Tailor-made metal-organic frameworks from functionalized molecular building blocks and length-adjustable organic linkers by stepwise synthesis

Article abstract of DOI:10.1002/chem.201200696

In this work, we have demonstrated a family of diamondoid metal-organic frameworks (MOFs) based on functionalized molecular building blocks and length-adjustable organic linkers by using a stepwise synthesis strategy. We have successfully achieved not only design and control to synthesize MOFs, but also the functionalization of both secondary building units (SBUs) and organic linkers in the same MOF for the first time. Furthermore, the results of N₂ and H₂ adsorption show that their surface areas and hydrogen uptake capacities are determined by the most optimal combination of functional groups from SBUs and organic linkers, interpenetration, and free volume in this system. A member of this series, DMOF-6 exhibits the highest surface area and H₂ adsorption capacity among this family of MOFs. Copyright

Full text of DOI:10.1002/chem.201200696

DOI: 10.1002/chem.201200696
Tailor-Made Metal–Organic Frameworks from Functionalized Molecular
Building Blocks and Length-Adjustable Organic Linkers by Stepwise
Synthesis
Ya-Qian Lan,[a, b] Shun-Li Li,[b] Hai-Long Jiang,[a] and Qiang Xu*[a]
Abstract: In this work, we have dem-
onstrated family of diamondoid
building units (SBUs) and organic link-
ers in the same MOF for the first time.
Furthermore, the results of N2 and H2
adsorption show that their surface
areas and hydrogen uptake capacities
are determined by the most optimal
combination of functional groups from
SBUs and organic linkers, interpenetra-
tion, and free volume in this system. A
member of this series, DMOF-6 exhib-
its the highest surface area and H2 ad-
sorption capacity among this family of
MOFs.
a
metal–organic frameworks (MOFs)
based on functionalized molecular
building blocks and length-adjustable
organic linkers by using a stepwise syn-
thesis strategy. We have successfully
achieved not only “design” and “con-
trol” to synthesize MOFs, but also the
functionalization of both secondary
Keywords: adsorption
·
building
blocks · metal–organic frameworks ·
synthetic methods
Introduction
(SBUs),[7] which are theoretically connected by organic link-
ers or metal cations to construct multifunctional MOFs from
predesigned MBBs by using a stepwise synthesis strategy.
However, it is largely limited in the construction of MOFs
due to the difficulties of selecting MBBs and the restriction
of solvothermal synthesis conditions. Hitherto, only a few
MOFs have been observed using this synthesis strategy by
the groups of Zhou, Zaworotko, and Su.[8] They have suc-
cessfully demonstrated some examples from 0D metal–or-
ganic polyhedra (MOP) to 3D MOFs by using predesigned
MBBs, in which the MOPs (tetrahedron,[8a] octahedron,[8b]
trigonal prism,[8c] and cuboctahedron[8d]) act as supramolec-
ular building blocks.
On the other hand, the functionalization of MOFs has at-
tracted ever increasing scientific interest for expanding the
chemical diversity and potential applications. The postsyn-
thetic modification (PSM) approach has made great ach-
ievements in the functionalization of MOFs.[9–11] The most
common is covalent PSM of the organic linkers within the
MOFs. Some discussion of dative PSM is the modification
of unsaturated metal sites located at the SBUs of MOFs
through a dative (i.e., metal–ligand) bond.[9e] However,
there is an unfavorable lack of investigation on the function-
alization of both the organic linker and SBU in the same
MOFs. Moreover, the functional MOFs of PSM often dis-
play poorer crystallinity and single-crystal data cannot be
obtained upon PSM process, which means that the accurate
structures cannot be determined. To overcome these diffi-
culties, it is necessary to introduce a new synthetic strategy.
If we can synthesize functionalized MBBs and combine
them with some ligands that are modified by functional
groups and alterable lengths, we will successfully achieve
the functionalization of MOFs that consist of both the func-
tionalized MBBs and length-adjustable and functional or-
Metal–organic frameworks (MOFs) have been the focus of
great interest due to not only their structural and chemical
diversities but also the potential structure-related applica-
tions, such as luminescence, gas storage, catalysis, separa-
tions, and drug delivery.[1,2] In general, MOFs are assembled
in “one-pot” solvothermal syntheses in which topology con-
trol is accomplished only by careful selection of the metal,
organic linker, and synthetic conditions.[3] Great successes
have been obtained through this simple synthetic route,
which is, however, limited for targeted syntheses and often
uncontrollable. One of the most important goals in the syn-
thesis of MOFs is to achieve “design” and “control” to
obtain tailor-made compounds with expected structures and
properties starting from well-characterized inorganic and or-
ganic precursors.[4] A stepwise synthesis strategy undoubted-
ly may help to shed light on this goal and lead to multifunc-
tional MOFs with special characteristics.
Recently, the molecular building block (MBB) approach
has been a powerful strategy for the design and construction
of MOFs.[5,6] The MBBs can act as secondary building units
[a] Dr. Y.-Q. Lan, Dr. H.-L. Jiang, Prof. Dr. Q. Xu
National Institute of Advanced Industrial Science
and Technology (AIST)
Ikeda, Osaka 563-8577 (Japan)
E-mail: q.xu@aist.go.jp
[b] Dr. Y.-Q. Lan, Dr. S.-L. Li
Faculty of Chemistry
Northeast Normal University
Changchun 130024 (P. R. China)
Supporting information for this article, including PXRD, TG curves
of compounds, additional figures and gas sorption isotherms, is avail-
able on the WWW under http://dx.doi.org/10.1002/chem.201200696.
8076
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FULL PAPER
have the advantage of being readily soluble in some organic
solvents while retaining their original structures according
to previous literature,[4,8a] to ensure the feasibility of the sub-
sequent cluster framework formation. 3) The tetratopic li-
gands with functional groups and adjustable length show tet-
rahedral coordination geometry, which facilitates the forma-
tion of a diamondoid network and functionalization of
MOFs.
