Syntheses, structures and properties of 1-ethyl-3-methylimidazolium salts of fluorocomplex anions

Article abstract of DOI:10.1039/b310162b

Fluoroacid-base reactions of a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium fluorohydrogenate (EMIm(HF)_2.3F, EMIm = 1-ethyl-3-methylimidazolium cation), and Lewis fluoroacids (BF₃, PF₅, AsF₅, NbF₅, TaF₅ and WF₆) give EMIm salts of the corresponding fluorocomplex anions, EMImBF₄, EMImPF₆, EMImAsF₆, EMImNbF₆, EMImTaF₆ and EMImWF₇, respectively. Attempts to prepare EMImVF₆ by both the acid-base reaction of EMIm(HF)_2.3F with VF₅ and the metathesis of EMImCl with KVF₆ failed due to the strong oxidizing power of the pentavalent vanadium, whereas EMImSbF₆ was successfully prepared only by the metathesis of EMImCl and KSbF₆. EMImBF₄, EMImSbF₆, EMImNbF₆, EMImTaF₆ and EMImWF₇ are liquids at room temperature whereas EMImPF₆ and EMImAsF₆ melts at around 330 K. Raman spectra of the obtained salts showed the existence of the EMIm cation and corresponding fluorocomplex anions. IR spectroscopy revealed that strong hydrogen bonds are not observed in these salts. EMImAsF₆ (mp 326 K) and EMImSbF₆ (mp 283 K) are isostructural with the previously reported EMImPF₆. The melting point of the hexafluorocomplex EMIm salt decreases with the increase of the size of the anion (PF₆^- < AsF₆^- < SbF₆^- < NbF₆^- ≈ TaF₆^-).

Full text of DOI:10.1039/b310162b

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Syntheses, structures and properties of 1-ethyl-3-methyl-
imidazolium salts of fluorocomplex anions†
Kazuhiko Matsumoto,‡a Rika Hagiwara,*a Ryuhei Yoshida,a Yasuhiko Ito,a Zoran Mazej,b
b
b
c
d
d
ˇ
ˇ
Primoz Benkicˇ, Boris Zemva, Osamu Tamada, Hideaki Yoshino and Seijiro Matsubara
a Graduate School of Energy Science, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan.
E-mail: hagiwara@energy.kyoto-u.ac.jp
b Department of Inorganic Chemistry and Technology, Jozˇef Stefan Institute, Jamova 39,
SI-1000 Ljubljana, Slovenia
c Graduate School of Human and Environmental Study, Kyoto University, Sakyo-ku,
Kyoto 606-8501, Japan
d Graduate School of Engineering, Kyoto University, Kyotodaigaku-katsura, Nishikyou-ku,
Kyoto 615-8510, Japan
Received 22nd August 2003, Accepted 6th November 2003
First published as an Advance Article on the web 27th November 2003
Fluoroacid–base reactions of a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium fluorohydrogenate
(EMIm(HF)2.3F, EMIm = 1-ethyl-3-methylimidazolium cation), and Lewis fluoroacids (BF3, PF5, AsF5, NbF5, TaF5
and WF6) give EMIm salts of the corresponding fluorocomplex anions, EMImBF4, EMImPF6, EMImAsF6,
EMImNbF6, EMImTaF6 and EMImWF7, respectively. Attempts to prepare EMImVF6 by both the acid–base
reaction of EMIm(HF)2.3F with VF5 and the metathesis of EMImCl with KVF6 failed due to the strong oxidizing
power of the pentavalent vanadium, whereas EMImSbF6 was successfully prepared only by the metathesis of
EMImCl and KSbF6. EMImBF4, EMImSbF6, EMImNbF6, EMImTaF6 and EMImWF7 are liquids at room
temperature whereas EMImPF6 and EMImAsF6 melts at around 330 K. Raman spectra of the obtained salts showed
the existence of the EMIm cation and corresponding fluorocomplex anions. IR spectroscopy revealed that strong
hydrogen bonds are not observed in these salts. EMImAsF6 (mp 326 K) and EMImSbF6 (mp 283 K) are isostructural
with the previously reported EMImPF6. The melting point of the hexafluorocomplex EMIm salt decreases with the
increase of the size of the anion (PF6Ϫ < AsF6Ϫ < SbF6Ϫ <NbF6Ϫ ≈ TaF6Ϫ).
been reported,6 which is the combination of RRЈIm cation and
Introduction
(HF)nFϪ anions (n = 2, 3) where the non-integer figure of 2.3 for
Molecular design, synthesis and characterization of room-
the room-temperature vacuum stable salt results from the exist-
temperature ionic liquids (RTILs, also called room-temperature
ence of both the (HF)2FϪ and (HF)3FϪ anion in this liquid
molten salts) are of current interest as electrolytes and green
(Scheme 1).7
solvents because of their negligibly small vapor pressure and
chemical stability over a wide range of temperatures.1 The
functionality of an RTIL strongly depends on the cationic or
anionic species and their combinations. After the synthesis
of air-stable 1-ethyl-3-methylimidazolium tetrafluoroborate
(EMImBF4) by Wilkes and Zaworotko,2 a number of reports
have been made on salts composed of organic cations and
Scheme 1 RRЈIm(HF)2.3F.
Ϫ
bulky fluoroanions such as PF6 or (CF3SO2)2NϪ.3 The alkyl-
imidazolium-based RTILs often exhibit a low melting point
and viscosity. However, limited to EMIm salts, the relationship
between the physical properties and the molecular size or
In the present study, EMIm(HF)2.3F is used as a fluorobase
to react with some binary fluorides (MFm) which act as fluoro-
acids to give fluorocomplex salts, EMImMFmϩ1. We confirmed
that this method effectively works for some binary fluorides.8
The physical properties of the obtained EMImMFmϩ1 are
reported as well as their solid-state structures and thermal
properties.
