Densities and viscosities of 1-butyl-3-methylimidazolium trifluoromethanesulfonate + H2O binary mixtures at T = (303.15 to 343.15) K

Article abstract of DOI:10.1021/je8003832

Densities and viscosities for the binary mixtures of H₂O (1) + 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][CF ₃SO₃]) (2) were measured over the entire mole fraction range from (303.15 to 343.15) K at atmospheric pressure. Excess molar volumes and viscosity deviations as a function of mole fraction average were derived, and the results were fitted to the Redlich-Kister equation using a multiparametric nonlinear regression method. Estimated coefficients of the Redlich-Kister equation and standard error calculated from the Redlich-Kister equation to the experimental data are also presented. The results show that the densities and viscosities are dependent on water content and temperature.

Full text of DOI:10.1021/je8003832

2408
J. Chem. Eng. Data 2008, 53, 2408–2411
Densities and Viscosities of 1-Butyl-3-methylimidazolium
Trifluoromethanesulfonate + H2O Binary Mixtures at T ) (303.15 to 343.15) K
Ming-Lan Ge,*,† Ru-Song Zhao,† Yu-Feng Yi,† Qi Zhang,† and Li-Sheng Wang‡
Department of Chemical Engineering, Beijing Institute of Petrochemical Technology, Beijing 102617, People’s Republic of
China, and School of Chemical Engineering and Environment, Beijing Institute of Technology,
Beijing 100081, People’s Republic of China
Densities and viscosities for the binary mixtures of H2O (1) + 1-butyl-3-methylimidazolium trifluoromethane-
sulfonate ([BMIM][CF3SO3]) (2) were measured over the entire mole fraction range from (303.15 to 343.15)
K at atmospheric pressure. Excess molar volumes and viscosity deviations as a function of mole fraction
average were derived, and the results were fitted to the Redlich-Kister equation using a multiparametric
nonlinear regression method. Estimated coefficients of the Redlich-Kister equation and standard error
calculated from the Redlich-Kister equation to the experimental data are also presented. The results show
that the densities and viscosities are dependent on water content and temperature.
Table 1. Comparison of Experimental Densities G and Viscosities η
Introduction
of [BMIM][CF3SO3] with Literature Values
Ionic liquids (ILs) are environmentally friendly solvents with
F/g·cm-3
η/mPa·s
exptl lit.
no detectable vapor pressure and good solubility for many
organic, inorganic, and polymeric substances. Because of this
combination of properties, ILs present many possible applica-
tions in many fields. Much of the interest has focused on their
application to catalytic reaction, separation process, and elec-
trochemistry. Systematic investigations of thermodynamic and
thermophysical properties of ILs and in particular of mixtures
containing ILs are still few.1
Densities and viscosities are needed for the design of new
processes involving ILs on an industrial scale. Further experi-
mental data of density and viscosity of a binary mixture are
important from a theoretical viewpoint to understand the liquid
theory. So, a study on excess thermophysical properties is
important to be able to predict the properties of mixtures
containing ILs. 2 Furthermore, the presence of water in the ionic
liquid phase can dramatically affect the physical properties.3-5
As noted, the high viscosities of ILs are a hindrance when used
in chemical processing.6
t/°C
exptl
1.3070a 1.2907
lit.
20
92.092a 907
1.3013 ( 0.0015 (22.6 °C)8
1.305511b
9910
109.640911b
1.306112
25
30
1.3028a 1.29879
75.282a
63.190
1.301511b
83.644511b
64.210
1.2984
1.2965 ( 0.0014 (30.8 °C)8
1.297511b
65.399211b
1.296612
35
40
1.2949
1.2914
1.293511b
51.729
42.458
52.238111b
44.110
1.2894 ( 0.0012 (40.2 °C)8
1.289511b
42.513311b
1.287612
45
50
1.2878
1.2844
1.285511b
35.174
29.553
35.173111b
30.910
1.2790 ( 0.0023 (55.6 °C)8
1.281511b
29.527111b
1.278712
60
70
1.2774
1.2705
1.270512
21.609
16.376
22.810
1.273511b
21.602711b
17.410
1.2700 ( 0.0038 (69.8 °C)8
1.265511b
16.476811b
1-Butyl-3-methylimidazolium
trifluoromethanesulfonate
1.262512
([BMIM][CF3SO3], CAS no. 174899-66-2) is one of the air-
and water-stable hydrophilic ionic liquids and is also thermally
stable. The densities and viscosities of [BMIM][CF3SO3]
reported in the literature7-12 are listed in Table 1. In previous
works, we have measured activity coefficient γ∞i data of 34
organic solutes in [BMIM][CF3SO3] from (303.15 to 363.15)
K.13,14
In this work, the densities and viscosities of mixtures
consisting of [BMIM][CF3SO3] and water were measured over
the entire range of their compositions from (303.15 to 343.15)
K. The excess molar volume VE and viscosity deviation ∆η of
this binary system have been obtained and fitted to the
Redlich-Kister equation. The effects of water content and
temperature on the physical properties have been analyzed, and
the interactions and structures were discussed in terms of the
a Extrapolated value from F ) b - aT and η ) η0 exp[B/(T - T0)];
b, a, η0, and T0 are fit parameters for the linear fitting. b Derived value
from correlating equations.