Fortunately, we have obtained a family of microporous di-
amondoid MOFs (DMOF-n, n=1–15) (Tables S1 and S2 in
the Supporting Information) based on single-crystal X-ray
structural and PXRD data, which are in agreement with our
prior expectations. To the best of our knowledge, these are
the first examples of MOFs based on functionalized MBBs
and length-extendable and functional organic linkers by
a stepwise synthesis strategy. Moreover, with the increase of
the length of the organic linker, the degrees of interpenetra-
tion have been regulated in the diamondoid topological
MOFs system. The results of N2 and H2 gas adsorption show
that their surface areas and hydrogen uptake capacities are
not linear, but are determined by the most optimal combina-
tion of functional groups, interpenetration, and free volume
in this system.
Scheme 1. Schematic illustration for functionalization of MOFs: a) the
general MOF, b) covalent PSM of the organic linkers, c) the modification
of unsaturated metal sites located at the SBUs of MOFs, and d) function-
alization of both SBUs and organic linkers.
ganic linkers in crystallinity system without using PSM
(Scheme 1). To date, there have been no reports using this
kind of system.
Results and Discussion
Single-crystal X-ray analysis revealed that TMBB-1 or 2
consists of five Zn cations and six deprotonated btz ligands
or their derivatives. The pentanuclear metal cluster shows
a tetrahedral structure, in which four Zn2+ ions are located
at each vertex of the tetrahedron and the fifth Zn2+ ion
inlays the center with distorted octahedral coordination ge-
ometry. Each Zn2+ ion at the apical positions bears a chelat-
ing nitrate or ClÀ group (Figure 1 and Figure S1 in the Sup-
porting Information). Comparison of the experimental
PXRD pattern of as-synthesized TMBB-3 with the simulat-
ed diffraction pattern of TMBB-2, the very high degree of
correspondence between the patterns indicates that the bulk
material has the same structure as TMBB-2 (Figure S23 in
the Supporting Information).
As shown above, we are looking for an ideal system of
a stepwise synthesis of MOFs that can achieve not only
design and control but also the functionalization of both
SBUs and length-adjustable organic ligands while keeping
the same framework topology. The four-connected diamond-
oid network plays an important role in MOFs.[12] Metal–or-
ganic materials first appeared on the scene when it was real-
ized that the geometric features of tetrahedral cations could
be used to design four-connected diamondoid networks[10]
by simply bonding the metal cations to linear bifunctional
organic ligands. We will use the predesigned tetrahedral
MBB (TMBB) and a series of tetratopic ligands with func-
tional groups and adjustable lengths to obtain the function-
alization of a diamondoid MOFs system by using a stepwise
synthesis strategy under solvothermal conditions. After care-
ful consideration, we chose the nanoscale pentanuclear
Isostructural [Zn
(btz)6(L1)
U
5ACHTUNGTRENNUNG(bm-
btz)6(L1)
E
R
ACHTUNGTRENNUNG
(DMOF-3) have been obtained based on TMBB-n and tet-
ratopic ligand H4L1 in DMF. DMOF-1 and DMOF-2 crystal-
lize in the monoclinic space group C2/c and DMOF-3 crys-
metal clusters [Zn
(dme-btz)6Cl4A(H2O)2] (TMBB-2), and [Zn
(H2O)2] (TMBB-3) (btz=benzotriazole, dme-btz=5,6-dime-
5ACHTNUTGERNNU(GN btz)6ACHUTNRTGE(NNU NO3)4ACUTNGHTRN(ENUNG H2O)] (TMBB-1), [Zn5-
A
N
CHTUNGTRENNUNG
¯
A
tallizes in the triclinic space group P1. As expected, all ni-
thylbenzotriazole, me-btz=5-methylbenzotriazole, Figure 1
and Scheme S8 in the Supporting Information) as initial re-
action precursors. We also deliberately designed a series of
tetratopic ligands with functional groups and adjustable
lengths (namely, H4L1, H4L2, H4L3, H4L4, H4L5, and H4L6,
Figure 1 and Scheme S9 in the Supporting Information) as
organic linkers. These precursors and ligands were chosen
based on the following considerations: 1) The tetrahedral
MBBs can be modified by changing the functional groups of
btz to readily obtain functionalized MBBs. 2) The MBBs
trate or ClÀ groups that were bonded to the apical sites of
TMBB-n were replaced by (L1)4À. The asymmetric unit con-
tains one pentanuclear metal cluster (named SBU-n), which
is TMBB-n losing anions, one deprotonated (L1)4À ligand
and one coordinated water molecule. Each SBU is connect-
ed by four carboxylate ligands (L1)4À to be a 4-connected
node, and each (L1)4À connects four SBUs, for which each
carboxylic group binds to one SBU. Such connectivity leads
to a highly porous extended 3D framework with a typically
dia network. Further study into the nature of this architec-
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Figure 1. Stepwise synthesis of MOFs based on functionalized MBBs and length-adjustable organic linkers with functional groups, the single adamanta-
noid cages in DMOF-1, DMOF-8, DMOF-9, and DMOF-13, and the twofold, threefold, and fourfold interpenetration topology in DMOF-1 to 6,
DMOF-7 and 8, and DMOF-9 to 15, respectively.
ture reveals that two types of cages arrange alternately to
form the single network, one is comprised of six SBUs and
four L1 ligands, and the other contains four SBUs and six L1
ligands The spacious nature of the single network allows
other identical dia networks to penetrate it in a normal
mode,[13] thus resulting in twofold interpenetrating dia
arrays (Figure 1 and Figures S2–S5 in the Supporting Infor-
mation).
