Influence of the counteranion on the ability of 1-dodecyl-3-methyltriazolium ionic liquids to form mesophases

Article abstract of DOI:10.1021/cg501564j

The influence of the counteranion on the ability of the mesogenic cation 1-methyl-3-dodecyl-triazolium to form mesophases is explored. To that avail, salts of the cation with anions of different size, shape, and hydrogen bonding capability such as Cl^-, Br^-, I^-, I₃^-, PF₆^-, and Tf₂N^- [bis(trifluorosulfonyl)amide] were synthesized and characterized. The crystal structures of the bromide, the iodide, and the triiodide reveal that the cations form bilayers with cations oriented in opposite directions featuring interdigitated alkyl tails. Within the layers, the cations are separated by anions. The rod-shaped triiodide anion forces the triazolium cation to align with it in this crystal structure but due to its space requirement reduces the alkyl chain interdigitation which prevents the formation of a mesophase. Rather the compound transforms directly from a crystalline solid to an (ionic) liquid like the analogous bis(trifluorosulfonyl)amide. In contrast, the simple halides and the hexafluorophosphate form liquid crystalline phases. Their clearing points shift with increasing anion radius to lower temperatures.

Full text of DOI:10.1021/cg501564j

Article
pubs.acs.org/crystal
Influence of the Counteranion on the Ability of 1‑Dodecyl-3-
methyltriazolium Ionic Liquids to Form Mesophases
†
†
†
,†,‡,§
̈
Kathrin Stappert, Derya Unal, Eike T. Spielberg, and Anja-Verena Mudring*
†Anorganische Chemie III − Materials Engineering and Characterization, Fakultat fur Chemie and Biochemie, Ruhr-Universitat
̈
̈
̈
Bochum, 44780 Bochum, Germany
‡Critical Materials Institute, Ames Laboratory, 333 Spedding Hall, Ames, Iowa 50011, United States
§Department of Materials Science and Engineering, Iowa State University, 2220 Hoover Hall, Ames, Iowa 50011, United States
S
* Supporting Information
ABSTRACT: The influence of the counteranion on the ability of the
mesogenic cation 1-methyl-3-dodecyl-triazolium to form mesophases is
explored. To that avail, salts of the cation with anions of different size, shape,
and hydrogen bonding capability such as Cl−, Br−, I−, I3 , PF6 , and Tf2N−
[bis(trifluorosulfonyl)amide] were synthesized and characterized. The crystal
structures of the bromide, the iodide, and the triiodide reveal that the cations
form bilayers with cations oriented in opposite directions featuring
interdigitated alkyl tails. Within the layers, the cations are separated by
anions. The rod-shaped triiodide anion forces the triazolium cation to align
with it in this crystal structure but due to its space requirement reduces the
alkyl chain interdigitation which prevents the formation of a mesophase.
Rather the compound transforms directly from a crystalline solid to an
(ionic) liquid like the analogous bis(trifluorosulfonyl)amide. In contrast, the
simple halides and the hexafluorophosphate form liquid crystalline phases. Their clearing points shift with increasing anion radius
to lower temperatures.
−
−
different imidazolium-based ILs and ILCs.14−17 For the 1,3-
INTRODUCTION
■
didodecylimidazolium cation, smectic A phases were observed
for the bromide, iodide, tetrafluoroborate, and perchlorate
anions,15,18,19 whereas no liquid crystalline behavior was
observed with other anions like triiodide, dicyanamide,
hexafluoroantimonate,15 or bis(trifluorosulfonyl)amide.20 In
the case of the 1,3-di(dodecyl)imidazolium cation,
[C12C12Im]+, the anion is able to alter the cation conformation
from U-shaped, to rod-shaped or V-shaped. We have made
similar observations for the didodecyltriazolium cation.21 Two
totally different conformations were found in the crystal
structure of the bromide (U-shaped) and the triiodide (rod-
shaped). Even a small change from bromide to iodide affected
not only the phase transition temperatures but also the type of
the adopted mesophase. Other prominent IL cation systems
also show a strong anion-dependent phase behavior.22
Ionic liquid crystals (ILCs) combine the research fields of liquid
crystals (LCs) and ionic liquids (ILs).1 ILs, salts with a melting
point below 100 °C, show unique properties such as low vapor
pressure, wide liquid range, good thermal stability, and ionic
conductivity.2 Due to the ionic composition, ILs are widely
tunable by variation of cations and anions. This adjustability is
