New N-methylimidazolium hexachloroantimonate: Synthesis, crystal structure, Hirshfeld surface and catalytic activity of in cyclopropanation of stryrene

Article abstract of DOI:10.1016/j.inoche.2020.108291

The N-methylimidazolium hexachloroantimonate salt Cl₆Sb·C₄H₇N₂ (MIMSb), was prepared and fully characterized. In ¹H NMR spectrum, the N-H proton shifted to downfield because of the presence of SbCl₆^? and appears as a triplet at 13.19 ppm. Characterization with IR spectroscopy shows strong absorption band at around 699 cm^?1 which is attributed to Sb?Cl stretching. Furthermore, UV–visible analysis at high concentrations in DMSO suggested that MIMSb interacts with DMSO leading to an absorption in visible region at λ_max of 426 nm. Electrochemical characterization using cyclic voltammetry demonstrates three redox processes with reduction peaks at 0.69, ?0.13 and ?0.50 V. Finally, molecular structure of the product was determined by X-ray diffraction analysis. The crystal structure determination was carried out with Mo-Kα X-ray and data measured at 100 K. The title compound crystallizes in monoclinic P21/c space group with unit cell parameters a = 7.1131 (5) ?, b = 12.4436 (9) ?, c = 14.1658 (11) ?, V = 1241.86 (16) ?³ and Z = 4. The crystal packing is stabilized by H—Cl interaction. The analysis of intermolecular interactions was realized through the mapping of contact descriptors d_norm, shape-index and the fingerprint reveling that the most significant contribution to the Hirshfeld surface (69.4%) is from H—Cl contacts. Finally, the catalytic activity of MIMSb was probed in the cyclopropanation of styrene with ethyl diazoacetate.

Full text of DOI:10.1016/j.inoche.2020.108291

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Short communication
New N-methylimidazolium hexachloroantimonate: Synthesis, crystal struc-
ture, Hirshfeld surface and catalytic activity of in cyclopropanation of stryrene
Koffi Sénam Etsè, Guillermo Zaragoza, Frédéric Boschini, Abdelfattah
Mahmoud
PII:
S1387-7003(20)30881-9
DOI:
https://doi.org/10.1016/j.inoche.2020.108291
INOCHE 108291
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Inorganic Chemistry Communications
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5 October 2020
5 October 2020
Please cite this article as: K. Sénam Etsè, G. Zaragoza, F. Boschini, A. Mahmoud, New N-methylimidazolium
hexachloroantimonate: Synthesis, crystal structure, Hirshfeld surface and catalytic activity of in cyclopropanation
of stryrene, Inorganic Chemistry Communications (2020), doi: https://doi.org/10.1016/j.inoche.2020.108291
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New N-methylimidazolium hexachloroantimonate: Synthesis, crystal
structure, Hirshfeld surface and catalytic activity of in
cyclopropanation of stryrene
Koffi Sénam Etsèa, Guillermo Zaragozab, Frédéric Boschinic, Abdelfattah Mahmoudc*
a Laboratory of Medicinal Chemistry, Center for Interdisciplinary Research on Medicines (CIRM), University of Liège,
Quartier Hôpital B36 Av. Hippocrate 15 B-4000 Liège, Belgium
b
Unidade de Difracción de Raios X, RIAIDT, Universidade de Santiago de Compostela, Campus VIDA, 15782
Santiago de Compostela, Spain
c GREENMAT, CESAM, Institute of Chemistry B6, University of Liège, 4000, Liège, Belgium
*Corresponding authors: abdelfattah.mahmoud@uliege.be
Abstract
The N’-methylimidazolium hexachloroantimonate salt Cl6Sb·C4H7N2 (MIMSb), was prepared and
1
fully characterized. In H NMR spectrum, the N-H proton shifted to downfield because of the
presence of SbCl6⁻ and appears as a triplet at 13.19 ppm. Characterization with IR spectroscopy
shows strong absorption band at around 699 cm−1 which is attributed to Sb−Cl stretching.
Furthermore, UV-visible analysis at high concentrations in DMSO suggested that MIMSb
interacts with DMSO leading to an absorption in visible region at λmax of 426 nm. Electrochemical
characterization using cyclic voltammetry demonstrates three redox processes with reduction peaks
at 0.69, -0.13 and -0.50 V. Finally, molecular structure of the product was determined by X-ray
diffraction analysis. The crystal structure determination was carried out with Mo-Kα X-ray and
data measured at 100 K. The title compound crystallizes in monoclinic P21/c space group with unit
cell parameters a = 7.1131 (5) Å, b = 12.4436 (9) Å, c = 14.1658 (11) Å, V = 1241.86 (16) Å3 and
Z = 4. The crystal packing is stabilized by H---Cl interaction. The analysis of intermolecular
interactions was realized through the mapping of contact descriptors dnorm, shape-index and the
fingerprint reveling that the most significant contribution to the Hirshfeld surface (69.4%) is from
H---Cl contacts. Finally, the catalytic activity of MIMSb was probed in the cyclopropanation of
styrene with ethyl diazoacetate.
Keyword: imidazolium salt, antimony, crystal structure, Hirshfeld surface, cyclic voltammetry,
cyclopropanation.