tional and length-extendable organic linkers. When using
longer H4L4 and H4L6 tetratopic ligands instead of the H4L1
ligand, for which the corresponding length increases from
8.5 to 10.6 and 12.7 ꢁ, respectively (the distance is between
the central C atom and the O atom of carboxyl group,
Scheme S9 in the Supporting Information), DMOF-9 to 11
and DMOF-13 to 15 with the same framework topology
were obtained. As noted previously for DMOF-1, DMOF-9,
DMOF-11, and DMOF-13 all crystallize in the monoclinic
space group C2/c. As anticipated, their structures are com-
The above-mentioned results encouraged us to expand
our studies to construct targeted networks based on func-
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Tailor-Made Metal–Organic Frameworks
FULL PAPER
posed of pentanuclear zinc clusters with different btz ligands
(or its derivatives) that are joined through long deprotonat-
ed (L4)4À and (L6)4À ligands, and again consist of similar dia
frameworks. With the increase in the length of the organic
ligands, the longest dimensions of cages change largely from
35.036 (DMOF-1) to 38.016 (DMOF-9) and 50.348 ꢁ
(DMOF-13) (Figure 1 and Figures S6–8 and S21 in the Sup-
porting Information). Four such independent networks inter-
penetrate to generate a fourfold interpenetrating dia frame-
work architecture in DMOF-9, DMOF-11, and DMOF-13
(Figure S5 in the Supporting Information), which is consis-
tent with the suggestion by Champness, Schçder, and co-
workers that the longer ligands lead to a greater degree of
interpenetration in the same topology.[14] The PXRD data of
DMOF-10 and DMOF-14/15 are in good agreement with
DMOF-9 and DMOF-13, respectively, which demonstrates
that DMOF-10, DMOF-14, and DMOF-15 have the similar
fourfold interpenetrating dia framework as DMOF-9 and
DMOF-13 except the different functional groups of btz (Fig-
ure S24 in the Supporting Information).
except with (L2)4À instead of (L1)4À and the absence of coor-
dinated water molecules (Figure 1 and Figures S11–13 and
S21 in the Supporting Information). Most importantly,
DMOF-5 and 6 have been successfully synthesized with the
functionalization of both SBUs and organic linkers in one
crystalline framework. The successful isolation of these com-
pounds demonstrates a rational strategy for functionaliza-
tion of MOFs, with which we can carefully select and effec-
tively combine different functional groups from SBUs and
organic linkers to synthesize targeted functionalized MOFs.
The PXRD data of DMOF-12 are in good agreement with
DMOF-9, which demonstrates that DMOF-12 has a similar
fourfold interpenetrating dia framework as DMOF-9 except
for the functional methoxy groups (Figure S24 in the Sup-
porting Information).
The family of microporous DMOF-n was successfully ach-
ieved, which proves that we can design and control this
system by using a stepwise synthesis strategy. To further
confirm our viewpoint, as a representative of this system, we
used btz ligands and Zn2+ ions as raw materials instead of
TMBB-1 to synthesize DMOF-1 with the same stoichiome-
try by using a one-pot reaction method. We obtained two
compounds: one was a small amount of DMOF-1, and the
other was 4,6-connected self-penetrating topological MOF-
01. The asymmetric unit of MOF-01 contains three depro-
tonated btz ligands, four Zn atoms and 3/2 deprotonated
(L1)4À ligands. Compared with DMOF-1, the SBU of MOF-
01 consists of three deprotonated btz ligands and four Zn
atoms, which is different from the tetrahedral SBU-1 in
DMOF-1 that contains six deprotonated btz ligands and five
Zn atoms (Figures S14–16 in the Supporting Information).
These experimental results indicate that the stepwise syn-
thetic routes using TMBB can be easily controlled to obtain
the targeted MOFs whereas it is difficult or uncontrollable
with the one-pot reaction method (Figure 2).
When using the similar ligand H4L3 with a naphthyl group
instead of H4L4, DMOF-7 and DMOF-8 [Zn
CHTUNGTRNE(NUNG bme-
15A
btz)18(L3)
3ACHTUNGTRENNUNG(H2O)2] (DMOF-8) were isolated based on
TMBB-1 and TMBB-2. DMOF-8 crystallizes in the chiral
space group C2. The asymmetric unit contains 3/2 pentanu-
clear metal clusters, 3/2 deprotonated (L3)4À ligands and two
coordinated water molecules (Figure 1 and Figures S9 and
S10 in the Supporting Information). The longest dimension
between the centers of the two pentanuclear zinc clusters is
38.685 ꢁ in the dia cages, which is similar to DMOF-9
(38.016 ꢁ) (Figure S21 in the Supporting Information). It is
interesting that DMOF-8 is a threefold interpenetrating dia
network, which is different from the fourfold interpenetra-
tion in DMOF-9 and DMOF-11. The reason may be due to
the larger steric hindrance from the naphthyl group of H4L3
than in H4L4, which is appropriate for the critical condition
of interpenetrating change (Figure S5 in the Supporting In-
formation). The experimental PXRD pattern of as-synthe-
sized DMOF-7 matches the simulated DMOF-8 powder dif-
fraction pattern, indicating that the microcrystal of DMOF-
7 has the same topological structure as DMOF-8 (Figure S24
in the Supporting Information).
The organic linkers H4L2 and H4L5 with functional me-
thoxy groups[15] were used to synthesize functionalized
MOFs.
[Zn
(btz)6(L2)
E
(DMOF-4),
[Zn5ACTHNGUTRENNU(G dme-
btz)6(L2)] (DMOF-5), [Zn
CTHUNGTRENNUNG
DMOF-12 were successfully obtained based on different
TMBBs in the similar solvothermal synthesis conditions as
for DMOF-1. Similar to DMOF-1, isostructural DMOF-4 to
6 all crystallize in the monoclinic space group C2/c and also
have twofold interpenetrating dia frameworks (Figure 1 and
Figure S5 in the Supporting Information). However, the
unit-cell parameters of DMOF-4 are different from those of
DMOF-1; the asymmetric unit of DMOF-4 contains half of
a pentanuclear metal cluster (SBU-1), half of a deprotonated
(L2)4À ligand and one coordinated water molecule. The
asymmetric units of DMOF-5/6 are similar to DMOF-2/3
Figure 2. Stepwise and one-pot reaction methods for the synthesis of
DMOF-n.
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Q. Xu et al.
