Achievement of Bulky Homochirality in Zeolitic Imidazolate-Related Frameworks

Article abstract of DOI:10.1021/acs.inorgchem.5b02337

Before this work, adding chiral C centers into zeolitic imidazolate frameworks (ZIFs) has never been realized. Presented here are the first examples on achieving bulky homochirality in ZIF systems, and three homochiral zeolitic imidazolate-related frameworks with sodalite and dia topologies are successfully synthesized by employing enantiopure imidazolate derivatives. The results open a new blueprint on the synthetic design of homochiral ZIFs for future applications.

Full text of DOI:10.1021/acs.inorgchem.5b02337

Communication
pubs.acs.org/IC
Achievement of Bulky Homochirality in Zeolitic Imidazolate-Related
Frameworks
Fei Wang,* Yu-Huan Tang, and Jian Zhang*
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou, Fujian 350002, P. R. China
*
S Supporting Information
and tetrahedral Zn2+ ion under different conditions leads to
structural diversity. Both SOD- and dia-type frameworks have
been obtained. Thus, we report here the details of these HZIrFs,
namely, Zn (5-mtz) [(R)-OH-bim]·DMF (HZIrF-1R; DMF =
ABSTRACT: Before this work, adding chiral C centers
into zeolitic imidazolate frameworks (ZIFs) has never been
realized. Presented here are the first examples on achieving
bulky homochirality in ZIF systems, and three homochiral
zeolitic imidazolate-related frameworks with sodalite and
dia topologies are successfully synthesized by employing
enantiopure imidazolate derivatives. The results open a
new blueprint on the synthetic design of homochiral ZIFs
for future applications.
2
3
N,N-dimethylformamide), Zn (5-mtz) [(S)-OH-bim]·DMF
2
3
(
(
HZIrF-1S), and dia-type Zn (5-mtz) [(R)-OH-bim]·DMF
2 3
HZIrF-2R).
Colorless crystals of HZIrF-1 were solvothermally synthesized
by the self-assembly of Zn(CH COO) ·2H O, 5-Hmtz, and (S)-
3
2
2
OH-bim [or (R)-OH-bim] in a mixed DMF and ethanol solvent.
Both HZIrF-1S and HZIrF-1R crystallize in the space group of
R3 with opposite absolute configuration. In the structure of
HZIrF-1R, each Zn2+ center has tetrahedral geometry and is
coordinated by three N atoms from three 5-mtz ligands and one
N atom from the (R)-OH-bim ligand (Figure 1a). Either the 5-
norganic zeolites and zeolitic metal−organic frameworks
I
(MOFs) have received much attention in recent years owing
to their fascinating tetrahedral structures, high stability, and wide
potential applications in various areas, such as gas adsorption and
mtz or (R)-OH-bim ligand is a μ -linker similar to 2-
2
1
−6
separation, luminescence, catalysis, and so on. Among them,
zeolitic imidazolate frameworks (ZIFs) built from tetrahedrally
methylimidazole in ZIF-8. A similar coordination environment
is presented in HZIrF-1R (Figure 1b). It is notable that the −OH
group in the (R)-OH-bim ligand has weak interactions with the
2
+
2+
2+
coordinated divalent cations (M = Zn or Co ) and
uninegative imidazolate ligands are of special merit in the
2+
6
4
Zn center. A cage (4 ·6 ) substructure consisting of 24 Zn
2
,3
employment of various imidazolate derivatives. It is commonly
known to add a chiral C center in the organic ligand, so that the
homochiral MOFs with such enantiopure ligands may be
generated for special enantioselective applications, which are
atoms, 9 (R)-OH-bim ligands, and 27 5-mtz ligands is observed
(
Figure 1c), which is a typical SOD cage with 4- and 6-membered
8
rings (Figure 1d). The 4-ring windows are blocked by the
substitutes of OH-bim and 5-mtz, just leaving 6-ring windows
with an effective size of about 3.3 Å (Figure S1). Each (R)-OH-
bim bridges two Zn centers, with the Zn···Zn distance being
7
not available with pure inorganic zeolites. Despite the fact that it
is not difficult to make enantiopure imidazolate ligands, so far
homochiral ZIFs based on enantiopure imidazolate ligands have
never been reported.
5
6
.854 Å, and the Zn···Zn distances separated by 5-mtz are from
.084 to 6.170 Å. The bond angle of Zn−OH-bim−Zn is ca. 138°,
In this work, two presynthesized enantiopure imidazolate
derivatives, (S)-2-(1-hydroxyethyl)benzimidazole [(S)-OH-
bim] and (R)-2-(1-hydroxyethyl)benzimidazole [(R)-OH-
bim], have been used to realize a pair of homochiral zeolitic
imidazolate-related frameworks (HZIrFs) with sodalite (SOD)
topology for the first time. The successful achievement of bulky
homochirality and zeotype structures in these HZIrFs is
dependent on not only the addition of a chiral C center to a
benzimidazole ligand but also the help of another 5-
and the bond angles of Zn−mtz−Zn are ca. 153° and 157°. As a
result, both enantiopure and achiral ligands link the tetrahedral
Zn centers into a three-dimensional (3D) framework with SOD
topology (Figure 1e,f). The solvent-accessible volume of ca.
4
4.1% of the crystal volume was found by the PLATON
9
program. These voids were filled by the structurally ordered
DMF molecules.
With additional HBF in the synthesis system of HZIrF-1,
4
another dia-type HZIrF-2R was obtained. This result reveals that
the pH plays an important role in tuning the structures of HZIrFs.
HZIrF-2R crystallizes in monoclinic C2 and shows a 3D open
framework with dia topology. The coordination environment in
HZIrF-2R is very similar to that in HZIrF-1R, where the
tetrahedral Zn centers are connected by the μ -5-mtz and μ -(R)-
