Confined water in imidazolium based ionic liquids: A supramolecular guest@host complex case

Article abstract of DOI:10.1039/c6cp03112a

It is well known that the macroscopic physico-chemical properties of ionic liquids (ILs) are influenced by the presence of water that strongly interferes with the supramolecular organization of these fluids. However, little is known about the function of water traces within this confined space and restricted ionic environments, i.e. between cations and anions. Using specially designed ILs namely 1,2,3-trimethyl-1H-imidazol-3-ium imidazol-1-ide (MMMI·Im) and 3-n-butyl-1,2-dimethyl-1H-imidazol-3-ium imidazol-1-ide (BMMI·Im), the structure and function of water have been determined in condensed, solution and gas phases by X-ray diffraction studies, NMR, molecular dynamics simulations (MDS) and DFT calculations. In the solid state the water molecule is trapped inside the ionic network (constituted of contact ion pairs formed by π⁺-π^- interaction) through strong H-bonds involving the water hydrogens and the nitrogens of two imidazolate anions forming a guest@host supramolecular structure. A similar structural arrangement was corroborated by DFT calculations and MDS. The presence of a guest@host species (H₂O@ILpair) is maintained to a great extent even in solution as detected by ¹H-¹H NOESY-experiments of the ILs dissolved in solvents with low and high dielectric constants. This confined water catalyses the H/D exchange with other substrates containing acidic-H such as chloroform.

Full text of DOI:10.1039/c6cp03112a

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Received 00th January 20xx,
Accepted 00th January 20xx
Confined water in imidazolium based ionic liquids: a
supramolecular guest@host complex case
DOI: 10.1039/x0xx00000x
Marcileia Zanatta, a Anne-Lise Girard, a Graciane Marin, a Gunter Ebeling, a Francisco P. dosSantos, a
Chiara Valsecchi, a Hubert Stassen, a Paolo R. Livotto, a William Lewisb and Jairton Dupont*, a, b
www.rsc.org/
It is well known that the macroscopic physico-chemical properties of ionic liquids (ILs) are influenced by the presence of
water that strongly interferes on the supramolecular organization of these fluids. However, little is known about the
function of water traces within this confined space and restricted ionic environments, i.e. between cations and anions.
Using especially designed ILs namely 1,2,3-trimethyl-1H-imidazol-3-ium imidazol-1-ide (MMMI⋅Im) and 3-n-butyl-1,2-
dimethyl-1H-imidazol-3-ium imidazol-1-ide (BMMI⋅Im), the structure and function of water has been determined in
condensed, solution and gas phases by X-Ray diffraction studies, NMR, molecular dynamic simulations (MDS) and DFT
calculations. In the solid state the water molecule is trapped inside the ionic network (constitute of contact ion pairs
formed by π+-π- interaction) through strong H-bonds involving the water hydrogens and the nitrogens of two imidazolate
anions forming a guest@host supramolecular structure. A similar structural arrangement was corroborated by DFT
calculations and MDS. The presence of a guest@host species (H2O@ILpair) is maintained to a great extends even in
solution as detected by 1H-1H NOESY-experiments of the ILs dissolved in solvents with low and high dielectric constants.
This confined water catalyses the H/D exchange with other substrates containing acidic-H such as chloroform.
experimentally pure ILs are extremely difficult to obtain,
especially water-free ones.25, 26 It is well recognized that the
presence of water may dramatically effect macroscopic
Introduction
Neat imidazolium based ionic liquids (ImILs) are highly
organized 3-D materials in the condensed phase with a broad
range of applications in chemistry, physics, materials and
biosciences.1-4 The physico-chemical properties at the
nanoscopic level of ImILs have been ascribed as a result of
various bond forces namely: electrostatic, hydrogen bonding
and dispersive forces. The structural organization of ImILs is
mainly controlled by an intricate interplay of intermolecular
interactions between anions and cations. In particular, ILs
based on the imidazolium cation are compounds in which π+-
π+ stacking interactions among the imidazolium rings5 may also
physico-chemical properties of ionic liquids27 such as viscosity,
density,28 diffusion, ionic mobility29 and gas solubility.30-32 On
the microscopic scale, computer simulations on IL/water
mixtures revealed the influence of water on the IL structure
and dynamical features.14, 33, 34 It is therefore reasonable also
to expect that even trace amounts of water may have a
profound impact at the nanoscopic level on the organization
and reactivity of these fluids. However, the function of water
within this confined space and restricted ionic environments,
i.e. between imidazolium cations and anions, has not yet been
experimentally firmly established.
7
be involved,6, and their interaction energy depends on the
The most important forces, present in the supramolecular
structure of neat imidazolium based ILs holding multiple ion
pairs together, consist mainly of dispersion interactions,
electrostatics and hydrogen bonds. Water molecules affect
different orientations adopted by the imidazolium rings.8-10
Thus, all these non-bonding interactions should be recognized
as a key component in the local structure of imidazolium based
compounds and they have been subject of several
theoretical11-15 and experimental studies.16-24 However,
36
these interactions.35, Thus, the structure and dynamics of
water traces in imidazolium based ILs37 can be regarded as a
consequence of a guest that is non-covalently bound to the ion
pairs network, i.e. the host forming a guest@host species
(H2O@ILpair). As in many guest@host complexes, the guest
(H2O) is relatively small compared with the host (IL pair) and
they should behave as a unit. Moreover, the IL ion pairs may
provide
a
cage that completely surrounds the guest
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(guest@cage) or provide a cavity (guest@cavity) that partially The two five-membered rings are in
a
quasi-staggered
surrounds the guest.38-40 Assuming this hypothesis, we have conformation in which the cation’s ring moiety is located in an
designed ImILs in which traces of water are experimentally anti-parallel position to the ring of the imidazolate anion
investigated in the condensed phase and in solution by NMR (Figure 2b). The most relevant aspect is the presence of water
experiments. In particular, ImILs associated with the molecules which are “trapped” inside the ionic network (constitute
imidazolate anion (Figure 1) display the desired structural and of contact ion pairs) through strong H-bonds involving one H of
electronic features such as possible π π cation-anion water and the nitrogens (N9 and N11) of two imidazolate anions
interactions in solution as well as nitrogen basic sites that can (Figure 2a).