1. Introduction
The class of ionic liquids (ILs) is well known in organic and organometallic chemistry for several
applications [1]. The well known and most used ILs are based on the imidazole heterocycle [2–4].
Numerous application of these salts as solvent [5,6], in Beckmann rearrangement [7], as
electrolytes for electrochemical capacitor [8] and exhibiting biological activity [9,10], catalytic
activity in various organic reactions [11–16] and anti-corrosion properties [3] are reported.
Furthermore, ILs are recognized as important precursors in the synthesis of N-heterocyclic
carbenes (NHCs) and their derivatives [17,18]. The interaction of the organic cation with the
different anions plays a crucial role in the physical and chemical properties of the ILs [6,19–21].
For that purpose, several imidazolium salt with various anions X⁻ were X is Cl, Br, I5, I3, CF3SO3,
BBr4, Al2Cl7, AlCl4, SnCl3, SnCl5, MoCl6,WCl7, TiCl5, SbCl6 are described [22]. Generally, the
imidazolium ionic liquids (IMILs) are synthesized by reaction of alkyl halide with imidazole
derivatives or by direct cyclisation starting from a diamine [23–25]. In order to obtain various
IMILs containing others counter ion, anion metathesis reaction is generally performed [26].
Recently, our group has been interest in alkylcarbonium hexachloroantimonate (2) described as
strong alkylation agent of week organic base as sulfonamide developed by Oishi and Meerwein
[27–29]. Since sulfonamides are recognized as inert towards common alkylation agents as well as
triethyloxonium tetrafluoroborate, the reagent 2 is therefore suggested to be used as alkylation
agent to prepare precursors salt of new family of N-heterocyclic carbene (NHC) based on
benzothiadiazine heterocycle like that reported by Jonek et al. [30]. The alkylation performance of
ethylcarbonium hexachloroantimonate on N-methylimidazol was examined. In best of our
knowledge, no 1-alkyl-3-methylimidazolium hexachloroantimonate salts have been reported using
alkylcarbonium hexachloroantimonate as reactant. The 1-butyl-3-methylimidazolium
hexachloroantimonate for instance, is generally prepared by reaction of 1-butyl-3-
methylimidazolium chloride with SbCl5 [22].
In the present paper, we report the NMR, IR, cyclic voltammetry, UV-visible characterization and
the crystal structure of the product of the reaction of N-methylimidazol with ethyl carbonium
hexachloroantimonate. Moreover, intermolecular contacts were analyzed using Hirshfeld surface
and exposed. Finally, the catalytic performance of the obtained imidazolium salt was examined in
the cyclopropanation reaction of styrene.