Ϫ
Ϫ
geometry of the anions is still unclear. BF4Ϫ, PF6 and AsF6
are known today as highly symmetric anions for the EMIm
salts.2–4 EMImSbF6 has been reported without its physical
properties; only the application as reaction solvent for organic
synthesis has been discussed.5 The salt of a larger anion appears
to have a lower melting point as a result of the decrease of the
electrostatic interactions between the cation and anion. How-
ever, in fact, the melting point of EMImBF4 (288 K) is
much lower than those of EMImPF6 and EMImAsF6 (333 and
326 K, respectively).2–4 This contradiction is probably caused
by the difference of the molecular geometries of the anions.
Systematic study is necessary to clarify the relationship between
the structures and properties of EMIm salts of fluorocomplex
anions. Furthermore, alternative preparative routes should be
developed to obtain RTILs with high purities. Recently, a series
of alkylimidazolium fluorohydrogenate (RRЈIm(HF)2.3F) have
Results and discussion
Syntheses of EMImMFm by fluoroacid–base reactions
Although EMImX (X = Cl, Br, I) are known, EMImF has never
been isolated as a pure unsolvated compound and is considered
to be unstable at room temperature. EMImMFmϩ1 cannot
be prepared by the simple acid–base reaction of EMImF and
MFm without forming any byproduct as in the case of alkyl-
imidazolium–chloroaluminate system.9 EMIm(HF)2.3F itself is
an RTIL in which FϪ is stabilized by making a covalent bond
with HF to form fluorohydrogenate anions such as (HF)2FϪ
and (HF)3FϪ.6,7 HF is a weak fluoroacid and is liberated by the
interaction of EMIm(HF)2.3F with MFm to give EMImMFmϩ1
according to the reaction below (Scheme 2).
† Electronic supplementary information (ESI) available: Raman and IR
assignments. See http://www.rsc.org/suppdata/dt/b3/b310162b/
‡ Research Fellow of Japan Society for the Promotion of Science.
D a l t o n T r a n s . , 2 0 0 4 , 1 4 4 – 1 4 9
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
144

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Table 1 Selected physical properties of EMImMFmϩ1
Tm a/K
ρa/g cmϪ3
σa/mS cmϪ1
ηa/cP
b
EMImBF4c
288
333
326
283
272
275
258
1.28
1.56
1.78
1.85
1.67
2.17
2.27
13.6
–
32
–
–
67
49
51
171
EMImPF6
Scheme 2 Syntheses of EMImMFmϩ1 by fluoroacid–base reactions.
EMImAsF6
EMImSbF6
EMImNbF6
EMImTaF6
EMImWF7
–
6.2
8.5
7.1
3.2
d
There are two common methods for the synthesis of dialkyl-
imidazolium-based RTILs.1 Metathesis such as the reaction of
EMImCl and MBF4 (M = ammonium, alkali metal or silver)
in water–ethanol to prepare EMImBF4 is a popular synthetic
route but has a problem of contamination by the byproduct
MCl. Preparation using an aqueous solution of protonic acid
such as the reaction of EMImCl and HBF4 (aq.) is applied for
the preparation of EMImBF4. However, this method is not
suitable for reactive metal fluorides which are hydrolyzed or
reduced by water. The benefit of the present method is that the
byproduct HF is volatile and easily removed by evacuation at
elevated temperatures, giving high purity of the reaction prod-
uct. All the reactions are highly exothermic and the reaction
vessel should be cooled occasionally by refrigerant. The reac-
tions with BF3, PF5, AsF5, NbF5, TaF5 and WF6 gave the
expected salts of singly charged anions. No trace of HF was
detected by IR spectroscopy or cyclic voltammetry of the
obtained salts. EMIm(HF)2.3F and VF5 violently reacted to give
black products due to the strong oxidizing power of VF5. The
metathesis of EMImCl and KVF6 in acetone also produced
black products without giving EMImVF6. In the case of the
reaction of EMIm(HF)2.3F with SbF5, the color of the liquid
immediately turned wine-red just after the addition of SbF5,
suggesting partial decomposition. In the Raman spectrum of
the liquid after the evacuation at 298 K, some peaks were
d
a Tm: Melting point, ρ: density at 298 K (the densities of EMImPF6 and
EMImAsF6 are crystallographically determined), σ: conductivity at 298
K, η: viscosity at 298 K. b Ref. 12. c Ref. 3. d Ref. 8.
Table 2 Summary of crystal data and refinement results for EMI-
mAsF6 and EMImSbF6 with crystal data of EMImPF6
c
EMImAsF6
EMImSbF6
EMImPF6
Formula
Mr
Crystal system
Space group
a/Å
b/Å
c/Å
H11C6N2F6As
300.09
Monoclinic
P21/c
8.871(10)
9.424(2)
13.786(2)
102.985(14)
1123.04(3)
4
1.775
298
0.0388
0.1039
H11C6N2F6Sb
346.92
Monoclinic
P21/c
8.942(8)
9.390(8)
13.849(12)
101.680(12)
1138.8(17)
4
2.024
200
0.0390
0.0939
H11C6N2F6P
255.24
Monoclinic
P21/c
8.757(2)
9.343(2)
13.701(3)
103.05(3)
1092.02
4
β/Њ
V/Å3
Z
Dc/g cmϪ3
T/K
1.558
283–303
–
a
R1
b
wR2
–
a R1 = Σ||Fo| Ϫ |Fc||/Σ|Fo|. b wR2 = [Σw[|Fo|2 Ϫ |Fc|2]2/Σw|Fo|2]1/2 c Ref. 3.