advantageous for several applications and the reason for the
name “designer solvents”.3 Initially applied in electrochemistry,4
they have received considerable attention as alternative solvents
in chemical synthesis.5 With certain structural compositions,
ILs may exhibit liquid crystalline phases and thus are then
called ionic liquid crystals (ILCs). One of the most important
properties of liquid crystals is the anisotropy of their physical
and chemical properties.6 Ionic liquid crystals are promising
candidates for electrolytes in dye-sensitized solar cells,7 self-
assembled nanomaterials,8 as ordered solvents,9 as switchable
fluids,10 and as soft luminescent and magnetic materials.11 In
recent years, a number of cation types for ionic liquid crystals
have been developed,12 but still by far, the most commonly
used are imidazolium cations. For many imidazolium-based
salts, the influence of the chain length and of the symmetry of
the cation on the phase behavior has been intensively studied.13
Although it was found that the cation plays a decisive role in
determining the phase behavior, it was realized that a variation
in the anion also may substantially alter the mesomorphic
properties.11 The role of the anion has been analyzed for
For that reason, we synthesized and characterized methyl-
dodecyltriazolium salts with different anions, which allows us to
examine the effect of the anion on the liquid crystalline
behavior in detail. Anions of different sizes, symmetry and
−
hydrogen bonding capability were chosen: Cl−, Br−, I−, I3 ,
−
PF6 , and Tf2N− (Figure 1). The halide anions Cl−, Br−, and I−
are ideally spherically shaped anion of decreasing ion strength
Received: October 21, 2014
Revised: November 24, 2014
Published: November 25, 2014
© 2014 American Chemical Society
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Article
Structural Analysis. Single crystals of 1-dodecyl-3-methyl-
1,2,3-triazolium bromide [(C12C1Tr)Br, 2], 1-dodecyl-3-meth-
yl-1,2,3-triazolium iodide [(C12C1Tr)I, 3] and 1-dodecyl-3-
methyl-1,2,3-triazolium triiodide [(C12C1Tr)I3, 4] could be
grown successfully from dichloromethane solution (Table 1). It
Figure 1. General structures of the synthesized compounds and
compound numbering scheme.
Table 1. Crystallographic and Refinement Details for
Compounds 2 and 3
(C12C1Tr)I
(3)
(C12C1Tr)I3
(4)
and Lewis basicity but are increasingly polarizable. The
hexafluorophosphate anion with Oh symmetry is a pseudos-
pherical anion of large size. Triiodide as a rod-shaped anion has
a large geometric anisotropy. Tf2N− is an anion commonly used
in ionic liquids because of its extremely weak coordinating
character, comparatively large, low ion strength and its
possiblitity to adopt multiple conformations which are
energetically not too far apart, leading to structural frustration
and the inhibition of crystallization. The obtained results of
their salts with triazolium cations were compared to the
analogous imidazolium ILCs to evaluate the influence of the
acidic proton.
(C12C1Tr)Br (2)
empirical formula
C15H30N3Br
332.3
C15H30N3I
379.38
C15H30N3I3
633.1
formula weight
(g/mol)
temperature (K)
crystal system
170
170
200
triclinic
triclinic
triclinic
space group
P1
̅
P1
̅
P1
̅
unit cell dimensions
a = 5.4934(2) Å
b = 8.7114(2) Å
c = 19.5010(5) Å
a =
5.6056(6) Å
a =
5.4494(1) Å
b =
8.9070(1) Å
b =
7.0744(1) Å
c =
19.523(3) Å
c =
28.9928(5) Å
α = 78.910(2)°
β = 85.390(3)°
γ = 84.046(2)°
909.11(42)
2
α = 79.80(2)° α = 90.430(2)°
β = 83.50(2)° β = 92.253(2)°
γ = 81.78(2)° γ = 82.929(2)°
RESULTS AND DISCUSSION
■
Synthesis. To obtain the 1-methyl-3-dodecyltriazolium
chloride (1) and bromide (2) methyltriazolium was alkylated
with the respective dodecyl halide (Scheme 1). For the iodide
volume
945.6(2)
2
1108.35(3)
Z
2
calculated density
(g/cm3)
1.21
1.332
1.9
a
Scheme 1. Syntheses of Triazolium Compounds 1−6
absorption
2.255
1.69
4.23
coefficient
(mm−1
)
Θ-range for data
2.4 to 25.00°
2.34 to 25.00°
2.8 to 25.0°
collection
reflections
collected/unique
8375/3033
8211/3342
9729/3692
refinement method
full-matrix least-
squares on F2
data/parameters
3033/174
0.901
3342/173
0.989
3692/190
1.149
goodness-of-fit
on F2
final R indices
[I > 2 sigma(I)]
R1 = 0.034
R1 = 0.045
R1 = 0.104
wR2 = 0.076
R1 = 0.048
wR2 = 0.080
wR2 = 0.071
R1 = 0.077
wR2 = 0.082
wR2 = 0.275
R1 = 0.151
wR2 = 0.291
R indices (all data)
was not possible to obtain crystals of the other compounds.
