Hydrogen storage in a potassium-ion-bound metal-organic framework incorporating crown ether struts as specific cation binding sites

Article abstract of DOI:10.1002/anie.201404265

To develop a metal-organic framework (MOF) for hydrogen storage, SNU-200 incorporating a 18-crown-6 ether moiety as a specific binding site for selected cations has been synthesized. SNU-200 binds K⁺, NH₄ ⁺, and methyl viologen(MV²⁺) through single-crystal to single-crystal transformations. It exhibits characteristic gas-sorption properties depending on the bound cation. SNU-200 activated with supercritical CO₂ shows a higher isosteric heat (Q_st) of H₂ adsorption (7.70 kJ mol^-1) than other zinc-based MOFs. Among the cation inclusions, K⁺ is the best for enhancing the isosteric heat of the H₂ adsorption (9.92 kJ mol^-1) as a result of the accessible open metal sites on the K⁺ ion. Crown ethers strut their stuff: The metal-organic framework SNU-200 incorporates 18-crown-6 moieties as a cation binding site. SNU-200 binds K⁺, NH₄⁺, and methyl viologen²⁺ (MV²⁺) and their counteranions. Its gas sorption properties depend on the bound cation. The K⁺/SCN ^- bound SNU-200 shows the highest isosteric heat (9.92 kJ mol ^-1) of H₂ adsorption, a result of the open metal sites on the K⁺ ions.

Full text of DOI:10.1002/anie.201404265

Angewandte
Chemie
DOI: 10.1002/anie.201404265
Metal–Organic Frameworks
Hot Paper
Hydrogen Storage in a Potassium-Ion-Bound Metal–Organic
Framework Incorporating Crown Ether Struts as Specific Cation
Binding Sites**
Dae-Woon Lim, Seung An Chyun, and Myunghyun Paik Suh*
Abstract: To develop a metal–organic framework (MOF) for
hydrogen storage, SNU-200 incorporating a 18-crown-6 ether
moiety as a specific binding site for selected cations has been
size and shape,[6] functionalization of the ligands,[7] and
creation of vacant coordination sites on metal ions[8] have
been conducted. The introduction of a guest-specific binding
site or active domain has proven to be difficult, and there has
been only one report to date, a pseudorotaxane-type MOF.[9]
The MOF had organic struts attaching a 34- or 36-membered
macrocyclic polyether pendant and it bound a paraquat
dication (PQT2+) guest by host–guest interactions. We
previously revealed that the inclusion of specific guest
molecules, 18-crown-6 and 15-crown-5, in the pores of
a MOF provided an electrostatic field to enhance the binding
energy of the H2 gas molecules.[10] In addition, the impregna-
tion of cations in a MOF has been shown to increase the gas-
storage properties of the MOF.[2b] However, the selective
inclusion of a desired cation in a MOF is still a challenging
problem.
synthesized. SNU-200 binds K+, NH4 , and methyl viologen-
+
(MV2+) through single-crystal to single-crystal transforma-
tions. It exhibits characteristic gas-sorption properties depend-
ing on the bound cation. SNU-200 activated with supercritical
CO2 shows a higher isosteric heat (Qst) of H2 adsorption
(7.70 kJmolÀ1) than other zinc-based MOFs. Among the
cation inclusions, K+ is the best for enhancing the isosteric
heat of the H2 adsorption (9.92 kJmolÀ1) as a result of the
accessible open metal sites on the K+ ion.