2. Experimental
The synthesis of the compounds described herein are realized under inert atmosphere of nitrogen.
Dry dichloromethane used as solvent was distillated using calcium hydride [31] and deoxygenated
prior to use in the reaction. The chemicals SbCl5, N-methylimidazol and deuterated solvents were
obtained from Sigma-Aldrich (Belgium) or Eurisotop (France) and used as received. Bruker DRX
NMR spectrometer was used to record proton and carbon NMR spectra at the working frequencies
of 400.13 and 100.61 Megahertz respectively. The chemical shifts are given in parts per million
(δ) related to the tetramethylsilane and in respect from the residual solvent peaks ((CH3)2CO: 2.05
ppm; (CH3)2CO: 29.84, 206.26 ppm; (CD3)2CO: 30.60, 205.87 ppm) [32] or TMS. The coupling
constants are expressed in Hertz and the spin multiplicities are indicated employing s, d, t and m
symbols for singlet, doublet, triplet and multiplet respectively.
2.1.
Synthesis
Diethoxycarbonium hexachloroantimonate 2 was first obtained by adding drop wise a triethyl
orthoformate (17 mmol, 1 eq, 2.8 ml) to antimony pentachloride (34 mmol, 2 eq, 10 g) in solution
in dry deoxygenated dichloromethane (50 ml) at 0 °C. After the addition, the mixture is stirred for
2 hours. At the end of the reaction, the white precipitate was collected by filtration and used directly
to the next step without further purification.
MIMSb was obtained by adding the early obtained diethoxycarbonium hexachloroantimonate
(1mmol, 1eq, 747.12 mg) to dry and deoxygenated dichloromethane solution of methylimidazol
(1mmol, 1eq, 82.2 mg). After 5 min of stirring, all the suspension is dissolved leading to uncolored
solution. At the end of the reaction (1h) the white precipitate is collected by filtration and dry over
vacuum.
White powder, yield 91 %.1H NMR (400 MHz, Acetone-d6, δ, ppm) 13.19 (t, J = 68 Hz, 1H), 9.13
13
(s, 1H), 7.78 (s, 2H), 4.15 (s, 3H). C NMR (101 MHz, Acetone-d6, δ, ppm) 135.95, 123.61,
119.95, 35.77. Tf: 172-174 °C. IR: ῡ (cm–1) 3378, 3141, 1582, 1549, 1085, 699. UV/Vis (DMSO,
λmax, nm): 273.
2.2.
IR and UV-visible analysis
UV-Visible spectrophotometer HP 8453 (Hewlett Packard, Waldbronn, Germany) equipped with
diode array detector was used to record the spectrum at ambient temperature. FT-IR spectrometer

IS5 instrument (Thermo Scientific) interfaced with an ID7 ATR module equipped with a
monolithic diamond crystal was used to register the infrared spectrum of the compound.
2.3.
Cyclic voltammetry
Electrochemical characterization was carried out by recording the cyclic voltammograms of the
compound at room temperature using a Bio-Logic SP-200 potentiostat. The traditional 3-electrode
procedure with the working and counter electrodes consisting in two platinum foils (1 cm2) and a
REF361 Ag/AgCl as reference electrode were used. For the analysis, 10 mg of MIMSb was
dissolved in a 0.1 M solution of (Bu4N)(ClO4) in dichloromethane (30 mL) and degazed during 10
min with nitrogen flow. Cyclic voltammograms were finally recorded in the voltage range of -1.5
to +2 V vs. Ag/AgCl and scan rate set at 100 mV.s−1.
2.4.
Crystal growth
Diluted solution of MIMSb (20 mg) in a mixture of acetone and dichloromethane kept at 6 °C for
2 weeks allow formation of monocrystals suitable for X-ray diffraction analysis. Crystals obtained
in 1 cm diameter tube were further isolated for analysis.
2.5.
X-ray crystallography analyses
Crystal data were collected using procedures we previous reported [33] on a Bruker APPEX II
diffractometer [34]. For molecular graphics presentation ORTEP for Windows [35] and Mercury
[36] software was used. Finally, Crystallographic data for MIMSb have been deposited at the
Cambridge Crystallographic Data Centre with the numbers CCDC-2021229.
3. Results and discussion
3.1.
Synthesis and NMR analysis
The reaction of N-methylimidazol with diethoxycarbonium hexachloroantimonate was performed
at room temperature in dry deoxygenated dichloromethane (Figure 1). At the end of the reaction,
the white precipitate was collected by filtration and characterized. Surprisingly, the analysis of
NMR spectrum did not confirm the formation of the desired N-ethyl N’-methylimidazolinium

hexachloroantimonate salt. Indeed, the absence of signals that can be attributed to the ethyl
substituent suggested the formation of N’-methylimidazolinium hexachloroantimonate (Figure 1).
N
N
SbCl6
SbCl6
O
CH2Cl2
3
x
N
N
N2, 1.5 h, r.t.
O
N
NH
1
2
SbCl6
MIMSb
Figure 1. Preparation pathway of MIMSb.
The comparison of the 1HNMR spectrum of the product with that of the N-methylimidazol is shown
in Figure 2. The proton spectrum of the product shows an interesting triplet signal at 13.19 ppm
assignable to N-H proton shifted downfield as a consequence of the electronic effect of the neighbor
SbCl6 group. The signal at 9.13 ppm is attributed to the C3-H proton link to the carbon atom located
between the two nitrogen atoms of the heterocycle. We can observe that the formation of the salt
induce a shift of the methyl protons from 3.68 ppm in the starting reactant to 4.15 ppm in the
product.

