An unprecedentedly huge square-grid copper(II) - Organic framework material built from a bulky pyrene-derived elongated cross-shaped scaffold

Article abstract of DOI:10.1021/ic900786b

A new bulky pyrene-derlved elongated cross-shaped organic scaffold was successfully Incorporated into a highly porous, nonInterpenetrated square-grid copper(II)-organic framework material with the unprecedentedly huge dimensions of 25.5 x 25.5 A², while the layer-to-layer NH ... N Interaction leads to a unique hydrogen-bonded 6⁴.8²-nbo net.

Full text of DOI:10.1021/ic900786b

8650 Inorg. Chem. 2009, 48, 8650–8652
DOI: 10.1021/ic900786b
An Unprecedentedly Huge Square-Grid Copper(II)-Organic Framework Material
Built from a Bulky Pyrene-Derived Elongated Cross-Shaped Scaffold
Chen-Chuan Tsai,† Tzuoo-Tsair Luo,† Jen-Fu Yin,‡ Hong-Cheu Lin,‡ and Kuang-Lieh Lu*,†
†Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan, and ‡Department of Materials Science and
Engineering, National Chiao Tung University, Hsin Chu 300, Taiwan
Received April 23, 2009
A new bulky pyrene-derived elongated cross-shaped organic
scaffold was successfully incorporated into a highly porous, non-
interpenetrated square-grid copper(II)-organic framework materi-
topology, if the building blocks are larger, the resulting
networks will expand: the larger the brick, the wider the
network opening.1c Thus, an intriguing research topic is the
synthesis of giant MOFs from the designed supermolecular
building blocks.4 Compared with the use of large metal
clusters as nodes, the creation of giant MOFs from very large
organic scaffolds is challenging and, therefore, rare.4d In
particular, because the desired highly porous giant MOFs
mainly favor some default nets,5 the organic scaffolds only
prefer high symmetry and high rigidity, even if they are very
bulky. Therefore, the following questions arise. How can the
large organic motifs be employed? To what extent can the
networks be extended? How large are the openings? Can the
degree of interpenetration be adequately controlled? To
develop additional innovative solutions, involving these
future giant MOF materials, the design and synthesis of the
very bulky organic ligands will provide a route to these
wonders, especially to the large aromatic, rigid multicarbox-
ylate ligands.2i
2
˚
al with the unprecedentedly huge dimensions of 25.5ꢀ25.5 A ,
while the layer-to-layer NH N interaction leads to a unique
3 3 3
hydrogen-bonded 64.82-nbo net.
A large number of wonders and advances have been made
possible by the synthesis of porous metal-organic frame-
works (MOFs) because they have a wide array of applica-
tions, ranging from gas storage to catalysis and drug
delivery.1 Thanks to several effective engineering strategies,2
systematic fabrication of porous MOFs can be achieved
through designer assembly from judiciously selected molec-
ular building blocks.3 Conceptually, with regard to network
As part of our ongoing efforts in the design and synthesis
of functional crystalline materials,6 herein we prepared a
bulky elongated cross-shaped dicarboxylate building block,
H2CIP, using a condensation-coupling reaction between 2,7-
di-tert-butylpyrene-4,5,9,10-tetraone and 4-carboxybenzal-
dehyde in the presence of NH4OAc (Scheme 1).7 For the
engineering of MOF materials, to our knowledge, this new
ligand is the longest dicarboxylate scaffold known to date.
The advantages of the ligand are apparent. First, the cross-
shaped skeleton with several aromatic rigid rings is bulky and
highly symmetric. It offers more opportunities to achieve
giant MOFs with default nets.5 Second, the dicarboxylate
*To whom correspondence should be addressed. E-mail: lu@chem.sinica.
edu.tw.
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Poeppelmeier, K. R. Science 2005, 309, 2008.
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Eddaoudi, M.; Kim, J. Science 2003, 423, 705. (b) Desiraju, G. R. Angew.
