Crystal structure and solid-state ionic conductivity of cyclic sulfonylamide salts with cyano-substituted quaternary ammonium cations

Article abstract of DOI:10.1246/cl.130874

Novel organic ionic plastic crystals containing cyclic perfluorosulfonylamide anions were synthesized by anion metathesis between a cyano-functionalized quaternary ammonium halide and Li[N(SO2CF2)2CF2] (LiCPFSA). The structure of [N(CH3)2(CH2CN)2][CPFSA] was disclosed by single-crystal X-ray diffraction study. This is the first report on the crystal structure of cyclic perfluorosulfonylamide anion.

Full text of DOI:10.1246/cl.130874

CL-130874
Received: September 21, 2013 | Accepted: October 7, 2013 | Web Released: October 16, 2013
Crystal Structure and Solid-state Ionic Conductivity of Cyclic Sulfonylamide Salts
with Cyano-substituted Quaternary Ammonium Cations
Makoto Moriya,*1 Takaaki Watanabe, Shohei Nabeno, Wataru Sakamoto, and Toshinobu Yogo*
,2
1
1
1
1
1
EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603
2
JST PRESTO, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012
(
E-mail: moriya@esi.nagoya-u.ac.jp, yogo@esi.nagoya-u.ac.jp)
Novel organic ionic plastic crystals containing cyclic
perfluorosulfonylamide anions were synthesized by anion
metathesis between a cyano-functionalized quaternary ammo-
nium halide and Li[N(SO2CF2)2CF2] (LiCPFSA). The structure
of [N(CH3)2(CH2CN)2][CPFSA] was disclosed by single-crystal
X-ray diffraction study. This is the first report on the crystal
structure of cyclic perfluorosulfonylamide anion.
O
O
S O
R
N
N
O
S
H3C
CH2CN
F2C
CF2
CH3
C
F2
Figure 1. Molecular structure of the obtained compounds (1;
R = CH3, 2; R = CH2CH3, 3; R = CH2CN).
been obtained. On the other hand, the crystal structure of the
CPFSA anion is crucial for understanding the physical proper-
ties of CPFSA-based OIPCs. Therefore, we attempted to prepare
and crystallize CPFSA salts with several organic cations to
reveal the structure of the CPFSA anion. In this paper, we
describe the synthesis of novel CPFSA salts, [N(CH3)2-
(CH2CN)R][CPFSA] (1; R = CH3, 2; R = CH2CH3, 3;
R = CH2CN), and the crystal structure of 3 (Figure 1). We also
evaluated the ability of 1 and 2 as a matrix material of solid
electrolytes.
The combination of organic cations and anions using ionic
liquids (ILs) and organic ionic plastic crystals (OIPCs) has
attracted considerable attention as a new strategy to fabricate
matrix materials as electrolytes of next-generation batteries
because of their thermal and electrochemical stability. In
particular, the use of OIPCs as a matrix for solid electrolytes has
been actively studied to fabricate all-solid batteries. However,
most of the reported OIPCs exhibit melting points of around
1
,2
1
00 °C, which is insufficient to support the safe operation of
3
batteries. Furthermore, addition of lithium salts toward OIPCs,
which is generally performed to generate lithium ion conduc-
tivity, often lowers the melting point of the solid electrolytes as
Introduction of cyano groups has been actively studied to
6
­9
generate specific functions of ILs and OIPCs,
such as IL
applications to improve charge­discharge properties of recharge-
4
6
compared to that of the pure OIPC matrix. Hence, OIPCs with
able batteries. Cyano groups are also utilized to increase the
high melting points are strongly required.