.
observed at the higher side of the strong peak at 655 cmϪ1
These peaks are typical for the polynuclear anions such as
Sb2F11
Ϫ 10 Successive heating under a dynamic vacuum to elim-
.
.
inate the byproduct HF and the excess SbF5 changed the color
of the sample to black. Thus the direct reaction of EMIm-
(HF)2.3F with SbF5 is not preferable to synthesize EMImSbF6.
The metathesis previously reported for other salts, the reaction
of EMImCl and KSbF6 in acetone, is the only viable method
for the synthesis of EMImSbF6 (Scheme 3).5
Scheme 3 Synthesis of EMImSbF6.
Properties of EMImMFm؉1
EMImBF4 is miscible with water whereas the solids EMImPF6
and EMImAsF6 are not. EMImSbF6 is immiscible with water
and sinks to the bottom of the vessel. However, the interface
gradually disappeared after contact with water overnight, prob-
ably due to the slow hydrolysis of EMImSbF6. EMImNbF6 and
EMImTaF6 are miscible with water. EMImWF7 rapidly reacts
with water to give a blue liquid.
Fig. 1 Cyclic voltammograms of Pt electrodes in (a) EMImBF4,
(b) EMImSbF6, (c) EMImNbF6, (d) EMImTaF6 and a glassy carbon
electrode in (e) EMImWF7: scan rate = 30 mV sϪ1
.
Selected physical properties of EMImMF6 are summarized
in Table 1. The conductivity of EMImSbF6 is a little lower than
that of EMImN(SO2CF3)2 (8.8 mS cmϪ1) or of EMImSO3CF3
(9.2 mS cmϪ1).3,11 EMImWF7 is a viscous RTIL with a viscosity
of 171 cP. EMImBF4 possesses the highest conductivity (13.6
mS cmϪ1) among the salts in the present study.12 Although the
conductivities of EMImSbF6, EMImTaF6 and EMImNbF6
increase in this order, the differences are not significant. The
conductivity of the RTIL of the largest anion, EMImWF7, is
the lowest among those of the salts in the present study. Cyclic
voltammograms at Pt electrodes in EMImBF4, EMImSbF6,
EMImNbF6 and EMImTaF6, and a glassy carbon electrode in
EMImWF7 are shown in Fig. 1. Their anodic limit potentials
are almost the same, ϩ1.5 V vs. Agϩ/Ag. The EMIm cation
is reported to be reduced at around Ϫ3.0 V vs. Agϩ/Ag.13
The cathodic limits of EMImBF4 and EMImTaF6 are around
Ϫ3.0 V, probably assigned to the reduction of EMIm cation,
whereas in the cases of EMImSbF6, EMImNbF6 and
EMImWF7, the anions in the RTILs are more easily reduced
than the cation and their electrochemical windows are narrower
than those of EMImBF4 and EMImTaF6.13
Structures and thermal properties of EMImMF6
Details of the data collection parameters and other crystallo-
graphic information for EMImAsF6 and EMImSbF6 are
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Table 3 Selected bond lengths and bond angles in EMImAsF6 and EMImSbF6 (Å, Њ)
EMImAsF6
EMImSbF6
EMImAsF6
EMImSbF6
EMImϩ
MF6Ϫ (M = As, Sb)
N1–C2
C2–N3
N3–C4
C4–C5
C5–N1
N1–C6
C6–C7
N3–C8
1.304(5)
1.314(5)
1.364(5)
1.326(7)
1.359(6)
1.472(5)
1.498(7)
1.461(5)
1.310(8)
1.313(7)
1.351(8)
1.334(10)
1.368(8)
1.472(7)
1.504(9)
1.460(8)
M–F1
M–F2
M–F3
M–F4
M–F5
M–F6
1.681(3)
1.684(3)
1.703(3)
1.663(3)
1.685(3)
1.671(3)
1.857(4)
1.842(5)
1.876(4)
1.824(5)
1.844(5)
1.840(5)
F1–M–F2
F1–M–F3
F1–M–F4
F1–M–F5
F1–M–F6
F2–M–F3
F2–M–F4
F2–M–F5
F2–M–F6
F3–M–F4
F3–M–F5
F3–M–F6
F4–M–F5
F4–M–F6
F5–M–F6
91.7(2)
179.68(17)
88.8(2)
87.61(17)
91.87(18)
88.2(2)
178.8(3)
89.5(3)
89.0(2)
90.8(2)
179.67(19)
90.2(3)
88.8(2)
90.8(2)
89.2(2)
179.0(3)
90.6(4)
89.2(3)
89.8(2)
90.8(2)
89.5(2)
89.6(4)
90.6(3)
179.6(3)
N1–C2–N3
C2–N3–C4
N3–C4–C5
C4–C5–N1
C5–N1–C2
C2–N1–C6
C5–N1–C6
N1–C6–C7
C2–N3–C8
C4–N3–C8
C2–N1–C6–C7
110.0(4)
107.7(4)
106.8(4)
108.2(4)
107.3(4)
126.3(4)
126.3(4)
111.4(4)
126.4(4)
125.9(4)
112.2(6)
109.9(5)
107.9(5)
107.7(6)
107.1(6)
107.5(5)
126.4(5)
126.1(5)
110.7(5)
125.7(5)
126.5(5)
116.6(9)
91.4(2)
92.10(17)
88.42(17)
89.4(3)
92.1(3)
178.4(2)
provided in Table 2. Selected bond distances and angles are
listed in Table 3. Both of the compounds are isostructural with
EMImPF6 of which the crystal data reported by Fuller et al. are
jointly listed in Table 2.3 Neither EMImAsF6 nor EMImSbF6