Figure 2. Compared 1H NRM spectra of MIMSb in black (a) and methylimidazole in red (b)
realized in Acetone-d6 at 298 K.
To best of our knowledge, in contrary to di-alkylimidazolium ILs, structural description of N-
−
−
−
−
methylimidazolium comprising AsF6 , SbF6 , NbF6 and TaF6 anions is not reported. The
structurally closer 1-ethyl-3-methylimidazolium (EMIM+) ILs containing these anions are
described and exhibited a melting point (Tm) lower than 60 °C [37,38]. Di-alkylimidazolium ILs
containing hexachloroantimonate are less investigated in contrary to those containing
hexafluorophosphate. The 1-butyl-3-methylimidazolium (BMIM+) hexachloroantimonate is

described as orange solid when BMIMSbF6 and BMIMPF6 are liquid at room temperature [22]. It
is generally admitted that high size of the anion leads to low Tm however, the low Tm values for the
salts with [BF4] − anion are not consistent with this trend and suggesting the importance of other
electronic factors [39]. Mono-alkylimidazolium salts so called protic ionic liquids (PILs) are
generally obtained by reacting alkylimidazole with Brønsted acids [40,41]. The physicochemical
−
behaviors of PILs are quite different compare to conventional ILs [42]. It comes out that the SbCl6
ion plays a significant role in the physical properties of MIMSb for which the melting point is
around 171 °C. For comparison, the N-methylimidazolium hexafluorophosphate melt at 116°C.
The exact mechanism leading to the product in this reaction condition is still unclear. Nevertheless,
the formation of such compound would result from a second order elimination reaction E2 in
competition with the second order nucleophilic substitution SN2 that generally occurs during the
formation of N-alkyl N-methylimidazolium salts [43]. In the present case nucleophile alkylation by
dialkoxycarbonium ions described by Kabuß [27] and Heinrich [29] allows to propose the
mecanism sketched and illustrated in Figure 3. Indeed, the addition of the N-methylimidazole on
the dimethoxycarbonium leads to the formation of the intermediates I1 and I2. These intermediates
are kinetically favored. In the following step, the reaction Path 1 is described to be a
thermodynamically controlled reaction [27]. One can suggest that the intermediate I1 could lead to
the IL 3 and the ethyl formate 4 as by-product is unfavoured because of the steric hindrance. Oishi
and coworkers suggested that in the protonated product, the proton could come from the ethyl
groups and they overcame the obtention of the protonated product by using dimethylcarbonium
hexachloroantimonate [28]. Although this hypothesis was never formally confirmed, it can be note
that the steric hindrance is reduced when the methyl form of the alkylating agent is used. The
reaction Path 2 is probably kinetically favoured since it is observed that the alkylated product is
obtained during long reaction time in contrary to the protonated product. The intermediate I2 is
therefore favoured and the formation of the product MIMSb could result by the elimination of
diethoxy carbene I3. This unstable singlet carbene I3, generally undergoes 1,2-migration
rearrangement to give ethyl propionate 5 or could be hydrolyzed in air to form diethoxymethanol
6 [44,45].

O
O
SbCl6
H
N
N
1
2
Path 2
Path 1
O
O
O
N
N
N
SbCl6
N
H
SbCl6
H
O
I2
I1
O
O
O
N
N
N
N
H
H
O
SbCl6
I3
SbCl6
4
3
1,2-migration
O
MIMSb
H2O
O
O
O
OH
5
6
Figure 3. Plausible mechanism for the formation of compound 3 and MIMSb.
3.2.
Infrared spectroscopy
The vibrational characterization of the product was ensured using infrared (IR) spectroscopy. The
IR spectrum obtained with a monolithic diamond ATR crystal of the title compound is shown in
Figure 4. The spectrum of MIMSb shows a broad band in the range of 3500−3200 cm−1 attributed
to stretching vibrations of ῡ(N−H). The vibration around 3150−3100 cm−1 correspond to the
(=C−H) asymmetric and symmetric stretches of the imidazolium ring and the weak absorption
bands at 1582 and 1239 cm−1 may be attributed to ῡ(C=N) and ῡ(C−N) stretching. Finally, the
strong band observed in the fingerprint region around 699 cm−1 can be attributed to all the Sb−Cl
stretching of SbCl6⁻ counter ion.

