Temperature-dependent penetration of argon molecules into ultramicroporous tunnel of a fluoroorganic molecular crystal with alteration of its unit cell size

Article abstract of DOI:10.1246/cl.2006.504

A molecular crystal of octamethylene (S,S)-bis(2-hydroxy-3,3,3- trifluoropropanoate) with an ultramicroporous tunnel (Φ = 2.5-2.8 A) starts to adsorb argon (Φ = 3.6 A) at 150-140 K with 7% increase of the one direction of the orthorhombic unit cell. The alteration of the unit cell size indicates the penetration of argon into the tunnel and the soft nature of the microporous molecular crystal. Copyright

Full text of DOI:10.1246/cl.2006.504

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04
Chemistry Letters Vol.35, No.5 (2006)
Temperature-dependent Penetration of Argon Molecules into Ultramicroporous Tunnel
of a Fluoroorganic Molecular Crystal with Alteration of Its Unit Cell Size
ꢀ
1
1
2
3
3
1
Toshimasa Katagiri, Satoshi Takahashi, Koji Kawabata, Yoshiyuki Hattori, Katsumi Kaneko, and Kenji Uneyama
1
Department of Applied Chemistry, Faculty of Engineering, Okayama University, Okayama 700-8530
2
Industrial Technology Center of Okayama Prefecture, Okayama 701-1296
Department of Chemistry, Faculty of Science, Chiba University, Chiba 263-8522
3
(Received February 16, 2006; CL-060201; E-mail: tkata@cc.okayama-u.ac.jp)
A molecular crystal of octamethylene (S,S)-bis(2-hydroxy-
,3,3-trifluoropropanoate) with an ultramicroporous tunnel
manometry
[
mmol/g]
[mol%]
3
˚
˚
(
1
ꢀ ¼ 2:5{2:8 A) starts to adsorb argon (ꢀ ¼ 3:6 A) at 150–
0
0
.8
.6
Ar at 77 K
3
2
1
0
0
0
40 K with 7% increase of the one direction of the orthorhombic
unit cell. The alteration of the unit cell size indicates the penetra-
tion of argon into the tunnel and the soft nature of the micropo-
rous molecular crystal.
0
0
.4
.2
Study on the gas adsorption properties of porous crystal with
1
ultramicropore has been the focus of wide interest. The next
target would be construction and utilization of microporous
0
0
.0
2
structures with dynamic functions. To date, a number of crystal-
line compounds, such as interpenetrated metal assembled frame-
works, have shown dynamic functions, gating phenomena in
Figure 2. Adsorption–desorption isotherm curve of argon gas
at 77 K by the ultramicroporous crystal of 1, which was observed
by BELSORP28SA.
3
their gas adsorption processes.
Recently, we prepared an organic crystal with an ultramicro-
pore from the octamethylene (S,S)-bis(2-hydroxy-3,3,3-trifluo-
4
(no less than 20 mol % per unit tunnel molecule). Figure 2 shows
the adsorption–desorption isotherm curve of the argon gas into
the crystal (needle shaped, 0.05–0.4 mm-length) at 77 K. The
curve was characterized by a sharp initial rising, which would
be attributed to an initial micropore filling and a large hysteresis
in the degassing process. The isotherm curve could be catego-
ropropanoate) (1) unit molecule. The molecular crystal has an
˚
infinite ultramicroporous tunnel (ꢀ ¼ 2:5{2:8 A). Figure 1 is a
cross section and a bottom view of the tunnel in the crystal.
The tunnel is too narrow to allow recrystallizing solvent mole-
cules in it.
7
The tunnel structure has alternating gates of two facing tri-
fluoromethyl (CF3) groups and rooms surrounded by four CF3
rized to an IUPAC type I.
A gradual gas adsorption after the initial micropore filling
and a large hysteresis even at the low p=p0 region in the degass-
ing process suggested a slow movement of the argon molecule in
the macrolength tunnel.
The crystal should be swelled by penetration of argon mole-
cules into the smaller tunnel. This was confirmed by a change in
the unit cell size of the crystal under an argon atmosphere at low-
er temperature (Figure 3). No such change was observed under
an N2 atmosphere up to 100 K.
˚
groups. The tunnel walls have no side holes larger than 1 A.
4
The walls of the tunnel are connected by hydrogen-bonding
chains and the floors are made by polymethylene backbones.
The tunnel would avoid collapse by a small van der Waals attrac-
tion and possible electrostatic repulsion between two negatively
5
charged facing CF3 groups.
A gas adsorption manometry measurement of the crystal in-
˚
dicated an unexpected argon gas (3.6 A diameter ) adsorption
6
The crystal was put in a thin glass capillary, which was filled
OH
O
O
CF3
OH
F3C
O
30
O
1
c
25
b axis
b
2
1
1
0
5
0
5
0
a
a axis
c axis
c
Figure 1. Cross-section view (left) and bottom view (right) of
the tunnel structure found in the crystal, which was cooled by
110
140 150
290
4
a nitrogen flow (120 K). (CCDC No. 246922). Unit cell size:
˚