behavior of the excess molar volume VE of the mixture of
[BMIM][CF3SO3] + water.
Experimental Section
Materials. In this work, all the aqueous solutions were
prepared with deionized water, and the chemicals for preparation
of ionic liquid ([BMIM][CF3SO3]) were of analytical grade and
used without further purification. The ionic liquid [BMIM]-
[CF3SO3] was prepared via the traditional two steps. First,
1-butyl-3-methylimidazolium bromide [BMIM][Br] was pre-
pared via the reaction of 1-methylimidazole (0.1 mol) and
1-bromobutane (0.11 mol). Second, [BMIM][CF3SO3] was
* Corresponding author. E-mail: geminglan@bipt.edu.cn.
† Beijing Institute of Petrochemical Technology.
‡ Beijing Institute of Technology.
10.1021/je8003832 CCC: $40.75
2008 American Chemical Society
Published on Web 09/06/2008

Journal of Chemical & Engineering Data, Vol. 53, No. 10, 2008 2409
Table 2. Experimental Densities G for Binary Mixture of H2O (1) +
[BMIM][CF3SO3] (2)
T/K
x1
303.15 308.15 313.15 318.15 323.15 333.15 343.15
F/g·cm-3
0.0000 1.2984 1.2949 1.2914 1.2878 1.2844 1.2774 1.2705
0.1032 1.2945 1.2910 1.2875 1.2838 1.2803 1.2731 1.2660
0.1939 1.2912 1.2877 1.2841 1.2804 1.2768 1.2697 1.2626
0.2987 1.2865 1.2830 1.2794 1.2758 1.2722 1.2650 1.2579
0.3999 1.2808 1.2773 1.2738 1.2702 1.2665 1.2593 1.2522
0.5010 1.2728 1.2693 1.2657 1.2620 1.2583 1.2511 1.2440
0.5923 1.2630 1.2595 1.2559 1.2522 1.2485 1.2413 1.2339
0.7023 1.2462 1.2425 1.2388 1.2349 1.2311 1.2234 1.2156
0.7990 1.2201 1.2166 1.2129 1.2089 1.2052 1.1972 1.1893
0.9010 1.1646 1.1606 1.1567 1.1530 1.1500 1.1426 1.1343
1.0000 0.9957 0.9940 0.9922 0.9902 0.9881 0.9832 0.9778
Figure 1. Excess molar volume VE vs molar fraction of water for H2O (1)
+ [BMIM][CF3SO3] (2). 9, 303.15 K; b, 308.15 K; 2, 313.15 K; 1, 318.15
K; [, 323.15 K; 0, 333.15 K; ∆, 343.15 K. The symbols represent
experimental values, and the solid curves are calculated with the
Redlich-Kister equation.
Table 3. Experimental Viscosities η for Binary Mixture of H2O (1)
+ [BMIM][CF3SO3] (2)
T/K
x1
303.15 308.15 313.15 318.15 323.15 333.15 343.15
η/mPa·s
0
63.190 51.729 42.458 35.174 29.553 21.609 16.376
in pH values of this IL between room temperature and 343 K
was less than 1 %. This phenomenon showed that this ionic
liquid will not hydrolyze at 343 K. Before use, the IL was
subjected to vacuum evaporation at (323 to 333) K over 24 h
to remove possible traces of solvents and moisture. Its densities
and viscosities at several temperatures are in good agreement
with those reported in the literature (in Table 1).