Compounds 2 and 3 both crystallize isotypic in the triclinic
space group P1 (no. 2) with two formula units in the unit cell
(Figure 2). The cations adopt a rodlike shape with a tilted
triazolium head reminind of a crank-handle. The conformation
̅
a
(i) Acetonitrile, reflux, 3 days; (ii) vinylacetate, 80 °C, 3 days; (iii)
acetonitrile, reflux, 3 days; (iv) 4: CH2Cl2, RT, 1 h and 5-6: CH2Cl2,
RT, 2 days.
(3), the synthesis started with the reaction of dodecylazide with
an excess of vinyl acetate to obtain the 1-dodecyl-1,2,3-triazole
(Scheme 1). (3a) was then alkylated at the N-3 position with
methyl iodide to yield the desired triazolium iodide (3). The
compounds 4−6 were prepared via anion metathesis with the
alkaline salt of the desired anions. All compounds were
obtained as white or, in the case of the iodide and triiodide,
brown solids. In contrast to the respective imidazolium salts,
which are highly hygroscopic,1,10 astonishingly none of the
produced substances is air sensitive or hygroscopic. Thus, no
protective atmosphere is required for the synthesis.
Figure 2. Crystals structures of compounds 2 (left) and 3 (right)
viewed along [100].
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Figure 3. Hydrogen-bonding interactions in detail for compounds 2 and 3.
of the alkyl chain is all trans. The rod-shaped cations form an
interdigitated bilayer structure with the triazolium cations not
facing each other directly but alternating with the bromide
anions (Figure 3). The hydrophobic alkyl tails of the triazolium
cation form apolar regions, which are clearly separated from the
charged, polar domains built up by the triazolium headgroup
and the hydrogen-bonded bromide anions. Hydrogen bonds
are formed between the bromide/iodide and one hydrogen of
the methyl groups (Figure 3).
Table 2. Phase Transition Temperatures of Compounds 1 to
6
88.6°C(10.82)
107.5°C(9.96)
159.1°C(1.06)
(C1C12Tr)Cl (1)
(C1C12Tr)Br (2)
Cr ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ X ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ SmA ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯→ L
93.2°C(14.86)
Cr XooooooooooooooY X 1Xo0o2o.o3o°ooCo(o1o7oo.0o3oo)Y SmA 1Xo5o5o.o1o°ooCo(o0o.o9o6o)Y L
53.7°C(−)
59.1°C(44.89)
149.8°C(1.48)
83.1°C(39.43)
Cr XoooooooooooooY SmA 1Xo3o5o.o3o°ooCo(o1o.o0o3o)Y L
(C1C12Tr)I (3)
30.0°C(40.04)
60.8°C(1.31)
126.6°C(1.05)
78.1°C(24.2)
Cr XooooooooooooY Cr′ XooooooooooooY SmA X1oo1o3o.o1o°oCoo(o0o.o8o)Y L
(C1C12Tr)PF6 (4)
(C1C12Tr)I3 (5)
(C1C12Tr)Tf2N (6)
1-Dodecyl-3-methyl-1,2,3-triazolium triiodide [(C12C1Tr)I3,
26.3°C(0.19)
33.9°C(39.3)
110.1°C(0.84)
4] also crystallizes in the triclinic space group P1 (no. 2) with
̅
48.9°C(52.32)
Cr XooooooooooooooY L
32.1°C(50.63)
two formula units in the unit cell (Figure 4). The triiodide
13.3°C(46.79)
Cr XoooooooooooooooY L
−10.6°C(41.49)
traces of the three monohalide salts. For the chloride (1) and
the bromide compound (2), three phase transitions could be
observed, whereas the iodide (3) shows only two thermal
events (Figure 5). In compound 3, temperature-dependent
POM identifies the first transition to be the flow point (S →
LC) and the second one belongs to the clearing point (LC →
L
ISO). Compound 2 exhibits a liquid crystalline phase above
102 °C and clears at 155 °C. The first transition at 93 °C is
proposed to correspond to a change from crystalline to another
liquid crystalline phase, but this phase could not be clearly
identified and thus is named X here. All these transitions are
reversible and reappear during cooling, albeit at slightly lower
temperatures (Table 2). Compound 1 shows similar behavior
to 2 with a mesophase existing between 108 and 158 °C.
Additionally, solid−solid phase transitions occur at around 40
and 50 °C (Figure 5). As the related enthalpies are small, they
should correspond to minor structural changes. From 150 °C
on, the baseline of the DSC heating trace of compound 1
increases, which indicates a decomposition. Thus, no transition
temperatures are listed for the subsequent cooling cycle. The
mesophases of compounds 1−3 were identified on the basis of
their optical defect textures: in all cases oily streak textures were
observed by POM, indicating smectic A phases (Figure 5,
panels b and c).
Figure 4. Crystal structure of compound 4 viewed along [100].
anion lines up in the crystal structure with the triazolium cation.
