Directional Intermolecular Interactions for Precise Molecular Design of a High- Tc Multiaxial Molecular Ferroelectric

Article abstract of DOI:10.1021/jacs.8b13223

Quasi-spherical molecules have recently been developed as promising building blocks for constructing high-performance molecular ferroelectrics. However, although the modification of spherical molecules into quasi-spherical ones can efficiently lower the crystal symmetry, it is still a challenge to precisely arouse a low-symmetric polar crystal structure. Here, by introducing directional hydrogen-bonding interactions in the molecular modification, we successfully reduced the cubic centrosymmetric Pm3m space group of [quinuclidinium]ClO₄ at room temperature to the orthorhombic polar Pna2₁ space group of [3-oxoquinuclidinium]ClO₄. Different from the substituent groups of -OH, -CH₃, and -CH₂, the addition of a -O group with H-acceptor to [quinuclidinium]⁺ forms directionally N-H?O-C hydrogen-bonded chains, which plays a critical role in the generation of polar structure in [3-oxoquinuclidinium]ClO₄. Systematic characterization indicates that [3-oxoquinuclidinium]ClO₄ is an excellent molecular ferroelectric with a high Curie temperature of 457 K, a large saturate polarization of 6.7 μC/cm², and a multiaxial feature of 6 equiv ferroelectric axes. This work demonstrates that the strategy of combining quasi-spherical molecule building blocks with directional intermolecular interactions provides an efficient route to precisely design new eminent molecular ferroelectrics.

Full text of DOI:10.1021/jacs.8b13223

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Article
Directional Intermolecular Interactions for Precise Molecular
c
Design of a High-T Multiaxial Molecular Ferroelectric
Chen-Kai Yang, Wang-Nan Chen, Yan-Ting Ding, Jing Wang, Yin
Rao, Wei-Qiang Liao, Yongfa Xie, Wennan Zou, and Ren-Gen Xiong
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 07 Jan 2019
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Directional Intermolecular Interactions for Precise Molecular Design
of a High-T Multiaxial Molecular Ferroelectric
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†
†
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†
Chen-Kai Yang, Wang-Nan Chen, Yan-Ting Ding, Jing Wang, Yin Rao, Wei-Qiang Liao, Yongfa
,
§
,‡
,†,#
Xie,* Wennan Zou,* and Ren-Gen Xiong*
†Ordered Matter Science Research Center, Nanchang University, Nanchang 330031, People’s Republic of China
‡Institute for Advanced Study, Nanchang University, Nanchang 330031, People’s Republic of China
§College of Chemistry, Nanchang University, Nanchang, 330031, People’s Republic of China
#Jiangsu Key Laboratory for Science and Applications of Molecular Ferroelectrics, Southeast University, Nanjing 211189,
People’s Republic of China
Supporting Information
ABSTRACT: Quasi-spherical molecules have recently been developed as promising building blocks for constructing high-
performance molecular ferroelectrics. However, although the modification of spherical molecules into quasi-spherical ones can
efficiently lower the crystal symmetry, it is still a challenge to precisely arouse a low-symmetric polar crystal structure. Here, by
introducing directional hydrogen-bonding interactions in the molecular modification, we successfully reduced the cubic centro-
̅
symmetric Pm3m space group of [quinuclidinium]ClO
oxo-quinuclidinium]ClO . Different from the substituent groups of –OH, –CH
to [quinuclidinium] forms directionally N–H···O=C hydrogen-bonded chains, which plays a critical role in the generation of polar
structure in [3-oxo-quinuclidinium]ClO . Systematic characterization indicates that [3-oxo-quinuclidinium]ClO is an excellent
4
at room temperature to the orthorhombic polar Pna2
1
space group of [3-
4
3
, and =CH , the adding of =O group with H-acceptor
2
+
4
4
2
molecular ferroelectric with a high Curie temperature of 457 K, a large saturate polarization of 6.7 μC/cm , and a multiaxial feature
of 6 equivalent ferroelectric axes. This work demonstrates that the strategy of combining quasi-spherical molecule building blocks
with directional intermolecular interactions provides an efficient route to precisely design new eminent molecular ferroelectrics.
INTRODUCTION
3 6
(C ), 3m (C3v), 6 (C ) and 6mm (C6v), allow ferroelectric be-
8
haviors. Specifically, molecules must be assembled in par-
ticular ways to make sure that their dipole moments do not
cancel each other out in order to achieve targeted polar crystal
structures. Choice of the molecular building blocks as well the
precise control over the assembly of them is therefore the han-
dle that permits crystal design of molecular ferroelectrics.
Together with scientists around the world, we have aimed at
this challenging goal. As a result, a series of molecular design
strategies have been developed and continuously improved
while getting deeper insight into the structure-property rela-
tionship. Earlier studies revealed that, spherical molecules,
such as 1,4-diazabicyclo[2.2.2]octonium (dabco), quinu-
clidinium (Q), and tetramethylammonium, often allow for
dynamic rotation or reorientation, the freezing of which would
easily induce a structural or even ferroelectric phase transi-
Ferroelectrics have become a workhorse in numerous tech-
nologies, finding applications in data storage, capacitors, sen-
sors, microactuators, and nonlinear optical devices. During
1
the century-long history, extensive efforts have been directed
toward the design and synthesis of new ferroelectric families,
including complex oxides, molecular crystals, polymers, and
2
liquid crystals. Ferroelectric oxides always stand at the fore-
3
front of materials science, whereas it is only in recent years
that the investigation of molecular ferroelectrics shows signs
4
of a revival. In contrast to the former with inherent structural
rigidity, molecular ferroelectrics naturally lend themselves to
the crafting of structure and function using the strategies of
5
crystal engineering. Such a broader design flexibility offers a
cornucopia of research opportunities to facilitate the develop-
ment of highly organized molecular systems in future low-cost
4c,9
6
tion. Then we also developed a pathway to introduce a di-
flexible devices and wearable devices. Nevertheless, effective
pole moment to the organic cation, so that the lowering of
molecular symmetry may trigger a low-symmetric polar crys-
tal structure, while the quasi-spherical geometry still makes
ways of controlling the crystal structure and of engineering
desired ferroelectric properties from designed building blocks
are still a largely uncharted territory.