Structure and behaviour of the water@ImIL in solution. The 1H
easily accommodate water molecules by hydrogen bonds.
For this study, we have chosen the symmetric 1,2,3-
NMR spectra of both ILs from Figures S9-S18 in the supporting
trimethylimidazolium cation (MMMI) that is solid and
information clearly present a decrease in the intensity of the
crystalline at room temperature (RT) yielding simplified NMR
C7 hydrogen signals (originally singlet at around 2.48 ppm) in
spectra. In addition, we employed the non-symmetric 1,2-
various solvents (CDCl3, CD3OD, CD3CN, [D6]DMSO and D2O)
dimethyl-3-n-butyl imidazolium BMMI analogue that possesses
and the appearance of a triplet and quintet corresponding to
CH2D and CHD2 (around 2.46 and 2.44 ppm). In the 13C NMR
a better solubility in organic solvents.
spectrum (Figures S6 and S8 in the supporting information),
we observed a triplet and a septuplet around 7.6 ppm
corresponding to the C7 carbon coupled to D. Some H/D
exchange at the cation’s C4/C5 position has also been
Figure 1. ImILs associated with the imidazolate anion.
detected but the deuteration occurs preferentially at C7 (see
We report herein our experimental and theoretical results Table 1) within 1h. In principle, this observation might be
revealing the impact of water in this confined and restricted explained by the solvated imidazolate anion acting as a base
space forming a guest@host complex by the interaction with catalyst. However, in that case the reaction should be more
the contact ion-pair (imidazolium cation-imidazolate anion).
efficient in D2O since it is well known that D incorporation is by
far more difficult to achieve in aprotic solvents such as CDCl3
than in protic polar solvents like D2O, partly due to the limited
strength of bases in a low dielectric constant medium.
Results and discussion
Table 1. Degree (%)[a] of deuteration of the C7 and C4-C5 hydrogens of the imidazolium
cation (0.2 M) in different solvents after 1h in solution.[b]
Synthesis and X-ray structure of the water@ImIL complex. The
MMMI
been prepared in quantitative yield by the reaction of
MMMI OH and BMMI OH (prepared by anion exchange of
chloride salts and NaOH using an anionic Amberlite resin),
respectively with imidazole. Crystals of MMMI Im suitable for
⋅Im (mp= 36 ⁰C) and BMMI⋅Im (mp= 23 ⁰C) ILs have
Entry
Solvent
CDCl3
IL
C7
88
91
91
97
90
31
3
C4/C5
12
15
34
16
80
23
3
⋅
⋅
1
2
MMMI⋅Im
BMMI⋅Im
MMMI⋅Im
BMMI⋅Im
MMMI⋅Im
BMMI⋅Im
CDCl3
⋅
3
CD3OD
CD3OD
CD3CN
CD3CN
X-ray diffraction have been obtained from the slow
4
evaporation of MeCN solution. The structure of
5
[MMM⋅Im]⋅[H2O] is illustrated in Figure 2 together with
6
selected bond angles and distances. Crystal data are
summarized in Table S1 of the supporting information. It is
clear from Figure 2a that each imidazolium cation is in relative
-
strong contact with the imidazolate anion through π+ π-
7
[D6]DMSO MMMI⋅Im
8
[D6]DMSO
BMMI⋅Im
MMMI⋅Im
BMMI⋅Im
8
0
9
D2O
32
14
27
17
10
D2O
[a] Determined by 1H NMR spectroscopy by the integral of the singlet of the C7
methyl group and the C4/C5 hydrogen atoms. [b] Reaction conditions: RT,
without stirring, 0.2 M. Dieletric constants: CDCl3 (4.89); CD3OD (32.66); CD3CN
(37.5); [D6]DMSO (46.45) and D2O (78.36).
interaction.
Most important, the 1H-1H NOESY experiments indicate the
presence of intimate contact ion pairs in CD3CN and [D6]DMSO
at relative low concentrations (0.2 M), and even in D2O,
although at higher concentrations (1 M) (see Figures S29 and
S30 and S35 supporting information). These results suggest
that the H/D reaction is probably catalysed by the contact ion-
pair41 of MMMI
⋅Im and BMMI⋅Im as already observed for
BMMI ILs associated with hydrogen carbonate and prolinate
anions.42 However, in the case of the imidazolate anion
studied here strongly interacting with imidazolium cations,
there is no “extra” basic site to perform the catalytic H/D
exchange reaction. Note that in most of the cases traces of
Figure 2. X-Ray structure of MMMI⋅Im containing the water H-bonded (trapped)
in the IL network (a) and the quasi-staggered conformation of the imidazolium-
imidazolate ion pair (b). (O1H1AN11= 172 (2)º, O1-N11= 2.780(16) Å; O1H1BN9=
170(2)º, O1N9= 2.8335(17) Å).