M
etal–organic frameworks (MOFs) have attracted consid-
erable attention because of their various potential applica-
tions such as hydrogen storage,[1] carbon dioxide capture,[2]
gas separation,[3] catalysis,[4] and fabrication of nanoparti-
cles.[5] In particular, MOFs have been considered to be
candidate materials for hydrogen storage, even though their
practical applications are still limited as a result of unsolved
problems, such as low gas-storage capacity at ambient
temperature and low stability against water. To enhance H2-
storage capacities of MOFs at ambient temperature, the
interaction energies between the frameworks and H2 gas
molecules should be increased. In general, MOFs interact
with the guest molecules included in the pores through weak
nonspecific interactions. To generate size-selective guest-
binding properties or to induce strong interactions with the
gas adsorbate, studies involving the control of pore aperture
Herein, we report a MOF incorporating a 18-crown-6
(18Cr6) moiety as
OH)2(TBADB-18Cr6)2·4DMF]·13DMF·12H2O (SNU-200;
TBADB-18Cr6 = 4,4’,5,5’-terabenzoic acid dibenzo-18-
a framework component, [Zn5(m3-
crown-6, DMF = N,N-dimethylformamide), which provides
specific guest binding sites for K+, NH4 , and methyl viologen
+
(MV2+) cations. Upon binding of these cations, the MOF
underwent a single-crystal to single-crystal transformation,
and the X-ray crystal structures of the K+ and NH4 bound
+
samples were able to be determined. The structure of the
MV2+ bound MOF was characterized by “locate simulations”
and powder X-ray diffraction (PXRD) patterns. SNU-200 and
the cation bound samples, after activation with supercritical
CO2, adsorb N2 and H2 gases. The gas-sorption properties of
the K+ bound sample were compared with those of SNU-200’
(prime stands for sample activated by using supercritical CO2)
[*] Dr. D.-W. Lim,[++] S. A. Chyun, Prof. M. P. Suh[+]
Department of Chemistry
+
and the NH4 bound MOF as well as the higher charged
Seoul National University
Seoul 151-747 (Republic of Korea)
E-mail: mpsuh@snu.ac.kr
organic cation MV2+ bound MOF. Contrary to the previously
reported MOFs,[11] the surface areas of the cation/counter-
anion guest bound (K+, NH4 , MV2+/ClÀ, SCNÀ) samples do
+
[+] Current address: Department of Chemistry, Hanyang University
Seoul 133-791 (Republic of Korea)
not decrease compared to that of SNU-200’. SNU-200’
exhibits enhanced isosteric heat (Qst) of H2 adsorption
E-mail: mpsuh@Hanyang.ac.kr
compared to common Zn-MOFs.[12] Among K+, NH4 , and
+
[
++] Current address: Neutron Science Division, Korea Atomic Energy
MV2+ bound SNU-200’ analogues, the K+ ion bound MOF
shows the most highly enhanced isosteric heat (Qst) of the H2
adsorption.
Research Institute (KAERI)
Daejeon, 305-353 (Republic of Korea)
E-mail: mpsuh@Hanyang.ac.kr
[**] This work was supported by National Research Foundation of Korea
(NRF) Grant funded by the Korean Government (MEST) (No. 2005-
0093842). We acknowledge the Pohang Accelerator Laboratory
(PAL) for the use of the synchrotron 2D(SMC) beamline. D.-W.L.
acknowledges support by Basic Science Research Fellowship from
Seoul National University.
To our knowledge, this is the first report on the gas-
adsorption properties of a MOF incorporating a crown ether
moiety as the framework component. Although there have
been several reports for the synthesis of rotaxane-type
MOFs,[13] they were incapable of adsorbing any gas molecules.
Colorless crystals of SNU-200 have been synthesized by
heating a mixture of Zn(NO3)2·6H2O and H4TBADB-18Cr6
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201404265.
Angew. Chem. Int. Ed. 2014, 53, 7819 –7822
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
7819

.
Angewandte
Communications
made of the six oxygen atoms
of 18Cr6 and it is coordinated
with two water molecules at
the axial sites (Figure 2, Fig-
ure S4).[15] In addition, one
SCNÀ ion replaces two DMF
molecules and one carboxy
oxygen atom coordinated at
Zn1 of the pristine MOF,
which alters the coordination
geometry of Zn1 from octahe-
dral to tetrahedral []N-Zn1-
O, av. 111.46 (0.13); ]O-Zn1-
O, av. 107.66 (0.19)] (Fig-
ure S1). The SCNÀ coordi-
nates to Zn1 through a N
atom as confirmed by a nCN
Figure 1. Synthesis and X-ray single crystal structure of doubly interpenetrated SNU-200. The networks are
represented by two different colors. Hydrogen atoms are omitted for clarity.
in DMF/H2O at 808C for 24 h. The X-ray crystal structure of
SNU-200 exhibits a doubly interpenetrated 3D network
generating 1D channels (8.4 ꢀ) that extend along the c-axis
(Figure 1). In a pore, two 18Cr6 face each other (Figure 2).
