Homochiral Dodecanuclear Lanthanide "cage in Cage" for Enantioselective Separation

Article abstract of DOI:10.1021/jacs.1c03652

It is extremely difficult to anticipate the structure and the stereochemistry of a complex, particularly when the ligand is flexible and the metal node adopts diverse coordination numbers. When trivalent lanthanides (LnIII) and enantiopure amino acid ligands are utilized as building blocks, self-assembly sometimes yields rare chiral polynuclear structures. In this study, an enantiopure carboxyl-functionalized amino acid-based ligand with C3 symmetry reacts with lanthanum cations to give a homochiral porous coordination cage, (Δ/λ)12-PCC-57. The dodecanuclear lanthanide cage has an unprecedented octahedral "cage-in-cage"framework. During the self-assembly, the chirality is transferred from the enantiopure ligand and fixed by the binuclear lanthanide cluster to give 12 metal centers that have either Δor λ homochiral stereochemistry. The cage exhibits excellent enantioselective separation of racemic alcohols, 2,3-dihydroquinazolinones, and multiple commercially available drugs. This finding exhibits a rare example of a multinuclear lanthanide complex with a dual-walled topology and homochirality. The highly ordered self-assembly and self-sorting of flexible amino acids and lanthanides shed light on the chiral transformation between different complicated artificial systems that mimic natural enzymes.

Full text of DOI:10.1021/jacs.1c03652

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Article
Homochiral Dodecanuclear Lanthanide “Cage in Cage” for
Enantioselective Separation
Chengfeng Zhu,* Haitong Tang, Keke Yang, Yu Fang,* Kun-Yu Wang, Zhifeng Xiao, Xiang Wu,
Yougui Li, Joshua A. Powell, and Hong-Cai Zhou*
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ABSTRACT: It is extremely difficult to anticipate the structure and the
stereochemistry of a complex, particularly when the ligand is flexible and
the metal node adopts diverse coordination numbers. When trivalent
lanthanides (LnIII) and enantiopure amino acid ligands are utilized as
building blocks, self-assembly sometimes yields rare chiral polynuclear
structures. In this study, an enantiopure carboxyl-functionalized amino
acid-based ligand with C3 symmetry reacts with lanthanum cations to give
a homochiral porous coordination cage, (Δ/Λ)12-PCC-57. The
dodecanuclear lanthanide cage has an unprecedented octahedral “cage-
in-cage” framework. During the self-assembly, the chirality is transferred
from the enantiopure ligand and fixed by the binuclear lanthanide cluster
to give 12 metal centers that have either Δ or Λ homochiral
stereochemistry. The cage exhibits excellent enantioselective separation
of racemic alcohols, 2,3-dihydroquinazolinones, and multiple commercially available drugs. This finding exhibits a rare example of a
multinuclear lanthanide complex with a dual-walled topology and homochirality. The highly ordered self-assembly and self-sorting of
flexible amino acids and lanthanides shed light on the chiral transformation between different complicated artificial systems that
mimic natural enzymes.
enantioseparation of the important chiral molecules or
intermediates to date.7 Furthermore, a chiral cage with dual-
walled topology has never been successfully applied in chiral
resolution.
INTRODUCTION
■
Porous coordination cages (PCCs), also known as metal−
organic cages (MOCs)or polyhedra (MOPs), are a class of
molecular architectures that bear well-defined nanosized
cavities.1 Such hollow architectures, similar to the natural
enzyme pockets, have received significant scientific attention in
catalysis, recognition, separation, and sensing, as they provide a
specific microenvironment in terms of chemical, geometrical,
and electronic attributes around the bound guest species.2 The
designated microenvironment can dictate the species that bind
as guests, modulate the geometry of the included molecules,
and tune the reactivity of encapsulated substrates.3 In the past
decades, assembly strategies for porous coordination cages
with specific configurations and functionality have been well
established by the groups of Stang, Fujita, Nitschke, and
others.4 Recently, extensive efforts have been devoted to the
development of enzyme-type chiral coordination cages with
enantioselective performance because of the increasing social
demand for optically pure compounds.5 Although many
examples of homochiral coordination cages, including the
well-known Pd6L4 octahedron, Ga4L6 tetrahedron,
[Pd6(RuL3)8]28+ octahedron, and Zn24(MnL)12 octahedron,
have been confirmed as effective chiral hosts for enantiose-
lective recognition and catalysis,6 only a handful of examples of
homochiral coordination cages are known to achieve
Many asymmetric cage structures with the point or helical
chirality have been reported. For example, Sun et al. prepared a
pair of homochiral tetranuclear tetrahedral lanthanide cages
and investigated their self-sorting behavior.8 However,
obtaining homochiral cages with sophisticated topology is
still difficult. Furthermore, most chiral cages in the literature
did not show good chiral recognition capability, even though
the frameworks themselves are asymmetric. We envision that
separation of enantiomers needs to efficiently discriminate the
two opposite isomers with identical chemical and physical
properties in an achiral environment. Thus, a supramolecular
cavity not only possessing an asymmetric environment but also
equipped with specific interactions is highly demanded.9
Inspired by the fact that natural enzyme pockets surrounded
Received: April 19, 2021
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Figure 1. View of the structures of the dual-walled coordination cage and its octahedral inner (purple) and outer (cyan) cage assembled by the
flexible ligand and lanthanum ion.