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given in the Supporting Information.
r
pubs.acs.org/IC
Published on Web 07/30/2009
2009 American Chemical Society

Communication
Inorganic Chemistry, Vol. 48, No. 18, 2009 8651
Scheme 1. Synthesis Route to the H2CIP Ligand
moiety helps to create a neutral framework without anions
inside the extraframework space. Third, the bulky skeleton
can rotate and has functional imidazole rings, which provide
effective hydrogen-bond interactions that control the result-
ing molecular arrangements. We successfully incorporated
CIP2- into a giant 44-sql framework,8,9 which has the foll-
owing empirical formula: {[Cu(CIP)(H2O)] 4H2O 5DMF}n
Figure 1. Ball-and-stick model of a huge square grid in MAS-1 (red =
Cu, green = O, blue = N, light gray = C, and yellow = H).
respectively. Although gridlike MOFs with a 44-sql type
topology are simple,11,12 these materials have useful intrinsic
properties that need to be explored.11a In particular, ex-
panded gridlike networks with very large dimensions (>
3
3
2
12
˚
20 ꢀ 20 A ) are currently limited. All of these networks,
which are nearly cationic, are almost synthesized using long
N,N0-type ligands. To the best of our knowledge, MAS-1 is
the largest porous neutral square-grid coordination network
known to date.
(MAS-1, MAS=Materials of Academia Sinica). Interestingly,
this unique giant MOF consists of square grids with the
2
˚
unprecedentedly large dimensions of 25.5 ꢀ25.5 A
(Figure 1); however, it is still highly porous and noninterpene-
trating.
As a result of the geometric characteristics of the CIP2-
ligand, the grids are virtually planar and noninterpenetrating
(Figure 2). The adjacent layers are stacked in an offset
ABCABC manner, giving rise to two types of openings with
MAS-1 was synthesized by the solvothermal reaction of
CuCl2 2H2O and H2CIP in N,N-dimethylformamide
3
(DMF) at 160 °C for 48 h as green crystals.8 Single-crystal X-
ray diffraction analysis revealed that MAS-1 crystallizes in
the space group C2/m and affords a neutral square-grid
network.10 As depicted in Figure 1, the grid with dimensions
2
˚
effective dimensions of 5ꢀ5 and 2ꢀ2 A , as viewed from
the grid plane (Figure 2a). Another interesting feature of
MAS-1 is that the side-chain groups of the CIP2- ligand can
protrude into the cavities of the adjacent sheets because of the
layer-to-layerNH N hydrogen-bond interactions (N N=
2
˚
of 25.5ꢀ25.5 A (measured between the midpoints of the Cu2
units) is built from paddle-wheel Cu2(CO2)4(H2O)2 clusters
and bulky CIP2- ligands, which act as nodes and linkers,
3 3 3
3 3 3
˚
2.94 A). As shown in Figure 3, the NH N hydrogen-bond
3 3 3
interactions in layers give rise to a unique 64.82-nbo topo-
logy.9 To our knowledge, as of this writing, this type of
hydrogen-bonded 44-sql framework is extremely rare.11e,13
The layers slip along the c axis, with a slipping separation of
(8) Synthesis of MAS-1: A mixture of CuCl2 2H2O (34.7 mg, 0.2 mmol),
3
H2CIP (31.7 mg, 0.05 mmol), and DMF (6 mL) was sealed in a 23-mL
Teflon-lined stainless steel Parr acid digestion bomb, heated at 160 °C for 48