Apparatus and Procedure. The mixtures of [BMIM]-
[CF3SO3] and water were prepared by mass. A TE2101-L
electronic digital balance accurate to within ( 0.1 mg was used.
The uncertainty in the mole fraction of the mixtures was
estimated to less than ( 0.0001. All molar quantities are based
on the IUPAC 2005 relative atomic mass table.15 The densities
of the ionic liquid [BMIM][CF3SO3] and its mixtures were
measured with a pycnometer (10 mL), and since its volume
varied with temperature, it was calibrated with pure water from
(303.15 to 343.15) K. The temperature was controlled by a water
bath to within an uncertainty of ( 0.05 K.
0.1032 45.696 37.227 30.927 25.041 21.507 16.069 12.443
0.1939 35.415 29.270 24.463 20.791 18.108 13.507 10.545
0.2987 28.969 24.276 20.532 17.549 15.173 11.613
9.1368
0.3999 23.248 19.951 16.880 14.377 12.618
0.5010 19.187 16.805 13.948 12.001 10.423
9.8800 7.8156
8.1008 6.6122
0.5923 15.467 13.202 11.210
9.9072 8.5157 6.7021 5.3842
0.7023 11.556 10.130 8.6049 7.4650 6.5763 5.1369 4.2397
0.7990 8.2063 6.9320 5.9890 5.3393 4.5704 3.6181 2.9364
0.9010 4.5521 3.8692 3.3759 3.1563 3.0054 2.0992 1.7141
1.0000 0.7977 0.7190 0.6532 0.6001 0.5470 0.4665 0.4040
Table 4. Excess Molar Volume VE for the Binary Mixture of H2O
(1) + [BMIM][CF3SO3] (2)
T/K
x1
303.15 308.15 313.15 318.15 323.15 333.15 343.15
VE/cm3 ·mol-1
0.1032 0.1693 0.1732 0.1770 0.1965 0.2155 0.2534 0.2908
0.1939 0.1958 0.2026 0.2234 0.2441 0.2783 0.3023 0.3393
0.2987 0.2059 0.2158 0.2380 0.2471 0.2930 0.3189 0.3551
0.3999 0.2253 0.2382 0.2506 0.2624 0.3058 0.3448 0.3801
0.5010 0.2567 0.2729 0.2979 0.3223 0.3634 0.4033 0.4385
0.5923 0.2711 0.2902 0.3165 0.3420 0.3809 0.4213 0.4810
0.7023 0.2167 0.2516 0.2856 0.3251 0.3677 0.4412 0.5217
0.7990 0.2075 0.2327 0.2666 0.3092 0.3429 0.4241 0.4983
0.9010 0.1632 0.2084 0.2491 0.2785 0.2863 0.3348 0.4090
Measurements of the viscosities were carried out in the same
water bath using an Ubbelohde capillary viscometer. The
capillary was calibrated for kinetic energy correction with
double-distilled water at the experimental temperature range
η
F
ν ) ) k1t - k2 ⁄ t
(1)
synthesized by metathesis reactions from [BMIM][Br] and
NaCF3SO3 in water. NaBr precipitate was removed by filtration,
and the remaining water was removed by rotary evaporation.
The crude product was dissolved in dichloromethane, and the
solution was washed with a small amount of cooled deionized
water five times until the aqueous solution did not form any
precipitate with AgNO3 solution. The solvent dichloromethane
was removed by rotary evaporation, and the [BMIM][CF3SO3]
was dried under high vacuum at 343 K for 8 h to remove volatile
impurities. Water mass fractions analyzed by Karl Fischer
where t is the flow time; k1 is the Ubbelhode capillary
microviscometer constant; and k2 is the Hagenbach correction.
The kinematic viscosity ν for calibration was obtained from
literature values of the absolute viscosity and density.16 An
electronic digital stopwatch with a readability of ( 0.01 s was
used for flow-time measurement. Experiments were repeated
at least four times at each temperature for all mixtures, and the
results were averaged. The uncertainty of viscosity measure-
ments depends on equilibrium temperature, flow time, mole
fraction, and calibration fluid.
From a propagation of error analysis, the experimental
average uncertainties of density and viscosity were estimated
to be ( 0.01. Accordingly, the deviations of VE and ∆η were
about ( 0.02.
