Comparative study between 1-Propyl-3-methylimidazolium bromide and trimethylene bis-methylimidazolium bromide ionic liquids by FTIR/ATR and FT-RAMAN spectroscopies

Article abstract of DOI:10.1016/j.molstruc.2017.04.076

In this study, we synthesized two ionic liquids based on imidazolium: one is a monocationic and the other is a dicationic. They are respectively 1-Propyl-3-methylimidazolium bromide ([PrMIM⁺][Br^?]) and trimethylene bis-methylimidazolium bromide ([M(CH₂)₃IM²⁺][2Br^?]). The structures of these two ionic liquids which are composed of ions with atoms of the same nature were first identified by ¹H,¹³C NMR, and then compared in a study by FT-RAMAN and FTIR/ATR spectroscopies. FT-RAMAN spectras of the dicationic ionic liquid are richer in modes in the different spectral regions. Hence this richness seems to be a consequence of the passage from one to two rings in the imidazolium cation. In particular, the vibrational modes in the spectral ranges 700–600?cm^?1, 1700–1500?cm^?1 and 3200–2700?cm^?1 by FTIR/ATR seem to be sensitive to the change from mono to dicationic than in FT-RAMAN. The spectral range in which the intermolecular interactions are present (200-50?cm^?1) is a marker of differentiation between the mono and the dicationic. The spectral ranges on 1700–1200?cm^?1 and 3200–2700?cm^?1 also show signs of upheaval between our two samples. We can also notice that there are much more active modes in FT-RAMAN spectroscopy than in FTIR/ATR spectroscopy.

Full text of DOI:10.1016/j.molstruc.2017.04.076

Accepted Manuscript
Comparative study between 1-Propyl-3-methylimidazolium bromide and
trimethylene bis-methylimidazolium bromide ionic liquids by FTIR/ATR and FT-
RAMAN spectroscopies
Mohamed Kadari, El Habib Belarbi, Taqiyeddine Moumene, Serge Bresson, Boumediene Haddad,
Ouissam Abbas, Brahim Khelifa
PII:
S0022-2860(17)30513-6
10.1016/j.molstruc.2017.04.076
MOLSTR 23699
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
14 November 2016
15 April 2017
17 April 2017
Please cite this article as: Mohamed Kadari, El Habib Belarbi, Taqiyeddine Moumene, Serge
Bresson, Boumediene Haddad, Ouissam Abbas, Brahim Khelifa, Comparative study between 1-
Propyl-3-methylimidazolium bromide and trimethylene bis-methylimidazolium bromide ionic liquids
by FTIR/ATR and FT-RAMAN spectroscopies, Journal of Molecular Structure (2017), doi: 10.1016/j.
molstruc.2017.04.076
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ACCEPTED MANUSCRIPT
Highlights
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Synthesis of ionic liquids ([PrMIM ][Br ]), ([M(CH ) IM ][2Br ]).
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FTIR/ATR and FT-RAMAN spectroscopy study of previous ionic liquids.
Comparison between dicationic ionic liquid and monocationic ionic liquid.
Each ionic liquid has a specific vibrational behavior.
The passage from mono to dicationic is responsible of important vibrational changes.

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Comparative study between 1-Propyl-3-methylimidazolium bromide and
trimethylene bis-methylimidazolium bromide ionic liquids by FTIR/ATR and
FT-RAMAN spectroscopies
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Mohamed KADARI , El Habib BELARBI , Taqiyeddine MOUMENE , Serge BRESSON ,
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Boumediene HADDAD , Ouissam ABBAS , Brahim KHELIFA
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Laboratoire de Synthèse et Catalyse Tiaret LSCT, Univ Tiaret, BP 78 RP, 14000 Tiaret, Algeria
2Centre Wallon de Recherche Agronomique, CRA-W, Bâtiment Maurice Henseval, chaussée de
Namur, 24, 50030 Gembloux, Belgium.
Laboratoire de Physique des Systèmes Complexes, Université Picardie Jules Verne, 33 rue S Leu
80039 Amiens cedex, France
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Abstract:
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In this study, we synthesized two ionic liquids based on imidazolium: one is a monocationic and the
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other is a dicationic. They are respectively 1-Propyl-3-methylimidazolium bromide ([PrMIM ][Br ]) and
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trimethylene bis-methylimidazolium bromide ([M(CH ) IM ][2Br ]). The structures of these two ionic
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liquids which are composed of ions with atoms of the same nature were first identified by H, C NMR,
and then compared in a study by FT-RAMAN and FTIR/ATR spectroscopies.
FT-RAMAN spectras of the dicationic ionic liquid are richer in modes in the different spectral regions.
Hence this richness seems to be a consequence of the passage from one to two rings in the imidazolium
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cation. In particular, the vibrational modes in the spectral ranges 700 – 600 cm , 1700 – 1500 cm and 3200
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– 2700 cm by FTIR/ATR seem to be sensitive to the change from mono to dicationic than in FT-RAMAN.
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The spectral range in which the intermolecular interactions are present (200-50 cm ) is a marker of
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differentiation between the mono and the dicationic. The spectral ranges on 1700 – 1200 cm and 3200 –
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2700 cm also show signs of upheaval between our two samples. We can also notice that there are much
more active modes in FT-RAMAN spectroscopy than in FTIR / ATR spectroscopy.
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Keywords: monocationic and dicationic ionic liquids, imidazolium, RAMAN spectroscopy, FTIR/ATR
spectroscopy.
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1. Introduction:
Ionic liquids are liquids that consist almost exclusively of ions (an organic cation associated
with an organic or inorganic anion). They are a class of salts with melting point temperature below
a hundred degrees. J. M. Crosthwaite et al. noticed that the ionic liquids based on pyridinium
become liquid around the 80°C [1]. J. D. Holbrey and K. R. Seddon obtained the same results for
ionic liquids based on imidazole [2]. In addition to their low melting points, ionic liquids are
characterized by exceptional thermal stability, enabling their use for applications at high
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temperatures. They have a good ionic conductivity, generally of the order of 10 .S.m [3]. Their
electrochemical window is wide as they can provide tension between 5-6 V [4], which has been
exploited in the field of fuel cells [5, 6]. The Ionic liquids have also remarkable solvation capacities
of organic and inorganic products comparable to polar solvents. Notwithstanding the fact that they
are used as solvents in the biocatalytic reactions [7], it is most interesting to note that their
physicochemical properties are adjustable by changing the nature of the anion and/or the cation
(alkyl chain).