4e
methyltetrazole (5-Hmtz) ligand (Scheme 1). Moreover, the
combining assembly of enantiopure OH-bim, achiral 5-Hmtz,
Scheme 1. Strategy on the Synthesis of HZIrFs
2
2
OH-bim ligands (Figure 2a). A typical cage substructure
including 10 Zn atoms, 3 (R)-OH-bim ligands, and 9 5-mtz
Received: October 12, 2015
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.5b02337
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Inorganic Chemistry
Communication
3
The total potential solvent-accessible volume is ca. 910 Å per
unit cell volume, and the pore volume ratio is 32.9%, as calculated
with the PLATON program.
To characterize the porosity of HZIrF-1R and HZIrF-2R,
methanol-exchanged samples were degassed by supercritical
CO , and N gas sorption experiments at 77 K on the activated
2
2
3
samples were measured. For HZIrF-1R, it has only ca. 31 cm /g
N uptake at 77 K (Figure S8), although it has 44.1% of solvent-
2
accessible volume, which may be mainly attributed to the narrow
window size. Further, CO gas sorption experiments at 195 K
2
were also measured, and it exhibits typical type I reversible
3
sorption isotherms and takes up CO2 to 220 cm /g,
corresponding to Langmuir and Brunauer−Emmett−Teller
2
(
BET) surface areas of 1082 and 1026 m /g, respectively (Figure
3
). A single data point at a relative pressure of 0.95 gives a
Figure 1. Coordination environment in HZIrF-1R (a) and HZIrF-1S
(
b). SOD cage of HZIrF-1R (c and d). 3D framework of HZIrF-1R (e)
Figure 3. Sorption isotherms for HZIrF-1R and HZIrF-2R at different
and SOD topology (f) along the c axis.
temperatures. CO uptake for HZIrF-1R at (a) 195, (b) 273, and (c) 293
2
K. N uptake for HZIrF-2R at 77 K (d). Solid symbols represent
2
adsorption, and open symbols represent desorption.
3
maximun pore volume of 0.26 cm /g by the Horvath−Kawazoe
equation. For HZIrF-2R, N gas sorption experiments at 77 K
2
were measured, and it exhibits type I reversible sorption
isotherms with a little hysteresis, corresponding to Langmuir
2
and BET surface areas of 415 and 285 m /g, respectively. A single
data point at a relative pressure of 0.98 gives a maximun pore
3
volume of 0.16 cm /g by the Horvath−Kawazoe equation. The
hysteresis loop of HZIrF-2R existed mainly because the samples
were partly amorphous after being degassed (Figure S7).
The adsorption isotherms of CO for HZIrF-1R were also
2
measured up to 1 bar at 273 and 293 K (Figure 3). The CO
2
3
uptake values were 73 cm /g (3.84 mmol/g) at 273 K and 40
3
cm /g (2.75 mmol/g) at 293 K. In comparison, the CO uptake
2
3
value of the SOD-type MAF-4 was only 29.3 cm /g at the same
conditions. The isosteric heats of adsorption (Q ) for HZIrF-
2c
st
1
R was calculated using the adsorption data collected at 273 and
2
93 K. At zero coverage, the enthalpy of CO adsorption for
2
Figure 2. (a) Coordination environment in HZIrF-2R. (b) Cage in
HZIrF-2R. (c) 3D framework of HZIrF-2R along the c axis. (d) dia
topology of HZIrF-2R.
HZIrF-1R is 23 kJ/mol (Figures S9 and S10), also higher than
that of MAF-4 (14.9 kJ/mol). The results show that the
uncoordinated N-heteroatom sites of tetrazole ligands may
remarkably increase the uptake and enthalpy of CO2.
ligands is presented (Figure 2b). The different spatial arrange-
ments of these ligands around Zn centers make a totally different
framework of HZIrF-2R (Figure 2c,d). The one-dimensional
channels along the c axis are filled by the structurally defined
DMF molecules. The effective window size is about 4.5 × 5.0 Å.
Furthermore, the CO uptake capacity of HZIrF-1R is also
2
higher than that of the currently best-performing ZIF-69 (70
3
2c
cm /g) under the same conditions (273 K and 1 atm).
The enantiopure environments within HZIrF-1R motivated
us to explore its potential for chiral recognition. Considering the
B
DOI: 10.1021/acs.inorgchem.5b02337
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Inorganic Chemistry
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small window size of HZIrF-1R (ca. 3.3 Å) and the rich H-bond
environment of the surface, it can be used to recognize the chiral
molecules, e.g., carvone including carbonyl O atom as theH-bond
acceptor, although carvone molecules can hardly enter the pores.
So, we just used the as-synthesized crystal samples (average size
of 0.1 mm) without guest exchange to do such experiments. A
solution of D-carvone and L-carvone inan ethanol solvent with the
same concentration (10 mol/L) and amount (1.5 mL) was
placed in the cell. Then the same amounts of the as-synthesized
samples of HZIrF-1R were added, and the circular dichroism
21221001 and 21425102), and Chunmiao Project of Haixi
Institute of Chinese Academy of Sciences (Grant CMZX-2015-
001).
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
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Experimental details, TGA diagrams, powder X-ray
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AUTHOR INFORMATION
Corresponding Authors
E-mail: wangfei04@fjirsm.ac.cn.
E-mail: zhj@fjirsm.ac.cn.
Notes
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ACKNOWLEDGMENTS
This work is supported by National Basic Research Program of
China (973 Program; Grant 2012CB821705), NSFC (Grants
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DOI: 10.1021/acs.inorgchem.5b02337
Inorg. Chem. XXXX, XXX, XXX−XXX