Organic Ferroelectric Vortex-Antivortex Domain Structure

Article abstract of DOI:10.1021/jacs.0c11416

Organic ferroelectrics are attracting tremendous interest because of their mechanical flexibility, ease of fabrication, and low acoustical impedance. Although great advances have been made in recent years, topological defects such as vortices remain relatively unexplored in the organic ferroelectric system. Here, from [quinuclidinium]ReO4 ([Q]ReO4), we applied the molecular design strategy of H/F substitution to successfully synthesize the organic ferroelectric [4-fluoroquinuclidinium]ReO4 ([4-F-Q]ReO4). Through H/F substitution, the Curie temperature and spontaneous polarization are respectively increased from 367 K and 5.83 μC/cm2 in [Q]ReO4 to 466 K and 11.37 μC/cm2 in [4-F-Q]ReO4. Moreover, under mechanical stress fields, three kinds of stripelike domains with various polarization directions emerge to form a windmill-like domain pattern in the thin film of [4-F-Q]ReO4, in which intriguing vortex-antivortex topological configurations can exist stably. This work provides an efficient strategy for optimizing the properties of organic ferroelectrics and exploring emergent phenomena.

Full text of DOI:10.1021/jacs.0c11416

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Organic Ferroelectric Vortex−Antivortex Domain Structure
Yuan-Yuan Tang,* Yongfa Xie, Yong Ai, Wei-Qiang Liao, Peng-Fei Li, Takayoshi Nakamura,
and Ren-Gen Xiong*
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ABSTRACT: Organic ferroelectrics are attracting tremendous interest because of
their mechanical flexibility, ease of fabrication, and low acoustical impedance. Although
great advances have been made in recent years, topological defects such as vortices
remain relatively unexplored in the organic ferroelectric system. Here, from
[quinuclidinium]ReO4 ([Q]ReO4), we applied the molecular design strategy of H/F
substitution to successfully synthesize the organic ferroelectric [4-
fluoroquinuclidinium]ReO4 ([4-F-Q]ReO4). Through H/F substitution, the Curie
temperature and spontaneous polarization are respectively increased from 367 K and
5.83 μC/cm2 in [Q]ReO4 to 466 K and 11.37 μC/cm2 in [4-F-Q]ReO4. Moreover,
under mechanical stress fields, three kinds of stripelike domains with various
polarization directions emerge to form a windmill-like domain pattern in the thin film
of [4-F-Q]ReO4, in which intriguing vortex−antivortex topological configurations can
exist stably. This work provides an efficient strategy for optimizing the properties of
organic ferroelectrics and exploring emergent phenomena.
density for memory applications.7 Over the past decade, owing
to the impressive developments in high-spatial-resolution
imaging techniques, particularly piezoresponse force micros-
copy (PFM), the ferroelectric vortex domains are gradually be
unveiled with the progressive emergence of experimental
evidence.8 Examples include the nanometer-scale long-range
ordered vortex−antivortex arrays observed in the superlattices
of alternating PbTiO3 and SrTiO3 layers,8a multistate vortex−
antivortex pairs revealed in improper ferroelectrics such as
hexagonal YMnO3 and LuMnO3,9 and the artificially created
ferroelectric vortex structure in BiFeO3 thin films by applying a
local electric field.5,8b To date, a wide spectrum of vortexlike
domain structures have been reported in the forms of single
crystals, thin films, oxide superlattices, and nanostructures,
with an emphasis on inorganic ferroelectric systems with a
perovskite structure. Nevertheless, the hard truth that these
ferroelectric vortex domains suffer from the problem of
metastability (sometimes lasting a few seconds) and the
difficulty in electric switching or other manipulations severely
limits the implementation of vortex memory devices. To that
end, an increasing number of experimental and theoretical
efforts must be imminently devoted to the overall ferroelectric
INTRODUCTION
■
Topological defects, such as domain walls, vortex structures,
and skyrmions, are attracting growing attention, while their
marvelous electronic, magnetic, and mechanical behaviors offer
a powerful playground for nanoscale device engineering.1
Domain states are inherent to ferroic materials, and it is
domain engineering that enables novel functionalities and
numerous technological applications.2 Obviously, the further
one explores the types, characteristics, and arrangements of
domains, a deeper understanding and broader exploitation of
these functional materials can be achieved. It has long been
predicted that magnetic spins or electric polarization vectors
might align in circles, not just linearly, which means that vortex
domain structures also exist in addition to the simple stripelike
or irregularly shaped structures.3 With their insensitivity to
disturbance, data storage in such vortex states can therefore
avoid the problem of “cross-talk” between adjacent information
bits as much as possible, leading to high-density nonvolatile
memories.4 Moreover, peculiar properties could also be
brought forth by this exotic topological state: for instance, an
enhanced electronic conductivity at vortex cores.5
As one of the currently key research focuses in condensed
matter physics, vortex domains are already well-known in
magnetism.1c In comparison with those well-studied ferro-
magnetic analogues, however, the study of ferroelectric vortex
domains is more in its embryonic stage. The theoretical
prediction of vortexlike domain configurations in ferroelectrics
was first reported in 2004.2a,6 Subsequently, Naumov et al.