exhibit any thermal peaks corresponding to phase transitions in
the DSC curves (above 163 K), the structure being considered
to be maintained below their melting points. The ORTEP14
diagram of EMImAsF6 is shown in Fig. 2. EMImAsF6 and
EMImSbF6 are composed of EMIm cations and expected
octahedral MF6Ϫ anions (cis-F–M–F angular distortion < 2.4Њ
for AsF6Ϫ and < 1.2Њ for SbF6Ϫ). Typical bond lengths and bond
angles are observed in the EMIm cations determined here. The
β-carbon of the ethyl group is out of the plane of the imid-
azolium five-membered ring with C2–N1–C5–C6 torsion angles
of 112.2(6) and 116.6(9)Њ for EMImAsF6 and EMImSbF6,
respectively. The cations are placed parallel to each other but
not in a stacked arrangement. The formula unit volumes for
EMImPF6, EMImAsF6 and EMImSbF6 are 273.0 at 273 K,
280.8 at 273 K and 284.7 Å3 at 200 K, respectively, changing
with the size of the anion, although the cell parameters of
EMImSbF6 were determined at 200 K. The hydrogen-bond
geometries in EMImAsF6 and EMImSbF6 are summarized in
Table 4. In general, relatively large complex anions in EMIm
salts make weaker hydrogen bonds with EMIm cation than
small anions such as halides.3,15 In EMImAsF6 and EMImSbF6,
the hydrogen-bond distances between H atoms in the cation
including methyl groups and F atoms of MF6Ϫ are not less than
2.5 Å, indicating that the hydrogen bonds in these salts are not
strong in terms of the van der Waals criterion (2.7 Å),16 the
coulombic force dominating the interaction between the cation
and anion. This observation agrees with the case of EMImPF6
and the results of IR spectra discussed below.3 Unfortunately,
the structure determination of EMImNbF6 and EMImTaF6
failed due to the poor quality of the crystals. The relationship
between the melting points and the sizes of the anions for the
fluorocomplex salts are shown in Fig. 3, where the radius of the
central atom in the fluorocomplex anion reported by Shannon
is plotted on the horizontal axis.17 The radius of seven-
coordinated Mo() is used for the unavailable data for W() of
seven coordination since the similarity is crystallographically
known for the radii of these atoms with the same oxidation
state and coordination environment. There is a tendency for the
melting point of the salt to decrease with increase in size of the
anion except for EMImBF4. The tetrahedral BF4Ϫ anion is con-
sidered to have a different interaction with the cation from
those of hexa- or heptafluoroanions and they cannot be treated
in the same manner as a singly charged rigid sphere.
Fig. 3 Relationship between the size of anion and melting point for
EMImMFmϩ1. The horizontal axis is referenced to the value of the
radius of the central atom of the anion reported by Shannon and
Ϫ
.
17
the radius of seven-coordinated Mo() is used for that of WF7
Vibrational spectra
Raman and IR frequencies of the obtained salts with their
assignments are summarized as ESI.† Vibrational spectra of
EMIm cations in some salts are well-characterized in previous
Fig. 2 ORTEP14 diagram of the EMIm cation and AsF6 anion in the
EMImAsF6 structure.
D a l t o n T r a n s . , 2 0 0 4 , 1 4 4 – 1 4 9
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Table 4 Hydrogen-bond geometries for EMImAsF6 and EMImSbF6 (Å, Њ)
EMImAsF6
EMImSbF6
D–H ؒ ؒ ؒ A
D–H
H ؒ ؒ ؒ A
D ؒ ؒ ؒ A
D–H ؒ ؒ ؒ A
D–H
H ؒ ؒ ؒ A
D ؒ ؒ ؒ A
D–H ؒ ؒ ؒ A
C(2)–H(2) ؒ ؒ ؒ F(1)
C(2)–H(2) ؒ ؒ ؒ F(5)
C(8)–H(8b) ؒ ؒ ؒ F(1)
C(8)–H(8c) ؒ ؒ ؒ F(3)
C(8)–H(8a) ؒ ؒ ؒ F(6)
0.93
0.93
0.96
0.96
0.96
2.59
2.67
2.54
2.62
2.69
3.254(4)
3.137(4)
3.396(3)
3.300(3)
3.221(4)
129
112
148
128
115
0.93
0.93
0.96
0.96
0.96
2.51
2.68
2.55
2.71
2.59
3.228(5)
3.108(7)
3.345(6)
3.304(6)
3.129(7)
134
109
140
121
116
reports.18 Assignment below 600 cmϪ1 contains some ambigu-
alent F atoms in EMImWF7 detected by 19F NMR spectro-
scopy indicates the presence of intramolecular ligand exchange
on the NMR time scale.