There are three crystallographically independent ZnII centers
(Zn1, Zn2, and Zn3), and they are linked by an OHÀ bridge as
well as eight different carboxylates to form a Zn5 cluster unit
with the inversion center at Zn3 (Supporting Information,
Figure S1). The Zn1 and Zn3 have an octahedral coordination
geometry []O-Zn1-O, av. 89.63(4); ]O-Zn3-O, av. 89.85(4)]
and Zn2 has
a tetrahedral geometry []O-Zn2-O, av.
109.66(6)]. The Zn1 atom is coordinated with two DMF
solvent molecules. The solvent-accessible void volume esti-
mated by PLATON is 39.2% of the whole structure.
Thermogravimetric analysis (TGA) data reveal a 41.0%
weight loss at 25–3008C, which corresponds to the loss of all
the coordinated DMF and guest solvent molecules (calcd
41.75% for 13DMF and 12H2O), and no chemical decom-
position up to 3508C (Supporting Information, Figure S2).
To see the specific cation binding in SNU-200, the crystals
of SNU-200 were immersed in DMF solutions of K+SCNÀ
+
(0.1m), NH4 ClÀ (0.01m), and methyl viologen dichloride
(MV2+ 2ClÀ, 0.01m), respectively, at room temperature for
3 days. K+ and NH4 ions have high binding constants for
+
18Cr6.[14] We expected that MV2+ would also interact with
18Cr6 strongly because it is electron deficient. KSCN was
chosen as a K+ source instead of KCl because of the easily
identifiable SCNÀ ion in the IR spectra, which would clearly
indicate if it is coordinated at the metal ion or simply included
in the pores of the MOFs. Furthermore, the solubility of KCl
in DMF was too low (2–7 mmollÀ1) while NH4Cl and
MV2+Cl2 have solubilities high enough to satisfy the reaction
conditions. After immersion, the extra salts included in the
pores of the samples and adsorbed on the surface of the
particles were removed by soaking the resulting crystals in
fresh DMF for 24 h. During the cation inclusion, SNU-200
underwent single-crystal to single-crystal transformations,
and the X-ray crystal structures of [K+ꢀSNU-200·SCNÀ]·G
Figure 2. X-ray single-crystal structures[20] of as-synthesized a) SNU-
200, b) [K+ꢀSNU-200·SCNÀ]·G, and c) [NH4 ꢀSNU-200]·ClÀ·G
+
(G=guest). d) Structure of [MV2+ꢀSNU-200]·2ClÀ·G obtained by
“locate simulation”, which is coincident with its PXRD data. Zn green,
C black, H white, O red, N blue, Cl pale green and S yellow spheres.
The binding sites of DMF molecules, cations, and their counteranions
are highlighted by dashed red boxes. The gray ellipsoids indicate the
location of MV2+ in the MOF.
+
and [NH4 ꢀSNU-200]·ClÀ·G (G, guest solvents) could be
determined.
The X-ray structure of [K+ꢀSNU-200·SCNÀ]·G indicates
that K+ ion is located 0.0764(0.0061) ꢀ above the mean plane
7820 www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 7819 –7822

Angewandte
Chemie
band appearing at 2087 cmÀ1 in the IR spectrum (Figure S3).
On activation of the framework with supercritical CO2 fluid,
two water molecules bound at each K+ ion were removed as
evidenced by the IR spectra (Figure S5).
evidenced by their PXRD patterns, which are highly broad-
ened on exposure to air for 2 h (Figure S7).
