Imidazolium 2-substituted 4,5-dicyanoimidazolate ionic liquids: Synthesis, crystal structures and structure-thermal property relationships

Article abstract of DOI:10.1002/chem.201304934

Thirty six novel ionic liquids (ILs) with 1-butyl-3-methylimidazolium and 3-methyl-1-octylimidazolium cations paired with 2-substitited 4,5-dicyanoimidazolate anions (substituent at C2=chloro, bromo, methoxy, vinyl, amino, methyl, ethyl, propyl, isopropyl

Full text of DOI:10.1002/chem.201304934

DOI: 10.1002/chem.201304934
Full Paper
&
Ionic Liquids
Imidazolium 2-Substituted 4,5-Dicyanoimidazolate Ionic Liquids:
Synthesis, Crystal Structures and Structure–Thermal Property
Relationships
Suvendu Sekhar Mondal,*[a] Holger Mꢀller,[a] Matthias Junginger,[a] Alexandra Kelling,[a]
Uwe Schilde,[a] Veronika Strehmel,[b] and Hans-Jꢀrgen Holdt*[a]
Abstract: Thirty six novel ionic liquids (ILs) with 1-butyl-3-
methylimidazolium and 3-methyl-1-octylimidazolium cations
paired with 2-substitited 4,5-dicyanoimidazolate anions (sub-
stituent at C2=chloro, bromo, methoxy, vinyl, amino,
methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl,
octyl, nonyl, decyl, undecyl and phenyl) have been synthe-
sized and characterized by using differential scanning calo-
rimetry (DSC), thermogravimetric analysis (TGA) and single-
crystal X-ray crystallography. The effects of cation and anion
type and structure on the thermal properties of the resulting
ionic liquids, including several room temperature ionic liq-
uids (RTILs) are examined and discussed. ILs exhibited large
liquid and crystallization ranges and formed glasses on cool-
ing with glass transition temperatures in the range of À22
to À688C. The effects of alkyl substituents of the imidazolate
anion reflected the crystallization, melting points and ther-
mal decomposition of the ILs. The Coulombic packing force,
van der Waals forces and size of the anions can be consid-
ered for altering the thermal transitions. Three crystal struc-
tures of the ILs were determined and the effects of changes
to the cations and anions on the packing of the structure
were investigated.
and solvent-free electrolytes in electrochemical devices[25–27]
and many others. ILs make a unique architectural platform
where the properties of cation and anion could be independ-
ently modified to design new functionalized ILs with low melt-
ing points and the effect of structural modification reflects the
properties of ILs. The nature of the anionic part controls the
main characteristics of the system. While much work has been
devoted to the wide range of applications of ILs, the basic un-
derstanding and study of their structure–property relationships
is of equivalent importance, but has lagged behind.[9,10] To
date, a large number of new ILs,[20] in particular, imidazoli-
um,[28,29] saturated quaternary ammonium,[30] and phosphoni-
um salts[31] with various anions, have been synthesized and
their structures and/or compositions have been well-character-
ized. However, few works have systematically studied the qual-
itative and/or quantitative relationships between the structures
of ILs and their fundamental properties, such as melting point,
viscosity, density, thermal and electrochemical stability, solvent
properties, and surface tension.[9,10,32,33] Moreover, the investi-
gations of potential ILs containing planar heterocyclic anions
and their structure–property relationship have been largely ne-
glected.
Introduction
In recent years, room temperature ionic liquids (RTILs) have
become one of the most rapidly growing areas in chemical re-
search, a fact manifested by the increasing number of publica-
tions on this topic.[1] The interest in this field is mainly growing
due to the advantageous properties of ionic liquids (ILs) over
traditional organic solvent and electrolytes, such as nonvolatili-
ty, nonflammability, wide liquid range and thermal stability, all
of which can make the chemical and electrochemical processes
more environmentally safe.[2–8] Presently, the growing interest
in ILs could be divided into two categories; the investigation
of the application and usefulness of the ILs in various research
areas and the newly designed ILs and their characterization for
understanding the structure–property relationship.[9,10] So far,
most effort in ILs have been focused on potential applications,
such as new media for chemical synthesis,[5,6,11–14] separation
science,[15–19] biocatalysts,[20,21] nanomaterial technology[22–24]
[a] Dr. S. S. Mondal, H. Mꢀller, Dr. M. Junginger, A. Kelling, Prof. Dr. U. Schilde,
Prof. Dr. H.-J. Holdt
Insitut fꢀr Chemie, Anorganische Chemie, Universitꢁt Potsdam
Karl-Liebknecht-Straße 26, 14476 Potsdam (Germany)
E-mail: smondal@uni-potsdam.de
Interestingly, few heterocyclic anion-based ILs have been re-
ported.[35–40] ILs containing azolate anions (imidazolate, triazo-
late, tetrazolate, benzimidazolate and benzotriazolate) have
gained less attention than those containing azolium cations, al-
though more results are now starting to appear.[41,42] A small
number of tetraalkylammonium and tetraalkylphosphonium
1,2,4-triazolates and imidazolates have been used as solvents
holdt@uni-potsdam.de
[b] Prof. Dr. V. Strehmel
Hochschule Niederrhein, University of Applied Sciences
Faculty of Chemistry and Institute for Coatings and Surface Chemistry
Adlerstraße 32, 47798 Krefeld (Germany)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201304934.
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and highly active catalysts for oligomerization of isocyanates in
the patent literature.[34] Rogers and co-workers have synthe-
sized low melting, planar 3,5-dinitro-1,2,4-triazolate anion-
based ionic liquids.[35] Ohno et al. described the preparation
and electrochemical properties of two ILs, 1-ethyl-3-methylimi-
dazolium tetrazolate and triazolate, which were prepared by
treatment of imidazolium hydroxide (generated by anion ex-
change from the halide) with the corresponding azole.[36,37]
Moreover, Shreeve and co-workers have reported a wide range
of energetic azolium azolate salts based on 4,5-dinitroimidazo-
late and 3,5-dinitro-1,2,4-triazolate anions with melting points
approaching the definition of ILs and with high heats of forma-
tion.[38–40] Over the past few years, Katritzky et al. have also in-
vestigated the possible use of azolate anions for the prepara-
tion of low melting energetic ionic liquids.[41,42] The use of such
anions to form energetic salts, specifically with the addition of
energetic substituents (nitro or cyano groups) to enhance their
energetic capabilities is a very interesting approach.
Scheme 1. Synthetic strategy of imidazolium imidazolate ILs.
To extend the scope for the synthesis of azolate anion-based
ILs, greater availability of organic anions providing the same,
or similar, architectural flexibility as the commonly used organ-
ic cations (e.g., substituted imidazolium cations) need to be
achieved. Parallel to this, improvements in the basic under-
standing of the key physical and chemical properties of com-
plex azolate-based ILs can be made. Here, we report the syn-
thesis and characterization of 36 novel ILs based on alkyl-sub-
stituted imidazolium cations combined with 2-substituted 4,5-
dicyanoimidazolate anions. The substituent at C(2)-position of
the imidazolate anion is tuned to electron-withdrawing groups
to electron-donating groups. The physical properties (e.g.,
glass transition (Tg), crystallization (Tc), melting temperature
(Tm) and decomposition temperature (Td)) of the resulting ILs
are determined. This work is of fundamental im-
acetone/dichloromethane (1:1, v/v) at room temperature gave
the corresponding imidazolium imidazolate ILs with high yields
after the removal of the precipitate of potassium chloride and
the evaporation of the organic solvents (see Scheme 1 and the
Experimental Section for details).
1
Experimental data were supported by H and 13C NMR spec-
troscopy, elemental analysis and mass spectrometry. All ionic
liquids were dried, prior to thermal analysis.
Thermal characterization
Thermal behavior of synthesized ILs was determined by differ-
ential scanning calorimetry (DSC) and thermal gravimetric anal-
portance to the design, and ultimately realizing
Table 1. Thermal transition temperatures of imidazolium imidazolate ILs.
ILs as “designer solvents” for specific applications,
as the properties of ILs is essentially governed by
the nature of both their cationic and anionic con-
stituents.
