room temperature, a slightly yellow solid
was isolated by filtration, washed sequentially with hot acetic acid,
water, and ethanol, and dried in air (0.25 g, 38.8%). Crystals of
[L2] · 2DMF · 5C6H6 (S2A) and [L2] · 2DMF · 4MeOH (S2B) were
grown from a mixture of DMF-benzene-MeOH by the same
layering method that was used for SOF-1. Elemental analysis for
L2 (or S2C), C40H24N10 (calcd/found): C, 74.52/74.49; H, 3.75/3.71;
N, 21.73/21.86. 1H NMR (DMSO-d6, δ, ppm): 10.41 (s, 2H, 1-H-
dihydropyridyl), 8.77 (d, J ) 5.6 Hz, 8H, 2,6-H-pyridyl), 7.65-7.71
ꢀ-Amino-ꢀ-(pyrid-4-yl)acrylonitrile, C8H7N3. Elemental analy-
sis (found/calcd): C, 66.15/66.19; H, 4.83/4.86; N, 28.94/28.95. IR
(KBr, νmax, cm-1): 3335, 2193. 1H NMR (DMSO-d6, δ, ppm): 8.63
(d, J ) 6.3 Hz, 2H), 7.57 (d, J ) 6.0 Hz, 2H), 7.02 (d, 2H), 4.40
(s, 1H).
9,10-Bis(4-formylphenyl)anthracene, C28H18O2. Elemental analy-
1
sis (found/calcd): C, 87.04/87.02, H, 4.68/4.69. H NMR (CDCl3,
δ, ppm): 10.24 (s, 2H, CHO), 8.18 (d, 4H, J ) 8.2 Hz, ArH), 7.71
(d, 4H, J ) 8.1 Hz, ArH), 7.65-7.61 (m, 4H, ArH), 7.42-7.39
(m, 4H, ArH). IR (KBr, νmax, cm-1): 1710 (CHO).
(m, 12H, H-Ar), 4.91 (s, 2H, 4-H-dihydropyridyl). IR (KBr, νmax
,
cm-1): 3314 (s, br), 2980 (m), 2207 (s), 1643 (s), 1599 (s), 1500
(m), 1412 (m), 1338 (m), 1290 (m), 1220 (m), 1152 (m), 1070
(m), 997 (m), 833 (m), 798 (m), 690 (m), 583 (m). Because of loss
of benzene solvent at room temperature, the elemental analysis
results of S2A were found to be variable. 1H NMR (DMSO-d6, δ,
ppm): 10.41 (s, 2H, 1-H-dihydropyridyl), 8.77 (d, 8H, J ) 6.0 Hz,
2,6-H-pyridyl), 7.95 (s, 2H, OdCH-DMF), 7.65-7.71 (m, 12H,
H-Ar), 7.36 (s, 24 H, H-benzene), 4.91 (s, 2H, 4-H-dihy-
dropyridyl), corresponding to the composition of [L2] · 2DMF ·
4C6H6. IR (KBr, νmax, cm-1): 3319 (br), 3189 (m), 3084 (m), 2982
(m), 2204 (s), 1654 (s), 1597 (s), 1546 (m), 1508 (m), 1411 (s),
1387 (m), 1342 (m), 1291 (w), 1252 (m), 1151 (w), 1100 (m), 1065
(m), 998 (m), 830 (s), 734 (m), 653 (m), 582 (m), 516 (m).
X-ray Crystallographic Studies. Diffraction data from single
crystals of SOF-1, S2A, S2B, and S2C were collected at 150(2) K
on Bruker SMART CCD area detector diffractometers equipped
with Oxford Cryosystems open-flow cryostats using graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å). The structures
were solved by direct methods, developed by subsequent difference
Fourier syntheses, and refined using the SHELXTL software
package.15a In SOF-1, one pyridine group of the ligand was
disordered and this disorder was modeled as major and minor
components of occupancy 0.7 and 0.3, respectively. Distance
similarity restraints were applied to the pyridine ring components.
In addition, C2′ had a rather high U value, almost twice that of the
other atoms in the same ring. Therefore, the U value of C2′ was
fixed as 0.05 Å2, which is close to that of the other atoms in the
same ring. A SADI restraint15a was applied to the disordered
pyridine ring. All ordered non-H atoms were refined with aniso-
tropic displacement parameters. All H atoms were placed in
calculated positions and refined using the riding model. For SOF-
1, PLATON/SQUEEZE15b,c was employed to calculate the dif-
fraction contribution of the solvent molecules and thereby produce
a set of solvent-free diffraction intensities. The final formula was
calculated from the SQUEEZE results combined with elemental
and TGA analytical data. Crystal and refinement data and for SOF-
1, S2A, S2B, and S2C are listed in Table 1, and selected bond
lengths and angles are given in Table 2. Further details of structure
refinements are given in Supporting Information.
9,10-Bis(4-((3,5-dicyano-2,6-dipyridyl)dihydropyridyl)phenyl)-
anthracene (L1), C60H36N10. Elemental analysis (found/calcd): C,
1
80.34/80.32; H, 4.05/4.03; N, 15.61/15.66. H NMR (DMSO-d6,
δ, ppm): 10.44 (s, 2H, NH), 8.80 (d, J ) 6.0 Hz, 8H, PyH), 7.83
(d, 4H, J ) 8.1 Hz ArH), 7.77 (d, J ) 6.1 Hz, 8H, PyH), 7.64-7.61
(m, 8H, ArH), 7.50-7.46 (m, 4H, ArH), and 5.08 (s, 2H, CH). IR
(KBr, νmax, cm-1): 3417 (br), 3062 (m), 2205 (vs), 1601 (s), 1549
(m), 1510 (s), 1440 (w), 1412 (s), 1385 (m), 1290 (s), 1109 (w),
1070 (w), 828 (s), 794 (m), 611 (m) cm-1
.
Crystal Growth of (L1)·2.5DMF ·3MeOH (SOF-1). A hot
DMF solution (5 mL) of L1 (46.5 mg, 0.052 mmol) in a glass vial
was covered with a layer of benzene (5 mL) and a further layer of
MeOH (4 mL). Slow diffusion of MeOH through the benzene buffer
into the DMF solution afforded a solvent mixture from which, 2
days later, yellow crystalline samples of SOF-1 were harvested by
filtration. The product was washed with benzene/MeOH and then
dried in air (yield: 55.6 mg, 91%). Elemental analysis for
C
70.5H65.5N12.5O5.50 (calcd/found): C, 72.01/74.25; H, 5.61/5.01; N,
14.89/15.13. The volatility of the cocrystallized solvent in the
sample contributes to the discrepancy in the elemental analysis.
