Isomer of linker for NU-1000 yields a newshe-type, catalytic, and hierarchically porous, Zr-based metal-organic framework

Article abstract of DOI:10.1039/d0cc07974j

The well-known MOF (metal-organic framework) linker tetrakis(p-benzoate)pyrene (TBAPy^4?) lacks steric hindrance between its benzoates. Changing the 1,3,6,8-siting of benzoates in TBAPy^4?to 4,5,9,10-siting introduces substantial steric hindrance and, in turn, enables the synthesis of a new hierarchically porous,she-type MOF Zr₆(μ₃-O)₄(μ₃-OH)₄(C₆H₅COO)₃(COO)₃(TBAPy-2)_3/2(NU-601), where TBAPy-2^4?is the 4,5,9,10 isomer of TBAPy^4?.NU-601shows high catalytic activity for degradative hydrolysis of a simulant for G-type fluoro-phosphorus nerve agents.

Full text of DOI:10.1039/d0cc07974j

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Isomer of linker for NU-1000 yields a new
she-type, catalytic, and hierarchically porous,
Zr-based metal–organic framework†
Cite this: Chem. Commun., 2021,
7, 3571
5
Received 8th December 2020,
Accepted 15th February 2021
ab
b
b
b
bc
Zhiyong Lu,
*
Rui Wang, Yijun Liao,
Omar K. Farha,
Wentuan Bi,
and
b
bd
b
b
Thomas R. Sheridan, Kun Zhang, Jiaxin Duan, Jian Liu
DOI: 10.1039/d0cc07974j
b
Joseph T. Hupp*
rsc.li/chemcomm
1
3–17
The well-known MOF (metal–organic framework) linker tetrakis zirconium-based MOFs.
Prominent within the group offering
4À
(
p-benzoate)pyrene (TBAPy ) lacks steric hindrance between its benzo- hierarchical porosity are csq-type Zr-MOFs (exemplified by
4À
11,13
10
ates. Changing the 1,3,6,8-siting of benzoates in TBAPy to 4,5,9, PCN-222/MOF-545,
0-siting introduces substantial steric hindrance and, in turn, enables expansions). Beyond those with csq topology, however, the
the synthesis of a new hierarchically porous, she-type MOF Zr (l -O) number and variety of Zr-MOFs presenting interconnected hier-
-OH) (C COO) (COO) (TBAPy-2)3/2 (NU-601), where TBAPy-2 is archical channel structures, are few.
the 4,5,9,10 isomer of TBAPy . NU-601 shows high catalytic activity for
degradative hydrolysis of a simulant for G-type fluoro-phosphorus nerve channels structures, exemplified by a new she-type Zr-MOF,
agents. NU-601.‡ Briefly, shifting the positions of benzoates in the
NU-1000, and their many reticular
1
6
3
4
4À
18
(
l
3
4
6
H
5
3
3
4À
Herein, we present a new way of obtaining hierarchical
4
À
4À
linker TBAPy (1,3,6,8-tetrakis(p-benzoate)pyrene ) from the
Metal–organic frameworks (MOFs) have shown promise for 1,3,6, and 8 carbons of pyrene to 4,5,9, and 10, amplifies ring
applications in gas storage and separations, chemical sensing, steric interactions, increases benzoate/pyrene dihedral angles,
1
–4
and catalysis.
For heterogeneous catalysis, MOFs with hier- and facilitates the formation of hierarchically porous NU-601,
(m -O) (m -OH) (C COO) (HCOO) (TBAPy-2)3/2
where formate and benzoate are displaceable, nonstructural
archical porosity (i.e., interconnected pores of differing size) are with formula Zr
often favoured over those offering pores of only a single size.