1 (R2 =Bu)
2 (R2 =oct)
R1
Tg
Tc
Tm
Td Tg
Tc
Tm
Td
[8C]
[8C]
[8C] [8C]
[8C] [8C]
[8C]
[8C]
a
b
c
d
e
f[41]
g
h
i
j
k
l
m
n
o
p
q
r
Cl
Br
À42.3
À56.8
–
–
–
–
229 À42.2
235 À57.9
250
235 À61.7
258 À22.0
247 À69.1
234 À60.6
–
–
248
255
251
238
238
246
–
À2.4
–
–
–
–
69.0
–
–
–
Results and Discussion
OMe À58.1
vinyl À58.3
9.7 27.8
–
–
–
–
–
–
–
–
Different kinds of ILs, combinations of imidazoli-
um cations and imidazolate anions, were synthe-
sized by metathesis reaction. In general, corre-
sponding potassium imidazolate was combined
with imidazolium halide to form a new IL in a sol-
vent mixture of acetone/dichloromethane at
room temperature (Scheme 1). The cations were
1-butyl-3-methylimidazolium (BMIm) and 3-
methyl-1-octylimidazolium (OMIm). The anions in-
cluded 2-substituted 4,5-dicyanoimidazolate. Po-
tassium 2-substituted 4,5-dicyanoimidazolate salts
were prepared by the treatment of the corre-
sponding imidazole with potassium carbonate
in acetone at 20–258C. Reaction of equimolar
amounts of imidazolium chloride and the potassi-
um 2-substituted 4,5-dicyanoimidazolate salts in
NH2
H
Me
Et
À21.5
À74.0
À63.0
À65.3
À66.4
À61.1
8.7
29.7,[a] 40.9 235
6.1 35.0
0.2 34.3
2.3 50.0
240 À65.5 À7.7
238 À66.9 À5.9
247 À61.1 16.5
250 À66.8 À15.6
37.0
256
Pr
39.2,[a] 47.4 255
50.1,[a] 58.5 245
iPr
Bu
À62.5 11.3 59.6
53.2
252
245
240
250
pent À65.3 12.5 36.5,[a] 45.9 250 À66.1 À0.8, À22.7, À50.4 52.2
hex
À65.9
–
–
–
–
250 À65.2 À0.6, À18.1, À54.8 60.4
hept À65.7
240 À63.0 À2.9, À28.8
62.5
oct
À66.4
À67.5
À66.4
4.4 31.6
2.8 23.4
3.7 34.6
260
250
250
243
–
–
–
–
À51.3, 12.2
À31.9, 22.8
À4.4, 9.8
3.4, 29.9
2.5
À41.8, 68.4 240
À24.7, 68.6 260
4.4, 67.5 250
18.9, 66.2 256
75.7
non
dec
undec À64.5 –16.8 43.8
s
Ph
À39.1 22.1 69.8
279 À41.1
266
Representative DSC traces were recorded from the transition onset temperature at a heat-
ing rate of 108CminÀ1 in the cooling/heating cycle. Decomposition temperatures were
determined by TGA, heating at 108CminÀ1; [a] solid–solid transition (Ts–s).
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ysis (TGA). The characterization data of 36 ILs are presented in
Table 1. The influence of structural variation in the cation and
anion moieties reflected their properties. The first type of be-
havior was observed by the ILs that showed a single glass tran-
sition (Tg) at low temperature during the cooling scan (Fig-
ure 1a). The second type of transition was noted with some ILs
(especially OMIm-based ILs, Figure 1b and Table 1) that exhibit-
ed one solid–solid/crystal–mesophase transition before melt-
ing. In Figure 1c, the third type of behavior of ILs shows the
crystalline or partially crystalline phase to isotopic liquid phase
transformation. This could be attributed to a solid–solid transi-
tion where the peak is less intensified. The fourth type of be-
havior is shown by the ILs that exhibit one solid–solid transi-
tion initially to form liquid crystalline state (Tm1) through melt-
ing (Tm2) at heating scan and at cooling scan, showing one
liquid crystalline state (Tc2) and crystalline state (Tc1, Figure 1d).
The fifth or major type of behavior was exhibited by the re-
maining ILs (Figure 2a). During the heating scan, these ILs
showed a Tg at low temperature to form a supercooled liquid
which transformed to an exothermic crystallization (Tc) peak at
relatively high temperature, followed by a sharp melting transi-
tion (Tm) as the temperature increased further.
Comparative studies of ILs are presented. We keep intact the
specific cation-like BMIm-based ILs. Hence, changing of the
alkyl substituent of the 2-substituted 4,5-dicyanoimidazolate
anion is presented. ILs 1a, 1b, 1d, 1e, 1g, 1m and 1n
showed only the glass transition (Table 1). ILs 1c, 1(h–k) and
1(o–s) exhibited glass transition followed by a broad crystalli-
zation peak and immediately by sharp melting. Interestingly,
1l showed a reversible phase transition on heating, it trans-
formed into a weakly glassy-like state and then soft glass ma-
terial leading to wide crystallization (À188C to 228C) and sud-
denly a sharp endothermic solid–solid transition after melting
transition (Figure 1b).
DSC curves of OMIm-based ILs indicated five different types
of thermal transitions by changing the alkyl substituent of the
2-substituted 4,5-dicyanoimidazolate anion. ILs 2a, 2b, 2d and
2e showed only the glass transition (Table 1). Interestingly, no
glass transition was observed for 2c, but the crystallization fol-
lowed by melting transition was visible. Moreover, propyl and
Figure 1. a) IL 1g shows only glass transition (Tg); b) 1l exhibits a glass transition, then the soft glassy material leads to crystallize widely followed by
a sudden endothermic solid–solid transition (Ts–s) before melting (Tm); c) 2i IL exhibits a weekly intensified solid–solid transition; d) at the cooling scan, 2r per-
forms a complete inhomogeneous crystallization and consists of two distinct temperatures and shows two different melting transitions during the heating
scan.
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showed two solid–solid transitions at around 298C with high
intensity and another at 418C, which is the melting transition.
The cooling cycle for 2h, 2k and 2s exhibited glass transition,
followed by a broad crystallization peak and sharp melting
(Table 1). On the heating scan, the first glass transition, fol-
lowed by remaining part crystallization and melting transitions
were observed for 2(l–n). On the cooling scan, such ILs only
show the crystallization peak. ILs 2(o–r) exhibited a complete
but inhomogeneous crystallization consisting of two distinct
temperatures that were observed at cooling scan and, without
showing glass transition and crystallization, ILs showed two
melting transitions (Table 1). Hence, with OMIm-based ILs,
higher chain length of imidazolate anion, one liquid crystalline
state (or mesophase) also is formed. Such a peak is observed
before crystallization. Therefore, with increase in the chain
length, more time was taken for orientation in liquid crystalline
state as the molecular volume increased.
Melting point (Tm): It has been reported that the melting
points of ILs are determined by the strength of their crystal lat-
tice, which is primarily controlled by three main factors, that is,
the conformational degree of freedom, intermolecular forces
and molecular symmetry of the molecules.[20,32,33] Changes of
aliphatic groups of imidazolium cation at N-position and the
change at 2-alkyl 4,5-dicyanoimidazolate anion have influenced
Tm.[9,10,33] In general, low symmetry and comparatively large
size cations combined with low symmetry and effective charge
distribution in the anion favor destabilization of the packing of
the compounds, which decreases the strength of the solids re-
sulting in lowering Tm.[43] In our study on BMIm-based ILs, by
incorporating a CH2 group at the 2-alkyl 4,5-dicyanoimidazo-
late anion, first the Tm increased and it maximized at the butyl
group, and then decrease as the nonyl substituent was
reached with the lowest temperature of 238C, after which
point the temperature again started to increase (Figure 3a).
The highlights of two competing effects on the melting points
of changing alkyl group substituents (methyl to undecyl) are
considered. It is noticeable that increasing the substituent
length initially increases the melting points of ILs (Figure 3a,
Table 1), with a major trend towards glass formation. On ex-
tending the alkyl chain lengths beyond a certain point (nonyl
group, 1p, Figure 3a), the melting point of the ILs starts to in-
crease again with increasing chain length, as van der Waals in-
teraction between the long hydrocarbon chains contribute to
the local structure by inducing microphase separation between
the covalent, hydrophobic alkyl chains and charged ionic re-
gions of the molecules. Initial lengthening of the substitution
leads to reduction of melting points through destabilization of
Coulombic packing and a trend towards glass formation.[43]
However, further increases in substitution lead to increased at-
tractive van der Waals forces between the hydrocarbon chains
and increased structural ordering, which can be seen with the
reemergence of higher melting points and formation of struc-
tured liquid crystalline phase (substituent=decyl and undecyl
and BMIm-based ILs, 1q and 1r, respectively). The intermedi-
ate region represents the glass-forming material in which crys-
tallization is inhibited through the attractive and dispersive
terms and the presence of many rotational modes that provide
Figure 2. a) IL 1q shows clear Tg, Tc and Tm. b), c) Thermal decomposition of
selected ILs.
isopropyl substitution-based ILs 2i and 2j melted at 47.4 and
58.58C, respectively, prior to the melting peak and one endo-
thermic peak (centered at 39.2 and 50.18C for 2i and 2j, re-
spectively) is observed. Potentially, this can be attributed to
a less intense solid–solid phase transition (Figure 1c). IL 2g
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a wide range of ion conformers with similar local energy
minima. Interestingly, the melting points of OMIm-based ILs
progressively increase if alkyl chain length at the anion is
longer (Figure 3a). However, the large sized cation tends to in-
crease in Tm because of the van der Waals interactions domi-
nate. With one anion kept constant, OMIm showed higher Tm
than BMIm because the size factor predominated over the con-
formational degree of freedom. In the case of increasing the
degree of chain branching, reflecting the changes in efficiency
of the crystal packing as free rotation volume decreases and
atom density is increased, this leads to an increase in the melt-
ing points (e.g., 1i vs. 1j and 2i vs. 2j). However, no clear cor-
relations are found between structure and chemical composi-
tion of the ILs and their melting points.
Glass transition (Tg): It appears that the Tg of ILs is mainly
governed by the strength of ion interactions, the ion size, as
well as the flexibility and polarizability of the anion.[32,33] The
alkyl chain slightly affects the Tg. Some ILs showed lower Tg
values because the counter anion showed much better charge
distribution or more conformational degree of freedom, which
weakens the ion–ion interaction and strength, and hence de-
creases the Tg values (Table 1). Phenyl-substituted imidazolates
ILs (1s and 2s) and amino-substituted ILs (1e and 2e) showed
a higher glass-transition temperature, which can be attributed
to the higher molecular weight and high charge distribution,
respectively. Among the same molecular weight based ILs
(propyl vs. isopropyl), isopropyl has higher Tg due to branching
(Table 1).
