Communications
3
12699 unit cell volume). A smaller percent effective free
procedures under the same conditions. These hydrogen
uptake results for 1 and 2 are comparable to H2 storage
capacities of purified single-walled carbon nanotubes and
only slightly inferior to the best MOFs (which have surface
areas of 5–10 times those of 1 and 2).[5,12,13] Methane-
adsorption measurements indicated a room-temperature
volume of 2 compared to 1 is consistent with the presence of
larger benzyloxy groups in 2. The void space of 2 is only
accessible along the c axis by open channels of approximately
1.3 4.5 .
Single-crystal X-ray diffraction studies, TGA, and ele-
mental analyses demonstrated the inclusion of disordered
guest molecules in 1 and 2. Powder X-ray diffraction studies
further indicated that the long-range order of the framework
structures of 1 and 2 was retained upon complete removal of
the guest molecules (see Supporting Information). Permanent
microporosity of 1 and 2 was unambiguously established with
CO2 adsorption measurements at 08C. Samples of 1 and 2
were soaked in CH2Cl2 overnight and then evacuated at 858C
for 12 h before CO2 adsorption measurements. Type 1behav-
ior was observed for the CO2 adsorption isotherms of both 1
and 2, which is characteristic of solids with micropores.
Compounds 1 and 2 possess a BET surface area of 502 and
396 m2 gÀ1, respectively. The micropore volume for 1 is
0.20 mLgÀ1 and for 2 is 0.13 mLgÀ1.[11] Smaller surface area
observed for 2 is consistent with its percent effective free
volume calculated with PLATON.
methane uptake of 11.0 wt% (154 mLgÀ1
) for 1 and
9.5 wt% (133 mLgÀ1) for 2. These methane storage capacities
are lower than those of the best MOFs, which is consistent
with the smaller microporous surface areas of 1 and 2.
Our results agree with an earlier observation that large
surface area and pore volume are not the only recipe for the
attainment of H2 storage materials.[13a] That significant H2
uptake is detected in the highly interpenetrated networks of 1
and 2 points to new directions for the design of efficient H2
storage materials by utilizing interpenetration to strengthen
the interaction between H2 molecules and the framework by
multiple contacts with several aromatic rings from the
interpenetrating networks. Similar to triple-junction sites in
carbon nanotube bundles,[6] such storage sites would have
higher H2 binding energy which is another key to the
development of practical H2 storage materials.
We have examined gas storage behaviors of 1 and 2 at
room temperature. Hydrogen adsorption isotherms were
taken using a pulse mass analyzer[12] in the 0.9–48 bar pressure
range on samples of 1 and 2 that had been heated at 1508C for
1h to remove the included solvent molecules. The H 2 uptakes
are calculated to be 1.12 wt% for 1 and 0.98 wt% for 2 at
48 bar (Figure 2, Table 1), which corresponds to H2 storage
capacity of 124.7 mLgÀ1 for 1 and 109.6 mLgÀ1 for 2.[12] The
In summary, we have synthesized and characterized two
novel fourfold interpenetrated MOFs of cubic topology that
exhibit significant H2 uptake at 258C. The ready tunability of
these MOFs should allow the optimization of both H2 storage
capacity and H2 binding energy in future generations of
MOFs.
H2 uptake of 1 and 2 is reversible for at least six times. For Experimental Section
comparison, MOF-5 reported by Rosi et al.[5] exhibits a H2
1: A mixture of Zn(ClO4)2·6H2O (3.7 mg, 0.01mmol) and L 1-H2
(0.01mmol) was placed in a small vial containing DMF (0.5 mL),
MeOH (0.2 mL), and N,N’-dimethylaniline (5 mL). The vial was
sealed, heated at 508C for 48 h, and allowed to cool to room
temperature. The crystals suitable for X-ray diffraction were collected
by filtration, washed with diethyl ether, and dried in air. Yield: 81%.
Elemental analysis calcd (%) for C135H136Cl6Zn4N6O30, C 57.97, H
4.86, N 3.00; found: C 57.96, H 4.85, N 3.79, IR: n˜ = 3487 (m), 2978
(w), 2924 (w), 1660 (m), 1603 (s), 1552 (m), 1508 (m), 1411 (s), 1373
(m), 1343 (s), 1324 (m), 1213 (w), 1189 (w), 1155 (w), 1088 (m), 1059
(w), 1019 (m), 948 (w), 866 (w), 816 (w), 788 (w), 723 (w), 699 (w),
625 cmÀ1 (w).
uptake of 1.65 wt% (ꢀ 1.5 times that of 1) using our
Carbon dioxide adsorption studies were carried out at 08C on a
Quantachrome-1C surface-area analyzer. Details of hydrogen
adsorption studies were described in ref. [12].
Received: July 6, 2004
Revised: August 12, 2004
Figure 2. Hydrogen adsorption isotherms of 1 and 2 at 258C. The data
points represent averages of six consecutive runs and the error bars
indicate run-to-run variations.
Keywords: coordination networks · crystal engineering ·
.
functional materials · hydrogen storage · zinc
Table 1: Porosity and gas storage capacity of 1 and 2.
Sample Surface area
m2 gÀ1[a]
Pore volume
mLgÀ1[b]
Void
wt% wt%
[1] a) B. Moulton, M. Zaworotko, Chem. Rev. 2001, 101, 1629 –
1658; b) M. Eddaoudi, D. B. Moler, H. Li, B. Chen, T. M.
Reineke, M. OꢀKeeffe, O. M. Yaghi, Acc. Chem. Res. 2001, 34,
319 – 330; c) N. G. Pschirer, D. M. Ciurtin, M. D. Smith, U. H. F.
Bunz, H. C. zur Loye, Angew. Chem. 2002, 114, 603 – 605;
Angew. Chem. Int. Ed. 2002, 41, 583 – 585.
volume %[c] H2
CH4
1
2
502
396
0.20
0.13
46.1
41.4
1.12 11.0
0.98 9.5
[a] Determined from fits of adsorption data to the BET equation.
[b] Calculated using the DR equation. [c] Estimated from PLATON
calculations
[2] a) O. R. Evans, W. Lin, Acc. Chem. Res. 2002, 35, 511 – 522; b) B.
Kesanli, W. Lin, Coord. Chem. Rev. 2003, 246, 305 – 326.
74
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Angew. Chem. Int. Ed. 2005, 44, 72 –75