by amino acid residues precisely direct the recognition of
biochemically active species in the living system via host−guest
interactions, we have developed a synthetic analogue by taking
full advantage of the unique properties of molecular cages.10
Herein, lanthanum-based enantiopure coordination cage, (Δ/
Λ)12-PCC-57, was constructed with a predesigned carboxylic-
acid-functionalized chiral ligand. The cage is employed for
enantioselective separation of multiple organic molecules and
important drug intermediates, giving a superb enantiomeric
excess (ee) value up to 99.9%.
coordination geometry with La−O bond lengths ranging
from 2.347(1) to 2.782(8) Å (Table S3), which are in good
agreement with reported lanthanide-based complexes.11 The
adjacent two La(III) ions with C2 symmetry are connected by
two bridging formic acids, generating a planar dimeric unit.
Besides, each metal is further coordinated by one bidentate
carboxylate group of one L ligand, one tridentate carboxylate
group of another L ligand, and two terminal aqua ligands. The
resulting La2(O2C)6(H2O)4 clusters, therefore, can be
considered as 4-connected nodes. Eight 3-connected L ligands
further link six binuclear La2 clusters, encapsulating a distorted
M12L8-type cage as shown in Figure 2.
A notable feature of the PCC-57 cage is the “dual-walled”
structure with an octahedral internal hollow cavity. When
taking a close look at the framework of PCC-57, a “cage-in-
cage” topology is revealed, in which one inner cage (Figure 1,
purple) is fully embedded by a second outer cage (Figure 1,
cyan). The inner and outer shells contain four L ligands,
sharing six La2 clusters on the octahedron vertex. Although
only one ligand species was used, the inner and the outer
organic ligands within the PCC-57 adopt totally different
configurations after coordination. The high flexibility of L
ligand and steric hindrance around the apexes of the
octahedron furnished two different geometries of the
coordinated ligand, which we have denoted as the “stretch”
and “fold” configurations. Under the coordination-driven
forces, four L ligands adopt the “stretch” configuration to
form the inner octahedral cage, possessing a chiral cavity of 1.5
nm in size, by bridging six La2 clusters with the assistance of
formic acid. In contrast, the other four ligands adopt the “fold”
configuration and form the outer octahedral cage. It is worth
noting that pairs of ligands, featuring “stretch” or “fold”
configuration, closely stack together via strong intermolecular
π−π stacking and hydrogen-bonding interactions and cover
one face of the octahedral cage. Notably, the arrangement of
the ligands endows the cage with four trigonal windows with
RESULTS AND DISCUSSION
■
Synthesis and Characterization. The enantiopure ligand
with C3 symmetry, H3L, was rationally designed and
synthesized from L-phenylalanine and 1,3,5-benzene-
tricarboxylic acid in four steps to give a high overall yield
(80%). The chiral ligand was fully characterized by 1H nuclear
magnetic resonance (NMR) spectroscopy, mass spectroscopy
(Figure S1), infrared (IR) spectroscopy (Figure S7), and
circular dichroism (CD) spectroscopy (Figure S10). A
solvothermal reaction of H3L with LaCl3 or La(NO3)3 (1,3
molar ratio) in a mixture of N,N-dimethylformamide (DMF),
ethanol (EtOH), water, and formic acid under 80 °C for 2 days
afforded colorless hexagonal crystals, [La12L8(O2C)12·24H2O]·
n(solvent), denoted as PCC-57, in good yield, which is stable
in methanol (MeOH), tetrahydrofuran (THF), dichloro-
methane (DCM), acetonitrile (MeCN), and other common
organic solvents. The composition of PCC-57 was supported
by the results of single-crystal X-ray analysis (Figures S2−S5),
thermogravimetric analysis (TGA) (Figure S6), IR, UV−vis
(Figure S8), and FL spectroscopy (Figure S9).