Crystallization (Tc): Almost all ILs showed a wide and broad
crystallization peak at the cooling scan because the molecules
took longer to reorient for crystallization. Figure 3b shows
a “zig-zag” motion with the addition of CH2 unit at C2-position
of imidazolate anion of a certain imidazolium-based ILs (Fig-
ure 3b). Also, it has been noticed that an odd number of car-
bons showed the crystallization peak at higher temperature
than nearby evens. This might be due to the reason that the
change of reorientational energy is higher for odd numbers of
carbon. The average crystallization temperature indicated that
at first by increasing the CH2 units at the C2 position of the
imidazolate anion of OMIm-based ILs, Tc increased. After that,
Tc decreased up to the hexyl substituent and then started to
increase (Figure 3b). Two competing factors control crystalliza-
tion points by changing the alkyl group substituents of the
anion; one is the volume and size factor and the other is con-
formational degree of freedom of alkyl side chains.
Decomposition temperature (Td): The thermal stability of
the ILs in the present study was examined by TGA. Generally,
thermal stability of the ILs is governed by the identity of the
cationic and anionic core and type of side chain of the cation
and anion.[32,33] Herein, ILs contain the same cationic and
anionic moieties; only the change of substituents at the C2 po-
sition at imidazolate anions affect the dramatic change of the
decomposition of ILs (Table 1, Figure 2b and c). As ILs are non-
volatile, the upper limit of the liquid range of ILs is usually
given by their thermal decomposition temperature, which gen-
erally lies between 250 and 4508C. 2-Substituted 4,5-dicyanoi-
midazolate anion-based ILs (substitution=methyl to undecyl
Figure 3. The thermal characteristics changes: a) melting, b) crystallization,
and c) decomposition on heating, at different temperature ranges of 2-alkyl
4,5-dicyanoimidazolate-based ILs.
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and methoxy) exhibited a complete mass loss and volatiliza-
tion of the component fragments occur during heating (Fig-
ure 2c, IL 1c, for example). In contrast, amine- or vinyl-substi-
tuted ILs (1d, 2d, 1e and 2e) showed the polymeric prod-
ucts.[44] Such ILs show that the decomposition occurs in two
distinct steps. The first decomposition can be found at around
3508C, probably representing the cleavage of alkyl chains. A
second decomposition step can be observed up to 3908C. This
leads to the assumption that first the IL reacts by the elimina-
tion of alkyl chains, maintaining the nitrogen-containing struc-
tural elements. Further, condensation of the material probably
proceeds by a trimerization of nitrile groups forming triazine
rings, which is a common reaction for nitriles.[44] Phenyl-substi-
tuted imidazolate-based ILs showed comparatively higher de-
composition temperatures.
Table 2. Crystallographic data.
2b
2g
1k
color/shape
formula
Mr
colorless/platelet colorless/platelet colorless/platelet
C17H23BrN6
391.32
C18H26N6
326.45
monoclinic
P21/n
C17H24N6
312.42
monoclinic
P21/c
crystal system
space group
T [K]
triclinic
¯
P
210(2)
100(2)
100(2)
a [ꢂ]
b [ꢂ]
c [ꢂ]
a [8]
8.9517(4)
10.5178(5)
11.3388(6)
64.074(4)
87.182(4)
81.841(4)
950.31(9)
2
12.7644(11)
10.5694(6)
14.1722(13)
90.00
101.997(7)
90.00
1870.2(3)
4
1.16
9.8937(7)
10.4408(4)
17.3097(12)
90.00
94.997(6)
90.00
1781.3(2)
4
1.16
b [8]
g [8]
V [ꢂ3]
Z
1calcd [gcmÀ3
]
1.37
2.17
6217
m [mmÀ1
refln collected
]
0.07
11811
3288
0.07
11020
3096
X-ray crystallography
independent refln 3155
Rint
0.122
0.076
0.0429
Crystals suitable for X-ray structure analysis were obtained for
three ILs (2b, 2g and 1k) by slow crystallization from dichloro-
methane/acetone mixtures (Table 2). ORTEP view of each asym-
metric unit and packing diagrams of ILs 2b, 2g and 1k are
shown in Figure 4 and Figure 5, respectively. The counter cat-
ions of previously reported azolate anion-based crystal struc-
tures are mostly substituted ammonium ions.[41,42] Here, we
report for the first time the crystal structures of imidazolium
cation-based azolate ILs. Nonclassical hydrogen bonds are rep-
resented as dotted lines. The asymmetric units contain corre-
sponding cation and anion. A nonclassical hydrogen bond
(C6ÀH6···N2=3.23 ꢂ) within the asymmetric unit occurs only in
2g. The middle part octyl group of the cationic part of 2g
(atoms C19, C20, C21, C22) are disordered over two equally oc-
cupied sites. Bond lengths and angles of the imidazoles are
shown in Tables S1 and S2 in the Supporting Information. A
comparison of the imidazoles indicates that there is little effect
of the substitution on the bond lengths and angles in the ring.
Layer structures are formed in the three ILs (Figure 5). The alkyl
substituents protrude in between two layers. In 2b and 1k the
layers are oriented along the a crystallographic axis. In con-
trast, 2g shows diagonal layers between the a and c axes. The
layers are connected by nonclassical hydrogen bonds. These
cation/anion contacts are listed in Table 3. Octyl groups of the
N-substituted imidazolium cations also form a layer.
R1/wR2 [I>2s(I)]
R1/wR2 (all data)
GoF F2
0.0518/0.1254
0.0546/0.1282
1.071
0.0477/0.1249
0.0604/0.1315
1.044
0.0440/0.1138
0.0454/0.1148
1.058
can be utilized to prepare correspondingly stabilized anionic
imidazolate anions, which lead to opportunities for the forma-
tion of ILs containing heterocyclic anions. The imidazolates
have been found to not only introduce properties required for
ILs, but also allow for the formation of low melting ILs, and
indeed in some cases ILs. They are surprisingly stable in the
systems explored, and allow a degree of structural modifica-
tion in a similar fashion to imidazolium cations. Hence, 36 new
ILs based on 2-substituted 4,5-dicyanoimidazolate anions were
synthesized. Some of these ILs are liquid at room temperature.
ILs were obtained with all combinations of 1-butyl-3-methyl-
imidazolium or 3-methyl-1-octylimidazolium cations and with
2-substituted 4,5-dicyanoimidazolate anions (substituent at
C2=chloro, bromo, methoxy, vinyl, amino, methyl, ethyl,
propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,
decyl, undecyl and phenyl). ILs showed large liquid and crystal-
lization ranges and forming glasses on cooling with glass tran-
sition temperatures in the range of À22 to À688C. Additional-
ly, one of the most interesting findings was the variation of Tc
Such alkyl layers exist in between two H-bonded
layers. In addition, these ILs are stabilized by p–p
Table 3. Cation···anion close-contact geometries.
stacking between cationic and anionic moieties of
corresponding ionic liquids (Table 4) and CÀH···p in-
teractions (Table 5).
DÀH···A
DÀH
H···A
[ꢂ]
D···A
[ꢂ]
DÀH···A Symmetry
[ꢂ]
[8]
code
2b
2g
C6ÀH6···N2
C7ÀH7···N1
C8ÀH8···N3
C6ÀH6···N2
C7ÀH7···N4
C8ÀH8···N1
0.84(4) 2.40(4) 3.239(4) 178(4)
0.78(4) 2.49(4) 3.266(4) 173(4)
0.93(4) 2.42(4) 3.312(5) 161(4)
0.95(2) 2.30(2) 3.229(2) 165(2)
0.97(2) 2.41(2) 3.342(2) 160(2)
0.97(2) 2.26(2) 3.214(2) 170(2)
x, 1+y, À1+z
x, 2+y, À1+z
À1+x, 2+y, À1+z
–
À0.5+x, 1.5Ày, 0.5+z
x, 1+y, z
Conclusion
Addition of electron-withdrawing cyano group leads
to an overall destabilization of the heterocyclic
cation relative to the corresponding imidazolium cat-
ions, thus restricting their applicability in the forma-
tion of conventional ILs. In contrast, the electron-
withdrawing characteristics of such functional group
C9ÀH9B···N2 1.00(3) 2.78(3) 3.508(2) 130(2)
1Àx, 1Ày, Àz
Àx, 1Ày, Àz
1k
C6ÀH6···N2
C7ÀH7···N4
C8ÀH8···N1
0.94(2) 2.29(2) 3.228(2) 178(1)
0.91(2) 2.44(2) 3.298(2) 157(1)
0.94(2) 2.31(2) 3.242(2) 170(1)
Àx, À0.5+y, À0.5Àz
Àx, Ày, Àz
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the variation of CH2 units at N atom of imidazolium
cations. To the best of our knowledge, for the first
time, we have investigated the influence of thermal
transition for structural variation of imidazolate anion-
based ILs by changing the alkyl substituents. Efficient
packing and subsequent crystallization are presumably
suppressed by the introduction of N-alkyl substituents,
which block close p–p stacking of cations and anions.