ities due to the overlap of C–H bending and ring bending
modes. The Raman spectra of the obtained salts (< 1200 cmϪ1
)
are shown in Fig. 4. Peaks assigned to the EMIm cation are
essentially the same as observed in the spectrum of EMImCl
(Fig. 4(h)). The positions of the peaks except for those of
EMIm cation are in good agreement with the fundamental
modes of the corresponding fluorocomplex anions reported in
the literature.19 Their IR spectra also exhibit the fundamental
modes of the fluorocomplex anions. Three candidates for the
geometry of a seven-coordinated molecule; the pentagonal bi-
pyramid (D5h), the monocapped octahedron (C3v) and the
monocapped trigonal prism (C2v) have similar energy levels and
the environment around the molecule determines the preferable
geometry.20 The first report of the Raman and IR spectra of
Hydrogen bonds in EMIm salts are often discussed based on
the IR spectra in the range 3000–3200 cmϪ1. The IR spectra of
this region for the present salts are shown in Fig. 5. A strong
hydrogen bond between the ring proton and anion is reflected in
the shift of the C–H stretching of the ring proton. In solid
EMImCl or basic EMImCl–AlCl3 ionic liquid for example, the
C–H stretching of the ring proton is observed between 3000
and 3100 cmϪ1 due to the strong hydrogen bond between the
ring proton and anions, whereas the C–H stretching of EMIm
cation in the weak hydrogen bond system is observed between
3100 and 3200 cm .
Ϫ1 18 As shown in Fig. 5, the absorption bands
of C–H aromatic stretchings in the IR spectra of all the present
fluorocomplex salts were observed in the latter region, suggest-
ing that the hydrogen bonds via ring protons are not strong in
these salts.
Ϫ
CsWF7 suggested that WF7 has D5h geometry.21 However, a
single crystal X-ray diffraction study performed nineteen years
later revealed that the actual geometry of WF7Ϫ in CsWF7 was
Ϫ
C3v.22 WF7 with the geometry of the monocapped trigonal
prism (C2v) was found in [WF4(bipy)2]2ϩؒ2[WF7]ϪؒCH3CN.23
Raman spectra of the two geometries are similar to each other
and characterized by a strong peak at around 700 cmϪ1 with
several small peaks. The appearance of the Raman spectrum
of EMImWF7 is close to that of CsWF7 rather than [WF4-
Ϫ
(bipy)2]2ϩؒ2[WF7]ϪؒCH3CN. Therefore WF7 is exposed to a
weaker ionic field in the liquid state than that in the solid and
may be concluded to have the C3v symmetry. The seven equiv-
Fig. 5 IR spectra of (a) EMImBF4, (b) EMImPF6, (c) EMImAsF6,
(d) EMImSbF6, (e) EMImNbF6, (f ) EMImTaF6, (g) EMImWF7 and
(h) EMImCl in the region between 2500–3500 cmϪ1
Experimental
Materials and methods
Volatile materials were handled in a vacuum line constructed
of SUS316 stainless steel and PFA (tetrafluoroethylene–
perfluroalkyl vinyl ether copolymer). Nonvolatile materials
were handled under argon atmosphere in a glove-box. A PFA
reaction tube combined with a stainless steel valve was used
as a reaction vessel for volatile materials. A T-shaped reactor
constructed of tubes and a T-joint made of PFA were used for
the reaction of nonvolatile materials. Anhydrous HF (Daikin
Industries, Co. Ltd., purity >99%) was treated with K2NiF6
(Ozark–Mahoning) for several days prior to use to remove
Fig. 4 Raman spectra of (a) EMImBF4, (b) EMImPF6, (c) EMIm-
AsF6, (d) EMImSbF6, (e) EMImNbF6, (f ) EMImTaF6, (g) EMImWF7
and (h) EMImCl.
D a l t o n T r a n s . , 2 0 0 4 , 1 4 4 – 1 4 9
147

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water. CAUTION: Anhydrous HF and some fluorides below
are highly toxic and must be handled using appropriate appar-
atus and protective gear. Acetone dehydrated (Wako Pure
Chemical Industries, water content <50 ppm), BF3 (Nippon
Sanso, purity 99.99%), PF5 (Nippon Sanso, purity 99%), SbF5
(PCR, purity >97%), NbF5 (Ozark–Mahoning, purity 99%),
TaF5 (Ozark–Mahoning, purity 99.5%), WF6 (Central Glass,
purity 99.999%) were used as supplied. AsF5 was prepared by
the reaction of As2O3 (Wako Pure Chemical Industries, purity
>98%) and F2 gas (Daikin Industries, purity 99.7%) at 573 K.
VF5 was prepared by the reaction of vanadium metal powder
(Nilaco, purity 99.5%) and F2 gas at 573 K. KVF6 was prepared
by the reaction of KF (Wako Pure Chemical Industries, purity
>98%) and VF5 in aHF. KSbF6 (Aldrich, purity 99%) was used
as supplied. EMImCl (Sanko Chemical Industry, purity 98.5%)
was purified by recrystallization in acetonitrile solution by
adding ethyl acetate. EMIm(HF)2.3F was synthesized by the
reaction of EMImCl and anhydrous HF.6 EMIm(HF)2.3F is
involatile and inert against borosilicate glassware at ambient
conditions, however, contact with reducing metals such as
aluminium should be avoided.
6.95–6.91 (m, 1H, H(4)), 6.88–6.85 (m, 1H, H(5)), 3.71 (q, 2H,
J = 21.9 Hz, H(6)), 3.40 (s, 3H, H(8)), 1.01 (t, 3H, J = 14.7 Hz,
H(7)). 19F NMR (neat), δ Ϫ113.69 (s, SbF6). The salt was
recrystallized from the neat salt at 273 K and provided for
single-crystal X-ray diffraction.