The linear form of the triiodide anion forces the triazolium
cation to adopt a totally linear shape with an all trans
conformation of the alkyl chain and the alkyl chain is in the
plane of the triazolium ring (Figure 4). No significant hydrogen
bonds to the anion can be found. The cations form
interdigitated bilayers similar to those of compounds 2 and 3
but feature a lower degree of alkyl tail interdigitation due to the
space requirements of the triiodide anion. However, the
interdigitated alkyl chains are much closer to each other than
in the halide salts, as the cations are strictly linear and the
imidazolium head not tilted with respect to the alkyl tail of the
cations as in 2 and 3.
Thermal Behavior. The thermal properties of all
compounds were examined by polarizing optical microscopy
(POM) and differential scanning calorimetry (DSC). The
transition temperatures, enthalpies, and phase transition
assignments are listed in Table 2. Figure 5 shows the heating
The hexafluorophosphate salt 4 features three endothermic
events upon heating (Figure 6). The first thermal change
around 60 °C is due to a solid−solid phase transition, which is
directly followed by the transition to a liquid crystalline phase
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Figure 5. (a) DSC-heating-traces of compounds 1, 2, and 3 and POM pictures of (b) compound 1 during heating at 144.9 °C and (c) compound 2
during cooling at 87.2 °C.
Figure 6. DSC-thermograms of compounds 4−6 (left) and POM-picture of compound 5 at 103.4 °C (right).
(78 °C). An oily streak texture was observed under polarized
light (Figure 6, right). This indicates a smectic A phase.
Compound 4 clears to an isotropic liquid at 113 °C.
Compounds 5 and 6 do not exhibit a mesophase but directly
melt into isotropic liquids at 13 and 49 °C, respectively (Figure
6).
Comparison of the phase transition temperatures of all
compounds illustrates the dependency of the mesophase
formation on the anion (Figure 7). With increasing size of
the anion, the clearing point temperature decreases. The
mesophase temperature window has the same size for the three
halides (1−3): with increasing anion sizes both the formation
temperature and the clearing temperature for the smectic A
phase decrease simultaneously (Figure 7). The interactions of
the positively charged headgroups of the cations with the
anions are more efficient for smaller anions. This leads to
formation of another more highly ordered mesophase for the
chloride (1) and the bromide (2) before the smectic A phase is
formed. The hexafluorophosphate salt (4) exhibits the smectic
A phase at an even lower temperature (60 °C) and melts into
an isotropic liquid at 118 °C. Thus, compound 4 has the
narrowest mesophase temperature window, as expected for a
larger anion with weaker hydrogen bonds. The smaller
Coulombic interaction with the cation leads presumably to a
lowering of the phase transition temperatures, but at the same
time, the large anion is not able to stabilize the order of the
mesophase as well as the smaller halide anions. For the largest
and less symmetric anions, triiode and bis(trifluorosulfonyl)-
amide, no mesophase was observed. The triiodide (5) melts
around 50 °C and the bis(trifluorosulfonyl)amide (6) is even
liquid at room temperature, which is expected since it is the
largest, least weakly coordinating anion among the investigated.
All triazolium salts show different thermal behavior compared
to the analogous imidazolium compounds (Table 3). The
imidazolium halides exhibit the smectic A phase at much lower
temperatures and also melt at lower temperatures. The
mesophase temperature window range of the triazolium
chloride is much narrower than that of the corresponding
imidazolium salt (Tri: 52 °C vs Im: 102 °C), whereas the
mesophase temperature windows of the bromides are just
slightly different: Tri: 53 °C versus Im: 58 °C but shifted to
Figure 7. Phase transition temperatures of compounds 1−6.
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Table 3. Comparison of DSC-Data of Triazolium and Imidazolium Salts
Cr/SmC → SmA [T (°C)]
SmA → Liso [T (°C)]
Cr → Liso [T (°C)]
(C1C12Tr)
(C1C12Im)
(C1C1C12Im)
(C1C12Tr)
(C1C12Im)
(C1C1C12Im)
(C1C12Tr)
(C1C12Im)
a
a
Cl
107.5
102.3
88.1
−2.823
42.024
26.426
−
−
159.1
155.1
135.3
113.1
104.41
100.22
68.03
−
−
Br
I
74.825
140.923
a
a
−
−
PF6
I3
78.1
85.1
123.3
−
48.9
6027
a
−
Tf2N
13.3
16.71
a
No literature available; C1C12Im = 1,2-dimethyl-3-dodecylimidazolium.
higher temperatures with the triazolium cation (Table 3). The
mesophase temperature range of the iodides is approximately
the same size (47 °C vs 42 °C) but shifted to higher
temperatures for the triazolium compound. 1-Methyl-3-alkyl-
imidazolium hexafluorophosphate salts with an alkyl chain
length of at least 14 carbons exhibit a smectic A phase.23 In
contrast to compound 4, which exhibits a smectic A phase from
78 until 113 °C, the 1-methyl-3-dodecyl-imidazolium hexa-
fluorophosphate does not show a mesophase and melts at 60
°C. Both salts with bis(trifluoromethanesulfonyl)amide-anion
do not form a mesophase and melt slightly below room
temperature (Tr:13.3 °C vs Im: 16.7 °C).