Figure 3. The effect of temperature decrease to the unit cell
sizes of 1 under an argon atmosphere.
a ¼ 8:061ð2Þ, b ¼ 22:846ð5Þ, c ¼ 5:1730ð10Þ A.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.5 (2006)
505
compound. This work was financially supported by The Mazda
Foundation Research Grant, JST Innovation Plaza Hiroshima,
and Okayama University Grant. We thank the VBL of Okayama
University for X-ray crystal diffraction measurements and
analysis.
b
c
a
References and Notes
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Figure 4. Cross-section view (left) and bottom view (right) of
the tunnel with argon (pale yellow sphere) observed at 105 K
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8
(
CCDC No. 256312). Unit cell size: a ¼ 7:986ð1Þ, b ¼
2
4:535ð4Þ, c ¼ 5:0851ð5Þ A˚ .
2358; S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem., Int. Ed.
2
004, 43, 2334.
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ray diffraction measurements. The crystal systems, orthorhom-
bic, were identical throughout the examined temperatures. The
unit cell size was not changed from room temperature (293 K)
to 150 K. Then, it changed sharply at 140 K. The length of the
2
3
J. Rousselet, L. Salome, A. Ajdori, J. Prost, Nature 1994, 370, 446;
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˚
b axis was increased by around 7.4% from 22.8 A at 150 K to
˚
4.4 A at 140 K. Meanwhile, that of the a and the c axes was
2
slightly decreased (<0:1 A).
˚
To confirm an existence of argon molecules in the crystal,
single crystal X-ray analysis at 105 K was done. The analysis
gave a molecular structure of the crystal of 1 bearing argon
molecules, as shown in Figure 4. The argon atom was found at
the center of the room surrounded by the four CF3 groups, and
occupancy of the room by the argon molecule was estimated
to be 67 mol % (0.67 molecule/room). This incomplete occupa-
tion of the rooms by the argon resulted in a large R residual of the
2420.
4
5
T. Katagiri, M. Duan, M. Mukae, K. Uneyama, J. Fluorine
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estimated to be 0.07 e by HF/6-31G level calcuration.
A. Bondi, J. Phys. Chem. 1964, 68, 441.
ꢀꢀ
8
6
7
analysis. Longer precooling of the crystal at <140 K for further
F. Rouquerol, J. Rouquerol, K. Sing, Adsorption by Powders &
Porous Solids, Academic Press, San Diego, 1999, pp. 18–21.
Tentative structural analysis result for Ar-adsorbed crystal. (CCDC
No. 256312) C14H20Ar0:67F6O6, Mr ¼ 425:02, orthorhombic, a ¼
stuffing of argon into the tunnel caused cracks in the crystal.
We found that the expansion of the b axis was caused by a
much more vertical orientation of the polymethylene chain to the
direction of the hydrogen-bonding chain (c axis) (Figure 4) than
that of vacant one (Figure 1).
8
˚
˚ 3
7
:9865ð14Þ, b ¼ 24:635ð4Þ, c ¼ 5:0851ð5Þ A, V ¼ 1000:5ð3Þ A ,
T ¼ 105 K, space group P21212 (# 18), Z ¼ 2, ꢁðMo KꢂÞ ¼
ꢁ
1
2
:49 cm , 1395 reflections measured, 924 unique, The final R ¼
:179, GOF ¼ 1:130, Residual electron density = 0.34/ꢁ0:40
A notable feature of the present argon gas penetration into
the ultramicroporous tunnel of the fluoroorganic molecular crys-
tal is the small extent of stabilization of the argon molecule, in
spite of the narrow tunnel width, whereas the unit cell size alter-
ation was started at 150–140 K. Here, the boiling point of argon
0
e A˚ . Crystallographic data reported in this manuscript have been
ꢁ
3
deposited with Cambridge Crystallographic Data Centre as supple-
mentary publication nos. CCDC-246922 and CCDC-256312. Copies
of the data can be obtained free of charge via www.ccdc.cam.ac.uk/
retriving.html (or from the Cambridge Crystallographic Data Centre,
12, Union Road, Cambridge, CB2 1EZ, UK; fax: +44 1223 336033;
or deposit@ccdc.cam.ac.jp).
9
is 87 K. Thus, the crystal stabilizes the argon molecules only at
1
0
5
3–63 K (<1:3 kcal/mol). This small extent of the thermal sta-
bilization would be due to a small van der Waals interaction of
the lattice molecule and destabilization by possible lattice strain.
Moreover, this small stabilization would allow argon molecules
to go deeply into the tight-fitted tunnel-type pore.
9
1
1
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1
1
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4
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2
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4
and mechanisms. We are now studying this phenomenon in
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We thank The Japan Energy Corporation for a fluorinated
Published on the web (Advance View) April 8, 2006; DOI: 10.1246/cl.2006.504