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water are necessary to activate the catalytic active species to the imidazolium substitutions C6, C7, and C8 and also close
(Scheme 1).
to one the N of the imidazolate anion. Such structural
arrangement is similar to the solid state X-Ray diffraction
structure and the geometrics optimized by DFT calculations
(see below). Therefore, the confined water in this restricted
ionic environment is activated acting as a catalyst base for the
H/D exchange reaction (Scheme 1). This is a typical case of
guest@host complexes, in which a relatively small guest (H2O)
behaves as a unit with the host (IL pair). MDS corroborated the
existence of the π+ π- contact ion pairs and their interaction
-
with water (see below). Therefore, it appears quite probable
that the confined water is mediating the intermolecular H/D
exchange between the D-solvent and the H of the C-7 Me
group of the imidazolium cation, explaining the preferential
H/D exchange at C-7 rather than at C4/C5 (see Table 1).
Scheme 1. Proposed reaction paths for the H/D exchange promoted by the
confined water in the contact ionic pair
.
It is also worth to note that the addition of H2O (25 µL) to the
Moreover, in the case of [D6]DMSO, in which H/D exchange
degree is lower than in the other used organic solvents, we
NMR tube containing MMMI⋅Im in [D6]DMSO (1 M) shifts the
water proton signal from 7.18 ppm to 4.83 ppm. We have not
been able to detect the signal of residual H2O in [D6]DMSO
that is usually observed at 3.33 ppm43 in the 1H NMR Spectrum
(see Figure 5). This behaviour was confirmed by de 2H NMR
(see Figure S24) in which the signal of water is shifted from
6.77 to 4.82 ppm after the addition of H2O.
observed the water (at 7.27 ppm for MMMI
⋅Im and at 4.58
ppm for BMMI
⋅
Im) signal in the 1H NMR spectra (see Figure
S15-S16 in the supporting information). Note that this signal
can hardly be detected in the case of the other wet organic
solvents suggesting a very rapid H/D exchange of the D-
solvents and H2O leading to D2O. Very important, the HDO
1
signal could be observed in the H-1H NOESY experiments (see
Figure 3 and Figure S30-S33 in the supporting information) and
the cross over peaks indicate that this species is exchanging H
with the C7-methyl group.
Figure
3
.
1H-1H NOESY cross-peak of C7 and C4/C5; C12/13 and C10 and
Im].[HDO] in [D6]DMSO (1 M).
H2O/HDO of the supramolecular complex [MMMI
⋅
In addition, the 1H-1H NOESY results exhibit cation–anion
interaction patterns with higher cross-peak intensity,
corresponding to higher relative cross-relaxation rates,
between HDO and the hydrogens of the three methyl groups
of the imidazolium cation (Figure 4).
Figure 5. 1H NMR spectra of MMMI
addition (a), addition of 25 µL H2O (b).
⋅Im in [D6]DMSO (1 M) in 72h: without water
In addition, such an activation of water was corroborated by
the facile H/D exchange between MMMI Im dissolved in D2O,
⋅
dried, and afterwards treated by CHCl3 furnishing CDCl3 (see
Scheme 2 and Figures S19- S22 in the supporting information).
Scheme 2. IL Confined water as D transfer agent.
Figure 4. 1H-1H NOESY cross-peak of NCH3 (C6 and C8) and C4/C5; C12/13 and
In these cases, in which the ImILs/water interaction could be
detected by NMR, the IL seems to be ‘‘frozen’’ with the water
molecule in an IL cage. These arrangements might be
C10 and H2O/HDO of the supramolecular complex [MMMI
[D6]DMSO (1 M).
⋅Im]⋅[HDO] in
represented by
a guest@cage, because the water is
These interaction patterns correspond to the preferential sites
for cation–anion interactions, in which water is located close
completely surrounded by the guest during this short time
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period (NMR time scale).40 However, on longer time scales, the kcal.mol-1, and very similar to the X-ray structure from Figure
IL pairs can separate to produce free volume through which 2.
the guest (H2O) can escape from the IL ion pairs cage (Scheme Intra-ionic structural parameters (bond lengths, bond angles
3).
and torsion angles) are summarized in Tables S9-S11
(supporting information) and compared with X-ray data. Final
coordinates for all the calculated geometries are presented in
Tables S2-S8 from the supporting information.
The interaction energy of the ion pair with the water molecule
(17.3 kcal.mol-1) indicates strong hydrogen bonding of the
water proton to the anion’s nitrogen atom. The corresponding
distance of 1.66 Å is much shorter than in the X-ray structure
(1.89 and 1.95 Å) due to the fact that only a single ion pairs has
been considered in the calculation, whereas the water
molecules bridges two ion pairs in the solid state. However,
the O-H-N angles in the DFT and crystal structures are in nice
agreement (168.5° and 170°, respectively). It is worth to
mention that the distances between MMMI’s methyl groups
and the water oxygen correspond to weak hydrogen bonds.
Molecular dynamics simulations. We have performed MDS on
Scheme 3. Topological view for the formation of the monomeric guest (water -
blue)@host (contact ion pair – red) complex in “ wet” solvents.
The same supramolecular model can be extended to other
guests than water such as in the case of carbon dioxide for
which it has been reported that the cooperative network
(dispersive forces and hydrogen bonds) of classical
imidazolium ILs BMI⋅BF4 and BMI⋅PF6 is only marginally
disrupted and the cation-anion contact ion pair is unaffected
by the inclusion of CO2.44, 45 The formation of liquid clathrate in
ionic liquid-aromatic mixtures can be also described as
guest@host complex formation.46 Moreover, the same water
function can explain the oxidation of iron nanoparticles to FeO
nanoparticles in oxygen free ImILs,47 the stabilisation of
enzymes at high temperatures,48 or the H/D exchange in
deuterated solvents of classical 1-alkyl-3-methyl imidazolium
ILs,49 for example.
the MMMI⋅Im and BMMI⋅Im ion pairs coordinated by a single
water molecule in chloroform. Several structural aspects of
these aggregates are described below.
