Synthesis and characterization of the iron-containing magnetic ionic liquids

Article abstract of DOI:10.1016/j.molliq.2012.02.005

Three species of room temperature magnetic ionic liquids (ILs) including 1-butyl-3-methylimidazolium tetrachloroferrate ([bmim]FeCl₄), N-butylpyridium tetrachloroferrate ([bPy]FeCl₄) and 1-butyl-1-methylpyrrolidium tetrachloroferrate ([bmP]FeCl₄) were synthesized via two-step in this paper. The intermediates and magnetic ILs were characterized by ultimate analysis, ¹H NMR, ESI-MS, FT-IR and Raman. In addition, the three magnetic ILs were quantitatively tested by magnetic property measurement system (superconducting quantum interference device), and the results indicated that they had similar magnetic susceptibilities and paramagnetic properties. This research expanded cationic types of magnetic ILs, and supplied fundamental data to application of magnetic ILs.

Full text of DOI:10.1016/j.molliq.2012.02.005

Journal of Molecular Liquids 169 (2012) 152–155
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Synthesis and characterization of the iron-containing magnetic ionic liquids
a
Jieli Wang a,b, Hongwei Yao b, Yi Nie b, Xiangping Zhang b, , Jianwei Li
⁎
a
College of Chemical Engineering and Technology, Beijing University of Chemical Technology, Beijing 100029, PR China
b
Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex System, Institute of Process Engineering, Chinese Academy of Sciences,
Beijing 100190, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 July 2011
Received in revised form 29 December 2011
Accepted 2 February 2012
Available online 29 February 2012
Three species of room temperature magnetic ionic liquids (ILs) including 1-butyl-3-methylimidazolium
tetrachloroferrate ([bmim]FeCl4), N-butylpyridium tetrachloroferrate ([bPy]FeCl4) and 1-butyl-1-methyl-
pyrrolidium tetrachloroferrate ([bmP]FeCl4) were synthesized via two-step in this paper. The intermedi-
ates and magnetic ILs were characterized by ultimate analysis, 1H NMR, ESI-MS, FT-IR and Raman. In
addition, the three magnetic ILs were quantitatively tested by magnetic property measurement system
(superconducting quantum interference device), and the results indicated that they had similar magnet-
ic susceptibilities and paramagnetic properties. This research expanded cationic types of magnetic ILs,
and supplied fundamental data to application of magnetic ILs.
Keywords:
Magnetic ionic liquid
Synthesis
Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
Characterization
Magnetic susceptibility
1. Introduction
with the same imidazole cationic rings. Therefore, it is necessary to ex-
ploit novel magnetic ILs with different cationic structures.
Ionic liquids (ILs) are used as green solvents or excellent media
due to their unique physicochemical properties [1–4], such as wide
liquid range, higher ionic conductivity, excellent solubility, thermal
stability and designability by appropriate modifications of cations or
anions in structures. Magnetic ILs not only have the above excellent
properties but also exhibit an unexpectedly strong response to an
additional magnet. These properties make magnetic ILs have more
advantages and potential application prospects than conventional
ILs in the fields of catalytic reactions [5–8], solvent effects [9–11]
and separation processes [12,13].
In this paper, two novel magnetic ILs with pyridine and pyrrolidine
cationic rings were synthesized and tested to show the same paramag-
netism, which hasn't been reported in the literatures. Their magnetic
susceptibilities are close to the imidazolium-based magnetic ILs in the
same test conditions. Furthermore, they possess the same paramagne-
tism at 5 K–300 K. This study will provide references for further synthe-
sizing magnetic ILs with stronger magnetism and offer many potential
chances for magnetic ILs in practical application in the near future.
2. Experimental
1-butyl-3-methylimidazolium tetrachloroferrate ([bmim]FeCl4)
with magnetism was synthesized and first reported by Hayashi et al.
[14] in 2004. Since then, the syntheses of magnetic ILs have been
focused on expanding synthesis with different alkyl chain length of
imidazole cations or different magnetic metal anions. Metal-containing
ILs and ionic liquid crystals based on imidazolium moiety were prepared
by Ivan J. B. Lin et al. [15] in 2005. A series of imidazolium-based magnetic
ILs with different alkyl substituent groups of cations were synthesized
by Sesto et al. [16] in 2007. Furthermore, a series of imidazolium-based
magnetic ILs with different complexing dysprosium metal anions were
prepared by Mallick et al. [17] in 2008. In 2010, it was reported that
1-ethyl-3-methylimidazolium tetrachloroferrate ([emim]FeCl4) clearly
showed a long-range antiferromagnetic ordering when it was frozen
[18]. All these studies were confined to synthesis the magnetic ILs
2.1. Materials
FeCl3·6H2O, pyridine, N-methylpyrrolidine, n-chlorobutane, aceto-
nitrile and ethyl acetate were of analytical grade and were used without
further purification. Crystalline 1-butyl-3-methylimidazolium chloride
([bmim]Cl) with purity 99% was purchased from Henan Lihua Pharma-
ceutical Co., Ltd.
2.2. Preparation of magnetic ionic liquids
The preparation of magnetic ILs, such as [bmim]FeCl4, N-
butylpyridium tetrachloroferrate ([bPy]FeCl4) and 1-butyl-1-methyl-
pyrrolidium tetrachloroferrate ([bmP]FeCl4), were prepared using the
following methods (shown in Scheme 1).
Firstly, intermediates N-butylpyridium chloride ([bPy]Cl) and 1-butyl-
1-methylpyrrolidium chloride ([bmP]Cl) were prepared by reaction of
equimolecular of pyridine (or N-methylpyrrolidine) and n-chlorobutane
⁎
Corresponding author. Tel.: +86 010 82544877; fax: +86 010 62558174.
E-mail address: xpzhang@home.ipe.ac.cn (X. Zhang).
0167-7322/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2012.02.005