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The applications of ionic liquids are dependent on their properties, while the latter dependent
on the nature of the cation and anion combination and the length of the alkyl chains incorporated on
the cation. The possible combinations of cations/anions are very numerous and continuously
evolving, such that in general the properties of ionic liquids are governed by Coulomb forces,
hydrogen bonding and Van der Waals interactions. In this paper, we will study two imidazolium-
based ionic liquids .
In our study of both ionic liquids: a monocationic and dicationic which are respectively 1-
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Propyl-3-methylimidazolium bromide ([PrMIM ][Br ]) and trimethylene bis-methyl imidazolium
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bromide ([M(CH ) IM ][2Br ]), the nature of atoms constituting the anions and cations of both
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(ILs) are similar. However the difference is that the cation of the monocationic (IL) is constituted of
a single imidazolium ring while the cation of the dicationic consists of two imidazolium rings. So
two singly charged cations linked by an alkyl chain and paired with two singly charged anions. In
this study, we wanted to compare the vibrational behavior of these two ILs. Research conducted on
the properties of ionic liquids and which is based on the understanding of the relationship between
the structure of the cation and that of the anion aims at obtaining (ILs) with better properties
whilst improving the theoretical model.
The study of the vibrational behavior of a material can be achieved by means of the following
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characterization techniques: FTIR spectroscopy, and RAMAN spectroscopy. These two non-
destructive techniques are complementary and represent the best performing and most widely used
tools. For monocationic ILs many studies have been carried out using these techniques [8, 9]. This
is not the case for dicationic ILs.
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2. Experimental
2.1. Reagents and materials
The reagents used in this study are 1-methylimidazole (98 wt.%), 1-bromopropane (99.5
wt.%). They were purchased from Fluka and used as received.
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2.2. NMR spectroscopy analysis
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H NMR (400 MHz), C NMR, spectra were recorded on a NMR 400 MHz spectrometer. The
chemical shifts (δ) are given in ppm and referenced to the internal solvent signal, TMS
(Tetramethylsilane) and CFCl , respectively.
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2.3. Synthesis and characterization of ionic liquids:
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2.3.1. Synthesis of ([PrMIM ][Br ]):
The synthesis was prepared according to procedures describe in the literature. Briefly, 1-
methylimidazole (6.79 ml, 85.26 mmol), and 1-bromopropane (9.87 ml, 89.03 mmol) were
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combined at a 1:1 ratio before being stired at 70°C for 6 hours. The [PrMIM ][Br ] was then washed
with ethyl acetate to remove any excess reactants or contaminants. Sebsequently,about 20 ml of
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ethyl acetate was added to the [PrMIM ] [Br ] and the mix shaken together in a separatory funnel.
After a few minutes, the mixture separated into two distinct layers;the top layer being ethyl acetate
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and all of the contaminants and the bottom layer was [PrMIM ] [Br ]. The top layer, which was
discarded later, was poured into a clean beaker. The bottom layer was saved in the original flask .
This washing procedure was repeated four times.
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2.3.2. Synthesis of ([M(CH ) IM ][2Br ]):
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In a flask of 100 ml, we prepared a mixture of 1-methyl imidazole (9.07 ml, 100 mmol) and
1,3-dibromopropane (5.21 ml, 49.98 mmol) and 23 ml of DMF. This reaction mixture is heated
under reflux with magnetic stirring for 4 hours while maintaining the temperature at 75°C. Bromide
trimethylene bis-methyl imidazolium was obtained as a slightly yellow solid (6.60g, 17.12 mmol)
with a yield of 63%.
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2.4. NMR results:
The spectra details are given below,
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H-NMR (CDCl ) δ (ppm) [PrMIM ][Br ] : 10.27 (1H, s, N CHN), 7.58 (1H, s, N CHCHNCH ),
3 H 3
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7.49 (1H, s, N CHCH), 4.26 (3H, s, NCH ), 1.95-1.93 (2H, m, N CH CH ), 1.87-1.85 (2H, m,
CH CH CH ), 0.91 (3H, t, J=6.8 Hz, N (CH ) CH ).
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C-NMR (CDCl ) δ (ppm) [M(CH ) IM ][2Br ]: 10.67 (CH CH CH ), 32.62 (CH CH CH ),
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36.62 (NCH ), 51.35 (N CH CH ), 122.32 (NCHCHN ), 123.75 (NCHCHN ), 137.01 (N CHN).
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2.5. FTIR/ATR and FT-RAMAN measurements
The measurements were realised in the Walloon Agricultural Research Center (CRA-W)
Belgium.
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2.5.1. FTIR/ATR measurements
All attenuated total reflectance Fourier transform mid-infrared (ATR/FTIR) spectra were
obtained on a Vertex 70-RAM II Bruker spectrometer (Bruker Analytical, Madison, WI) operating
with a Golden Gate TM diamond ATR accessory (Specac Ltd, Slough, UK).
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FTIR/ATR spectra [4000-600 cm ] were collected with a resolution of 1 cm by co-adding 64
scans for each spectrum. The OPUS 6.0 software for windows of Bruker Instruments was used for
instrument management.
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2.5.2. FT-RAMAN measurements
FT-RAMAN spectra were obtained on a Vertex 70-RAM II Bruker FT-RAMAN spectrometer.