1
0
molecular reorientation easy to arouse ferroelectric ordering.
That is how we designed the metal-free perovskite ferroelec-
tric [Me-dabco]NH (Me-dabco is N-methyl-N′-
diazabicyclo[2.2.2] octonium) more recently.
Ferroelectricity, which means the spontaneous polarization
can be switched by applying an external electric field, is close-
4 3
I
7
ly related to the crystal structures. Only the ten polar point
11
1 2 4
groups: 1 (C ), 2 (C ), m (C1h), mm2 (C2v), 4 (C ), 4mm (C4v), 3
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Scheme 1. The design of molecular ferroelectric [3-O-Q]ClO4 by modifying molecular structure of non-ferroelectric [Q]ClO4.
Disappointedly but admittedly, it seems that the above ideas
are not always going to work very well. For example, we syn-
roelectric axes. This work demonstrates that only taking into
account the roles of both the molecule building blocks and
intermolecular interactions can fully enable the deliberate de-
sign of ferroelectricity. We believe it will be illuminating in
the field of molecular ferroelectrics and greatly widen the
scope of this chemistry.
thesized quinuclidinium perchlorate ([Q]ClO
4
) in the hope of
obtaining another new high-temperature molecular ferroelec-
4
c,9f
tric like the reported [Q]ReO
4
and [Q]IO
4
,
but it adopts a
̅
centrosymmetric cubic space group Pm3m at room tempera-
ture. And, the attachment of a hydroxyl group to the high
+
symmetric [Q] cation failed to change the crystal structure
RESULTS AND DISCUSSION
+
symmetry, as the 3-hydroxyl-quinuclidinium ([3-OH-Q] )
Quinuclidine is a spherical molecule analogous to 1,4-
diazabicyclo[2.2.2]octane. By using quinuclidine as a building
unit, we obtained two high Curie temperature ferroelectrics,
cations remain severe disorder in [3-OH-Q]ClO
replacing –OH by another flexible –CH group lowers the
crystal symmetry to the orthorhombic Pnma space group and
restrains the motion of cations in [3-methyl-
quinuclidinium]ClO ([3-CH -Q]ClO ), the centrosymmetric
nature has not been changed. Even further attempt of a rigid
CH group can’t address such situation. [3-methylene-
quinuclidinium]ClO ([3-CH -Q]ClO ) also has the Pnma
symmetry, although the [3-CH -Q] becomes ordered. At this
4
. Although
3
[
Q]IO
4
and [Q]ReO
4
, possessing the polar Pmn2
1
space group
has a centrosym-
4c,9f
at room temperature.
However, [Q]ClO
4
4
3
4
̅
metric structure with cubic Pm3m space group at 298 K, in
which the quinuclidinium cation and perchlorate anion are
highly disordered (Figure S1 and Table S1). The centrosym-
metric structure excludes the possibility to have above-room-
temperature ferroelectricity. Although it shows a phase transi-
tion at 289 K, the structure below 289 K in the low-
temperature phase (LTP) is still a centrosymmetric one (Fig-
=
2
4
2
4
+
2
point, every door seems to be close to us, is there any avenue
of endowing ferroelectricity? The answer is exploiting inter-
molecular interactions. The shapes, sizes, and symmetries of
molecules are important in the close packing principle, where-
as intermolecular interactions cause deviations from close
packing and hence affect the crystal structures and properties
4
ure S1). Apparently, [Q]ClO is not a ferroelectric.
In order to induce crystallization in a polar space group for
ferroelectric, we then made a subtle molecular modification
for quinuclidine by adding a substituent group to the third
position to change the crystal symmetry (Scheme 1). We first
introduce the flexible –OH group. Unfortunately, [3-OH-
1
2
at a more subtle level. A long-standing issue at the core of
crystal engineering is the balance between close-packing ef-
1
3
fects and intermolecular interactions. Towards the desired
crystal packing and fine-tuning properties, one can employ
numerous intermolecular interactions to assemble molecular
crystals, among which hydrogen bonding with pronounced
directionality and relatively high strength is undoubtedly the
̅
Q]ClO
at 93 K below the phase transition temperature of 210 K (Fig-
ure S2 and Table S1), isostructural to [Q]ClO . The quasi-
4
still adopts the cubic Pm3m space group at 298 K and
4
+
spherical [3-OH-Q] cation also shows freely motion in the
isotropically spherical disorder state. When introducing the
1
4
most effective and widely used tool for crystal design. Here-
+
3 3 4
flexible –CH group, the crystal symmetry of [3-CH -Q]ClO
reduced to the orthorhombic centrosymmetric space group
Pnma at 298 K (Figure S3 and Table S1). The motion of the
cation is obviously restricted, but the [3-CH
in we equipped a =O group to the [Q] cation, and expected
that the formation of the typical and well-known N–H···O=C
hydrogen bond once found in amino acids, peptides and pro-
teins would aid the self-assembly process. The results didn’t
+
3
-Q] cation as
+
+
+
well as perchlorate anion are still orientationally disordered.