1
analysis were less than 10-3. The chemical shifts for the H
NMR spectrum (parts per million, D2O) appear as follows: δ
8.626 [s, 1H, H(2)], 7.408 [s, 1H, H(4)], 7.360 [s, 1H, H(5)],
4.147 [t, 2H, NCH2], 3.826 [s, 3H, NCH3], 1.805 [m, 2H,
NCH2-CH2], 1.287 [m, 2H, NCH2CH2-CH2], and 0.879 [t,
3H, CH3]. The 13C NMR spectrum (parts per million, D2O)
contains peaks: 136.07 [C(2)], 123.81 [C(4)], 122.47 [C(5)],
118.67 [F3-C-SO3], 49.49 [N-CH2], 35.85 [NCH3], 31.60
[NCH2-CH2], 19.00 [NCH2CH2-CH2], and 12.79 [CH3].
Impurity peaks were not observed in the 1H NMR and 13C NMR
spectra. The purity of the ionic liquid was > 99 %. The change
Result and Discussion
The densities and viscosities of the [BMIM][CF3SO3] + H2O
mixture, as a function of water content over the temperature
range from (303.15 to 343.15) K, are presented in Tables 2 and

2410 Journal of Chemical & Engineering Data, Vol. 53, No. 10, 2008
Table 5. Viscosity Deviation ∆η for Binary Mixture of H2O (1) + [BMIM][CF3SO3] (2)
T/K
x1
303.15
308.15
313.15
318.15
323.15
333.15
343.15
∆η/mPa·s
-6.5649
-7.6789
-7.2974
-6.9704
-5.8513
-4.7886
-3.4277
-2.2101
-0.8665
0.1032
0.1939
0.2987
0.3999
0.5010
0.5923
0.7023
0.7990
0.9010
-11.055
-15.678
-15.584
-14.993
-12.746
-10.770
-7.8175
-5.1340
-2.4245
-9.2381
-12.568
-12.217
-11.380
-9.3686
-8.3141
-5.7750
-4.0409
-1.9007
-7.2166
-9.8881
-9.4376
-8.8587
-7.5642
-6.4846
-4.4912
-3.0644
-1.4131
-5.0524
-5.8211
-5.7166
-5.3366
-4.5989
-3.8587
-2.6078
-1.8091
-0.4158
-3.3579
-4.0031
-3.6816
-3.2754
-2.9175
-2.3863
-1.6262
-1.1008
-0.4636
-2.2836
-2.7329
-2.4669
-2.1714
-1.7596
-1.5291
-0.9162
-0.6747
-0.2675
Table 6. Coefficients of the Redlich-Kister Equation for VE and
∆η of H2O (1) + [BMIM][CF3SO3 ] (2) System
3. It can be readily observed that an increase in water content
or temperature causes density or viscosity to decrease. Therefore,
physical properties of ionic liquids can be adjusted to meet the
needs of applications for hydrophilic ionic liquids, e.g.,
[BMIM][CF3SO3], by adding water or changing temperature.
The excess molar volumes VE and the viscosity deviations
∆η were calculated from the measurements according to the
following equations17,18
property
T/K
A0
A1
A2
A3
σ
VE/cm3 ·mol-1 303.15
0.977 0.128
1.036 0.179
1.120 0.205
1.196 0.398
1.368 0.452
1.528 0.667
1.691 0.908
0.981 -0.250 0.020
308.15
313.15
318.15
323.15
333.15
343.15
1.218
1.470
1.778
0.048 0.022
0.323 0.024
0.129 0.024
1.819 -0.050 0.021
2.326 -0.105 0.017
2.958 -0.124 0.020
x1M1 + x2M2 x1M1 x2M2
V E )
-
-
(2)
(3)
∆η/mPa·s
303.15 -51.230 44.038 -36.244 25.340 0.264
308.15 -38.325 34.162 -35.954 26.153 0.230
313.15 -30.102 25.782 -26.698 23.424 0.202
318.15 -22.802 18.493 -25.024 31.519 0.226
323.15 -18.055 13.509 -16.639 25.881 0.174
333.15 -11.113 9.352 -13.725 16.246 0.106
343.15 -6.984 7.190 -10.095 10.243 0.077
F
F1
F2
∆η ) η - (x1η1 + x2η2)
where F and η are density and viscosity of mixtures; x1 and x2
are mole fractions; M1 and M2 are molar masses; F1 and F2 are
densities; and η1 and η2 are the viscosities of H2O (1) and ionic
liquid [BMIM][CF3SO3] (2), respectively.
