Crystal structure of zwitterionic bisimidazolium sulfonates

Article abstract of DOI:10.1016/j.molstruc.2012.02.021

Crystal structures of three zwitterionic bisimidazolium salts 1-3 in which imidazolium sulfonate moieties were connected with aromatic linkers, p-xylylene, 4,4′-dimethylenebiphenyl, and phenylene, respectively, were examined. The latter two were obtained

Full text of DOI:10.1016/j.molstruc.2012.02.021

Journal of Molecular Structure 1015 (2012) 6–11
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Crystal structure of zwitterionic bisimidazolium sulfonates
a
a
a
a
Shigeo Kohmoto a, , Shinpei Okuyama , Nobuyuki Yokota , Masahiro Takahashi , Keiki Kishikawa ,
⇑
Hyuma Masu b, Isao Azumaya c
a Department of Applied Chemistry and Biotechnology, Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
b Chemical Analysis Center, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
c Faculty of Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University, 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Crystal structures of three zwitterionic bisimidazolium salts 1–3 in which imidazolium sulfonate moie-
ties were connected with aromatic linkers, p-xylylene, 4,40-dimethylenebiphenyl, and phenylene, respec-
tively, were examined. The latter two were obtained as hydrates. An S-shaped molecular structure in
which the sulfonate moiety was placed on the imidazolium ring was observed for 1. A helical array of
hydrated water molecules was obtained for 2 while a linear array of hydrated water molecules was
observed for 3.
Received 5 December 2011
Received in revised form 7 February 2012
Accepted 7 February 2012
Available online 16 February 2012
Keywords:
Ó 2012 Elsevier B.V. All rights reserved.
Crystal structure
Zwitterionic salts
Hydrates
Hydrogen bonding
Imidazolium
1. Introduction
plates for the generation of zwitterionic water channels [44]. Two
units of imidazolium carboxylate are linked with an aromatic
In recent years, there has been a growing interest in the chem-
istry of imidazolium salts as ionic liquids [1–8] and ionic liquid
crystals [9–16]. Imidazolium-based ionic liquids are particularly
versatile and the most commonly used ionic liquids for extraction
and reaction media. Imidazolium salts are often utilized as ionic
liquid crystalline materials as well. Owing to the ionic nature of
imidazolium an efficient phase separation of it from lipophilic alkyl
chains can be expected, which stabilize the generated liquid
crystalline phases. They are investigated as potential ion-conduc-
tive materials [17–19]. Some X-ray crystallographic studies of
imidazolium-based ionic liquids [20–29] and ionic liquid crystal-
line materials [30–37] have been reported. However, the examples
of zwitterionic type imidazolium salts are very limited. To the best
of our knowledge, a few examples of the crystal structures of zwit-
terionic imidazolium carboxylates [38,39] and sulfonates [40–43]
were reported. Zwitterionic imidazolium carboxylates were
applied to the generation of water channels [39]. The synthetic
water channels generated by zwitterionic coordination polymer
with zinc were demonstrated to be mimicking to some extent aqu-
aporins, membrane water channels that play critical roles in con-
trolling the water contents of cells [39]. Recently, we have
developed zwitterionic bisimidazolium carboxylates as good tem-
spacer. Our idea is to clip water molecules by zwitterionic moieties
as ionic clips which are arranged at both ends of biszwitterionic
salts. Usage of aromatic spacers has an advantage to create a
hydrophobic wall by stacking of them to confine water molecules.
Fabrication of water channels in this manner is schematically illus-
trated in Fig. 1. Since much attention has been focused on water
clusters of organic and metal organic compounds to elucidate the
nature of bulk water [45–50] and to fabricate unique synthetic
water channels, such as helical arrays of water clusters [39,51–
53] and water nanotubes [54–56], it is desirable to seek efficient
templates for them.
In order to examine the efficacy of the counter anion part of
biszwitterionic imidazolium salts for the generation of zwitterionic
water channels, we replaced carboxylate to sulfonate and synthe-
sized zwitterionic bisimidazolium sulfonates. Some of them
included water molecules in their crystal lattice but they could
not generate zwitterionic water channels. Even though the present
bisimidazolium sulfonates are not appropriate for the generation
of water channels, their crystal structures are unique. It is also
worthwhile to investigate their crystal structures, since some zwit-
terionic imidazolium sulfonates have been known as potential
ionic liquids with high ion conductivity [57–61]. Herein, we report
on the crystal structures of zwitterionic bisimidazolium sulfonates
and their hydrogen-bonding network in cooperation with hydrated
water molecules.
⇑
Corresponding author. Tel.: +81 43 290 3420; fax: +81 43 290 3422.
E-mail address: kohmoto@faculty.chiba-u.jp (S. Kohmoto).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2012.02.021