Overall, the development of ILs based on imidazolium
imidazolate cores seems to be an attractive avenue
for solvent properties of ILs, in particular.
Experimental Section
General methods
Elemental analysis (C, H, N) was performed on Elementar
Vario EL elemental analyzer. The TG measurements were
performed in a stationary air atmosphere (no purge) from
room temperature up to 9008C using a Linseis thermal
analyzer (Linseis, Germany) working in the vertical mode.
The heating rate was 108CminÀ1. The samples were
1
placed in cups of aluminium oxide. H and 13C NMR spec-
tra of all compound were performed on Bruker Advanced
300 spectrometer. Resonances for NMR spectra are report-
ed relative to Me4Si (d=0.0 ppm) and calibrated based
1
on the solvent signal for H and 13C. The ESI-MS spectra
were recorded using a Micromass Q-TOFmicro mass spec-
trometer in positive and negative electrospray mode.
Melting point, crystallization and glass transition tempera-
tures of the ILs were determined by differential scanning
calorimetry using Mettler Toledo DSC 822e. Data were col-
lected under a flow of nitrogen, using an average sample
weight of 5–8 mg placed in an aluminum pan sealed by
using pin-hole caps. Experiments were performed by
heating the samples at a rate of 108CminÀ1. The DSC in-
strument was adjusted so that zero heat flow was be-
tween 0 and À0.5 mW and the baseline drift was less
than 0.1 mW over the temperature range À120 to 1208C.
An empty sample pan was considered as reference.
Materials
Reagents, 1-butyl-3-methylimidazolium chloride, 3-
methyl-1-octylimidazolium chloride and solvents were
used as purchased from commercial suppliers (Sigma–Al-
drich, Fluka and others) without further purification, if not
stated otherwise. 2-Substituted 4,5-dicyanoimidazoles
(substituent=amino, hydrogen) were bought from chem-
ical suppliers and 2-substituted 4,5-dicyanoimidazoles
(substituent=chloro,[44] bromo,[45] vinyl,[46] methoxy,[47]
ethyl,[47] propyl,[47] isopropyl,[47] butyl[47] and phenyl[47]) are
prepared according to published procedures. The remain-
ing imidazoles (substituent=pentyl, hexyl, heptyl, octyl,
nonyl, decyl and undecyl) are newly synthesized
(Scheme 2).
Figure 4. ORTEP views of the asymmetric units: a) 2b, b) 2g and c) 1k. 50% probabili-
ty ellipsoids.
Synthesis and characterization
and Tm by increasing the CH2 unit at C2 position of the 4,5-di-
cyanoimidazolate anions. Coulombic packing force, van der
Waals forces, size factor and conformational degree of freedom
of the anions can be considered. Such behavior is similar to
Procedure for the preparation of orthoester: A 250 mL, three-
necked, round-bottomed flask was connected via a safety glass
tube to a hydrogen chloride water trap. A stream of nitrogen was
Chem. Eur. J. 2014, 20, 1 – 13
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Figure 5. Packing diagrams: a) along the c axis, and b) along the a axis for 2b; c) packing diagram for 2g, and d) packing diagram for 1k.
stopper was placed in each neck of the flask and kept in
a refrigerator at 5 8C. White precipitate was formed and
filtered under nitrogen atmosphere environment. Solid
imidic hydrochloride salt, dry hexane and dry methanol
were placed in a 250 mL, two-necked, round-bottomed
flask. The reaction mixture was stirred for 48 h and then
filtered under suction to remove the precipitated. The
colorless liquid was distilled under high vacuum to get
corresponding orthoester to prepare imidazole (see
Scheme 2 and the Supporting Information).[48]
Table 4. The p–p stacking parameters observed in the ionic liquids.
Ionic
Interacting
CgÀCg
a
b
CgJ_perp
[ꢂ]
Symmetry
code
liquids imidazole rings [ꢂ]
[ꢂ]
[ꢂ]
2b
C···C
A···C
A···A
A···C
A···C
4.561(2)
4.270(2) 15.3(2)
4.845(2)
4.670(1) 21.51(9) 39.3
4.825(1) 25.55(8) 39.4
0
45.3 À3.206(2)
47.7 À2.873(2)
47.5 À3.272(2)
2Àx, 3Ày, À2Àz
2Àx, 1Ày, À1Àz
2Àx, Ày, Àz
0
2g
1k
2.8360(7) 1Àx, 1Ày, Àz
3.7302(6)
–
C=cation, A=anion.
General procedure for the preparation of 2-substitut-
ed 4,5-dicyanoimidazole (l–s): Diaminomaleonitrile
(1.1 equiv) and orthoester in CH3CN as a solvent were
placed in a 250 mL one-necked round-bottomed flask.
The mixture was stirred under reflux for 7 h. The solvent
was evaporated under vacuum and the residue was di-
luted with xylene and the solution was refluxed for 7 h.
After being cooled on an ice bath, precipitates were col-
lected by filtration and the filtrate was dried in vacuum
and the compound was purified through column chro-
matography. The product was crystallized from the
hexane-ethyl acetate mixture (see Scheme 2 and the
Supporting Information).[47]
Table 5. XÀH···p ring interactions.
Ionic XÀH···Cg
H···Cg H_perp g
[ꢂ] [ꢂ] [8]
XÀH···Cg X···Cg
[8] [ꢂ]
Symmetry
code
liquids [J]
2b
2g
C17ÀH17A···A 2.78
2.73
2.67(3) 2.65
9.99 156
3.672(5) 2Àx, Ày, Àz
3.554(2) 1Àx, 1Ày, Àz
3.733(4) 1Àx, 1Ày, 1Àz
3.798(3) 0.5+x, 1.5Ày, 0.5+z
3.473(2) –
C9ÀH9B···A
7.87 148(3)
C14ÀH14B···A 2.97
C16ÀH16A···C 2.88
À2.76 21.69 136
À2.80 13.29 159
1k
C9ÀH9C···A
2.96
2.96
3.14 114
General procedure for the preparation of ILs
[1/2(a–s)]: Anhydrous potassium carbonate was added
introduced in another neck. The flask was flame dried and allowed
to cool. The stopper was removed from another neck and alkyl cy-
anide (1.0 equiv) was added in tert-butylethyl methyl ether as a sol-
vent and dry methanol (1.2 equiv). The flask was cooled at À58C
by immersion in an ice-salt bath and hydrogen chloride was al-
lowed to bubble through the reaction mixture for 10–15 min. A
to a solution of the appropriate imidazole in acetone. The mixture
was stirred for 2–4 h at 258C. Solution of the appropriate imidazoli-
um chloride in dichloromethane was added and the reaction mix-
ture was stirred for 3–6 h. The resultant precipitate of potassium
halide was removed by filtration and the solvents were evaporated
under vacuum. The product was extracted with acetone, the ex-
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d=0.87 (t, J=7.3 Hz, 3H), 1.28 (sext, J=7.4 Hz, 2H), 1.78 (m, J=
7.5 Hz, 2H), 2.27 (s, 3H), 3.90 (s, 3H), 4.11 (t, J=7.4 Hz, 3H), 7.32 (d,
2H), 9.10 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=13.1, 16.7, 19.2,
31.7, 36.4, 49.9, 116.8, 117.7, 122.4, 123.7, 135.85, 157.5 ppm; ESI-
MS: m/z (%): 139 (100) for cation, 131 (100) for anion; elemental
analysis calcd (%) for C14H18N6 (270.3): C 62.20, H 6.71, N 31.09;
found: C 61.88, H 6.89, N 30.93.
1-Butyl-3-methylimidazolium
4,5-dicyano-2-ethylimidazolate
(1h): Light yellow liquid (yield: 97%); 1H NMR (300 MHz, CDCl3):
d=0.89 (t, J=7.3 Hz, 3H), 1.21 (t, J=7.5 Hz, 3H), 1.30 (sext, J=
7.4 Hz, 2H), 1.80 (m, J=7.5 Hz, 2H), 2.63 (q, J=7.6 Hz, 2H), 3.92 (s,
3H), 4.14 (t, J=7.4 Hz, 2H), 7.34 (d, 2H), 9.10 ppm (s, 1H); 13C NMR
(75 MHz, CDCl3): d=13.1, 13.5, 19.3, 24.5, 31.7, 36.5, 50.0, 117.2,
117.7, 122.4, 123.7, 135.8, 163.1 ppm; ESI-MS: m/z (%): 139 (100) for
cation, 145 (100) for anion; elemental analysis calcd (%) for
C15H20N6 (284.2): C 63.36, H 7.09, N 29.55; found: C 63.11, H 6.81, N
29.82.
Scheme 2. Synthesis of 2-substituted 4,5-dicyanoimidazole (l–r).
tract was filtered and solvent was removed to obtain the ILs
(Scheme 1).