In Figure 7, we illustrate the time evolution of the shortest
distances between any atom of the cation and the anion as
well as the water molecule. Along the simulation time of 60 ns,
Figure 7 demonstrates that the ion pair formed by the
imidazolate anion with both cations remains stable in
chloroform. In addition, the water molecule maintains contact
with the ion pairs during the simulation. Figure 7 reveals only
short periods of larger separations between the cations and
the water molecule. Radial pair distribution functions g(r) for
all the atom pairs (cation-anion, cation-water, anion-water)
have been computed from the last 20 ns of the simulation
DFT calculations. The ion pair has been optimized first without
the inclusion of a water molecule employing DFT (Figure 6a
and Figure S36 in the supporting information). Two stable ions
pairs have been obtained, one containing an anti-parallel π+
-
π-
cation-anion stack, the other with an almost parallel π+
-
π-
cation-anion stacking. The anti-parallel configuration (Figure
6a) is energetically slightly favoured by 1.9 kcal.mol-1,
presenting a value of 93.9 kcal.mol-1 for the cation-anion
interaction.
containing the MMMI⋅
between 20 and 40 ns of the BMMI
Im/water system and for the period
Im/water simulation.
⋅
Figure 6. Optimized structure obtained by DFT of ionic pair of MMMI
the ionic pair MMMI Im (anti-parallel displaced) with water (b).
⋅Im (a) and
Figure 7. Time evolution of the minimum distances between the cation and
⋅
anion (green) and between the cation and the water molecule (red) in
chloroform solution. Left panel: MMMI⋅Im, right panel: BMMI⋅Im.
A single water molecule has been added to these ion pair
configurations. The optimized final structures are displayed in
Figures 6b and S36 (supporting information). It becomes
These functions correspond to probability distributions for
interatomic distances in the simulated systems with the
reference being an ideal gas at the same number density.
From the X-ray structure and the DFT calculations discussed
above, the water coordination has been revealed due to
hydrogen bonding between the water protons and the
negatively charged nitrogen atoms of the anion. In Figure 8,
evident that both configurations maintained the π+
However, starting with the parallel π+ π- stack, we observed a
tendency to anti-parallelize the two ring systems whereas the
anti-parallel π+ π- stack is conserved more stable by 1.3
-
π- stacking.
-
-
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we present the g(r) for these nitrogen atoms and the water Comparing the cation coordination of the water protons from
atoms. These correlations exhibit the features typical for Figures 9 and S37, we find larger amplitudes in the BMMI
strong hydrogen bonding with N-H distances of 1.84 Å (X-ray: system for the protons at C4 and C6 indicating the steric
1.89 and 1.95 Å, DFT: 1.66 Å) and N- O distances of 2.75 Å (X- interference of the butyl substitution at C1 for water contacts
ray: 2.78 and 2.83 Å, DFT: 2.73 Å). The integrals of the first at the hydrogens of C5 and C8. NMR has also revealed these
sharp peaks in these functions yield 0.5 hydrogens and differences as demonstrated by Figure S31.1.
oxygens consistent with the picture that on average one of the In Figures 10 and S38, we depicted these functions for the ion
water hydrogens is strongly coordinated to one of the anion’s pairs focusing on correlations between the cation’s and the
nitrogen atoms. Figure 8 also reveals that these findings are anion’s hydrogen atoms. Note that the g(r) for the ion pairs
independent on the choice of the cation.
from these figures are not affected by the added water
molecule. We compared these functions with those obtained
from simulations of the ion pair without water molecule in
chloroform (not shown here) and could not find any
differences. Thus, the water molecule is not intercalated
between cation and anion.
Figure 8. Radial pair distribution functions between the nitrogen atoms of the
anion and the protons (blue) and oxygens (red) of the water molecule. Full lines:
MMMI cation, dotted lines: BMMI cation.
From the spatial distribution functions (see graphical abstract),
the X-ray structure and the DFT calculations, it becomes
evident that the ion pair is maintained to a certain degree by
Figure 10. Radial distribution functions for distances between the cation’s
hydrogens and the anion’s H10 (left panel) and the anion’s H12 and H13 (right
π-stacking even when the water molecules are coordinated. panel) in the MMMI system.
These configurations are characterized by the H-H contacts
These figures exhibit short-range contacts between all the
obtained from NMR data as illustrated in Figures 3 and 4. In
Figure 9, we depict the H-H pair distributions for the protons
of cation and anion with water hydrogens for the MMMI
system, in Figure S37 (supporting information) for the BMMI
system. These function present sharper peaks for correlations
of the water protons with the anion’s hydrogens with the
shortest distances below 3 Å observed for the H12 and H13.
The g(r) involving the cation is very broad with lower
amplitudes and no significant differences between the various
hydrogens. However, peak maxima at 3.5 Å correspond well
with the detected correlations of these protons with water
hydrogens in the NMR signals from Figures 3 and 4.
combinations of hydrogen atoms as observed in the NMR
spectra. Distributions with the anion’s H10 proton exhibit
larger amplitudes than those involving the proton’s H12 and
H13. The g(r) involving the cation's ring protons H4 and H5 are
somewhat sharper and more intense the correlations for the
methyl protons H6, H7, and H8. Figure S38 demonstrates that
the butyl group affects these functions furnishing more
pronounced correlations at the N-methyl side of the cation as
observed above in the correlations with the water molecule.
Conclusions
Water traces in ImILs can be regarded as guest@host
supramolecular complexes with the water molecules trapped
inside the ionic network (constitute of contact ion pairs
+
formed by
-
- interaction) through strong H-bonds involving
the water hydrogens and the nitrogens of imidazolate anions.