S. Kohmoto et al. / Journal of Molecular Structure 1015 (2012) 6–11
7
2.2. Synthesis
2.2.1. Zwitterionic bisimidazolium sulfonate (1)
A mixture of 1,4-bis((1H-imidazol-1-yl)methyl)benzene (0.20 g,
0.84 mmol) and 1,3-propanesultone (0.31 g, 2.52 mmol) in aceto-
nitrile (20 mL) was refluxed for 12 h. The solvent was removed un-
der reduced pressure and the remaining solid was washed with
acetone and THF to give 1 (0.36 g) as a white powder in 95% yield.
Recrystallisation was carried out from water pervaded with ace-
tone vapor. Mp. > 270 °C (dec.); 1H NMR (300 MHz, D2O) d 2.25
(tt, J = 6.5 and 6.8 Hz, 4H), 2.83 (t, J = 6.8 Hz, 4H), 4.30 (t,
J = 6.5 Hz, 4H), 5.37 (s, 4H), 7.41(s, 4H), 7.44 (s, 2H), 7.51 (s, 2H),
8.81 (s, 2H); IR (KBr)
m 3139, 3092, 3063, 2976, 2941, 2872,
1456, 1230, 1188 cmꢁ1; HRMS (ESI) calcd for C20H26N4O6NaS2
[M + Na]+ 505.1186, found 505.1183.
2.2.2. Zwitterionic bisimidazolium sulfonate (2)
In a similar manner as for the synthesis of 1, bisimidazolium
sulfonate 2 was prepared in 98% yield from 4,40-bis((1H-imida-
zol-1-yl)methyl)biphenyl and 1,3-propanesultone as a tetrahy-
drate. Mp. > 270 °C (dec.) (H2O/acetone). 1H NMR (300 MHz, D2O)
d 2.21 (t, J = 7.1 Hz, 4H), 2.83 (t, J = 7.2 Hz, 4H), 4.29 (t, J = 7.2 Hz,
4H), 5.37 (s, 4H), 7.41 (s, 2H), 7.44 (s, 4H), 7.50 (s, 2H), 7.67 (s,
2H), 7.69 (s, 2H), 8.82 (s, 2H); IR (KBr)
m
;
3139, 3092, 3063, 2976,
HRMS (ESI) calcd for
Fig. 1. Schematic representation of the formation of zwitterionic water channels by
clipping of water molecules with zwitterionic bisimidazolium sates. In the case of
Xꢁ = carboxylate, see Ref. [42].
2941, 2872, 1456, 1230, 1188 cmꢁ1
C
26H30N4O6NaS2 [M + Na]+ 581.1499, found 581.1494.
2.2.3. Zwitterionic bisimidazolium sulfonate (3)
In a similar manner as for the synthesis of 1, bisimidazolium
sulfonate 3 was prepared in 87% yield from 1,4-di(1H-imidazol-
1-yl)benzene and 1,3-propanesultone as dihydrate. Mp. > 270 °C
(dec.) (H2O/acetone). 1H NMR (300 MHz, D2O) d 2.28 (quint,
J = 7.2 Hz, 2H), 2.87 (t, J = 7.2 Hz), 4.37 (t, J = 7.2 Hz, 2H), 7.66 (s,
2. Experimental
2.1. General
2H), 7.77 (s, 4H), 7.86 (s, 2H); IR (KBr)
1580, 1529, 1312, 1267, 1200, 1182 cmꢁ1; HRMS (ESI) calcd for
18H22O6N4NaS2 [M + Na]+ 477.0873, found 477.0863.
m 3450, 3139, 3073, 2949,
All the reagents and solvents employed were commercially
available and used as received without further purification. Single
crystal X-ray diffraction data of the crystals were collected on a
C
CCD diffractometer with graphite monochromated MoK
a
(k = 0.71073 Å) radiation. Data collections were carried out at low
temperature [100 K for 1 and 150 K for 2ꢀ4H2O and 3ꢀ2H2O] by
using liquid nitrogen. The crystal structure was solved by direct
methods SHELXS-97 [62] and refined by full-matrix least-squares
SHELXL-97 [62]. All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were included as their calculated positions
except for that of water molecules. The positions of hydrogen
atoms of water molecules in crystals 2 and 3 were determined
based on the electron density distribution. Crystal data for 1
(CCDC-773971), 2ꢀ4H2O (CCDC-773972), and 3ꢀ2H2O (CCDC-
796292) are presented in Table 1.
3. Results and discussion
Chemical diagrams of zwitterionic bisimidazolium sulfonates,
1–3, examined in this study are shown in Scheme 1. Two imidazo-
lium sulfonate moieties are connected with aromatic linkers,
p-xylylene, 4,40-dimethylenebiphenyl, and phenylene for 1, 2, and
3, respectively. They were prepared by the reaction of the corre-
sponding imidazole derivatives with 1,3-propanesultone. All of
them gave single crystals which were obtained by recrystallization
from water with diffusion of acetone vapor. Fig. 2 shows the pack-
ing diagram and characteristic interactions observed in the crystal
structure of 1. Oxy anions play significant roles in the molecular
packing. Due to an electrostatic interaction between the positively
charged imidazolium and the negatively charged sulfonate intra-
molecularly, the sulfonate 1 has an S-shaped structure. The
distance between the centroid of the imidazolium ring and
the neighboring sulfonate oxygen atom is 3.32 Å (Fig. 2a). The S-
shaped molecules are stacked to form a column with multiple
intermolecular CH/O interactions [63,64] between the sulfonate
oxygen atoms and an imidazolium hydrogen atom at the 2-posi-
tion, or a methylene hydrogen atom with the O–C atomic distances
Table 1
Crystallographic data for zwitterionic bisimidazolium sulfonates 1–3.
Sulfonate
1
2ꢀ4H2O
3ꢀ2H2O
Formula
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C
20H26N4O6S2 C26H30N4O6S2ꢀ4H2O
C18H22N4O6S2ꢀ2H2O
Monoclinic
P21/c
7.322(3)
15.437(6)
10.767(3)
116.78(2)
1086.5(7)
1.500
Monoclinic
P21/c
Monoclinic
P21/c
5.636(1)
11.383(2)
15.962(3)
90.865(3)
1024.0(3)
1.565
12.395(3)
8.543(2)
14.766(3)
109.751(2)
1471.6(5)
1.423
of 3.20–3.37 Å. There exist inter-columnar CH/O and CH/p interac-
b (°)
tions [65,66] (Fig. 2b). The O–C atomic distances between the sul-
fonate oxygen atoms and the carbon atoms at the 4-position of
imidazolium moieties are 3.25 and 3.28 Å. The O–C atomic
distances between the sulfonate oxygen atom and the benzylic
carbon atom and the methylene carbon atom connected to the imi-
dazolium moiety are 3.37 and 3.43 Å, respectively. The C–C atomic
V (Å3)
Dc (Mg mꢁ3
)
Z
2
2
2
T (K)
100
150
150
R1, [I > 2
wR2 [I > 2
r
r
(I)]
0.0423
0.0366
0.0885
0.0452
0.0983
(I)] 0.0750