Figure 4. Infrared spectrum of MIMSb.
3.3.
UV-visible analysis
The UV-visible characterization of the methyl imidazolinium hexachloroantimonate complex was
also investigated (Figure 5). The title compound was dissolved in dimethylsulfoxyde with good
solubility. The spectrum shows high absorption of MIMSb at λmax of 273 nm assigned to the π-π*
transition. At low concentration, only absorption at 273 nm and shoulder around 333 nm were
observed. However, for high concentrations, one more peak appears at λmax of 426 nm and the
solution takes flash yellow coloration. The intense absorption in visible region is probably the
consequence of MIMSb···DMSO interaction and reliable to n⎯π* transition.

Figure 5. UV-visible spectra of MIMSb solution in DMSO at different concentration.
3.4.
X-ray diffraction analyses
To complete the characterization, the exact molecular structure of the product was unambiguously
assured by X-ray analysis (Figure 6). Monocrystal of MIMSb suitable for X-ray diffraction
analyses was obtained by slow evaporation of dichloromethane/acetone diluted solution. The
crystal structure determination was carried out with Mo-Kα X-ray and crystal data are reported in
Table 1. The MIMSb crystallizes in the monoclinic P21/c space group with unit cell parameters a
= 7.1131 (5) Å, b = 12.4436 (9) Å, c = 14.1658 (11) Å, V = 1241.86 (16) Å3 and Z = 4.

Figure 6. Molecular structure of MIMSb showing intra molecular hydrogen bonds. The thermal
ellipsoids drawn at the 50% probability level.
In MIMSb, C1—C2 distance is characteristic of carbon–carbon double bond with a value of 1.360
(6) Å and the distances of C3—N bond of the carbon between the two nitrogen of the imidazolium
cycle are closer with 1.377 and 1.366 Å [46]. These results come probably from the positive charge
delocalized on N1—C3—N2 bonds. Bonds distances and angles (Table 2) indicate a typical
octahedral coordination for SbCl6⁻ anion. The most significative variations in bond distances are
oriented in Cl1— Sb—Cl4 direction where the chlorine atoms are in trans position. The lowest
Sb—Cl distance (2.3445 Å) is obtained for Sb—Cl1 while the highest bond length corresponds for
Sb—Cl4 (2.4018 Å) where Cl4 is implicated in attractive H-bond interaction with the imidazolium
H2N···Cl4 (Table 3). These bonds distances do not produce great distortion in Quadratic
Elongation terms (QE=1.001) but produce angular changes in respect to perpendicular chlorine
atoms, that affects to octahedral distortion in Angle Variance terms (AV = 1.72 °2) [47]. All angles
between Cl1 and perpendicular Cl atoms are greater than 90 °, especially Cl1-Sb1-Cl6 (92.88 °)
and all angles between Cl4 and perpendicular Cl atoms are less than 90 ° particularly Cl4-Sb1-Cl3
(87.46 °) (Table 2).

Table 1. Crystal data of MIMSb
Crystal data
Chemical formula
Mr
MIMSb
Cl6Sb·C4H7N2
417.58
Crystal system
Space group
Temperature (K)
a (Å)
Monoclinic
P21/c
100
7.113 (5)
12.443 (1)
14.165 (1)
1241.86 (2)
4
b(Å)
c (Å)
V(Å3)
Z
Radiation type
μ(mm−1)
Mo-Kα radiation
3.47
Crystal size (mm)
Data collection
Diffractometer
0.15 × 0.06 × 0.03
Bruker APEX-II
Multi-scan
Absorption correction
SADABS2014/5 - Bruker AXS area detector scaling
and absorption correction
0.807, 0.914
Tmin, Tmax
(sin θ/λ)max (Å−1)
0.667
H atoms treated by a mixture of independent and
constrained refinement
3079/0.047
H-atom treatment
Independent reflections/Rint
R[F2 > 2σ(F2)], wR(F2), S
Δρmax/Δρmin (eÅ−3)
0.031, 0.067, 1.06
0.93, −0.75

