J. Am. Chem. Soc. 1998, 120, 8571-8572
8571
Establishing Microporosity in Open Metal-Organic
Frameworks: Gas Sorption Isotherms for Zn(BDC)
BDC ) 1,4-Benzenedicarboxylate)
(
Hailian Li, Mohamed Eddaoudi, Thomas L. Groy, and
O. M. Yaghi*
Department of Chemistry and Biochemistry
Arizona State UniVersity, Tempe, Arizona 85287
ReceiVed May 14, 1998
Construction of microporous metal-organic frameworks by
copolymerization of organic molecules with metal ions has
received widespread attention in recent years, with significant
strides made toward the development of their synthetic and
structural design chemistry.1 Cognizant of the fact that access
to the pores and understanding the inclusion chemistry of these
materials are essential to their ultimate utility, we prepared rigid
frameworks that maintain their structural integrity and porosity
during anion-exchange and guest sorption from solution and in
the absence of guests.2
-4
Although gas sorption isotherm
measurements are often used to confirm and study microporosity
in crystalline zeolites and related molecular sieves, such studies
Figure 1. The building block unit including the asymmetric unit present
in crystalline Zn(BDC)‚(DMF)(H O) with non-hydrogen atoms repre-
2
sented by thermal ellipsoids drawn at the 50% probability level. Atoms
labeled with an additional letter “A, B or C” are symmetrically equivalent
to those atoms without such designation. Atoms of the DMF guest
molecule are labeled with an additional letter “S”.
5
have not been established in the chemistry of open metal-organic
6
frameworks thus leaving unanswered vital questions regarding
the existence of permanent porosity in this class of materials.
Herein, we present the synthesis, structural characterization, and
gas sorption isotherm measurements for the Zn(BDC) microporous
bonded to two zinc atoms in a di-monodentate fashion. Each
zinc is also linked to a terminal water ligand to form an overall
arrangement that is reminiscent of the carboxylate bridged M-M
bonded molecular complexes. Although the Zn-Zn distance
framework of crystalline Zn(BDC)‚(DMF)(H O) (BDC ) 1,4-
2
benzenedicarboxylate and DMF ) N,N′-dimethylformamide).
Slow vapor diffusion at room temperature of triethylamine
(0.05 mL) and toluene (5 mL) into a DMF solution (2 mL)
(
Zn1-Zn1A ) 2.940 (3) Å) is indicative of some M-M
containing a mixture of Zn(NO O (0.073 g, 0.246 mmol)
3
)
2
‚6H
2
9
interaction, it does not represent an actual bond. The structure
extends into the (011) crystallographic plane by having identical
Zn-Zn units linked to remaining carboxylate functionalities of
BDC to yield 2-D microporous layers. These layers are held
together along the a axis by hydrogen-bonding interactions
between water ligands of one layer and carboxylate oxygens of
an adjacent layer as illustrated in a. Stacking of the layers in the
and the acid form of BDC (0.040 g, 0.241 mmol) diluted with
toluene (8 mL) yields colorless prism-shaped crystals that were
O).7 X-ray single-crystal
formulated as Zn(BDC)‚(DMF)(H
2
8
analysis on a sample obtained from the reaction product revealed
an extended open-framework structure composed of the building
unit shown in Figure 1. A total of four carboxylate units of
different, but symmetrically equivalent, BDC building blocks are
(1) (a) Lu, J.; Paliwala, T.; Lim, S. C.; Yu, C.; Niu, T.; Jacobson, A. J.
Inorg. Chem. 1997, 36, 923. (b) Losier, P.; Zaworotko, M. J. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 2779. (c) Gardner, G. B.; Venkataraman, D.; Moore,
J. S.; Lee, S. Nature 1995, 374, 792-795. (d) Yaghi, O. M.; Li, G.; Li, H.
Nature 1995, 378, 703-706. (e) Fujita, M.; Kwon, Y. J.; Sasaki, O.;
Yamaguchi, K.; Ogura, K. J. Am. Chem. Soc. 1995, 117, 7287-7288. (f)
Carlucci, L.; Ciani, G.; Proserpio, D. M.; Sironi, A. J. Chem. Soc., Chem.