Powder X-ray Diffraction. To identify the mesophase and
to comprehend the molecular arrangement of the triazolium
salts, temperature-dependent powder-XRD measurements in
the low to wide angle region were carried out. The X-ray
powder pattern of compound 1 is displayed in Figure 8.
Table 4. Layer Spacing (d, Å) of the Triazolium Salts in the
Different Phases
no.
formula
crystal
smectic A
1
2
3
4
5
6
(C1C12Tr)Cl (1)
(C1C12Tr)Br (2)
(C1C12Tr)I (3)
20.9
19.0
19.0
20.4
28.6
28.0
28.8
27.8
27.7
(C1C12Tr)PF6 (4)
(C1C12Tr)I3 (5)
(C1C12Tr)Tf2N (6)
a
a
−
−
a
Not measured due to the low crystallization temperature.
20 Å). Apparently, the degree of alkylchain interdigitation in 5
is too low to allow for a stabilization of a mesophase, and
rather, a direct transition from the crystalline to the liquid
crystalline state is observed.
CONCLUSION
Salts of 1-methyl-3-dodecyl-triazolium cation with anions of
■
different size and shape: Cl−, Br−, I−, I3 , PF6 , and Tf2N− were
synthesized and characterized with the aim of studying the
influence of the anion on the mesophase formation of these
ionic liquids. The three halide salts and the hexafluorophos-
phate salt exhibit a smectic A phase before melting to the
isotropic liquid. The triiodide is an ionic liquid, due to the
melting point at 49 °C but does not form a mesophase. Neither
does the bis(trifluormethylsulfonyl)amide form a mesophase.
This room temperature ionic liquid melts at 13 °C. For the
three simple halide salts, the clearing point temperature
decreases with increasing size of the anion (Cl−, 158 °C; Br−,
155 °C; and I−, 135 °C). Due to a similar decrease in the flow
point temperature, the mesophase temperature range does not
change significantly. In the hexafluorophosphate salt, the
transition temperatures are even lower due to the increased
anion size (the compound exhibits the smectic A phase at 78
°C and melts into an isotropic liquid at 113 °C), but the
mesophase temperature window is narrower (35 °C compared
to 50 °C for the halides).
In summary, it is observed that the thermal behavior of the 1-
methyl-3-dodecyl-triazolium salts strongly depends on the
anion and some trends could be noticed: with highly symmetric
anions mesophase formation can be observed. The larger the
anion, the lower the phase transition temperatures and the less
stable the mesophase. With the nonspherical and large anions
triiodide and Tf2N, no formation of a liquid crystalline phase
was observed; instead low melting ionic liquids formed.
Compared to the respective analogous imidazolium com-
pounds mesophases of the triazolium halides form at higher
temperatures. In contrast to the imidazolium hexafluorophso-
phate salt, which directly melts into an isotropic liquid, the
respective triazolium compound exhibits a smectic A phase. For
−
−
Figure 8. Temperature-dependent powder X-ray pattern of compound
1.
Compounds 1−4 show similar patterns with several sharp
peaks in the small angle region as well as in the wide angle
region (Figure 7). The layer distances, calculated from Bragg’s
law are listed in Table 4. The halide salts (1, 2, and 3) and the
hexafluorophosphate (4) have a layer distance of 19−20 Å in
the crystalline state. Comparing to the SXRD studies, this
distance corresponds to the interlayer distance, as shown in
Figure 2. The layer distance in the smectic A phase is much
larger for all four compounds (Table 4: 27.7−28.8 Å). The
increase in layer spacing can be attributed to partial melting of
the alkyl chain melting and simultaneous decrease of
interdigitation. The triiodide, which does not show a liquid
crystalline phase features a quite large layer distance in the
crystalline state compared to the halides (Table 4: 28.6 vs 19−
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(C15H30N3I): C, 47.5; H, 7.97; N, 11.08. Found: C, 47.61; H, 7.38;
N, 11.16.
the extremely low melting Tf2N salts, no mesophase formation
was observed for the 1-methyl-3-dodecylimidazolium as well as
the 1-methyl-3-dodecyltriazolium cation. Nevertheless, it
appears that mesophase formation is favored for triazolium
salts compared to imidazolium salts, an observation which we
already have made for symmetric 1,3-dodecyl salts.19
Preparation of 1-Methyl-3-dodecyl-1,2,3-triazolium triiodide (4).
To a solution of 500 mg (1.32 mmol) of 1-methyl-3-dodecyl-1,2,3-
triazolium iodide (3) in dichloromethane, 1 eq (330 mg, 1.32 mmol)
iodide was added and stirred for 1 h. The solvent was evaporated, and
n-pentane was added to the residue. The precipitated product was
filtered off and washed with n-pentane. The product was dried at RT in
dynamic vacuum to give a golden brown solid.