Table 2. Selected bond lengths (Å) for MIMSb.
Bond lengths (Å)
C1—C2
1.360 (6)
1.377 (5)
0.95
C4—H4B
C4—H4C
N2—H2N
Sb1—Cl1
Sb1—Cl6
Sb1—Cl5
Sb1—Cl2
Sb1—Cl3
Sb1—Cl4
0.98
C1—N1
0.98
C1—H1
0.77 (6)
C2—N2
1.366 (6)
0.95
2.3445 (10)
2.3581 (10)
2.3597 (11)
2.3667 (10)
2.3739 (10)
2.4018 (10)
C2—H2
C3—N2
1.314 (6)
1.330 (5)
0.95
C3—N1
C3—H3
C4—N1
1.452 (5)
0.98
C4—H4A
Angles (o)
Cl1-Sb1-Cl2
Cl1-Sb1-Cl3
Cl1-Sb1-Cl5
Cl1-Sb1-Cl6
90.79(4)
90.61(4)
90.31(4)
92.88(4)
Cl4-Sb1-Cl2
Cl4-Sb1-Cl3
Cl4-Sb1-Cl5
Cl4-Sb1-Cl6
89.65(4)
87.46(4)
89.25(4)
89.06(4)
Table 3. Hydrogen-bond geometry (Å, °)
D—H···A
D—H (Å)
0.95
H···A (Å)
D···A (Å)
3.738 (4)
3.499 (4)
3.719 (5)
3.544 (4)
3.754 (5)
3.868 (5)
3.332 (4)
D—H···A ( °)
C1—H1···Cl3i
C2—H2···Cl2ii
C2—H2···Cl5
C3—H3···Cl4iii
C4—H4A···Cl5i
C4—H4C···Cl6iv
N2—H2N···Cl4
2.87
2.91
2.8
152.4
121.2
162.7
155.5
150.5
152.6
137 (5)
0.95
0.95
0.95
2.66
2.87
2.97
2.73 (6)
0.98
0.98
0.77 (6)
Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, −y+3/2, z+1/2; (iii) −x+2, y−1/2, −z+1/2; (iv) x,
y−1, z.

The crystal packing of the compound MIMSb shows that this compound is stabilized by multiple
intermoleculars short hydrogen interactions H···Cl (Figure 7.a). The hydrogens bonds geometries
are reported in Table 3. Other interesting intermolecular interaction is produced between Cl and
aromatic ring (Figure 8). The distance from the Cl2 atom to the ring centroid is 3.368 Å (r) and the
distance from Cl2 atom and nearest atom of the imidazolium ring is 3.373 Å (r’). These distandes
indicate Cl-π "face on" interaction (|r-r´| ≤ 0.3 Å) is produced between Cl2 and the imidazolium
heterocycle. This interaction is similar to those analized by Imai et al. [48] to avoid unfavorable
molecular contatcs in protein-ligand complexes.

Figure 7. Hydrogen bonds interactions of the imidazolium ring with surrounding
hexachloroantimonate ions (a) and hydrogen bonds in crystal packing of MIMSb viewed along c
axes (b).

Figure 8. Cl-Pi interactions.
The correlation between the presence, the number of H-bonds and the properties of ILs have been
examined by Dong et al. [49]. As observed in the case of MIMSb, it turns out that the main
characteristic of PILs is the presence of N—H···Anion strong HBs and the proton transfer, leading
to the existence of proton-donor and proton-acceptor sites and the formation of H-bonding network
that could modify notably the ILs properties [49]. The present results are in line with the X-ray
−
−
studies in the case of some PF6 and SbF6 imidazolium ILs where the ions are also connected by
π interaction [50,51]. The regular network observed in MIMSb thanks to H-bonding network and
Cl-π interaction are at the origin of compact stacking, low void volume and therefore act as
−
counterpoise for the size effect of the SbCl6 anion in the MIMSb Tm value.
3.5.
Hirshfeld surface analysis
The intermolecular interactions were also evaluated using Hirshfeld surface (HS) analysis obtained
using the program CrystalExplorer 17.5 [52]. The transparency of the surfaces enables easier
observation and identification of the atoms involved in the different interactions. The maps of di
and de on molecular Hirshfeld surface of MIMSb are shown in Figure 9a and 9b. In the MIMSb,
C—H and N—H atoms are identified as nuclei closest to the surface leading to visible red spots on