1-Butyl-3-methylimidazolium
2-chloro-4,5-dicyanoimidazolate
(1a): Light brown liquid (yield: 95%); 1H NMR (300 MHz, CDCl3):
d=0.92 (t, J=7.3 Hz, 3H), 1.34 (sextet, J=7.5 Hz, 2H), 1.85 (pentet,
J=7.4 Hz, 2H), 4.05 (s, 3H), 4.27 (t, J=7.3 Hz, 2H), 7.41 (d, 2H),
10.25 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=13.7, 19.8, 32.4,
36.9, 50.2, 115.8, 119.4, 122.3, 123.9, 138.1 ppm; ESI-MS: m/z (%):
139 (100) for cation, 151 (100) for anion; elemental analysis calcd
(%) for C13H15N6Cl (290.7): C 53.70, H 5.20, N 28.90; found: C 53.41,
H 5.44, N 28.72.
1-Butyl-3-methylimidazolium
4,5-dicyano-2-propylimidazolate
1
(1i): Light brown liquid (yield: 97%); H NMR (300 MHz, CDCl3): d=
0.87 (tt, J=3.6 Hz, 6H), 1.29 (sext, J=7.4 Hz, 2H), 1.65 (sext, J=
7.4 Hz, 2H), 1.79 (quint, J=7.5 Hz, 2H), 2.56 (t, J=7.6 Hz, 2H), 3.91
(s, 3H), 4.13 (t, J=7.4 Hz, 2H), 7.33 (d, 2H), 9.23 ppm (s, 1H);
13C NMR (75 MHz, CDCl3): d=13.1, 13.9, 19.2, 24.5, 31.7, 33.3, 36.4,
49.9, 117.1, 117.6, 117.7, 122.3, 122.4, 123.5, 123.7, 136.0,
162.1 ppm; ESI-MS: m/z (%): 139 (100) for cation, 159 (100) for
anion; elemental analysis calcd (%) for C16H22N6 (298.2): C 64.40, H
7.43, N 28.16; found: C 64.11, H 7.23, N 28.45.
1-Butyl-3-methylimidazolium 2-bromo-4,5-dicyanoimidazolate
(1b): Colorless liquid (yield: 98%); 1H NMR (300 MHz, CDCl3): d=
0.91 (t, J=7.4 Hz, 3H), 1.34 (sextet, J=7.5 Hz, 2H), 1.85 (pentet, J=
7.4 Hz, 2H), 4.00 (s, 3H), 4.21 (t, J=7.4 Hz, 2H), 7.39 (d, 2H),
9.25 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=13.6, 19.8, 32.3,
37.1, 50.5, 115.6, 120.4, 122.9, 124.2, 132.0, 136.5 ppm; ESI-MS: m/z
(%): 139 (100) for cation, 195 (100) for anion; elemental analysis
calcd (%) for C13H15N6Br (335.2): C 46.58, H 4.51, N 25.07; found: C
46.83, H 4.39, N 24.88.
1-Butyl-3-methylimidazolium 4,5-dicyano-2-isopropylimidazolate
1
(1j): Light brown semisolid (yield: 91%); H NMR (300 MHz, CDCl3):
d=0.89 (t, J=7.3 Hz, 3H), 1.23 (d, J=6.8 Hz, 6H), 1.30 (sext, J=
7.5 Hz, 2H), 1.81 (quint, J=7.5 Hz, 2H), 2.96 (sept, J=6.9 Hz, 1H),
3.93 (s, 3H), 4.14 (t, J=7.4 Hz, 2H), 7.35 (d, 2H), 9.13 ppm (s, 1H);
13C NMR (75 MHz, CDCl3): d=13.1, 19.3, 22.5, 30.5, 31.7, 36.5, 50.4,
117.2, 117.5, 122.5, 122.4, 123.8, 123.7, 135.8, 167.0 ppm; ESI-MS:
m/z (%): 139 (100) for cation, 159 (100) for anion; elemental analy-
sis calcd (%) for C16H22N6 (298.2): C 64.40, H 7.43, N 28.16; found: C
64.05, H 7.22, N 28.44.
1-Butyl-3-methylimidazolium 4,5-dicyano-2-methoxyimidazolate
1
(1c): Light brown liquid (yield: 95%); m.p. 278C; H NMR (300 MHz,
CDCl3): d=0.94 (t, J=7.4 Hz, 3H), 1.35 (m, 2H), 1.85 (m, 2H), 3.90
(s, 3H), 4.00 (s, 3H), 4.21 (t, J=7.4 Hz, 2H), 7.36 (m, 2H), 9.62 ppm
(s, 1H); 13C NMR (75 MHz, CDCl3): d=13.7, 19.8, 32.3, 36.9, 50.4,
56.5, 115.8, 117.2, 122.6, 124.0, 137.3, 164.6 ppm; ESI-MS: m/z (%):
139 (100) for cation, 147 (100) for anion; elemental analysis calcd
(%) for C14H18N6O (286.3): C 58.73, H 6.34, N 29.35; found: C 58.59,
H 6.53, N 29.01.
1-Butyl-3-methylimidazolium
2-butyl-4,5-dicyanoimidazolate
1
(1k): Colorless crystals (yield: 92%); H NMR (300 MHz, CDCl3): d=
0.89 (m, J=7.1 Hz, 6H), 1.32 (sext, J=7.4 Hz, 4H), 1.66 (quint, J=
7.3 Hz, 2H), 1.82 (quint, J=7.4 Hz, 2H), 2.63 (t, J=7.7 Hz, 2H), 3.94
(s, 3H), 4.15 (t, J=7.4 Hz, 2H), 7.31 (m, 2H), 9.01 ppm (s, 1H);
13C NMR (75 MHz, CDCl3): d=13.2, 13.8, 19.3, 22.6, 31.1, 31.6, 31.8,
36.5, 50.1, 117.3, 117.7, 122.5, 123.8, 135.9, 162.2 ppm; ESI-MS: m/z
(%): 139 (100) for cation, 173 (100) for anion; elemental analysis
calcd (%) for C17H24N6 (312.4): C 65.36, H 7.74, N 26.90; found: C
64.98, H 7.45, N 26.72.
1-Butyl-3-methylimidazolium
4,5-dicyano-2-vinylimidazolate
(1d): Light brown oil (yield: 97%) 1H NMR (300 MHz, CDCl3): d=
0.92 (t, J=7.3 Hz, 3H), 1.32 (sextet, J=7.4 Hz, 2H), 1.81 (pentet, J=
7.4 Hz, 2H), 3.93 (s, 3H), 4.14 (t, J=7.5 Hz, 2H), 5.19 (dd, J=10.9,
1.8 Hz, 1H), 5.90 (dd, J=17.5, 1.8 Hz, 1H), 6.63 (dd, J=17.6,
10.9 Hz, 1H), 7.31 (m, 2H), 9.21 ppm (s, 1H); 13C NMR (75 MHz,
CDCl3): d=13.6, 19.8, 32.2, 36.9, 50.5, 115.2, 117.2, 119.4, 122.7,
124.1, 131.3, 136.6, 158.8 ppm; ESI-MS: m/z (%): 139 (100) for
cation, 143 (100) for anion; elemental analysis calcd (%) for
C15H18N6 (282.3): C 63.81, H 6.43, N 29.77; found: C 63.41, H 6.10, N
30.01.
1-Butyl-3-methylimidazolium
4,5-dicyano-2-pentylimidazolate
1
(1l): Light brown solid (yield: 97%); H NMR (300 MHz, CDCl3): d=
0.86 (t, J=6.9 Hz, 3H), 0.95 (t, J=7.37, 3H), 1.23–1.41 (m, 6H) 1.70
(quint, J=7.5 Hz, 2H), 1.84 (quint, J=7.3 Hz, 2H), 2.64 (t, J=7.8 Hz,
2H), 3.94 (s, 3H), 4.17 (t, J=7.4 Hz, 2H), 7.31 (m, 2H), 9.16 ppm (s,
1H); 13C NMR (75 MHz, CDCl3): d=13.1, 13.8, 19.3, 22.4, 29.5, 31.1,
31.6, 31.8, 36.5, 50.1, 117.3, 117.7, 122.5, 123.8, 135.9, 162.2 ppm;
ESI-MS: m/z (%): 139 (100) for cation, 187 (100) for anion; elemen-
tal analysis calcd (%) for C18H26N6 (326.4): C 66.23, H 8.03, N 25.74;
found: C 65.88, H 8.28, N 26.03.
1-Butyl-3-methylimidazolium
2-amino-4,5-dicyanoimidazolate
1
(1e): Brown oil (yield: 94%); H NMR (300 MHz, CDCl3): d=0.94 (t,
J=7.2 Hz, 3H), 1.35 (m, 2H), 1.82 (m, 2H), 3.90 (s, 3H), 4.19 (t, J=
7.5 Hz, 2H), 7.1 (m, 4H), 9.44 ppm (s, 1H); 13C NMR (75 MHz, CDCl3):
d=13.7, 19.8, 32.4, 36.9, 50.4, 116.4, 118.9, 119.8, 122.3, 137.3,
160.2 ppm; ESI-MS: m/z (%): 139 (100) for cation, 132 (100) for
anion; elemental analysis calcd (%) for C13H17N7 (273.3): C 57.55, H
6.32, N 36.14; found: C 57.59, H 6.68, N 35.88.