[3-CH -Q]ClO undergoes a symmetry-breaking phase transi-
tion from space group Pnma to P2 /n, which is not among the
88 species of ferroelectric phase transition. We then select a
rigid =CH substituent group. The motion of the cation is fur-
ther frozen in [3-CH -Q]ClO , which also crystalizes in an
orthorhombic Pnma space group at 298 K (Figure S4 and
let us down, through trial from [Q] to [3-OH-Q] , [3-CH
3
-Q] ,
-Q] , and [3-oxo-quinuclidinium] ([3-O-Q] ) compo-
nent, we finally harvest an excellent molecular ferroelectric,
3-O-Q]ClO , belonging to the polar orthorhombic space
group Pna2 and having a high Curie temperature (T ) of 457
K, a large saturate spontaneous polarization (P ) of 6.7
μC/cm , and a multiaxial characteristic with 6 equivalent fer-
+
+
3
4
[
3-CH
2
1
1
5
[
4
2
1
c
2
4
S
2
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Table S1). The cation becomes an ordered one, forming a At 473 K in the high-temperature phase, [3-O-Q]ClO
4
1
2
3
4
5
6
7
8
9
hydrogen-bonded dimer with the perchlorate anion though N–
H···O=Cl hydrogen bonds, where the H acceptor is O atom
from the perchlorate anion. The centrosymmetric Pnma space
adopts a real cubic centrosymmetric space group Pm 3̅ m (point
group m 3̅ m) with the CsCl-type structure (Table S1 and Fig-
ure 1c). Both the [3-O-Q] cation and perchlorate anion lie on
+
group maintains at 93 K, which indicates that [3-CH
2
-Q]ClO
4
high-symmetry special cites, which results in a totally disor-
dered state to satisfy the site symmetry. The quasi-spherical
is still a non-ferroelectric. It is found that in molecular crystals,
intermolecular interactions including hydrogen bonds and
+
[3-O-Q] cation was refined as a totally spherical molecule in
9
c,10a
+
halogen bonds also affect the crystal symmetry.
We thus
spite of its molecular geometry, meaning that the [3-O-Q]
further replace the =CH by another rigid substituent group =O,
2
cation shows isotropic motion. It is noted that the high-
in which the O atom can act as a H acceptor. As a result, the
hydrogen-bonding interactions change significantly in [3-O-
temperature structure of [3-O-Q]ClO is isostructural to the
4
room-temperature structure of [Q]ClO . After the introduction
4
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
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6
0
1
2
3
4
5
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0
1
2
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1
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0
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2
3
4
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8
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0
+
+
Q]ClO
polar space group Pna2
4
, which successfully crystalizes in the orthorhombic
at room temperature (Table S1). This
of small rigid =O group to spherical [Q] cation, [3-O-Q]
1
cation still has the quasi-spherical geometry, which is able to
become a totally spherical one at high temperature, as ob-
served for other quasi-spherical cations such as [MeHdab-
space group belongs to the mm2 point group, among the ten
point groups for ferroelectrics.
2
+ 11
11
co] ,
3-ammonioquinuclidinium,
(R)-3-
4
The crystal structure of [3-O-Q]ClO at 298 K is comprised
1
6
17
+
hydroxlyquinuclidinium, and 3-ammoniopyrrolidinium.
of two basic components, one [3-O-Q] cation and one per-
chlorate anion (Figure 1a). Although occupying general
symmetry positions, both of them show some degree of disor-
From the viewpoint of polarization, the direction of [3-O-
+
Q] dipole is nearly perpendicular to the polar c-axis at 298 K
+
+
der. The atomic coordinate of the O atom of [3-O-Q] cation
(Figure 1b), the ferroelectric polarization from [3-O-Q] di-
was split into two parts while the atomic coordinates of all the
four O atoms of perchlorate anion needed to be split to get a
better refinement result. One [3-O-Q] cation connects with
pole is thus negligible. Therefore, we can employ the point
charge model to evaluate the ferroelectric polarization from
ionic part by assuming the positive center is located at N atom
and the negative center is Cl atom. From the atom coordinate,
the distance between positive and negative centers is about
+
another one through N–H···O=C hydrogen bonds with donor-
acceptor distance of 3.045 Å, forming one-dimensional hydro-
gen-bonded chains along the a-axis in a head-to-tail arrange-
ment (Figure 1a). For ionic crystals, this kind of directional
hydrogen-bonding arrangement is favorable to induce crystal-
lization in polar space groups, as found in many ionic ferroe-
2
1.04 Å, which will lead to a polarization of 6.86 μC/cm along
the c-axis. Thus, the ferroelectricity in [3-O-Q]ClO crystal
4
+
mainly stem from charge misalign between [3-O-Q] cations
and perchlorate anions. When an external electric field is ap-
plied, the molecular cations and anions will flip to their oppo-
site but equivalent position through their equilibrium states to
reverse the whole ferroelectric polarization. In this process, the
transition state may be referred to the structural configuration
in paraelectric phase but with lower degree of disorder be-
cause the paraelectric configuration can be thought as the su-
perposition of all equivalent ferroelectric polarization states.
9
c
9c
lectrics such as [Hdabco]ClO
4
,
[Hdabco]BF
4
,
and (R)-3-
1
6
+
hydroxlyquinuclidinium chloride. Additionally, the [3-O-Q]
cation also forms N–H···O=Cl hydrogen bonds with the per-
chlorate anion, which have a directional arrangement as well
(
Figure 1a). In the packing view along the [011] direction,
+
each [3-O-Q] cation sits at the center of eight perchlorate
anions, showing a pseudo-cubic CsCl-type packing structure
(Figure 1b).