6
3
4
3
4
6
H
5
3
3
,
5
–8
Thus, micropores, and associated molecular confinement, can ligands. Notably, the activated, water-equilibrated version of
be advantageous for catalytic selectivity, while mesopores can NU-601 (a 6-connected MOF) exhibits higher catalytic activity
9
facilitate efficient mass transport – the ‘‘highways and byways’’ than 8-connected NU-1000 for hydrolytic degradation of nerve
of molecular-scale porosity. Or, mesopores can serve to host agent simulants.
larger biological moieties like enzymes, with interconnected
In the synthesis of Zr-MOFs, variations in linker structure
micropores size-excluding these same species and thereby and auxiliary ligand structure (remnent synthesis modulators),
providing routes for delivering substrates and removing rather than node structure, tend to provide structural diversity,
1
0–12
products.
6 3 4 3 4
as the majority feature the same Zr (m -O) (m -OH) node. For
Among the most promising as heterogeneous catalysts and tetratopic carboxylate linkers, differences in symmetry and in
as catalyst supports are chemically and thermally robust, the geometry of the connections to inorganic nodes lead to differ-
4À
ences in MOF topology. Taking the linker tetrakis( carboxyphenyl)-
porphyrin (TCPP) in Scheme 1 as an example, a TCPP linker with
a
b
c
19
College of Mechanics and Materials, Hohai University, Nanjing 210098, China.
E-mail: johnlook1987@gmail.com
C2h symmetry will lead to the scu-type NU-902, but a small
variation of the torsion angle between the terminal benzene ring
Department of Chemistry, Northwestern University, 2145 Sheridan Road,
Evanston, Illinois 60208, USA. E-mail: j-hupp@northwestern.edu
Department of Chemistry, University of Science and Technology of China,
Hefei 230026, China
and the central porphyrin ring leads to the shp-type PCN-223
20
(Fig. S12, ESI†). When the linker’s configuration possesses C2v
symmetry, the torsion angle jcc between the central plane (green
plane in Scheme 1) and the terminal carboxylic plane (blue in
Scheme 1) drives the topology toward either csq or she. As illustrated
in Scheme 1, when jcc is close to or less than 601, the overall
dihedral angle between adjacent linker would be 1201, leads to a
d
School of Chemical Engineering, Nanjing University of Science & Technology,
Nanjing 210094, China
†
Electronic supplementary information (ESI) available: Details of synthesis,
31
single-crystal data, PXRD, P NMR spectra. CCDC 2015123 and 2015124. For
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
d0cc07974j
11
csq-type MOF. If jcc is larger (about 801), adjacent linkers will be
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Scheme 1 Illustration of linker geometries and configurations leading to hierarchical Zr-MOFs with different topologies.
21
6 5 3 3
nearly perpendicular, which leads to the she-type net. This angle is (C H COO) (HCOO) (TBAPy-2)3/2 (NU-601-as-syn). To remove the
largely correlated with the torsion angle jcb between the central modulators, NU-601-as-syn was heated in 8 M aq. HCl in DMF
plane and the plane of the terminal benzene ring (blue in Scheme 1). overnight at 100 1C, yielding NU-601-activated. NU-601 in micro-
When jcb is sufficiently small (less than 601), jcc is less likely to crystalline powder form (NU-601-p) was synthesized by the solvo-
4 4
exceed 801, which disfavours an she-net. In TCPP, benzene rings are thermal reaction of H TBAPy-2 with ZrCl in N,N-diethylformamide
partially hindered by neighbouring pyrrole rings, thus jcb always (DEF) in the presence of formic acid as a modulator. By controlling
10
22
exceeds 601. However, for the linkers of NU-1000, PCN-128, and the reaction time and the concentration of formic acid, crystallites of
1
2
PCN-608-OH, due to conjugation between the linker and B1 mm, B5 mm, or B10 mm (designated NU-601-1 lm, NU-601-5
peripheral benzenes, jcb in every case has been less than 601 lm, or NU-601-10 lm) can be created.
(
Table S2, ESI†), and thus, no she-type MOFs utilizing these
linkers have been synthesized until now.