To verify the porosity of the samples activated with
supercritical CO2 fluid, the adsorption–desorption isotherms
+
+
In the X-ray structure of [NH4 ꢀSNU-200]·ClÀ·G, the
of [SNU-200’], [K+ꢀSNU-200’·SCNÀ], [NH4 ꢀSNU-
coordination modes of the Zn ions in the Zn5 cluster are the
same as those of SNU-200, and each Zn1 still coordinates two
200’]·ClÀ, and [MV2+ꢀSNU-200’]·2ClÀ were measured for
N2 and H2 gases at various temperatures (Table 1). The N2 gas
sorption isotherms of all samples show a type I curve,
characteristic of the microporous materials (Figure S8). Con-
trary to other common MOFs,[11] the BET surface areas of the
compounds including cations/counteranions are higher than
that of SNU-200. This is because during the activation, the
MOFs incorporating the cation bound 18Cr6 moieties
together with the counteranion inclusions shrink less, than
SNU-200.
+
DMF molecules. The NH4 ion is positioned 1.577 (0.035) ꢀ
+
above the mean plane of 18Cr6. The NH4 ion forms
hydrogen bonds with the oxygen atoms of the crown ether
with an average N–O distance of 2.949 (0.067) ꢀ. The ClÀ
counteranions are found in the channels. The elemental
analysis data indicate that there are 1.09 NH4+ molecules per
18Cr6, implying that all the 18Cr6 moieties in the MOF bind
NH4+ ions.
In [MV2+ꢀSNU-200]·2ClÀ·G, SNU-200 also maintains
single crystallinity after the immersion in a DMF solution of
methyl viologen (ca. 0.01m). However, even with the syn-
chrotron X-ray diffraction data collected at 100 K, the
included methyl viologen species could not be located
because of thermal disorder. Therefore, a “locate simulation”
Low pressure H2 adsorption isotherms were measured at
77 K and 87 K under 1 atm (Figure 3). SNU-200’ uptakes H2
gas up to 1.06 wt% at 77 K and 0.72 wt% at 87 K. It shows the
was performed using
a sorption module of Materials
Studio.[16] The Metropolis Monte Carlo method was chosen
for the calculation of the global minimum locations. Universal
force field (UFF) was selected for the energy calculation, and
the charge equilibration (QEq) method was used for the
calculation of point atomic charges. The results indicate that
MV2+ resides beside the 18-crown-6 moiety of SNU-200
(Figure 2), and a maximum of 4 methyl viologen molecules
could be accommodated per unit cell, that is, one molecule
per formula unit of SNU-200 (Supporting Information).
The powder X-ray diffraction (PXRD) patterns also
indicate that the structure of SNU-200 is maintained even
after the inclusion of KSCN, NH4Cl, and methyl viologen
dichloride inside or near the crown ether moiety (Figure S6).
In particular, the PXRD pattern for the simulated structure of
MV2+ loaded SNU-200 is coincident with the measured
PXRD data of [MV2+ꢀSNU-200]·2ClÀ·G, and the new peaks
at the low-angle regions must correspond to the MV2+ guest
molecules. After activation, however, the PXRD patterns of
SNU-200’ and [MV2+ꢀSNU-200’]·2ClÀ are slightly broad-
ened together with the shift of the (101) peaks to a higher
angle region (Figure S7), indicating shrinkage of the frame-
works. Interestingly, the PXRD patterns for the activated
samples of K+ and NH4+ bound MOFs show better crystalline
properties than the activated SNU-200 and [MV2+ꢀSNU-
200]·2ClÀ. We assume that this occurs because the K+ and
NH4+ ions are bound within the 18Cr6 moieties, which make
the framework more rigid upon activation compared to the
other samples. All activated compounds are air sensitive, as
Figure 3. Gas-adsorption properties of SNU-200’ (black), [K+ꢀSNU-
200’·SCNÀ] (navy), [NH4 ꢀSNU-200’]·ClÀ (green) and [MV2+ꢀSNU-
+
200’]·2ClÀ (red) a) H2 gas sorption isotherms at 77 K (square) and
87 K (triangle). Filled shape: adsorption; open shape: desorption.
b) Isosteric heat (Qst) of H2 adsorption.