h, and then cooled for 72 h. Green rhombic crystals of MAS-1 were formed in
48% yield (27.8 mg, based on H2CIP). The solid product was washed with
deionized water and ethanol and dried in air. The PXRD patterns of the
samples are in good agreement of the patterns simulated from the single-
crystal diffraction data of MAS-1. Elem anal. Calcd for C55H77CuN9O14: C,
57.35; H, 6.74; N, 10.94. Found: C, 57.38; H, 6.59; N, 11.07. The formula
[Cu(CIP)(H2O)] 4H2O 5DMF was assigned by elemental microanalysis,
˚
11.97 A (one c-axis length). Moreover, rectangular channel
openings with dimensions of 8ꢀ4 A running along the c axis
2
˚
(11) (a) Ruben, M.; Rojo, J.; Romero-Salguero, F. J.; Uppadine, L. H.;
Lehn, J. M. Angew. Chem., Int. Ed. 2004, 43, 3644. (b) Bradshaw, D.; Warren,
J. E.; Rosseinsky, M. J. Science 2007, 315, 977. (c) Halder, G. J.; Kepert, C. J.;
Moubaraki, B.; Murray, K. S.; Cashion, J. D. Science 2002, 298, 1762. (d) Kondo,
A.; Noguchi, H.; Carlucci, L.; Proserpio, D. M.; Ciani, G.; Kajiro, H.; Ohba, T.;
Kanoh, H.; Kaneko, K. J. Am. Chem. Soc. 2007, 129, 12362. (e) Uemura, K.;
Kitagawa, S.; Fukui, K.; Saito, K. J. Am. Chem. Soc. 2004, 126, 3817. (f) Suh,
M. P.; Moon, H. R.; Lee, E. Y.; Jang, S. Y. J. Am. Chem. Soc. 2006, 128, 4710.
(g) Kondo, A.; Noguchi, H.; Ohnishi, S.; Kajiro, H.; Tohdoh, A.; Hattori, Y.; Xu,
W. C.; Tanaka, H.; Kanoh, H.; Kaneko, K. Nano Lett. 2006, 6, 2581.
(12) (a) Biradha, K.; Hongo, Y.; Fujita, M. Angew. Chem., Int. Ed. 2000,
39, 3843. (b) Pschirer, N. G.; Ciurtin, D. M.; Smith, M. D.; Bunz, U. H. F.; zur
Loye, H. C. Angew. Chem., Int. Ed 2002, 41, 583. (c) Ohmura, T.; Usuki, A.;
Fukumori, K.; Ohta, T.; Ito, M.; Tatsumi, K. Inorg. Chem. 2006, 45, 7988.
(d) Carlucci, L.; Ciani, G.; Proserpio, D. M.; Porta, F. CrystEngComm 2005, 7,
78. (e) Ohmori, O.; Kawano, M.; Fujita, M. CrystEngComm 2004, 6, 51. (f) Wu,
C. D.; Lin, W. Inorg. Chem. 2006, 45, 7278. (g) Wu, C. D.; Ma, L.; Lin, W. Inorg.
Chem. 2008, 47, 11447.
3
3
TGA, and single-crystal X-ray diffraction studies.
(9) In order to identify uniquely nets and topologies, Mike O’Keeffe
proposed a three-letter code as the codename for nets (similar to zeolite
names). See: (a) Friedrichs, O. D.; O’Keeffe, M.; Yaghi, O. M. Acta
Crystallogr. 2003, A59, 22. (b) O'Keeffe, M.; Peskov, M. A.; Ramsden, S. J.;
Yaghi, O. M. Acc. Chem. Res. 2008, 41, 1782. Or visit the Reticular Chemistry
Structure Resource (RCSR) website of O'Keeffe at http://rcsr.anu.edu.au/. The
topological analyses were performed using the freely available software TOPOS
(http://www.topos.ssu.samara.ru) and (c) Blatov, V. A. IUCr Compcomm Newsl.
2006, 7, 4.
(10) Crystal data for MAS-1: C40H38CuN4O7 (for [Cu(CIP)-
˚
(H2O)] 2H2O), Mr = 750.28, monoclinic, C2/m, a = 17.214(1) A, b =
3
3
˚
˚
˚
35.418(3) A, c = 11.973(1) A, β = 124.662(4)°, V = 6004.0(8) A , Z = 4,
F
calcd=0.830 g cm-3, μ=0.398 mm-1, F(000)=1564, T=293(2) K. A total of
22 147 reflections were collected in the range of θ=1.15-25.03°, of which
5162 were unique (Rint=0.1027). Final R indices: R1=0.0634, wR2=0.1724
for 2603 reflections [I > 2σ(I)]; R1 = 0.1221, wR2 = 0.1865 for 5162
independent reflections (all data) and 282 parameters, GOF=0.946.