1-Butyl-3-methylimidazolium
4,5-dicyano-2-hexylimidazolate
(1m): Light yellow liquid (yield: 96%); 1H NMR (300 MHz,
(CD3)2CO): d=0.86 (t, J=6.8 Hz, 3H), 0.95 (t, J=7.2, 3H), 1.20–1.45
(m, 8H), 1.93 (quint, J=7.5 Hz, 2H), 2.05(quint, J=7.4 Hz, 2H), 2.54
(t, J=7.5 Hz, 2H), 4.08 (s, 3H), 4.38 (t, J=7.2 Hz, 2H), 7.31 (d, 2H),
1-Butyl-3-methylimidazolium 4,5-dicyano-2-methylimidazolate
(1g): Light yellow liquid (yield: 96%); 1H NMR (300 MHz, CDCl3):
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9.30 ppm (s, 1H); 13C NMR (75 MHz, (CD3)2CO): d=13.1, 13.8, 19.3,
22.8, 29.5, 30.1, 31.7, 32.1, 32.3, 36.2, 49.7, 117.7, 117.9, 122.9, 124.4,
137.2, 161.5 ppm; ESI-MS: m/z (%): 139 (100) for cation, 201 (100)
for anion; elemental analysis calcd (%) for C19H28N6 (340.5): C 67.03,
H 8.29, N 24.68; found: C 66.76, H 8.52, N 24.91.
(100) for cation, 193 (100) for anion; elemental analysis calcd (%)
for C24H38N6 (332.4): C 68.65, H 6.06, N 25.28; found: C 68.41, H
6.34, N 25.11.
3-Methyl-1-octylimidazolium
2-chloro-4,5-dicyanoimidazolate
(2a): Light yellow oil (yield: 95%); 1H NMR (300 MHz, CDCl3): d=
0.84 (t, J=6.7 Hz, 3H), 1.16–1.30 (m, 10H), 1.88 (m, 2H), 4.06 (s,
3H), 4.26 (t, J=7.4 Hz, 2H), 7.37 (m, 2H), 10.32 ppm (s, 1H);
13C NMR (75 MHz, CDCl3): d=14.4, 22.9, 26.6, 29.3, 29.4, 30.6, 32.0,
36.9, 50.6, 115.8, 117.3, 119.4, 122.2, 123.8, 138.4 ppm; ESI-MS: m/z
(%): 195 (100) for cation, 151(100) for anion; elemental analysis
calcd (%) for C17H23N6Cl (346.8): C 58.87, H 6.68, N 24.23; found: C
58.67, H 6.93, N 23.94.
1-Butyl-3-methylimidazolium
4,5-dicyano-2-heptylimidazolate
(1n): Light brown oil (yield: 96%); 1H NMR (300 MHz, CDCl3): d=
0.84 (t, J=6.8 Hz, 3H), 0.93 (t, J=7.5 Hz, 3H), 1.24–1.42 (m, 10H),
1.69 (quint, J=7.4 Hz, 2H), 1.83 (quint, J=7.5 Hz, 2H), 2.64 (t, J=
7.8 Hz, 2H), 3.95 (s, 3H), 4.16 (t, J=7.4 Hz, 2H), 7.32 (d, 2H),
9.03 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=13.7, 14.5, 19.8,
23.0, 29.5, 29.8, 29.9, 31.8, 32.2, 32.3, 37.0, 50.5, 117.4, 118.1, 122.8,
124.2, 136.4, 162.4 ppm; ESI-MS: m/z (%): 139 (100) for cation, 215
(100) for anion; elemental analysis calcd (%) for C20H30N6 (354.5): C
67.76, H 8.53, N 23.71; found: C 67.53, H 8.69, N 23.92.
3-Methyl-1-octylimidazolium
2-bromo-4,5-dicyanoimidazolate
(2b): Colorless microcrystals from acetone (yield: 95%); 1H NMR
(300 MHz, CDCl3): d=0.84 (t, J=6.6 Hz, 3H), 1.22–1.31 (m, 10H),
1.88 (m, 2H), 4.01 (s, 3H), 4.22 (t, J=7.5 Hz, 2H), 7.38 (m, 2H),
9.30 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=14.4, 22.9, 26.5,
29.2, 29.3, 30.5, 31.9, 37.1, 50.8, 115.6, 120.4, 122.8, 124.2, 132.0,
136.6 ppm; ESI-MS: m/z (%): 195 (100) for cation, 195 (100) for
anion; elemental analysis calcd (%) for C17H23N6Br (391.3): C 52.18,
H 5.92, N 21.48; found: C 52.40, H 6.11, N 21.84.
1-Butyl-3-methylimidazolium
4,5-dicyano-2-octylimidazolate
(1o): Light brown oil (yield: 98%); 1H NMR (300 MHz, CDCl3): d=
0.84 (t, J=6.7 Hz, 3H), 0.93 (t, J=7.3 Hz, 3H), 1.21–1.38 (m, 12H),
1.68 (quint, J=7.6 Hz, 2H), 1.83 (quint, J=7.5 Hz, 2H), 2.63 (t, J=
7.8 Hz, 2H), 3.91 (s, 3H), 4.17 (t, J=7.4 Hz, 2H), 7.33 (m, 2H),
9.22 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=13.7, 14.5, 19.8,
23.0, 29.6, 29.8, 30.0, 31.9, 32.2, 32.3, 37.0, 50.5, 117.6, 118.2, 122.8,
124.1, 136.6, 162.4 ppm; ESI-MS: m/z (%): 139 (100) for cation, 229
(100) for anion; elemental analysis calcd (%) for C21H32N6 (368.5): C
68.44, H 8.75, N 22.80; found: C 68.14, H 8.52, N 22.97.
3-Methyl-1-octylimidazolium 4,5-dicyano-2-methoxyimidazolate
(2c): Light brown liquid (yield: 95%); 1H NMR (300 MHz, CDCl3):
d=0.79 (t, J=6.7 Hz, 3H), 1.30–1.50 (m, 10H), 1.81 (m, 2H), 3.89 (s,
3H), 3.49 (s, 3H), 4.14 (t, J=7.4 Hz, 2H), 7.26 (m, 2H), 9.55 ppm (s,
1H); 13C NMR (75 MHz, CDCl3): d=14.3, 22.9, 26.6, 29.2, 29.3, 30.4,
32.0, 36.9, 50.7, 115.8, 117.2, 122.5, 117.2, 122.5, 123.9, 137.3,
164.5 ppm; ESI-MS: m/z (%): 195 (100) for cation, 147 (100) for
anion; elemental analysis calcd (%) for C18H26N6O (342.4): C 63.13,
H 7.65, N 24.54; found: C 63.02, H 7.85, N 24.38.
1-Butyl-3-methylimidazolium
4,5-dicyano-2-nonylimidazolate
(1p): Light yellow oil (yield: 95%); 1H NMR (300 MHz, CDCl3): d=
0.83 (t, J=6.8 Hz, 3H), 0.91 (t, J=7.3 Hz, 3H), 1.17–1.39 (m, 14H),
1.67 (quint, J=7.5 Hz, 2H), 1.82 (quint, J=7.4 Hz, 2H), 2.62 (t, J=
7.8 Hz, 2H), 3.94 (s, 3H), 4.16 (t, J=7.4 Hz, 2H), 7.34 (m, 2H),
9.19 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=13.7, 14.4, 19.8,
23.0, 29.7, 29.9, 30.0, 30.1, 31.9, 32.2, 32.3, 37.0, 50.5, 117.6, 118.2,
122.8, 124.2, 136.5, 162.4 ppm; ESI-MS: m/z (%): 139 (100) for
cation, 243 (100) for anion; elemental analysis calcd (%) for
C22H34N6 (382.5): C 69.07, H 8.96, N 21.97; found: C 86.89, H 9.11, N
22.29.
3-Methyl-1-octylimidazolium
4,5-dicyano-2-vinylimidazolate
1
(2d): Light brown oil (yield: 94%); H NMR (300 MHz, CDCl3): d=
0.85 (t, 3H), 1.19–1.25 (m, 10H), 1.83 (t, 2H), 3.95 (s, 3H), 4.14 (t,
J=7.5 Hz, 2H), 5.20 (dd, J=10.9, 1.8 Hz, 1H), 5.96 (dd, J=17.5,
1.8 Hz, 1H), 6.64 (dd, J=17.6, 10.9 Hz, 1H), 7.30 (m, 2H), 9.20 ppm
(s, 1H); 13C NMR (75 MHz, CDCl3): d=14.3, 22.9, 26.5, 29.2, 29.3,
30.4, 31.9, 37.0, 50.8, 115.2, 117.2, 119.4, 122.6, 124.1, 131.3, 136.6,
158.7 ppm; ESI-MS: m/z (%): 195 (100) for cation, 143 (100) for
anion; elemental analysis calcd (%) for C19H26N6 (338.4): C 67.43, H
7.74, N 24.83; found: C 67.11, H 8.02, N 24.54.
1-Butyl-3-methylimidazolium
4,5-dicyano-2-decylimidazolate
1
(1q): Light brown oil (yield: 96%); H NMR (300 MHz, CDCl3): d=
0.83 (t, J=7.1 Hz, 3H), 0.91 (t, J=7.4 Hz, 3H), 1.19–1.38 (m, 16H),
1.66 (quint, J=7.4 Hz, 2H), 1.82 (quint, J=7.5 Hz, 2H), 2.61 (t, J=
7.8 Hz, 2H), 3.94 (s, 3H), 4.16 (t, J=7.3 Hz, 2H), 7.34 (m, 2H),
9.27 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=13.6, 14.4, 19.7,
23.0, 29.7, 29.9, 30.0, 30.1, 31.9, 32.3, 32.4, 36.9, 50.4, 117.6, 118.1,
122.8, 124.1, 136.6, 162.6 ppm; ESI-MS: m/z (%): 139 (100) for
cation, 257 (100) for anion; elemental analysis calcd (%) for
C23H36N6 (396.6): C 69.66, H 9.15, N 21.19; found: C 70.01, H 9.09, N
20.90.