A single-crystal X-ray diffraction (SC-XRD) study reveals
that PCC-57 is a neutral coordination cage crystallized in the
chiral hexagonal P63 space group with one formula unit in its
asymmetric unit (Figure 1). In the structure, each central
La(III) ion exhibits a 9-coordinate square antiprismatic
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Figure 2. (a) Illustration of the connectivity of the bridging ligand and binuclear metal node in the dual-walled PCC-57. (b) View of the packing
mode of the dual-walled cage (highlighted as the yellow ball) along the c-axis and the large cavity (highlighted as the green ball) formed via the
orderly arrangement of PCC-57.
dimensions of ∼13.0 × 13.0 Å2, opening up a pathway for the
inclusion of guest molecules. More importantly, the periphery
point chirality of the ligand derived from L-phenylalanine has
transferred to La(III) centers during the self-assembly of the
cage. All the 12 La(III) centers are endowed with helical
chirality adopting the same Δ-configuration.12 Therefore, the
resulting homochiral cage, (Δ)12-PCC-57, may exhibit a
multichiral microenvironment, showing excellent enantiose-
lectivity toward the encapsulated guest molecules.
Furthermore, most reported coordination cages are usually
only investigated for their internal cavities because of the
discrete nature, with the space between individual discrete
cages usually being ignored. However, we believe that both the
internal cavity and the external cavity between adjacent cages
can play essential roles in mass transportation. When viewing
the cage in packing mode, the intermolecular C−H···π
interactions give rise to a porous 3D supramolecular structure,
in which a new cavity (Figure 2b, green color) with a
maximum inner width of ∼24.3 Å forms via the orderly
arrangement of 12 PCC-57 cages (Figure 2b, yellow color). In
particular, the open trigonal windows of PCC-57 are oriented
toward the newly produced intrinsic porosity, which ensures
the mass transfer between the octahedral cages. What is more,
the large chiral cavity in PCC-57 is decorated with multiple
hydrophilic amide groups pointing inward, which provides an
ideal platform to modulate the interactions of the cage
framework with chiral guests for recognition and discrim-
ination of different enantiomers. To date, only a few examples
of chiral lanthanide coordination cage were reported.8,12c,13,14
Such a chiral molecular architecture featuring a “cage-in-cage”
structure is even rarer.
disappears upon complexation, which indicates the successful
coordination of the ligand with the lanthanum ions (Figure
S7). UV−vis spectrum analysis indicates that the main
absorption signals around 250 nm of PCC-57 are inherited
from the organic bridging ligand (H3L) (Figure S8). On the
other hand, the emission signals (385 nm) of PCC-57 exhibit a
red-shift of about 30 nm compared to its ligand precursor
(Figure S9). The CD spectra of PCC-57 made from L- and D-
enantiomers of H3L are mirrored conformations of each other,
which demonstrates their enantiomeric nature as expected
(Figure S10). Calculations using PLATON software indicate
that 57.5% of the total volume of the PCC-57 is occupied by
solvent molecules.15 The porosity of PCC-57 was further
confirmed by rhodamine B (RhB) and methylene blue (MB)
adsorptions in the solution. PCC-57 could readily adsorb
∼2.07 RhB molecules (ca. 1.3 × 1.1 × 0.7 nm3 in size) or
∼3.23 MB molecules (MB, 1.25 × 0.50 × 0.38 nm3 in size) per
formula unit (Figure S11).
Enantioselective Separation. The excellent enantiose-
lective performance of chiral selectors may be endowed by the
rational combination of an asymmetric environment and
sufficient interactions between the substrate and the chiral
selector.16 Luckily, PCC-57 possesses both the large chiral
cavities and multiple substrates docking sites, which prompted
us to perform separation experiments on a range of racemates.