The common nature of DMOF-n is that only two of the
four hands from the tetratopic ligand link SBUs to form an
infinite helical chain in one single diamondoid net. In two-
fold interpenetrating compounds DMOF-1 to 6, two infinite
helical chains from two individual diamondoid nets with the
same chirality entangle each other to form a double helical
unit (Figure S17 in the Supporting Information). In three-
fold interpenetrating DMOF-8, three infinite helical chains
from individual diamondoid nets show the same chirality
and one chain enwinds simultaneously the other two helical
chains that are arranged in parallel without intertwinement
to form a special triple-stranded helix, which is different
from conventional triple-stranded helices and a molecular
braid reported recently[15] (Figures S18–S20 in the Support-
ing Information). In DMOF-9, DMOF-11, and DMOF-13,
four such helical chains from four individual dia nets are di-
vided into two groups; each group is composed of a pair of
non-intertwined helices of opposite helicity. Two groups of
non-intertwined double helices are interwoven in such
a way that the openings generated by one group of helices
are alternately penetrated by two helices of the other group,
thus resulting in an inextricable quadruple-stranded braid
(Figures S19 and S20 in the Supporting Information). This
peculiar entangled topology in MOFs was only reported re-
cently.[8a]
Furthermore, compared with the size of the adamantanoid
cage in DMOF-n, we find that the degrees of interpenetra-
tion are dependent on the shortest distances of cages, which
are less than 28.972 ꢁ in DMOF-1 to 6 showing a twofold
interpenetrating dia framework, equal to 34.806 ꢁ in
DMOF-8 with threefold interpenetration, and larger than
36.494 ꢁ in DMOF-9, 11, and 13 showing fourfold inter-
penetrating networks (Figures S5 and S21 in the Supporting
Information). Despite the interpenetration, the frameworks
of DMOF-n remain microporous and have free porosities
that are occupied by crystallographically unresolved solvent
molecules. The space-filling models of DMOF-n along the
different directions exhibit those feature of microporous ma-
terials. DMOF-1 has microporous channels (about 4ꢂ8 ꢁ2,
the van der Waals radii are excluded) viewed along the
b axes. The sizes of micropores are approximately 5ꢂ6 and
4ꢂ4/8ꢂ15 ꢁ2 (the van der Waals radii are excluded) in
threefold interpenetrating DMOF-8 and fourfold interpene-
trating DMOF-11/13 viewed along the c-axis, respectively
(Figure S22 in the Supporting Information). PLATON[17]
analysis showed that the highest porosity is 66.4% in
DMOF-1 and the lowest is 49.2% in DMOF-11, owing to
the influence of different functional groups and the degrees
of interpenetration in DMOF-n (Table S3 in the Supporting
Information).
which can be explained by the dynamic feature and cage
effect of the frameworks (Figure 3 and Figures S25–27 in the
Supporting Information).[18] The H2 uptake capacity of two-
fold interpenetrating DMOF-1 to 6 is 1.06, 0.69, 0.88, 0.59,
0.84, and 1.28 wt% (77 K, 1 bar), respectively. The trend of
H2 uptake capacity is consistent with the change of their N2
adsorption amounts and surface areas in DMOF-1 to 6. The
H2 adsorption capacity of DMOF-5 (0.84 wt%) and DMOF-
6 (1.28 wt%) with functional methoxy groups is higher than
DMOF-2 (0.69 wt%) and DMOF-3 (0.88 wt%) without me-
thoxy groups, respectively. The N2 adsorption amount of
DMOF-7 (142.7 cm3 gÀ1) is higher than DMOF-8
(110.5 cm3 gÀ1) in the 3-fold interpenetrating framework,
whereas it presents opposite results in the H2 uptake capaci-
ty (DMOF-8, 1.02 wt% and DMOF-7, 0.84 wt%) (Fig-
ure S28 in the Supporting Information). It is assumed that
methyl groups favor H2 adsorption. The H2 uptake capacity
is 0.55, 0.48, 0.74, and 0.30 wt% in 4-fold interpenetrating
DMOF-9 to 12 based on the similar length of H4L4 and
H4L5, respectively. Relative to their low BET surface areas
(179, 43, 120, and 2 m2 gÀ1), the H2 adsorption capacity is
gratifying, indicating that the catenation is beneficial to H2
loading at low pressure.[19] The H2 gas sorption isotherms for
4-fold interpenetrating DMOF-13 to 15 reveal that the H2
adsorption capacity of 15 (0.98 wt%) is higher than those of
13 (0.89 wt%) and 14 (0.76 wt%), which is consistent with
the change of their surface areas. Among DMOF-n, DMOF-
6 with the functionalization of both SBUs and organic link-
ers exhibits the highest BET and Langmuir surface areas
(971 and 1106 m2 gÀ1), and H2 adsorption amount
(142.9 m3 gÀ1, 1.28 wt%). For the DMOFs constructed from
the organic linkers with the same length, the H2 adsorption
capacity of DMOF based on TMBB-3 with one methyl
group is higher than those based on TMBB-1 and TMBB-2
except for DMOF-3, which is lower than that of DMOF-1.
From the N2 and H2 adsorption results, it is obvious that the
surface areas and hydrogen uptake capacities are deter-
mined by the most optimal combination of functional
groups from SBUs and organic linkers, interpenetration, and
free volume in the system.[20] Bearing this in mind, we may
carefully select and effectively combine functional groups of
SBUs and organic linkers to improve hydrogen uptake (Fig-
ure 3and Table S3 and Figures S25–32 in the Supporting In-
formation).
Conclusion
A family of microporous diamondoid MOFs was synthesized
based on functionalized MBBs and length-extendable organ-
ic linkers with functional groups by using a stepwise synthe-
sis strategy. As expected, we successfully achieved not only
design and control to synthesize the MOFs but also the
functionalization of both SBUs and organic linkers in the
same MOFs for the first time. Moreover, with the increase
in length of the organic linker, the degrees of interpenetra-
tion were regulated with the framework topology remaining
The porosities of DMOF-n make their frameworks possi-
ble for use in gas storage, and provide us with the chance to
study the influence of the functional groups of the MBBs
and organic linkers, and interpenetration on gas storage.
The N2 sorption isotherms of DMOF-n at 77 K show charac-
teristic type I behavior for microporous materials with
a slight hysteresis between the adsorption and desorption,
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Tailor-Made Metal–Organic Frameworks
FULL PAPER
Figure 3. The gas sorption isotherms for DMOF-n at 77 K. a) The H2 gas sorption isotherms for twofold interpenetrating DMOF-1 to 6. b) The N2 and
H2 gas sorption isotherms for threefold interpenetrating DMOF-7 and 8. c) and d) The H2 gas sorption isotherms for fourfold interpenetrating DMOF-9
to 15. The filled and open graphs represent adsorption and desorption branches, respectively.