3-Methyl-1-octylimidazolium
2-amino-4,5-dicyanoimidazolate
(2e): Dark brown oil (yield: 93%); 1H NMR (300 MHz, CDCl3): d=
0.86 (t, J=6.8 Hz, 3H), 1.21–1.33 (m, 10H), 1.82 (m, 2H), 3.92 (s,
3H), 4.14 (t, J=7.4 Hz, 2H), 7.22 (m, 4H), 9.10 ppm (s, 1H);
13C NMR (75 MHz, CDCl3): d=14.4, 26.5, 29.2, 29.3, 30.4, 32.0, 36.9,
50.7, 116.4, 117.5, 122.4, 123.9, 136.9, 160.3 ppm; ESI-MS: m/z (%):
195 (100) for cation, 132 (100) for anion; elemental analysis calcd
(%) for C17H25N7 (327.4): C 62.36, H 7.70, N 29.94; found: C 62.11, H
8.05, N 29.74.
1-Butyl-3-methylimidazolium 4,5-dicyano-2-undecylimidazolate
(1r): Light brown oil (yield: 95%); 1H NMR (300 MHz, CDCl3): d=
0.83 (t, 3H), 0.9 (t, 3H), 1.29–1.38 (m, 18H), 1.66 (qn, 2H), 1.81 (qn,
2H), 2.61 (t,2H), 3.93 (s, 3H), 4.14 (t, 2H), 7.32 (d, 2H), 9.18 ppm (s,
1H); 13C NMR (75 MHz, CDCl3): d=13.2, 14.0, 19.3, 22.5, 29.2, 29.4,
29.5, 29.6, 29.7, 29.8, 31.5, 31.5, 31.8, 36.5, 50.0, 117.2, 117.7, 122.3,
123.7, 136.3, 162.2 ppm; ESI-MS: m/z (%): 139 (100) for cation, 271
(100) for anion; elemental analysis calcd (%) for C24H38N6 (410.6): C
70.20, H 9.33, N 20.47; found: C 70.41, H 9.09, N 20.91.
3-Methyl-1-octylimidazolium 4,5-dicyano-2-methylimidazolate
(2g): Colorless crystals from acetone (yield: 98%); 1H NMR
(300 MHz, CDCl3): d=0.80 (t, 3H), 1.19–1.25 (m, 10H), 1.82 (t, 2H),
2.29 (s, 3H), 3.92 (s, 3H), 4.13 (t, 2H), 7.32 (m, 2H), 9.16 ppm (s,
1H); 13C NMR (75 MHz, CDCl3): d=13.8, 16.8, 22.4, 26.0, 28.6, 28.7,
29.9, 31.4, 36.5, 50.3, 116.9,117.0, 122.3, 123.7, 135.9, 157.5 ppm;
ESI-MS: m/z (%): 195 (100) for cation, 131 (100) for anion; elemen-
tal analysis calcd (%) for C18H26N6 (326.2): C 66.23, H 8.03, N 25.74;
found: C 65.91 H 8.29, N 25.42.
1-Butyl-3-methylimidazolium 4,5-dicyano-2-phenylimidazolate
(1s): Light gray solid (yield: 95%); 1H NMR (300 MHz, CDCl3): d=
0.86 (t, 3H), 1.22 (sext, 2H), 1.68 (quint, 2H), 3.78 (s, 3H), 3.96 (t,
2H), 7.14–7.34 (m, 5H), 8.02 (d, 2H), 8.77 ppm (s, 1H); 13C NMR
(75 MHz, CDCl3): d=13.2, 19.3, 31.7, 36.4, 50.0, 116.6, 119.4, 122.2,
123.6, 125.8, 127.6, 128.4, 134.6, 158.4 ppm; ESI-MS: m/z (%): 139
3-Methyl-1-octylimidazolium
4,5-dicyano-2-ethylimidazolate
(2h): Light yellow liquid (yield: 95%); 1H NMR (300 MHz, CDCl3):
d=0.82 (t, 3H), 1.23 (m, 14H), 1.83 (qn, 2H), 2.65 (q, 2H), 3.94 (s,
3H), 4.14 (t, 2H), 7.34 (d, 2H), 9.20 ppm (s, 1H); 13C NMR (75 MHz,
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CDCl3): d=13.6, 14.0, 22.4, 24.5, 26.1, 28.7, 28.8, 29.9, 31.5, 36.5,
50.3, 117.2, 117.8, 122.3, 123.7, 136.0, 163.1 ppm; ESI-MS: m/z (%):
195 (100) for cation, 145 (100) for anion; elemental analysis calcd
(%) for C19H28N6 (240.2): C 67.03, H 8.29, N 24.68; found: C 66.74, H
8.41, N 24.40.
anion; elemental analysis calcd (%) for C24H38N6 (410.6): C 70.20, H
9.33, N 20.47; found: C 69.94, H 9.35, N 20.37.
3-Methyl-1-octylimidazolium
4,5-dicyano-2-octylimidazolate
1
(2o): Light brown solid (yield: 97%); H NMR (300 MHz, CDCl3): d=
0.84–0.89 (m, 6H), 1.23–1.35 (m, 20H), 1.71 (quint, J=7.5 Hz, 2H),
1.87 (quint, J=7.4 Hz, 2H), 2.66 (t, J=7.8 Hz, 2H), 3.98 (s, 3H), 4.18
(t, J=7.4 Hz, 2H), 7.30 (d, 2H), 9.24 ppm (s, 1H); 13C NMR (75 MHz,
CDCl3): d=14.4, 14.5, 22.9, 23.0, 26.6, 29.2, 29.3, 29.7, 29.9, 30.1,
30.4, 31.9, 32.0, 32.3, 37.1, 50.8, 117.6, 118.2, 122.6, 124.1, 136.7,
162.6 ppm; ESI-MS: m/z (%): 195 (100) for cation, 229 (100) for
anion; elemental analysis calcd (%) for C25H40N6 (424.6): C 70.71, H
9.49, N 19.79; found: C 70.35, H 9.75, N 19.23.
3-Methyl-1-octylimidazolium
4,5-dicyano-2-propylimidazolate
1
(2i): Light brown liquid (yield: 94%); H NMR (300 MHz, CDCl3): d=
0.81(t, 3H), 0.89 (t, 3H), 1.23 (m, 10H), 1.68 (sx, 2H), 1.82 (qn, 5H),
2.59 (t, 2H), 3.92 (s, 3H), 4.13 (t, 2H), 7.34 (m, 2H), 9.13 ppm (s,
1H); 13C NMR (75 MHz, CDCl3): d=13.8, 13.9, 22.4, 22.6, 26.0, 28.6,
28.7, 29.9, 31.4, 33.4, 35.5, 50.3, 117.2, 117.7, 122.4, 123.8, 136.0,
162.0 ppm; ESI-MS: m/z (%): 195 (100) for cation, 159 (100) for
anion; elemental analysis calcd (%) for C20H30N6 (354.5): C 67.76, H
8.53, N 23.71; found: C 67.85, H 8.33, N 23.54.
3-Methyl-1-octylimidazolium
4,5-dicyano-2-nonylimidazolate
(2p): Light brown semisolid (yield: 97%); 1H NMR (300 MHz, CDCl3):
d=0.83–0.87 (m, 6H), 1.22–1.33 (m, 22H), 1.71 (quint, J=7.5 Hz,
2H), 1.87 (quint, J=7.4 Hz, 2H), 2.66 (t, J=7.8 Hz, 2H), 3.98 (s, 3H),
4.18 (t, J=7.4 Hz, 2H), 7.29 (d, 2H), 9.19 ppm (s, 1H); 13C NMR
(75 MHz, CDCl3): d=14.4, 14.5, 22.9, 23.0, 26.6, 29.2, 29.3, 29.7,
29.9, 30.1, 30.4, 31.9, 32.0, 32.3, 37.1, 50.8, 117.6, 118.2, 122.6, 124.0,
136.6, 162.5 ppm; ESI-MS: m/z (%): 195 (100) for cation, 243 (100)
for anion; elemental analysis calcd (%) for C26H42N6 (438.6): C 71.19,
H 9.65, N 19.16; found: C 70.95, H 9.44, N 19.43.
3-Methyl-1-octylimidazolium 4,5-dicyano-2-isopropylimidazolate
1
(2j): Light brown semi-solid (yield: 96%); H NMR (300 MHz, CDCl3):
d=0.81 (t, 3H), 1.20 (m, 10H), 1.23 (s, 3H), 1.83 (quint, J=7.3, 2H),
2.97 (sept, 1H), 3.93 (s, 3H), 4.14 (t, 2H), 7.36 (m, 2H), 9.18 ppm (s,
1H); 13C NMR (75 MHz, CDCl3): d=14.4, 22.9, 23.0, 26.5, 29.1, 29.6,
30.4, 31.0, 31.9, 37.0, 50.8, 117.7, 118.0, 118.8, 122.9, 124.3, 136.4,
167.5 ppm; ESI-MS: m/z (%): 195 (100) for cation, 159 (100) for
anion; elemental analysis calcd (%) for C20H30N6 (354.5): C 67.76, H
8.53, N 23.71; found: C 67.48, H 8.39, N 23.88.