These water interactions strongly interfere on the
supramolecular organization of the fluids. The supramolecular
guest@host complex is maintained in solution even in solvents
with high dielectric constants such as DMSO. The
supramolecular organization (H2O@ILpair) has been
corroborated by both experimental (NMR) and computational
chemistry. The water is confined in this restricted ionic
environment and behaves as base catalyst promoting the H/D
exchange reaction with both, the hydrogens of the
Figure 9. Radial distribution functions for distances between the water protons
and the hydrogens of the cation (left panel) and the anion (right panel) for the
MMMI system.
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imidazolium cation, and as well as other acidic compounds. D2O) δ 144.0, 139.0, 123.0, 121.4, 34.1, 7.4. ES-MS(+) (m/z)
This model might be very useful to rationalize and predict the elem. anal. calcd. for: C6H11N2+ 111.0922; found 111.0785. ES-
-
behaviour of physical and chemical processes occurring in MS(-) (m/z) elem. anal. calcd. for: C3H3N2 67.0302; found
“wet” ionic liquids. Therefore, the presence of activated water 67.0600.
in ILs should be taken into consideration when employing and 3-n-butyl-1,2-dimethyl-1H-imidazol-3-ium
imidazolate
analysing the physico-chemical properties of these fluids.
(BMMI⋅
Im):52
3-n-butyl-1,2-dimethyl-1H-imidazol-3-ium
chloride (3.77 g, 20 mmol) was eluted through the column to
resulting an orange semisolid (4.05 g, 92 % yield). 1H NMR (400
MHz, D2O) δ 7.63 (s, 1H), 7.24 (s, 1H), 7.21 (s, 1H), 7.02 (s, 1H),
4.00 (t, 2H, J = 7.3), 3.66 (s, 3H), 2.47 (s, 3H), 1.69 (m, 2H), 1.25
(m, 2H), 0.86 (t, 3H, J = 7.4). 13C NMR (101 MHz, D2O) δ 143.8,
137.3, 122.3, 121.9, 120.5, 47.7, 34.3, 30.8, 18.7, 12.7, 8.4.
NMR Experiments. All NMR experiments were performed on a
Bruker Avance 400 spectrometer equipped with a BBO 5 mm
probe with z-gradient operating at 400.06 MHz for 1H, and
100.46 MHz for 13C. Spectra were obtained at a probe
temperature of 298 K referenced to Me4Si under conditions for
1H (spectral width 6400 Hz with 32 K data points and zero filled
to 128 K to give a digital resolution of 0.05 Hz/pt). Chemical
shifts were reported in parts per million (ppm, δ) and
Experimental
Materials and instruments. All reagents were obtained from
Sigma-Aldrich and used without purification. Deuterated
solvents were purchased from Cambridge Isotope
Laboratories. The NMR samples were prepared by dissolving
the corresponding ionic liquid in 500 µL of deuterated solvent
and the analysis was carried out at 25 °C. Infrared spectra were
performed with an ALPHA Bruker FT-IR spectrometer. High
resolution mass spectrometry electrospray ionization (HRMS-
ESI) data, in a positive and negative mode, were collected
using a Micromass Q-Tof instrument. Samples were infused by
a 100 µL syringe at a flow rate of 30 µL min-1 for all samples.
Typical operating conditions were: a capillary voltage of 2980
V, a sample cone voltage of 30 V, an extraction cone voltage of
3.0 V, and a desolvation gas temperature of 60 °C. N2 was used
as the desolvation gas and deionized water as the solvent of
the samples.
1
referenced to solvent pick; CDCl3 (δ 7.26 in H and 77.0 in 13C),
1
1
D2O (δ 4.79 in H) [D6]DMSO (δ 2.50 in H and 39.43 in 13C),
1
1
CD3CN, (δ 1.94 in H and 1.39 in 13C) and CD3OD (δ 3.31 in H
and 49.00 in 13C). For 1H NMR spectra, multiplicities are
reported as s (singlet), d (doublet), t (triplet), q (quartet), quint
(quintet), sex (sextet),
m (multiplet), br (broad), or a
Synthesis of 1,2,3-trimethyl-1H-imidazol-3-ium iodide
(MMMI⋅
I):50 Methyl iodide (14.91 g, 105 mmol) was added at
combination of these. The 2D-NOESY spectra were recorded
using 256 F1 increments and 4096 F2 complex points. The
experimental data sets were zero-filled in both the F1 and F2
dimension to form a 4096 X 512 data matrix. The mixing time
was 800 ms and the delay between two experiments (d1) was 2
s. The resulting data were processed using a sine bell
transformation function (implemented in the Topspin2.1
software) in both dimensions prior to Fourier transformation.
room temperature under magnetic stirring to 1,2-
dimethylimidazole (9.61 g, 100 mmol), dissolved in acetonitrile
(30 mL). The exothermic reaction was controlled with an
external water-ice bath and the reaction mixture was stirred
for further 45 min. The resulting crystalline solid was filtered,
washed with small portions of cold acetonitrile and dried
under reduced pressure, leaving the desired 1,2,3-trimethyl-
1H-imidazol-3-ium iodide as colorless crystals (20.94 g, 88 %
yield). Melting point: 310-314 °C (dec.). 1H NMR (400 MHz;
D2O): δ 7.37 (s, 2H), 3.84 (s, 6H), 2.66 (s, 3H).
X-Ray
Diffraction
analysis.