Due to the conjugation in H TBAPy, jcc in H
sufficiently small to form a hierarchical csq-type net, NU-1000. linkers in a 2 : 3 ratio. Each Zr
Meanwhile, although H TBAPy exhibits lower symmetry than crystallographically independent Zr atoms (Zr1 and Zr2) and eight
Single-crystal X-ray structure analysis revealed that NU-601-as-
syn crystallizes in the cubic space group Pm3%m, with a = b =
4
4
6
TBAPy is c = 34.8374(5) Å. This new MOF contains Zr nodes and TBAPy-2
6
cluster consists of two kinds of
4
TCPP, the widths of both meso- and micro-pores are solely m3-O/OH entities. Each cluster ligates three nonstructural for-
dependent on the length of one edge of the planar linker, as mates, and three nonstructural benzoates, and is connected to
shown in Scheme 1 by the edge parallel to the x axis. However, six TBAPy-2 linkers. Zr1 is eight-coordinated by two O atoms
for she-type Zr-MOFs, the pore size is dependent on both edge from carboxylates of two different TBAPy-2 linkers, four m -O/OH
3
lengths of a nominally rectangular linker, and so unequal entities, and two O atoms of two different formates. Zr2 is also
lengths along x and y axes are anticipated to yield orthogonal eight-coordinated by two O atoms from carboxylates of two
3
hierarchal channels. A pyrene core could still be used to intro- different TBAPy-2 linkers and four m -O/OH entities, but is coor-
duce different edge lengths to obtain an she-type Zr-MOF, but dinated by two O atoms of two different benzoates (Fig. 1a). Three
alteration of the linker structure would be necessary. To avoid Zr1 and three Zr2 atoms are connected by eight m -O/OH atoms,
3
forming csq-type structures, jcc could be altered – for example, forming a Zr O cluster with C symmetry, which makes further
6
8
3v
by relocating benzene rings and engendering steric interference connections via six TBAPy-2 linkers. The space group of NU-601-
between them. As shown in Scheme 1, this can be accomplished, activated remains Pm3%m, with unit cell parameters of a = b =
4À
and unequal edge lengths can be created, by replacing TBAPy
c = 35.081(15) Å. However, the nonstructural benzoate ligands
with TBAPy-2 , an isomer featuring p-benzoate substituents at were successfully removed from NU-601-as-syn and no obvious
the 4, 5, 9, and 10 carbons of pyrene. formate could be assigned in the crystal structure, likely due to
4À
With the isomer in hand, the desired new she-type MOF, NU-601, severe local disorder. Therefore, all the coordinated terminal oxy-
proved straightforward to obtain in phase-pure, single-crystal gen atoms were assigned as terminal H O/OH entities, although
2
form. Solvothermal reaction of H TBAPy-2 with ZrOCl Á8H O in evidence for three labile formates per Zr node could be found in
4
2
2
6
1
N,N-dimethylformamide (DMF) in the presence of benzoic acid as the H NMR spectra of base-digested NU-601-activated (Fig. S7,
a modulator produced colourless cubic crystals, Zr
6
(m
3
-O)
4
(m
3
-OH)
4
ESI†). In both NU-601-as-syn and NU-601-activated, the rings
3
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Fig. 2 (a) N
2
adsorption isotherm and pore size distribution (inserted) of
NU-601-Activated; (b) PXRD patterns of NU-601 and NU-1000.
as H O. In studies that admittedly are limited, relative activities of
2
various Zr-MOFs increase with increasing numbers of reactant-
accessible Zr(IV) sites – but by amounts that are far greater than
anticipated based solely on differing numbers of sites. In any case,
NU-601 (6-connected) presents more candidate Lewis acid sites (6)
than does either NU-1000 (8-connected Zr
6
node; 4 potential
27
active-sites) or UiO-66 (nominally 12-connected; ca. 0–2 active
28,29
sites).
