Kagome type extra-large microporous solid based on a paddle-wheel Cu2+ dimer

Article abstract of DOI:10.1039/b806616g

A robust extra-large microporous coordination polymer with a Kagome type structure was synthesized by carboxylate/amine multifunctional ligand with a Cu²⁺ cluster and the hexagonal 1D channels (～15 A) showed type I and IV adsorption isotherms for gas molecules. The Royal Society of Chemistry.

Full text of DOI:10.1039/b806616g

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´
Kagome type extra-large microporous solid based on a paddle-wheel
Cu2+ dimerw
a
Satoshi Horike,z Shinpei Hasegawa,a Daisuke Tanaka,a Masakazu Higuchia and
Susumu Kitagawa*ab
Received (in Cambridge, UK) 21st April 2008, Accepted 10th June 2008
First published as an Advance Article on the web 21st July 2008
DOI: 10.1039/b806616g
A robust extra-large microporous coordination polymer with a
´
Kagome type structure was synthesized by carboxylate/amine
multifunctional ligand with a Cu2+ cluster and the hexagonal 1D
˚
channels (B15 A) showed type I and IV adsorption isotherms
for gas molecules.
Metal–organic coordination polymers with open frameworks
(porous coordination polymers: PCPs) have been an area of
intense research due to their rich structural chemistry and
potential applications in storage, catalysis and separation
processes.1 Generally porous solids with a pore diameter of
less than 2 nm are microporous and those in the range from 2
to 50 nm are mesoporous materials.2 Although the immense
variety of reports on PCPs has been updated in recent years, in
fact, almost all structures cover the microporous region with
pore diameters of less than 1 nm and there are still few
guidelines to create an extra-large microporous or mesoporous
framework with a pore diameter of 41.5 nm, because ligand
extension is often accompanied by thermal unstability or
framework interpenetration. The large micropores with com-
plete crystalline pore walls have been desired because of their
functional significance for high performance catalysis, the
separation of large molecules and also as drug delivery sys-
tems.3 The crystalline extra-large microporous solids have
been limited to inorganic motifs such as silicates or phos-
phates,4 and recently a couple of reports on the creation of
PCPs with large pore diameters have been observed.5
Scheme 1 Preparation of bis(4-carboxy-benzyl)amine (4-bcba-H3).
Conditions: (a) MeOH, 25 1C, 14 h; (b) NaBH3CN, MeOH, 0 1C, 20 h.
by employing the Cu2+ paddle-wheel cluster and a newly
synthesized ligand (4-bcba-H3: bis(4-carboxy-benzyl)amine)
which has two carboxylate groups at the terminal position,
and one aliphatic amine group between the benzoxy groups.
These different coordination groups would react with equa-
torial and axial positions of paddle-wheel type dimer to extend
an open 3D framework. The 4-bcba-H3 was synthesized via
two steps (Scheme 1). 4-(Aminomethyl)benzoic acid in MeOH
was added to a MeOH solution of terephthalaldehydic acid.
Then NaBH3CN was added to an imine product in dehydrated
MeOH at 273 K and after stirring the solution for 20 h, the
4-bcba-H3 was collected with a yield of 85.4%.w
The three-dimensional porous compound, {[Cu(4-bcba-H)]ꢀ
H2O}n (1*H2O) was prepared by reaction of Cu(NO3)2ꢀ
2.5H2O with 4-bcba-H3 and excess Et3N in DMF at room
temperature and obtained as blue hexagonal single crystals.
The crystal structure of 1*H2O around the Cu2+ center is
It is well known that the paddle-wheel type cluster
M2(COO)4 with a bicarboxylate and an N-donor linker
affords 3D porous networks with high thermal stability.6
The coordination geometry of the equatorial and axial posi-
tions of the cluster provides a square grid type open frame-
work with high designability. Herein we present a new
synthetic approach for an extra-large microporous framework
shown in Fig. 1a.y The asymmetric unit consists of one Cu2+
,
4-bcba-H and a guest water molecule. The equatorial position
of the Cu2+ ion in the paddle-wheel cluster is coordinated to
the carboxylate group and the axial position is occupied by N
atoms of the amine group of 4-bcba-H. The ligands are
bending to connect each Cu2+ dimer to form 1D chains along
the c axis and the chains are linked via another carboxy-benzyl
group to construct a robust 3D framework (Fig. 1b). As a
result, the structure of 1*H2O has two kinds of straight 1D
channels which are large and hexagonal with dimensions of
14.3 ꢁ 13.2 A2 and triangular with dimensions of 3.3 ꢁ 4.2 A2,
both along the c axis. This network on the ab plane is a
a Department of Synthetic Chemistry and Biological Chemistry,
Graduate School of Engineering, Kyoto University, Katsura,
Nishikyo-ku, Kyoto 615-8510, Japan.
