The stabilization energies for the formation (Eform) of 11 ion pairs of protic and aprotic ionic liquids were studied by MP2/6-311G** level ab initio calculations to elucidate the difference between the interactions of ions in protic ionic liquids and those in aprotic ionic liquids. The interactions in the ion pairs of protic ionic liquids (diethylmethylammonium [dema] and dimethylpropylammonium [dmpa] based ionic liquids) are stronger than those of aprotic ionic liquids (ethyltrimethylammonium [etma] based ionic liquids). The Eform for the [dema][CF3SO3] and [dmpa][CF3SO3] complexes (−95.6 and −96.4 kcal/mol, respectively) are significantly larger (more negative) than that for the [etma][CF3SO3] complex (−81.0 kcal/mol). The same trend was observed for the calculations of ion pairs of the three cations with the Cl, BF4, TFSA anions. The anion has contact with the N–H bond of the dema+ or dmpa+ cations in the most stable geometries of the dema+ and dmpa+ complexes. The optimized geometries, in which the anions locate on the counter side of the cations, are 11.0–18.0 kcal/mol less stable, which shows that the interactions in the ions pairs of protic ionic liquids have strong directionality. The Eform for the less stable geometries for the dema+ and dmpa+ complexes are close to those for the most stable etma+ complexes. The electrostatic interaction, which is the major source of the attraction in the ion pairs, is responsible for the directionality of the interactions and determining the magnitude of the interaction energy. Molecular dynamic simulations of the [dema][TFSA] and [dmpa][TFSA] ionic liquids show that the N–H bonds of the cations have contact with the negatively charged (oxygen and nitrogen) atoms of TFSA anion, while the strong directionality of the interactions was not suggested from the simulation of the [etma][CF3SO3] ionic liquid.

1.
T.
Welton
,
Chem. Rev.
99
,
2071
2083
(
1999
).
2.
S. G.
Cull
,
J. D.
Holbrey
,
V.
Vargas-Mora
,
K. R.
Seddon
, and
G. J.
Lye
,
Biotech. Bioeng.
69
,
227
233
(
2000
).
3.
P.
Wasserscheid
and
W.
Keim
,
Angew. Chem., Int. Ed.
39
,
3772
3789
(
2000
).
4.
K.
Xu
,
Chem. Rev.
104
,
4303
4417
(
2004
).
5.
H. L.
Chum
,
V. R.
Koch
,
L. L.
Miller
, and
R. A.
Oesteryoung
,
J. Am. Chem. Soc.
97
,
3264
3265
(
1975
).
6.
J. S.
Wilkes
,
J. A.
Levisky
,
R. A.
Wilson
, and
C. L.
Hussey
,
Inorg. Chem.
21
,
1263
1264
(
1982
).
7.
D. M.
Ryan
,
T. L.
Reichel
, and
T.
Welton
,
J. Electrochem. Soc.
149
,
A371
A378
(
2002
).
8.
C.
Lagrost
,
D.
Carrie
,
M.
Vaultier
, and
P.
Hapiot
,
J. Phys. Chem. A
107
,
745
752
(
2003
).
9.
H.
Tokuda
,
S.
Tsuzuki
,
M. A. B. H.
Susan
,
K.
Hayamizu
, and
M.
Watanabe
,
J. Phys. Chem. B
110
,
19593
19600
(
2006
).
10.
T.
Takahashi
,
S.
Tanase
,
O.
Yamamoto
, and
S.
Yamauchi
,
J. Solid State Chem.
17
,
353
361
(
1976
).
11.
M.
Hirao
,
H.
Sugimoto
, and
H.
Ohno
,
J. Electrochem. Soc.
147
,
4168
4172
(
2000
).
12.
W.
Wieczorek
,
G.
Zukowska
,
R.
Borkowska
,
S. H.
Chung
, and
S. A.
Greenbaum
,
Electrochem. Acta
46
,
1427
1438
(
2001
).
13.
W.
Xu
and
C. A.
Angell
,
Science
302
,
422
425
(
2003
).
14.
C. A.
Angell
,
N.
Byrne
, and
J.-P.
Belieres
,
Acc. Chem. Res.
40
,
1228
1236
(
2007
).
15.
T. L.
Greaves
and
C. J.
Drummond
,
Chem. Rev.
108
,
206
237
(
2008
).
16.
A.
Noda
,
M. A. B. H.
Susan
,
K.
Kudo
,
S.
Mitsushima
,
K.
Hayamizu
, and
M.
Watanabe
,
J. Phys. Chem. B
107
,
4024
4033
(
2003
).
17.
M. A. B. H.
Susan
,
A.
Noda
,
S.
Mitsushima
, and
M.
Watanabe
,
Chem. Commun.
2003
,
938
939
.
18.
H.
Nakamoto
and
M.