enhanced isosteric heat (Qst, 7.70 kJmolÀ1) of the H2 adsorp-
tion compared to those of common Zn-MOFs (4.1–
6.2 kJmolÀ1).[12]
Interestingly,
among
the
samples,
[K+ꢀSNU-200’·SCNÀ] shows the highest H2 uptake capacity,
1.19 wt% at 77 K and 0.78 wt% at 87 K, although its surface
area is smaller than that of [MV2+ꢀSNU-200’]·2ClÀ. The
zero-coverage isosteric heat of the H2 adsorption in
[K+ꢀSNU-200’·SCNÀ], which is estimated from the H2
adsorption isotherms measured at 77 K and 87 K by using
the virial equation, increases to 9.92 kJmolÀ1 from
7.70 kJmolÀ1 of SNU-200’ (Table 1, Figure 3). This enhance-
Table 1: H2 sorption data of SNU-200’ and cation-bound SNU-200’ samples.
Compound
Ratio of cation/18Cr6
SABET [m2 gÀ1
]
H2 uptake [wt%]
Qst of H2 ads. [kJmolÀ1
]
SNU-200’
N/A
736
823
818
935
1.06 (77 K)[d] 0.72 (87 K)[d] 0.26 (298 K)[e]
1.19 (77 K)[d] 0.78 (87 K)[d] 0.28 (298 K)[e]
1.09 (77 K)[d] 0.71 (87 K)[d]
7.70
9.92
6.41
7.62
[K+ꢀSNU-200’·SCNÀ]
0.92[a] (1.00)[c]
1.09[b] (1.00)[c]
0.36[b] (0.50)[c]
[NH4 ꢀSNU-200’]·ClÀ
+
[MV2+ꢀSNU-200’]·2ClÀ
0.86 (77 K)[d] 0.54 (87 K)[d]
[a] Based on the ICP data (found). [b] Based on the elemental analysis data. [c] Theoretical value (molcation/molligand). [d] 1 atm. [e] 70 bar.
Angew. Chem. Int. Ed. 2014, 53, 7819 –7822 ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
7821

.
Angewandte
Communications
ment (by 2.22 kJmolÀ1) by the inclusion of the K+ ion in the
present MOF is much higher than the (by ca. 1.1 kJmolÀ1
[2] a) H.-S. Choi, M. P. Suh, Angew. Chem. 2009, 121, 6997 – 7001;
Angew. Chem. Int. Ed. 2009, 48, 6865 – 6869; b) H. J. Park, M. P.
Suh, Chem. Sci. 2013, 4, 685 – 690; c) D. H. Hong, M. P. Suh,
Chem. Commun. 2012, 48, 9168 – 9170; d) T. K. Kim, M. P. Suh,
Chem. Commun. 2011, 47, 4258 – 4260.
[3] a) H. J. Park, Y. E. Cheon, M. P. Suh, Chem. Eur. J. 2010, 16,
11662 – 11669; b) H. J. Park, M. P. Suh, Chem. Commun. 2010,
46, 610 – 612.
)
previously reported values for the MOFs that included alkali-
metal or alkali-earth-metal ions in the pores, which still
coordinated the solvent molecules.[17] It is comparable to
those of the Li+ based MOFs.[18] The enhancement of the H2
adsorption energy in [K+ꢀSNU-200’·SCNÀ] is attributed to
the K+ ion having accessible open sites that were generated by
the removal of the water molecules bound at K+ ion upon
activation of the sample. Although it was reported that the
type of anions coordinated at the metal center of a MOF
greatly affected the binding energy of the H2 molecule,[1c] an
anion effect on the Qst values is not observed in the present
case. At high pressure (70 bar) and 298 K, the amount
(0.28 wt%) of H2 adsorbed in [K+ꢀSNU-200’·SCNÀ] is
slightly higher than that (0.26 wt%) of SNU-200’ (Fig-
ure S10). The best MOF for hydrogen storage reported to
date, [Ni(HTBC)(4,4’-bpy)], has an H2 uptake capacity of
1.2 wt% at 298 K and 72 bar with the Qst value of
8.8 kJmolÀ1.[19] In this respect, the Qst value of the K+ bound
SNU-200 represents a significant finding. However, further
work must be done to develop MOFs that have both high
hydrogen uptake capacities at 298 K and high Qst values.