proposed that such structures could be switchable in a
nanoferroelectric system, thus resulting in a nontrivially high
Received: October 30, 2020
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systems to visualize vortex structures and probe the related
properties.
Organic ferroelectrics, another main branch of ferroelectrics
as the inorganic ferroelectrics, have experienced their
renaissance during the last dozen years.10 The merits of
lightweight, low cost, mechanical flexibility, low acoustical
impedance, structural tunability, and ease of processing make
this unique material system promising for future flexible and
wearable devices. It is inspiring to note that the emergent
organic ferroelectrics are comparable with the conventional
inorganic ferroelectrics such as BaTiO3 in terms of Curie
temperature (Tc),10a,11 spontaneous polarization (Ps),10a and
multiaxial nature.12 For example, Harada et al. have recently
reported that some plastic crystals such as [quinuclidinium]-
ReO4 ([Q]ReO4) and 1-azabicyclo[2.2.1]heptanium perrhen-
ate ([AH]ReO4) can exhibit multiaxial ferroelectricity, which
allows excellent ferroelectric performance even in polycrystal-
line forms.12a,13 Distinct from the inorganic ferroelectrics, they
even can introduce homochiral centers to design ferroelectrics
and endow them with multifunctional properties of chiral
molecules, filling the void of homochiral ferroelectrics.14 Now,
this is an opportune moment for us to shift away from the
macroscopic physical performances to the microscopic
topological domains, for the sake of triggering novel physical
phenomena and fascinating applications. Both stripelike and
irregularly shaped domains are ubiquitous in the family of
organic ferroelectrics, whereas an unexplored area remains the
study of vortex domain states.
Herein, from [Q]ReO4, we applied the chemical design
strategy of fluorine substitution and successfully obtained a
new high-temperature molecular ferroelectric with improved
ferroelectric performance, [4-fluoro-quinuclidinium]ReO4 ([4-
F-Q]ReO4). By taking advantage of the powerful PFM
technique, we present the observation of intrinsic vortex
domains in the organic ferroelectric system. Moreover, the Tc
and Ps values respectively increased from 367 K and 5.83 μC/
cm2 in [Q]ReO4 to 466 K and 11.37 μC/cm2 in [4-F-Q]ReO4.
This work presents an unprecedented view of domain
structures and is favorable for a complete view of the universal
topological domain features in ferroelectrics. Notably, the
robust vortex domain states offer opportunities for further
exploring their intriguing properties and give a foundation for
on-demand manipulation to fit the practical requirements of
high-density vortex devices.
Figure 1. Design of the organic ferroelectric [4-F-Q]ReO4. Crystal
structures of [4-F-Q]ReO4 at (a) 293 K in the Pn phase I and (b) 403
K in the Amm2 phase III. (c) By applying the molecular design
strategy of H/F substitution, the direction of the molecular dipole
moment can be switched from the quinuclidine molecule to the 4-
fluor-quinuclidine molecule (see the Supporting Information for
detailed synthetic procedures). (d) Variation of polarization as a
function of the dynamic path connecting the ferroelectric phase (λ =
1) to the reference phase (λ = 0) configuration for [Q]ReO4 and [4-
F-Q]ReO4.
space group (Figures 1b and Figure S1b). The symmetry
position of the [4-F-Q]+ cation and [ReO4]− anion changes to
mm2. Consequently, the [4-F-Q]+ cation becomes 2-fold
orientationally disordered to meet the symmetry requirement.