Single
crystals
of
C9H16N4O [MMMI
⋅
Im] were obtained from slow evaporation of
a MeCN solution at RT. A suitable crystal was selected and [in
fomblin film on a micromount] on a SuperNova, Dual, Cu at
zero, Atlas diffractometer. The crystal was kept at 120(2) K
during data collection. Using Olex2,53 the structure was solved
with the olex2.solve54 structure solution program using Charge
Flipping and refined with the ShelXL55 refinement package
using Least Squares minimization. Crystal Data for C9H16N4O
(M =196.26 g.mol-1): monoclinic, space group P21/n (no.
14), a = 7.3864(4) Å, b = 12.0203(7) Å, c = 12.5938(7) Å, β =
103.725(6)°, V = 1086.24(11) Å3, Z = 4, T = 120(2) K, μ(CuKα) =
0.669 mm-1, Dcalc = 1.200 g/cm3, 4439 reflections measured
Synthesis
of
3-n-butyl-1,2-dimethyl-1H-imidazol-3-ium
chloride (BMMI
⋅
Cl): The ionic liquid was prepared according to
known procedures,51 to give a white crystalline solid. Melting
point: 94-96 °C. 1H NMR (400 MHz; CDCl3): δ 7.90 (d, 1H, J =
1.9), 7.66 (d, 1H, J = 1.9), 4.28 (t, 2H, J = 7.3), 4.07 (s, 3H), 2.85
(s, 3H), 1.81 (m, 2H), 1.39 (m, 2H), 0.96 (t, 3H).
General procedure of anion exchange: The corresponding
imidazolium salt (20 mmol) was dissolved in a minimum
amount of water and eluted through an ion exchange resin
column (Amberlite IRA 400, 100mL, basic form). Imidazole
(1.36 g, 20 mmol) was added to the resulting aqueous
corresponding imidazolium hydroxide solution and the water
was evaporated under reduced pressure.
(10.316° ≤ 2Θ ≤ 149.746°), 2149 unique (Rint = 0.0296, Rsigma
=
0.0272) which were used in all calculations. The final R1 was
0.0509 (I > 2σ(I)) and wR2 was 0.1456 (all data).
DFT calculations. Considering that the studied ionic pairs were
significantly influenced by dispersive interactions, Density
Functional Theory (DFT) calculations, using the long-range
corrected wB97X-D hybrid density functional were realized.56
This functional furnishes a good accuracy for calculations of
thermodynamic properties for bonded systems including non-
bonded interactions. The spAug-cc-pVTZ basis set was used for
1,2,3-trimethyl-1H-imidazol-3-ium imidazolate (MMMI⋅Im):
1,2,3-trimethyl-1H-imidazol-3-ium iodide (4.76 g, 20 mmol)
was eluted through the column to resulting a yellow semisolid
residue that has been re-crystallized with acetonitrile/ethyl
acetate, giving very hygroscopic pale yellow crystals (3.34 g, 94
1
% yield). H NMR (400 MHz; D2O): δ 7.2 (s, 1H), 6.85 (s, 2H),
6.71 (s, 2H), 3.32 (s, 6H), 2.05 (m, 3H); 13C NMR (101 MHz,
6 | J. Name., 2012, 00, 1-3
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Journal Name
ARTICLE
all atoms. This basis set is comprised by the cc-pVTZ basis set57
5. R. P. Matthews, T. Welton and P. A. Hunt, Phys. Chem. Chem.
Phys., 2014, 16, 3238-3253.
augmented with
s and p diffuse functions. Geometry
6. J. S. Wilkes and M. J. Zaworotko, J. Chem. Soc., Chem. Commun.,
1992, DOI: 10.1039/C39920000965, 965-967.
optimizations were conducted using the default algorithm with
the TIGHT convergence criteria, followed by frequency
calculations to ensure the nature of the stationary points. All
calculations were performed with the Gaussian 09 package.58
Molecular Dynamics Simulations. We have performed
molecular dynamics (MD) computer simulations on single ion
pairs and a single added water molecule in the solvent
chloroform. We considered ion pairs of the MMMI and BMMI
cations with the imidazolate anion. Force field parameters for
7. A. Garcia-Saiz, I. de Pedro, P. Migowski, O. Vallcorba, J.
Junquera, J. A. Blanco, O. Fabelo, D. Sheptyakov, J. C.
Waerenborgh, M. T. Fernandez-Diaz, J. Rius, J. Dupont, J. A.
Gonzalez and J. R. Fernandez, Inorg Chem, 2014, 53, 8384-8396.
8. A. Mele, G. Romanò, M. Giannone, E. Ragg, G. Fronza, G. Raos
and V. Marcon, Angew. Chem. Int. Ed., 2006, 45, 1123-1126.
9. H. Li, J. A. Boatz and M. S. Gordon, J. Am. Chem. Soc., 2008, 130,
392-393.
10. A. R. Choudhury, N. Winterton, A. Steiner, A. I. Cooper and K. A.
Johnson, J. Am. Chem. Soc., 2005, 127, 16792-16793.
11. Y. Wang and G. A. Voth, J. Am. Chem. Soc., 2005, 127, 12192-
12193.
12. B. A. Marekha, O. N. Kalugin and A. Idrissi, Phys. Chem. Chem.
Phys., 2015, 17, 16846-16857.
13. M. L. Sha, H. Z. Dong, F. B. Luo, Z. F. Tang, G. L. Zhu and G. Z.
Wu, J. Phys. Chem. Lett., 2015, 6, 3713-3720.
14. C. Spickermann, J. Thar, S. B. C. Lehmann, S. Zahn, J. Hunger, R.
Buchner, P. A. Hunt, T. Welton and B. Kirchner, J. Chem. Phys.,
2008, 129.