J. Wang et al. / Journal of Molecular Liquids 169 (2012) 152–155
153
Scheme 1. synthetic pathway to [bmim]FeCl4, [bPy]FeCl4 and [bmP]FeCl4.
at 80 °C ([bmP]Cl at 100 °C) with a magnetic stirring for five days.
3. Results and discussion
The intermediate products were repeatedly recrystallized from
acetonitrile, subsequently washed three times with ethyl acetate
and dried in vacuum at last.
Secondly, the intermediates including [bmim]Cl [19], [bPy]Cl and
[bmP]Cl were respectively mixed with equimolecular of FeCl3·6H2O
together under N2 atmosphere with a mechanical stirring at room
temperature ([bPy]FeCl4 at 50 °C, [bmP]FeCl4 at 30 °C). The products
were washed with ether and deionized water, purified by reduced
pressure distillation and dried in vacuum successively. Then the mag-
netic ILs, [bmim]FeCl4, [bPy]FeCl4 and [bmP]FeCl4, were obtained.
The physical properties of magnetic ILs are mainly affected by
their structures, and their purities also have great influence on their
physical parameters. Therefore, structures and purities of the ILs are
characterized by some analytical methods so as to achieve the aims
of the study. In the experiment, the intermediates were mainly char-
acterized by ultimate analysis, 1H NMR, and the synthetic magnetic
ILs were characterized by ESI-MS, FT-IR, Raman and MPMS (SQUID).
3.1. Ultimate analysis of the intermediates
2.3. Characterization
The intermediates [bPy]Cl and [bmP]Cl are extremely easy to absorb
water. This phenomenon will result in the test values of hydrogen con-
tents of the intermediates greater than the theoretical values. To avoid
such deviation appearing, experimental treatment and sample handling
should be done as soon as possible in the analytical process. In data pro-
cessing, the test values of N, C and H elements are compared with the
theoretical values, and the test N/C ratios of intermediates are also com-
pared with theoretical N/C ratios. Test data are as follow: Anal. calcd for
C9H14ClN: C, 62.97%; H, 8.22%; N, 8.16%; found: C, 62.95%; H, 8.26%; N,
8.14%; Anal. calcd for C9H20ClN: C, 60.83%; H, 11.34%; N, 7.88%; found:
C, 60.81%; H, 11.37%; N, 7.85%. The results manifest that the test values
of intermediates are basically consistent with the theoretical values.
Nitrogen, carbon and hydrogen element contents of the synthesized
intermediates were determined by combustion analysis in a Vario EL-III
elemental analyzer (Germany, Elementar). 1H NMR spectra of the inter-
mediates were recorded on a BRUKER AVANCE 600 MHz spectrometer
(Germany, Bruker) using DMSO-d6 as an internal reference. Chemical
shifts (δ) are given in ppm and coupling constants (J) are given in Hz.
The multiplicities of signals in H NMR are given with chemical shifts
1
(s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet).
ESI-MS analysis of the magnetic ILs was performed using a Bruker
Daltonics APEX-II (America, Bruker Daltonics Inc). FT-IR spectra were
registered with a Nicolet Magna-IR-560 Spectrometer infrared spec-
trophotometer (America, Nicolet). Raman spectra were detected by
a microscopic confocal Raman spectrometer LabRAM HR-800 (France,
Horiba Jobin Yvon) using a 785 nm laser beam and a charge-coupled
detector (CCD) with 4 cm−1 resolution. The magnetic susceptibilities of
magnetic ILs were measured by a MPMS (SQUID) (America, Quantum
Design) in Peking University.
1
3.2. H NMR spectra of the intermediates
The cationic structures and purities of the intermediates [bPy]Cl
1
and [bmP]Cl are primarily confirmed using the H NMR spectra, and
the data are listed as follow.

