Reversible phase transition of 4-ethoxybenzenammonium iodide

Article abstract of DOI:10.1002/zaac.201200406

A new phase transition compound 4-ethoxybenzenammonium iodide (1) (C ₈H₁₂ON⁺·I^-) was determined. Differential scanning calorimetry (DSC) results show sharp peaks appear at 157.93 K (-115.22 °C) on heating and 157.00 K (-116.15 °C) on cooling with ΔH = 120.34 J·mol^-1, ΔS = 0.762 J·mol^-1·K^-1. The dielectric measurements appear clear slope change, which matches well as observed in the DSC results. The crystal structure analyze shows that the space group changes from P2 ₁ at 103(2) K to P2₁/c at 298(2) K during the phase transition process. The essential difference between the two temperature structures is the relative orientation of the oxyethyl group to the benzene ring, slight displacements of the anionic iodine and the packing of the molecular species. Copyright

Full text of DOI:10.1002/zaac.201200406

SHORT COMMUNICATION
DOI: 10.1002/zaac.201200406
Reversible Phase Transition of 4-Ethoxybenzenammonium Iodide
Wen-Xiang Wang*[a] and Xue-Qun Fu[a]
Keywords: Phase transition; Dielectric; Reversible; Ferroelectrics; Iodine
Abstract. A new phase transition compound 4-ethoxybenzenammon-
ium iodide (1) (C8H12ON+·I–) was determined. Differential scanning
the DSC results. The crystal structure analyze shows that the space
group changes from P21 at 103(2) K to P21/c at 298(2) K during the
calorimetry (DSC) results show sharp peaks appear at 157.93 K phase transition process. The essential difference between the two tem-
(–115.22 °C) on heating and 157.00 K (–116.15 °C) on cooling with perature structures is the relative orientation of the oxyethyl group to
ΔH = 120.34 J·mol–1, ΔS = 0.762 J·mol–1·K–1. The dielectric measure-
ments appear clear slope change, which matches well as observed in
the benzene ring, slight displacements of the anionic iodine and the
packing of the molecular species.
Introduction
Results and Discussion
Evaporation of the ethanol solution containing 4-ethoxy-
benzenamine and HI (45%, w/w) leads to the colorless crystals
of 1 (Scheme 1)
With the capability of storing and releasing large amounts
of energy when melting and solidifying at certain temperature,
phase change materials (PCMs) are widely used in nonvolatile
memory storage, electronics, optics, and telecom shelters.[1,2]
Most PCMs used now involve state changes from solid to li-
quid, such as water (from ice to water) and paraffin (from solid
wax to liquid wax). However, smart PCMs with reversible
structural changes without state change have long been an at-
tractive target for scientists and also a great challenge. Gen-
erally, any kind of phase transition is accompanied by an
anomaly of the dielectric constant and heat anomaly during
heating and cooling process.[3] In order to search for phase
transition material, we usually judge by whether anomaly of
the dielectric constant and heat anomaly occurred during heat-
ing and cooling process of the compound.[4]
Scheme 1. Structure of compound 1.
One of the best ways to detect whether phase transition of
the compound is triggered by temperature is to perform DSC
measurement to confirm the existence of heat anomaly oc-
curred during heating and cooling process. Upon heating and
cooling, the crystalline sample of compound 1 undergoes a
single reversible phase transition at ca. Tc = 157 K, showing
an endothermic peak at 157.9 K on heating and an exothermic
peak at 157.0 K on cooling (Figure 1). From the DSC measure-
ment, the value of ΔH = 120.34 J·mol–1 and an entropy in-
In our exploration on multiferroic compounds and searching
for new phase transition materials,[5–11] we discovered that
4-ethoxybenzenammonium iodide (1) undergoes a reversible crease, ΔS = ΔH/T = 0.762 J·mol–1·K–1, are obtained.
phase transition from room temperature to a low temperature
at ca. 157 K. Of great importance is the fact that 1 displays a
dielectric anomaly and sharp peaks in DSC. Interestingly the
similar structure compounds show no such characters.[12]
Herein, we report the synthesis, crystal structure, and dielectric
properties of 1.
* Dr. W.-X. Wang
Fax: +86-25-52090626
E-Mail: wxwang@seu.edu.cn
[a] Ordered Matter Science Research Center
College of Chemistry and Chemical Engineering
Southeast University
Nanjing 211189, P. R. China
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201200406 or from the au-
thor.
Figure 1. DSC diagram of 1.
Z. Anorg. Allg. Chem. 2013, 639, (3-4), 471–474
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
471

W.-X. Wang, X.-Q. Fu
SHORT COMMUNICATION
The temperature-dependent dielectric response, especially in that consists of 4-ethoxybenzenammonium cations and iodine
relatively high frequency range, is very useful in searching anions. The structures of the low temperature phases (LTP)
for phase transition materials in this system. The temperature- and room temperature phase (RTP) are very similar, differing
dependent changes of the real part εЈ of the dielectric constant only in the orientation of the oxyethyl group relative to the
ε*(ε* = εЈ–iεЈЈ) of the powder sample of compound 1 is pre- benzene ring, slight displacements of the anionic iodine and
sented on three selected frequencies, 10 Hz, 100 Hz, and the packing of the molecular species. Crystal data of the title
1 MHz. (see Figure 2) A clear slope of εЈ can be seen as the compound of RTP was refined to a wR2 of 0.24 and LTP was
structural phase transition occur in the vicinity of ca. 160 K, correspondingly 0.27, which seems to be not as good as ex-
which matches well as observed in the DSC results.
pected, but they clearly show how the phase transition occurs.
The absolute configuration of LTP structure is determined
using anomalous scattering.
A precise analysis of the important packing and interaction
differences between the two structures is needed to discover
how the phase transition occurs. The most obvious difference
in conformation between the two phases is the orientation of
the oxyethyl group relative to the benzene ring. This can be
seen by comparison to Figure 3(a) and (b), where both views
Figure 2. Temperature dependencies of the real part of the permittivity
of 1 at 10–1000 kHz.
Structural determinations, especially variable-temperature
single-crystal X-ray diffraction, act as direct methods to show
these structural symmetry changes to reveal microscopic
mechanisms of phase transition. However, structural analysis
of phase transition of a crystal compound is often difficult be-
cause small displacements of the ions are highly correlated
with each other and with thermal parameters, which can result
in inaccurate refined values and multiple solutions. Single
crystal X-ray analysis (Table 1) reveals that the structures of
Figure 3. View of the asymmetry unit of 1 with atomic numbering
the two isomorphs both contain the same basic structural unit scheme (a) at 298(2) K and (b) 103(2) K.
Table 1. Summary of crystallographic data for compound 1 at 298 K and 103 K.
1, 298 K, RTP
1, 103 K, LTP
Empirical formula
Mr
C8H12NO,I
265.09
C8H12NO,I
265.09
Crystal system, space group
Temperature /K
monoclinic, P21/c
298
monoclinic, P21
103
a /Å
b /Å
c /Å
12.165(2),
6.9284(14),
12.700(3)
97.96(3)
1060.1(4)
4
12.079(2),
6.9033(14),
6.1103(12)
99.59(3)
502.39(17)
2
β /°
V /Å3
Z
Radiation type
Absorption correction
Crystal size /mm
F(000)
Mo-Kα
Mo-Kα
Multi-scan
0.45ϫ0.40ϫ0.40
512
Multi-scan
0.45ϫ0.40ϫ0.40
256
Tmin / Tmax
Flack parameter
h, k, l (min, max)
wR2
0.273 / 0.304
–-
(–15, 15); (–8, 8); (–16, 16)
0.2466
0.266 / 0.285
0.1 (3)
(–15, 13); (–8, 8); (–7,7)
0.2706
R1
0.0874
0.1085
472
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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 471–474

Reversible Phase Transition of 4-Ethoxybenzenammonium Iodide
along the direction of benzene ring perpendicular to the paper.
In the RTP structure, all non-hydrogen atoms in the 4-ethoxy-
benzenammonium are nearly coplanar and a mirror plan passes
through the 4-ethoxybenzenammonium plan with the dihedral
angle between oxyethyl group and benzene ring 7.5°, whereas
in the LTP structure, the oxyethyl group deviates from the
benzene ring gives the dihedral angle 99.6°, which leads to the
loss of the mirror plan.
This conformation is stabilized by electrostatic interactions
between cations and anions. The N1···I1, and C6···I1 distances
are 3.526 Å and 4.558 Å, respectively, in the RTP structure. In
the LTP structure, the corresponding values are 3.489 Å and
4.185 Å. Furthermore, the bond length of N1···C6 in the cation
is decreased from1.454 Å in the RTP structure to 1.488 Å in
the LTP structure. (Table S1, Supporting Information)
Beside the electrostatic interactions of the iodine ion and
ammonium cation, the N–H···I hydrogen bonds are main mole-
cule interaction. Both structures of 1 (4-ethoxybenzenammon-
ium cations related by the translation along the b axis) are
linked by N–H···I hydrogen bonds to form one-dimensional
chains. Compared with the RTP structure, the hydrogen bond
lengths [N···I 3.58 Å, N–H···I 139.6° at 298 K] decrease a little
[N···I, 3.51 Å, N–H···I 136.6°at 103 K]. (Table S2, Supporting
Information)
The two adjacent benzene rings are approximately vertical
along c axis with the dihedral angle 86.5° in the RTP structure,
whereas the corresponding rings in the LTP structure are com-
pletely parallel. From the cell packing view along the c axis,
molecules in the RTP structure at 298(2) K are a little twisty
and the oxyethyl units have two different orientations. In the
LTP structure at 103(2) K, molecules are overlapped along c
axis and the oxyethyl units have the same orientation (Fig-
ure 4).
The RTP structure shows that 1 crystallizes in a centrosym-
metric space group (P21/c) belonging to a nonpolar point
group (C2h), whereas the LTP structure reveals that the mirror
plane disappears, resulting in a decrease in the number of sym-
metric elements from four (E, I, C2, and δh) to two (E and C2)
(space group P21). The new point group (C2), which is a sub-
group of the paraelectric phase (point group C2h), obeys the
Landau theory and suggests that this phase transition may be
successive. At the same time, this phase transition obeying the
Aizu rule, written as 2/mF2,[13] is a continuous second-order
phase transformation. A similar case occurred in triglycine
sulfate (TGS), where the mirror disappears from a paraelectric
phase (space group P21/m, point group C2h) above TC (49 °C)
to a ferroelectric phase (space group P21, point group C2) upon
a temperature decrease, halving the number of symmetric ele-
ments from four (E, I, C2, and δh) to two (E and C2) in accord
with Landau second-order phase transition theory and an Aizu
presentation of 2/mF2.[13,14]
Figure 4. Packing diagrams (a) at 298(2) K and (b) 103(2) K of 1
viewed along the c axis, the dashed lines show the hydrogen bonding.
and sufficient requirements for ferroelectrics. This phase tran-
sition obeys the Landau second-order phase transition theory
and an Aizu rule presentation of 2/mF2. The combined DSC
measurement, dielectric measurement, and structural analysis
reveal that the phase transition shows reversible characters at
about 157 K.
Experimental Section
General: Chemicals and solvents in this work were commercially ob-
tained as chemically pure and used without any further purification.
Infrared spectra were taken with a Bruker Vector 22 spectrophotometer
as KBr pellets in the 4000–400 cm–1 region. Powder X-ray diffraction
measurements were made with a Rigaku/ D-MAX diffraction system,
equipped with a copper X-ray tube [λ(Cu-Kα) = 1.5406 ] and a graphite
monochromator. The powder patterns reported are the result of ad-
dition of three single scan patterns from 2θ = 5° to 2θ = 50° at 5° per
min with an increment of 0.02°. Single-crystal data were collected at
298(2) K and 103(2) K with a Rigaku SCXmini CCD diffractometer
equipped with graphite-monochromated Mo-Kα radiation. DSC mea-
surements were performed with a PerkinElmer Diamond DSC in a
nitrogen atmosphere in aluminum crucibles with a heating or cooling
rate of 10 K·min–1. Dielectric permittivities were measured with an
Agilent or a TH2828A impedance analyzer.
Preparation: Complex 1 was readily obtained as colorless lamellate
crystals by slow evaporation at room temperature out of an ethanol
solution of an equimolar ratio of 4-ethoxybenzenamine and hydroiodic
acid. 1H NMR (300 MHz, D2O): δ = 7.15 (d, J = 9.0 Hz, 2H in phenyl
Conclusions
The title compound 1 undergoes a phase transition from a
paraelectric phase (P21/c) at room temperature to a ferroelec-
tric phase (P21) at low temperature and meets the necessary ring), 6.90 (d, J = 9.0 Hz, 2H in phenyl ring), 3.94 (q, 2H in ethyl),
Z. Anorg. Allg. Chem. 2013, 471–474
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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W.-X. Wang, X.-Q. Fu
SHORT COMMUNICATION
1.19 (t, 3H in ethyl) (Figure S1; Supporting Information). IR (KBr):
ν˜ = 3414 (s), 3126 (s), 2902 (s), 2852 (m), 1620 (w), 1575 (w), 1500
(w), 1087 (w), 962 (w) cm–1 (Figure S2). The powder XRD pattern of
1 match very well with the pattern simulated from the single-crystal
structure at room temperature. (Figure S3)
References
[1] J. Valasek, Phys. Rev. 1921, 17, 475.
[2] G. H. Haertling, J. Am. Ceram. Soc. 1999, 82, 797.
[3] S. Horiuchi, Y. Tokura, Nat. Mater. 2008, 7, 357.
[4] T. Akutagawa, H. Koshinaka, D. Sato, S. Takeda, S. Noro, H.
Takahashi, R. Kumai, Y. Tokura, T. Nakamura, Nat. Mater. 2009,
8, 342.
[5] L. Z. Chen, H. Zhao, J. Z. Ge, R. G. Xiong, H. W. Hu, Cryst.
Growth Des. 2009, 9, 3828.
[6] W. Zhang, L. Z. Chen, R. G. Xiong, T. Nakamura, S. D. Huang,
J. Am. Chem. Soc. 2009, 131, 12544.
[7] W. Zhang, H. Y. Ye, R. G. Xiong, Coord. Chem. Rev. 2009, 253,
2980.
[8] H. Zhao, Z. R. Qu, H. Y. Ye, R. G. Xiong, Chem. Soc. Rev. 2008,
37, 84.
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-783606 and CCDC-783607 (Fax: +44-1223-336-033;
E-Mail: deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
[9] Q. Ye, X. S. Wang, H. Zhao, R. G. Xiong, Chem. Soc. Rev. 2005,
34, 208.
[10] R. G. Xiong, J. L. Zuo, X. Z. You, H. K. Fun, S. S. S. Raj, New
J. Chem. 1999, 23, 1051.
[11] Z. F. Chen, R. G. Xiong, J. L. Zuo, Z. J. Guo, X. Z. You, H. K.
Fun, J. Chem. Soc. Dalton Trans. 2000, 22, 4013.
[12] X. Q. Fu, Acta Crystallogr. Sect. E 2010, 66, o1944.
[13] K. Aizu, Phys. Rev. B 1970, 2, 754.
Supporting Information (see footnote on the first page of this article):
Details of 1H NMR, the IR spectra, as well as the powder XRD pattern
of 1 (Figures S1–S3); bond lengths and angles of 1 (Table S2); hydro-
gen bond lengths (Table S2).
[14] X. Solans, M. Font-Altaba, F. Franco, J. Fernandez-Ferrer, Ferro-
electrics 1984, 59, 241.
Acknowledgements
This work was supported by the National Natural Science Foundation
of China (21071030) and Jiangsu Province (BK2010425).
Received: September 12, 2012
Published Online: December 14, 2012
474
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Z. Anorg. Allg. Chem. 2013, 471–474