To determine the position of an adsorbed H2 molecule in
[K+ꢀSNU-200·SCNÀ], as-synthesized sample, we performed
Grand Canonical Monte Carlo (GCMC) calculations by using
a sorption module of Materials Studio (for detailed informa-
tion, see Supporting Information).[16] The theoretical results
indicate that a H2 molecule is located above the K+ ion in the
crown ether moiety near the metal cluster, while it is
[4] A. Corma, H. Garcia, F. X. L. Xamena, Chem. Rev. 2010, 110,
4606 – 4655.
[5] a) H. R. Moon, D.-W. Lim, M. P. Suh, Chem. Soc. Rev. 2013, 42,
1807 – 1824; b) D.-W. Lim, J. W. Yoon, K. Y. Ryu, M. P. Suh,
Angew. Chem. 2012, 124, 9952 – 9955; Angew. Chem. Int. Ed.
2012, 51, 9814 – 9817; c) Y. E. Cheon, M. P. Suh, Angew. Chem.
2009, 121, 2943 – 2947; Angew. Chem. Int. Ed. 2009, 48, 2899 –
2903.
[6] a) J.-R. Li, R. J. Kuppler, H.-C. Zhou, Chem. Soc. Rev. 2009, 38,
1477 – 1504; b) L. Du, Z. Lu, K. Zheng, J. Wang, X. Zheng, Y.
Pan, X. You, J. Bai, J. Am. Chem. Soc. 2013, 135, 562 – 565.
[7] a) J. L. C. Rowsell, O. M. Yaghi, J. Am. Chem. Soc. 2006, 128,
1304 – 1315; b) K. K. Tanabe, S. M. Cohen, Chem. Soc. Rev. 2011,
40, 498 – 519; c) J. Park, Z. U. Wang, L.-B. Sun, Y.-P. Chen, H.-C.
Zhou, J. Am. Chem. Soc. 2012, 134, 20110 – 20116.
[8] Y.-G. Lee, H. R. Moon, Y. E. Cheon, M. P. Suh, Angew. Chem.
2008, 120, 7855 – 7859; Angew. Chem. Int. Ed. 2008, 47, 7741 –
7745.
ˇ
[9] Q. Li, W. Zhang, O. S. Miljanic, C.-H. Sue, Y.-L. Zhao, L. Liu,
C. B. Knobler, J. F. Stoddart, O. M. Yaghi, Science 2009, 325,
855 – 859.
[10] H. J. Park, M. P. Suh, Chem. Commun. 2012, 48, 3400 – 3402.
[11] a) K. L. Mulfort, O. K. Farha, C. L. Stern, A. A. Sarjeant, J. T.
Hupp, J. Am. Chem. Soc. 2009, 131, 3866 – 3868; b) K. L.
Mulfort, J. T. Hupp, Inorg. Chem. 2008, 47, 7936 – 7938.
[12] a) B. Panella, M. Hirscher, Adv. Mater. 2005, 17, 538 – 541;
b) J. Y. Lee, D. H. Olson, L. Pan, T. J. Emge, J. Li, Adv. Funct.
Mater. 2007, 17, 1255 – 1262; c) W. Zhou, H. Wu, M. R. Hartman,
T. Yildirim, J. Phys. Chem. C 2007, 111, 16131 – 16137; d) Z.
Hulvey, D. A. Sava, J. Eckert, A. K. Cheetham, Inorg. Chem.
