Thermal properties of alkyloctamethylferrocenium salts with TFSA and TCNE (TFSA = bis(trifluoromethylsulfonyl)amide and TCNE = tetracyanoethylene)

Article abstract of DOI:10.1016/j.tca.2011.01.013

Butyl- and hexyloctamethylferrocenium salts with bis(trifluoromethylsulfonyl)amide (TFSA) and tetracyanoethylene (TCNE) were prepared, and their thermal properties were investigated by differential scanning calorimetry (DSC) measurements. The TFSA salts were ionic liquids with melting points of 34.4 °C and 27.7 °C, respectively. The TCNE salts were prepared by annealing the mixture of alkyloctamethylferrocene and TCNE. These salts exhibited high melting points of 100.2 °C and 80.9 °C, respectively; they were thermally unstable at higher temperatures. A butyloctamethylferrocenium salt with PCNP (pentacyanopropenide), obtained by a reaction with TCNE under ambient conditions, was crystallographically characterized. The structure was severely disordered, consisting of alternately stacked cations and anions.

Full text of DOI:10.1016/j.tca.2011.01.013

Thermochimica Acta 532 (2012) 78–82
Contents lists available at ScienceDirect
Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Thermal properties of alkyloctamethylferrocenium salts with TFSA and TCNE
(TFSA = bis(trifluoromethylsulfonyl)amide and TCNE = tetracyanoethylene)
Yusuke Funasako, Ken-ichi Abe, Tomoyuki Mochida∗
Department of Chemistry, Graduate School of Science, Kobe University, Rokkodai, Nada, Hyogo 657-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 26 January 2011
Butyl- and hexyloctamethylferrocenium salts with bis(trifluoromethylsulfonyl)amide (TFSA) and tetra-
cyanoethylene (TCNE) were prepared, and their thermal properties were investigated by differential
scanning calorimetry (DSC) measurements. The TFSA salts were ionic liquids with melting points of 34.4 ◦C
and 27.7 ◦C, respectively. The TCNE salts were prepared by annealing the mixture of alkyloctamethylfer-
rocene and TCNE. These salts exhibited high melting points of 100.2 ◦C and 80.9 ◦C, respectively; they
were thermally unstable at higher temperatures. A butyloctamethylferrocenium salt with PCNP (penta-
cyanopropenide), obtained by a reaction with TCNE under ambient conditions, was crystallographically
characterized. The structure was severely disordered, consisting of alternately stacked cations and anions.
Keywords:
Ionic liquids
Alkyloctamethylferrocene
Bis(trifluoromethylsulfonyl)amide
Tetracyanoethylene
Thermal properties
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
The TCNE anion reacts with oxygen to form the PCNP anion
[7,9]. We herein describe the crystal structure of 1·PCNP, which
Ionic liquids (ILs) are interesting materials from the viewpoint of
fundamental physical chemistry and electrochemistry [1]. Most ILs
involve onium cations such as imidazolium, ammonium, and phos-
phonium cations. Bis(trifluoromethylsulfonyl)amide (TFSA) and its
derivatives are frequently used as their counteranions [2]. Recently,
metal-containing ILs with additional functionalities have been
prepared [3]. We have developed various ferrocene-based ILs com-
posed of alkylferrocenium [4a] and ferrocenylimidazolium cations
[4b,c].
In this study, salts of butyloctamethylferrocene (1) and hexyloc-
tamethylferrocene (2) with TFSA and tetracyanoethylene (TCNE)
(Fig. 1) were prepared, and their thermal properties were investi-
gated. The magnetic properties of 1·TFSA are reported elsewhere
[5]. The use of octamethylferrocenium cations lends greater air sta-
bility to the ILs. Thus far, ILs with cyano-containing anions such as
[N(CN)2]−, [C(CN)3]−, [C(CN)2X]− (X = SO2CF3, NO, NO2), and PCNP
(pentacyanopropenide; Fig. 1b) have been reported [6], but there
seems to be no ILs containing TCNE. The TCNE anion is a radical;
its complexes exhibit interesting magnetic properties. For exam-
ple, decamethylferrocene–TCNE is the first molecular ferromagnet
(Tc = 4.8 K) [7]. In addition, TCNE can form complexes that do not
adhere to 1:1 donor/acceptor stoichiometry [8]. In this study, we
found that mixing TCNE and alkyloctamethylferrocenes and subse-
quent annealing afforded the desired TCNE salts.
was obtained in the reaction using TCNE.