Therefore, we tested the catalytic performance of NU-601 for
the hydrolysis of dimethyl 4-nitrophenyl phosphonate (DMNP),
a simulant for G-type fluoro-phosphorus nerve agents such as
sarin. The activity was assessed with 6 mol% of the MOF/
catalyst, and the DMNP conversion was monitored by in situ
6
Fig. 1 (a) The coordination environment of Zr node; (b) and (c) are the
6
simplification of Zr node and TBAPy-2, respectively; (d) micro- and meso-
channels in NU-601; (e) topology of NU-601; (f) intersected channels in
NU-601.
3
1
P NMR. As shown in Fig. 3 and Table S3 (ESI†), the initial
reaction half-life is about 5 min (NU-601-5 lm), with conversion
comprising each pair of benzenes in TBAPy-2 are in close proximity, reaching 90% after 30 min, which is substantially faster than
but are unable to conjugate with the pyrene core. Instead, due to observed with NU-1000 samples featuring similar particle size
2
7,30
their mutual steric interference, they are nearly perpendicular to (3–4 mm, half-life t1/2 = 11 min).
As both MOFs possess
pyrene, with a torsion angle of 851. In turn, jcc is ca. 821, which hierarchical porosity, we must look elsewhere to understand
gives rise to a (4,6)-connected she-net with the point symbol
4
2
6 6 3
{
4
(
4 Á6 }
-connected node and each Zr
Fig. 1b, c and e).
The difference in edge length of TBAPy-2 along the x and y
3
{4 Á6 Á8 }
2
,
where each TBAPy-2 is simplified as
a
6 8
O
simplified as a 6-connected node
directions, as shown in Scheme 1, leads to the hierarchical
channels in NU-601 (Fig. 1d and f). The channel widths are
2.2 and 1.2 nm. Each type of channel is intersectional with itself
and is separated by linkers, as shown in Fig. 1f. The solvent-
accessible volume, as estimated by PLATON, is 76%.
The permanent porosity of NU-601-activated was analysed
2 2
based on N sorption at 77 K. As shown in Fig. 2a, the N
adsorption for NU-601-activated exhibits a reversible type IVb
isotherm with a plateau starting at P/P0 E 0.2. This type of
isotherm is typical for MOFs that present both micro- and
mesopores. The limiting N
2
uptake by NU-601-activated is
3
À1
510 cm g . The BET (Brunauer–Emmer–Teller) surface area
2
À1
of NU-601-activated is 1130 m g . NL-DFT-analysed pore-size
distributions indicate pore diameters of ca. 13 and 23 Å,
consistent with the single-crystal structure.
Zr-MOFs have been widely explored for catalytic hydrolytic
detoxification of organophosphate-based nerve agents and
2
3–26
their simulants.
include Lewis acidic sites (such as Zr(IV)) that can activate
hydrolysis targets via target displacement of labile ligands such with NU-601 and NU-1000.
Minimum requirements for catalytic activity
Fig. 3 (a) Hydrolysis reaction of DMNP. (b) Hydrolysis profiles of DMNP
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the difference in catalytic activity. We suggest that the activity
advantage for NU-601 is related to: (a) the aforementioned
difference in node-linker connectivity and its effect upon the
number and potential strength of Lewis acid sites, and (2) faster
substrate transport by isotropic (3D) diffusion in NU-601
compared with predominantly anisotropic (1D) diffusion in
NU-1000. Consistent with a rate-constraining role for substrate
transport, replacing NU-601-5 lm with NU-601-1 lm pushes the
half-life for catalytic hydrolysis of DMNP to below 2 min.
Reducing the loading of NU-601-1 lm to 3 mol%, increases
the reaction half-life to 3.5 min and yields an initial ‘‘per node’’
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À1
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4
À
À
she-type Zr-MOF, NU-601, by replacing the linker TBAPy
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,
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1
This work was supported as part of the Inorganometallic
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hydrolysis of nerve-agent simulants we gratefully acknowledge
DTRA (grant HDTRA1-18-1-0003). Z. L. gratefully acknowledges
support from the National Natural Science Foundation of
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