1H NMR (DMSO-d6, δ, ppm) for SOF-1 exposed to open air for
(11) (a) McKeown, N. B.; Budd, P. M. Chem. Soc. ReV. 2006, 35, 675. (b)
Mastalerz, M. Angew. Chem., Int. Ed. 2008, 47, 445. (c) Wood, C. D.;
Tan, B.; Trewin, A.; Su, F.; Rosseinsky, M.; Bradshaw, D.; Sun, Y.;
Zhou, L.; Cooper, A. I. AdV. Mater. 2008, 20, 1916. (d) Campbell,
N. L.; Clowes, R.; Ritchie, L. K.; Cooper, A. I. Chem. Mater. 2009,
21, 204. (e) Tozawa, T.; Jones, J. T. A.; Swamy, S. I.; Jiang, S.;
Adams, D. J.; Shakespeare, S.; Clowes, R.; Bradshaw, D.; Hasell, T.;
Chong, S. Y.; Tang, C.; Thompson, S.; Parker, J.; Trewin, A.; Bacsa,
J.; Slawin, A. M. Z.; Steiner, A.; Cooper, A. I. Nat. Mater. 2009, 8,
973.
(12) (a) Sozzani, P.; Comotti, A.; Simonutti, R.; Meersmann, T.; Logan,
J. W.; Pines, A. Angew. Chem., Int. Ed. 2000, 39, 2695. (b) Couderc,
G.; Hertzsch, T.; Behrnd, N. R.; Kramer, K.; Hulliger, J. Microporous
Mesoporous Mater. 2006, 88, 170. (c) Hertzsch, T.; Gervais, C.;
Hulliger, J.; Jaeckel, B.; Guentay, S.; Bruchertseifer, H.; Neels, A.
AdV. Funct. Mater. 2006, 16, 268.
(13) Nolze, G.; Kraus, W. Powder Diffr. 1998, 13, 256. (b) http://
www.ccdc.cam.ac.uk/ products/mercury.
Measurements of Gas Isotherms. N2, CO2, and CH4 isotherms
were recorded using an IGA gravimetric adsorption apparatus at
the University of Nottingham, U.K. The host sample was thermally
activated by heating at 130 °C under ultrahigh vacuum (10-8 mbar)
overnight. All isotherm data points were fitted by the IGASwin
system software, version 1.03.143 (Hiden Isochema, 2004) using
(14) (a) Teki, Y.; Miyamoto, S.; Nakatsuji, M.; Miura, Y. J. Am. Chem.
Soc. 2001, 123, 294. (b) Yamagushi, Y.; Katsuyama, I.; Funabiki, K.;
Matsui, M.; Shibata, K. J. Heterocycl. Chem. 1998, 35, 805.
(15) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112. (b) Spek,
A. L. PLATON, Acta Crystallogr., Sect. D 2009, 65, 148. (c) Sluis, P.
v. d.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, 194.
9
14460 J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010

Thermal Stability in a SOF
A R T I C L E S
Table 1. Crystal Data and Structure Refinement for SOF-1, S2A, S2B, and S2C
compound
parameter
[L1]·2.5DMF·3MeOH (SOF-1)
[L2]·2DMF·5C6H6 (S2A)
[L2]·2DMF·5C6H6 (S2A)
[[L2]·2DMF·4MeOH (S2B)
L2 (S2C)
chemical formula
FW
C70.5H65.5N12.5O5.50
1175.85
0.31 × 0.21 × 0.12
P21/c
14.319(2)
6.8536(8)
32.694(4)
90
93.782(2)
90
3201.5(7)
1.220
C76H68N12O2
1181.42
C76H68N12O2
1181.42
C50H54N12O6
919.05
C40H24N10
644.699
0.21 × 0.17 × 0.07
P21/n
10.617(3)
13.214(4)
11.835(3)
90
91.952(6)
90
1659.4(14)
1.290
crystal size (mm3)
space group
a (Å)
0.37 × 0.34 x0.10
0.49 × 0.18 x0.16
0.22 × 0.22 x0.20
j
j
j
P1
P1
P1
8.3803(9)
12.1013(12)
16.1017(16)
87.352(2)
88.209(2)
79.709(2)
1604.5(3)
1.223
8.3720(14)
12.087(2)
16.072(3)
87.336(3)
88.089(3)
79.577(3)
1597.3(5)
1.228
9.0709(7)
10.9421(8)
12.7964(10)
93.573(1)
99.335(1)
104.496(1)
1206.32(16)
1.265
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
F
calcd (g/cm3)
θ
min, θmax (deg)
2.79, 27.49
0.080
1240
2.09, 27.54
0.076
624
2.18, 27.19
0.076
624
2.36, 27.53
0.086
486
2.3, 26.85
0.081
668
µ (mm-1
F(000)
)
no. of reflns
no. of unique reflns
no. of paras
Rint
19894
7876
309
0.069
0.0783, 0.188
0.854
0.40/-0.29
14190
7163
408
0.058
0.0419, 0.1048
1.019
0.25/-0.17
14285
7146
409
0.0227
0.0499, 0.1273
1.031
0.45/-0.19
8696
5190
382
0.0244
0.0487, 0.113
1.046
0.29/ -0.20
9679
3922
226
0.053
0.082, 0.162
1.01
0.31/-0.28
b
R,a Rw
GOFc
max/min residuals (e Å-3
)
c
a R ) ∑|Fo| - |Fc|/∑|Fo. b Rw ) [∑w(Fo - Fc2)2/∑w(Fo )2]1/2
.
GOF ) {∑[ w(Fo - Fc2)2]/(n - p)}1/2
.
2
2
2
a
Scheme 3. Synthesis of L1 and L2
a Precursors 9,10-bis(4-formylphenyl)anthracene and ꢀ-amino-ꢀ-(pyrid-4-yl)acrylonitrile were prepared according to previously described methods.14
a linear driving force model when >98% equilibration had been
reached. The adsorption isotherms of acetylene at various temper-
atures were measured with BELSORP-max volumetric adsorption
equipment from Bel Japan, Inc. Acetylene gas of high purity
(>99.9999%) was used. The host sample was treated under reduced
pressure (<10-3 Pa) at 400 K for more than 12 h before each
measurement. Measurement temperatures were precisely controlled
by a closed helium cycle refrigerator based cryostat. Each point in
the adsorption isotherm has an uncertainty of (0.25% imposed by
the resolution of the pressure gauge.