2. Results and discussion
2.1. Preparation and thermal properties
Differential scanning calorimetry (DSC) measurements of 1 and
2 revealed that they show only glass transitions, at Tg of −87.9 ◦C
and −82.7 ◦C, respectively, on cooling from the liquid state. Dur-
ing heating, however, crystallization occurred at around −12.5 ◦C
and −33.8 ◦C, respectively. Their melting points (Tm) were 27.6 ◦C
and 22.1 ◦C, respectively. A phase transition with a small entropy
change was observed in both 1 and 2, appearing as a shoulder at
approximately 5 K below Tm. The values of Tm/Tg for 1 and 2 are
0.63 and 0.65, respectively, which are consistent with the empirical
relationship Tg/Tm ≈ 2/3 [10].
1·TFSA and 2·TFSA were prepared by reactions of alkyloc-
tamethylferrocene and AgTFSA [5]. 1·TCNE and 2·TCNE were
obtained by annealing the mixture of alkyloctamethylferrocene
and TCNE in a DSC pan, or by simply grinding the mixture with an
agate and mortar under a nitrogen atmosphere. For technical rea-
sons, samples with a donor–acceptor molar ratio of 0.51:0.49 were
used for measurements. In the infrared spectrum of 1·TCNE, C
N
,
stretching peaks [11] were observed at 2184 cm−1 and 2145 cm−1
which indicated the formation of a 1:1 salt containing the TCNE
anion and ferrocenium cation. The TCNE salts were unstable in air.
∗
Table 1 lists the melting points (Tm) and melting entropies (ꢀSm
of 1, 2, and their salts with TFSA and TCNE, as determined by the
)
Corresponding author. Tel.: +81 78 803 5679; fax: +81 78 803 5679.
E-mail address: tmochida@platinum.kobe-u.ac.jp (T. Mochida).
0040-6031/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2011.01.013

Y. Funasako et al. / Thermochimica Acta 532 (2012) 78–82
79
Table 1
Melting points (Tm) and melting entropiesa (ꢀSm) of 1, 2, and their TFSA and TCNE
salts.
Tm (◦C)
ꢀSm (J K−1 mol−1
)
1
2
27.6
22.1
34.4
27.7
100.2
80.9
80.6
84.7
86.3
84.6
93.9
110.0
1·TFSA
2·TFSA
1·TCNEb
2·TCNEc
a
Sum of transition entropies.
Determined for as-prepared samples in a DSC pan with a mixing ratio of
b
0.51:0.49.
c
Melting accompanied by slight decomposition.
DSC measurements. The values of ꢀSm for 1, 2, and 2·TFSA are the
sums of their transition entropies from the stable phase to the liquid
state. Compared to the melting points of 1 and 2, the melting points
of the TFSA salts (34.4 ◦C for 1·TFSA and 27.7 ◦C for 2·TFSA) were
higher by approximately 6 K, while those of the TCNE salts (100.2 ◦C
for 1·TCNE and 80.9 ◦C for 2·TCNE) were much higher. The high
melting points of the latter salts are probably due to the planarity
and high symmetry of the anion, leading to stronger intermolecular
forces.
In the case of both TFSA and TCNE salts, increasing the alkyl chain
length from n = 4 (salts of 1) to n = 6 (salts of 2) led to a decrease in
melting point, which is in accordance with the general tendency
observed in conventional ILs [1e]. One methylene group represents
an entropy of 10.6 J K−1 mol−1 in molecular compounds with long
alkyl chains [12]. The values of ꢀSm, however, for the TFSA salts and
their precursors were comparable (81–86 J K−1 mol−1), while the
value for the TCNE salts increased by 16.1 J K−1 mol−1 on increas-
ing the alkyl chain length from n = 4 to n = 6. Hence the effect of the
increase in the alkyl chain length is small; their thermal proper-
ties are probably dominated by the octamethylferrocenyl moiety,
which has much larger volume than the alkyl chains.
Fig. 2. Gibbs free energy curves of 2·TFSA. The inset shows a schematic illustration
of the phase diagram.
diagrams for 2·TFSA, in which the temperature dependence is
approximated by straight lines. Upon cooling from the liquid state,
crystallization to phase I occurred, followed by a transition to a
metastable phase (phase II). During the heating run, a reverse phase
sequence was often traced, but the transformation to phase III
occurred occasionally.