Watanabe
,
Chem. Commun.
2007
,
2539
2541
.
19.
H.
Nakamoto
,
A.
Noda
,
K.
Hayamizu
,
S.
Hayashi
,
H.
Hamaguchi
, and
M.
Watanabe
,
J. Phys. Chem. C
111
,
1541
1548
(
2007
).
20.
S.-Y.
Lee
,
A.
Ogawa
,
M.
Kanno
,
H.
Nakamoto
,
T.
Yasuda
, and
M.
Watanabe
,
J. Am. Chem. Soc.
132
,
9764
9773
(
2010
).
21.
T.
Yasuda
,
A.
Ogawa
,
M.
Kanno
,
K.
Mori
,
K.
Sakakibara
, and
M.
Watanabe
,
Chem. Lett.
38
,
692
693
(
2009
).
22.
H.
Sakaebe
and
H.
Matsumoto
,
Electrochem. Commun.
5
,
594
598
(
2003
).
23.
H.
Sakaebe
,
H.
Matsumoto
, and
K.
Tatsumi
,
J. Power Sources
146
,
693
697
(
2005
).
24.
A.
Lewandowski
and
A.
Swiderska-Mocek
,
J. Power Sources
194
,
601
609
(
2009
).
25.
S.
Tsuzuki
,
H.
Tokuda
,
K.
Hayamizu
, and
M.
Watanabe
,
J. Phys. Chem. B
109
,
16474
16481
(
2005
).
26.
S.
Tsuzuki
,
W.
Shinoda
,
H.
Saito
,
M.
Mikami
,
H.
Tokuda
, and
M.
Watanabe
,
J. Phys. Chem. B
113
,
10641
10649
(
2009
).
27.
S.
Tsuzuki
,
K.
Hayamizu
, and
S.
Seki
,
J. Phys. Chem. B
114
,
16329
16336
(
2010
).
28.
S.
Tsuzuki
,
ChemPhysChem
13
,
1664
1670
(
2012
).
29.
V.
Chaban
,
Phys. Chem. Chem. Phys.
13
,
16055
16062
(
2011
).
30.
S.
Tsuzuki
,
H.
Matsumoto
,
W.
Shinoda
, and
M.
Mikami
,
Phys. Chem. Chem. Phys.
13
,
5987
5993
(
2011
).
31.
K.
Fumino
and
A.
Wulf
,
Angew. Chem., Int. Ed.
48
,
3184
3186
(
2009
).
32.
K.
Fumino
,
V.
Fossog
,
K.
Wittler
,
R.
Hempelmann
, and
R.
Ludwig
,
Angew. Chem., Int. Ed.
52
,
2368
2372
(
2013
).
33.
A.
Bagno
,
C.
Butts
,
C.
Chiappe
,
F.
D’amico
,
J. C. D.
Lord
,
D.
Pieraccini
, and
F.
Rastrelli
,
Org. Biomol. Chem.
3
,
1624
1630
(
2005
).
34.
D. R.
MacFarlane
,
J. M.
Pringle
,
K. M.
Johansson
,
S. A.
Forsyth
, and
M.
Forsyth
,
Chem. Commun.
2006
,
1905
1917
.
35.
B.
Nuthakki
,
T. L.
Greaves
,
I.
Krodkiewska
,
A.
Weerawardena
,
M. I.
Burgar
,
R. J.
Mulder
, and
C. J.
Drummond
,
Aust. J. Chem.
60
,
21
28
(
2007
).
36.
K.
Ueno
,
Z.
Zhao
,
M.
Watanabe
, and
C. A.
Angell
,
J. Phys. Chem. B
116
,
63
70
(
2012
).
37.
M.
Yoshizawa
,
W.
Xu
, and
C. A.
Angell
,
J. Am. Chem. Soc.
125
,
15411
15419
(
2003
).
38.
J. A.
Widegren
,
A.
Laesecke
, and
J. W.
Magee
,
Chem. Commun.
2005
,
1610
1612
.
39.
T. L.
Greaves
,
A.
Weerawardena
,
C.
Fong
,
I.
Krodkiewska
, and
C.
Drummond
,
J. Phys. Chem. B
110
,
22479
22487
(
2006
).
40.
M. S.
Miran
,
H.
Kinoshita
,
T.
Yasuda
,
M. A. B. H.
Susan
, and
M.
Watanabe
,
Phys. Chem. Chem. Phys.
14
,
5178
5186
(
2012
).
41.
H.
Ohno
and
M.
Yoshizawa
,
Solid State Ionics
154–155
,
303
309
(
2002
).
42.
Z. Y.
Du
,
Z. P.
Li
,
S.
Guo
,
J.
Zhang
,
L. Y.
Zhu
, and
Y. Q.
Deng
,
J. Phys. Chem. B
109
,
19542
19546
(
2005
).
43.
M.