All values of VE and ∆η for the mixtures of H2O (1) +
[BMIM][CF3SO3] (2) were fitted to the Redlich-Kister poly-
nominal equation19-21
The data of excess molar volume and viscosity deviation are
given in Tables 4 and 5. The excess molar volumes VE and the
viscosity deviations ∆η versus the mole fraction of water are,
respectively, shown in Figures 1 and 2. Table 6 lists the values
of the parameters Ai together with the standard deviations.
The excess thermodynamic properties, which depend on the
composition and/or temperature, are of great importance in
understanding the nature of molecular aggregation that exists
in the binary mixtures. As shown in Figure 1, the values of
excess molar volume were positive for H2O + [BMIM]-
[CF3SO3] mixtures at all temperatures and over the entire range
of compositions. The excess molar volumes VE increase slightly
with the increase of temperature from (303.15 to 343.15) K.
The dependence of the viscosity deviations ∆η on mole
fraction x1 is presented in Figure 2. The values of viscosity
deviations were negative over the whole range of compositions,
and the minimum existed at x1 ) 0.2 within the whole region
of experimental temperatures. Simultaneously, viscosity devia-
tions increased slightly from (303.15 to 343.15) K.
m
Y ) x (1 - x ) A (2x - 1)i
(4)
∑
1
1
i
1
i)0
where Y ) VE or ∆η; Ai are adjustable parameters; and x1 is
the mole fraction of water (1). The optimum number of
coefficients Ai was determined from an examination of variation
of standard derivation
1
2
σ(Y) )
(Ycalcd - Yexptl)2 ⁄ (n - m)
(5)
[∑
]
n is the number of experimental data, and m is the number of
coefficients of the Redlich-Kister equation.
Conclusions
The densities and viscosities for the binary mixtures of H2O
+ [BMIM][CF3SO3] over the whole range of compositions were
measured as a function of the temperature at atmospheric
pressure. The changes in viscosity and the excess molar volume
have been adequately fitted to the Redlich-Kister polynomial
equation. Estimated coefficients and standard error values are
also presented. The results show that water content has stronger
effects on the physical properties and excess thermodynamic
properties of ILs for the binary system of H2O + [BMIM]-
[CF3SO3]. The volumetric and transport properties of the
hydrophilic ILs can be significantly varied by adding water or
changing temperature to meet the needs of industrial require-
ment. Furthermore, the present results add useful data on
imidazolium-based ILs to the growing database on ionic liquid
Figure 2. Viscosity deviation ∆η vs molar fraction of water for H2O (1) +
[BMIM][CF3SO3] (2). 9, 303.15 K; b, 308.15 K; 2, 313.15 K; 1, 318.15
K; [, 323.15 K; 0, 333.15 K; ∆, 343.15 K. The symbols represent
experimental values, and the solid curves are calculated with the
Redlich-Kister equation.

Journal of Chemical & Engineering Data, Vol. 53, No. 10, 2008 2411
(12) Gardas, R. L.; Freire, M. G.; Carvalho, P. J.; Marrucho, I. M.; et al.
High-pressure densities and derived thermodynamic properties of
imidazolium-based ionic liquids. J. Chem. Eng. Data 2007, 52, 80–
88.
properties, a database which is essential for the many applica-
tions of these liquids currently under exploration.
(13) Ge, M.-L.; Wang, L.-S.; Li, M.-Y.; Wu, J.-S. Activity coefficients at
infinite dilution of alkanes, alkenes, and alkyl benzenes in 1-butyl-3-
methylimidazolium trifluoromethanesulfonate using gas-liquid chro-
matography. J. Chem. Eng. Data 2007, 52, 2257–2260.
(14) Ge, M.-L.; Wang, L.-S. Activity coefficients at infinite dilution of polar
solutes in 1-butyl-3-methylimidazolium trifluoromethanesulfonate us-
ing gas-liquid chromatography. J. Chem. Eng. Data 2008, 53, 846–
849.
(15) Wieser, M. E. Atomic weights of the elements 2005. Pure Appl. Chem.
2006, 78, 2051–2066.
(16) Speight, J. G. Lange’s Handbook of Chemistry, 16th ed.; McGraw-
Hill: New York, 2005.