E-mail: kitagawa@sbchem.kyoto-u.ac.jp; Fax: +75-383-2732;
Tel: +75-383-2734
b Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto
University, 69 Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501,
Japan
Kagome
´
-type structure7 and the pore diameter of B15 A is in
the range of an extra-large micropore. The estimated solvent-
accessible void volume is 63.9% of the total crystal volume by
PLATON program.8
w Electronic supplementary information (ESI) available: Experimental
details, elemental analysis. CCDC reference number 685829. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b806616g
Evacuation procedure at 140 1C for 1*H2O provided the
dehydrated sample of 1. The thermal stability of 1 was checked
z Current address: Department of Chemistry, University of California,
Berkeley, CA 94720-1460, USA. E-mail: horike@berkeley.edu
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Fig. 3 Simulated and observed X-ray powder diffraction patterns of
1 for each temperature (l = 0.8 A).
hexagonal pore acts as a gas accommodation channel. The
pore size distribution of 1, which was calculated by DFT
methods in Fig. 5b, showed a pore diameter of only 15 A
dominating the distribution, which is consistent with the
crystallographic results of large hexagonal 1D channels.w
The adsorption isotherms of guests are dependent on the
shape and intramolecular interaction of the guests at each
temperature. In the case of CO2, the isotherm at 195 K in
Fig. 4b shows a type IV isotherm with no hysteresis loop. The
pore filling with multilayers of adsorptive molecules causes
sharp capillary condensation observed at P/P0 from 0.21 to
0.23 which indicates a narrow distribution of pores in the
mesoscale range. The absence of hysteresis during desorption
is a common feature of materials containing hexagonally
aligned 1-D pores with widths of o40 A.9 For MeOH and
MeCN (Fig. 4c and d) at 298 K, we also have type-IV
isotherms without hysteresis. The relative pressure of capillary
condensation of MeOH (P/P0 = 0.22) is larger than that of
MeCN and the saturated adsorption amount of MeOH is also
larger than for MeCN. The extra-large micropores of 1 with
high crystallinity provide the different adsorption profiles
which are dependent on both the chemical and physical
properties of the guest molecule.
Fig. 1 Crystal structure of 1*H2O showing (a) the coordination
environment around the Cu2+ dimers, (b) the 3D assembled porous
framework along the c axis. Guest waters and H atoms are omitted
and Cu, C, O, N are green, red, gray and blue.
by thermogravimetric analysis (Fig. 2), which revealed a
temperature range (300 to 510 K) of stability with no obser-
vable weight loss. We also measured variable temperature
X-ray powder patterns for 1 (Fig. 3). In the range of 90 to
400 K, the powder patterns show sharp peaks and do not
change at all, matching the simulation from single crystal
X-ray analysis. This indicates that the porous framework
possesses high crystallinity and robustness over a wide range
of temperatures.
We estimated the adsorption property for 1. The N2 iso-
therm at 77 K (Fig. 4a) exhibits a type-I profile, which means
the presence of permanent micropores. The adsorption
amount is 500 mL gꢃ1 (STP) at P/P0=0.9 and the desorption
profile does not show any hysteresis and the BET
(Brunauer–Emmett–Teller) surface area of 1 calculated from
the N2 adsorption isotherm is 1715 m2 gꢃ1 (Fig. 5a).w The
small triangular pore is too narrow to pass gases and only the
In summary, we synthesized a robust, large microporous
coordination polymer with a Kagome type structure consisting
´
of a carboxylate-amine ligand and a Cu2+ paddle-wheel
cluster. This motif could be applied to create a crystalline
guest-accessible space with intermediate region of micro- and
mesoscale chemistry.
Fig. 2 Thermogravimetric analysis of 1 over the temperature range
from 300 to 723 K at a heating rate of b = 5 K minꢃ1
Fig. 4 Adsorption isotherms of 1 for (a) N2 (77 K), (b) CO2 (195 K),
.
(c) MeOH (298 K) and (d) MeCN (298 K).
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Lin, A. J. Blake, C. Wilson, X. Z. Sun, N. R. Champness, M. W.
George, P. Hubberstey, R. Mokaya and M. Schroder, J. Am. Chem.
¨
Soc., 2006, 128, 10745; M. Sabo, A. Henschel, H. Froede, E. Klemm
and S. Kaskel, J. Mater. Chem., 2007, 17, 3827; D. J. Collins and H.
C. Zhou, J. Mater. Chem., 2007, 17, 3154; J. S. Seo, D. Whang, H.
Lee, S. I. Jun, J. Oh, Y. J. Jeon and K. Kim, Nature, 2000, 404, 982;
D. N. Dybtsev, A. L. Nuzhdin, H. Chun, K. P. Bryliakov, E. P.
Talsi, V. P. Fedin and K. Kim, Angew. Chem., Int. Ed., 2006, 45,
916; B. L. Chen, C. D. Liang, J. Yang, D. S. Contreras, Y. L.