EXPERIMENTAL SECTION
■
Yield: 0.67 g, (81%). 1H NMR (200 MHz, CDCl3): δ [ppm] = 8.76
(s, 1H), 8.63 (s, 1H), 4.75−4.64 (m, 2H), 4.52 (s, 3H), 2.21−2.02 (m,
2H), 1.48−1.17 (m, 18H), 0.88 (t, J = 6.4 Hz, 3H). 13C NMR (50
MHz, CDCl3): δ = 132.6, 131.4, 55.5, 32.0, 29.7, 29.6, 29.6, 29.5, 29.0,
26.5, 22.8, 14.3. MS (FAB+): m/z = 84 (12%, K+-C12H24), 252 (100%,
K+). Elemental analysis (%) calcd for (C15H30N3I3): C, 28.46; H, 4.78;
N, 6.64. Found: C, 28.55; H, 4.76; N, 6.62.
Synthesis. Dodecylazide was synthesized according to a common
literature method.28 All other starting materials and solvents were
purchased from standard commercial sources and were used without
further purification. No protective atmosphere was required during
synthesis.
Preparation of 1-Methyl-1,2,3-triazole (1a). Four milliliters of (68
mmol) 1-H-1,2,3-triazol and 19.05 g (137.75 mmol) of potassium
carbonate were dissolved in 75 mL of tetrahydrofuran. 6.46 mL (103
mmol) of methyl iodide was added, and the mixture was stirred for 3 h
at room temperature. After filtration, the solution was concentrated
and the residue dried in dynamic vacuum to receive the 1-methyl-
1,2,3-triazole.
Preparation of 1-Methyl-3-dodecyl-1,2,3-triazolium hexafluoro-
phosphate (5). 0.27 g (1.45 mmol) of Potassium hexafluorophosphate
was added to a solution of 0.5 g (1.32 mmol) of 1-methyl-3-dodecyl-
1,2,3-triazolium iodide (3) in dichloromethane and stirred for 3 days at
room temperature. The white precipitate was filtered off. The organic
phase was washed with small volumes of water until no precipitation of
AgCl occurred in the aqueous phase upon addition of AgNO3 solution.
The organic phase was dried over Na2SO4, filtered, the solvent was
removed, and the residue dried under dynamic vacuum to give a
colorless product.
1
Yield: 4.79 g (83.7%), H NMR (200 MHz, CDCl3): δ [ppm] =
7.68 (s, 1H), 7.53 (s, 1H), 4.11 (s, 3H).
General Procedure for the Preparation of 1-Methyl-3-dodecyl-
1,2,3-triazolium chloride/bromide (1/2). Twelve mmol (1 g) 1-
methyl-1,2,3-triazole were dissolved in acetonitrile, and 27 mmol of
the respective dodecylhalide were added. The solution was heated
under reflux for 3 days and then poured into cold ethyl acetate and
stored at −40 °C for 20 h. The white precipitate was filtered off and
dried under dynamic vacuum at room temperature to give the
products in good yields and purity.
Yield: 3.23 g, (71%), 1H NMR (200 MHz, CDCl3): δ = 9.30 (d, J =
1.2 Hz, 1H), 9.05 (d, J = 1.3 Hz, 1H), 4.73−4.61 (m, 2H), 4.50 (s,
3H), 2.04 (d, J = 7.3 Hz, 2H), 1.38−1.20 (m, 18H), 0.88 (t, J = 6.5 Hz,
3H). 13C NMR (50 MHz, CDCl3): δ 132.5, 131.4, 54.6, 40.9, 32.0,
29.7, 29.7, 29.6, 29.5, 29.4, 28.9, 26.3, 22.8, 14.3. MS (FAB+): m/z =
1
−
84 (15%, K+-C12H24), 252 (100%, K+), 649 (2%, 2*K+ + PF6 ).
1-Methyl-3-dodecyl-1,2,3-triazolium chloride (1). H NMR (200
MHz, CDCl3): δ = 9.90 (s, 1H), 9.71 (s, 1H), 4.72 (t, J = 7.4 Hz, 2H),
4.53 (s, 3H), 2.02 (d, J = 6.9 Hz, 2H), 1.37−1.14 (m, 18H), 0.87 (t, J
= 6.4 Hz, 3H). 13C NMR (50 MHz, CDCl3): δ = 132.8, 131.9, 54.2,
40.5, 32.0, 29.7, 29.7, 29.6, 29.4, 28.9, 26.3, 22.8, 14.2. MS (FAB+): m/
z = 84 (15%, K+-C12H24), 252 (100%, K+), 539 (6%, 2*K+ + Cl−).