the Hirshfeld surface mapped over di. In contrary, the red spots observed on the de surface are
essentially located around the SbCl6 group. Such observation demonstrates that the chlorine atoms
are the nearest external nuclei from the point of the surface behaving like acceptor group. High
resolution three-dimensional HS was further mapped over dnorm with a fixed colour scale of -0,2174
(red) to 1,0332 (blue) (Figure 9c-d). The short-contact descriptor dnorm of MIMSb revels red spots
on the surface resulting in distance shorter than the sum of the van der Waals radii (vdWr). The
pseudo-HS mapped over dnorm only around the imidazolium cycle shown in Figure 9c, highlight
the internal interactions between N2—H2N···Cl4 and C2—H2···Cl5 as red spots. When
considering the whole salt, the dominant interactions appear as red spots on the dnorm surfaces and
correspond to intermolecular C—H···Cl hydrogen bonds highlighted by dashed yellow lines. On
that surface, white and blue domains indicate distance equal and longer than that the sum of vdWr
respectively [53].
The HS of the title imidazolium salt mapped with shape-index (in the range -1.0 to 1.0 Å) was
obtained to explored others weak contacts (Figure 9e). On the shape-index surface of MIMSb,
convex blue and concave red regions indicates the presence of hydrogen-donor and hydrogen-
acceptor groups respectively [54, 55]. The presence of several red colored regions indicates weak
intermolecular interactions. Furthermore, the presence of one region with adjacent red and blue
triangles on the Shape index map indicates and confirms a presence of π···π interactions in the
crystal packing (Figure 8).

Figure 9. The Hirshfeld surface of MIMSb mapped over (a) di (0.9619 to 2.7009 Å), (b) de
(0.9638 to 2.6834 Å). (c) present the pseudo Hirshfeld surface mapped over dnorm of only the
imidazolium ion and (d) is for overall MIMSb using a fixed colour scale of -0.2174 (red) to
1.0332 (blue). The Cl···H contacts hydrogen bonds are highlighted by dashed yellow lines. (e)
Hirshfeld surfaces of MIMSb mapped with shape-index.

The existence of short intermolecular interactions in the crystal packing results in various contacts
points leading to voids in the crystal structure. Voids description are based on the sum of spherical
atomic electron densities at the appropriate nuclear position. All the interactions described in Table
3 and Figures 7-9, lead to interconnected voids throughout the material. The voids parameters of
the title compound were obtained thank to CrystalExplorer 17.5 program under 0.002. u.a. isovalue.
Figure 10 shows a view along a crystallographic axis of crystal voids of the imidazolium salt.
Calculations show very low void volume of 89.44 Å3 in the crystal. With the calculated void
volume, the porosity is low with a percentage of 7%. Total void area of 381.80 Å2, a globularity of
0.253 and asphericity value of 0.127 are obtained. As shown in Figure 10, the electron-density
isosurfaces are highly open as a result of the presence of many Sb—Cl···H contacts.
Figure 10. View along a crystallographic axis of crystal voids present in the title compound.
Total contribution of atom pairs contacts is resumed to form the two-dimensional fingerprint plots
of MIMSb (Figure 11). The decomposition atom pairwise of the fingerprint allow therefore to
identify the different contacts components present in the crystal packing. The results reveal that the

most significant contribution to the Hirshfeld surface (69.4%) is from H···Cl contacts, which
appear in the external region of the fingerprint plot (Figure 10b). The red spots in the middle of the
fingerprint histogram appearing near de = di ≃ 1.8–2.1 Å correspond to close Cl···Cl interplanar
contacts contributing to 14.7% of the total Hirshfeld surface (Figure 10c). H···H interactions with
3.2% appear as blue spikes in Figure 11f. Others N···Cl, N···H and C···C contacts contribute for
3.2, 1.7 and 0.6% respectively in the Hirshfeld surface (Figure 11g-i).
Figure 11. Total and decomposed two-dimensional fingerprint plots of compound MIMSb.
Various close contacts and their relative contributions are indicated.
3.6.
Cyclic voltammetry
The electrochemical properties of 0.5 mM dichloromethane solution of methylimidazolinium
hexachloroantimonate complex were explored by cyclic voltammetry (CV) using Bu4NClO4 as a
supporting electrolyte. The cyclic voltammogram of the first three cycles performed at the scan