Clancy, E. B. Lobkovsky, O. M. Yaghi and S. Dai, Angew. Chem.,
Int. Ed., 2006, 45, 1390.
2 K. S. W. Sing, D. H. Everett, R. A. W. Haul, L. Moscou, R. A.
Pierotti, J. Rouquerol and T. Siemieniewska, Pure Appl. Chem.,
1985, 57, 603.
3 M. E. Davis, Chem.–Eur. J., 1997, 3, 1745; S. Tontisirin and S.
Ernst, Angew. Chem., Int. Ed., 2007, 46, 7304; P. Horcajada, C.
´
Serre, M. Vallet-Regi, M. Sebban, F. Taulelle and G. Ferey, Angew.
Fig. 5 (a) BET plot and (b) DFT/Monte-Carlo differential pore
volume distribution of 1, which were calculated from N2 adsorption
at 77 K.
Chem., Int. Ed., 2006, 45, 5974.
4 C. H. Lin, S. L. Wang and K. H. Lii, J. Am. Chem. Soc., 2001, 123,
4649; J. Liang, J. Y. Li, J. H. Yu, P. Chen, Q. R. Fang, F. X. Sun
and R. R. Xu, Angew. Chem., Int. Ed., 2006, 45, 2546; Y. L. Yang,
N. Li, H. B. Song, H. G. Wang, W. B. Chen and S. H. Xiang, Chem.
Mater., 2007, 19, 1889.
5 Q. R. Fang, G. S. Zhu, Z. Jin, Y. Y. Ji, J. W. Ye, M. Xue, H. Yang,
Y. Wang and S. L. Qiu, Angew. Chem., Int. Ed., 2007, 46, 6638; X.
S. Wang, S. Q. Ma, D. F. Sun, S. Parkin and H. C. Zhou, J. Am.
Chem. Soc., 2006, 128, 16474; Y. K. Park, S. B. Choi, H. Kim, K.
Kim, B. H. Won, K. Choi, J. S. Choi, W. S. Ahn, N. Won, S. Kim,
D. H. Jung, S. H. Choi, G. H. Kim, S. S. Cha, Y. H. Jhon, J. K.
Yang and J. Kim, Angew. Chem., Int. Ed., 2007, 46, 8230.
6 K. Seki, Chem. Commun., 2001, 1496; D. N. Dybtsev, H. Chun and
K. Kim, Angew. Chem., Int. Ed., 2004, 43, 5033.
We thank Prof. Yoshiki Kubota for measurement of XRPD
at BL02B2 line at SPring-8, Hyogo, Japan. This work was
supported by ERATO, JST and a Grant-in-Aid for Scientific
Research in a Priority Area ‘‘Chemistry of Coordination
Space’’ (#434) from the Ministry of Education, Culture,
Sports, Science and Technology, Government of Japan.
Notes and references
y Crystal data for 1*H2O: C16H15CuNO5, FW = 364.84, trigonal,
space group R3, a = 41.28(2) A, c = 9.864(4) A, V = 14556.3(115) A ,
3
ꢀ
Z = 18, reflections collected: 56084, independent reflections: 7391, T =
223 K, Dc = 0.745 g cmꢃ1; final R indices [I 4 2s(I)]: R1 = 0.0830,
wR2 = 0.1480, GOF = 0.903. CCDC 685829. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b806616g
7 B. Moulton, J. J. Lu, R. Hajndl, S. Hariharan and M. J. Zaworotko,
Angew. Chem., Int. Ed., 2002, 41, 2821; D. G. Nocera, B. M.
Bartlett, D. Grohol, D. Papoutsakis and M. P. Shores, Chem.–Eur.
J., 2004, 10, 3851; J. A. Brant, Y. L. Liu, D. F. Sava, D. Beauchamp
and M. Eddaoudi, J. Mol. Struct., 2006, 796, 160.
1 G. Fe
´
rey, Chem. Soc. Rev., 2008, 37, 191; A. R. Millward and O. M.
Yaghi, J. Am. Chem. Soc., 2005, 127, 17998; S. Kitagawa, R.
Kitaura and S. Noro, Angew. Chem., Int. Ed., 2004, 43, 2334; X.
8 A. L. Spek, J. Appl. Crystallogr., 2003, 36, 7.
´
9 A. P. Cote, A. I. Benin, N. W. Ockwig, M. O’Keeffe, A. J. Matzger
and O. M. Yaghi, Science, 2005, 310, 1166.
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4438 | Chem. Commun., 2008, 4436–4438