DSC traces of 2·TFSA are shown in Fig. 3. Upon cooling at
10 K min−1 from the liquid state, crystallization to phase I occurred
at −10.6 ◦C, which was immediately followed by a transition to
phase II (Fig. 3a). Upon cooling at 1 K min−1, these peaks could be
separated, and upon heating at 1 K min−1 from phase II, a reverse
phase sequence was observed. However, as noted above, heat-
ing phase II at 10 K min−1 occasionally gave rise to an exothermic
2.2. Thermal properties of TFSA salts
1·TFSA underwent only melting (Tm = 34.4 ◦C) and crystalliza-
tion (Tc = 18.9 ◦C), exhibiting no crystalline phase transitions. By
contrast, 2·TFSA exhibited three crystalline phases (phases I–III),
and phase I melting at 26.3 ◦C. Fig. 2 shows the Gibbs free energy
Fig. 1. Chemical formulas of (a) alkyloctamethylferrocenes and (b) anions used in
this study.
Fig. 3. DSC traces of 2·TFSA (see text).

80
Y. Funasako et al. / Thermochimica Acta 532 (2012) 78–82
Fig. 4. DSC traces of an equimolar mixture of 1 and TCNE (x = 0.49) before (cycle
1) and after (cycle 2) annealing. Tg (1), Tc (1), and Tm (1) are the glass transition, crys-
tallization, and melting temperatures of 1, respectively. Tm (salt) and Tc (salt) are the
melting and crystallization temperatures, respectively, of 1·TCNE.
Fig. 5. DSC traces of (1)1−x(TCNE)x for various x (x < 0.5). Tg (1), Tc (1), and Tm (1) are the
glass transition, crystallization, and melting temperatures of 1, respectively. Tm (salt)
denotes the melting temperature of 1·TCNE.
DSC traces of (1)1−x(TCNE)x for various values of x (x < 0.5) after
annealing are shown in Fig. 5. As the proportion of TCNE was
increased, the peaks corresponding to crystallization and melt-
ing of excess 1 decreased, disappearing at x ≈ 0.5. This result
indicated the formation of a 1:1 salt. The possible formation of
a 1:2 salt in the TCNE-rich region (x > 0.5) could not be exam-
ined because a rapid exothermic decomposition reaction occurred
after melting in this region. Since the melting point of TCNE
(Tm = 199 ◦C, ꢀHm = 24.9 kJ mol−1 [13]) is higher than that of the
1:1 salt, the melting of excess TCNE could not be observed
owing to decomposition. The melting points of the 1:1 salt and
residual alkyloctamethylferrocene for (1)1−x(TCNE)x are listed in
Table 2. The melting temperatures of the 1:1 salt and alkyloc-
tamethylferrocene were found to be almost independent of x.
Although the slight scattering of the values of Tm is probably due
to an effect of decomposition, the tendency of Tm to decrease
below x = 0.19 seems to indicate the onset of a steep decrease in
the vicinity of x = 0, where a eutectic point probably exists. The
melting peaks became slightly broader as the ratio approached
1:1.
transition to phase III, as can be seen in Fig. 3a (heating run).
In this figure, the transition occurred at −10 ◦C, which was fol-
lowed by a transition to phase I at 21.4 ◦C and melting at 27 ◦C.
A DSC pattern as shown in Fig. 3b was also observed several
times, which revealed phase transitions from phase II to phase
I at −2.1 ◦C (ꢀH = 9.4 kJ mol−1, ꢀS = 34.5 J mol−1 K−1), from phase
I to phase III with a broad exothermic peak at 10 ◦C, and again
back to phase I, and subsequent melting. This re-entrant behav-
ior was often observed when the compound was heated directly
after crystallization. Cooling from phase I at 2 K min−1 gave phase
III, as shown in Fig. 3c. Phase I is probably a highly disordered phase,
in view of the small value of ꢀS (21 J mol−1 K−1) associated with its
melting.