On the other hand, in the room temperature structure of [3-
+
CH
2
-Q]ClO
4
, all the [3-CH
2
-Q] cations canceled with each
other exactly (Figure S5), resulting into a centrosymmetric
symmetry of space group Pnma, under which the ferroelectric-
ity is not allowed. Compared with polar [3-O-Q]ClO
the underlying mechanism for the centrosymmetric array in [3-
CH -Q]ClO may lies to the molecular length extension due to
4
crystal,
2
4
the additional two H atoms from C=C parts, which favors an-
tiparallel packing fashion sterically.
To have a deep insight into the structural difference among
[
4 3 2
3-X-Q]ClO (X = H, OH, CH , CH , and O) series, electron
densities of these crystals from X-ray diffraction data are
modelled, providing us with a comprehensive characterization
of chemical bonding in crystals. As shown in Figures 2, S6
and S7, the highly ionic bond nature can be seen from the
electron density distribution (slice) picture, supporting the
effectiveness of the abovementioned point charge model anal-
ysis. Particularly, weak intermolecular interactions, such as
hydrogen bonding effect, are quite different between [3-O-
4 2 4 4
Q]ClO and [3-CH -Q]ClO crystals. In the [3-O-Q]ClO crys-
tal, the N–H···O=Cl interaction is homo-directional and fur-
ther stabilized by additionally directional N–H···O=C interac-
tions (Figure 1a). Such an arrangement is responsible for the
polarization along polar the c-axis. During the polarization
reversal process, the directional hydrogen bond should be bro-
ken in the initial process, but rebuilt immediately when the
opposite polarization state generates. In other words, the hy-
Figure 1. (a) Crystal structure of [3-O-Q]ClO
head-to-tail type one-dimensional hydrogen-bonded chains along
the a-axis. Packing views of [3-O-Q]ClO at (b) 298 K and (c)
73 K.
4
at 298 K, showing
4
4
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drogen bond is generated to stabilize the ferroelectric polariza-
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tion states, which should be destroyed during the ferroelectric
reversal process. The energy required for hydrogen bond
breaking is a part of energy barrier for the polarization inver-
sion. However, in [3-CH -Q]ClO , the main intermolecular
2 4
interaction is the N–H···O=Cl interaction, whose spatial ar-
rangement is forced by the static molecular hindrance. Thus,
the main structural difference between [3-O-Q]ClO
4
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CH -Q]ClO crystals originates from the spatial arrangement
2
4
governed by weak intermolecular interactions and static mo-
lecular hindrance. In addition, the situation that lack of direc-
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tional intermolecular interaction is also found in [3-CH
Q]ClO crystal (Figure S6), which adopts a centrosymmetric
packing pattern with space group of P2 /n even at 93 K. With
regard to [3-OH-Q]ClO and [Q]ClO crystals, the highly dis-
3
-
4
1
4
4
ordered behavior of both cations and anions shows high sym-
metric electron density distribution (Figure S7), which is
broadly similar to the high-temperature phase of [3-O-Q]ClO
Differential scanning calorimetry (DSC) curves of [3-O-
Q]ClO clearly present a pair of large heat anomalies in the
heating-cooling run with a hysteresis of approximately 35 K,
indicating a reversible first-order phase transition at T = 457
K (Figure 3a). Such a high T is rarely seen in molecular fer-
roelectrics, which is even significantly greater than that of
the inorganic ferroelectric BaTiO (393 K). The high T makes
3-O-Q]ClO be able to adapt high-temperature working con-
dition. Entropy change (ΔS) in the heating process is about
4
.
4
c
Figure 2. Electron density distribution ((010) slice) on the y = 1/4
plane in (a) [3-O-Q]ClO and (b) [3-CH -Q]ClO
c
4
2
4
.
5,8
3
c
[
4
-
1
-1
18.2 Jmol K , which gives a N (the ratio of the numbers of
respective geometrically distinguishable orientations) value of
9
according to the Boltzmann equation, ΔS = RlnN (where R is
the gas constant). The large N value suggests an order-
disordered type phase transition, in which the relatively or-
+
dered [3-O-Q] cations and perchlorate anions in the room-
temperature phase become highly disordered in the high-
temperature phase. This is consistent with the structural analy-
sis. In general, a phase transition will accompany anomalous
dielectric behavior. As expected, the real part (ε′) of the com-
plex dielectric constant of [3-O-Q]ClO displays an obvious
4
dielectric anomaly in both the heating and cooling process
(Figure 3b). The tremendous change of ε′ value in the vicinity
c
of T at 1 MHz for polycrystalline sample reveals a ferroelec-
tric-to-paraelectric phase transition feature.