Synthesis of EMImNbF6
EMImNbF6 was synthesized in the same manner as previously
reported.8 Anal. Calc. for C6F4H11N2Nb: C, 22.65; H, 3.46; N,
8.81. Found: C, 22.95; H 3.27; N, 8.80%. 1H NMR (neat), δ 8.99
(br s, 1H, H(2)), 7.70 (br s, 1H, H(4)), 7.64 (br s, 1H, H(5)), 4.40
(br s, 2H, H(6)), 4.09 (br s, 3H, H(8)), 1.64 (br s, 3H, H(7)). 19
F
NMR (neat), δ Ϫ127.25 (br s, NbF6).
Synthesis of EMImTaF6
EMImTaF6 was synthesized in the same manner as previously
reported.8 Anal. Calc. for C6F4H11N2Nb: C, 17.74; H 2.71; N,
6.90. Found: C, 17.89; H 2.60; N, 6.85%. 1H NMR (neat), δ 8.34
(br s, 1H, H(2)), 7.30 (br s, 2H, H(4), H(5)), 4.12 (br s, 2H,
H(6)), 3.81 (br s, 3H, H(8)), 1.42 (br s, 3H, H(7)). 19F NMR
(neat), δ Ϫ191.48 (s, TaF6).
Synthesis of EMImBF4
Synthesis of EMImWF7
EMIm(HF)2.3F (9.88 mmol) and a large excess of BF3 were
reacted in a PFA tube. A colorless liquid was obtained after
the removal of liberated HF and excess BF3 under dynamic
vacuum at 343 K. Spectroscopic methods and elemental analy-
sis identified the liquid as EMImBF4 (9.84 mmol). Anal. Calc.
for BC6F4H11N2: C, 36.38; H 5.56; N, 14.15. Found: C, 36.38;
H 5.42; N, 14.30%. 1H NMR (neat), δ 8.35 (s, 1H, H(2)), 7.30 (s,
1H, H(4)), 7.23 (s, 1H, H(5)), 3.97 (q, 2H, J = 21.6 Hz, H(6)),
3.66 (s, 3H, H(8)), 1.19 (t, 3H, J = 14.7 Hz, H(7)). 19F NMR
(neat), δ Ϫ150.35 (s, BF4).
EMIm(HF)2.3F (3.34 mmol) and a large excess of WF6 were
reacted in a PFA tube. After the reaction, phase separation of
the excess WF6 beneath the liquid of the reaction mixture was
observed. A yellow liquid EMImWF7 (3.31 mmol) was
obtained after the removal of liberated HF and excess WF6
under dynamic vacuum at 343 K. Anal. Calc. for C6F7H11N2W:
C, 16.83; H, 2.57; N, 6.55. Found: C, 17.09; H, 2.74; N, 6.67%.
1H NMR (neat), δ 8.47 (br s, 1H, H(2)), 7.51 (br s, 1H, H(4)),
7.46 (br s, 1H, H(5)), 4.24 (br s, 2H, H(6)), 3.93 (br s, 3H, H(8)),
1.50 (br s, 3H, H(7)). 19F NMR (neat), δ Ϫ90.61 (s, WF7).
Synthesis of EMImPF6
X-Ray diffraction analysis
EMIm(HF)2.3F (6.51 mmol) and a large excess of PF5 were
reacted in a PFA tube. A white powdered sample was obtained
after the removal of liberated HF and excess PF5 under
dynamic vacuum at 343 K. Spectroscopic methods and chem-
ical analysis identified the solid as EMImPF6 (6.69 mmol).
Anal. Calc. for C6F6H11N2P: C, 28.13; H 4.30; N, 10.94. Found:
For EMImAsF6, X-ray diffraction data were collected using a
Nonius KappaCCD diffractometer with a CCD area detector
and monochromated Mo-Kα radiation at 298 K. The single
crystal which was fixed in a quartz capillary under argon
atmosphere was mounted on a goniometer head. The obtained
data were processed by the program DENZO-SMN.24 The
program SORTAV was used for the absorption correction.25
For EMImSbF6, X-ray diffraction data were collected using
a Rigaku AFC7 diffractometer with a Mercury CCD area
detector and monochromated Mo-Kα radiation at 200 K. The
single crystal fixed on a glass fiber in a cooled oil (C10F18) was
mounted on the goniometer head. The obtained data were pro-
cessed by the program CRYSTAL CLEAR.26 The SHELX-97
suite of programs were used for the solution and refinement of
the structures.27 All the non-hydrogen atoms were determined
by the direct method and difference Fourier synthesis by intro-
ducing anisotropic displacement parameters, whereas all the
hydrogen atoms were refined using appropriate riding models,
with C–H distances of 0.97 Å for CH2, 0.96 Å for CH3 and
0.93 Å for aromatic groups. The displacement parameters of H
atoms were fixed at 1.2Ueq of their parent atoms (1.5Ueq for
methyl groups).
1
C, 28.23; H 4.33; N, 10.91%. H NMR (DMSO-d6), δ 9.07 (s,
1H, H(2)), 7.75 (t, J = 3.6 Hz, H(4)), 7.66 (t, J = 3.6 Hz, H(5)),
4.17 (q, J = 22.2 Hz, H(6)), 3.83 (s, H(8)), 1.40 (t, J = 14.7 Hz,
H(7)). 19F NMR (DMSO-d6), δ Ϫ70.7 (d, J = 704 Hz, PF6).