The C−F bonds align along the polar c axis, which will induce
polarization in this direction from the 4-F-quinuclidine dipole.
The structures have been deposited at the Cambridge
Crystallographic Data Centre (deposition numbers: CCDC
1938429−1938433, and 1942602) and can be obtained free of
charge from the CCDC via www.ccdc.cam.ac.uk/getstructures.
We tried to solve the crystal structure in the high-
temperature phase (phase IV), but the diffraction data were
significantly poor. We thus employed the measurement of
variable-temperature powder X-ray diffraction (PXRD) (Figure
S3). The experimental PXRD patterns at 293 K in the phase I
are consistent with those calculated from the single-crystal
structures at 293 K. From phase I to phases II and III, the main
difference is that two new peaks at around 35 and 41° emerge
in phases II and III. The position of peaks at 493 K in phase IV
becomes very different from that in phase III, which suggests a
significant change in the crystal symmetry. The patterns at 573
K show no diffraction peaks, indicating that the sample has
deteriorated. As calculated, the indexing of the PXRD pattern
at 493 K shows an orthorhombic crystal system. The Pawley
refinements suggest the most possible space group to be Cmcm
(point group mmm) in phase IV. In summary, the transition of
point groups that accompany the phase transitions of [4-F-
Q]ReO4 should be m (ferroelectric phase I) → mm2
(ferroelectric phase II) → mm2 (ferroelectric phase III) →
mmm (paraelectric phase IV).
RESULTS AND DISCUSSION
■
The crystal structures of [4-F-Q]ReO4 were determined by
single-crystal X-ray diffraction measurements at various
temperatures (Table S1). In the low-temperature phase
(phase I, obtained at 93, 173, and 293 K), [4-F-Q]ReO4
crystallizes in the polar monoclinic Pn space group, different
from Pmn21 in non-fluorine-substituted [Q]ReO4.12a,15 The
basic structure contains the two components [4-F-Q]+ cation
and [ReO4]− anion, both of which are ordered. As shown in
Figure 1a and Figure S1a, the C−F bonds of all [4-F-Q]+
cations are close to the c axis direction, meaning that the dipole
of the [4-F-Q]+ cation will contribute to the polarization nearly
along the c axis. The structure shows a CsCl-type cubic packing
similar to that of [Q]ReO4, with the [4-F-Q]+ cation and
[ReO4]− anion located in the center and the eight corners of
the cube, respectively (Figure S2). At 363 and 403 K in the
intermediate-temperature phases (phases II and III, isomor-
phous), [4-F-Q]ReO4 adopts the polar orthorhombic Amm2
On consideration of the concise molecular packing of the [4-
F-Q]ReO4 crystal, the ionic part of ferroelectric polarization is
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first evaluated by a point charge model (see the Supporting
Information for details). The obvious displacement between
positively charged [4-F-Q]+ and negatively charged [ReO4]−
gives a major source of polarization at about 8.19 μC/cm2,
which is obviously larger than that in the [Q]ReO4 crystal at
7.58 μC/cm2.15 More importantly, the net dipole moment of
the quinuclidine molecule is antiparallel to the total polar-
ization direction, causing the total polarization to be partially
canceled out (5.83 μC/cm2 in [Q]ReO4).15 To change the
direction of the molecular dipole moment to increase the total
polarization, we applied the molecular design strategy of H/F
substitution to successfully obtain the organic ferroelectric [4-
F-Q]ReO4 (Figure 1c).
In order to gain deep insight into the ferroelectric
polarization, density functional theory (DFT) calculations
were carried out to evaluate the origin of polarization. A
dynamic path between the ferroelectric phase and reference
phase configuration is constructed on the basis of the crystal
structure obtained from single-crystal X-ray diffraction.