The temperature-dependent second harmonic generation
Figure 3. Ferroelectric related properties of [3-O-Q]ClO
4
. (a)
(
SHG) intensity experiments also verify the first-order phase
transition in [3-O-Q]ClO . As shown in Figure 3c, in the heat-
ing process, the SHG intensity decreases very slowly below T
and changes abruptly to zero at around T . The zero SHG in-
tensity above T and strong SHG intensity below T manifests
DSC curves in a heating-cooling run, showing a high T of 457 K.
c
4
(b) Temperature dependent ε′ (the real part of complex dielectric
permittivity). (c) SHG intensity as a function of temperature. (d)
P−E hysteresis loops measured at 293 K by using the double-
wave method.
c
c
c
c
a centrosymmetric and non-centrosymmetric phase, respec-
tively, corresponding to the phase transition from the centro-
We then directly detect the ferroelectricity of [3-O-Q]ClO
by the measurement of polarization−electric field (P−E) hyste-
resis loops. [3-O-Q]ClO shows a typical ferroelectric J−E
4
̅
symmetric space group Pm3m in room-temperature phase to
the polar one Pna2 in high-temperature phase. Therefore, [3-
O-Q]ClO clearly undergoes a paraelectric-to-ferroelectric
phase transition belonging to the m3mFmm2 type from the
4
1
curve with two opposite peaks at 293 K (Figure 3d). By ac-
4
cumulating the current, we obtained a standard P−E hysteresis
̅
2
loop. The saturate polarization (P
s
) is about 6.7 μC/cm , which
1
5
̅
Aizu rule. The paraelectric point group m3m and ferroelec-
tric point group mm2 have 48 and 4 symmetry elements, re-
spectively, which reveals a multiaxial ferroelectric with 12
crystallographically equivalent polarization directions, corre-
sponding to 6 equivalent ferroelectric axes.
is among the largest one in molecular ferroelectrics. The P
[3-O-Q]ClO is much higher than those for other perchlorate
based ferroelectrics including 4-(cyanomethyl)anilinium per-
s
of
4
2 18
2 9e
chlorate (0.75 μC/cm ) and [Hdabco]ClO
4
(4 μC/cm ) , and
some classical molecular ferroelectrics such as Rochelle salt
2
2
(
(
0.25 μC/cm ), thiourea (3.2 μC/cm ), and triglycine sulfate
2
5a
s
3.8 μC/cm ). The experimental P is comparable to the po-
larization obtained from point charge model.
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To further investigate the ferroelectricity of [3-O-Q]ClO
4
,
1
2
3
4
5
6
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8
9
we have also carried out PFM measurements on its thin film,
which is an effective characterization tool for addressing the
statics and dynamics of ferroelectric domains with no need of
any special treatment. By measuring the amplitude and phase
parameters in a PFM image, the relative strength of piezoelec-
tric coefficient and the polarization orientation of domain can
be acquired, respectively. Figure 4 shows the vertical and
lateral PFM phase and amplitude images for the thin film of
1
9
[
3-O-Q]ClO
4
in the annealed state, which emerges generally in
a reconstructed domain structure after heat treatment above T
c
.
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0
It is clear that the phase patterns are significantly different in
two components, supporting the large amount of domains with
various polarization directions. Moreover, the amplitude pat-
terns are consistent well with the corresponding phase patterns,
where the domain walls appear as darker lines.
Figure 5. The domain switching for the thin film of [3-O-Q]ClO
The panels in each row are arranged as the sequence: topography
top), vertical PFM amplitude (middle) and phase (bottom) imag-
es of the film surface. The images in each column are arranged as
the sequence of (a) Initial state. (b) After the switching produced
by applying with the tip bias of -60 V for 1.5 s.
4
.
(
Domain switching dynamic is an important subject in the
physics of ferroelectrics, which needs an understanding on the
sub-micrometer scale before considering any practical applica-
tions. We then performed the local PFM spectroscopic meas-
4
urements on the thin film of [3-O-Q]ClO for studying the
polarization switching behavior. As shown in Figure 4e,f, the
typical hysteresis and butterfly loops triggered by the applied
voltages are solid evidence for the polarization switching of
ferroelectric domains. Meanwhile, we have also conducted
PFM tip poling experiments to clearly visualize the domain
Figure 4. Vertical and lateral PFM phase (a, c) and amplitude (b,
d) images for the thin film of [3-O-Q]ClO . (e, f) Vertical PFM
4
phase and amplitude signals as functions of the tip voltage for the
selected point, showing local PFM hysteresis and butterfly loops.
switching process, on the thin film of [3-O-Q]ClO with a
4
selected area of 50 μm × 50 μm. For the as-grown state, the
piezoresponse in most regions is almost uniform in both phase
and amplitude images, indicating single-domain state of these
area (Figure 5a). Subsequently, a tip bias of -60 V is applied
to a selected position for 1.5 s. From Figure 5b, the bidomain
pattern with two-tone color contrast and the domain walls with
nearly null signals occurred in the respective phase and ampli-
tude images, which further confirms the polarization switching
of ferroelectric domain. The generated bidomain pattern is not
predefined, which depends on the lateral movement of domain
wall. These PFM results constitute an abundant proof for the
presence of stable and switchable polarization in the thin film
4
of [3-O-Q]ClO .
CONCLUSION
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In summary, we successfully designed a new molecular fer-
roelectric [3-O-Q]ClO by utilizing hydrogen-bonding interac-
tions in the molecular modification of the non-ferroelectric
[Q]ClO . Different from the substituent groups of –OH, –CH
and =CH
Colourless crystals of [Q]ClO
4 4 3
, [3-OH-Q]ClO , [3-CH -
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
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3
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3
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6
Q]ClO and [3-CH -Q]ClO , were obtained by slow evapora-
4
4
2
4
tion of aqueous solutions containing equimolar amounts of
perchloric acid and quinuclidine, 3-hydroxyl-quinuclidine, 3-
methyl-quinuclidine and 3-methylene-quinuclidine, respec-
tively. Slowly evaporating the aqueous solution of equimolar
sodium perchlorate and 3-oxo-quinuclidinium chloride ob-
4
3
,
+
2
, the introduce of =O group with H acceptor to [Q]
results in the formation of N–H···O=C hydrogen bonds. The
directionally head-to-tail type hydrogen bonded chains in [3-
O-Q]ClO
4
facilitate the crystallization in a polar space group
4
tained colourless crystals of [3-O-Q]ClO . Powder X-ray dif-
+
at room temperature. The quasi-spherical [3-O-Q] cation be-
comes a isotropically spherical one in the high-temperature
phase, inducing a paraelectric-to-ferroelectric phase transition.
fraction (PXRD) (Figure S8) and infrared (IR) spectroscopy
(Figure S9) results confirmed the phase purity of all the as-
grown crystals.