Synthesis of EMImAsF6
The reaction of EMIm(HF)2.3F (3.97 mmol) and a large excess
of AsF5 in the same manner as for EMImPF6 gave a white
powder of EMImAsF6 (4.12 mmol). Anal. Calc. for AsF6-
C6H11N2: C, 24.01; H 3.67; N, 9.34. Found: C, 23.84; H 3.61;
1
N, 9.25%. H NMR (DMSO-d6), δ 9.08 (s, 1H, H(2)), 7.76 (t,
J = 3.3 Hz, H(4)), 7.67 (t, J = 3.3 Hz, H(5)), 4.17 (q, J = 22.2 Hz,
H(6)), 3.83 (s, H(8)), 1.40 (t, J = 14.7 Hz, H(7)). 19F NMR
(DMSO-d6), δ Ϫ68.4 (q, J = 2788 Hz, AsF6). The salt was
recrystallized from a cooled methanol solution at 268 K and
provided for single-crystal X-ray diffraction.
CCDC reference numbers 217826 and 217827.
Synthesis of EMImSbF6
See http://www.rsc.org/suppdata/dt/b3/b310162b/ for crystal-
lographic data in CIF or other electronic format.
EMImCl (93.1 mmol) and KSbF6 (93.1 mmol) were reacted in
dehydrated acetone. After stirring for 72 h, the reaction mixture
was filtered through a glass frit. The precipitate was identified
as KCl by X-ray powder diffraction. The filtrate was dried by
evacuation at 343 K in a PFA vessel. A colorless liquid was
obtained. Spectroscopic methods and elemental analysis iden-
tified the liquid as EMImSbF6 (74.7 mmol, yield 80.2%). Anal.
Calc. for F6C6H11N2Sb: C, 20.76; H, 3.17; N, 8.07. Found: C,
20.74; H, 3.09; N, 8.18%. 1H NMR (neat), δ 7.88 (s, 1H, H(2)),
Spectroscopic and thermal analyses
The Raman spectra of solid and liquid samples were obtained
by FTS-175C (BIO-RAD Laboratories) using 1064 nm line of
Nd:YAG laser as an excitation line at room temperature. The
samples for Raman spectroscopy were loaded in NMR Pyrex
test tubes. The IR spectra of solid and liquid samples were
D a l t o n T r a n s . , 2 0 0 4 , 1 4 4 – 1 4 9
148

View Article Online
5 (a) C. E. Song, W. H. Shim, E. J. Roh and J. H. Choi, J. Chem. Soc.,
Chem. Commun., 2000, 1695; (b) T. Itoh, E. Akasaki, K. Kudo and
S. Shirakami, Chem. Lett., 2001, 262.
obtained by FTS-165 (BIO-RAD Laboratories). The samples
were sandwiched by a pair of AgCl windows fixed in a stain-
1
less airtight cell. H NMR measurements of the samples were
6 (a) R. Hagiwara, T. Hirashige, T. Tsuda and Y. Ito, J. Fluorine
Chem., 1999, 99, 1; (b) R. Hagiwara, T. Hirashige, T. Tsuda and
Y. Ito, J. Electrochem. Soc., 2002, 149, D1; (c) R. Hagiwara,
K. Matsumoto, Y. Nakamori, T. Tsuda, Y. Ito, H. Matsumoto and
K. Momota, J. Electrochem. Soc., 2003, 150, D195.
7 (a) J. H. Clark, J. Emsley, D. J. Jones and R. E. Overrill, J. Chem.
Soc., Dalton Trans., 1981, 1219; (b) T. v. Rosenvinge, M. Parrinello
and M. L. Klein, J. Chem. Phys., 1997, 107, 8013; (c) W. D.
Chandler, K. E. Johnson and J. L. E. Campbell, Inorg. Chem., 1995,
34, 4943; (d ) I. Gennick, K. M. Harmon and M. M. Potvin,
Inorg. Chem., 1977, 16, 2033.
performed using a Varian Mercury-300BB NMR spectrometer
(300 MHz) and the obtained spectra were referenced to tetra-
methylsilane. 19F NMR measurements of the samples were
performed using a Varian Mercury-300BB NMR spectro-
meter (282 MHz) and the obtained spectra were referenced to
trichlorofluoromethane; C6D6 was used as an external standard
for the measurements of the neat salts. All the data were
recorded as chemical shifts. Differential scanning calorimetric
analysis (DSC) was performed on the sample in a platinum cell
under nitrogen gas flow using a Shimadzu DSC-60. A scanning
rate 5 K minϪ1 was used.
8 K. Matsumoto, R. Hagiwara and Y. Ito, J. Fluorine Chem., 2002,
115, 133.
9 (a) J. S. Wilkes, J. A. Levisky, R. A. Wilson and C. L. Hussey,
Inorg. Chem., 1982, 21, 1263; (b) A. A. Fanning, Jr., D. A. Floreani,
L. A. King, S. S. Landers, B. J. Piersma, D. J. Stech, R. L. Vaughn,
J. S. Wilkes and J. L. Williams, J. Phys. Chem., 1984, 88, 2614.
10 (a) H. Willner, M. Bodenbinder, R. Bröchler, G. Hwang, S. J. Rettig,
J. Trotter, B. Ahsen, U. Westphal, V. Jonas, W. Thiel and F. Aubke,
J. Am. Chem. Soc., 2001, 123, 588; (b) R. Minkwitz, S. Reinemann,
R. Seelbinder, D. Konikowski, H. Hartl, I. Bru1dgam, J. Hegge,
B. Hoge, J. A. Sheehy and K. O. Christe, Inorg. Chem., 2001, 40,
4404.
11 E. I. Cooper and E. J. M. O’Sullivan, Proc. 8th Int. Symp. Molten
Salts, The Electrochemical Society, Pennington, NJ, 1992, p. 386.
12 A. Noda, K. Hayamizu and M. Watanabe, J. Phys. Chem. B, 2001,
105, 4603.