Accordingly, the structure of the low-temperature ferroelectric
phase at 93 K is used as the ferroelectric configuration (λ = 1),
while the reference phase (λ = 0) configuration is obtained
from the matrix transformation of the coordinates of λ = 1,
considering both the rotation of the organic cations and
anionic [ReO4]−. The variations of polarization as a function of
the dynamic path are shown in Figure 1d, from which a
ferroelectric polarization of 11.37 μC/cm2 can be extracted
from the initial point of the λ = 1 configuration. On
consideration of the ionic polarization 8.19 μC/cm2 from
point charge analysis, the reason for such a slightly larger value
obtained by DFT calculations is due to the net dipole moment
of the 4-F-quinuclidine molecule being parallel to the total
polarization direction. In order to evaluate the dipole moment
of the 4-F-quinuclidine molecule, different theoretical algo-
rithms were carried out within the Gaussian program, and the
results (1.29 D under b3lyp/6-31+G(d) and 1.32 D under
MP2/aug-cc-pvdz) are almost the same. Such a dipole
amplitude can contribute 1.72−1.76 μC/cm2 to the total
polarization, in good accordance with the mismatch between
DFT calculations and a point charge analysis, since the latter
only considers the ionic polarization.
To dissect the total polarization during the dynamic path, we
also evaluated the dynamics of protonated 4-F-Q and the ReO4
separately (Figure S6). From the polarization path, the total
polarization is mainly contributed by the 4-F-Q part, as the
ReO4 part only contributes a minor amount to the total
polarization. Therefore, the ferroelectric polarization increases
obviously from both the ionic and molecular dipole parts due
to the 4-F substitution. The total polarization of [4-F-Q]ReO4
(11.37 μC/cm2) is nearly double that in [Q]ReO4 (5.83 μC/
cm2). From this point of view, the well-designed F atom
substitution is an effective strategy to enhance the ferroelectric
polarization performance.
Figure 2. Ferroelectric properties of [4-F-Q]ReO4. (a) DSC curves of
[4-F-Q]ReO4. (b) SHG intensity of [4-F-Q]ReO4 as a function of
temperature. (c) Temperature dependence of the ε′ values of a [4-F-
Q]ReO4 powder sample at several frequencies. (d) P−E hysteresis
loops measured at 323 K on the thin film of [4-F-Q]ReO4 by using
the double-wave method.
both of which may be caused by decomposition or one of
which may be caused by decomposition and the other by a
phase transition. We also detected the symmetry change
accompanying the phase transition by the temperature-
dependent second harmonic generation (SHG) intensity
(Figure 2b). The SHG intensity has nonzero values below
T3, corresponding to the noncentrosymmetric space group in
phase I (Pn) and phases II and III (Amm2). However, the
SHG intensity drops sharply to zero at around T3, indicating
the transition to the centrosymmetric structure in phase IV,
consistent with the possible Cmcm space group from PXRD
results. Therefore, the phase transition at T3 is a ferroelectric to
paraelectric transition. It is noted that the Curie temperature
(T3 = 466 K) of [4-F-Q]ReO4 is much higher than that (367
K) of [Q]ReO4 and is among the highest Curie temperatures
in organic ferroelectrics. The substitution of an H atom by an F
atom increases the energy barrier for rotating the [4-F-Q]+
cation in the phase transition process, which results in the
enhancement of the Curie temperature, as found in the case of
(R)- and (S)-3-(fluoropyrrolidinium)MnCl3.16
The ferroelectric to paraelectric transition nature at T3
(Curie temperature) is also shown in the temperature-
dependent real part (ε′) of the complex dielectric constant
of the powder sample, which displays tremendous dielectric
anomalies near T3 (Figure 2c). In the vicinity of T1 and T2,
small dielectric anomalies are observed, confirming the phase
transitions at these two temperatures. We then further verify
[4-F-Q]ReO4 to be a ferroelectric by polarization−electric field
(P−E) hysteresis loop experiments. The thin-film sample
shows a good P−E hysteresis loop at 323 K (Figure 2d),
directly confirming the ferroelectric nature. The obtained
spontaneous polarization (Ps) and remnant polarization (Pr)
have equal values of 11.2 μC/cm2, consistent with the
theoretical calculation results. The Ps value of [4-F-Q]ReO4
is almost twice that of the [Q]ReO4 thin-film sample (5.2 μC/
cm2)15 and is larger than those of most of the organic
ferroelectrics, including the classical triglycine sulfate (3.5 μC/
cm2)17 and PVDF (8.0 μC/cm2)17 and the recently reported
The sequential structural phase transformations in [4-F-
Q]ReO4 were confirmed by the heat anomalies in the
differential scanning calorimetry (DSC) curves, which show
three phase transitions at around T1 = 345 K, T2 = 387 K, and
T3 = 466 K, respectively (Figure 2a). The entropy change
(ΔS) for the phase transition at T3 (22.3 J mol−1 K−1) is
significantly larger than that at T2 (1.44 J mol−1 K−1) and T1
(0.08 J mol−1 K−1), in good accordance with the ferroelectric
to paraelectric transition. Figure S7 also displays two DSC
peaks after the decomposition, T4 = 568 K and T5 = 574 K,
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[3-oxoquinuclidinium]ClO4 (6.7 μC/cm2)18 but is smaller
than that of diisopropylammonium bromide (23 μC/cm2).10a
The remarkable increase in Ps can be attributed to the dipole
enhancement of the [4-F-Q]+ cation in comparison to the
[Q]+ cation.