154
J. Wang et al. / Journal of Molecular Liquids 169 (2012) 152–155
Fig. 1. ESI-MS spectra of [bmim]+(1), [bPy]+(2), [bmP]+(3) and [FeCl4]-(4).
[bPy]Cl, 1H NMR (DMSO-d6, δ, ppm): 0.96 (3H, t, J=7 Hz); 1.34–1.43
4000 cm− 1), there are no differences except the sharper peaks
appearing in the complexes spectra. The analysis indicates that the
intermediates corresponding complexes have the same cationic
structures with the intermediates and the anions of complexes
have little effect on the chemical displacements of complexes.
(2H, m); 1.98–2.06 (2H, m); 4.64 (2H, t, J=7 Hz); 8.09 (2H, t, J=6 Hz);
8.57 (1H, t, J=8 Hz); 8.88 (2H, d, J=6 Hz).
[bmP]Cl, 1H NMR (DMSO-d6, δ, ppm): 0.97 (3H, t, J=7.4 Hz);
1.36–1.46 (2H, m); 1.76–1.84 (2H, m); 2.23 (4H, s); 3.06 (3H, s);
3.33–3.37 (2H, m); 3.52 (4H, s).
1
The H NMR spectra show that the approximate ratios of integral
peak area are concordant with the ratios of the number of hydrogen
3.5. Raman spectra of the magnetic ILs
atoms at different shift in an allowable error range. Meanwhile,
there are not additional peaks existing in the H NMR spectra of the
intermediates. Therefore, it can be concluded that [bPy]Cl and [bmP]
Cl have been synthesized successfully.
1
Raman spectra were recorded from 50 cm−1 to 1600 cm−1 on a
laboratory made near-infrared multichannel Raman system. The
785 nm laser was used as the excitation source in order to avoid
fluorescence from impurities. The Raman spectra of magnetic ILs
[bmim]FeCl4, [bPy]FeCl4 and [bmP]FeCl4 are very well in keeping
with each other in 50–500 cm−1 (see Fig. 2). In Fig. 2, the two
peaks appear at 113.24 cm−1 and 333.20 cm−1 in the spectra of
three magnetic ILs. Those peaks were reported and assigned to the
symmetric Fe–Cl bond stretch vibrations of [FeCl4]- in the literature
[14]. Thus, it can be confirmed that the tested samples contain the
same [FeCl4]- anions.
3.3. ESI-MS spectra of the magnetic ILs
In order to analyze and determine the structures and purities of the
synthesized magnetic ILs, they were tested by ESI-MS spectra (Fig. 1).
In Fig. 1, it can be seen that the characteristic ionic peaks appear at
m/z139.1, m/z136.1 and m/z142.1 successively corresponding to the
cationic molecular weight of the magnetic ILs. Therefore, the informa-
tion about the cationic structures of magnetic ILs is definitely deter-
mined. The anions of magnetic ILs have the very similar ESI-MS
spectra, which appears one characteristic ionic peak at m/z198.8.
Furthermore, there are rarely impurity peaks in the ESI-MS spectra
of anions and cations of magnetic ILs. Therefore, it can be inferred that
the magnetic ILs have been synthesized with high purities. Test results
are as follow: Electrospray MS+m/z: 139.1 [bmim]+; MS-m/z: 198.8
[FeCl4]-; Electrospray MS+m/z: 136.1 [bPy]+; MS-m/z: 198.8 [FeCl4]-;
Electrospray MS+m/z: 142.1 [bmP]+; MS-m/z: 198.8 [FeCl4]-.
3.4. FT-IR spectra of the magnetic ILs
Compared FT-IR spectra of intermediates with their correspond-
ing complexes, it can be found that spectra of intermediates are
quite similar to their corresponding complexes. From fingerprint
area (400–1300 cm− 1) to characteristic frequency area (1300–
Fig. 2. Raman spectra of [bmim]FeCl4(a), [bPy]FeCl4(b) and [bmP]FeCl4(c) at room
temperature.

