Journal of the American Chemical Society
Communication
higher than those of 1 (Figure 3 and Table 1). Meanwhile, the
N2, O2, and Ar sorption isotherms of 2 exhibit hysteretic
a nanocage chain structure. The hydrophobic bulky group plays
a vital role in the formation of the novel structure. By changing
the hydrophobicity/hydrophilicity of the solvent mixture for
assembly, reversible transformation between the shish kabob
(2) and discrete nanocages (1) can be achieved. The solvent-
responsive process mimics the stimuli responsiveness of natural
processes, such as micelle formation, protein folding, and
membrane construction. More importantly, the stability and
gas-adsorption capacity of 2 were greatly improved compared
with those of 1. This provides a strategy for the assembly of
coordination nanocages with higher stability and permanent
porosity, which may have general implications in the control of
assembly processes through dimension augmentation.
ASSOCIATED CONTENT
■
S
* Supporting Information
Full details for sample preparation and characterization results,
and crystallographic data (CIF). This material is available free
AUTHOR INFORMATION
■
Corresponding Author
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the U.S. Department of Energy
(DE-SC0001015 and DE-AR0000073), the National Science
Foundation (CBET-0930079), and the Welch Foundation (A-
1725). We are thankful to Dr. Joseph H. Reibenspies and Dr.
George. M. Sheldrick to providing access to SHELXL 2012
software.
Figure 3. The sorption isotherms of N2, O2, H2, Ar at 77 K, and CO2,
CH4 at 195 K, for 1 and 2 (equilibrium time is 5 s for both 1 and 2).
behavior on the desorption-branch with an equilibrium time of
5 s during the measurement. To explore the cause of the
hysteresis, we measured Ar isotherms in different conditions.
The results indicated that the hysteresis loop was effectively
decreased when raising the adsorption temperature from 77 to
87 K. A similar phenomenon was observed when adsorbate was
introduced slowly into the pore by extending the equilibrium
time. However, the hysteresis cannot be completely eliminated
even when the equilibrium time was extended to 20 s (Figure
S9). This type of sorption behavior most likely arises from a
porous structure with small openings connecting large cavities,
leading to the trapping of relatively large gas molecules at low
temperatures.7 At higher temperatures, such as in the cases of
195 and 87 K or when the gas molecules are smaller, as in the
case of hydrogen albeit at 77 K, the hysteresis vanishes,
reminiscent of the adsorption behavior of the mesh-adjustable
molecule sieves.6,7 This phenomenon corroborates well with
the crystal structure, in which the nanocage possesses two types
of openings that are much smaller than the size of the cavity.
More importantly, the enhancement of gas adsorption capacity
of various gases of up to 43 folds (for N2) implies the power of
dimension augmentation. In going from 0D to 1D, the internal
surfaces of the molecular cages became more exposed. It is
tempting to extrapolate this dimension augmentation strategy
further to 2D and 3D; this work is currently under way in our
laboratory.
REFERENCES
■
(1) (a) Eddaoudi, M.; Kim, J.; Wachter, J. B.; Chae, H. K.; O’Keeffe,
M.; Yaghi, O. M. J. Am. Chem. Soc. 2001, 123, 4368. (b) Ghosh, K.;
Hu, J.; White, H. S.; Stang., P. J. J. Am. Chem. Soc. 2009, 131, 6695.
(c) Chen, C.; Zhang, J.; Su, C. Eur. J. Inorg. Chem. 2007, 2997.
(d) Lim, S. H.; Su, Y.; Cohen, S. M. Angew. Chem., Int. Ed. 2012, 51,
5106. (e) Liu, M.; Liao, W.; Hu, C.; Du, S.; Zhang, H. Angew. Chem.,
Int. Ed. 2012, 51, 1585. (f) Sun, Q.-F.; Sato, S.; Fujita, M. Nature
Chem. 2012, 4, 330.
(2) (a) Fer
Dutour, J.; Surble,
́
ey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F.;
S.; Margiolaki, I. Science 2005, 309, 2040. (b) Sun,
́
Q.-F.; Iwasa, J.; Ogawa, D.; Ishido, Y.; Sato, S.; Ozeki, T.; Sei, Y.;
Yamaguchi, K.; Fujita, M. Science 2010, 328, 1144. (c) Abrahams, B. F.;
FitzGerald, N. J.; Robson, R. Angew. Chem., Int. Ed. 2010, 49, 2896.
(d) Wang, Z. J.; Brown, C. J.; Bergman, R. G.; Raymond, K. N.; Toste,
F. D. J. Am. Chem. Soc. 2011, 133, 7358. (e) Mal, P.; Breiner, B.;
Rissanen, K.; Nitschke, J. R. Science 2009, 324, 1697. (f) McManus, G.
J.; Wang, Z.; Zaworotko., M. J. Cryst. Growth Des. 2004, 4, 11.
(3) Seidel, S. R.; Stang., P. J. Acc. Chem. Res. 2002, 35, 972.
(4) (a) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. Rev. 2000, 100,
853. (b) Tranchemontagne, D. J.; Ni, Z.; O’Keeffe, M.; Yaghi, O. M.
Angew. Chem., Int. Ed. 2008, 47, 5136.
(5) Li, J.-R.; Zhou, H.-C. Nat. Chem. 2010, 2, 893.
(6) (a) Ma, S.; Sun, D.; Wang, X.-S.; Zhou, H.-C. Angew. Chem., Int.
Ed. 2007, 46, 2458. (b) Ma, S.; Sun, D.; Yuan, D.; Wang, X.-S.; Zhou,
H.-C. J. Am. Chem. Soc. 2009, 131, 6445.
(7) Zhao, D.; Yuan, D.; Krishna, R.; van Baten, J. M.; Zhou, H.-C.
Chem. Commun. 2010, 46, 7352.
In conclusion, we have presented a shish kabob of nanocages
in which the discrete nanocages are mutually interdigitated by
bulky hydrophobic groups and linked by Cu−O bonds to form
(8) (a) Nagarajan, R.; Ganesh, K. J. Chem. Phys. 1989, 90, 5843.
(b) Alawi, S. M.; Akhter, M. S. J. Mol. Liquids 2011, 160, 63.
17360
dx.doi.org/10.1021/ja306150x | J. Am. Chem. Soc. 2012, 134, 17358−17361