rate of 100 mV.s-1 in the voltage range of -1.5 to +2 V vs. Ag/AgCl are shown in Figure 12. Three
redox processes were detected with reversible reduction peaks at 0.69, -0.13 and -0.50 V. In
contrary to other redox reactions, the reduction occurred at -0.50 V is more strong indication
probably the reduction of Sb(V) to Sb(III). The oxidation process shows two peaks to -0.1 and 1.35
V with lower intensity compared to the peaks recorded during the reduction which indicates that
the complex undergoes an irreversible reaction process which is due to the first-order formation-
dissociation equilibrium of the complex. Starting from the second cycle, we notice that the anodic
peak potentials moved toward the positive direction and the corresponding cathodic peak potentials
shifted slightly toward the negative values of the voltage.
Figure 12. Cyclic voltammogram of methylimidazolinium hexachloroantimonate in the voltage
range of -1.5 to +2 V at 100 mV.s–1 scan rate.
3.7.
Catalytic activity
The catalytic activity of the methylimidazolinium hexachloroantimonate was evaluated in
cyclopropanation reaction of styrene with ethyl diazoacetate (EtDA). At the end of the reaction,
the yields are determined by gas chromatography based on EtDA. Results show that the mixture of
cis and trans isomers of ester cyclopropane was obtained in good yield with 83% and 95% when

working at 60 and 100 °C respectively. By measuring the rate of nitrogen evolution monitored
during the cyclopropanation of styrene, results show clearly that the reaction performed at 100 °C
is faster. As shown in Figure 13, after one hour the addition of EtDA (5 h) only 25% yield of
cyclopropanes 7 are obtained at 60 °C in contrary to ∼ 70% at 100 °C. The slowness of the reaction
leads to the formation of high among (17%) of byproducts like diethylmaleate and fumarate (8).
Nevertheless, the trans ethyl 2-phenylcyclopropanecarboxylate was obtained as a major product
(Table 4).
Table 4. Catalytic evaluation of MIMSb in cyclopropanation of styrene.
H
CO2Et
EtO2C
MIMSb
T, -N2
CO2Et
+
+
N2
Ph
Ph
CO2Et
7
8
Cyclopropanes 6
Yield (%) cis/trans ratio
Dimers 7
Yield (%) cis/trans ratio
Temperature (°C)
60
87
95
0.48
0.53
13
5
1.72
2.85
100
Experimental conditions: MIMSb (0.005 mmol), styrene (2 mL) and EtDA (1 mmol) diluted with
styrene up to 1 mL and added in 4 h at 60 °C and 100 °C; 50 h total reaction time. Yield determined
by GC (relative errors are ± 5%).

Figure 13. Rate of N2 evolution measured during the cyclopropanation reaction catalyzed by
MIMSb at 60 °C and 100 °C.
4. Conclusion
The first attempt of the synthesis of new di-alkylimidazolium salt using diethoxycarbonium
hexachloroantimonate as alkylating agent is presented in this work. The reaction of N-
methylimidazol with diethoxycarbonium hexachloroantimonate leads to N-methylimidazolium
hexachloroantimonate (MIMSb) in contrary to the expected 1-ethyl-3-methylimidazolinium
hexachloroantimonate. A mechanism leading to the formation of MIMSb has been proposed and
described. The new IL has been fully characterized using NMR, IR, UV-visible spectroscopy and
cyclic voltammetry techniques. Furthermore, the molecular structure of the MIMSb is obtained by
X-ray diffraction analysis and the description of molecular interactions present in the crystal
packing were analyzed through the mapping of the Hirshfeld surface contacts descriptors and the
two-dimensional fingerprint. In contrary to the analogous ILs, MIMSb shows a relative high
melting point. Finally, in the catalytic test, MIMSb have shown good catalytic activity in the
cyclopropanation of styrene with ethyl diazoacetate. Thanks to these results, further investigations
are now under way focusing on the application of MIMSb as electrode material for secondary
batteries and as catalyst in oxidation reaction of alcohol and aldehyde.

Authors contributions statement
Koffi Senam Etse: Design and Synthesis, Writing - original draft, Investigation, Data curation,
Formal analysis, Conceptualization, Review & editing, Methodology. Guillermo Zaragoza: Data
curation, Crystal data collection and analysis. Abdelfattah Mahmoud: Data curation, Formal
analysis, Visualization, Investigation, Writing - review & editing.
Acknowledgements
The authors are grateful to the University of Liege and FRS_FNRS for equipment grants. A.
Mahmoud also thanks the Walloon Region for a Beware Fellowship Academia 2015-1, RESIBAT
n°1510399.
Data Availability Statement
The data related to the study and results presented herein are available from the authors upon
reasonable request.

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