2.3. Thermal properties of TCNE salts
The
dependence
of
the
thermal
behavior
of
alkyloctamethylferrocenium–TCNE salts on the mixing ratio of
alkyloctamethylferrocene and TCNE was investigated for various
mixing ratios (1)1−x(TCNE)x. DSC traces for an equimolar mixture
(x = 0.49) before and after annealing are shown in Fig. 4. In the first
heating run before annealing, glass transition (Tg = −88.1 ◦C), crys-
tallization (Tc = −38.6 ◦C), and melting (Tm = 27.4 ◦C) corresponding
to those of 1 contained in the mixture were observed (Fig. 4, cycle
1). Upon further heating, an exothermic peak corresponding to the
formation of 1·TCNE was observed at around 85 ◦C, at which the
sample was annealed for 3 min and then cooled. The enthalpy of
the formation of the salt estimated from the exothermic peak was
approximately 38 kJ mol−1. In the second heating run (Fig. 4, cycle
2), the peaks of the precursor disappeared, and a melting peak
was observed for the salt (Tm = 100.2 ◦C). Upon repetition of the
cycle, the melting point decreased by approximately 3 K, which
can be attributed to slight decomposition of the salt. A similar
result was obtained for 2·TCNE. However, characterization of this
salt was more difficult owing to the gradual formation of the salt
upon heating, which was accompanied by partial melting and
decomposition.
In this study, the use of TCNE allowed convenient preparation of
salts by mixing and annealing, but their melting points were high,
and decomposition in the TCNE-rich region precluded the determi-
Table 2
Thermal propertiesa of (1)1−x(TCNE)x obtained by DSC measurement.
x
Tm (salt) (◦C)
Tc (1) (◦C)
Tg (1) (◦C)
Tm (1) (◦C)
0.00
0.06
0.19
0.24
0.31
0.34
0.38
0.42
0.46
0.49
–
92.3
98.9
100.6
100.2
98.7
100.0
100.9
100.4
100.2
−29.1
−39.0
−40.6
−40.1
−41.6
−42.4
−42.4
−44.8
−43.6
–
−89.0
−87.9
−88.2
−88.2
−88.3
−89.5
−87.2
−89.4
−90.0
–
27.6
27.5
27.3
27.2
27.1
27.1
26.9
26.2
25.6
–
aOnset temperatures of endothermic peak (Tm (salt) and Tm (1)), heat capacity change
(Tg (1)), and exothermic peak (Tc (1)).

Y. Funasako et al. / Thermochimica Acta 532 (2012) 78–82
81
nation of the complete phase diagram. In the case of an IL formed
by an acid–base reaction of imidazole and HTFSA (Tm = 73 ◦C), a
phase diagram with respect to the mixing ratio has been reported,
revealing a clear eutectic behavior [14]. Phase diagrams of charge-
transfer (CT) complexes of alkylbenzenes and TCNE, which form
neutral complexes with ratios of 1:1 and 2:1, have been reported
[13].
2.4. Crystal structure of butyloctamethylferrocenium–PCNP
Dark green crystals of 1·PCNP were obtained by slow diffu-
sion of 1 and TCNE in diethyl ether. The presence of infrared C
N
stretching peaks at 2200 cm−1 [15] indicated that PCNP was the
only anion in the isolated crystals. The anion was formed probably
because of contamination by oxygen during manipulation. Under
strict exclusion of oxygen, only powdered CT salts were obtained,
which suggests that 1·TCNE has poor crystallinity.
Fig. 7. Schematic illustration of twofold disorder of the PCNP anion with a 0.5
occupancy in 1·PCNP.
Table 3
Crystallographic parameters for 1·PCNP.
The packing diagram of 1·PCNP, projected along the c-axis, is
shown in Fig. 6. In the crystal, the cations and anions are stacked
alternately along the b-axis via ␲–␲ contacts. The C5Me4H ring
and an adjacent PCNP are well overlapped, but the C5Me4Bu ring
and an adjacent PCNP are in a slipped configuration due to steric
hindrance of the butyl group. In the cation, the average Fe–C(Cp)
Formula
C30H33FeN5
Formula weight
T (K)
519.46
100
Crystal system
Space group
Monoclinic
P21/c
˚
a (A)
15.906(3)
˚
b (A)
11.296(2)
˚
distance is 2.085 A, which is comparable to the value observed for
˚
c (A)
16.392(3)
111.770(2)
2735.2(9)
the decamethylferrocenium cation [16]. It should be noted that
the structure was severely disordered. The four methyl groups in
the C5Me4H ring were observed to be disordered over five sites
with an occupancy of 0.8. In addition, the C5Me4Bu ring, together
with the butyl group, exhibited a twofold disorder. The PCNP anion
exhibited a twofold disorder, with two inverted PCNP molecules
overlapping and sharing one C–C bond, as shown schematically in
Fig. 7. These extensive disorders, which are probably responsible for
the high R value (12.4%), are consistent with the nearly symmetrical
crystal environment around the cation and anion. The crystal struc-
tures of [decamethylferrocenium][PCNP] [7] and the PCNP salts of
triaminoguanidine derivatives [17] are comparable examples; the
latter involves a disordered anion.