0
1
2
3
4
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2
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0
1
2
3
4
5
6
7
8
9
0
[
4
3-O-Q]ClO shows a high Curie temperature of 457 K, a large
Measurements. The methods of single-crystal X-ray dif-
fraction, DSC, dielectric, SHG, P−E hysteresis loop, PFM,
2
saturate polarization of 6.7 μC/cm , and a multiaxial character-
istic with 6 equivalent ferroelectric axes. These ferroelectric
performances are outstanding among molecular ferroelectrics.
This finding demonstrates that the combination of quasi-
spherical molecule building blocks and directional intermolec-
ular interactions is an efficacious design strategy for achieving
superior molecular ferroelectrics.
PXRD, and IR experiments were described in detail
4,10
4
previously. The as-grown crystals of [3-O-Q]ClO were too
small for us to prepare the single crystal sample along the po-
larization direction for P−E hysteresis loop measurements. We
thus used the thin film sample of [3-O-Q]ClO
used for the PFM measurement. The precursor solution was
prepared by dissolving 15 mg [3-O-Q]ClO in 1 mL deionized
water. Spreading 20 µL of the precursor solution on a clean
indium-doped tin oxide (ITO) glass substrate resulted the for-
mation of thin film crystals after the slow solvent evaporation.
The experimental PXRD patterns of the thin film sample
matching well with the simulated ones verifies its phase purity
4
, which was also
4
EXPERIMENTAL SECTION
Materials. Quinuclidine, 3-hydroxyl-quinuclidine, and 3-
oxo-quinuclidinium chloride were commercially available. 3-
Methylene-quinuclidine and 3-methyl-quinuclidine were syn-
thesized by the following procedure.
(
Figure S10). The PXRD patterns also indicate that the thin
3
-methylene-quinuclidine.
Methyltriphenylphosphonium
film clearly shows the (002) polarization direction (Figure
S10). For the P−E hysteresis loop measurement, we dropped
the liquid GaIn eutectic on the thin film sample as the top elec-
trode to form a ITO/[3-O-Q]ClO
architecture.
bromide(142.8 g, 0.4 mol) was added to a suspension of t-
BuOK (33.6 g, 0.3 mol) in anhydrous THF (500 mL) at room
2
temperature under N gas. The mixture was stirred at room
o
4
thin film/GaIn capacitor
temperature for 1 hour, and then heated to 45 C for 1 hour.
The mixture was turned into yellow suspension. After cooling
to room temperature, 3-oxo-quinuclidine (25.0 g, 0.2 mol) (3-
oxo-quinuclidine was neutralized by NaOH aqueous of its
commercially available 3-oxo-quinuclidinium chloride salt) in
anhydrous THF (100 mL) was added dropwise to the yellow
mixture at room temperature. The mixture was heated to reflux
for 4 hours. After cooling to room temperature, the mixture
was filtered, then the filtrate was concentrated by vacuum
ASSOCIATED CONTENT
Supporting Information.
Figures S1–S10, Table S1, and discussion. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
2
evaporator. Et O/petroleum (1/1, 300 mL) was added to the
resultant residue. The obtained white suspension was filtered
through celite and the filter cake was washed with petroleum
(3 × 50 mL). The filtrate was concentrated and dissolved in
200 mL ethyl acetate and then extracted with 1.0 M HCl aque-
ous (3 × 150 mL). The combined water phases were washed
*
xiongrg@seu.edu.cn; *zouwn@ncu.edu.cn; *xieyf@ncu.edu.cn
Notes
The authors declare no competing financial interests.
with CH
NaOH, and extracted with ethyl acetate (3 × 300 mL). The
combined organic phases were dried over Na SO , filtered,
and concentrated to afford a pale yellow oil (15.0 g, yield:
2 2
Cl (3 × 200 mL), then adjusted to pH = 12 with
ACKNOWLEDGMENT
2
4
This work was supported by the National Natural Science Foun-
dation of China (21427801, 21831004 and 91856114).
1
6
(
2
1%) (without further purification for next step). H NMR
CDCl , 400 MHz) δ 4.75 (m, 1H), 4.64 (m, 1H), 3.46 (s, 2H)
.92-2.78 (m, 4H), 2.39-2.36 (m, 1H), 1.74-1.67 (m, 4H).
-methyl-quinuclidine. 3-methylene-quinuclidine (8.0 g,
5.0 mmol) in 50 mL ethanol was added to a suspension of
(0.45g, 2.0 mmol) in ethanol (300 mL) at room tempera-
ture under H gas (with a H gas balloon). The mixture was
REFERENCES
3
(
9
1) (a) Scott, J. Applications of Modern Ferroelectrics. Science 2007, 315,
54; (b) Setter, N.; Damjanovic, D.; Eng, L.; Fox, G.; Gevorgian, S.;
3
Hong, S.; Kingon, A.; Kohlstedt, H.; Park, N.; Stephenson, G.,
Ferroelectric Thin Films: Review of Materials, Properties, and
Applications. J. Appl. Phys. 2006, 100, 051606.