This instrument is equipped with a Nd: YAG laser (yttrium aluminium garnet crystal doped with
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triply ionized neodymium) with a wavelength for incident laser at 1064 nm (9398,5 cm ). The
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maximum laser power was 1.5 W. The measurement accessory was pre-aligned, only the Z-axis of
the scattered light was adjusted to set the sample in the appropriate positioin relation to the local
point. The RAM II spectrometer is equipped with a liquid-nitrogen cooled Ge detector. FT-
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RAMAN spectra [4000-45cm ] were collected with a resolution of 1 cm by co-adding 256 scans
for each spectrum. The OPUS 6.0 software was used for the spectral acquisition, manipulation and
transformation.
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3. Results and Discussion
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3.1. Comparison between the FTIR/ATR spectra of ionic liquids: ([PrMIM ][Br ]) and
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([M(CH ) IM ][2Br ]):
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Table 1 below shows the observed FTIR/ATR bands and their assignments in the spectral
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region of 600 cm to 3420 cm of two ionic liquids mono and di-cationic [PrMIM ] [Br ] and
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([M(CH ) IM ][2Br ]). Figures 1, 2 and 3 show the infrared spectra of the two samples in the
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spectral regions 1200 cm to 600 cm , 1800 cm to 1200 cm and 3700 cm to 2700 cm
respectively. There are 30 peaks in this zone for the dicationic and 34 peaks for the monocationic.
Table 1
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Observed FTIR/ATR bands of ([PrMIM ][Br ] and ([M(CH ) IM ][2Br ]) and their assignments
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(vw = very weak; w = weak; m = medium, s = strong; sh = shoulder; ν=str=stretching; δ=def=
deformation; bend = bending deformation; ω=wagging; ρ= rocking; γ=bending out-of-plane;
t=twist=twisting, s = symmetric; as = antisymmetric, * = fitted value).
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[M(CH
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IM ][2Br ]
[PrMIM ][Br ]
Vibrational assignment
Refs.
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20 (vs)
618 (s)
CH
γ(N-H)
CH NCN str
CH def–vib, NH
Out-of-plane C-H def vib
CH (N) and CH (N)CN str
δHCCH/Ring HCCH asym bend/ω(C-H)
Ring HCCH asym bend/CH rocking def- vib
NC(H)N bend/CCH bend/ω(CH ) and ω(CH)
ω(C-H)/CH out-of-plane def vib
C-H out-of-plane vib/CH rocking vib
ν(C-C)/ρ(C–H) [ip]/CH rocking vib
ρ(CH ), t(CH )/CH rocking vib and CN str
CC str, NCH twist/CH rocking vib
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(N)CN str
[12]
39 (m)
47 (m)
60 (m)
94 (w)
14 (w)
56 (m)
[17]
649 (m)
660 sh
3
[9]
2
wagging vib
[15]
696 (w)
[15]
2
3
[10]
752 (m)
[8]/[13]
[8]/[15]
[12]/[11]
[11]/[15]
[15]
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00 (m)
2
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26+836 (m)
827 (m)
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64 (m)
00 (w)
010 (w)
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[11]/[15]
[11]/[15]
[8]/[15]
[12]/[11]
[11]
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022 (w)
062 (w)
097 (m)
1019 (w)
1049 (w)
1089 (w)
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CC str/ρ(N–C)
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116 (w)
1168 (vs)
230 (vw)
ρ(C-H)
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165 (vs)
CH
CH
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(N) and CH
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(N)CN str, CC str
[8]
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2
twisting vib/ν(CC)
[15]/[17]
[17]/[15]
253 (vw)
t(CH
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272 (w)
297 (w)
CH
CH
CH
CH
CH
CH
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wagging vib/ρ(C-H)
twisting vib/γ(C-H)
[15]/[11]
[17]
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339 (w)
389 (m)
1336 (w)
345 (w)
1385 (w)
428 (w)
(N) and CH
(N), CH (N) CN str
(N) CN bend, CH (N) and CH
(N) str, CH (N) HCH sym bend or NC(CH
)/CCH HCH asym bend, CH (N)HCH sym bend, CH
ν(N=C)/ρ(C–H)
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(N) CN str
[8]
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3
[8]
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(N) CN str/ρ(N-H)
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(N) str
[8]/[13]
[8]
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458 (m)
562 (s)
574 (s)
655 (s)
858 (vw)
1458 (m)
1564 (s)
1570 (s)
δ(CH
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[18]/[12]
[11]
ring ip sym/asym str, CH
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(N) str, CH
2
(N) CN str
[12]
ν(C=C), ν(C–N), δ(N-H)
[17]
2859*
v
s
(CH
2
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[17]
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876 (w)
ν
ν
ν
as(CH
2
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[18]
2
2
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928* sh
952 (w)
030* sh
085 (m)
145 (m)
245* sh
362* sh
430 (s)
2933* sh (m)
2964 (m)
3014* sh
3062 (m)
3140 (w)
s
(CH
3
)
[18]
as(CH
2
HCH)
[8]/[12]
[11]
ν(C-H)
ν(C-H)
[11]
ν(C-H)
[8]
Free N-H str
Free N-H str
Free N-H str
Free N-H str
[15]
3385* (w)
3450* (w)
[15]
[15]
495* sh
[15]
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3.1.1. The region 1200-600 cm :
Almost the same number of peaks were observed for the two samples in this spectral zone: 15
peaks for the monocationic and 13 peaks for the dicationic. Although the spectra of these two
samples are similar, there are peaks in the spectrum of the mono that do not exist in the spectrum of
dicationic, and vice versa. With regard to the modes present in the two spectra, some peaks which
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have undergone wavenumber shifts of the order of 4 cm were observed.. The Peaks at 620, 694,
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756, 1022 and 1165 cm for the dicationic corresponded respectively to the peaks at 618, 696, 752,
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1019 and 1168 cm for the monocationic. These peaks are assigned to the stretching vibration of
CH (N)CN and CH (N) bonds [8, 9, 12] and C-N stretching [15]. It is also noted that in the region
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675-635 cm the peak at 649 cm with a shoulder at 660 cm became a triplet for the case of
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dicationic ionic liquid: 639, 647 and 660 cm . Therefore the passage from one to two rings
imidazolium has an influence on the vibrational behavior of ring bonds. Furthermore the following
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observations were made: deformation (HCCH) and wagging (C-H) for 752 cm [13], stretching (C-
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C) for 1168 cm [11], rocking (CH and CH ) and twisting (CH ) for 1019 cm [11] and out-of-
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plane C-H def-vib for 696 cm [15]. Therefore, this passage also has an effect on the vibrational
modes of other bonds of the cation. Other peaks underwent more important wavenumber shifts of
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the order of 12 cm , for example the peaks at 1062 and 1097 cm for the dicationic corresponded
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to the ones at 1049 and 1089 cm for the monocationic. In the literature, these peaks are attributed
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to the stretching vibration of the (C-C) bond [8,12], the rocking of the (N-C) [11] and the twisting
of NCH [8] indicating that this zone is very sensitive to the passage of the mono to dicationic ionic
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liquid.