Commun. 1994, 2755. (g) Robson, R.; Abrahams, B. F.; Batteen, S. R.; Gable,
R. W.; Hoskins, B. F.; Liu, J. Supramolecular Architecture: Synthetic Control
in Thin Films and Solids; Bein, T., Ed.; American Chemical Society:
Washington, DC, 1992; Chapter 19. (h) Iwamoto, T. in Inclusion Compounds;
Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Eds.: Oxford: New York,
1
991; Vol. 5, p 177. (i) Stein, A.; Keller, S. W.; Mallouk, T. E. Science 1993,
59, 1558-1564. (j) Fagan, P. J.; Ward, M. D. Sci. Am. 1992, 267, 48-54.
crystal leads to a 3-D network having extended 1-D pores of
nearly 5 Å in diameter where DMF guests reside, as shown in
Figure 2. Each DMF guest molecule forms a hydrogen-bonding
2
(
2) Yaghi, O. M.; Li, H. J. Am. Chem. Soc. 1996, 118, 295-296.
(3) Yaghi, O. M.; Davis, C. E.; Li, G.; Li, H. J. Am. Chem. Soc. 1997,
1
19, 2861-2868.
(4) Li, H.; Davis, C. E.; Groy, T. L.; Kelley, D. G.; Yaghi, O. M. J. Am.
(8) Colorless prismatic crystals of Zn(BDC)‚(DMF)(H
at 20 ( 1°C: monoclinic, space group P2 /n with a ) 6.718 (3) Å, b )
15.488 (7) Å, c ) 12.430 (8) Å, â ) 102.83 (4)°, V ) 1261.0 (11) Å , Z )
2
O) were analyzed
Chem. Soc. 1998, 120, 2186-2187.
5) Breck, D. W. Zeolite Molecular SieVes, John Wiley & Sons: New York,
974.
6) Reports on gas sorption isotherms for metal-organic systems have
1
3
(
-
3
-1
1
4, dcalcd ) 1.689 g‚cm and µ (Mo KR) ) 1.970 mm . Data were collected
a
(
on a Siemens R3m/V autodiffractometer using graphite-monochromated Mo
KR radiation and full 1.60° wide ω scans to a maximum of 2θ ) 25.04°,
giving 2508 unique reflections. The structure was solved by direct methods
(SHELXTL PC V. 5.03), and the resulting structural parameters were refined
appeared in the literature for molecular solids such as Werner complexes (a)
and a lithium cobalt cyanide compound (b). A recent report of gas sorption
into a metal-organic extended network suggests microporosity; however, high
pressure (30 atm) conditions were employed, thus prohibiting determination
of surface area and pore volume (c). (a) Allison, S. A.; Barrer, R. M. J. Chem.
Soc. A 1969, 1717-1723. (b) Ramprasad, D.; Pez, G. P.; Toby, B. H.; Markley,
T. J.; Pearlstein, R. M. J. Am. Chem. Soc. 1995, 117, 10694-10701. (c) Kondo,
M.; Yoshitomi, T.; Seki, K.; Matsuzaka, H.; Kitagawa, S. Angew. Chem., Int.
Ed. Engl. 1997, 36, 1725.
by least-squares techniques to a standard discrepancy index R ) 0.0458 and
2
R ) 0.0923 for 2219 reflections with F > 2σ (F) and goodness of fit on F
w
) 1.079. Anisotropic thermal parameters were refined for all non-hydrogen
atoms, and fixed thermal parameters were used for included hydrogens.
2
+
(9) Considering that the mean value for Hg-Hg bonds in coordination
compounds is 2.51 Å, then similar Zn-Zn interactions should be less. Wells,
A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon Press: Oxford, U.K.,
1984; p 1157.
(7) Anal. Calcd for Zn(BDC)‚(DMF)(H
2
6
O) ) C11H13NO Zn: C, 41.21;
H, 4.09; N, 4.37; Zn, 20.39. Found: C, 41.04; H, 4.18; N, 4.52; Zn, 20.33.
S0002-7863(98)01669-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 08/11/1998