coordination and solubilizing ability of ILs for their application
in the extraction of precious metals and in catalytic reactions.
7
,8
For the fabrication of OIPCs for solid electrolytes, bis(tri-
fluoromethanesulfonyl)amide, N(SO2CF3)2 (TFSA), is widely
used as a counter anion. The TFSA anion is selected owing to
its high ionicity, which results from the electron-withdrawing
character of the perfluorosulfonylamide group. However, TFSA-
based OIPCs often have a low melting point. The linear structure
of the TFSA anion and the consequent conformational versatility
of the molecule might be the reason for the low melting point of
TFSA-based OIPCs.
In an attempt to expand the operational temperature range of
OIPCs, we recently selected the cyclic perfluorosulfonylamide
anion instead of TFSA as an anion constituent. Based on this
idea, we reported the synthesis of OIPCs, using perfluorosulfon-
ylamide anion with six-membered cyclic structure,
N(SO2CF2)2CF2 (CPFSA), focusing on the restricted structural
flexibility of this anion because of its cyclic structure in order
to increase the melting point of OIPCs. We successfully
synthesized a class of novel OIPCs, [N(CH3)n(CH2CH3)4¹n]-
Considering these studies, we fabricated CPFSA salts 1­3
containing cyano-functionalized ammonium cations by anion
metathesis between the substituted quaternary ammonium halide
1
0
and LiCPFSA. By the use of CPFSA anion, 1­3 were obtained
as white powders at room temperature, whereas the TFSA-based
analogs, [N(CH ) (CH CN)][TFSA] and [N(CH ) (CH CH )-
3
3
2
3 2
2
3
6
b,6c
(CH2CN)][TFSA], are reported to be ILs.
To understand the structural details of these compounds, we
performed a single-crystal X-ray crystallographic study of 3.
1
1
Although we could not obtain single crystals of 1 and 2 suitable
for X-ray crystallography, powder X-ray diffraction patterns of 1
and 2 measured at room temperature showed sharp reflections,
suggesting that these compounds possess long-range-ordered
5
1
2
structures in the solid state.
The crystal structure of 3 is shown in Figure 2. The unit cell
of 3 consisted of eight ionic combinations of N(CH3)2(CH2CN)2
cations and CPFSA anions. The six-membered ring of the
CPFSA anion of 3 was in the chair conformation. The N­S,
S­C, and C­C bond lengths were estimated to be approximately
1.58, 1.84, and 1.54 ¡, respectively. The S­N­S, N­S­C, S­C­C,
and C­C­C bond angles within the ring structure were
calculated to be 119.9, 101.5, 113.3, and 115.6°, respectively.
To the best of our knowledge, this is the first report on the crystal
[
N(SO2CF2)2CF2] (N1222CPFSA; n = 1, N1122CPFSA; n = 2,
N1112CPFSA; n = 3).5 These OIPCs show plastic crystalline
behavior and solid-state ionic conductivity over a wide temper-
ature range, from approximately ¹30 to 250 °C.
The use of the CPFSA anion expands the operational
temperature range of the OIPCs as plastic crystalline materials.
However, the crystal structure of the CPFSA anion has not been
reported yet, since single crystals of [N(CH ) (CH CH ) ]-
1
2
structure of CPFSA anions.
All cyano groups of the cation moiety were located in the ac
plane (Figure 3). In this molecular arrangement, short intermo-
3
n
2
3 4¹n
[N(SO2CF2)2CF2] suitable for X-ray structural analysis have not
108 | Chem. Lett. 2014, 43, 108–110 | doi:10.1246/cl.130874
© 2014 The Chemical Society of Japan