J. Wang et al. / Journal of Molecular Liquids 169 (2012) 152–155
155
Fig. 3. Magnetization of [bmim]FeCl4, [bPy]FeCl4 and [bmP]FeCl4 as a function of
applied magnetic field at 300 K.
Fig. 4. Magnetization of [bmim]FeCl4, [bPy]FeCl4 and [bmP]FeCl4 as a function of
temperature under an applied magnetic field at 10,000 Oe.
Table 1
field. The results show that the magnetic susceptibility of [bmP]FeCl4 is
the lowest among the three ILs and the magnetic susceptibility of [bPy]
FeCl4 is a little higher than that of [bmim]FeCl4 at the same order of
magnitude. In addition, the magnetic properties of [bmim]FeCl4, [bPy]
FeCl4 and [bmP]FeCl4 are paramagnetic from 5 K to 300 K.
Predictably, iron-containing magnetic ILs [bPy]FeCl4 and [bmP]
FeCl4 will be applied as solvent and catalyst in chemical reactions or
separation technology as well as [bmim]FeCl4 system in the near
future.
The magnetic susceptibilities of magnetic ionic liquids.
Compound
Temperature/K
Magnetic susceptibility×105/emu g−1
[bmim]FeCl4
[bPy]FeCl4
[bmP]FeCl4
300
300
300
4.04
4.11
0.95
3.6. Magnetic property analysis of the magnetic ILs
The magnetic susceptibilities of the three magnetic ILs were mea-
sured by the MPMS (SQUID). A small amount of [bmim]FeCl4
(45.72 mg), [bPy]FeCl4 (27.45 mg) or [bmP]FeCl4 (42.23 mg) was
contained respectively in a pharmaceutical cellulose capsule and
measured at 300 K in the magnetic field range from −10,000 Oe to
10,000 Oe. The results are shown in Fig. 3. It can be seen that magne-
tization intensities of the three magnetic ILs show linear response to
the magnetic field. From the slopes of the three fitted lines, the mag-
netic susceptibilities of [bmim]FeCl4, [bPy]FeCl4 and [bmP]FeCl4 are
determined (see Table 1). From Table 1, it can be seen that [bmim]
FeCl4 and [bPy]FeCl4 have the same order of magnitude. In an allow-
able error range, the experimental value of [bmim]FeCl4 is in accord
with literature value [14]. The interdependencies between magnetic
moment and magnetic field indicate that the three magnetic ILs are
paramagnetic and there are no strong couplings among the spin an-
gular momenta of the cations.
Acknowledgements
This work was supported by Key Program of National Natural Sci-
ence Foundation of China (No.21036007) and General Program Youth
of National Natural Science Foundation of China (No.21006107).
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Two novel types of magnetic ILs with pyridine and pyrrolidine cat-
ionic rings were synthesized via two-step, and varieties of magnetic
ILs were expanded and enriched. The structures and major existing
forms of the synthesized magnetic ILs were ascertained in detail by
1H NMR, ESI-MS, FT-IR and Roman analytical methods.
Magnetic susceptibilities of the three species magnetic ILs were
measured at a certain temperature or with proper intension of magnetic