ˇ (◦)
3
˚
V (A )
Z
4
Dcalc (g cm−3
)
1.261
0.572
ꢁ (mm−1
)
Reflections collected
Independent reflections
F(0 0 0)
15,177
6184 (Rint = 3.2%)
1096
Parameters
474
Final R1, wR2 (I > 2␴)
Final R1, wR2 (all data)
Goodness of fit on F2
R1 = 0.1240, wR2 = 0.2522
R1 = 0.1483, wR2 = 0.2638
1.155
3. Conclusion
Alkyloctamethylferrocenium salts [R = butyl (1) and hexyl (2)]
with TFSA were found to be room-temperature ILs; their melt-
ing points were slightly higher than those of their precursors
(1 or 2). Alkyloctamethylferrocenium salts with TCNE anions
were conveniently prepared by annealing the mixture of alkyloc-
tamethylferrocene and TCNE. Their melting points, however, were
much higher than those of the TFSA salts, probably owing to the pla-
narity and high symmetry of the anion. The donor–acceptor ratio of
the TCNE salts was 1:1, which was independent of the mixing ratio,
and these salts were thermally unstable above their melting points.
Single crystals of TCNE salts could not be isolated, and a PCNP salt
of 1 was obtained instead, probably because of contamination by
oxygen. This salt exhibited alternate stacking of the cations and
anions.
4. Experimental
4.1. General methods
The preparation of 1, 2, and their TFSA salts was performed
as reported elsewhere [5]. Sample purities (>99.7%) were checked
by elemental analyses. TCNE was purchased from TCI Co. Ltd. and
used after recrystallization from chlorobenzene. All manipulations
of TCNE salts were carried out in a glove box under a nitrogen atmo-
sphere. Solvents were degassed by bubbling with nitrogen before
use. Infrared spectra were recorded using KBr pellets on a JASCO
FT-IR 230 spectrometer.
Fig. 6. Packing diagram of 1·PCNP viewed along the c-axis.

82
Y. Funasako et al. / Thermochimica Acta 532 (2012) 78–82
DSC measurements were performed using a Q100 differential
(b) A. Stark, K.R. Seddon, in: Kirk-Othmer (Ed.), Kirk-Othmer Encyclopedia of
scanning calorimeter (TA instruments) at 10 K min−1, and other
rates when necessary, in a temperature range down to 100 K. For
the DSC measurements of (1)1−x(TCNE)x and (2)1−x(TCNE)x, sam-
ples with a total mass of about 5 mg were placed in Al hermetic
pans under a nitrogen atmosphere and subjected to measurement.
The slight deviation from the 1:1 donor–acceptor ratio (0.51:0.49)
for 1·TCNE and 2·TCNE occurred owing to the difficulty in loading
the starting materials into the DSC pans.
Chemical Technology, vol. 26, 5th ed., Wiley–Interscience, 2007, p. 836;
(c) M. Armand, F. Endres, D.R. MacFarlane, H. Ohno, B. Scrosati, Nat. Mater. 8
(2009) 621–629;
(d) P. Hapiot, C. Lagrost, Chem. Rev. 108 (2008) 2238–2264;
(e) N.V. Plechkova, K.R. Seddon, Chem. Soc. Rev. 37 (2008)
123–150.
[2] (a) H. Weingärtner, Angew. Chem., Int. Ed. 47 (2008) 654;
(b) S. Lee, Chem. Commun. (2006) 1049;
(c) Y. Yoshida, G. Saito, Phys. Chem. Chem. Phys. 12 (2010) 1675–1684.
[3] (a) W. Wang, R. Balasubramanian, R.W. Murray, J. Phys. Chem. C 112 (2008)
18207–18216;
(b) Y. Gao, B. Twamley, J.M. Shreeve, Inorg. Chem. 43 (2004) 3406–3412;
(c) H. Matsumoto, JP Patent 277393 (2003);
(d) C.K. Lee, K.-M. Hsu, C.-H. Tsai, C.K. Lai, I.J.B. Lin, Dalton Trans. (2004)
1120–1126;
4.2. X-ray crystallography
Dark green single crystals of 1·PCNP for X-ray structure
determination were obtained by slow diffusion of butyloctamethyl-
ferrocene and TCNE in an H-shaped pyrex cell, using diethyl
ether as a solvent. X-ray diffraction data were collected at 100 K
on a Bruker SMART APEX CCD diffractometer equipped with a
graphite crystal incident beam monochromator using MoK␣ radi-
(e) M. Iida, C. Baba, M. Inoue, H. Yoshida, E. Taguchi, H. Furusho, Chem. Eur. J.