Measurement of electrochemical and physical properties
Electrochemical measurements were performed using a Pt or
glassy carbon working electrode, and a glassy carbon counter
electrode with the aid of Hokuto Denko, HZ-3000 electro-
chemical measurement system. The reference electrode was
made of silver wire immersed in EMImBF4 containing 0.05 M
AgBF4 which was separeted from the electrolyte by Polyflon
filter (Advantec). Conductivities were measured by the
impedance technique using a cell with platinum disk electrodes
calibrated by KCl standard aqueous solution. Viscosity meas-
urements were performed using an Ostwald viscometer made of
PFA. Densities were measured by weighing samples in a PFA
vessel whose volume was calibrated by distilled water.
13 Y. Katayama, S. Dan, T. Miura and T. Kishi, J. Electrochem. Soc.,
2001, 148, C102.
14 L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 365.
15 (a) A. K. Abdul-Sada, A. M. Greenway, P. B. Hitchcock, T. J.
Mohammed, K. R. Seddon and J. A. Zora, J. Chem. Soc., Chem.
Commun., 1986, 1753; (b) A. Elaiwai, P. B. Hitchcock, K. R.
Seddon, N. Srinivasan, Y. Tan, T. Welton and J. A. Zora, J. Chem.
Soc., Dalton Trans., 1995, 3467.
16 J. E. Huheey, Inorganic Chemistry: Principles of Structure and
Reactivity, Harper Collins College Publisher, 4th edn., 1993.
17 R. D. Shannon, Acta Crystallogr., Sect. A, 1976, 32, 751.
18 (a) S. Tait and R. A. Osteryoung, Inorg. Chem., 1984, 23, 4352;
(b) J. L. E. Campbell, K. E. Johnson and J. R. Torkelson,
Inorg. Chem., 1994, 33, 3340; (c) K. M. Dieter, C. J. Dymek,
N. E. Helmer, J. W. Rovang and J. S. Wilkes, J. Am. Chem. Soc.,
1988, 110, 2722.
19 K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds. Part A. Theory and Application in
Inorganic Chemistry, Wiley Interscience, New York, 5th edn., 1997,
p. 216.
20 (a) K. Seppelt, Inorganic Fluorine Chemistry ACS Symposium Series
555, ed. J. S. Thrasher and S. Strauss, American Chemical Society,
Washington, DC, 1992, p. 56; (b) K. O. Christe, E. C. Curtis, D. A.
Dixon, H. P. A. Mercier, J. C. P. Sanders, G. J. Schrobilgen and W. W.
Wilson, Inorganic Fluorine Chemistry ACS Symposium Series 555,
ed. J. S. Thrasher and S. Strauss, American Chemical Society,
Washington, DC, 1992, p. 66.
Acknowledgements
EMImCl used in this study was provided by Sanko Chemical
Industry, Co., Ltd.. WF6 was supplied by Central Glass, Co.,
Ltd. This work was supported by a Grant in Aid for Scientific
Research by Japan Society for the Promotion of Science
(No. 13555237), The 21st Century COE Program “Establish-
ment of COE on Sustainable-Energy System” from Japanese
Ministry of Education, Culture, Sports, Science and Tech-
nology, Iketani Science and Technology Foundation, Kansai
Research Foundation for Technology Promotion, and Toyota
High-tech Research Grant Program. One of the authors,
K. M., thanks the Japan Society for the Promotion of Science
for financial support as a research fellow.
References
1 (a) T. Welton, Chem. Rev., 1999, 99, 2071; (b) K. R. Seddon,
J. Chem. Technol. Biotechnol., 1997, 68, 351; (c) P. Wasserscheid and
W. Kein, Angew. Chem., Int. Ed., 2000, 39, 3772; (d ) R. Hagiwara
and Y. Ito, J. Fluorine Chem., 2000, 105, 221; (e) R. Hagiwara,
Electrochemistry, 2002, 70, 130.
21 A. Beuter, W. Kuhlmann and W. Sawodny, J. Fluorine Chem., 1975,
6, 367.
2 J. S. Wilkes and M. J. Zaworotko, J. Chem. Soc., Chem. Commun.,
1992, 965.
3 (a) J. Fuller, R. T. Carlin, H. C. De Long and D. Haworth, J. Chem.
Soc., Chem. Commun., 1994, 299; (b) A. J. Carmichael and K. R.
Seddon, J. Phys. Org. Chem., 2000, 13, 591; (c) P. Bonhôte, A.-P.
Dias, M. Armand, N. Papageorgiou, K. Kalyanasundaram and
M. Grätzel, Inorg. Chem., 1996, 35, 1168.
22 S. Giese and K. Seppelt, Angew. Chem., Int. Ed. Engl., 1994, 33, 461.
23 L. Arnaudet, R. Bougon, B. Ban, M. Lance, A. Navaza, M. Neirlich
and J. Vigner, J. Fluorine Chem., 1994, 67, 17.
24 Z. Otwinowski and W. Minor, Methods Enzymol., 1997, 276, 307.
25 R. H. Blessing, Acta Crystallogr., Sect. A, 1995, A51, 33.
26 CRYSTAL CLEAR, Rigalu Corporation, The Woodlands, TX,
1999.
4 A. B. McEwen, H. L. Ngo, K. LeCompte and J. L. Goldman,
J. Electrochem. Soc., 1999, 146, 1687.
27 G. M. Sheldrick, SHELX-97, University of Göttingen, Germany,
1997.
D a l t o n T r a n s . , 2 0 0 4 , 1 4 4 – 1 4 9
149