Synthesis of TMMB-2 [Zn5ACHTNUTRGENN(GU bme-btz)6Cl4CAHTUNGTNERN(UGN H2O)2]: A solution of ZnCl2
unchanged. In addition, the results of N2 and H2 adsorption
show that the surface areas and hydrogen uptake capacities
are determined by the most optimal combination of func-
tional groups, interpenetration, and free volume in the
system. DMOF-6 with the functionalization of both SBUs
and ligands exhibits the highest surface area and H2 adsorp-
tion capacity among this family of MOFs. With the stepwise
synthesis strategy, as a general approach, rational choices of
predesigned MBBs with different geometric polyhedra and
functional organic linkers should lead to the discovery of
abundant targeted porous materials with diverse characteris-
tics in the near future.
(68 mg, 0.5 mmol) and 5,6-dimethylbenzotriazole hydrate (88 mg,
0.6 mmol) in methanol/DMA (1:2, 9 mL) was heated at 1208C for 3 days
in a Teflon-lined steel container. The resulting colorless crystals TMBB-2
were collected, washed with Et2O, and dried at room temperature (yield:
95 mg, 69% based on Zn).
Synthesis of TMMB-3: A solution of ZnCl2 (68 mg, 0.5 mmol) and 5-
methylbenzotriazole (80 mg, 0.6 mmol) in methanol/DMA/H2O (2:2:1,
10 mL) was heated at 1208C for 3 days in a Teflon-lined steel bomb. The
resulting colorless microcrystals were collected, washed with Et2O, and
dried at room temperature (yield: 74 mg, 57% based on Zn).
Synthesis of DMOF-1 [Zn5ACTHUNTGRENNUG ACHUTNGTRENNUGN
(btz)6(L1)(H2O)]: A solid mixture of H4L1
(61.6 mg, 0.10 mmol) and TMBB-1 (130.2 mg, 0.10 mmol) was dissolved
in DMF (5 mL) in a 20 mL Teflon-lined stainless steel container. The
clear reaction solution was heated in an isotherm oven at 858C for 72 h,
resulting in colorless crystals that were isolated by washing with DMF
(5ꢂ5 mL) and were immersed in dichloromethane for 24 h. After the re-
moval of dichloromethane by decanting, the sample was dried under a dy-
namic vacuum at room temperature overnight. Yield: 125.0 mg, 75%
based on H4L1. IR (KBr): n˜ =3447 (m), 2931 (m), 1672 (s), 1602 (s), 1504
(m), 1385 (s), 1303 (m), 1245 (s), 1171 (s), 1094 (s), 1057 (w), 1017 (w),
929 (w), 864 (w), 785 (s), 754 (m), 697 (w), 662 (m), 554 (w), 434 cmÀ1
(w).
Experimental Section
Synthesis of TMMB-1 [Zn
5ACHTUNGTRNEN(UNG btz)6AHCTUNGRETGNN(NU NO3)4ACHTUGNRETNN(UG H2O)]: A solution of [Zn-
ACHTUNGTRENNUNG
methanol/DMA (1:1, 10 mL) was heated at 858C for 3 days in a Teflon-
lined steel container. The resulting colorless crystals were collected,
washed with Et2O, and dried at room temperature (yield: 84.6 mg, 65%
based on Zn).
Synthesis of MOF-01 [Zn8(L1)
0.10 mmol), [Zn(NO3)2·4H2O] (131 mg, 0.5 mmol) and benzotriazole
(69 mg, 0.6 mmol) was dissolved in DMF (5 mL) in a 20 mL Teflon-lined
(btz)6]: A solid mixture of H4L1 (61.6 mg,
3ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
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Q. Xu et al.
stainless steel container. The clear reaction solution was heated in an iso-
therm oven at 858C for 72 h, resulting in two kinds of colorless crystals,
of which one is DMOF-1 and the other is MOF-01.
(bme-btz)6(L1)
Synthesis of DMOF-2 [Zn5ACTHNUTRGENNUG CAHTUNGTERN(NUGN H2O)]: The same synthetic
conditions as those used for the preparation of DMOF-1 were used
except with TMBB-2 instead of TMBB-1. The colorless block crystals
were isolated by washing with DMF and were immersed in dichlorome-
thane for 24 h. After the removal of dichloromethane by decanting, the
sample was dried under a dynamic vacuum at room temperature over-
night. Yield: 106.4 mg, 58% based on H4L1. IR (KBr): n˜ =3859 (w), 3742
(w), 3673 (w), 3649 (w), 3444 (w), 2937 (w), 1867 (w), 1672 (s), 1606 (m),
1541 (m), 1506 (m), 1456 (m), 1390 (s), 1296 (w), 1245 (m), 1199 (w),
1167 (m), 1095 (m), 1001 (w), 854 (s), 782 (m), 663 (s), 495 (s), 464 (s),
419 cmÀ1 (s).
DMF and were immersed in dichloromethane for 24 h. After the removal
of dichloromethane by decanting, the sample was dried under a dynamic
vacuum at room temperature overnight. Yield: 142.4 mg, 69% based on
1 mol of H4L3. IR (KBr): n˜ =3924 (w), 3859 (w), 3742 (m), 3673 (w),
3649 (w), 3591 (m), 3564 (m), 3445 (m), 2976 (s), 2939 (m), 2884 (m),
1671 (s), 1541 (s), 1514 (m), 1456 (s), 1395 (s), 1297 (w), 1262 (m), 1212
(s), 1109 (m), 1025 (w), 944 (w), 856 (w), 824 (w), 765 (w), 672 (w), 644
(w), 495 (m), 418 cmÀ1 (s).
Synthesis of DMOF-9 [Zn5ACTHNUTRGNEUNG
(btz)6(L4)]: The same synthetic conditions as
those used for the preparation of DMOF-1 were used except with H4L4
instead of H4L1. The colorless block crystals were isolated by washing
with DMF and were immersed in dichloromethane for 24 h. After the re-
moval of dichloromethane by decanting, the sample was dried under a dy-
namic vacuum at room temperature overnight. Yield: 147.2 mg, 84%
based on 1 mol of H4L4. IR (KBr): n˜ =3438 (s), 2940 (m), 2882 (m), 1664
(s), 1604 (s), 1508 (s), 1390 (s), 1300 (m), 1236 (s), 1173 (s), 1099 (m),
1031 (w), 987 (w), 834 (w), 782 (w), 750 (m), 643 (w), 555 cmÀ1 (m).