15. B. Kirchner, F. Malberg, D. S. Firaha and O. Holloczki, J Phys
Condens Matter, 2015, 27, 463002.
16. D. A. Turton, J. Hunger, A. Stoppa, G. Hefter, A. Thoman, M.
Walther, R. Buchner and K. Wynne, J. Am. Chem. Soc., 2009,
131, 11140-11146.
17. J. Dupont, J. Braz. Chem. Soc., 2004, 15, 341-350.
18. F. H. Allen, Acta Crystallogr. Sect. B: Struct. Sci., 2002, 58, 380-
388.
19. I. de Pedro, A. García-Saiz, J. Dupont, P. Migowski, O. Vallcorba,
J. Junquera, J. Rius and J. Rodríguez Fernández, Cryst. Growth
Des., 2015, 15, 5207-5212.
20. C. Roth, T. Peppel, K. Fumino, M. Köckerling and R. Ludwig,
Angew. Chem. Int. Ed., 2010, 49, 10221-10224.
21. B. A. Marekha, O. N. Kalugin, M. Bria and A. Idrissi, Phys. Chem.
Chem. Phys., 2015, 17, 23183-23194.
22. S. R. Prabhu and G. B. Dutt, J. Phys. Chem. B, 2015, 119, 10720-
10726.
23. M. A. Ab Rani, A. Brant, L. Crowhurst, A. Dolan, M. Lui, N. H.
Hassan, J. P. Hallett, P. A. Hunt, H. Niedermeyer, J. M. Perez-
Arlandis, M. Schrems, T. Welton and R. Wilding, Phys. Chem.
Chem. Phys., 2011, 13, 16831-16840.
the ions have been established within the AMBER directives as
59
described in
from geometries optimized quantum-
mechanically at the B3LYP//RHF6-311G(d,p) (cations) and
B3LYP//RHF6-311++G(d,p) (imidazolate) levels. Intramolecular
parameters for the methyl group at the cation's C7 have been
defined as in the toluene molecule.
The simulations have been performed with the GROMACS
4.5.5 package.60 We employed the NpT ensemble maintaining
the temperature at 298 K by velocity rescaling61 and the
pressure at 1 bar with the Parrinello-Rahman barostat.62 Bond
lengths were constrained by the LINCS63 and, in the case of the
water molecule, by the SETTLE algorithms.64 Equations of
motion have been integrated using a time step of 0.002 ps.
The PME65 method was utilized to correct for long-range
electrostatic interactions. A cut-off distance of 13 Å has been
applied.
The chloroform solvent was obtained as a cubic box containing
1000 molecules from the GROMACS Molecule & Liquid Data
Bases66 within the GAFF parameterization.67
The TIP3P model68 was employed for the water molecule.
Starting configurations have been generated simulating a
single cation with the imidazolate anion for 100 ps in a cubic
box with dimensions perfectly matching the size of the solvent
box. Afterwards, single water molecule was added before
solvating the system with the chloroform. If necessary, a short
energy minimization procedure was applied before simulating
for 60 ns. Density, inter- and intramolecular energy terms were
monitored during the simulations. The convergence of these
properties indicated that the systems were equilibrated within
a few nanosceconds.
24. T. Koddermann, C. Wertz, A. Heintz and R. Ludwig, Angew.
Chem. Int. Ed., 2006, 45, 3697-3702.
25. J. P. Armstrong, C. Hurst, R. G. Jones, P. Licence, K. R. J.
Lovelock, C. J. Satterley and I. J. Villar-Garcia, Phys. Chem. Chem.
Phys., 2007, 9, 982-990.
26. K. R. J. Lovelock, A. Deyko, P. Licence and R. G. Jones, Phys.
Chem. Chem. Phys., 2010, 12, 8893-8901.
Acknowledgements
Thanks are due to CNPq, CAPES and FAPERGS (Brazil) for
partial financial support.
27. K. R. Seddon, A. Stark and M. J. Torres, Pure Appl. Chem., 2000,
72, 2275-2287.
28. J. Jacquemin, P. Husson, A. Padua and V. Majer, Green Chem.,
2006, 8, 172-180.
Notes and references
1. J. Dupont, Acc. Chem. Res., 2011, 44, 1223-1231.
2. S. J. Zhang, J. Sun, X. C. Zhang, J. Y. Xin, Q. Q. Miao and J. J. 29. U. Schröder, J. D. Wadhawan, R. G. Compton, F. Marken, P. A. Z.
Wang, Chem. Soc. Rev., 2014, 43, 7838-7869.
3. R. Ferraz, L. C. Branco, C. Prudencio, J. P. Noronha and Z.
Petrovski, ChemMedChem, 2011, 6, 975-985.
4. P. A. Hunt, C. R. Ashworth and R. P. Matthews, Chem. Soc. Rev.,
2015, 44, 1257-1288.
Suarez, C. S. Consorti, R. F. de Souza and J. Dupont, New J.
Chem., 2000, 24, 1009-1015.
30. D. Fu, X. Sun, J. Ou and S. Zhao, J. Chem. Eng. Data, 2006, 51,
371-375.
This journal is © The Royal Society of Chemistry 20xx
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ARTICLE
Journal Name
31. N. Hollingsworth, S. F. Taylor, M. T. Galante, J. Jacquemin, C.
Longo, K. B. Holt, N. H. de Leeuw and C. Hardacre, Angew.
Chem. Int. Ed., 2015, 54, 14164-14168.
32. S. F. R. Taylor, C. McCrellis, C. McStay, J. Jacquemin, C.
Hardacre, M. Mercy, R. G. Bell and N. H. de Leeuw, J. Solution
Chem., 2015, 44, 511-527.