620
1165
dicationic ionic liquid
monocationic ionic liquid
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39
47
660
6
756
1097
836 826
7
14 694
1062 1022
1168
618
752
649
800
827
864
1089
1019
1116
1010
1049
900
696
1200 1150 1100 1050 1000 950 900 850 800 750 700 650 600
Wavenumber (cm-1
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Fig.1. FTIR/ATR spectra of: [PrMIM ][Br ] and ([M(CH ) IM ][2Br ]) in the region
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1200-600 cm .
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3.1.2. The region 1800-1200 cm :
In this spectral region, there were more peaks in the case of monocationic than in the case of
dicationic, which can be explained by a congestion masking certain vibrational modes for the
dicationic. The monocationic spectrum peaks are a little broader than the dicationic ones,
suggesting more order in the dicationic structure. We observed a very intense new peak at 1655 cm-
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1
1
1
1
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in the case of dicationic. In the literature, this peak is attributed to stretching vibration of (C=C)
and (C-N) bonds, and deformation of (N-H) bond [17]. Its appearance and its intensity can be
explained by the increase in the number of these bonds ((C=C), (C-N), (N-H)) that represent a
signature of the passage of the mono to dicationic ionic liquid.
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dicationic ionic liquid
monocationic ionic liquid
1655
1574
1562
1389
1458
1339
1253
1564
1570
1458
1345 1336
1
428 1385
1297
1272
1230
1800 1750 1700 1650 1600 1550 1500 1450 1400 1350 1300 1250 1200
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Wavenumber (cm )
1
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2+
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Fig.2. FTIR/ATR spectra of: ([PrMIM ][Br ]) and ([M(CH ) IM ][2Br ]) in the region from
2 3
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1800 to 1200 cm .
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3.1.3. The region 3700-2700 cm :
In this region, almost the same number of peaks for both samples was seen, 9 peaks for the
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monocationic and 10 peaks for the dicationic. The spectral band between 3500 - 3200 cm was
much higher in intensity for the dicationic compared to the monocationic. An actual rollover was
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observed in intensity in the spectral regions 3200-2800 cm and 3500-3200 cm between the
monocationic and dicationic. This phenomenon was explained by computing different intensity
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1
1
1
1
1
1
ratios shown in Table 2 by referring to the peak at 2955 cm . The increase in intensity is obvious,
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especially on the modes corresponding to ν(CH) at 3145 cm [8] and ν(NH) at 3430 cm . The
-
1
number of vibrational modes in the spectral region 3500-3200 cm also increased, 2 modes for
monocationic, 4 modes for dicationic assigned to ν(NH). All these variations seem to be explained
by the increased number of N-H bonds.
+
-
2+
-
Table 2. Reports of intensity of many peaks of [PrMIM ][Br ] and [M(CH ) IM ][2Br ] in the
2
3
-1
spectral range 3500-2800 cm .
Mono or dicationic
I2850/I
2955
I3075/I2955 I3145/I2955 I3430/I2955
ionic liquid
+
-
[
PrMIM ][Br ]
0.48± 0.02 0.92± 0.02 0.36± 0.02 0.20± 0.02
2
+
-
[
M(CH ) IM ][2Br ] 0.68± 0.02 1.68± 0.02 1.16± 0.02 2.27± 0.02
2
3
8

ACCEPTED MANUSCRIPT
monocationic liquid
dicationic liquid
3145
2952
2858
2964
2876
2859
3140
3700 3600 3500 3400 3300 3200 3100 3000 2900 2800 2700
Wavenumber (cm-1)
1
2
+
-
2+
-
Fig.3. FTIR/ATR spectra of: :([PrMIM ][Br ]) and ([M(CH ) IM ][2Br ]) in the region 3700-
2
3
-
1
3
2700 cm .
(b)
(a)
3700 3600 3500 3400 3300 3200 3100 3000 2900 2800
-1
Wavenumber (cm )
4
5
+
-
Fig.4. The Results of Lorentzian curve fitting of FTIR / ATR spectra for: (a) ([PrMIM ][Br ])
2
+
-
-1
6
7
8
and (b) ([M(CH ) IM ][2Br ]) in the region 3700-2700 cm .
2 3
9

ACCEPTED MANUSCRIPT
+
-
1
2
3
4
5
6
7
8
9
0
1
2
3
3.2. Comparison between FT-RAMAN spectra of ionic liquids ([PrMIM ][Br ]) and
2
+
-
([M(CH ) IM ][2Br ]):
2
3
Table 3 below represents the observed FT-RAMAN bands and their assignments for both ionic
+
-
2+
-
liquids ([PrMIM ][Br ]) and ([M(CH ) IM ][2Br ]). Figures 5, 6, 7 and 8 show the FT-RAMAN
2
3
-1
-1
-1
-1
spectra of the two samples in the spectral regions 1000 cm to 45 cm , 200 cm to 45 cm , 1700
-1
-1
-1
-1
cm to 1000 cm and 3200 cm to 2700 cm respectively. We noticed that the FT-RAMAN
spectrum of dicationic was richer in vibrational modes than that of monocationic: 75 peaks for the
dicationic and 38 picks for the monocationic.