is a signature feature of ferroelectric materials. To visualize the
domain-switching process, we performed local switching tests
on the thin film of [4-F-Q]ReO4 (Figure 4 and Figure S12).
To minimize the depolarizing field and compensate for the
mechanical stress fields due to crystal imperfections and the
effect of substrate clamping, multiple ferroelectric domains
with different polarization directions emerge in phase I on the
thin film of [4-F-Q]ReO4. As shown in Figure 3a,b and Figure
Figure 4. Domain switching of [4-F-Q]ReO4 in phase I. Out-of-plane
PFM phase and amplitude images in the initial state (a, c) and 12 days
later after writing the box-in-box pattern with a reversed DC bias of
60 V in the center (b. d). In (a. b), the circle and dot indicate the
polarization direction oriented upward, and the circle and X indicate
the polarization direction oriented downward.
Figure 3. PFM of [4-F-Q]ReO4 in phase I. Windmill-like ferroelectric
domain structures seen in PFM images constructed by (a) phase and
(b) amplitude signals of the in-plane piezoresponse. (c) Schematic
illustrations of the local domain structures over an enlarged area,
denoted with a gray square in (a), where different color codes mark
the domains with various polarization directions, demonstrating the
presence of vortex−antivortex topological domain configurations. (d)
Hysteretic dependence of the out-of-plane PFM phase and amplitude
on the applied DC bias for a [4-F-Q]ReO4 film.
After writing box-in-box patterns with a reversed DC bias of
60 V in a region with uniform phase contrast, the bipolar
domain pattern with a clear reversal of phase contrast
demonstrates the switching of polarization in [4-F-Q]ReO4.
Meanwhile, as shown in Figures S13−S16, PFM measurements
also display the ferroelectric domains and domain switching on
the thin film of [4-F-Q]ReO4 in phases II and III, respectively,
confirming the ferroelectricity in these two phases. Further-
more, in comparison with the two molecular ferroelectrics
(4,4-difluoropiperidinium)2PbI4 (sensitive to air and light) and
2-(hydroxymethyl)-2-nitro-1,3-propanediol (sublimation) with
vortex domains discovered by our group, [4-F-Q]ReO4 is more
stable under environmental conditions.19 Such switchable and
stable polarization and the stability of vortex domains are
excellent for organic ferroelectrics and thus afford [4-F-
Q]ReO4 great application potentials.
To further clarify the effect of intermolecular interactions on
the crystal structure and physical properties, both Hirshfeld
surfaces and two-dimensional (2D) fingerprint plots of Q and
4-F-Q have been calculated and will be discussed (Figure 5 and
Table S2). Obviously, the interactions between the organic
cation and the surrounding molecules in [4-F-Q]ReO4 are
stronger than those in [Q]ReO4 from the Hirshfeld surfaces,
which also can be directly seen from the minimums (di, de) in
[4-F-Q]ReO4 (0.826, 1.000) and [Q]ReO4 (0.945, 1.000).
Moreover, after H/F substitution, the globularity of the
organic cation becomes slightly smaller, forming a quasi-
spherical 4-F-Q cation. These attributes lead to a change in
symmetry, from mm2 in [Q]ReO4 to m in [4-F-Q]ReO4 at
room temperature.12a The stronger interactions and quasi-
spherical cations in [4-F-Q]ReO4 make it difficult to reach the
cubic phase because of the higher potential energy barrier for
S8, there are three kinds of stripelike domains with various
polarizations distributed in different directions along the film
surface. In some regions, these domains converge to form an
intriguing windmill-like domain pattern with 3-fold symmetry.