The performance was first evaluated by enantioseparation of 1-
phenylethanol (PE) because of the great importance of
enantiopure alcohols in the pharmaceutical industry.17 After
screening a variety of adsorption and separation conditions
including various solvents and concentrations, we found that
solvent-exchanged crystals of (Δ)12-PCC-57 served as a solid
adsorbent that could afford a 99.9% enantiomeric excess (ee)
of PE molecules, with the S-enantiomer being in excess by
using an optimized procedure. The identity of the enantiomer
was confirmed by comparing the retention time with that of
the standard sample. In contrast, when (Λ)12-PCC-57 made
from the D-enantiomer of H3L was utilized as the adsorbent,
the R-enantiomer of PE can be obtained with a 99.8% ee
(Figure S13), demonstrating that the chiral nature of the
resolved alcohols was manipulated by the chirality of the cage
The consistency of the observed powder X-ray diffraction
(PXRD) pattern of PCC-57 and the simulated one obtained
from single-crystal data demonstrates the phase purity of its
bulk samples (Figure S12). Thermogravimetric analysis (TGA)
reveals that the cage framework decomposes around 350 °C
and that guests such as ethanol, water, and DMF molecules can
be readily removed in the temperature range of 30−230 °C
(Figure S6). The IR spectrum shows that the characteristic
COOH νCO stretch at 1725 cm−1 of the free H3L ligand
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Figure 3. Result of enantioseparation for chiral secondary alcohols (a) and chiral DHZQs (b) by (Δ)12-PCC-57.
framework. Furthermore, the adsorption kinetics were studied
by monitoring the 1H NMR over the course of the adsorption
experiment, which showed that the adsorption of (Δ)12-PCC-
57 to PE reached an equilibrium in 2.5 h, generating a
transient host−guest complex with a ratio of ca. 1:5.5 (PCC-
57:PE) (Figure S14). Besides, we performed the control
experiment of enantioseparation of PE by using chiral
hydroxypropyl-β-cyclodextrin (HP-β-CD), cellulose triacetate
(CTA), and cellulose tribenzyl carbamate (CTBC) as
adsorbents. The results showed that the cage adsorbent
(Δ)12-PCC-57 afforded enhanced capacity and enantioselec-
tivity for PE molecules under the established separation
condition.
Subsequently, we examined the substrate tolerance of (Δ)12-
PCC-57 toward a variety of aromatic alcohols with different
electronic and steric properties under the optimized separation
conditions (Figure 3a). First, PE and its derived alcohols with
electron-rich groups on the aromatic ring, including bulkier 1-
(2-naphthalenyl)ethanol, give rise to very high enantioselec-
tivity, with ee values ranging from 99.1% to 99.9% (1a−1f).
Second, when the aromatic ring of PE was functionalized with
electron-deficient groups, such as −F, −Cl, or −Br, (Δ)12-
PCC-57 also exhibits excellent enantioselectivities of 96.7−
97.1% (1g−1i). Third, the enantioseparation also works well
with 1-phenylpropanol, 1-phenyl-2-propanol, and their ana-
logues (1j−1n), affording the optically pure products with ee
values of 99.3−99.9%. Finally, benzoin, a component of several
chiral pharmaceuticals, also can be resolved by (Δ)12-PCC-57,
yielding enantioselectivity up to 99.9%. The superb enantio-
selectivity and broad substrate scope clearly showed that PCC-
57 represents one of the best cage-like adsorbents for the
separation of racemic alcohols reported to date.7a−c
electron-rich substituents or heteroaromatic pyridyl or thienyl
rings on its framework, can be efficiently resolved by the (Λ)12-
PCC-57, affording the enantiopure targeted products with ee
value up to 99.9%. Such chiral products are generally obtained
by asymmetric synthesis, but the aminal carbon chiral center is
sensitive to racemization during reactions, making it difficult to
synthesize pure enantiomers. Therefore, this work not only
provides an alternative approach for making optically pure
DHZQs but also represents the first example of enantiosepara-
tion of racemic DHZQs by utilizing chiral coordination cages
as adsorbents.