Elemental analysis (%) calcd for (C15H30N3Cl): C, 65.36; H, 8.35; N,
8.92. Found: C, 65.44; H, 7.91; N, 9.19.
Elemental analysis (%) calcd for (C15H30N3PF6): C, 45.34; H, 7.61; N,
10.57. Found: C, 47.11; H, 7.68; N, 10.89.
Preparation of 1-Methyl-3-dodecyl-1,2,3-triazolium bis-
(trifluormethylsulfonyl)amide (6). This compound was synthesized
by the same procedure described for the synthesis of compound 5.
From 0.42 g (1.45 mmol) of lithium bis(trifluormethylsulfonyl)amide
and 0.5 g (1.32 mmol) of 1-methyl-3-dodecyl-1,2,3-triazolium iodide
(3), 1-methyl-3-dodecyl-1,2,3-triazolium bis(trifluormethylsulfonyl)-
amide was obtained as a highly viscous oil.
1
1-Methyl-3-dodecyl-1,2,3-triazolium bromide (2). H NMR (200
MHz, CDCl3): δ = 9.77 (d, J = 1.2 Hz, 1H), 9.61 (d, J = 1.3 Hz, 1H),
4.74 (t, J = 7.4 Hz, 2H), 4.54 (s, 3H), 2.04 (t, J = 7.2 Hz, 2H), 1.37−
1.21 (m, 18H), 0.87 (t, J = 6.4 Hz, 3H). 13C NMR (50 MHz, CDCl3):
δ = 132.6, 131.7, 54.3, 40.7, 31.9, 29.8, 29.7, 29.6, 29.4, 28.9, 26.2, 22.8,
14.2. MS (FAB+): m/z = 84 (14%, K+-C12H24), 252 (100%, K+), 406
(1.3%, K+-CH3 + C12H25), 583 (22%, 2*K+ + Br−). Elemental analysis
(%) calcd for (C15H30N3Br): C, 54.12; H, 9.1; N, 12.64. Found: C,
53.06; H, 10.01; N, 12.24.
Yield: 0.55 g, (78%). 1H NMR (200 MHz, CDCl3): δ 8.48 (s, 1H),
8.43 (d, J = 1.1 Hz, 1H), 4.57 (t, J = 7.5 Hz, 2H), 4.36 (s, 3H), 2.09−
1.93 (m, 2H), 1.38−1.21 (m, 18H), 0.87 (t, J = 6.3 Hz, 3H). 13C, MS
(FAB+): m/z = 84 (13%, K+-C12H24), 252 (100%, K+), 784 (0.6%,
2*K+ + Tf2N−). Elemental analysis (%) calcd for (C17F6H30N4O4S2):
C, 38.34; H, 5.68; N, 10.52; S, 12.04. Found: C, 38.26; H, 5.50; N,
10.71; S, 12.01.
Instrumentation. Differential scanning calorimetry (DSC) was
performed with a computer-controlled PhoenixDSC 204 F1 thermal
analyzer (Netzsch, Selb, Germany). Measurements were carried out at
a heating rate of 5 °C/min in sealed aluminum crucible with an argon
flow rate of 20 mL/min. The samples were placed in aluminum pans
which were cold-sealed. Given temperatures correspond to the onset
of the respective thermal processes.
Preparation of 1-Dodecyl-1,2,3-triazole (3a). 5 g of Dodecylazide
(23.7 mmol) and 10 mL vinyl acetate were heated in a closed glass
tube for 3 days. After addition of 200 mL n-hexane, the suspension was
filtered and the solution cooled to −40 °C for 24 h. The precipitated
product was filtered off and dried overnight under a dynamic vacuum
at room temperature.
1
Yield: 3.98 g (71%). H NMR (200 MHz, CDCl3): δ = 7.69 (s,
1H), 7.52 (s, 1H), 4.38 (t, J = 7.2 Hz, 2H), 1.92 (dd, J = 12.4, 5.7 Hz,
2H), 1.25 (s, 18H), 0.88 (t, J = 6.3 Hz, 4H).
Optical analyses were made by heated-stage polarized optical
microscopy (POM) with an Axio Imager A1 microscope (Carl Zeiss
Preparation of 1-Methyl-3-dodecyl-1,2,3-triazolium iodide (3).
1.27 g (5.35 mmol) of 1-dodecyl-1,2,3-triazole and 3 eq of methyl
iodide (1 mL) were added to 50 mL of acetonitrile and heated under
reflux for 72 h. After cooling down to room temperature, ethyl acetate
was added, and the resulting solution was stored at −40 °C for 24 h.
The precipitated product was filtered off and dried overnight under
dynamic vacuum at room temperature.
MicroImaging GmbH,Gottingen, D) equipped with a hot stage,
̈
THMS600 (Linkam ScientificInstruments Ltd., Surrey, U.K.), and
Linkam TMS 94 temperature controller (Linkam Scientific Instru-
ments Ltd., Surrey, U.K.). Images were recorded at a magnification of
100× as a video with a digital camera during heating and cooling the
sample which was placed between two coverslips. Heating and cooling
rates were 5 K/min−1.