Table 3:
1
1
1
1
Observed FT-RAMAN bands and their assignments (vw = very weak; w = weak; m = medium, s =
strong; sh = shoulder; ν = str = stretching; δ = def = deformation; bend = bending deformation; ω =
wagging, ρ= rocking, τ=torsion; t= twist=twisting; β=bending in-plane, s=symmetric; as =
antisymmetric, [ip]=in plane, [op]=out of plane).
2
+
-
+
-
[M(CH
2
)
3
IM ][2Br ]
[PrMIM ][Br ]
Vibrational assignment
Refs.
5
6
8
8
1
1
1
1
7 (s)
8 (s)
0 (s)
57 (vs)
Intermolecular vibration
Intermolecular vibration
Intermolecular vibration
Intermolecular vibration
Intramolecular vibration
Intramolecular vibration
Intermolecular vibration
Intermolecular vibration /τ(N–C)/ρ(CH
β(CCC)
[14]
[14]
[14]
[14]
[14]
[14]
[14]
[14]/[11]
[11]
[11]
[15]
[8]
6 (vs)
00 (s)
27 (m)
46 (m)
89 (m)
2
)
2
2
28 (vw)
82 (vw)
2
56 sh+267 (w)
ρ(N–C)
CH
CH
CH
3
2
2
torsional vib
2
3
99 (vw)
17 (vw)
(N) and CH
(N) and CH
3
3
(N)CH bend
(N)CH bend
316 (vw)
65 (vw)
[8]
3
ν(C–C)
t(CH
[11]
[11]
[15]
[15]
[11]
[10]/[12]
[11]
[11]
[11]
[11]
[15]
[15]
[8]
4
4
4
5
6
6
6
6
6
7
18 (m)
418 (vw)
2
)
29 (vw)
75 (w)
CC def vib [op]
ν(C-H)
461 (vw)
601 (w)
95 (vw)
13 (m)
ω(N-C)
ω(N-H)/CH
2 3
str, CH (N)CN str
21sh+624 (w)
41 (vw)
63 (m)
621 (w)
ν (N-CH ) [ip]
3
ρ(CH
ρ(CH
2
2
), ρ(CH)
661 (vw)
697 (vw)
)
95 (w)
ω(C-H)
CH rocking
CH def-vib
s
ν (CC), ring HCCH sym bend, NC(H)N sym [op]
18 (vw)
2
7
8
38 (vw)
03 (vw)
7
81 (w)
Ring HCCH sym bend, NC(H)N bending [op]
CH def vib [op]
[8]
8
8
29+841 (w)
[15]
[13]
65 sh+872+884 (w,m)
868 (w)
NC(H)N bend/CCH bend
1
0

ACCEPTED MANUSCRIPT
8
92 (vw)
CH def vib [op]/CH
3
rocking vib
[15]
9
05 (vw)
CH def vib [op]
[15]
9
1
1
1
1
1
1
1
1
1
76 (w)
ν(CC), ring asym bend [ip]
1012 sh+1021 (m) ν(C-C)/ρ(C–H)
[12]
010+1018 (s)
029 (m)
039 (m)
056 (vw)
094 (w)
[11]
CH
3
3
(N) str, CH
(N) str, CH
2
2
(N) str/ρ(C–H)
(N) str/ν(N–C)
[12]/[11]
[12]/[11]
[11]/[8]
[12]
1045 (w)
CH
ν(N–C)/ν(CC), ring CN asym ip str [ip]
1094 sh (w)
1116 (w)
ν(CC), ring HCCH sym bend, ring sym bend [ip]
107 (m)
123 (w)
ν(CC), ring HCCH sym bend, ring sym str [ip]
[12]
ν(CC)
ρ(CH)
ρ(CH)
[13]
163 (vw)
189 (vw)
1173 (vw)
[11]
[11]
1
207 (vw)
γ(CH) [op] ,ρ(CH
2
),ν(CC) [ip]
[17]
1
228 (vw)
ν(C-N), ρ(N-H)
[11]
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
277 (m)
1272 (vw)
1295 (vw)
ρ(C-H) [ip], t(CH
2
) [ip]
[17]
291 (vw)
t(CH
2
2
) [op] ,γ(CH)
) [op], γ(CH)
[17]
307 (w)
t(CH
[17]
333 (m)
1336 (m)
Ring sym str [ip], CC str, CH
2
2
(N) and CH
(N) and CH
3
3
(N) CN str
(N) CN str
[8]
346 (m)
Ring sym str [ip], CC str, CH
[8]
358 (w)
ρ(CH
ρ(CH
ρ(CH
2
2
2
), ρ(CH)/CH
), ρ(CH)
2
(N) str, ν(CC), CH
2
(N)CN str
[11]/[12]
[11]
365 (w)
382+ 1386 (m)
410 sh+1415+1428 (m,s,vs)
439 (m)
1385 (m)
1416 (s)
), ρ(CH)/δ(CH
2
) [op], ω(CH), ω(NH)
[11]/[17]
[13]
CH
δ(CH
CH (N) HCH sym bend/δ(CH)
CCH HCC sym bend, CH (N)HCH sym bend
ν(N–C), δ(CH
ν(N–C)/CH (N) and CH
CH def-vib [ip]
2
(N)/CH
3
(N)CN str
2
)
[13]
443 sh (m)
460 (m)
3
[8]/[11]
[12]
1454 (m)
1469 (m)
1564 (w)
3
467 (m)
2
)
[11]
557 sh+1565+1575 sh (vw,w,vw)
708 (vw)
2
3
(N) CN str
[11]/[8]
[15]
755 (vw)
2748 (vw)
2828 (w)
ν
ν
ν
ν
ν
s
s
s
s
s
(CH
(CH
(CH
(CH
(CH
3
3
2
2
3
)
[15]
811 (vw)
)/νas(CH
3
)
[15]
837 (vw)
)/ν
)/CH
)/νas(CH
HCH sym str
), ν(CH)
HCH asym str, ethyl HCH asym str
)/N-H str
s
(CH
HCH sym str/νas(CH
), ν (CH
3
)
[13]/[15]
[17/12/13]
[15]/[17]
[12]
2
876 (s)
3
2
)
2
2
2
896 (m)
928 (m)
948 (s)
2898 (m)
2
s
2
)
Ring CH
3
2943 (vs)
νas(CH
2
[17]
2
3
972 sh (s)
063 (w)
CH
2
[12]
2
3
982+3000 sh (m)
045 (w)
νas(CH
3
[13]/[15]
[13]
ν(C-H)
ν(C-H)
[13]
3
3
3
087+3098 (w)
136 (vw)
ν(C-H)/CH
3
(N)HCH asym Str
[11]/[13]
[16]/[13]
[16/13/15]
3138 (vw)
ring (HCCH and N–(C–H)–N) C–H str/ν(C-H)
156 (vw)
ring (HCCH and N–(C–H)–N) C–H str/ν(C-H)/ν(N-H)
-
1
1
2
3
4
3.2.1. The region 200-45 cm :
In this region an important difference between the two spectra was observed. The spectrum of
the monocationic ionic liquid had a wideband with a single peak that characterizes the amorphous
phase, while the spectrum of dicationic ionic liquid showed several peaks, indicating in this case the
1
1

ACCEPTED MANUSCRIPT
1
2
3
4
5
6
7
8
9
0
1
presence of a crystalline phase.