Synthesis of DMOF-3 [Zn5ACTHNUTRGENNUG CAHTUNGTREN(NUGN H2O)]: The same synthetic con-
(me-btz)6(L1)
ditions as those used for the preparation of DMOF-2 were used except
with TMBB-3 instead of TMBB-1. The colorless block crystals were iso-
lated by washing with DMF and were immersed in dichloromethane for
24 h. After the removal of dichloromethane by decanting, the sample was
dried under a dynamic vacuum at room temperature overnight. Yield:
108.5 mg, 62% based on H4L1. IR (KBr): n˜ =3445 (m), 2929 (m), 1672
(s), 1601 (s), 1502 (m), 1386 (s), 1301 (m), 1246 (s), 1198 (s), 1168 (s),
1095 (s), 1057 (m), 1011 (m), 864 (w), 834 (w), 808 (w), 784 (m), 763 (w),
661 (m), 623 (w), 596 (w), 499 (w), 471 cmÀ1 (w).
Synthesis of DMOF-10: The same synthetic conditions as those used for
the preparation of DMOF-2 were used except with H4L4 instead of H4L1.
The colorless microcrystals were isolated by washing with DMF and were
immersed in dichloromethane for 24 h. After the removal of dichlorome-
thane by decanting, the sample was dried under a dynamic vacuum at
room temperature overnight. IR (KBr): n˜ =3438 (m), 2975 (s), 2938 (w),
1671 (s), 1602 (s), 1510 (m), 1429 (s), 1391 (s), 1303 (m), 1237 (s), 1171
(s), 1109 (m), 1003 (w), 826 (m), 785 (w), 747 (w), 641 (w), 497 (m),
465 cmÀ1 (w).
Synthesis of DMOF-4 [Zn5ACTHUNTGRENNUG ACHUTNGTRENNUGN
(btz)6(L2)(H2O)2]: A solid mixture of H4L2
(73.6 mg, 0.10 mmol) and TMBB-1 (130.2 mg, 0.10 mmol) was dissolved
in a mixture of DMF and 1-methyl-2-pyrrolidinone (NMP) (5.0/5.0 mL)
in a 20 mL Teflon-lined stainless steel container. The clear reaction solu-
tion was heated in an isotherm oven at 858C for 72 h, resulting in color-
less crystals, which were isolated by washing with DMF (5ꢂ5 mL) and
were immersed in dichloromethane for 24 h. After the removal of di-
chloromethane by decanting, the sample was dried under a dynamic
vacuum at room temperature overnight. Yield: 146.1 mg, 81% based on
1 mol of H4L2. IR (KBr): n˜ =3742 (w), 3443 (s), 2936 (m), 1672 (s), 1548
(m), 1507 (s), 1454 (s), 1389 (s), 1300 (s), 1265 (s), 1221 (m), 1112 (m),
1017 (w), 929 (w), 784 (m), 754 (m), 662 (w), 555 (w), 471 (w), 425 cmÀ1
(w).
Synthesis of DMOF-11 [Zn5ACTHNUTRGNEUNG
(me-btz)6(L4)]: The same synthetic condi-
tions as those used for the preparation of DMOF-3 were used except
with H4L4 instead of H4L1. The colorless block crystals were isolated by
washing with DMF and were immersed in dichloromethane for 24 h.
After the removal of dichloromethane by decanting, the sample was
dried under a dynamic vacuum at room temperature overnight. Yield:
145.0 mg, 79% based on 1 mol of H4L4. IR (KBr): n˜ =3438 (m), 2970 (s),
2940 (w), 1671 (s), 1603 (s), 1510 (m), 1430 (s), 1391 (s), 1303 (m), 1237
(s), 1171 (s), 1109 (m), 1033 (w), 826 (m), 785 (w), 749 (w), 641 (w),
497 cmÀ1 (m).
Synthesis of DMOF-12: The same synthetic conditions as those used for
the preparation of DMOF-4 were used except with H4L5 instead of H4L2.
The colorless microcrystals were isolated by washing with DMF and were
immersed in dichloromethane for 24 h. After the removal of dichlorome-
thane by decanting, the sample was dried under a dynamic vacuum at
room temperature overnight. IR (KBr): n˜ =3436 (m), 2935 (m), 1670 (s),
1595 (s), 1510 (s), 1448 (s), 1386 (s), 1264 (s), 1201 (s), 1134 (m), 1091
(m), 1026 (m), 850 (w), 814 (w), 783 (w), 751 (m), 719 (w), 642 (w),
555 cmÀ1 (w).
Synthesis of DMOF-5 [Zn5ACTHNUTRGNEUNG
(bme-btz)6(L2)]: The same synthetic condition
as that of DMOF-4 was used except for TMBB-2 instead of TMBB-1.
The colorless block crystals were isolated by washing with DMF and
were immersed in dichloromethane for 24 h. After the removal of di-
chloromethane by decanting, the sample was dried under a dynamic
vacuum at room temperature overnight. Yield: 0153.0 mg, 79% based on
1 mol of H4L2. IR (KBr): n˜ =3429 (s), 2974 (m), 2500 (w), 1663 (s), 1596
(s), 1511 (s), 1461 (s), 1365 (s), 1281 (m), 1264 (s), 1112 (m), 1025 (m),
851 (w), 798 (m), 657 (w), 497 cmÀ1 (w).
Synthesis of DMOF-13 [Zn5ACTHNUTRGENNUG CAHTUNGTREN(NUGN H2O)]: The same synthetic condi-
(btz)6(L6)
Synthesis of DMOF-6 [Zn
N
tions as those used for the preparation of DMOF-4 were used except
with H4L6 instead of H4L2. The colorless block crystals were isolated by
washing with DMF and were immersed in dichloromethane for 24 h.