(2) (a) Damjanovic, D. Ferroelectric, Dielectric and Piezoelectric
Properties of Ferroelectric Thin Films and Ceramics. Prog. Phys. 1998, 61,
267; (b) Lovinger, A. J. Ferroelectric Polymers. Science 1983, 220, 1115;
c) Meyer, R. B. Ferroelectric Liquid Crystals; A Review. Mol. Cryst. Liq.
Cryst. 1977, 40, 33.
(3) Haertling, G. H. Ferroelectric Ceramics: History and Technology. J.
Am. Ceram. Soc. 1999, 82, 797.
6
PtO
2
2
2
stirred at room temperature for 3 hours (TLC showed all of 3-
methylene-quinuclidine reacted completely). The mixture was
1
(
filtered through celite and the filtrate was concentrated to ob-
1
tain a colorless oil (7.4 g, yield: 91%). H NMR (CDCl
3
, 400
MHz) δ 3.06-2.99 (m, 1H), 2.82-2.69 (m, 4H), 2.26-2.20 (m,
H) 1.73-1.44 (m, 5H), 1.35-1.28 (m, 1H), 0.96-0.95 (d, 3H, J
6.96).
1
=
(4) (a) Fu, D.-W.; Cai, H.-L.; Liu, Y.; Ye, Q.; Zhang, W.; Zhang, Y.; Chen,
X.-Y.; Giovannetti, G.; Capone, M.; Li, J.; Xiong, R.-G.
Diisopropylammonium Bromide Is
a High-Temperature Molecular
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Page 7 of 8
Journal of the American Chemical Society
Ferroelectric Crystal. Science 2013, 339, 425; (b) Liao, W.-Q.; Zhang, Y.;
(16) Li, P. F.; Tang, Y. Y.; Wang, Z. X.; Ye, H. Y.; You, Y. M.; Xiong, R.
G. Anomalously Rotary Polarization Discovered in Homochiral Organic
Ferroelectrics. Nat. Commun. 2016, 7, 13635.
(17) Pan, Q.; Liu, Z.-B.; Tang, Y.-Y.; Li, P.-F.; Ma, R.-W.; Wei, R.-Y.;
Zhang, Y.; You, Y.-M.; Ye, H.-Y.; Xiong, R.-G. A Three-Dimensional
Hu, C.-L.; Mao, J.-G.; Ye, H.-Y.; Li, P.-F.; Huang, S. D.; Xiong, R.-G. A
Lead-Halide Perovskite Molecular Ferroelectric Semiconductor. Nat.
Commun. 2015, 6, 7338; (c) Tang, Y.-Y.; Li, P.-F.; Shi, P.-P.; Zhang, W.-
Y.; Wang, Z.-X.; You, Y.-M.; Ye, H.-Y.; Nakamura, T.; Xiong, R.-G.
Visualization of Room-Temperature Ferroelectricity and Polarization
Rotation in the Thin Film of Quinuclidinium Perrhenate. Phys. Rev. Lett.
1
2
3
4
5
6
7
8
9
3
Molecular Perovskite Ferroelectric: (3-Ammoniopyrrolidinium)RbBr . J.
Am. Chem. Soc. 2017, 139, 3954.
2
017, 119, 207602; (d) You, Y.-M.; Liao, W.-Q.; Zhao, D.; Ye, H.-Y.;
(18) Cai, H.-L.; Zhang, W.; Ge, J.-Z.; Zhang, Y.; Awaga, K.; Nakamura,
T.; Xiong, R.-G. 4-(cyanomethyl)anilinium Perchlorate: New
Displacive-Type Molecular Ferroelectric. Phys. Rev. Lett. 2011, 107,
147601.
(19) (a) Lee, D.; Lu, H.; Gu, Y.; Choi, S.-Y.; Li, S.-D.; Ryu, S.; Paudel, T.
R.; Song, K.; Mikheev, E.; Lee, S.; Stemmer, S.; Tenne, D. A.; Oh, S. H.;
Tsymbal, E. Y.; Wu, X.; Chen, L.-Q.; Gruverman, A.; Eom, C. B.
Emergence of room-temperature ferroelectricity at reduced dimensions.
Science 2015, 349, 1314; (b) Balke, N.; Winchester, B.; Ren, W.; Chu, Y.
H.; Morozovska, A. N.; Eliseev, E. A.; Huijben, M.; Vasudevan, R. K.;
Maksymovych, P.; Britson, J.; Jesse, S.; Kornev, I.; Ramesh, R.; Bellaiche,
L.; Chen, L. Q.; Kalinin, S. V. Enhanced electric conductivity at
Zhang, Y.; Zhou, Q.; Niu, X.; Wang, J.; Li, P.-F.; Fu, D.-W.; Wang, Z.;
Gao, S.; Yang, K.; Liu, J.-M.; Li, J.; Yan, Y.; Xiong, R.-G. An Organic-
Inorganic Perovskite Ferroelectric with Large Piezoelectric Response.
Science 2017, 357, 306; (e) Liao, W.-Q.; Tang, Y.-Y.; Li, P.-F.; You, Y.-
M.; Xiong, R.-G. Competitive Halogen Bond in the Molecular
Ferroelectric with Large Piezoelectric Response. J. Am. Chem. Soc. 2018,
A
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
(
7
40, 3975.
5) (a) Horiuchi, S.; Tokura, Y. Organic Ferroelectrics. Nat. Mater. 2008,
, 357; (b) Shi, P.-P.; Tang, Y.-Y.; Li, P.-F.; Liao, W.-Q.; Wang, Z.-X.;
Ye, Q.; Xiong, R.-G. Symmetry Breaking in Molecular Ferroelectrics.