(17) Tejraj, M. A. Thermodynamic interactions in binary mixture of
ethyenylbenzene with methanol, ethanol, butan-1-ol in the temperature
range 298.15-308.15 K. J. Chem. Eng. Data 1999, 44, 1291–1297.
(18) Weng, W. L. Densities and viscosities for binary mixtures of
butylamine with aliphatic alcohols. J. Chem. Eng. Data 2000, 45, 606–
609.
(19) Zhou, Q.; Wang, L.-S.; Chen, H.-P. Densities and viscosities of 1-butyl-
3-methylimidazolium tetrafluoroborate + H2O binary mixtures from
(303.15 to 353.15) K. J. Chem. Eng. Data 2006, 51, 905–908.
(20) Zhang, S.-J.; Li, X.; Chen, H.-P.; Wang, J.-F.; Zhang, J.-M.; Zhang,
M.-L. Determination of physical properties for the binary system of
1-ethyl-3-methylimidazolium tetrafluoroborate + H2O. J. Chem. Eng.
Data 2004, 49, 760–764.
Literature Cited
(1) Heintz, A. Recent developments in thermodynamics and thermophysics
of non-aqueous mixtures containing ionic liquids. A review. J. Chem.
Thermodyn. 2005, 37, 525–535.
(2) Huddleston, J. G.; Visser, A. E.; Reichert, W. M.; Willauer, H. D.;
Broker, G. A.; Rogers, R. D. Characterization and comparison of
hydrophilic and hydrophobic room-temperature ionic liquids incor-
porating the imidazolium cation. Green Chem. 2001, 3, 156–164.
(3) Seddon, K. R.; Stark, A.; Torres, M. J. Influence of chloride, water
and organic solvents on the physical properties of ionic liquids. Pure
Appl. Chem. 2000, 72, 2275–2287.
(4) Carmichael, A. J.; Seddon, K. R. Polarity study of some 1-alkyl-3-
methylimidazolium ambient-temperature ionic liquids with the sol-
vatochromic dye, Nile Red. J. Phys. Org. Chem. 2000, 13, 591–595.
(5) Law, G.; Watson, P. R. Surface orientation in ionic liquids. Chem.
Phys. Lett. 2001, 345, 1–4.
(6) Marsh, K. N.; Boxall, J. A.; Lichtenthaler, R. Room temperature ionic
liquids and their mixturessa review. Fluid Phase Equilib. 2004, 219,
93–98.
(7) Bonhote, P.; Dias, A. P.; Papageorgiou, N.; Kalyanasundaram, K.;
Gratzel, M. Hydrophobic, highly conductive ambient-temperature
molten salts. Inorg. Chem. 1996, 35, 1168–1178.
(8) Fredlake, C. P.; Crosthwaite, J. M.; Hert, D. G.; Aki, S. N. V. K.;
Brennecke, J. F. Thermophysical properties of imidazolium-based ionic
liquids. J. Chem. Eng. Data 2004, 49, 954–964.
(9) Arce, A.; Rodr´ıguez, O.; Soto, A. tert-Amyl ethyl ether separation
from its mixtures with ethanol using the 1-butyl-3-methylimidazolium
trifluoromethanesulfonate ionic liquid: liquid-liquid equilibrium. Ind.
Eng. Chem. Res. 2004, 43, 8323–8327.
(10) Seddon, K. R.; Stark, A.; Torres, M.-J. Viscosity and density of 1-alkyl-
3-methylimidazolium ionic liquids. Am. Chem. Soc. Symp. Ser. 2002,
819, 34–49.
(21) Nath, J.; Pandey, J. G. Excess molar volumes of heptan-ol + heptane,
+ hexane, + octane, and + 2,2,4-trimethylpentane at 293.15 K.
J. Chem. Eng. Data 1997, 42, 1137–1139.
Received for review May 28, 2008. Accepted August 11, 2008. We
thank Beijing Municipal Organization Department Foundation for
Excellent Talents through project 20081D0500500140 and Beijing
Municipal Natural Science Foundation for the financial support through
Project 2052010.
(11) Tokuda, H.; Hayamizu, K.; Ishii, K.; et al. Physicochemical properties
and structures of room temperature ionic liquids. 1. Variation of anionic
species. J. Phys. Chem. B 2004, 108, 16593–16600.
JE8003832