33. S. Feng and G. A. Voth, Fluid Phase Equilib., 2010, 294, 148-156.
34. T. Mendez-Morales, J. Carrete, O. Cabeza, L. J. Gallego and L. M.
Varela, J Phys Chem B, 2011, 115, 6995-7008.
35. L. Cammarata, S. G. Kazarian, P. A. Salter and T. Welton, Phys.
Chem. Chem. Phys., 2001, 3, 5192-5200.
36. M. Brehm, H. Weber, A. S. Pensado, A. Stark and B. Kirchner,
Phys. Chem. Chem. Phys., 2012, 14, 5030-5044.
37. P. Stange, K. Fumino and R. Ludwig, Angew. Chem. Int. Ed.,
2013, 52, 2990-2994.
38. J. M. Lehn, Angew. Chem. Int. Ed., 1988, 27, 89-112.
39. J. M. Lehn, Angew. Chem. Int. Ed., 1990, 29, 1304-1319.
40. N. J. Turro, Proc. Natl. Acad. Sci. U. S. A., 2005, 102, 10765-
10765.
41. H. K. Stassen, R. Ludwig, A. Wulf and J. Dupont, Chem. Eur. J.,
2015, 21, 8324-8335.
Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd,
E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi,
J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S.
Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J.
E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G.
Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S.
Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J.
Cioslowski, and D. J. Fox, Journal, 2013.
59. J. de Andrade, E. S. Boes and H. Stassen, J. Phys. Chem. B, 2002,
106, 13344-13351.
60. B. Hess, C. Kutzner, D. van der Spoel and E. Lindahl, J. Chem.
Theory Comput., 2008, 4, 435-447.
61. G. Bussi, D. Donadio and M. Parrinello, J. Chem. Phys., 2007,
126, AN:014101.
62. M. Parrinello and A. Rahman, J. Appl. Phys., 1981, 52, 7182-
7190.
63. B. Hess, H. Bekker, H. J. C. Berendsen and J. Fraaije, J. Comput.
Chem., 1997, 18, 1463-1472.
64. S. Miyamoto and P. A. Kollman, J. Comput. Chem., 1992, 13,
952-962.
42. M. Zanatta, A. L. Girard, N. M. Simon, G. Ebeling, H. K. Stassen,
P. R. Livotto, F. P. dos Santos and J. Dupont, Angew. Chem. Int. 65. U. Essmann, L. Perera, M. L. Berkowitz, T. Darden, H. Lee and L.
Ed., 2014, 53, 12817-12821. G. Pedersen, J. Chem. Phys., 1995, 103, 8577-8593.
43. H. E. Gottlieb, V. Kotlyar and A. Nudelman, J. Org. Chem., 1997, 66. C. Caleman, P. J. van Maaren, M. Y. Hong, J. S. Hub, L. T. Costa
62, 7512-7515. and D. van der Spoel, J. Chem. Theory Comput., 2012, 8, 61-74.
44. M. C. Corvo, J. Sardinha, S. C. Menezes, S. Einloft, M. Seferin, J. 67. J. M. Wang, R. M. Wolf, J. W. Caldwell, P. A. Kollman and D. A.
Dupont, T. Casimiro and E. J. Cabrita, Angew. Chem. Int. Ed.,
2013, 52, 13024-13027.
45. M. C. Corvo, J. Sardinha, T. Casimiro, G. Marin, M. Seferin, S.
Einloft, S. C. Menezes, J. Dupont and E. J. Cabrita,
ChemSusChem, 2015, 8, 1935-1946.
Case, J. Comput. Chem., 2004, 25, 1157-1174.
68. W. L. Jorgensen, J. Chandrasekhar, J. D. Madura, R. W. Impey
and M. L. Klein, J. Chem. Phys., 1983, 79, 926-935.
1
46. J. D. Holbrey, W. M. Reichert, M. Nieuwenhuyzen, O. Sheppard,
C. Hardacre and R. D. Rogers, Chem. Commun., 2003, 476-477.
47. B. C. Leal, J. D. Scholten, M. C. Alves, J. Morais, I. de Pedro, L.
Fernandez Barquin and J. Dupont, Inorg. Chem., 2016, 55, 865-
870.
48. P. Lozano, T. de Diego, D. Carrie, M. Vaultier and J. L. Iborra,
Chem. Commun., 2002, 692.
49. R. Giernoth and D. Bankmann, Eur. J. Org. Chem., 2008, DOI:
10.1002/ejoc.200700784, 2881-2886.
50. A. Furstner, M. Alcarazo, R. Goddard and C. W. Lehmann,
Angew. Chem. Int. Ed., 2008, 47, 3210-3214.
51. V. Farmer and T. Welton, Green Chem., 2002, 4, 97-102.
52. X. Chen, X. Li, H. Song, Y. Qian and F. Wang, Tetrahedron Lett.,
2011, 52, 3588-3591.
53. O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard and
H. Puschmann, J. Appl. Crystallogr., 2009, 42, 339-341.
54. R. J. Gildea, L. J. Bourhis, O. V. Dolomanov, R. W. Grosse-
Kunstleve, H. Puschmann, P. D. Adams and J. A. K. Howard, J.
Appl. Crystallogr., 2011, 44, 1259-1263.
55. G. M. Sheldrick, Acta Crystallogr. Sect. A, 2008, 64, 112-122.
56. J. D. Chai and M. Head-Gordon, Phys. Chem. Chem. Phys., 2008,
10, 6615-6620.
57. R. A. Kendall, T. H. Dunning and R. J. Harrison, J. Chem. Phys.,
1992, 96, 6796-6806.
58. G. W. T. M. J. Frisch, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J.
R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A.
Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,A. F.
Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M.
Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A.
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