Notably, the enantiopure ligand H3L alone cannot resolve
the enantiomers of the tested alcohols and DHZQs under the
optimized condition, indicating that the enantioselective
resolution process is manipulated by the well-defined chiral
microenvironment of the cage framework. Furthermore,
control experiments were performed by adsorption of the
bulky alcohol (1p: ∼2.2 nm × 1.0 nm in size) and DHZQ (2l:
∼3.1 nm × 1.5 nm in size) substrates with PCC-57 for 5 h; the
results monitored by 1H NMR reveal that the bulky substrates
cannot have access to the chiral cavities of PCC-57 due to the
size exclusion and experienced no chiral resolution (Figure
S15), which conversely confirms the enantiosorption indeed
occurs within the chiral cavities for other smaller chiral
molecules.
To identify the origins of the superb enantioselectivity
displayed by (Δ)12-PCC-57, we carefully examined the
composition of the crystal structure, accompanied by computer
simulation. First, the chirality of (Δ)12-PCC-57 comes from 12
metal chiral centers and 24 chiral carbon centers. The chiral
metal center is owing to the Δ-configuration of the lanthanum
ions. The chiral carbon center is inherent to the ligand and
transferred to the metal center; that is, S-type chiral ligands
furnished a Δ-configuration in the metal center. When focusing
on the chiral cavity in the crystal structure of (Δ)12-PCC-57, it
was revealed that the cavity is decorated with 24 hydrophilic
amide groups pointing inward, which may serve as a docking
site for the substrate. The success in separating racemates may
originate from such a delicate chiral microenvironment, which
modulates the intermolecular interactions between the cage
PCC-57 also showed remarkable resolution capability
toward racemic 2,3-dihydroquinazolinones (DHQZs), an
important class of chiral intermediates that constitute various
biologically active compounds and therapeutic drugs.18 Under
the optimized separation conditions, a variety of DHQZs
substituted with aryl groups on the carbon 2 chiral center were
evaluated. As shown in Figure 3b, all the examined 2-aryl-
DHQZ derivatives, bearing either electron-deficient or
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framework and chiral guests for recognition and discrimination
of different enantiomers. Unfortunately, our attempts to get
the single-crystal structure of the inclusion adduct were
unsuccessful because of the weak diffraction, even though
neutron diffraction (Shanghai) was applied. Consequently, the
grand canonical Monte Carlo (GCMC) method was used in
Material Studio 6.0 to gain insight into the adsorption process
of the chiral cage.19 It was found that there were two kinds of
adsorption sites in the coordination cage: one was located in
the internal cavity of the cage, and the other site was formed by
the packing of different cages (Figure S16). The host−guest
interactions between (Δ)12-PCC-57 and chiral PE molecules
were further studied by the Forcite module, which showed that
the cage had stronger interactions with S-enantiomer of PE
(Table S1). A possible mechanism is proposed that the chiral
separation may result from guest exchange dynamics (Figure
S17).7b Because of the distinct combination energies, the
encapsulation of the S-enantiomer within the (Δ)12-PCC-57
can be more favored than the R-enantiomer, resulting in the
enantioseparation. This result was further confirmed through
the competitive adsorption experiment of (Δ)12-PCC-57
toward R- and S-enantiomers of PE (Figure S18).
Moreover, the durability of the chiral adsorbent was
evaluated by the recycle separation experiments of PE and 2-
phenyl-DHZQ. The solid adsorbent (Δ)12-PCC-57 can be
recovered easily by filtration and washing and reused for the
following consecutive separations, affording PE with enantio-
selectivities of 99.9%, 99.8%, 99.8%, 99.6%, and 99.6% ee and
2-phenyl-DHZQ with enantioselectivities of 99.1%, 99.1%,
99.0%, 99.0%, and 99.0% ee. The PXRD patterns of the
recovered adsorbent revealed that PCC-57 retained its
crystallinity, although a slight distortion appeared. These
results suggest excellent recyclability of PCC-57 in the
enantioseparation of chiral molecules.
Encouraged by the superb enantioselectivity, size selectivity,
and recycling ability of PCC-57 in the resolution of various
racemates, we further examine its potential in the separation of
the enantiomers of chiral drugs. Herein, we performed this
separation reaction by applying six commercially available
small molecular drugs (thalidomide, tembamide, lansoprazole,
ibuprofen, flurbiprofen, and ketoprofen) as model molecules
because their enantiomers may differ markedly in potency,
toxicity, and behavior in biological systems and can even cause
significant side effects.20 Gratifyingly, enantiomers of the
examined racemic drug substances could be separated with
(Δ)12-PCC-57 and (Λ)12-PCC-57, producing the single
enantiomeric drug molecules with ee value up to 99.9% (as
shown in Figure 4). These results prove once again the
remarkable selectivity and versatility of PCC-57 in the
enantioselective separation of chiral molecules. We assume
that the excellent performance of PCC-57 may arise from the
combination of the chiral cavity of appropriate sizes and the
hydrophilic inner surface decorated with amide groups. This
combination allows for bioanalogous interaction of the cage
framework with adsorbate species during the inclusion process.