14 (2008) 5047–5056.
[4] (a) T. Inagaki, T. Mochida, Chem. Lett. 39 (2010) 572–573;
(b) Y. Miura, F. Shimizu, T. Mochida, Inorg. Chem. 49 (2010) 10032–10040;
(c) T. Mochida, Y. Miura, F. Shimizu, Cryst. Growth Des. 11 (2010) 262–268.
[5] Y. Funasako, T. Mochida, T. Inagaki, T. Sakurai, H. Ohta, K. Furukawa, T. Naka-
mura, submitted for publication.
[6] (a) Y. Yoshida, K. Muroi, A. Otsuka, G. Saito, M. Takahashi, T. Yoko, Inorg. Chem.
43 (2004) 1458–1462;
˚
ation (ꢂ = 0.71073 A). The data were corrected for absorption using
the SADABS program [18]. The structures were solved by the direct
method (SHELXS 97 [19]) and expanded using Fourier techniques.
Crystallographic parameters are listed in Table 3. The ORTEP-3 [20]
program was used for drawing the packing diagram. Crystallo-
graphic data for the structure in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplemen-
tary publication no. CCDC 778957. These data can be obtained
free of charge from the Cambridge Crystallographic Data Centre
at www.ccdc.cam.ac.uk/data request/cif.
(b) Y. Yoshida, M. Kondo, G. Saito, J. Phys. Chem. B 113 (2009) 8960–8966.
[7] J.S. Miller, J.C. Calabrese, H. Rommelmann, S. Chittipeddi, J.H. Zhang, W.M. Reiff,
A.J. Epstein, J. Am. Chem. Soc. 109 (1987) 769–781.
[8] A. Quazi, W.M. Reiff, R.U. Kirss, Hyperfine Int. 93 (1994) 1597–1603.
[9] M. Rosenblum, R.W. Fish, C. Bennett, J. Am. Chem. Soc. 86 (1964)
5166–5170.
[10] D.
Turnbull, M.H. Cohen, in: J.D. Mackenzie (Ed.), Modern
Aspect of the Vitreous State, vol. 1, Butterworth, London, 1960,
p. 38.
[11] J.S. Miller, D.T. Glatzhofer, D.M. O’Hare, W.M. Reiff, A. Chakraborty, A.J. Epstein,
Inorg. Chem. 28 (1989) 2930–2939.
[12] (a) M. Sorai, K. Tsuji, H. Suga, S. Seki, Mol. Cryst. Liq. Cryst. 59 (1980) 33–58;
(b) Y. Shimizu, Y. Ohte, Y. Yamamura, K. Saito, Chem. Phys. Lett. 470 (2009)
295–299.
[13] M. Radomska, R. Radomski, J. Therm. Anal. 37 (1991) 693–704.
[14] A. Noda, Md.A.B.H. Susan, K. Kudo, S. Mitsushima, K. Hayamizu, M. Watanabe,
J. Phys. Chem. B 107 (2003) 4024–4033.
[15] K.W. Hipps, U. Geiser, U. Mazur, R.D. Willett, J. Phys. Chem. 88 (1984)
2498–2504.
[16] A.S. Perucha, M. Bolte, Acta Cryst. E63 (2007) m1703.
[17] H. Gao, Z. Zeng, B. Twamley, J.M. Shreeve, Chem. Eur. J. 14 (2008)
1282–1290.
Acknowledgements
We thank T. Inagaki and Y. Furuie for their help with sam-
ple preparation and DSC measurements. This work was supported
by a Grant-in-Aid for Scientific Research (No. 21350077) from
Japan Society for the Promotion of Science (JSPS). M. Nakama
(WarpStream Ltd., Tokyo) is acknowledged for providing Web-DB
systems.
[18] G.M. Sheldrick, SADABS. Program for Semi-empirical Absorption Correction,
University of Göttingen, Germany, 1996.
[19] G.M. Sheldrick, Program for the Solution for Crystal Structures, University of
Göttingen, Germany, 1997.
[20] ORTEP-3 for Windows, L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.
References
[1] (a) R.D. Rogers, K.R. Seddon (Eds.), Ionic Liquids: Industrial Applications
to Green Chemistry, ACS Symposium Series, American Chemical Society,
Washington, DC, 2002;