The slight swinging motion of the imidazolium ring, an absent phenomenon in the non-
aromatic ionic liquids must be expressed in the RAMAN spectra of both ionic liquids: a broad peak
-1
-1
at ≈57 cm in the case of monocationic ionic liquid, which becomes relatively narrow at 86 cm in
the case of dicationic, due here to the presence of the crystalline phase. Furthermore the results of
C. Penna et al. [14] indicate that the RAMAN spectrum must present other peaks attributed to the
-1
-1
-1
mode linked to the rocking motion: 146 cm and 189 cm (the wavenumber 189 cm from the
literature can also be attributed to twisting of the bond (N-C) or to rocking (CH ) [11]). The number
2
and intensities of the peaks show the influence of the passage of a monocationic ionic liquid to a
-1
-1
1
1
dicationic ionic liquid. The peaks at 100 cm and 127 cm are attributed to intramolecular
interactions [14].
86
80 68
57
dicationic ionic liquid
monocationic ionic liquid
100
127
146
421sh/424
865
613
189
8
72
418
267
663
475
6
18
95
595
7
9
256
8
92
84
429
1
9
976
781
3
2
7
8
57
641
621
868
697
601
282
228
461
418 365 316
905
8
03 738
661
1
000950 900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50
-
1
wavenumber(cm )
1
1
2
3
+
-
2+
-
Fig.5. The FT-RAMAN spectra of: [PrMIM ][Br ] and ([M(CH ) IM ][2Br ]) in the region 1000-
2
3
-
1
1
1
1
1
1
1
2
2
4
5
6
7
8
9
0
1
1045 cm .
-1
-1
-1
The frequencies ≈57 cm , ≈68 cm and ≈80 cm are attributed to partial character of acoustic
excitations for a crystalline physical state (intermolecular vibrational modes) [14]. This character is
compatible with the fact that we found these vibrational modes regardless of the specific molecular
structure. Therefore, these modes are also independent of the alkyl chain length of the cation, either
be it an aromatic or a non-aromatic ionic liquid. On the other hand, these modes depend on the
strength of the cation-anion interactions. Penna et al. [14] studied two monocationic ionic liquids
[C C im][Tf N] and [C C im]Br in crystalline phase. When passing from [C C im][Tf N] to
6
1
2
6
1
6
1
2
1
2

ACCEPTED MANUSCRIPT
-
1
1
2
3
4
5
6
[C C im]Br, they noticed in this zone of low frequencies a wavenumber shift of about 10 cm ,
6 1
which shows the influence of the nature of the anion. Moreover, for our dicationic ionic liquid
which represents the crystalline phase and at the same time their cations, they contain two
imidazolium rings. We also registered a wavenumber shift with a higher order than the previous,
which indicates that the number of cycles in the imidazolium cation also has an influence on the
modes of intermolecular vibrations.
57
monocationic liquid
dicationic liquid
86
80
68
100
146
127
189
200
180
160
140
120
100
80
60
40
-
1
wave number (cm )
7
8
+
-
2+
-
Fig.6. The FT-RAMAN spectra of [PrMIM ] [Br ] and ([M(CH ) IM ][2Br ]) in the region
2
3
-1
9
200-45 cm .
-
1
1
1
1
1
1
1
1
1
1
1
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3.2.2. The region 1000-200 cm :
In this region, there were 14 peaks for the monocationic ionic liquid and 23 peaks for the
dicationic, indicarting, for the latter, a richer RAMAN spectrum in vibration modes.
While passing from the monocationic ionic liquid to the dicationic ionic liquid, we observed
-
1
the appearance of several new peeks: at 256 and 267 cm , attributed to rocking mode of the (N-C)
-1
bond [11], and at 299 cm attributed to modes CH (N) and CH (N)CH bend [8]. In addition several
2
3
-1
other more or less intense peaks: 429, 641, 718, 781, 829, 841, 892 and 976 cm were observed. At
-1
613 cm a peak was present with medium intensity assigned to ω(NH) mode, the stretching of
(CH ) or (CH (N)CN) [12].
2
3
-1
We also noticed deconvolutions of peaks: 621 cm in the case of the monocationic which
-1
corresponded to a doublet 621 and 624 cm in the case of dicationic,is attributed to the vibration
-1
mode in the plane (stretching of the (N-CH ) bond) [11]. The peak at 868 cm in the case of
3
-1
-1
monocationic became a doublet for the dicationic: 872 and 884 cm with a shoulder at 865 cm , all
1
3

ACCEPTED MANUSCRIPT
1
2
3
4
5
6
assigned to vibrations NC(H)N bend and CCH bend [13].