Figure 2. Crystal structure of CPFSA salt 3. (a) N(CH3)2-
CH2CN)2 moiety, (b) CPFSA moiety (C: gray, N: blue, O: red,
(
F: green, S: dark yellow. Thermal ellipsoid corresponds to 40%
probability. Hydrogen atoms are omitted for clarity.).
Figure 4. Intermolecular interactions in the crystal structure of
(dashed lines). (a) cation­cation interactions, (b) cation­anion
3
interactions (C: gray, N: blue, O: red, F: green, S: dark yellow.
Thermal ellipsoid corresponds to 40% probability. Hydrogen
atoms are omitted for clarity.).
Figure 3. Packing view of 3 along b axis (C: gray, N: blue, O:
red, F: green, S: dark yellow. Thermal ellipsoid corresponds to
40% probability. Hydrogen atoms are omitted for clarity.).
lecular C­N distances were observed between the nitrogen atom
of the cyano group and the methyl carbon attached to the
nitrogen of the ammonium ion. The N3­C1, N3­C2, N4­C1,
and N4­C2 distances were estimated to be 3.443, 3.496, 3.335,
and 3.569 ¡, respectively (Figure 4a and Supporting Informa-
Figure 5. DSC curves of 1­3.
crystals under thermal conditions. The melting peak of 3 at
250 °C is broad, whereas those of 1 and 2 are relatively sharp.
Similar broadenings of melting peak are reported for several
12
tion ). These distances suggested the formation of multiple
hydrogen bonds among N(CH ) (CH CN) units. The presence
4
b,4d,14
OIPC systems.
The broadening of the peak might result
3
2
2
2
of hydrogen bonds between cations and anions (C­H£O­S) was
also suggested for C3­O4, C5­O2, and C5­O4, with calculated
distances of 3.293, 3.125, and 3.158 ¡, respectively (Figure 4b).
The electron-withdrawing character of the cyano groups and the
cationic nitrogen centers of the N(CH3)2(CH2CN)2 units in 3
enhance the acidity of the methyl or methylene protons,
inducing the formation of three-dimensional hydrogen bonds.
The electron-withdrawing character of the cyano groups might
also be responsible for the close contact between the C­H
moiety neighboring the cyano groups and the S=O moiety of
sulfonyl amides. In fact, similar anion­cation and cation­cation
interactions were observed for the structure of crystallized ILs
with cyano-functionalized pyridinium, pyrrolidium, and piper-
idinium cations and TFSA anions.9
from the formation of crystal defect and the fluctuation of the
local crystallite packing and volume change during PC­liquid
transition. The results of X-ray crystallography and thermal
analysis indicate the role of the anion as a static element to
maintain the crystal lattice and that of the cation as a dynamic
unit to generate plastic crystalline properties.
The heating of compounds 1­3 resulted in not only melting
but also a color change (from white to dark brown) above
1
2
140 °C. Such a phenomenon was not observed during the
5
heating of [N(CH ) (CH CH ) ][N(SO CF ) CF ]. This sug-
3
n
2
3 4¹n
2
2 2
2
gests that decomposition or transformation of the cyano-
functionalized moiety in 1­3 occurs before melting. Detailed
studies of the thermal behavior of 1­3 around the melting
temperatures are currently underway.
The phase transitions of 1­3 were measured by differential
scanning calorimetry (DSC) from ¹100 to 300 °C (Figure 5).
Melting points of 1­3 were observed at 216.7, 156.4, and
The ionic conductivities of 1 and 2 as a function of
temperature between 60 and 120 °C are displayed in Figure 6,
1
2
and these values are compared with those previously reported
for OIPCs containing CPFSA anions, [N(CH3)n(CH2CH3)4¹n]-
2
50.7 °C, respectively. The entropies of fusion for 1, 2, and 3
¹
1
¹1
5
were calculated to be 19.0, 10.1, and 20.4 J mol
K
, respec-
[CPFSA] (n = 1, 2, or 3). The ionic conductivities of 1 and 2
tively. The entropy values of these compounds almost satisfied
were observed above 60 °C, around their solid­solid phase-
transition temperatures. The ionic conductivity of 1 is similar
to that of N1112CPFSA. Both 1 and N1112CPFSA possess three
methyl groups at the nitrogen center of the ammonium moiety.
The similarity in the ionic conductivity and structure between 1
13
Timmermans’ criterion for molecular plastic crystals (¦Sf <
¹
1
¹1
2
0 J K mol ). Furthermore, these compounds gave endother-
mic peaks attributable to solid­solid phase transition in the DSC
curves. These results strongly support that 1­3 behave as plastic
Chem. Lett. 2014, 43, 108–110 | doi:10.1246/cl.130874
© 2014 The Chemical Society of Japan | 109

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© 2014 The Chemical Society of Japan