Results and Discussion
Structure of SOF-1. The polypyridyl tecton L1 was synthe-
sized from ꢀ-amino-ꢀ-(pyrid-4-yl)acrylonitrile and 9,10-bis(4-
formylphenyl)anthracene in acetic acid (Scheme 3). Crystalli-
9
J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010 14461

A R T I C L E S
Yang et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) and Hydrogen Bond Data for [L1]·2.5DMF·3MeOH (SOF-1), [L2]·2DMF·5C6H6 (S2A),
[L2]·2DMF·4MeOH (S2B), and L2 (S2C)
SOF-1
N(1)-C(5)
C(1)-C(2)
C(3)-C(4)
C(3)-C(6)
C(4)-C(5)
N(2)-C(6)
C(6)-C(7)
C(8)-C(9)
1.342(5)
1.373(5)
1.377(5)
1.534(5)
1.387(5)
1.384(3)
1.370(3)
1.520(3)
C(8)-C(18)
C(9)-C(17)
C(10)-C(11)
N(3)-C(13)
C(11)-C(15)
N(4)-C(17)
C(18)-C(23)
C(19)-C(20)
1.521(3)
1.425(4)
1.487(3)
1.345(3)
1.387(4)
1.136(4)
1.389(4)
1.387(4)
C(20)-C(21)
C(21)-C(22)
C(24)-C(25)
C(26)-C(27)
C(27)-C(28)
C(28)-C(30)#1
C(29)-C(30)
C(29)-C(25)#1
1.382(4)
1.385(4)
1.398(4)
1.361(4)
1.409(4)
1.353(4)
1.439(4)
1.440(4)
C(1)-N(1)-C(5)
C(2)-C(3)-C(4)
N(1)-C(5)-C(4)
C(10)-N(2)-C(6)
C(6)-C(7)-C(16)
C(7)-C(8)-C(18)
C(7)-C(8)-H(8A)
N(4)-C(17)-C(9)
116.6(5)
119.7(4)
123.7(5)
121.4(2)
120.0(3)
111.2(2)
108.5
177.9(3)
D-H· · · A
d(D-H)
d(H· · ·A)
d(D· · ·A)
∠(DHA)
N(2)-H(2B)· · ·N(3)#2
C(2)-H(2A)· · ·N(5)#3
C(8)-H(8A)· · ·N(5)#4
C(19)-H(19A)· · ·N(4)#5
C(23)-H(23A)· · ·N(5)#4
0.86
0.93
0.98
0.93
0.93
2.03
2.50
2.63
2.54
2.63
2.873(3)
3.362(5)
3.529(4)
3.300(4)
3.371(4)
164.9
154.2
153.1
139.6
136.7
1
1
symmetry code: (#1) -x + 3, -y + 1, -z; (#2) -x + 2, y + /2, -z - /2; (#3) -x + 2, -y + 1, -z; (#4) -x + 2, -y, -z; (#5) x, y + 1, z
S2A
N(1)-C(5)
N(1)-C(1)
C(2)-C(3)
N(2)-C(10)
1.3365(18)
1.3415(18)
1.3931(17)
1.3395(19)
C(6)-C(7)
C(7)-C(8)
N(3)-C(15)
C(12)-C(16)
1.3830(19)
1.3910(18)
1.3760(15)
1.4321(17)
C(12)-C(13)
C(13)-C(14)
N(5)-C(17)
C(18)-C(20)
1.5270(17)
1.5248(16)
1.1496(16)
1.3932(17)
C(14)-C(13)-C(12)
C(14)-C(13)-C(18)
C(12)-C(13)-C(18)
108.36(10)
112.77(10)
111.45(10)
D-H· · · A
d(D-H)
d(H· · ·A)
d(D· · ·A)
∠(DHA)
N(3)-H(3A)· · ·O(1)
C(22)-H(22B)· · ·N(4)#1
C(29)-H(29A)· · ·N(1)#2
0.88
0.98
0.95
1.91
2.60
2.53
2.7795(14)
3.424(2)
3.433(2)
170.6
142.1
159.9
symmetry code: (#1) x, y - 1, z; (#2) -x + 1, -y, -z
S2B
N(1)-C(5)
N(1)-C(1)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
N(2)-C(10)
C(6)-C(7)
1.336(2)
1.337(2)
1.381(2)
1.3926(19)
1.391(2)
1.385(2)
1.3719(17)
1.3538(19)
C(6)-C(3)
C(7)-C(16)
C(7)-C(8)
C(8)-C(9)
C(8)-C(18)
C(9)-C(10)
C(9)-C(17)
C(10)-C(13)
1.4834(18)
1.432(2)
1.5278(18)
1.5253(19)
1.5308(19)
1.353(2)
N(3)-C(11)
C(11)-C(12)
C(12)-C(13)
C(14)-C(15)
C(16)-N(4)
C(17)-N(5)
C(18)-C(20)
C(19)-C(20)#1
1.335(2)
1.385(2)
1.3916(19)
1.382(2)
1.1462(19)
1.146(2)
C(2)-C(3)-C(6)
120.00(12)
C(10)-N(2)-C(6)
C(7)-C(6)-N(2)
C(6)-C(7)-C(16)
C(9)-C(8)-C(7)
C(7)-C(8)-C(18)
C(9)-C(8)-H(8A)
N(4)-C(16)-C(7)
121.07(12)
120.75(12)
120.34(12)
107.98(11)
112.04(11)
108.3
1.427(2)
1.4890(19)
1.3850(19)
1.389(2)
176.79(15)
D-H· · · A
d(D-H)
d(H· · ·A)
d(D· · ·A)
∠(DHA)
N(2)-H(2B)· · ·O(1)
O(1)-H(1B)· · ·N(3)#2
O(3)-H(3A)· · ·O(2)
0.88
0.84
0.84
1.97
1.94
1.97
2.8526(16)
2.7695(16)
2.780(6)
178.7
169.8
162.8
symmetry code: (#1) -x, -y + 2, -z; (#2) -x, -y + 1, -z + 1
S2C
N(1)-C(1)
N(2)-C(10)
N(3)-C(13)
N(4)-C(16)
N(5)-C(17)
C(1)-C(2)
1.331(7)
1.376(4)
1.330(5)
1.135(5)
1.140(5)
1.377(7)
C(3)-C(4)
C(4)-C(5)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
C(8)-C(18)
1.382(5)
1.392(5)
1.343(5)
1.510(5)
1.514(5)
1.530(4)
C(9)-C(10)
C(10)-C(11)
C(11)-C(15)
C(11)-C(12)
C(12)-C(13)
C(18)-C(19)
1.343(4)
1.479(4)
1.380(4)
1.390(4)
1.383(5)
1.373(4)
C(7)-C(8)-C(9)
108.7(3)
C(7)-C(8)-C(18)
C(9)-C(8)-C(18)
C(7)-C(8)-H(8A)
N(4)-C(16)-C(9)
N(5)-C(17)-C(7)
110.4(3)
112.8(3)
108.3
174.4(4)
174.4(7)
D-H· · · A
d(D-H)
d(H· · ·A)
d(D· · ·A)
∠(DHA)
N(2)-H(2B)· · ·N(3)#1
C(5)-H(5A)· · ·N(5)#2
0.88
0.95
2.43
2.41
3.206(4)
3.327(7)
148
162
1
1
1
symmetry code: (#1) -x, -y, -z; (#2) x - /2, -y - /2, z - /2
9
14462 J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010

Thermal Stability in a SOF
A R T I C L E S
Figure 1. Crystal structure of SOF-1. (a) View of the molecular structure of L1 and hydrogen bonding for the symmetric unit in SOF-1. Symmetry codes
1
1
are as follows: (1) -x + 3, -y + 1, -z; (2) -x + 2, y + /2, -z - /2; (3) -x + 2, -y + 1, -z; (4) -x + 2, -y, -z; (5) x, y + 1, z. (b) View of 3D
supramolecular organic framework of SOF-1. (c) Side view of the nanochannel in SOF-1. Color codes are as follows: C, dark gray; H, green; N, blue;
covalent bonds, dark solid lines; hydrogen bonds, red dashed lines (H atoms not involved in hydrogen bonds are omitted for clarity).