Chem. Soc. Rev. 2016, 45, 3811; (c) Tayi, A. S.; Kaeser, A.; Matsumoto,
M.; Aida, T.; Stupp, S. I. Supramolecular ferroelectrics. Nat. Chem. 2015,
3
ferroelectric vortex cores in BiFeO . Nat. Phys. 2012, 8, 81.
7
, 281.
(6) Tang, Y.-Y.; Li, P.-F.; Liao, W.-Q.; Shi, P.-P.; You, Y.-M.; Xiong, R.-
G. Multiaxial Molecular Ferroelectric Thin Films Bring Light to Practical
Applications. J. Am. Chem. Soc. 2018, 140, 8051.
(7) Lines, M. E.; Glass, A. M. Principles and applications of ferroelectrics
and related materials. Oxford university press: 1977.
(8) (a) Zhang, W.; Xiong, R.-G. Ferroelectric Metal–Organic Frameworks.
Chem. Rev. 2012, 112, 1163; (b) Hang, T.; Zhang, W.; Ye, H.-Y.; Xiong,
R.-G. Metal–Organic Complex Ferroelectrics. Chem. Soc. Rev. 2011, 40,
3
577.
(9) (a) Shi, P.-P.; Tang, Y.-Y.; Li, P.-F.; Ye, H.-Y.; Xiong, R.-G. De Novo
Discovery of [Hdabco]BF Molecular Ferroelectric Thin Film for
Nonvolatile Low-Voltage Memories. J. Am. Chem. Soc. 2017, 139, 1319;
b) Szafrański, M.; Katrusiak, A.; McIntyre, G. J. Ferroelectric Order of
4
(
Parallel Bistable Hydrogen Bonds. Phys. Rev. Lett. 2002, 89, 215507; (c)
Katrusiak, A.; Szafrański, M. Ferroelectricity in NH···N Hydrogen
Bonded Crystals. Phys. Rev. Lett. 1999, 82, 576; (d) Tang, Y.-Y.; Li, P.-F.;
Zhang, W.-Y.; Ye, H.-Y.; You, Y.-M.; Xiong, R.-G. A Multiaxial
Molecular Ferroelectric with Highest Curie Temperature and Fastest
Polarization Switching. J. Am. Chem. Soc. 2017, 139, 13903; (e) Tang, Y.-
Y.; Zhang, W.-Y.; Li, P.-F.; Ye, H.-Y.; You, Y.-M.; Xiong, R.-G.
Ultrafast Polarization Switching in a Biaxial Molecular Ferroelectric Thin
4
Film: [Hdabco]ClO . J. Am. Chem. Soc. 2016, 138, 15784; (f) You, Y.-M.;
Tang, Y.-Y.; Li, P.-F.; Zhang, H.-Y.; Zhang, W.-Y.; Zhang, Y.; Ye, H.-Y.;
Nakamura, T.; Xiong, R.-G. Quinuclidinium Salt Ferroelectric Thin-Film
with Duodecuple-Rotational Polarization-Directions. Nat. Commun. 2017,
8
, 14934.
(10) (a) Hua, X.-N.; Liao, W.-Q.; Tang, Y.-Y.; Li, P.-F.; Shi, P.-P.; Zhao,
D.; Xiong, R.-G. A Room-Temperature Hybrid Lead Iodide Perovskite
Ferroelectric. J. Am. Chem. Soc. 2018, 140, 12296; (b) Liao, W.-Q.; Tang,
Y.-Y.; Li, P.-F.; You, Y.-M.; Xiong, R.-G. Large Piezoelectric Effect in a
Lead-Free Molecular Ferroelectric Thin Film. J. Am. Chem. Soc. 2017,
139, 18071; (c) Zhang, W.-Y.; Tang, Y.-Y.; Li, P.-F.; Shi, P.-P.; Liao, W.-
Q.; Fu, D.-W.; Ye, H.-Y.; Zhang, Y.; Xiong, R.-G. Precise Molecular
Design of High-T
MeHdabco]RbI
diazoniabicyclo[2.2.2]octane). J. Am. Chem. Soc. 2017, 139, 10897.
11) Ye, H.-Y.; Tang, Y.-Y.; Li, P.-F.; Liao, W.-Q.; Gao, J.-X.; Hua, X.-
c
3D Organic–Inorganic Perovskite Ferroelectric:
[
3
(MeHdabco N-Methyl-1,4-
=
(
N.; Cai, H.; Shi, P.-P.; You, Y.-M.; Xiong, R.-G. Metal-Free Three-
Dimensional Perovskite Ferroelectrics. Science 2018, 361, 151.
(12) Desiraju, G. R.; Vittal, J. J.; Ramanan, A. Crystal engineering: a
textbook. World Scientific: 2011.
(13) Desiraju, G. R. Crystal Engineering: a Holistic View. Angew. Chem.,
Int. Ed. 2007, 46, 8342.
(14) (a) Arunan, E.; Desiraju, G. R.; Klein, R. A.; Sadlej, J.; Scheiner, S.;
Alkorta, I.; Clary, D. C.; Crabtree, R. H.; Dannenberg, J. J.; Hobza, P.
Definition of the Hydrogen Bond. Pure Appl. Chem. 2011, 83, 1637; (b)
Desiraju, G. R. Hydrogen Bridges in Crystal Engineering: Interactions
without Borders. Acc. Chem. Res. 2002, 35, 565.
(15) Aizu, K. J. Possible Species of “Ferroelastic” Crystals and of
Simultaneously Ferroelectric and Ferroelastic Crystals. Phys. Soc. Jpn.
1
969, 27, 387.
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