Halder
,
L. S.
Headley
,
P.
Mukherjee
,
X.
Song
, and
J. W.
Petrich
,
J. Phys. Chem. A
110
,
8623
8626
(
2006
).
44.
W.
Ogihara
,
T.
Aoyama
, and
H.
Ohno
,
Chem. Lett.
33
,
1414
1415
(
2004
).
45.
T. H.
Dunning
 Jr.
,
J. Phys. Chem. A
104
,
9062
9080
(
2000
).
46.
S.
Tsuzuki
,
T.
Uchimaru
,
K.
Matsumura
,
M.
Mikami
, and
K.
Tanabe
,
J. Chem. Phys.
110
,
11906
11910
(
1999
).
47.
E. R.
Talaty
,
S.
Raja
,
V. J.
Storhaug
,
A.
Dolle
, and
W. R.
Carper
,
J. Phys. Chem. B
108
,
13177
13184
(
2004
).
48.
P. A.
Hunt
and
I. R.
Gould
,
J. Phys. Chem. A
110
,
2269
2282
(
2006
).
49.
T. I.
Marrow
and
E. J.
Maginn
,
J. Phys. Chem. B
106
,
12807
12813
(
2002
).
50.
E. A.
Turner
,
C. C.
Pye
, and
R. D.
Singer
,
J. Phys. Chem. A
107
,
2277
2288
(
2003
).
51.
H.
Markusson
,
J.-P.
Belieres
,
P.
Johansson
, and
C. A.
Angell
,
J. Phys. Chem. A
111
,
8717
8723
(
2007
).
52.
K.
Fumino
,
A.
Wulf
, and
R.
Ludwig
,
Phys. Chem. Chem. Phys.
11
,
8790
8794
(
2009
).
53.
E.
Bodo
,
S.
Mangialardo
,
F.
Ramondo
,
F.
Ceccacci
, and
P.
Postorino
,
J. Phys. Chem. B
116
,
13878
13888
(
2012
).
54.
R. W.
Berg
,
J. N. C.
Lopes
,
R.
Ferreira
,
L. P. N.
Rebelo
,
K. R.
Seddon
, and
A. A.
Tomaszowska
,
J. Phys. Chem. A
114
,
10834
10841
(
2010
).
55.
K.
Mori
,
T.
Kobayashi
,
K.
Sakakibara
, and
K.
Ueda
,
Chem. Phys. Lett.
552
,
58
63
(
2012
).
56.
S.
Zahn
,
J.
Thar
, and
B.
Kirchner
,
J. Chem. Phys.
132
,
124506
(
2010
).
57.
S.
Zahn
,
K.
Wandler
,
L.
Delle Site
, and
B.
Kirchner
,
Phys. Chem. Chem. Phys.
13
,
15083
15093
(
2011
).
58.
T. L.
Greaves
,
D. F.
Kennedy
,
S. T.
Mudie
, and
C. J.
Drummond
,
J. Phys. Chem. B
114
,
10022
10031
(
2010
).
59.
T. M.
Chang
,
L. X.
Dang
,
R.
Devanathan
, and
M.
Dupuis
,
J. Phys. Chem. A
114
,
12764
12774
(
2010
).
60.
R.
Hayes
,
S.
Imberti
,
G. G.
Warr
, and
R.
Atkin
,
Angew. Chem., Int. Ed.
51
,
7468
7471
(
2012
).
61.
M. J.
Frisch
,
G. W.
Trucks
,
H. B.
Schlegel
 et al, Gaussian 03, Revision E.01, Gaussian, Inc., Wallingford, CT,
2004
.
62.
The effects of electron correlation correction and the BSSE correction on the geometry optimization were evaluated. The BSSE corrected MP2/6-311G** level interaction energies for the three optimized geometries of the [dema][BF4] complex were compared. The interaction energy calculated for the BSSE uncorrected MP2/6-311G** level optimized geometry is −99.8 kcal/mol. The interaction energy calculated for the BSSE-corrected MP2/6-311G** level optimized geometry is −99.6 kcal/mol. These values are nearly identical to the interaction energy calculated for the BSSE-uncorrected HF/6-311G** level optimized geometry (−99.0 kcal/mol). These results show that the effects of electron correlation and BSSE correction in the geometry optimization on the calculated interaction energy are not large.
63.
C.
Møller
and
M. S.
Plesset
,
Phys. Rev.
46
,
618
622
(
1934
).
64.
M.
Head-Gordon
,
J. A.
Pople
, and
M. J.
Frisch
,
Chem. Phys. Lett.
153
,
503
506
(
1988
).
65.
B. J.
Ransil
,
J. Chem. Phys.
34
,
2109
(
1961
).
66.
S. F.
Boys
and
F.
Bernardi
,
Mol. Phys.
19
,
553
(
1970
).
67.
S.