zation of L1 affords an unprecedented supramolecular organic
framework with a composition of L1 ·2.5DMF·3MeOH (SOF-
1), which crystallizes in the monoclinic space group P21/c with
two molecules of L1 per unit cell. The structure of SOF-1 shows
L1 lying across a crystallographic inversion center, which is
coincident with the centroid of the anthracene moiety, and
comprises two 3,5-dicyano-2,6-dipyridyldihydropyridyl units
bridged by the 9,10-bis(phenyl)anthracene moiety (Figure 1a).
X-ray diffraction analysis confirms that C8 in the dihydropyridyl
ring (C6-C7-C8-C9-C10-N2) has a sp3 configuration, and
consequently the dihydropyridyl rings are nearly perpendicular
to the phenyl spacer (dihedral angle: 82.36°) and have a dihedral
angle of 71.76° with respect to the central anthracene moiety.
This defined geometry (Scheme 2) coupled to functional centers
affords extensive hydrogen bonding between the two N-H
protons and eight proton-acceptor N-sites and π-π stacking
interactions between the molecular building units. Each molecule
of L1 thus participates in the construction of three different
hydrogen bonded motifs, strong N-H· · ·Npyridyl and weak
C-H· · ·Npyridyl and C-H· · ·Ncyano, resulting in a 3D supramo-
lecular organic framework structure with pyridyl-functionalized
channels along the b axis. These channels have a diameter of
∼7.8 Å (Figure 1b). Further π-π stacking interactions between
the molecular building units along the b axis contribute further
to the stabilization of the overall network. The solvent-accessible
voids were estimated using PLATON/VOID15b to be 34.0% of
the total crystal volume, giving a calculated density of 0.93 g
cm3 g-1 for the desolvated organic framework.
High Thermal Stability of SOF-1. Thermogravimetric analysis
(TGA) of SOF-1 reveals (Figure 2) a rapid weight loss of
23.33% up to 175 °C, corresponding to thermal removal of three
MeOH and 2.5 DMF molecules (calculated weight loss 23.68%),
followed by a wide plateau region. The major weight loss
starting beyond 420 °C corresponds to decomposition of the
material. The thermal stability of SOF-1 is quite remarkable,
much higher than that of organic framework materials reported
9
J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010 14463

A R T I C L E S
Yang et al.
N-H· · ·O hydrogen bonds between dihydropyridyl rings and
solvent DMF molecules. These terminal DMF molecules prevent
the dicyanodipyridyldihydropyridyl moiety from participating
in additional hydrogen bonds. However, the crystal structure
features π-π stacking interactions between pyridyl rings to form
a 2D layered assembly with π-π stacked columns of ligands.
Packing of these layers generates 1D nanochannels along the
crystallographic a and b axes which host DMF and benzene
molecules (Figure 3). In S2B, each L2 ligand participates in
hydrogen bonding via an N-H · · · O interaction between the
N-H of the dihydropyridyl ring and the O of a MeOH molecule,
with N · · ·H-O hydrogen bonding between the N-center of a
pyridine ring and the H-O of a second MeOH molecule. The
presenceoftheL2-HOMehydrogenbondspreventsligand-ligand
hydrogen bonding, and there are no π-π stacking interactions
between pyridyl moieties. As a result, S2B crystallizes as one-
dimensional hydrogen bonded chains rather than as an extended
3D network (Figure 4).
Figure 2. TGA trace for [L1]·2.5DMF·3MeOH (SOF-1).
previously2-7 and comparable to thermally stable metal-organic
frameworks.16 It appears that the presence of a large aromatic
spacer, 9,10-bis(phenyl)anthracene, and strong N-H· · ·Npy
hydrogen bonds play an important role in stabilizing the guest-
free framework of SOF-1a. It is noteworthy that the fully
evacuated framework (SOF-1a), which was obtained by heating
a crystalline sample of SOF-1 at 130 °C under a dynamic
ultrahigh vacuum (10-8 mbar) for 12 h, remains structurally
unchanged on desolvation, as confirmed by powder X-ray
diffraction studies, producing nanospace for accommodation of
other guest molecules. SOF-1a has the formula C60H36N10 (L1),
as confirmed by elemental analysis and 1H NMR spectroscopic
data.