Thus, the molecular cage provides a potential chiral drug
resolution platform, showing excellent separation efficiency
and reusability.
Figure 4. Enantioseparation of chiral drugs with (Δ)12-PCC-57
(blue) and (Λ)12-PCC-57 (black).
demonstrated its remarkable enantioselective abilities to
separate a variety of racemic aromatic alcohols, 2,3-dihydro-
quinazolinones, and small, commercially available drug
molecules. Further work aims to develop this assembly strategy
to synthesize enzyme-typed porous coordination cages with a
larger cavity and a functionalized interior surface and further
explore enantioselective processes.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
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Experimental procedures and characterization data
(PDF)
Accession Codes
CCDC 1912348 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
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AUTHOR INFORMATION
Corresponding Authors
■
Chengfeng Zhu − Anhui Province Key Laboratory of
Advanced Catalytic Materials and Reaction Engineering,
School of Chemistry and Chemical Engineering, Hefei
University of Technology, Hefei 230009, P. R. China;
orcid.org/0000-0002-9676-6750; Email: ZhuCF@
hfut.edu
Yu Fang − State Key Laboratory for Chemo/Bio-Sensing and
Chemometrics, College of Chemistry and Chemical
Engineering, Hunan University, Hunan 410082, P. R.
China; orcid.org/0000-0001-6911-4047;
Email: yu.fang@hnu.edu.cn
Hong-Cai Zhou − Department of Chemistry, Texas A&M
University, College Station, Texas 77843-3255, United
States; Department of Materials Science and Engineering,
Texas A&M University, College Station, Texas 77843-3003,
United States; orcid.org/0000-0002-9029-3788;
Email: zhou@chem.tamu.edu
Authors
CONCLUSIONS
Haitong Tang − Anhui Province Key Laboratory of Advanced
Catalytic Materials and Reaction Engineering, School of
Chemistry and Chemical Engineering, Hefei University of
Technology, Hefei 230009, P. R. China
■
In conclusion, we have presented the assembly of a homochiral
dodecanuclear lanthanide double-shell porous coordination
cage from the highly flexible amino acid-derived ligand and
E
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Keke Yang − Anhui Province Key Laboratory of Advanced
Catalytic Materials and Reaction Engineering, School of
Chemistry and Chemical Engineering, Hefei University of
Technology, Hefei 230009, P. R. China
Kun-Yu Wang − Department of Chemistry, Texas A&M
University, College Station, Texas 77843-3255, United
States; orcid.org/0000-0001-8982-0547
Zhifeng Xiao − Department of Chemistry, Texas A&M
University, College Station, Texas 77843-3255, United States
Xiang Wu − Anhui Province Key Laboratory of Advanced
Catalytic Materials and Reaction Engineering, School of
Chemistry and Chemical Engineering, Hefei University of
Technology, Hefei 230009, P. R. China; orcid.org/0000-
0001-5428-9063
Yougui Li − Anhui Province Key Laboratory of Advanced
Catalytic Materials and Reaction Engineering, School of
Chemistry and Chemical Engineering, Hefei University of
Technology, Hefei 230009, P. R. China
Joshua A. Powell − Department of Chemistry, Texas A&M
University, College Station, Texas 77843-3255, United States
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.1c03652
Author Contributions
H.T., K.Y., and K.-Y.W. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Fundamental Research Funds
for the Central Universities of China (No. PA2021GDSK0067,
PA2020GDKC0011). We thank the support of the Postdoc-
toral Scientific Research Station of Material Science and
Engineering at Hefei University of Technology, the support of
Anhui Province Key Laboratory of Environment-friendly
Polymer Materials, and the assistance of the staff from the
BL17B beamline of NFPS at the Shanghai Synchrotron
Radiation Facility during crystal data collection. We also
thank the support of the Robert A. Welch Foundation through
a Welch Endowed Chair to H.-C.Z. (A-0030) and Qatar
National Research Fund under Award NPRP9-377-1-080.
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