3-Methyl-1-octylimidazolium
4,5-dicyano-2-decylimidazolate
1
(2q): Light brown solid (yield: 97%); H NMR (300 MHz, CDCl3): d=
0.84 (m, 6H), 1.16–1.37 (m, 24H), 1.68 (quint, J=7.5 Hz, 2H), 1.84
(quint, J=7.4 Hz, 2H), 2.63 (t, J=7.9 Hz, 2H), 3.95 (s, 3H), 4.15 (t,
J=7.4 Hz, 2H), 7.33 (m, 2H), 9.12 ppm (s, 1H); 13C NMR (75 MHz,
CDCl3): d=14.4, 14.5, 22.9, 23.0, 26.5, 29.2, 29.3, 29.7, 29.9, 30.1,
30.2, 30.3, 30.4, 30.5, 31.9, 32.2, 37.0, 50.8, 117.6, 118.2, 122.8, 124.2,
136.4, 162.6 ppm; ESI-MS: m/z (%): 195 (100) for cation, 252 (100)
for anion; elemental analysis calcd (%) for C27H44N6 (452.7): C 71.64,
H 9.80, N 18.57; found: C 71.43, H 10.28, N 18.22.
3-Methyl-1-octylimidazolium
2-butyl-4,5-dicyanoimidazolate
1
(2k): Light gray semi-solid (yield: 97%); H NMR (300 MHz, CDCl3):
d=0.83 (t, 3H), 0.87 (t, 3H), 1.28 (m, 13H), 1.66 (quint, 2H), 1.82
(quint, 2H), 2.63 (t, 2H), 3.94 (s, 3H), 4.14 (t, 2H), 7.33 (m, 2H),
9.13 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=13.8, 13.9, 22.4,
22.6, 26.1, 28.7, 28.8, 29.5, 31.2, 31.5, 31.6, 36.5, 50.3, 117.3, 117.8,
122.3, 123.7, 123.8, 136.0, 162.2 ppm; ESI-MS: m/z (%): 195 (100)
for cation, 173 (100) for anion; elemental analysis calcd (%) for
C21H32N6 (368.5): C 68.44, H 8.75, N 22.80; found: C 68.13, H 8.92, N
22.54.
3-Methyl-1-octylimidazolium 4,5-dicyano-2-undecylimidazolate
(2r): Light gray solid (yield: 94%); 1H NMR (300 MHz, CDCl3): d=
0.82 (m, 6H), 1.20–1.26 (m, 28H), 1.67 (qn, 2H), 1.83 (qn, 2H), 2.62
(t, 2H), 3.93 (s, 3H), 4.13 (t, 2H), 7.32 (d, 2H), 9.12 ppm (s, 1H);
13C NMR (75 MHz, CDCl3): d=13.9, 14.1, 22.4, 22.5, 26.1, 28.7, 28.8,
29.2, 29.5, 29.6, 29.9, 31.5, 31.8, 36.5, 50.3, 117.2, 117.7, 122.3, 123.7,
135.9, 162.2 ppm; ESI-MS: m/z (%): 195 (100) for cation, 266 (100)
for anion; elemental analysis calcd (%) for C28H48N6 (466.7): C 71.75,
H 10.32, N 17.93; found: C 71.33, H 10.61, N 17.79.
3-Methyl-1-octylimidazolium
4,5-dicyano-2-pentylimidazolate
(2l): Light gray semisolid (yield: 95%); 1H NMR (300 MHz, CDCl3):
d=0.79 (m, 6H), 1.19–1.23 (m, 14H), 1.63 (quint, J=7.4 Hz, 2H),
1.79 (quint, J=7.5 Hz, 2H), 2.63 (t, J=7.8 Hz, 2H), 3.94 (s, 3H), 4.14
(t, J=7.4 Hz, 2H), 7.33 (d, 2H), 9.08 ppm (s, 1H); 13C NMR (75 MHz,
CDCl3): d=13.5, 14.3, 19.8, 21.4, 22.7, 28.6, 29.2, 31.1, 31.5, 31.9,
36.5, 50.3, 117.3, 117.8, 122.3, 123.7, 123.8, 136.4, 162.3 ppm; ESI-
MS: m/z (%): 195 (100) for cation, 187 (100) for anion; elemental
analysis calcd (%) for C22H34N6 (382.5): C 69.07, H 8.96, N 21.97;
found: C 68.87, H 9.11, N 21.86.
3-Methyl-1-octylimidazolium
4,5-dicyano-2-phenylimidazolate
(2s): Light gray solid (yield: 94%); 1H NMR (300 MHz, CDCl3): d=
0.84 (t, 3H), 1.19 (m, 10H), 1.69 (quint, 2H), 3.78 (s, 3H), 3.93 (s,
3H), 7.13–7.34 (m, 5H), 8.02 (d, 2H), 8.75 ppm (s, 1H); 13C NMR
(75 MHz, CDCl3): d=13.9, 13.9, 22.5, 26.0, 28.7, 28.8, 29.8, 31.5,
36.4, 50.3, 116.6, 119.4, 122.2, 123.6, 125.8, 127.6, 128.4, 134.7,
135.6, 158.4 ppm; ESI-MS: m/z (%): 195 (100) for cation, 193 (100)
for anion; elemental analysis calcd (%) for C23H28N6 (388.5): C 71.10,
H 7.26, N 21.63; found: C 71.41, H 7.21, N 21.55.
3-Methyl-1-octylimidazolium
4,5-dicyano-2-hexylimidazolate
1
(2m): Light brown oil (yield: 93%); H NMR (300 MHz, CDCl3): d=
0.85 (m, 6H), 1.22–1.35 (m, 16H), 1.99 (quint, J=7.4 Hz, 2H), 2.16
(quint, J=7.8 Hz, 2H), 2.63 (t, J=7.4 Hz, 2H), 2.29 (t, J=7.8 Hz,
2H), 3.97 (s, 3H), 4.18 (t, J=7.5 Hz, 2H), 7.32 (d, 2H), 9.29 ppm (s,
1H); 13C NMR (75 MHz, CDCl3): d=14.3, 14.4, 22.9, 23.0,26.6, 29.2,
29.3, 29.7, 29.8, 30.5, 31.8, 32.0, 37.0, 50.8, 117.5, 118.1, 122.7, 124.1,
136.7, 162.4 ppm; ESI-MS: m/z (%): 195 (100) for cation, 201(100)
for anion; elemental analysis calcd (%) for C23H36N6 (396.5): C 69.66,
H 9.15, N 21.19; found: C 69.41, H 9.29, N 20.97.
X-ray crystallographic studies
The crystals were embedded in perfluoropolyalkylether oil and
mounted on a glass fiber. Intensity data were collected at 210 K
using a STOE imaging plate diffraction system IPDS-2 with graphite
monochromatized MoKa radiation (l=0.71073 ꢂ) at 50 kV and
40 mA (180 frames, Dw=18, exposure time per frame: 1 min (2b,
1k) or 3 min (2g)). The data were corrected by a spherical absorp-
tion correction using the program X-Area (Stoe, 2004) as well as
for Lorentz and polarization effects. The structure was resolved
with direct methods using SHELXS-97[49] and refined with full-
matrix least-squares on F2 using the program SHELXL-97[50] (Shel-
3-Methyl-1-octylimidazolium
4,5-dicyano-2-heptylimidazolate
1
(2n): Light brown solid (yield: 92%); H NMR (300 MHz, CDCl3): d=
0.82–0.88 (m, 6H), 1.18–1.37 (m, 18H), 1.69 (quint, J=7.5 Hz, 2H),
1.85 (quint, J=7.8 Hz, 2H), 2.65 (t, J=7.8 Hz, 2H), 3.95 (s, 3H), 4.15
(t, J=7.4 Hz, 2H), 7.30 (m, 2H), 8.99 ppm (s, 1H); 13C NMR (75 MHz,
CDCl3): d=14.4, 14.5, 22.9, 23.0, 26.6, 29.2, 29.3, 29.7, 29.8, 30.4,
31.7, 32.0, 32.2, 37.0, 50.8, 117.2, 118.0, 122.7, 124.1, 136.3,
162.2 ppm; ESI-MS: m/z (%): 195 (100) for cation, 215 (100) for
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Received: December 17, 2013
Revised: April 23, 2014
Published online on && &&, 0000
&
&
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
12
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
ILs at ease: Work on the synthesis and
characterization of 36 imidazolium 2-
substituted 4,5-dicyanoimidazolate ionic
liquids (ILs, see figure) is presented. Var-
iation of the substituents at C2 position
of the imidazolate anion reflects the
melting points, crystallization and ther-
mal degradation of ILs.
&
Ionic Liquids
S. S. Mondal,* H. Mꢀller, M. Junginger,
A. Kelling, U. Schilde, V. Strehmel,
H.-J. Holdt*
&& – &&
Imidazolium 2-Substituted 4,5-
Dicyanoimidazolate Ionic Liquids:
Synthesis, Crystal Structures and
Structure–Thermal Property
Relationships
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
13
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