After the removal of dichloromethane by decanting, the sample was
dried under a dynamic vacuum at room temperature overnight. Yield:
167.5 mg, 85% based on 1 mol of H4L6. IR (KBr): n˜ =3447 (m), 2931
(m), 1672 (s), 1602 (s), 1504 (m), 1390 (s), 1299 (m), 1240 (s), 1174 (s),
1095 (s), 1017 (w), 864 (w), 785 (s), 740 (m), 662 (m), 594 (w), 474 cmÀ1
(w).
as those use for the preparation of DMOF-4 were used except with
TMBB-3 instead of TMBB-1. The colorless block crystals were isolated
by washing with DMF and were immersed in dichloromethane for 24 h.
After the removal of dichloromethane by decanting, the sample was
dried under a dynamic vacuum at room temperature overnight. Yield:
135.2 mg, 62% based on 1 mol of H4L2. IR (KBr): n˜ =3427 (m), 2933
(m), 1665 (s), 1600 (s), 1550 (m), 1509 (m), 1455 (s), 1415 (s), 1384 (s),
1266 (s), 1220 (s), 1110 (m), 1009 (m), 881 (w), 834 (w), 782 (m), 661 (m),
620 (w), 597 (w), 498 (w), 470 (w), 433 cmÀ1 (w).
Synthesis of DMOF-14: The same synthetic conditions as those used for
the preparation of DMOF-5 were used except with H4L6 instead of H4L2.
The colorless block crystals were isolated by washing with DMF and
were immersed in dichloromethane for 24 h. After the removal of di-
chloromethane by decanting, the sample was dried under a dynamic
vacuum at room temperature overnight. IR (KBr): n˜ =3443 (s), 2933 (w),
1672 (s), 1502 (s), 1390 (s), 1299 (s), 1258 (s), 1174 (m), 1095 (m), 853
(w), 783 (w), 659 (m), 469 cmÀ1 (s).
Synthesis of DMOF-7: The same synthetic conditions as those used for
the preparation of DMOF-1 were used except with H4L3 instead of H4L1.
The colorless microcrystals were isolated by washing with DMF and were
immersed in dichloromethane for 24 h. After the removal of dichlorome-
thane by decanting, the sample was dried under a dynamic vacuum at
room temperature overnight. IR (KBr): n˜ =3741 (w), 3443 (m), 3062 (m),
2930 (m), 1672 (s), 1627 (s), 1481 (s), 1382 (s), 1256 (s), 1209 (s), 1090
(m), 1026 (m), 866 (w), 783 (m), 750 (s), 650 (w), 553 (w), 474 cmÀ1 (w).
(bme-btz)18(L3)3
Synthesis of DMOF-8 [Zn15ACTHNUGTRENNUG AHCTUNGTRNE(NUNG H2O)2]: The same synthetic
conditions as those used for the preparation of DMOF-2 were used
except with H4L3 instead of H4L1 and N,N-diethylformamide (DEF) in-
stead of DMF. The colorless block crystals were isolated by washing with
Synthesis of DMOF-15: The same synthetic conditions as those used for
the preparation of DMOF-6 were used except with H4L6 instead of H4L2.
The colorless microcrystals were isolated by washing with DMF and were
immersed in dichloromethane for 24 h. After the removal of dichlorome-
thane by decanting, the sample was dried under a dynamic vacuum at
8082
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 8076 – 8083

Tailor-Made Metal–Organic Frameworks
FULL PAPER
room temperature overnight. IR (KBr): n˜ =3419 (m), 2935 (w), 1634 (s),
1497 (s), 1398 (s), 1267 (s), 1240 (s), 1187 (s), 1012 (s), 863 (w), 834 (m),
808 (w), 784 (m), 740 (w), 594 (m), 474 cmÀ1 (m).
Bu, J. Am. Chem. Soc. 2010, 132, 17062–17064; j) B. Zheng, J. Bai,
J. Duan, L. Wojtas, M. J. Zaworotko, J. Am. Chem. Soc. 2011, 133,
748–751; k) G. Xu, X. Zhang, P. Guo, C. Pan, H. Zhang, C. Wang, J.
Am. Chem. Soc. 2010, 132, 3656–3657.
X-ray crystallography: Single-crystal X-ray data of TMBB-1, TMBB-2,
and DMOF-1, 2, 3, 4, 5, 6, 8, 9, 11, 13, and MOF-01 were recorded by
using a Bruker Apex CCD diffractometer with graphite-monochromated
MoKa radiation (l=0.71073 ꢁ) at T=293 K. Absorption corrections
were applied by using a multiscan technique. All the structures were
solved by the direct method of SHELXS-97 and refined by full-matrix
least-squares techniques using the SHELXL-97 program within WINGX.
The solvent molecules are highly disordered, and attempts to locate and
refine the solvent peaks were unsuccessful. Contributions to scattering
due to these solvent molecules were removed using the SQUEEZE rou-
tine of PLATON; structures were then refined again using the data gen-
erated. Crystal data are summarized in Table S1 in the Supporting Infor-
mation. CCDC-854810 (TMBB-1), CCDC-854811 (TMBB-2), CCDC-
854812 (DMOF-1), CCDC-854813 (DMOF-2), CCDC-854814 (DMOF-
3), CCDC-854815 (DMOF-4), CCDC-854816 (DMOF-5), CCDC-854817
(DMOF-6), CCDC-854818 (DMOF-8), CCDC-854819 (DMOF-9),
CCDC-854820 (DMOF-11), CCDC-854821 (DMOF-13) and CCDC-
854822 (MOF-01) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
[3] a) B. J. Burnett, P. M. Barron, C. Hu, W. Choe, J. Am. Chem. Soc.
2011, 133, 9984–9987; b) Z. Zhang, S. Xiang, Y. S. Chen, S. Ma, Y.
Lee, T. Phely-Bobin, B. Chen, Inorg. Chem. 2010, 49, 8444–8448.
[4] Y. L. Bai, J. Tao, R.-B. Huang, L.-S. Zheng, Angew. Chem. 2008,
120, 5424–5427; Angew. Chem. Int. Ed. 2008, 47, 5344–5347.
[5] J. D. Wuest, Chem. Commun. 2005, 5830–5837.
[6] a) M. W. Hosseini, CrystEngComm 2004, 6, 318–322; b) M. W. Hos-
seini, Acc. Chem. Res. 2005, 38, 313–323.