Although analysis using PLATON/VOID15b suggests the
possibility of a high solvent-accessible volume of 57.9%, S2A
undergoes a transformation to a denser phase S2C upon thermal
removal of solvents at 160 °C under N2. Indeed, this transfor-
mation also occurs on exposure to air where crystals of S2A
gradually convert to S2C at room temperature, as revealed by
PXRD studies. S2C crystallizes in the monoclinic space group
P21/n and has a 3D supramolecular network featuring strong
N-H· · ·Npy and weak C-H· · ·Ncyano bonds and π-π contacts
(Figure 5). However, S2C does not exhibit any evidence of
microporosity, since the removal of solvent molecules from S2A
results in conversion to the denser phase S2C. In addition to
the role of hydrogen bonding and π-π interactions, hydrophobic
and van der Waals interactions between the walls of the channel
host and guest molecules will also play a role in stabilizing the
structure of SOF-1, and these weak, isotropic interactions will
be far fewer in the S2 series because of their much smaller linker
group thus leading to more close-packed structures.
Effect of Aromatic Ring on Thermal Stability and Porosity. To
study the effect of the aromatic spacer on the stability and
porosity of the resultant material, we synthesized the less bulky
analogue 1,4-bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropyridyl)-
benzene (L2). By use of the same layering techniques applied
to SOF-1 (L1), it is possible to obtain L2 as crystalline materials.
Two different crystalline solvates of L2, solvate A [L2] ·
2DMF·5C6H6 (S2A) and solvate B [L2]·2DMF·4MeOH (S2B),
were obtained. S2A and S2B both crystallize in the triclinic
Gas Adsorption Properties of SOF-1a. The high stability of
the organic framework SOF-1 provides an opportunity to study
its gas adsorption properties. Desolvated SOF-1a shows sig-
nificant CO2 adsorption at 195 K (Figure 6) especially at low
j
space group P1 as pale yellow tablets and slightly yellow blocks,
respectively. Each L2 molecule in S2A participates in two
Figure 3. (a) View of molecular structure and hydrogen bonds in [L2]·2DMF·5C6H6 (S2A). (b) A space-filling view of the 3D supramolecular framework
of S2A with nanochannels capturing DMF (red) and benzene molecules (yellow). Color codes are as follows: C, black; N, blue. H atoms are omitted for
clarity.
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14464 J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010

Thermal Stability in a SOF
A R T I C L E S
Figure 4. (a) View of asymmetric unit and hydrogen bonds in [L2]·2DMF·4MeOH (S2B). (b) View of the 1D chain in S2B, formed by L2 and MeOH
molecules via N-H· · ·O and O-H· · ·N bonds. H atoms on carbons are omitted for clarity.
relative pressures (3.9 mmol g-1 at P ) 0.2 bar), confirming
the presence of permanent microporosity. The CO2 absorption
follows a type-I isotherm,17 with a measured capacity of 5.6
mmol g-1 (24.6 wt % or 125 cm3 (STP) g-1) and an estimated
maximum filling of 6.5 mmol g-1 (28.5 wt % or 145 cm3 (STP)
g-1), significantly exceeding the capacities previously reported
for other supramolecular organic frameworks (Table 3).2b,3c,6j,n
Even at ambient temperature, evacuated SOF-1a still shows a
noticeable CO2 adsorption with some 3 mol of CO2 absorbed
per mole of host at 16 bar and 298 K, corresponding to 69 cm3
g-1 at STP. This value, which does not represent full capacity,
is already effectively twice that of TBC[4]DHQ (35 cm3 g-1 at
35 bar and 298 K) previously described as the most effective
molecular organic assembly for absorbing CO2.6j
In contrast, the N2 absorption capacity of SOF-1a at 77 K
is very low with only 0.63 mmol g-1 uptake at 1 bar,
indicating that N2 molecules are unable to enter the pores.
This sorption behavior may be due to the low thermal energy
of the framework and the low kinetic energy of N2,8p,q,18
because the results at 125 K and upward are quite different
to those at 77 K. The saturation N2 adsorption at 125 K is
6.55 mmol g-1 (or 143 cm3 g-1), 10 times greater than that
measured at 77 K. As expected, adsorption equilibrium was
achieved far more rapidly than at 77 K. The pore volumes
of SOF-1a calculated from the N2 isotherm at 125 K and
the CO2 isotherm at 195 K are 0.227 and 0.244 cm3 g-1
,
respectively. These values are relatively low compared to
MOFs8,16 and COFs1,19 but are significant for molecular
organic solids (Table 3).3-6 The pore size (7.4 Å) obtained
by applying the Dubinin-Astakhov (DA)20 equation to the
N2 sorption data at 125 K is consistent with the crystal
structure. The amount of N2 adsorbed then reduces on
increasing temperature, with uptakes at 20 bar of 6.36, 4.37,
and 2.46 mmol g-1 at 125, 175, and 195 K, respectively.
Adsorption isotherms for C2H2 uptake were measured at
different temperatures (Figure 6). SOF-1a adsorbs a significant
amount of C2H2 at 195 K, with an uptake of 124 cm3 (STP)
g-1 (5.52 mmol g-1) at 1 bar. With increasing temperature, the
adsorption of C2H2 gradually decreases but becomes more
reversible. The amounts of C2H2 adsorbed at 1 bar at 210, 230,
250, and 270 K are 104, 87, 72, and 61 cm3 g-1, respectively.
When these values are fitted to the double-exponential-decay
expression
(16) (a) Humphrey, S. M.; Chang, J. S.; Jhung, S. H.; Yoon, J. W.; Wood,
P. T. Angew. Chem., Int. Ed. 2007, 46, 272. (b) Perles, J.; Iglesias,
M.; Martin-Luengo, M.-A.; Monge, M. A.; Ruiz-Valero, C.; Snejko,
N. Chem. Mater. 2005, 17, 5837. (c) Lin, X.; Blake, A. J.; Wilson,
C.; Sun, X.; Champness, N. R.; George, M. W.; Hubberstey, P.;
Mokaya, R.; Schro¨der, M. J. Am. Chem. Soc. 2006, 128, 10745. (d)
Sun, D.; Ma, S.; Ke, Y.; Petersen, T. M.; Zhou, H.-C. Chem. Commun.
2005, 2663.
n ) n0 + A1exp(-T/b1) + A2exp(-T/b2)
where n is absorbed amount, T is temperature (K), and n0, A1,
A2, b1, and b2 are coefficients, the amount of adsorbed C2H2
(17) Rouquerol, J.; Rouquerol, F.; Sing, K. W. Adsorption by Powders and
Porous Solids: Principles, Methodology and Applications; Academic
Press: London, 1999.
(18) Chandler, B. D.; Cramb, D. T.; Shimizu, G. K. H. J. Am. Chem. Soc.
2006, 128, 10403.
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J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010 14465

A R T I C L E S
Yang et al.