8
S. Kohmoto et al. / Journal of Molecular Structure 1015 (2012) 6–11
Scheme 1. Chemical diagrams of zwitterionic bisimidazolium sulfonates 1–3 examined in this study.
distances for CH/
p interactions are 3.48 and 3.78 Å. The CH/O
interactions are indicated with black dashed lines in Fig. 2a and
b. Distances and angles of inter- or intramolecular interactions in
the crystal of 1 are presented in Table S1 (Supplementary data).
The 4,40-dimetylenebiphenyl-linked sulfonate 2 was obtained
as a tetrahydrate. Because of the inclusion of water molecules,
it has a linear molecular structure which is different from the
S-shaped molecular structure of 1. Fig. 3 illustrates the way of
hydrogen bonding among included water molecules and sulfonate
moieties. Hydrogen bonds are indicated with black dashed lines.
Two molecules of water are clipped by hydrogen bonds with the
sulfonate moieties. The O–O atomic distances between the hydro-
gen-bonded water molecules are 2.84 Å and those between water
molecules and sulfonate moieties are 2.74 and 2.93 Å, respectively.
Two oxygen atoms of a sulfonate moiety are connected to different
water molecules. Thus, the consecutive hydrogen bonding in an
alternating way forms an infinite 1D helical array of water mole-
cules and sulfonate moieties in the direction of the b axis (Fig. 3a
and b). Moreover, the hydrogen bonding between water molecules
and sulfonate moieties in the neighboring array construct a 3D net-
work structure (Fig. 3c). Both clockwise and counterclockwise heli-
ces exist in the crystal structure; therefore, the crystal is achiral.
Fig. 3d shows a schematic representation of the helical structure.
A space-filling model exhibiting the helical arrangement of water
molecules and sulfonate moieties is indicated in Fig. 3e in which
other parts of the molecules are omitted for clarity. A helical pitch
is found to be 8.54 Å (Fig. 3e). Multiple intermolecular CH/O and
CH/p interactions also stabilize its network structure. Distances
and angles of intermolecular interactions in the crystal of 2 are pre-
sented in Table S2 (Supplementary data).
In order to examine the effect of the shape of the linker, the
p-phenylene-bridged bisimidazolium 3 was subjected for X-ray
crystallographic analysis and compared with that of 1. In contrast
to the bending conformation of the p-xylylene linker which re-
sulted in the S-shaped conformation of 1, a straight shaped molec-
ular structure was derived from the phenylene linker. It is difficult
whether this difference is originated in the difference of the shape
of the linker or is due to the inclusion of water molecules. Fig. 4
shows packing diagrams of the dihydrate of 3 in which hydrogen
bonds and CH/O interactions are indicated with black and green
dashed lines, respectively (Fig. 4a). Water molecules are hydrogen
bonded with sulfonate oxy anions and arranged linearly. A herring-
bone-arrangement of 3 is observed viewed from the direction of
the c axis (Fig. 4b). Multiple intermolecular CH/O interactions are
Fig. 2. Single crystal X-ray structure of 1. (a) Stacked columnar structure along the a
axis. (b) Characteristic interactions among the columns. Intra- or intermolecular
interactions are shown with black dotted lines. A centroid of imidazolium ring is
shown with a green sphere. (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this article.)