(13) Baburin, I. A.; Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. V.
CrystEngComm 2008, 10, 1822.

8652 Inorganic Chemistry, Vol. 48, No. 18, 2009
Tsai et al.
Figure 3. Simplified stacking diagrams of MAS-1 highlighting (a) the
unique layer-to-layer NH N hydrogen bonds and (b) the distorted
3 3 3
64.82-nbo network topology.
indicated that the peaks, after resolvation, gradually returned
to those characteristic of the as-synthesized compound. The
framework flexibility can beattributedto theunique layer-to-
layer NH N hydrogen bonds.11e
3 3 3
The available porosity of MAS-1 was verified by gas-
sorption studies. A freshly prepared sample of MAS-1 was
activated at 140 °C under vacuum for 16 h, showing a large
weight loss of 35%, as expected. A nitrogen-sorption study
indicated a typical type I isotherm with a Brunauer-Em-
mett-Teller surface area of 389 m2 g-1 and a pore volume of
0.109 cm3 g-1 (using the Dubinin-Radushkevich equation).
In addition, the hydrogen adsorption isotherm indicates
good H2 uptake of 97 cm3 g-1 (0.87 wt %) at 77 K and 1 atm.
In conclusion, we successfully utilized a bulky elongated
cross-shaped dicarboxylate ligand in the preparation of a
highly porous square-grid giant MOF with the unprecedent-
Figure 2. Crystal structures of MAS-1: (a) space-filling representation
of the top view of four square-grid layers showing the distinct openings
with various sizes; (b) view of the stacking nets along the c axis; (c) side
view of the stacking nets.
were apparent (Figure 2b). Seemingly, the ABCABC stack-
ing pattern should reduce the free space in MAS-1,10 but the
calculated density of MAS-1 (in the absence of all guests) is
only 0.79 g cm-3. Analysis using the PLATON14 software
indicated that the extraframework volume per unit cell is
approximately 54.2%. If a long-chain linear ligand is em-
ployed in the creation of extended gridlike MOFs, interpene-
tration frequently occurs.2g,2h Because of the intrinsic
properties of the cross-shaped CIP2- ligand, interpenetration
is not observed in MAS-1, despite the high porosity.
Thermogravimetric analysis (TGA) of MAS-1 indicated a
weight loss of 37% (calcd 38%) during heating from room
temperature to approximately 230 °C, which corresponds to
the loss of four water and five DMF guest molecules. Powder
X-ray diffraction (PXRD) studies imply that the square-grid
layers of MAS-1 are capable of slight slipping with respect to
each other, when the guest molecules are lost (two types of
PXRD patterns were observed at approximately 50 and
150 °C). After desolvation at 200 °C, the PXRD patterns
2
˚
edly large dimensions of 25.5 ꢀ 25.5 A . Because of the
NH N hydrogen bonds in layers, a unique hydrogen-
3 3 3
bonded 64.82-nbo network was formed of a stacking of the
44-sql type layers. This giant MOF has well-ordered micro-
porosity, thus exhibiting good hydrogen-storage efficiency.
The incorporation of this type of bulky organic scaffold into
other potential giant MOF materials remains an interesting,
but challenging, research topic. Furthermore, using a suitable
pillared ligand to replace the coordinated water molecules is
certainly an acceptable approach for preparing a genuine
MOF. Additional studies are currently underway.
Acknowledgment. We thank Academia Sinica and the
National Science Council, Taiwan, for financial support.
Supporting Information Available: Crystallographic details in
CIF format for MAS-1, experimental section, additional pic-
tures, gas sorption, and TGA, PXRD, and IR data. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(14) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7.