Figure 5. (a) View of L2 molecules in S2C are connected via N-H· · ·Npyridyl bonds into 1D supramolecular chains. (b) View of 2D supramolecular sheet
in S2C (adjacent 1D chains highlighted with different colors, viewed along [1, 0, -1] direction). (c) View of π-π contacts connecting these supramolecular
layers into a 3D network (adjacent layers highlighted with different colors, π-π stacking interactions between layers highlighted in space-filling mode;
viewed along b axis). Hydrogen bonds are shown as dashed lines.
above 270 K can be estimated as 50 cm3 g-1 at 298 K and 48
cm3 g-1 at 303 K. These values are comparable or superior to
the C2H2 uptakes reported for other microporous adsorbents
under similar conditions (298 K and 1 atm) (Table 4).6k,10b,21
SOF-1a shows methane uptake at 195 K and 1 bar of 69
cm3 (STP) g-1, exceeding that of organic absorbents such as
tris-o-phenylenedioxycyclotriphosphazene (33.2 cm3 (STP)
g-1),2b L-alanyl-L-valine (50 cm3 (STP) g-1) and L-valyl-L-
3c
alanine (35 cm3 (STP) g-1
)
under similar conditions (195 K
(19) (a) Han, S. S.; Furukawa, H.; Yaghi, O. M.; Goddard, W. A. J. Am.
Chem. Soc. 2008, 130, 11580. (b) Furukawa, H.; Yaghi, O. M. J. Am.
Chem. Soc. 2009, 131, 8875.
and 1 atm) (Table 5). When the pressure of CH4 is increased to
10 bar, the amount adsorbed is 106 cm3 (STP) g-1, but this
does not represent its full capacity. The CH4 uptake significantly
(20) Dubinin, M.-M. Carbon 1989, 27, 457.
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14466 J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010

Thermal Stability in a SOF
A R T I C L E S
Figure 6. Gas isotherms for SOF-1a: (a) CO2 at 195, 273, and 298 K; (b) N2 at 125 and 175 K; (c) C2H2 at 195, 210, 230, 250, and 270 K; (d) CH4 at 195,
270, and 298 K. Black solid symbols indicate adsorption, and red open symbols indicate desorption.
Table 3. Comparison of N2 and CO2 Sorption Data for Supramolecular Organic Frameworks (SOFs)
SA, m2 g-1
Langmuird
V (CO2) [cm3 g-1
]
materiala
V (N2)b [cm3 g-1
]
BETd
V(N2)c [cm3 g-1
]
195 Kh
298 K
ref
f g
143c
90
55
85
98
474e
230
639e (671)f
0.227e g (0.244) ,
125
16h (69)i
35j
this work
6j, 10c
2b, 10b
10b
10c
10d
3c
3c
6o
6n
,
SOF-1a
TBC[4]DHQ
TPP
CB[6]
TMSBP
CBDU
VA
AV
AC[6]
AC[7]
0.14
0.088
0.13
0.16
240
61
210
278
341f
72
91
78
37
55
a Molecular structures and corresponding abbreviations are shown in Scheme 1. TBC[4]DHQ ) p-tert-butylcalix[4]dihydroquinone; TPP ) tris-
o-phenylenedioxycyclotriphosphazene; CB[6] ) cucurbit[6]uril; TMSBP ) 3,3′,4,4′-tetra(trimethylsilylethynyl)biphenyl; VA ) L-valyl-L-alanine; AV )
L-alanyl-L-valine; CBDU ) cyclic bis(4,4′-oxybis(benzyl))diurea; AC[6] ) azacalix[6]arene; AC[7] ) azacalix[7]arene. b Amount of nitrogen adsorbed
at 77 K and 1 atm except where indicated. c Amount of nitrogen adsorbed at 125 K and 1 bar. d Calculated from N2 isotherm at 77 K except where
g
indicated. e Calculated from N2 isotherm at 125 K. f Calculated from CO2 isotherm at 195 K. F(N2, 77K) ) 0.808 g cm-3 and F(CO2, at triple point) )
1.18 g cm-3 were applied to calculate the pore volume. h Amount of CO2 adsorbed at 1 atm or 1 bar. i Amount of CO2 adsorbed at 16 bar. j Amount of
CO2 adsorbed at 35 atm.
decreases with increasing temperature, but the density of
adsorbed CH4 (0.09 g cm-3 at 298 K and 16 bar) is still
comparable to the values reported for COFs (0.06- 0.13 g cm-3
at 298 K and 35 bar).19b
High Selectivity of Gas Adsorption on SOF-1a. It is interesting
to compare the adsorption properties of SOF-1a toward different
gases at the same temperatures. At 195 K, the absorption of
C2H2 at 200 mbar reaches 4.3 mmol g-1 (75% maximum
loading); even at pressures as low as 50 mbar the absorption is
still extremely efficient (Figure 7). In contrast, the adsorption
of CH4 with increasing pressure presents a significantly smaller
slope, and the C2H2/CH4 ratios thus become greatly advanta-
geous below 50 mbar, reaching values as high as 18. However,
from a practical application point of view, it is critical to be
able to achieve separation of C2H2 from CH4 at ambient
temperature and normal pressure. The C2H2 uptake at 1 bar and
(21) (a) Matsuda, R.; Kitaura, R.; Kitagawa, S.; Kubota, Y.; Belosludov,
R. V.; Kobayashi, T. C.; Sakamoto, H.; Chiba, T.; Takata, M.;
Kawazoe, Y.; Mita, Y. Nature 2005, 426, 238. (b) Samsonenko, D. G.;
Kim, H.; Sun, Y.; Kim, G.-H.; Lee, H.-S.; Kim, K. Chem.sAsian J.
2007, 2, 484. (c) Zhang, J.-P.; Chen, X.-M. J. Am. Chem. Soc. 2009,
131, 5516. (d) Zhang, J.-P.; Kitagawa, S. J. Am. Chem. Soc. 2008,
130, 907. (e) Xiang, S.; Zhou, W.; Gallegos, J. M.; Liu, Y.; Chen, B.
J. Am. Chem. Soc. 2009, 131, 12415. (f) Reid, C. R.; Thomas, K. M.
Langmuir 1999, 15, 3206.
9
J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010 14467

A R T I C L E S
Yang et al.