We observed for the other peaks minor wavenumber shifts of the order of 2 cm (from 316 cm
-1
-
1
-1
-1
-1
-1
for the mono to 317 cm for the dicationic, from 661 cm to 663 cm and 697 to 695 cm ), the
-1
peak at 418 cm remained unchanged for mono and dicationic. Still there were two peaks with
-1
-1
remarkable wavenumber shifts (from 461 cm to 475 cm assigned to (C-H) stretching [15] and
-1
-1
from 601 cm to 595 cm assigned to ω(N-C) [11]).
-
1
7
8
9
0
1
2
3
4
5
3.2.3. The region 1700-1000 cm :
In this region, we observed 30 peaks for the dicationic versus 15 peaks for the monocationic.
So also in this region, the spectrum of dicationic is richer in modes than the spectrum of
monocationic. New peaks appeared in the case of dicationic: two less intense peaks at 1056 cm-1
1
1
1
1
1
1
-1
and 1358 cm , other peaks slightly more intense at 1029, 1123, 1189, 1207, 1307, 1346, 1365, 1439
-1
-1
cm and a shoulder at 1443 cm , the assignments of these peaks are in table (3). Among these
-1
peaks the most remarkable one is at 1346 cm assigned to Ring sym str [ip], CC str, CH (N) and
2
CH (N) CN str [8].
3
1
428
dicationic ionic liquid
monocationic ionic liquid
1415
1010
1018
1
410
386
382
346
333
1
1
1
277
1
1
439
1
1467
1
460
1
291
1029
1
107
1094
1
039
1
443
1189
1
1307
1
565
1123
163
1557
1365
416
1056
1207
1
575
1358
1
1021
1385
1454
1336
2
1469
1
0
1
1295
1116
1094
1045
1564
1272
1228
1173
1700 1650 1600 1550 1500 1450 1400 1350 1300 1250 1200 1150 1100 1050 1000
-
1
wavenumber(cm )
1
1
6
7
+
-
2+
-
Fig.7. FT-RAMAN spectra of: [PrMIM ][Br ] and ([M(CH ) IM ][2Br ])
2
3
-
1
1
1
2
8
9
0
in the region 1700 -1000 cm .
-1
Deconvolutions of the peaks was also observed in this region. The peak at 1385 cm for mono
-1
became a doublet for the dicationic: 1382 and 1386 cm . These peaks are attributed in the literature
1
4

ACCEPTED MANUSCRIPT
-
1
1
2
3
4
5
6
7
8
9
to the CH bond vibration or the NH bond [8, 17]. The peak at 1416 cm changed into a triplet: 1410
-1
-1
-1
cm , 1415 cm and 1428 cm . These peaks are assigned to the stretching vibration of CH (N) and
2
-1
-1
-1
CH (N) CN [13]. Also a peak at 1564 cm changed into a triplet: 1557 cm , 1565 cm and 1575
3
-1
cm . These frequencies are also attributed to stretching vibration of CH (N) and CH (N) CN [8]
2
3
and ν(N–C) [11]. For the rest of the peaks, we observed more or less significant shifts of the order
-1
-1
of 2 cm to 10 cm .
It is also envisaged that the peaks of the RAMAN spectrum of the dicationic are narrower than
for the monocationic, which means that it has more order in the dicationic structure than the
monocationic.
-
1
1
1
1
1
1
1
1
1
1
1
2
2
0
1
2
3
4
5
6
7
8
9
0
1
3.2.4. The region 3200-2700 cm :
-1
As in previous regions, in region 3200-2700 cm , the dicationic spectrum was richer in
vibration modes than the monocationic one, with 14 peaks versus 8 peaks observed. New peaks
-1
-1
were present at 2708 cm (assigned to CH in-plane def-vib ), 2811 cm (assigned to sym CH str,
3
-1
-1
-1
asym CH str), 2928 cm (assigned to ring CH HCH sym str), 2982 cm and 3000 cm (assigned
3
3
-1
-1
-1
-1
to ν (CH )) , 3045 cm , 3087 cm and 3098 cm (assigned to ν(CH)), and 3156 cm (assigned to
as
3
-
1
-1
-
the ring (HCCH and N(CH)N)CH str/ν(CH)). In the literature 2982 cm , 3000 cm and 3156 cm
1
are attributed to the stretching vibration of NH bond. For modes present in both spectra, we had a
-
1
-1
frequency shift of the order of 2 cm to 9 cm .
Therefore, all spectral regions of the FT-RAMAN spectrum that we saw above show sensitivity
towards the passage of mono to di-cationic by more peaks in the case of dicationic and wavenumber
shifts.
1
5

ACCEPTED MANUSCRIPT
2948
dicationic ionic liquid
monocationic ionic liquid
2928
2982
2896
3045 3000
3087
3098
3136
2837
2811
3156
2755
2708
2943
2876
2972
2898
3063
2828
3138
2748
3200 3175 3150 3125 3100 3075 3050 3025 3000 2975 2950 2925 2900 2875 2850 2825 2800 2775 2750 2725 2700
-1
wavenumber(cm )
1
2
+
-
Fig.8. The FT-RAMAN spectra of: [PrMIM ] [Br ] ( monocationic) and
2
+
-
- 1
3
([M(CH ) IM ][2Br ]) (dicationic), in the region 3200-2700 cm .
2 3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
4. Conclusion:
This study showed that in passing of an imidazolium-based monocationic (IL) where the cation
is composed of a one imidazolium ring to a dicationic (IL) where the cation is composed of a two
imidazolium rings, there is a change of environment for ions, hence more or less freedom of
movement. This was expressed on the FT-RAMAN spectrum in a wide spectral region by the
appearance of new vibrational modes (37 new peaks), deconvolutions and wavenumber shifts,
which can serve as a signing of differentiation between these (ILs).
1
1
1
1
1
1
1
1
1
1
2
2
2
This change in the number of imidazolium rings in the cation also influences the intermolecular
(anion-cation interaction) and intramolecular vibration modes. Indeed in the spectral zone 200-45
-1
cm , representative of these modes, we could see: a broadband with only a single peak for the
monocationic, characteristic of an amorphous phase, versus several peaks for the dicationic,
characteristic of a crystalline phase. So the self-organization known to ionic liquids was manifested
in the case of dicationic. Therefore, this spectral zone is a signature of the physical state of the (IL),
than the change of the number of imidazolium rings in the cation.