Yield: 1.47 g (72%), 1H NMR (200 MHz, CDCl3): δ = 9.50 (d, J =
1.3 Hz, 1H), 9.34 (d, J = 1.4 Hz, 1H), 4.80−4.66 (m, 2H), 4.53 (s,
3H), 2.12−1.99 (m, 2H), 1.25 (s, 18H), 0.88 (t, J = 6.5 Hz, 4H). 13C
NMR (63 MHz, CDCl3): δ 132.6, 131.6, 54.6, 41.2, 31.9, 29.6, 28.9,
26.2, 22.8, 14.2. MS (FAB+): m/z = 84 (11%, K+-C12H24), 252 (100%,
K+), 631 (6%, 2*K+ + I−). Elemental analysis (%) calcd for
Mass spectrometric analysis was carried out on a VG Autospec mass
spectrometer with EBEE geometry (VG instruments). Fast atom
bombardment (FAB) was used to ionize the samples.
Elemental analysis was conducted with a Vario EL C, H, N, S
analyzer of the company Elmentar (Hanau, Germany).
757
DOI: 10.1021/cg501564j
Cryst. Growth Des. 2015, 15, 752−758

Crystal Growth & Design
Article
Nuclear magnetic resonance measurements (1H NMR and 13C
NMR) were made using a Bruker Advance DPX 200 spectrometer
(Karlsruhe, Germany). The frequencies used were 200 and 50 MHz.
Deuterated chloroform (Deutero GmbH) was used as the solvent. The
chemical shift δ is given in ppm. The peak multiplicities are
abbreviated as follows: s = singlet, d = doublet, t = triplet, q =
quartet, and m = multiplet.
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Powder diffraction X-ray experiments were carried out with a D8
Advanced diffractometer (Bruker) at the Institute of Crystallography
of the Ruhr-Universitat Bochum.
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Single crystals of 1-dodecyl-3-methyl-1,2,3-triazolium bromide
[(C12C1Tr)Br,2], 1-dodecyl-3-methyl-1,2,3-triazolium iodide
[(C12C1Tr)I, 3], and 1-dodecyl-3-methyl-1,2,3-triazolium triiodide
[(C12C1Tr)I3, 4] could be grown successfully from a dichloromethane
solution. Measurements were carried out on a Stoe IPDS-I single-
crystal X-ray diffractometer with graphite monochromated Mo Kα
radiation (λ = 0.71073 Å at 100 K). Crystal structure solution by direct
methods using SIR 9229 yielded the heavy atom positions. Refinement
with SHELXL-9730 allowed for the localization of the remaining atom
positions. Hydrogen atoms were added and treated with the riding
atom mode. Data reduction was performed with the program package
X-Red,31 and numerical absorption correction was carried out with the
program X-Shape.32 To illustrate the crystal structures, the program
Diamond33 was used.
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M.; Mudring, A.-V.; Wasserscheid, P.; Meyer, K. Chem. Commun.
2009, 7405−7407.
ASSOCIATED CONTENT
■
(19) Yang, M.; Mallick, B.; Mudring, A.-V. Cryst. Growth Des. 2014,
14, 1561−1571.
S
* Supporting Information
CIF files. This material is available free of charge via the
Internet at http://pubs.acs.org.
(20) Rohini, R.; Lee, C.-K.; Lu, J.-T.; Lin, I. J. B. J. Chin. Chem. Soc.
2013, 60, 745−754.
̈
(21) Stappert, K.; Unal, D.; Mallick, B.; Mudring, A.-V. J. Mater.
Chem. C 2014, 2, 7976−7986.
AUTHOR INFORMATION
■
(22) Yoshio, M.; Ichikawa, T.; Shimura, H.; Kagata, T.; Hamasaki, A.;
Mukai, T.; Ohno, H.; Kato, T. Bull. Chem. Soc. Jpn. 2007, 80, 1836−
1841.
Corresponding Author
*E-mail: anja.mudring@ruhr-uni-bochum.de and mudring@
iastate.edu. Tel: +49-234-32-27408 and +1 515-509-5616.
(23) Bradley, A. E.; Hardacre, C.; Holbrey, J. D.; Johnston, S.;
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635.
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1196.
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Long, H. C.; Trulove, P. C. Green Chem. 2003, 5, 724−727.
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Mater. Chem. 1998, 8, 2627−2636.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported in part by the German Science
Foundation DFG through the DFG Cluster of Excellence
RESOLV (EXC 1069), Iowa State University and the Critical
Materials Institute, an Energy Innovation Hub funded by the
U.S. Department of Energy, Office of Energy Efficiency and
Renewable Energy, Advanced Manufacturing Office.
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Org. Chem. 2009, 74 (1), 21−25.
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