Table 4. Comparison of Acetylene Sorption in Porous
Supramolecular Organic Frameworks (SOFs)
Table 5. Comparison of CH4 Sorption in Porous Supramolecular
Organic Frameworks (SOFs)
C2H2 uptake (cm3 g-1
at 1 atm or 1 bar
)
CH4 uptake, cm3 g-1
CH4 density,g
g cm-3
materiala
195 Kb
298 Kd
Qst, kJ mol-1
ref
materiala
195 K
270 K
298 K
Qst (kJ mol-1
)
ref
SOF
SOF-1a 69, 106c
32e
0.09
23.76h (20.84)i this work
SOF system
SOF-1a
124
91
61
50b
52
36.2d(43.3)e
59.4e
this work
10b
6k
TPP
33
12b
6d
TBC[4]
TPC[4]
VA
AV
IV
24
CB[6]
31f
6d
TBC[4]
carbon molecular
sieve
18
9i
3c
3c
3c
45c
20
50
35
40
9i
19i
a Abbreviations: CB[6]
)
cucurbit[6]uril; TBC[4]
)
p-tert-bu-
a TPP
)
tris-o-phenylenedioxycyclotriphosphazene; TBC[4]
)
tylcalix[4]arene. b Estimated by fitting the acetylene absorbed amounts at
1 bar at different temperatures (195, 210, 230, 250, and 270 K) to a
p-tert-butylcalix[4]arene; TPC[4] ) p-tert-pentylcalix[4]arene; VA )
L-valyl-L-alanine; AV ) L-alanyl-L-valine; IV ) L-isoleucyl-L-valine.
double-exponential-decay equation. Vads (STP) at 303 K. d Calculated
c
b Vads (STP) at 195 K and 1 atm (or 1 bar) except where indicated. Vads
c
from the adsorption isotherms at 230, 250, and 270 K by using virial
d
method
2
at zero coverage. e Calculated by using the Clausius-
(STP) at 195 K and 10 bar. Vads (STP) at 35 bar or 35 atm, room
e
f
temp, except where indicated. Vads (STP) at 298 K and 16 bar. Vads
(STP) at 32 atm, room temp. g Calculated density of adsorbed CH4 at
room temp in pore volume (Vp). h Estimated by a modified version of
the Clausius-Clapeyron equation at low coverage (0.1 mmol g-1).
i Estimated by virial method.
Clapeyron equation at low coverage.
270 K is 2.75 mmol g-1, while the CH4 uptake under the similar
conditions (1 bar and 273 K) is 0.38 mmol g-1. To calculate
the C2H2(270 K)/CH4(273 K) selectivity from the corresponding
Henry’s Law constants, a nonlinear fitting of the adsorption
isotherms was performed using the To´th model.8e Accordingly,
the Henry’s Law selectivity of C2H2 over CH4 is calculated to
be 33.7, indicating a significantly stronger interaction of C2H2
molecules with the host framework (possibly due to polar
pyridyl groups in the pores) compared to CH4.
superiority of C2H2 adsorption over CO2 adsorption is apparent
at near ambient temperature and up to atmospheric pressure
(Figure 7b). The calculated Henry’s Law selectivity of C2H2(270
K) over CO2(273 K) is 6.02, while the C2H2(270 K)/CO2(273
K) ratio of uptake at 1 bar is 2.05, significantly higher than the
values for those of carbon molecular sieves (1.25),21f TBC[4]
(1.25),6k and MOFs (1.34-1.48),21a-e suggesting that SOF-1a
can distinguish these gas molecules.
At 195 K, the C2H2/CO2 ratios are 1.09 ( 0.07 between 0.1
and 1 bar, indicating low adsorption selectivity. However, the
Figure 7. Comparison of gas adsorption on SOF-1a. (a) C2H2 (black), CO2 (red), CH4 (blue), and N2 (magenta) at 195 K (triangles), 270 (or 273) K (circles) and
298 K (stars). (b) Expanded view of the adsorption isotherms in the low pressure range (0-1 bar). The solid lines are fitted using the To´th equation. (c) Variation
of isosteric heat (Qst) of adsorption with amount of C2H2, CO2, CH4, and N2 adsorbed on SOF-1 (calculated using virial methods).
9
14468 J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010

Thermal Stability in a SOF
A R T I C L E S
Clearly, adsorption of CO2 on SOF-1a is markedly greater
than that of CH4 or N2. At 195 K, the CO2/CH4 and CO2/N2
ratios of adsorption at pressures below 50 mbar are very high,
reaching values of 5-8 and 20-37, respectively. Even at
ambient temperature (273 or 298 K), the CO2/CH4 and CO2/N2
ratios of adsorption are still higher than 2 and 7, respectively,
over the pressure range measured, indicating that this material
may have practical applications in gas purification. The corre-
sponding Henry’s Law selectivity SA/B of gas A (CO2) over B
(CH4 or N2) is listed in Table S6.
To further probe the gas affinity of SOF-1a, the isosteric heats
(Qst) of N2, CO2, C2H2, and CH4 adsorption were estimated from
the sorption isotherms at various temperatures using virial-type
expressions.22 This confirms (Figure 7c) an order of enthalpy
of adsorption at zero coverage of N2 < CH4 < CO2 < C2H2 (11.2,
20.8, 27.6, and 36.2 kJ mol-1, respectively). The enthalpies of
N2 and CO2 adsorption for SOF-1a suggest that the affinity
) 2,3-pyrazinedicarboxylate; pyz ) pyrazine) (42.5 kJ
mol-1).21a For SOF-1a, as C2H2 loading increases, the Qst values
decrease gradually to 28.4 kJ mol-1 at 3.2 mol g-1 loading
(Figure 7c).
Conclusions and Perspectives
In summary, we have prepared the multifunctional and
multidirectional tecton L1, and by exploiting the weak coopera-
tive interactions of hydrogen bonds and π-π stacking interac-
tions, we have successfully obtained a porous organic framework
(SOF-1) with pyridyl-decorated channels. Desolvated SOF-1a
exhibits an unusually high thermal stability, and its gas
adsorption properties have been investigated. The measurements
of uptake of C2H2, CO2, CH4, and N2 show a type-I isotherm,
but in some cases slight hysteresis was observed on desorption.
High C2H2 uptake (61 cm3 g-1) and high C2H2/CO2 (2), C2H2/
CH4 (7), C2H2/N2 (36), CO2/CH4 (4), CO2/N2 (17), and CH4/N2
(5) uptake ratios at ambient temperature (270 K for C2H2 and
273 K for other gases) and 1 bar are revealed, indicating that
SOF-1a has potential to emerge as an important material for
C2H2 and natural gas purification and for removal of CO2 from
the air.
toward N2 and CO2 molecules is in the same range as those
23
observed for many MOF compounds: N2, 7.68-16 kJ mol-1
;
24
CO2, 25-35 kJ mol-1
.