Tsuzuki
,
K.
Hayamizu
,
S.
Seki
,
Y.
Ohno
,
Y.
Kobayashi
, and
H.
Miyashiro
,
J. Phys. Chem. B
112
,
9914
9920
(
2008
).
68.
A. J.
Stone
,
A.
Dullweber
,
M. P.
Hodges
,
P. L. A.
Popelier
, and
D. J.
Wales
, Orient: A program for studying interactions between molecules, version 3.2, University of Cambridge,
1995
.
69.
A. J.
Stone
and
M.
Alderton
,
Mol. Phys.
56
,
1047
(
1985
).
70.
A. J.
Stone
,
The Theory of Intermolecular Forces
(
Clarendon Press
,
Oxford
,
1996
).
71.
A. J.
Stone
,
J. Chem. Theory Comput.
1
,
1128
(
2005
).
72.
73.
P. T.
van Duijnen
and
M.
Swart
,
J. Phys. Chem. A
102
,
2399
(
1998
).
74.
See http://staff.aist.go.jp/w.shinoda/index.html for the web site for MPDyn.
75.
M. P.
Allen
and
D. J.
Tildesley
,
Computer Simulation of Liquids
(
Clarendon Press
,
Oxford
,
1987
).
76.
J. P.
Ryckaert
,
G.
Ciccotti
, and
H. J. C.
Berendsen
,
J. Comput. Phys.
23
,
327
341
(
1977
).
77.
M.
Tuckerman
and
B. J.
Berne
,
J. Chem. Phys.
97
,
1990
2001
(
1992
).
78.
G. J.
Martyna
,
M. E.
Tuckerman
,
D. J.
Tobias
, and
M. L.
Klein
,
Mol. Phys.
87
,
1117
1157
(
1996
).
79.
G. J.
Martyna
,
M. L.
Klein
, and
M.
Tuckerman
,
J. Chem. Phys.
97
,
2635
2643
(
1992
).
80.
H. C.
Andersen
,
J. Chem. Phys.
72
,
2384
2393
(
1980
).
81.
J. N. A. C.
Lopes
,
J.
Deschamps
, and
A. A. H.
Padua
,
J. Phys. Chem. B
108
,
2038
2047
(
2004
).
82.
J. N. A. C.
Lopes
and
A. A. H.
Padua
,
J. Phys. Chem. B
108
,
16893
16898
(
2004
).
83.
J. N. A. C.
Lopes
and
A. A. H.
Padua
,
J. Phys. Chem. B
110
,
19586
19592
(
2006
).
84.
J. N. A. C.
Lopes
,
A. A. H.
Padua
, and
K.
Shimizu
,
J. Phys. Chem. B
112
,
5039
5049
(
2008
).
85.
U. C.
Singh
and
P. A.
Kollman
,
J. Comput. Chem.
5
,
129
145
(
1984
).
86.
B. H.
Besler
,
K. M.
Merz
 Jr.
, and
P. A.
Kollman
,
J. Comput. Chem.
11
,
431
439
(
1990
).
87.
Recently Addicoat et al demonstrated the importance of taking into account conformational flexibility in ionic liquid clusters. We have started geometry optimizations of the complexes from large numbers of initial geometries for taking into account conformational flexibility (conformation of alkyl chains, position and orientation of cation and anion). We started the geometry optimizations of the [dmpa][Cl] complex from 25 initial geometries.
88.
M. A.
Addicoat
,
S.
Fukuoka
,
A. J.
Page
, and
S.
Irle
,
J. Comput. Chem.
34
,
2591
2600
(
2013
).
89.
Different hydrogen bonding structures (linear, bifurcated, trifurcated) are found for the complexes of primary alkyl ammonium cations.
90.
R.
Hayes
,
S.
Imberti
,
G. G.
Warr
, and
R.
Atkin
,
Angew. Chem., Int. Ed.
52
,
4623
4627
(
2013
).
91.
The directionality of the interaction of imidazolium cation with anion was reported (Ref. 25). The BF4 anion prefers to have contact with the C2-H of imidazolium. The local minimum structure, in which the BF4 anion has contact with the C4-H and C5-H is less stable.
92.
Fumino et al reported that the binding energy calculated for the 1-butyl-3-methylimidazolium nitrate by DFT method is larger than that of propylammonium nitrate (Ref. 52). Our calculations suggests that the interactions of tertiary alkyl ammonium cations with anions are stronger than the interactions of quaternary alkyl ammonium cations as in the case of the primary ammonium cation.
93.
See supplementary material at http://dx.doi.org/10.1063/1.4827519 for the details of the conditions of molecular dynamics simulations. Optimized geometries and stabilization energies (Eform) calculated for ion pairs. Site-site radial distribution functions of [dmpa][TFSA].

Supplementary Material

You do not currently have access to this content.