We note that for the FTIR/ATR spectroscopy the clutter of ions masked certain vibration
modes for the dicationic. Yet, we had more or less important wavenumber shifts, peaks with
-1
pronounced intensities in the case of dicationic such as the new peak at 1655 cm , and a failover in
-
1
intensity from the monocationic and dicationic between the spectral regions 3200-2800 cm and
-
1
-1
3500-3200 cm . The number of vibrational modes in the spectral region 3500-3200 cm also
1
6

ACCEPTED MANUSCRIPT
1
2
3
4
5
6
increased, which can be explained by an increase in the number of N-H bonds. Therefore, these
spectral regions are sensitive to the change of the number of imidazolium rings.
Such as the FT-RAMAN spectroscopy, we also have for FTIR/ATR spectroscopy an indicator
of the existence of the order for the dicationic. This indicator is represented by the peaks in the
spectrum of the dicationic being slightly narrower than the peaks in the spectrum of the
monocationic.
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
Acknowledgment
The authors thank the ATRST-DGRSDT for the financial support. We would like to thank Quentin
Arnould, technician of Walloon Agricultural Research Centre (CRA-W), who participated to FT-
RAMAN and FTIR/ATR measurements.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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[1] J. M. Crosthwaite, M. J. Muldoon, J. K. Dixon, J. L. Anderson, and J. F. Brennecke, “Phase
transition and decomposition temperatures, heat capacities and viscosities of pyridinium ionic
liquids,” The Journal of Chemical Thermodynamics, vol. 37, no. 6, pp. 559–568, 2005.
[2] J. D. Holbrey and K. R. Seddon, “The phase behaviour of 1-alkyl-3-methylimidazolium
tetrafluoroborates; ionic liquids and ionic liquid crystals,” Journal of the Chemical Society,
Dalton Transactions, no. 13, pp. 2133–2140, 1999.
[3] R. Hagiwara and Y. Ito, “Room temperature ionic liquids of alkylimidazolium cations and
fluoroanions,” Journal of Fluorine Chemistry, vol. 105, no. 2, pp. 221–227, 2000.
[4] F. Endres, M. Bukowski, R. Hempelmann, and H. Natter, “Electrodeposition of
nanocrystalline metals and alloys from ionic liquids,” Angewandte Chemie International
Edition, vol. 42, no. 29, pp. 3428–3430, 2003.
[5] H. Ohno, Electrochemical aspects of ionic liquids. John Wiley & Sons, 2011.
[6] M. Freemantle, An introduction to ionic liquids. Royal Society of chemistry, 2010.
[7] A. J. Walker and N. C. Bruce, “Cofactor-dependent enzyme catalysis in functionalized ionic
solvents,” Chemical communications, no. 22, pp. 2570–2571, 2004.
[8] K. Noack, P. S. Schulz, N. Paape, J. Kiefer, P. Wasserscheid, and A. Leipertz, “The role of the
C2 position in interionic interactions of imidazolium based ionic liquids: a vibrational and
NMR spectroscopic study,” Physical Chemistry Chemical Physics, vol. 12, no. 42, pp. 14153–
14161, 2010.
[9] A. M. Moschovi, S. Ntais, V. Dracopoulos, and V. Nikolakis, “Vibrational spectroscopic study
of the protic ionic liquid 1-H-3-methylimidazolium bis (trifluoromethanesulfonyl) imide,”
Vibrational Spectroscopy, vol. 63, pp. 350–359, 2012.
[10] T. Moumene, E. H. Belarbi, B. Haddad, D. Villemin, O. Abbas, B. Khelifa, and S. Bresson,
“Vibrational spectroscopic study of ionic liquids: Comparison between monocationic and
dicationic imidazolium ionic liquids,” Journal of Molecular Structure, vol. 1065, pp. 86–92,
2014.
[11] K. Malek, A. Puc, G. Schroeder, V. I. Rybachenko, and L. M. Proniewicz, “FT-IR and FT-
Raman spectroscopies and DFT modelling of benzimidazolium salts,” Chemical physics, vol.
327, no. 2, pp. 439–451, 2006.
[12] J. Kiefer, J. Fries, and A. Leipertz, “Experimental vibrational study of imidazolium-based
ionic liquids: Raman and infrared spectra of 1-ethyl-3-methylimidazolium bis
(trifluoromethylsulfonyl) imide and 1-ethyl-3-methylimidazolium ethylsulfate,” Applied
spectroscopy, vol. 61, no. 12, pp. 1306–1311, 2007.
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[13] T. Moumene, E. H. Belarbi, B. Haddad, D. Villemin, O. Abbas, B. Khelifa, and S. Bresson,
“Study of imidazolium dicationic ionic liquids by Raman and FTIR spectroscopies: The effect
of the nature of the anion,” Journal of Molecular Structure, vol. 1083, pp. 179–186, 2015.
[14] T. C. Penna, L. F. Faria, J. R. Matos, and M. C. Ribeiro, “Pressure and temperature effects on
intermolecular vibrational dynamics of ionic liquids,” The Journal of chemical physics, vol.
138, no. 10, p. 104503, 2013.
[15] G. Socrates, Infrared and Raman characteristic group frequencies: tables and charts. John
Wiley & Sons, 2004.
[16]M. Koel, Ionic liquids in chemical analysis. CRC Press, 2008.
[17]K. Malek, E. Podstawka, J. Milecki, G. Schroeder, and L. M. Proniewicz, “Structural features
of the adenosine conjugate in means of vibrational spectroscopy and DFT,” Biophysical
chemistry, vol. 142, no. 1, pp. 17–26, 2009.
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[18]S. Bresson, D. Rousseau, S. Ghosh, M. E. Marssi, and V. Faivre, “Raman spectroscopy of the
polymorphic forms and liquid state of cocoa butter,” European Journal of Lipid Science and
Technology, vol. 113, no. 8, pp. 992–1004, 2011.
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