However, the enthalpy of adsorption
observed for methane on SOF-1a (20.8 kJ mol-1) is one of the
highest values reported so far (cf 22 kJ mol-1 for microporous
polymers and 23 kJ mol-1 for PCN-93c,25) and significantly
exceeds those of organic microporous crystal of L-alanyl-L-valine
(AV) (9 kJ mol-1),3c aluminosilicate zeolites (17.0-17.8 kJ
mol-1),26 and other porous metal-organic frameworks (12-17
kJ mol-1).24,27 The large isosteric heat of adsorption (Qst) for
CH4 observed in SOF-1a indicates that although the CH4 is
highly symmetric and nonpolar, some enhancement of binding
strength is still possible.25 The adsorption enthalpy for C2H2 at
zero coverage (Qst,n)0 ) 36.2 kJ mol-1) is higher than or
comparable with those for previously studied absorbents which
generally show values of 28.4-38.5 kJ mol-1.21b-d Interestingly,
The analogue bis(4-(3,5-dicyano-2,6-dipyridyl)dihydropy-
ridyl)benzene (L2) has been shown to form two different solvates
under the same crystallization conditions; this should be
recognized as a potentially complicating but interesting factor
in the production of SOFs. Thermal removal of solvents from
S2A resulted in a conversion to denser phase S2C with no
effective porosity. Thus, compared with the phenyl analogue
(L2), introduction of 9,10-bis(phenyl)anthracene group (L1) leads
to a stable porous organic material SOF-1. The increased role of
hydrogen bonding, π-π, hydrophobic, and van der Waals interac-
tions between the walls of the channel host and guest molecules
account for the stabilization of SOF-1. These interactions will thus
be fewer in the S2 series because of their much smaller spacer
group leading to more close-packed structures.
ZIF-8 shows a lower value of 13.3 kJ mol-1 at a coverage of
21e
0.02 mmol g-1
,
while increased values are observed for
cucurbit[6]uril (59.4 kJ mol-1)10b and [Cu2(pzdc)2(pyz)] (pzdc2-
(22) (a) Rowsell, J. L. C.; Yaghi, O. M. J. Am. Chem. Soc. 2006, 128,
1304. (b) Jagiello, J.; Bandosz, T. J.; Schwarz, J. A. Langmuir 1996,
12, 2837. (c) Zhao, X. B.; Xiao, B.; Fletcher, A. J.; Thomas, K. M. J.
Phys. Chem. B 2005, 109, 8880. (d) Chen, B.; Zhao, X.; Putkham,
A.; Hong, K.; Lobkovsky, E. B.; Hurtado, E. J.; Fletcher, A. J.;
Thomas, K. M. J. Am. Chem. Soc. 2008, 130, 6411. (e) Czepirski, L.;
Jagiello, J. Chem. Eng. Sci. 1989, 44, 797.
The successful synthesis of stable SOF-1 opens up the
possibility of obtaining new porous materials by using large
polyfunctional organic tectons in which a part of cooperative
functional groups (i.e., dihydropyridyl and cyano groups in SOF-
1) stabilizes the supramolecular assembly, while the other polar
organic sites (i.e., pyridyl groups in SOF-1) remain available
for host-guest interactions within decorated pores. To probe
this further, we are currently undertaking the challenge of
applying core decoration of carboxaldehydes to the synthesis
of further functionalized dihydropyridyl derivatives and the
formation of their corresponding porous organic assemblies and
related polymorphs.
(23) (a) Matsuda, R.; Kitaura, R.; Kitagawa, S.; Kubota, Y.; Kobayashi,
T. C.; Horike, S.; Takata, M. J. Am. Chem. Soc. 2004, 126, 14063.
(b) Matsuda, R.; Kitaura, R.; Kitagawa, S.; Kubota, Y.; Kobayashi,
T. C.; Horike, S.; Takata, M. J. Am. Chem. Soc. 2004, 126, 14063.
(c) Bradshaw, D.; Prior, T. J.; Cussen, E. J.; Claridge, J. B.;
Rosseinsky, M. J. J. Am. Chem. Soc. 2004, 126, 6108. (d) Noro, S.;
Kitaura, R.; Kondo, M.; Kitagawa, S.; Ishii, T.; Matsuzaka, H.;
Yamashita, M. J. Am. Chem. Soc. 2002, 124, 2568.
(24) (a) Bourrelly, S.; Llewellyn, P. L.; Serre, C.; Millange, F.; Loiseau,
T.; Fe´rey, G. J. Am. Chem. Soc. 2005, 127, 13519. (b) Loiseau, T.;
Lecroq, L.; Volkringer, C.; Marrot, J.; Fe´rey, G.; Haouas, M.; Taulelle,
F.; Bourrelly, S.; Llewellyn, P. L.; Latroche, M. J. Am. Chem. Soc.
2006, 128, 10223.
Acknowledgment. We thank EPRSC for support. M.S. grate-
fully acknowledges receipt of a Royal Society Wolfson Merit Award
and of an ERC Advanced Grant.
(25) (a) Ma, S.; Zhou, H.-C. J. Am. Chem. Soc. 2006, 128, 11734. (b) Ma,
S.; Sun, D.; Simmons, J. M.; Collier, C. D.; Yuan, D.; Zhou, H.-C.
J. Am. Chem. Soc. 2008, 130, 1012.
Supporting Information Available: Experimental details,
additional views of the crystal structures, PXRD data, detailed
analysis of gas adsorption isotherms analyses, and crystal-
lographic data (in CIF format) for SOF-1, S2A (both forms),
S2B, and S2C. This material is available free of charge via
the Internet at http://pubs.acs.org.
(26) (a) Guillot, A.; Follin, S.; Poujardieu, L. R. Soc. Chem.sCharact.
Porous Solids 1997, 213, 573. (b) Himeno, S.; Komatsu, T.; Fujita,
S. J. Chem. Eng. Data 2005, 50, 369.
(27) (a) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; OKeeffe,
M.; Yaghi, O. M. Science 2002, 295, 469. (b) Wang, X.-S.; Ma, S.;
Rauch, K.; Simmons, J. M.; Yuan, D.; Wang, X.; Yildirim, T.; Cole,
W. C.; Lo´pez, J. J.; de Meijere, A.; Zhou, H.-C. Chem. Mater. 2008,
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J. AM. CHEM. SOC. VOL. 132, NO. 41, 2010 14469