2011, 50, 403 – 405.
positioned beside the metal clusters in the NH4 and MV2+
+
bound MOFs (Figure S11).
In conclusion, a MOF incorporating a 18Cr6 crown ether
moiety in the strut provides specific/selective binding sites for
K+, NH4 , and MV2+ ions. Pristine SNU-200’ has a higher
+
[13] a) Q. Li, C.-H. Sue, S. Basu, A. K. Shveyd, W. Zhang, G. Barin,
L. Fang, A. A. Sarjeant, J. F. Stoddart, O. M. Yaghi, Angew.
Chem. 2010, 122, 6903 – 6907; Angew. Chem. Int. Ed. 2010, 49,
6751 – 6755; b) A. Coskun, M. Hmadeh, G. Barin, F. Gꢁndara, Q.
Li, E. Choi, N. L. Strutt, D. B. Cordes, A. M. Z. Slawin, J. F.
Stoddart, J.-P. Sauvage, O. M. Yaghi, Angew. Chem. 2012, 124,
2202 – 2205; Angew. Chem. Int. Ed. 2012, 51, 2160 – 2163; c) Y.-L.
isosteric heat of H2 adsorption than the general Zn type
MOFs. Among the cation/counteranion bound MOFs, the K+
bound MOF exhibits the highest Qst value of H2 adsorption
(9.92 kJmolÀ1) as a result of the accessible open metal sites on
K+, which are generated during activation. This work presents
a significant step forward in tailoring MOFs to accommodate
specific cations, which ultimately enhances the hydrogen-
storage properties of this material.
ˇ
´
Zhao, L. Liu, W. Zhang, C.-H. Sue, Q. Li, O. S. Miljanic, O. M.
Yaghi, J. F. Stoddart, Chem. Eur. J. 2009, 15, 13356 – 13380.
[14] H. K. Frensdorff, J. Am. Chem. Soc. 1971, 93, 600 – 606.
[15] J. W. Steed, Coord. Chem. Rev. 2001, 215, 171 – 221.
[16] Materials Studio v5.5, Accelrys Inc., San Diego, CA, 2010.
[17] F. Nouar, J. Eckert, J. F. Eubank, P. Forster, M. Eddaoudi, J. Am.
Chem. Soc. 2009, 131, 2864 – 2870.
Received: April 12, 2014
Published online: June 18, 2014
[18] a) S. Yang, X. Lin, A. J. Blake, G. S. Walker, P. Hubberstey, N. R.
Champness, M. Schrçder, Nat. Chem. 2009, 1, 487 – 493; b) S.
Yang, G. S. B. Martin, J. J. Titman, A. J. Blake, D. R. Allan, N. R.
Champness, M. Schrçder, Inorg. Chem. 2011, 50, 9374 – 9384.
[19] Y. Li, L. Xie, Y. Liu, R. Yang, X. Li, Inorg. Chem. 2008, 47,
10372 – 10377.
Keywords: cation inclusion · crown ethers · hydrogen storage ·
metal–organic frameworks · potassium ion
.
[1] a) M. P. Suh, H. J. Park, T. K. Prasad, D.-W. Lim, Chem. Rev.
2012, 112, 782 – 835; b) J. Sculley, D. Yuan, H.-C. Zhou, Energy
Environ. Sci. 2011, 4, 2721 – 2735; c) K. Sumida, D. Stuck, L.
Mino, J.-D. Chai, E. D. Bloch, O. Zavorotynska, L. J. Murray, M.
Dinca, S. Chavan, S. Bordiga, M. Head-Gordon, J. R. Long, J.
Am. Chem. Soc. 2013, 135, 1083 – 1091.
[20] CCDC CCDC-920678 (SNU-200), 922626 ([K+ꢀSNU-200·SCN-
+
]·G), and 949494 ([NH4 ꢀSNU-200]·Cl-·G), contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
7822
www.angewandte.org
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2014, 53, 7819 –7822