S. Kohmoto et al. / Journal of Molecular Structure 1015 (2012) 6–11
9
Fig. 3. Single crystal X-ray structure of 2ꢀ4H2O showing the hydrogen-bonding network. (a) A view from the direction of the a axis. Hydrogen bonds are shown with black
dotted lines. (b) A view along the direction of the b axis. (c) An expanded packing diagram from the direction of the b axis. (d) A schematic representation of the helical
structure. (e) A space-filling model exhibiting the helical arrangement of water molecules and sulfonate moieties in which other parts of the molecules are omitted for clarity.
observed between the oxygen atoms of sulfonate and the hydrogen
atoms of imidazolium with the O–C atomic distances of 3.06–
3.12 Å. Distances and angles of intermolecular interactions in the
crystal of 3 are presented in Table S3 (Supplementary data).

10
S. Kohmoto et al. / Journal of Molecular Structure 1015 (2012) 6–11
4. Conclusion
We examined single crystal X-ray structures of three zwitter-
ionic bisimidazolium sulfonates. Unlike our previous work on zwit-
terionic bisimidazolium carboxylates which created water
channels, the present bisimidazolium sulfonates did not furnish
them. However, we found their unique crystal structures, an
S-shaped molecular structure and a helical array of hydrated water
molecules.
Acknowledgment
This work was partly supported by a Grant-in-Aid for Scientific
Research (C) (No. 22550118) from the Japan Society for the Promo-
tion of Science.
Appendix A. Supplementary material
CCDC-773971, 773972, and 796292 for compounds 1, 2ꢀ4H2O,
and 3ꢀ2H2O respectively, contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1233 336 033; or e-mail: depos-
it@ccdc.cam.ac.uk. Thermal ellipsoid models of crystals 1–3 and ta-
bles of distances and angles of inter- or intramolecular interactions
in crystals of them are available. Supplementary data associated
with this article can be found, in the online version, at
doi:10.1016/j.molstruc.2012.02.021.
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