Various contrasts in the phase and amplitude images suggest
the coexistence of variant domains with different polarization
directions. To identify them and analyze the local structure, we
have carried out comprehensive PFM studies for one of the
windmill-like domain patterns, where a series of in-plane PFM
images were detected with different cantilever-sample
orientations to visualize the exact in-plane polarization
(Figures S9−S11). As shown in Figure 3c, a windmill-like
pattern is formed by four types of domains with distinct
polarization directions, whose boundaries merge at four 3-fold
vertices. Around two of the vertices, three domains form a
vortex (green circular arrow) and the other three domains
form an antivortex (purple circular arrow). These results
provide direct experimental evidence for the presence of
vortex−antivortex topological domain configurations in [4-F-
Q]ReO4. In addition, the windmill-like domain structure and
the vortex−antivortex pair are perfectly stable for more than 12
days (Figures S9 and S10). Meanwhile, Figure 3d exhibits the
characteristic piezoelectric hysteresis and butterfly loops, which
D
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Crystallographic data (CIF)
AUTHOR INFORMATION
■
Corresponding Authors
Yuan-Yuan Tang − Ordered Matter Science Research Center,
Nanchang University, Nanchang 330031, People’s Republic
of China; orcid.org/0000-0002-8369-572X;
Email: tangyuanyuan@ncu.edu.cn
Ren-Gen Xiong − Ordered Matter Science Research Center,
Nanchang University, Nanchang 330031, People’s Republic
of China; orcid.org/0000-0003-2364-0193;
Email: xiongrg@seu.edu.cn
Authors
Yongfa Xie − Ordered Matter Science Research Center,
Nanchang University, Nanchang 330031, People’s Republic
of China; orcid.org/0000-0001-5004-5483
Yong Ai − Ordered Matter Science Research Center, Nanchang
University, Nanchang 330031, People’s Republic of China
Wei-Qiang Liao − Ordered Matter Science Research Center,
Nanchang University, Nanchang 330031, People’s Republic
of China; orcid.org/0000-0002-5359-7037
Peng-Fei Li − Ordered Matter Science Research Center,
Nanchang University, Nanchang 330031, People’s Republic
of China
Figure 5. Comparison for Hirshfeld dnorm surfaces between (a) Q and
(b) 4-F-Q at room temperature. Comparison of 2D fingerprint plots
between (c) Q and (d) 4-F-Q at room temperature.
rotating, which may lead to the cubic phase (probably the
̅
same Pm3m space group as that of the paraelectric phase in
Takayoshi Nakamura − Research Institute for Electronic
Science, Hokkaido University, Sapporo, Hokkaido 001-0020,
Japan
[Q]ReO4 and [3-F-Q]ReO4)12a,20 above the decomposition
temperature, as implied by Figure S17. The possible symmetry
̅
change with an Aizu notation of m3mFm will allow the
Complete contact information is available at:
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spontaneous polarization in phase I to be generated and
switched along any of the 12 symmetry-equivalent ferroelectric
axes.21 In combination with the mechanical stress fields
induced by crystal imperfections and the effect of substrate
clamping, three kinds of stripelike domains with various
polarization directions emerge to form a windmill-like domain
pattern, and a vortex−antivortex topological configuration
appears.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The manuscript was improved by insightful reviews by the
anonymous reviewers. This work was supported by the
National Natural Science Foundation of China (21991142,
21831004, 21911540068, 21975114, and 11904151).
CONCLUSION
■
We report the observation of robust vortex−antivortex
topological configurations in the organic ferroelectric [4-F-
Q]ReO4. Because of its multiaxial nature, domains with various
polarization directions form a beautiful windmill-like pattern,
whose boundaries merge at four 3-fold vertices. By rotation of
the polarization states, the polar vortex−antivortex pair is
present around two of the vertices. The stabilization of such an
intriguing polarization topology offers an outlook for future
trends and developments in organic ferroelectrics, which would
engineer functionalities previously inaccessible for these
materials.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.0c11416.
■
sı
Experimental procedures, supplementary text, and
figures and tables as described in the text (PDF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Crystallographic data (CIF)
Crystallographic data (CIF)
E
https://dx.doi.org/10.1021/jacs.0c11416
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
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https://dx.doi.org/10.1021/jacs.0c11416
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX