Ionic liquid crystals based on 1-alkyl-3-methylimidazolium cations and perfluorinated sulfonylimide anions

Article abstract of DOI:10.1016/j.cplett.2015.04.003

Abstract In contrast to the studies on ionic liquids based on perfluorinated sulfonylimide anions, their ionic liquid crystals were seldom reported. In the present study, four 1-alkyl-3-methylimidazolium perfluorinated sulfonylimide salts ([C_xMIm][N(SO₂R_F)₂], x = 18 and 22; R_F = F (FSI) and CF₃ (TFSI)) have been synthesized and characterized. [C₂₂MIm][FSI], [C₁₈MIm][FSI], and [C₂₂MIm][TFSI] show smectic A₂ liquid crystalline mesophase. Single-crystal XRD revealed that [C₁₈MIm][FSI] and [C₂₂MIm][TFSI] show layered structures of low-polar and high-polar layers alternate with each other in the crystalline phase. It is suggested that perfluorinated sulfonylimide anions have relatively weak coulomb interactions with imidazolium headgroups, making them relatively difficult to form mesophase.

Full text of DOI:10.1016/j.cplett.2015.04.003

Accepted Manuscript
Title: Ionic Liquid Crystals Based on
1-Alkyl-3-methylimidazolium Cations and Perfluorinated
Sulfonylimide Anions
Author: Ting Li Fei Xu Wei Shi
PII:
S0009-2614(15)00227-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.cplett.2015.04.003
CPLETT 32904
To appear in:
Received date:
Revised date:
Accepted date:
9-2-2015
24-3-2015
5-4-2015
Please cite this article as: T. Li, F. Xu, W. Shi, Ionic Liquid Crystals Based on 1-Alkyl-
3-methylimidazolium Cations and Perfluorinated Sulfonylimide Anions, Chem. Phys.
Lett. (2015), http://dx.doi.org/10.1016/j.cplett.2015.04.003
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

Highlights
●
●
●
●
1-Alkyl-3-methylimidazolium perfluorinated sulfonylimide ionic liquid crystals.
Smectic A liquid crystalline mesophase was observed.
Layered structure was determined for the crystalline phase by single-crystal XRD.
Perfluorinated sulfonylimide anion is relatively difficult to form liquid crystal.
1
Page 1 of 21

Graphical Abstract
Thermal and Structural Properties of 1-Alkyl-3-methylimidazolium Perfluorinated
Sulfonylimide Ionic Liquid Crystals, and explanation for why ionic liquid crystals based on
perfluorinated sulfonylimide anions are rare.
2
Page 2 of 21

Ionic Liquid Crystals Based on 1-Alkyl-3-
methylimidazolium Cations and Perfluorinated
Sulfonylimide Anions
Ting Li,a Fei Xu,*b Wei Shi*c
a
College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan,
430074, China
b School of Power and Mechanical Engineering, Wuhan University, Wuhan, 430072, China
c College of Science, Huazhong Agricultural University, Wuhan, 430070, China
* Email: xufei2058@163.com (Fei Xu), shiwei@mail.hzau.edu.cn (Wei Shi)
3
Page 3 of 21

Abstract
In contrast to the studies on ionic liquids based on perfluorinated sulfonylimide anions, their ionic liquid
crystals were seldom reported. In the present study, four 1-alkyl-3-methylimidazolium perfluorinated
sulfonylimide salts ([CxMIm][N(SO2RF)2], x = 18 and 22; RF = F (FSI) and CF3 (TFSI)) have been
synthesized and characterized. [C22MIm][FSI], [C18MIm][FSI], and [C22MIm][TFSI] show smectic A2
liquid crystalline mesophase. Single-crystal XRD revealed that [C18MIm][FSI] and [C22MIm][TFSI]
show layered structures of low-polar and high-polar layers alternate with each other in the crystalline
phase. It is suggested that perfluorinated sulfonylimide anions have weak interactions with imidazolium
headgroups, making them relatively difficult to form mesophase.
Keywords
Ionic liquids, Liquid crystals, Mesophases, Smectic, Perfluorinated sulfonylimide
4
Page 4 of 21

Introduction
Ionic liquid crystals (ILCs) are substances that possess the properties of both ionic liquids (ILs) and
liquid crystals.1,2 Ionic liquid crystals have an anisotropic structural organization composed of only ionic
species, which makes them superior candidates to design one-dimensional,3–5 two-dimensional,6,7 or
three-dimensional8,9 ion-conductive materials, as well as anisotropic reaction media.10 Because of the
widespread use of imidazolium-based ILs with low melting point and low viscosity, imidazolium-based
ILCs are frequently studied by combination with various functional groups to form different liquid
crystalline (LC) mesophases.1,2 In particular, ILCs based on 1-alkyl-3-methylimidazolium cations
(CxMIm+, where x denotes the carbon number of the alkyl chain) attract special research interest, not
only because of their potential application in dye-sensitized solar cells,11–14 but also due to their
structural simplicity to investigate the effects of alkyl chain length and anionic species on the properties.
For example, 1-alkyl-3-methylimidazolium cations with long alkyl chains were combined with a variety
–
–
of anions such as chloride (Cl–),15 bromide (Br–),16 tetrachlorometallate (CoCl4 and NiCl4 ),15
–
– 18,19
–
–
–
–
tetrafluoroborate (BF4 ),17 hexafluorocomplex (PF6 ,
AsF6 , SbF6 , NbF6 , and TaF6 ),20
–
trifluoromethylsulfonate (OSO2CF3 ),16 fluorohydrogenate ((FH)nF–),21,22 perhalogeno carborane
2–
3–
(B10Cl10
and B12Cl122–),23 bromoeuropate ([EuBr6]3–Br–),24 hexabromoterbate (TbBr6 ),25
3–
3–
fluoroaluminate (Al2F9 ),26 and hexanitratolanthanate (La(NO3)6 ).27 The temperature range of LC
mesophase observed for these salts increases with increasing alkyl chain length, although the alkyl chain
length where mesophase appears depends on the anionic species.
Perfluorinated sulfonylimide anions ([N(SO2RF)2]–, where RF denotes perfluoroalkylsulfonyl groups
or F atoms) draw continuous research interest, because of their delocalized negative charge and high
conformational degrees of freedom, originated from the electron-withdrawing perfluoroalkylsulfonyl
groups or F atoms conjugated by the flexible S–N–S bonds. Such a weak coordinating nature makes
them superior anions for designing IL electrolytes.28 For example, ILs based on
bis(trifluoromethanesulfonyl)imide ([N(SO2CF3)2]–, TFSI–) or bis(fluorosulfonyl)imide ([N(SO2F)2]–,
FSI–) anions show low viscosities, high conductivities, and wide electrochemical windows, which are
advantageous for electrolytes used in lithium secondary batteries.29–32 Besides, mixtures of alkali salts
5
Page 5 of 21

based on FSI– or TFSI– anions have also been demonstrated to be superior intermediate-temperature IL
electrolytes for sodium or lithium secondary batteries.33,34 However, in contrast to the numerous
researches on the ILs, reports on ILCs based on perfluorinated sulfonylimide anions are relatively
fewer.35,36 For example, for the 1-alkyl-3-methylimidazolium cations, although some attempts have been
made by the combination of it with TFSI– anion,37–43 ILCs were only encountered in quite limited
cases.42,43 Hence, it is necessary to investigate why the perfluorinated sulfonylimide anions are
relatively more difficult to form ILCs.
Herein, four 1-alkyl-3-methylimidazolium perfluorinated sulfonylimide salts ([CxMIm][N(SO2RF)2], x
= 18 and 22; RF = F (FSI) and CF3 (TFSI)) were synthesized and characterized. The imidazolium
cations with a normal alkyl chain were chosen because such a simple cation structure is preferable to
investigate the effects of the anion on the thermal and structural properties, especially when compared
with previous reported CxMIm-based ILCs. Physicochemical properties and structures of the obtained
salts were studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and
X-ray diffraction (XRD). Crystal structures of two salts, [C18MIm][FSI] and [C22MIm][TFSI], were also
determined.
Results and discussion
Thermal properties. All the four salts are white hydrophobic solid at room temperature. Figure 1
shows the DSC curves of the four salts (heating process), and Figures 2 and 3 show the detailed DSC
curves of [C18MIm][FSI] and [C22MIm][TFSI], respectively. Table 1 summarizes the obtained DSC data
(phase transition temperature, ΔH, and ΔS). Identical DSC curves are observed during the first and
second heating processes for all the four salts, suggesting they are thermally stable up to 200 °C. As
shown in Figure 1, the largest endothermic peak corresponds to melting (phase transition from crystal to
liquid crystal or isotropic liquid). The relatively large ΔH (and thus ΔS) at the melting point is ascribed
to the breakup of a three-dimensionally positional order of the crystal lattice. The small peak
corresponding to clearing (phase transition from liquid crystal to isotropic liquid) above the melting
point is observed for [C22MIm][FSI], indicating the formation of LC mesophase. The small ΔH (and
6
Page 6 of 21

thus ΔS) at the clearing point illustrates liquid crystal is a state of high disorder, namely more like liquid
rather than crystal. It is noteworthy that a small exothermic peak appeared for [C18MIm][FSI] around
70 °C during the cooling process (Figure 2). This transition is quite near the melting point and can only
be observed in the heating process at a lower scan rate of 0.5 °C min–1 (Figure 2, insert), similar with the
previously reported [C14MIm][PF6].20 Although a small peak was also found in the cooling step for
[C22MIm][TFSI] (Figure 3), the phase transition temperature (65.4 °C, Table 1) is slightly lower than
the melting point (65.9 °C, Table 1), and no peak was found above the melting point during the heating
process even at a scan rate as low as 0.5 °C min–1 (Figure 3, insert). The results above demonstrate
[C18MIm][FSI] shows a narrow enantiotropic LC mesophase whereas [C22MIm][TFSI] shows a
monotropic one. As listed in Table 1, the C22MIm salts have a higher melting point than the
corresponding C18MIm ones. This can be interpreted by their special crystal structures (see the crystal
structure section). Extension of the alkyl chain of the amphipathic cation enhances a clear phase-
segregation of high-polar (imidazolium headgroups and anions) and low-polar (long alkyl chains)
regions, leading to a higher packing order and thus higher melting point.17,18,20 Similar phenomena were
also observed for other CxMIm-based ILCs and such a packing mode is not an uncommon case.18–
20,24,44,45
For a given anion, extension of the alkyl chain (from [C18MIm][FSI] to [C22MIm][FSI])
strengthens the van der Waals interaction and increases the clearing point considerably, resulting in a
wider LC mesophase.15,17,18,20,21 For a given cation, [C22MIm][FSI] shows a wider LC mesophase (51.4
°C) than [C22MIm][TFSI] (9.2 °C, but not thermodynamically stable), due to the smaller anion and thus
stronger coulombic interaction.
7
Page 7 of 21

Figure 1. Differential scanning calorimetric curves (heating process) for the four salts at 5 °C min–1.
Figure 2. Differential scanning calorimetric curves of heating and cooling processes for [C18MIm][FSI]
at 5 °C min–1 and heating process at 0.5 °C min–1 (insert).
8
Page 8 of 21

Figure 3. Differential scanning calorimetric curves of heating and cooling processes for
[C22MIm][TFSI] at 5 °C min–1 and heating process at 0.5 °C min–1 (insert).
Table 1. Summary of the DSC data
Transitiona
T (°C)
67.1
77.9
129.3
65.9
65.4
56.2
40.1
65.7
65.6
69.6
52.2
ΔH (kJ mol–1) ΔS (J mol–1 K–1)
Cryst1–Cryst2
Cryst2–SmA2
SmA2–Iso
6.5
41.2
0.6
19.0
117.0
1.4
[C22MIm][FSI]
Cryst–Iso
Iso–SmA2b
45.5
0.6
134.1
1.8
[C22MIm][TFSI]
SmA2–Cryst b
Cryst1–Cryst2
Cryst2–Iso
Cryst2–SmA2c
SmA2–Isoc
44.8
0.2
136.0
0.6
4.1
12.1
11.5
[C18MIm][FSI]
3.9
0.03
0.09
[C18MIm][TFSI] Cryst–Iso
39.9
122.7
aThe symbols, Cryst, Iso, and SmA2 denote crytstal, isotropic liquid, and smectic A2
liquid crystal, respectively. bThese transitions were determined from the cooling process.
cThese transitions were determined from DSC recorded at 0.5 °C min–1.
It was illustrated in previous reports that for the CxMIm-based ILCs, both the van der Waals
interaction between the alkyl chains and the interaction between the imidazolium headgroup and anion
assist the formation of LC mesophase.15–18,20,21 Consequently, the shortest alkyl chain needed to form
9
Page 9 of 21

LC mesophase reflects the strength of the interaction between the anion and imidazolium headgroup.
For example, [CxMIm][BF4], [CxMIm][PF6], and [CxMIm][AsF6] shows LC mesophase from x = 12,17
14,18–20 and 16,20 respectively, which is in good agreement with the decreasing coulombic interaction
with increasing anion size. Usually, n-octadecyl (x = 18) is long enough for the CxMIm+ cation to form
LC mesophase with most anions.15–18,20,21 However, [C18MIm][FSI] only gives a narrow LC mesophase
(4.0 °C, Table 1), and [C18MIm][TFSI] shows no LC properties. This result indicates that the
perfluorinated sulfonylimide anions has a weak cation-anion interaction with the imidazolium
headgroups, and calls for a longer alkyl chain (x = 22, and thus stronger van der Waals interaction) to
form LC mesophase. On the other hand, a comparison of ΔH at the clearing point can also shed light on
the strength of the cation-anion interactions. For instance, [C18MIm][FSI] gives a ΔH of 0.03 kJ mol–1
(Table 1), which is much lower than other C18MIm-based ILCs (e.g., 1.7 kJ mol–1 for [C18MIm][Cl],16
1.0 kJ mol–1 for [C18MIm][BF4],17 and 1.1 kJ mol–1 for [C18MIm][PF6]).20 This is also indicative of the
weak cation-anion interaction between FSI– anion and imidazolium headgroup. It is thus suggested from
the results above that, the weak cation-anion interaction between the perfluorinated sulfonylimide
anions and imidazolium headgroups makes them relatively difficult to form LC mesophase.37–43
Structural properties. The crystal structures of [C18MIm][FSI] (25 °C, cryst1 in Table 1) and
[C22MIm][TFSI] (–100 °C) are determined, which are the first cases for ILCs based on perfluorinated
sulfonylimide anions to the best of our knowledge. Determination of the crystal structure for
[C18MIm][FSI] at –100 °C was relatively difficult, as the crystal collapsed upon the crystal-crystal phase
transition (40 °C) during the cooling process. Table 2 gives the crystallographic data and refinement
results. Figure 4 shows the crystal structure of [C18MIm][FSI] at 25 °C (see Figure 4a for the
asymmetric unit with atom labelling). The long alkyl chain of the cation keeps an all-trans conformation
from C6 to C23. The FSI– anion shows a cis conformation, where cis or trans indicate the F atoms
locate on the same or opposite sides, respectively, relative to the plane defined by the S−N−S bonds.
Although the trans conformer is more stable than the cis one according to the gas-phase computation,46–
the energy barrier is small and both conformers could be found in previous reports.49–56 The bond
48
lengths and bond angles for the FSI– anion here are generally in good agreement with previously
10
Page 10 of 21

reported values (Tables S1 and S2, Supporting Information).51–56 As shown in Figures 4b and 4c, the
packing mode is described as a layered structure of high-polar and low-polar domains. The high-polar
domain is consisted of a double layered imidazolium headgroups and FSI– anions, and in each layer the
anion is located in the center of four imidazolium headgroups (Figure 4d). The high-polar domains are
separated by interdigitated alkyl chains (low-polar domains) tilted relative to the ionic layers (see Table
S3, Supporting Information, for the calculated tilted angles). This packing mode is quite similar with
previously reported [C14MIm]Cl·H2O,44 [C12MIm]Br·H2O, and [C14MIm]Br·H2O,45 only with different
low-polar layer thickness, because of the different alkyl chain lengths. Table S4 lists the D–H∙∙∙A
interactions for [C18MIm][FSI]. All the O and N atoms of the FSI– anion are involved in short contacts
(below the sum of van der Waals radii) with H atoms of the imidazolium ring (O1, O2, O3, and N11) or
that of the alkyl side-chains (O3 and O4). Bifurcation of the D–H···A bonds is observed for H atoms
(H2 and H5) which interacts with two atoms (O1 and O3, O2 and N11, respectively) of FSI–. No D–
H∙∙∙A interaction is observed for the two F atoms of the FSI– anion.
Table 2. Summary of crystal data and refinement results for [C18MIm][FSI] and [C22MIm][TFSI]
[C18MIm][FSI]
C22H43F2N3O4S2
515.71
[C22MIm][TFSI]
C28H51F6N3O4S2
671.84
Formula
Fw
crystal size (mm)
T (°C)
0.30×0.28×0.14
25
0.36×0.30×0.12
–100
crystal system
space group
a (Å)
Triclinic
P–1
Triclinic
P–1
5.4261(9)
8.0014(13)
32.313(5)
85.694(3)
85.871(3)
81.293(3)
1380.2(4)
2
8.0810(12)
13.337(2)
31.734(5)
89.084(4)
84.378(3)
88.172(3)
3401.7(9)
4
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
ρcalcd (g cm–3)
F(000)
μ (mm–1)
λ (Å)
1.241
1.312
556
1432
0.237
0.225
0.71073
0.71073
11
Page 11 of 21

Reflns collected/unique
R1(Fo)a
11788/5365
0.0922
11836/11836
0.0566
0.1573
0c
2 b
wR2(Fo )
0.2692
Rint
0.0580
2
2 2
aR1 = ∑||Fo| – |Fc||/∑|Fo| for I > 2σ(I). bwR2 = {∑[w(Fo – Fc2)2]/∑[w(Fo ) ]}1/2 for I
> 2σ(I). cCrystal twinning.
Figure 4. Crystal structure of [C18MIm][FSI] at 25 °C. Thermal ellipsoids are drawn at the 50%
probability level. a) Asymmetric unit with atom labelling scheme, b) packing diagram along a axis, c)
packing diagram along b axis, d) configuration of imidazolium headgroups and FSI– anions along c axis.
Figure 5 shows the crystal structure of [C22MIm][TFSI] at –100 °C. The asymmetric unit contains two
pairs of cations and anions, which show quite similar structures (Figures 5a and 5b). For both cations
(Cation 1 in Figure 5a and Cation 2 in Figure 5b), the long alkyl chain keeps an all-trans conformation,
but the C–N bond which links the imidazolium headgroup (N1–C6 and N31–C36) shows a gauche
conformation relative to the alkyl chain, similar with a previously reported [C6MIm][TFSI].57 Both
anions (Anion 1 in Figure 5a and Anion 2 in Figure 5b) show a trans conformation (–CF3 groups locate
on the opposite sides of the plane defined by the S−N−S bonds), which is more stable than the cis
conformer due to the bulky –CF3 group.58,59 The bond lengths and bond angles for the TFSI– anion here
12
Page 12 of 21

are generally in good agreement with previously reported values (Tables S1 and S2, Supporting
Information).57,59–62 Phase-segregation of high-polar (imidazolium headgroups and anions) and low-
polar (long alkyl chains) regions is also observed in the packing mode (Figures 5c and 5d). The double
layered ion configuration of imidazolium headgroups and anions resembles that of [C18MIm][FSI] case
(Figure S1). It is interesting to note that [C22MIm][TFSI] has a smaller c cell parameter (31.734 Å,
Table 2) than [C18MIm][FSI] (32.313 Å, Table 2), in spite of a longer alkyl chain and a larger anion,
indicating a larger tilted angle for the alkyl chains (Table S3, Supporting Information). The increase in
tilted angle is due to the larger TFSI– anion and weaker cation-anion interaction, since it is revealed in
[CxMIm][PF6] series that extension of the alkyl chain will not change the tilted angle or ion
configuration (the imidazolium cations and anions) significantly.18–20 Table S5 lists D–H∙∙∙A interactions
for [C22MIm][TFSI]. All the O and N atoms of the TFSI– anion are involved in short contacts with H
atoms of the imidazolium ring (O3, O5, and O7) or that of the alkyl side-chains (O1, O2, O3, O4, O6,
O8, N11, and N41), and only one F atom (F5) is found to form D–H∙∙∙A interactions. Bifurcation of the
D–H···A bonds is not observed. The results of D–H∙∙∙A interactions for [C18MIm][FSI] and
[C22MIm][TFSI] suggest the negative charge is mainly located on the N and O atoms of the FSI– and
TFSI– anions.
13
Page 13 of 21

Figure 5. Crystal structure of [C22MIm][TFSI] at –100 °C. Thermal ellipsoids are drawn at the 50%
probability level. a) Atom labelling scheme for Cation 1 and Anion 1, b) atom labelling scheme for
Cation 2 and Anion 2, c) packing diagram along b axis, d) packing diagram along a axis.
Figure 6 shows the polarized optical microscopic (POM) textures of [C22MIm][FSI], [C18MIm][FSI],
and [C22MIm][TFSI]. Smooth fan-like or focal conic defect textures were seen in the mesophase, along
with black pseudo-isotropic regions, indicating the formation of uniaxial smectic A LC mesophase. The
broken fan-like texture which is indicative of the smectic C mesophase was not observed in the LC
mesophase on cooling from the isotropic phase to the crystalline phase.42,63 These results of POM
combined with the XRD study below suggest that the LC mesophase is assigned to smectic A
type.1,15,17,18,21 Such a smectic A LC mesophase is common for the CxMIm-based ILCs, since the cation
is much larger than the anion and dominates the formation of the smectic layers.15–18,21 Monotropic
mesophase was confirmed for [C22MIm][TFSI], on the basis that the textures were observed only in the
cooling process (Figure 6c), in good accordance with the DSC results.
Figure 6. Polarized optical microscopic texture of a) [C22MIm][FSI] at 100 °C (heating from the crystal
phase), b) [C18MIm][FSI] at 68 °C and c) [C22MIm][TFSI] at 65 °C (cooling from the isotropic phase).
14
Page 14 of 21

Figure S2 shows the XRD patterns (2° < 2θ < 30°) of [C22MIm][FSI] (100 °C) and [C18MIm][FSI]
(68 °C) in the LC mesophase (See Figure S3, Supporting Information, for XRD patterns of the
crystalline phase). Measurement below 2° was prevented to protect the detector. Patterns of the LC
mesophase were difficult to obtain for [C22MIm][TFSI], as the monotropic LC mesophase is
thermodynamically unstable. As seen in Figure S2, no peak is observed in the 2θ range of 2°–30° for
[C22MIm][FSI] and [C18MIm][FSI]. This result combined with the POM observation indicates the peak
ascribed to the smectic layered structure is in the range lower than 2°, and thus the interlayer spacing is
larger than 44.1 Å, which is larger than the fully extended length of the cation (about 32 Å for C22MIm+
and 25 Å for C18MIm+). Hence, it is suggested that the cations form a bilayer structure in the smectic A
mesophase (smectic A2) for [C22MIm][FSI].16 Absence of peaks in the high-angle region suggests the
loss of positional order within the smectic layer plane, which fits the characteristics of smectic A
mesophase. To the best of our knowledge, all the CxMIm-based ILCs show the same type of LC
mesophase of smectic A2, since the bulky cation is much larger than the anion and dominates the type of
mesophase.15–18,20,21
Conclusions
Thermal and structural properties of four 1-alkyl-3-methylimidazolium perfluorinated sulfonylimide
salts were investigated. [C22MIm][FSI] and [C18MIm][FSI] show enantiotropic LC mesophases, and
[C22MIm][TFSI] shows a monotropic one. It is suggested by a comparison with previous reported
CxMIm-based ILCs that, the weak cation-anion interaction between the perfluorinated sulfonylimide
anions and imidazolium headgroups makes them relatively difficult to form LC mesophase. All the
present LC mesophases are determined as smectic A2 bilayer structures. X-ray crystallography reveals
that [C18MIm][FSI] and [C22MIm][TFSI] have layered structures in the crystalline phase, where the
low-polar layer (interdigitated alkyl chains) and high-polar layer (imidazolium headgroups and anions)
alternate with each other. The alkyl chains tilt relative to the high-polar layer, and [C22MIm][TFSI] has
a larger tilted angle than [C18MIm][FSI], due to the larger anion size and weaker cation-anion
interaction.
15
Page 15 of 21

Experimental
Apparatus and Materials. All the solvents were purchased from Sinopharm Chemical Reagent Co.,
Ltd. (China) or Shanghai Chemical Reagent Co., Ltd. (China), and dried and purified with standard
procedures prior to use. The 1-alkyl-3-methylimidazolium bromides, [CxMIm]Br (x = 18 and 22), were
prepared by reactions of 1-methylimidazole (Shanghai Chemical Reagent Co., Ltd., 98%) and equimolar
quantities of the corresponding bromoalkanes (1-bromooctadecane (Shanghai Chemical Reagent Co.,
Ltd., 98%) and 1-bromodocosane (TCI, 98%)) at 80 °C for three days. Purification of the bromides was
performed by dissolving the bromide salts in acetonitrile and then precipitating from the solution by
adding ethyl acetate. Potassium bis(trifluoromethylsulfonyl)imide (K[TFSI]) was purchased from
Rhodia. Potassium bis(fluorosulfonyl)imide (K[FSI]) were purchased from Dai-ichi Kogyo Seiyaku
Co., Ltd..
Synthesis of [C18MIm][FSI]. The two starting materials, [C18MIm]Br (2.493 g, 6.00 mmol) and
K[FSI] (1.381 g, 6.30 mmol), were dissolved in acetone (30 mL), and the mixture was stirred vigorously
overnight. A slightly excess amount of K[FSI] was used for the thorough removal of Br–. The solution
was separated from the mixture, and the acetone was removed under vacuum. Testing for the presence
of residual bromide impurities with a 1M AgNO3 aqueous solution gave no precipitation of AgBr. The
product was dissolved in 30 mL of dichloromethane and the mixture was stirred vigorously overnight.
The dichloromethane solution was separated from the precipitate, and dichloromethane was removed
under vacuum up to 50 °C. (2.830 g, 5.49 mmol). 1H NMR (400 MHz, CDCl3): 8.65 (s, 1H), 7.31 (dd, J
= 11.1, 1.7 Hz, 2H), 4.19 (t, J = 7.5 Hz, 2H), 3.97 (s, 3H), 1.42–1.21 (m, 32H), 0.90 (t, J = 6.8 Hz, 3H).
19F NMR (376 MHz, DMSO): 53.28–53.09 (m).
1
Synthesis of [C18MIm][TFSI]. The same procedure as for [C18MIm][FSI] was used. H NMR (400
MHz, CDCl3): 8.82 (s, 1H), 7.30 (dd, J = 8.4, 6.7 Hz, 2H), 4.18 (dd, J = 14.6, 7.0 Hz, 2H), 3.97 (s, 3H),
1.31 (d, J = 27.7 Hz, 32H), 0.90 (t, J = 6.8 Hz, 3H). 19F NMR (376 MHz, DMSO): –78.70 (d, J = 4.0
Hz).
16
Page 16 of 21

1
Synthesis of [C22MIm][FSI]. The same procedure as for [C18MIm][FSI] was used. H NMR (400
MHz, DMSO): 9.09 (s, 1H), 7.73 (dt, J = 26.0, 1.7 Hz, 2H), 4.15 (t, J = 7.2 Hz, 2H), 3.85 (s, 3H), 1.24
(s, 40H), 0.86 (t, J = 6.8 Hz, 3H). 19F NMR (376 MHz, DMSO): 53.28–53.09 (m).
1
Synthesis of [C22MIm][TFSI]. The same procedure as for [C18MIm][FSI] was used. H NMR (400
MHz, DMSO): 9.10 (s, 1H), 7.73 (d, J = 26.2 Hz, 2H), 4.34–3.96 (m, 2H), 3.85 (s, 3H), 1.24 (s, 40H),
0.86 (t, J = 6.7 Hz, 3H). 19F NMR (376 MHz, DMSO): –78.70 (d, J = 4.0 Hz).
Spectroscopic and thermal analyses. The DSC curves were recorded under a dry Ar gas flow on a
Shimadzu DSC-60, at a scanning rate of 5 or 0.5 °C min–1. The sample was placed in an Al sealed cell
for DSC analysis. Polarized optical microscopy was carried out using an Olympus BX51 digital
microscope under cross-polarized light at ×50 magnification. The sample was placed between two
pieces of bare glass substrate (several micrometers apart). The temperature was controlled by Linkam
HFS91 hot stage.
X-Ray Diffraction Analyses. a. Powder Diffraction. X-ray diffraction was performed using a
Bruker D8 Advance diffractometer (Cu-Kα, λ = 1.542 Å). The data were recorded in the 2θ ranges of 2–
30° (scanning rate of 2° per minute) with a step of 0.02°. The sample was sealed in a vacuum cell. The
heating and cooling rate of 5 °C min–1 was used.
b. Single-Crystal Diffraction. Crystals of [C18MIm][FSI] and [C22MIm][TFSI] were grown by slow
evaporation of the solvent from the dichloromethane solution. Suitable crystals were fixed on an X-ray
diffractometer (Bruker Smart Apex2) equipped with an imaging plate area detector and graphite-
monochromated Mo Kα radiation (0.71073 Å). Data collection was performed at –100 °C for
[C22MIm][TFSI] and 25 °C for [C18MIm][FSI], using φ and ω scans. Integration, scaling, and
absorption corrections were performed using Apex2 (Bruker, 2004). The structure was solved using
SIR-92 and refined by SHELXL-97 linked to Win-GX. Anisotropic displacement factors were
introduced for all atoms except for hydrogen.
17
Page 17 of 21

Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (Nos.
21403305, 51402113, and 21202050), Natural Science Foundation of Hubei Province of China
(2014CFB930), and the Fundamental Research Funds for the Central Universities, South-Central
University for Nationalities (Grant Number CZQ14007).
Supporting Information Available: Results of single-crystal XRD and powder XRD data are
available free of charge.
References
(1) Binnemans, K. Chem. Rev. 2005, 105, 4148–4204.
(2) Axenov, K. V.; Laschat, S. Materials 2011, 4, 206–259.
(3) Yoshio, M.; Mukai, T.; Ohno, H.; Kato, T. J. Am. Chem. Soc. 2004, 126, 994–995.
(4) Yoshio, M.; Kagata, T.; Hoshino, K.; Mukai, T.; Ohno, H.; Kato, T. J. Am. Chem. Soc. 2006, 128,
5570–5577.
(5) Shimura, H.; Yoshio, M.; Hoshino, K.; Mukai, T.; Ohno, H.; Kato, T. J. Am. Chem. Soc. 2008, 130,
1759–1765.
(6) Yoshio, M.; Mukai, T.; Kanie, K.; Yoshizawa, M.; Ohno, H.; Kato, T. Adv. Mater. 2002, 14, 351–
354.
(7) Mukai, T.; Yoshio, M.; Kato, T.; Yoshizawa, M.; Ohno, H. Chem. Commun. 2005, 1333–1335.
(8) Ichikawa, T.; Yoshio, M.; Hamasaki, A.; Mukai, T.; Ohno, H.; Kato, T. J. Am. Chem. Soc. 2007,
129, 10662–10663.
(9) Ichikawa, T.; Yoshio, M.; Hamasaki, A.; Kagimoto, J.; Ohno, H.; Kato, T. J. Am. Chem. Soc. 2011,
133, 2163–2169.
18
Page 18 of 21

(10) Lee, C. K.; Huang, H. W.; Lin, I. J. B. Chem. Commun. 2000, 1911–1912.
(11) Yamanaka, N.; Kawano, R.; Kubo, W.; Kitamura, T.; Wada, Y.; Watanabe, M.; Yanagida, S.
Chem. Commun. 2005, 740–742.
(12) Yamanaka, N.; Kawano, R.; Kubo, W.; Masaki, N.; Kitamura, T.; Wada, Y.; Watanabe, M.;
Yanagida, S. J. Phys. Chem. B 2007, 111, 4763–4769.
(13) Kawano, R.; Nazeeruddin, M. K.; Sato, A.; Grätzel, M.; Watanabe, M. Electrochem. Commun.
2007, 9, 1134–1138.
(14) Wang, M.; Pan, X.; Xiao, S.; Zhang, C.; Li, W.; Dai, S. J. Mater. Chem. 2012, 22, 2299–2305.
(15) Bowlas, C. J.; Bruce, D. W.; Seddon, K. R. Chem. Commun. 1996, 1625–1626.
(16) Bradley, A. E.; Hardacre, C.; Holbrey, J. D.; Johnston, S.; McMath, S. E. J.; Nieuwenhuyzen, M.
Chem. Mater. 2002, 14, 629–635.
(17) Holbrey, J. D.; Seddon, K. R. J. Chem. Soc. Dalton Trans. 1999, 2133–2139.
(18) Gordon, C. M.; Holbrey, J. D.; Kennedy, A. R.; Seddon, K. R. J. Mater. Chem. 1998, 8, 2627–
2636.
(19) De Roche, J.; Gordon, C. M.; Imrie, C. T.; Ingram, M. D.; Kennedy, A. R.; Lo Celso, F.; Triolo,
A. Chem. Mater. 2003, 15, 3089–3097.
(20) Xu, F.; Matsumoto, K.; Hagiwara, R. Dalton Trans. 2012, 41, 3494–3502.
(21) Xu, F.; Matsumoto, K.; Hagiwara, R. Chem. Eur. J. 2010, 16, 12970–12976.
(22) Xu, F.; Matsumoto, K.; Hagiwara, R. J. Phys. Chem. B 2012, 116, 10106–10112.
(23) Nieuwenhuyzen, M.; Seddon, K. R.; Teixidor, F.; Puga, A. V.; Viñas, C. Inorg. Chem. 2009, 48,
889–901.
(24) Getsis, A.; Tang, S.; Mudring, A. -V. Eur. J. Inorg. Chem. 2010, 2172–2177.
(25) Getsis, A.; Mudring, A. -V. Eur. J. Inorg. Chem. 2011, 3207–3213.
(26) Xu, F.; Matsumoto, K.; Hagiwara, R. Dalton Trans. 2013, 42, 1965–1968.
(27) Ji, S. -P.; Tang, M.; He, L.; Tao, G. -H. Chem. Eur. J. 2013, 19, 4452–4461.
(28) Armand, M.; Endres, F.; MacFarlane, D. R.; Ohno, H.; Scrosati, B. Nat. Mater. 2009, 8, 621–629.
19
Page 19 of 21

(29) Ishikawa, M.; Sugimoto, T.; Kikuta, M.; Ishiko, E.; Kono, M. J. Power Sources 2006, 162, 658–
662.
(30) Mcwen, A. B.; Ngo, H. L.; Le Compte, K.; Goldman, J. L. J. Electrocem. Soc. 1999, 146, 1687–
1695.
(31) Sakaebe, H.; Matsumoto, H. Electrochem. Commun. 2003, 5, 594–598.
(32) Matsumoto, H.; Sakaebe, H.; Tatsumi, K.; Kikuta, M.; Ishiko, E.; Kono, M. J. Power Sources
2006, 160, 1308–1313.
(33) Watarai, A.; Kubota, K.; Yamagata, M.; Goto, T.; Nohira, T.; Hagiwara, R.; Ui, K.; Kumagai, N.
J. Power Sources 2008, 183, 724–729.
(34) Fukunaga, A.; Nohira, T.; Kozawa, Y.; Hagiwara, R.; Sakai, S.; Nitta, K.; Inazawa, S. J. Power
Sources 2012, 209, 52–56.
(35) Douce L.; Suisse J. -M.; Guillon D.; Taubert A. Liq. Cryst. 2011, 38, 1653–1661.
(36) Schenkel M. R.; Hooper J. B.; Moran M. J.; Robertson L. A.; Bedrov D.; Gin D. L. Liq. Cryst.
2014, 41, 1668–1685.
(37) Dobbs, W.; Douce, L.; Allouche, L.; Louati, A.; Malbosc, F.; Welter, R. New J. Chem. 2006, 30,
528–532.
(38) Trilla, M.; Pleixats, R.; Parella, T.; Blanc, C.; Dieudonné, P.; Guari, Y.; Man, M. W. C. Langmuir
2008, 24, 259–265.
(39) Ma, K.; Lee, K. -M.; Minkova, L.; Weiss, R. G. J. Org. Chem. 2009, 74, 2088–2098.
(40) Lava, K.; Binnemans, K.; Cardinaels, T. J. Phys. Chem. B 2009, 113, 9506–9511.
(41) Goossens, K.; Lava, K.; Nockemann, P.; Van Hecke, K.; Van Meervelt, L.; Driesen, K.; Görller-
Walrand, C.; Binnemans, K.; Cardinaels, T. Chem. Eur. J. 2009, 15, 656–674.
(42) Goossens, K.; Lava, K.; Nockemann, P.; Van Hecke, K.; Van Meervelt, L.; Pattison, P.;
Binnemans, K.; Cardinaels, T. Langmuir 2009, 25, 5881–5897.
(43) Fernandez, A. A.; de Haan, L. T.; Kouwer, P. H. J. J. Mater. Chem. A 2013, 1, 354–357.
(44) Downard, A.; Earle, M. J.; Hardacre, C.; McMath, S. E. J.; Nieuwenhuyzen, M.; Teat, S. J. Chem.
Mater. 2004, 16, 43–48.
20
Page 20 of 21

(45) Getsis, A.; Mudring, A. -V. Cryst. Res.Technol. 2008, 43, 1187–1196.
(46) Fujii, K.; Fujimori, T.; Takamuku, T.; Kanzaki, R.; Umebayashi, Y.; Ishiguro, S. I. J. Phys. Chem.
B 2006, 110, 8179–8183.
(47) Lopes, J. N. C.; Shimizu, K.; Padua, A. A. H.; Umebayashi, Y.; Fukuda, S.; Fujii, K.; Ishiguro, S.
I. J. Phys. Chem. B 2008, 112, 9449–9455.
(48) Tsuzuki, S.; Hayamizu, K.; Seki, S. J. Phys. Chem. B 2010, 114, 16329–16336.
(49) Sawyer, J. F.; Schrobilgen, G. J.; Sutherland, S. J. J. Chem. Soc., Chem. Commun. 1982, 210–211.
(50) Sawyer, J. F.; Schrobilgen, G. J.; Sutherland, S. J. Inorg. Chem. 1982, 21, 4064–4072.
(51) Zak, Z.; Ruzicka, A.; Michot, C. Z. Kristallogr. 1998, 213, 217–222.
(52) Beran, M.; Prihoda, J.; Zak, Z.; Cernik, M. Polyhedron 2006, 25, 1292–1298.
(53) Hiemisch, O.; Henschel, D.; Blaschette, A.; Jones, P. G. Z. Anorg. Allg. Chem. 1997, 623, 324–
332.
(54) Farrugia, L. J.; Holfter, H.; Klapotke, T. M. J. Fluorine Chem. 1996, 78, 51–53.
(55) Begley, M. J.; Sowerby, D. B.; Verma, R. D.; Vig, A. J. Organomet. Chem. 1994, 481, 243–246.
(56) Isenberg, W.; Noltemeyer, M.; Sheldrick, G. M. Acta Crystallogr., Sect. B 1982, 38, 2887–2889.
(57) Paulechka, Y. U.; Kabo, G. J.; Blokhin, A. V.; Shaplov, A. S.; Lozinskaya, E. I.; Golovanov, D.
G.; Lyssenko, K. A.; Korlyukov, A. A.; Vygodskii, Y. S. J. Phys. Chem. B 2009, 113, 9538–9546.
(58) Fujii, K.; Fujimori, T.; Takamuku, T.; Kanzaki, R.; Umebayashi, Y.; Ishiguro, S. J. Phys. Chem. B
2006, 110, 8179–8183.
(59) Xue, L.; Padgett, C. W.; DesMarteau, D. D.; Penningtion, W. T. Solid State Sci. 2002, 4, 1535–
1545.
(60) Holbrey, J. D.; Reichert, W. M.; Rogers, R. D. Dalton Trans. 2004, 2267–2271.
(61) Xue, L.; DesMarteau, D. D.; Pennington, W. T. Solid State Sci. 2005, 7, 311–318.
(62) Matsumoto, K.; Hagiwara, R.; Tamada, O. Solid State Sci. 2006, 8, 1103–1107.
(63) Dierking, I. Textures of Liquid Crystals; WILEY-VCH: Weinhelm, Germany, 2003.
21
Page 21 of 21