[7] a) M. Eddaoudi, D. B. Moler, H. Li, B. Chen, T. M. Reineke, M.
OꢃKeeffe, O. M. Yaghi, Acc. Chem. Res. 2001, 34, 319–330; b) O. M.
Yaghi, M. OꢃKeeffe, N. W. Ockwig, H. K. Chae, M. Eddaoudi, J.
Kim, Nature 2003, 423, 705–714.
[8] a) X. L. Wang, C. Qin, S. X. Wu, K. Z. Shao, Y. Q. Lan, S. Wang,
D. X. Zhu, Z. M. Su, E. B. Wang, Angew. Chem. 2009, 121, 5395–
5399; Angew. Chem. Int. Ed. 2009, 48, 5291–5295; b) J. R. Li, D. J.
Timmons, H. C. Zhou, J. Am. Chem. Soc. 2009, 131, 6368–6369;
c) A. Schoedel, L. Wojtas, S. P. Kelley, R. D. Rogers, M. Eddaoudi,
M. J. Zaworotko, Angew. Chem. 2011, 123, 11623–11626; Angew.
Chem. Int. Ed. 2011, 50, 11421–11424; d) H. N. Wang, X. Meng,
G. S. Yang, X. L. Wang, K. Z. Shao, Z. M. Su, C. G. Wang, Chem.
Commun. 2011, 47, 7128–7130.
[9] a) Z. Wang, S. M. Cohen, Chem. Soc. Rev. 2009, 38, 1315–1329;
b) K. K. Tanabe, S. M. Cohen, Chem. Soc. Rev. 2011, 40, 498–519;
c) S. M. Cohen, Chem. Sci. 2010, 1, 32–36; d) Y.-F. Song, L. Cronin,
Angew. Chem. 2008, 120, 4713–4715; Angew. Chem. Int. Ed. 2008,
47, 4635–4637; e) S. M. Cohen, Chem. Rev. 2012, 112, 970–1000.
[10] B. F. Hoskins, R. Robson, J. Am. Chem. Soc. 1990, 112, 1546–1554.
[11] Y.-H. Kiang, G. B. Gardner, S. Lee, Z. Xu, E. Lobkovsky, J. Am.
Chem. Soc. 1999, 121, 8204–8205.
Acknowledgements
We gratefully thank the AIST and JSPS for financial support. Y.Q.L.
thanks the JSPS for a postdoctoral fellowship.
[12] M. J. Zaworotko, Nat. Chem. 2009, 1, 267–268.
[13] S. R. Batten, R. Robson, Angew. Chem. 1998, 110, 1558–1595;
Angew. Chem. Int. Ed. 1998, 37, 1460–1494.
[14] A. J. Blake, N. R. Champness, S. S. M. Chung, W. S. Li, M. Schrçder,
Chem. Commun. 1997, 1005–1006.
[15] Y.-Q. Lan, H.-L. Jiang, S.-L. Li, Q. Xu, Adv. Mater. 2011, 23, 5015–
5020.
[16] X.-J. Luan, Y.-Y. Wang, D.-S. Li, P. Liu, H.-M. Hu, Q.-Z. Shi, S.-M.
Peng, Angew. Chem. 2005, 117, 3932–3935; Angew. Chem. Int. Ed.
2005, 44, 3864–3867.
[1] a) M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M.
OꢃKeeffe, O. M. Yaghi, Science 2002, 295, 469–472; b) G. Fꢄrey, C.
Mellot-Draznieks, C. Serre, F. Millange, Acc. Chem. Res. 2005, 38,
217–225; c) S. Kitagawa, R. Kitaura, S. Noro, Angew. Chem. 2004,
116, 2388–2430; Angew. Chem. Int. Ed. 2004, 43, 2334–2375; d) K.
Otsubo, Y. Wakabayashi, J. Ohara, S. Yamamoto, H. Matsuzaki, H.
Okamoto, K. Nitta, T. Uruga, H. Kitagawa, Nat. Mater. 2011, 10,
291–295; e) J. R. Li, H.-C. Zhou, Nat. Chem. 2010, 2, 893–898;
f) D. J. Lun, G. I. N. Waterhouse, S. G. Telfer, J. Am. Chem. Soc.
2011, 133, 5806–5809.
[2] a) J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon, K. Kim,
Nature 2000, 404, 982–986; b) L. Pan, D. H. Olson, L. R. Ciemno-
lonski, R. Heddy, J. Li, Angew. Chem. 2006, 118, 632–635; Angew.
Chem. Int. Ed. 2006, 45, 616–619; c) A. M. Shultz, O. K. Farha, J. T.
Hupp, S. T. Nguyen, J. Am. Chem. Soc. 2009, 131, 4204–4205;
d) Y. E. Cheon, M. P. Suh, Angew. Chem. 2009, 121, 2943–2947;
Angew. Chem. Int. Ed. 2009, 48, 2899–2903; e) H. L. Jiang, Q. Xu,
Chem. Commun. 2011, 47, 3351–3370; f) H. Kitagawa, Nat. Chem.
2009, 1, 689–690; g) B. Chen, S. Xiang, G. Qian, Acc. Chem. Res.
2010, 43, 1115–1124; h) R. E. Morris, X. Bu, Nat. Chem. 2010, 2,
353–361; i) S.-T. Zheng, J. T. Bu, Y. Li, T. Wu, F. Zuo, P. Feng, X.
[17] A. L. Spek, J. Appl. Crystallogr. 2003, 36, 7–13.
[18] J. T. Jia, F. X. Sun, Q. R. Fang, X. Q. Liang, K. Cai, Z. Bian, H. J.
Zhao, L. X. Gao, G. S. Zhu, Chem. Commun. 2011, 47, 9167–9169.
[19] J. Sculley, D. Yuan, H.-C. Zhou, Energy Environ. Sci. 2011, 4, 2721–
2735.
[20] H. Deng, C. J. Doonan, H. Furukawa, R. B. Ferreira, J. Towne, C. B.
Knobler, B. Wang, O. M. Yaghi, Science 2010, 327, 846–850.
Received: March 2, 2012
Published online: May 22, 2012
Chem. Eur. J. 2012, 18, 8076 – 8083
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8083