Controlled introduction of metal cations into polymerizable ionic liquid-polyoxomolybdate hybrid crystals

Article abstract of DOI:10.1039/C8CE01658E

A polymerizable ionic-liquid cation having methacryl group and imidazolium moieties (denoted as MAImC₁) was successfully hybridized with octamolybdate (Mo₈O₂₆^4?, Mo₈) to obtain inorganic-organic hybrid crystals containing monovalent metal cations. The hybrid crystals were initially prepared as sodium ion-containing hybrid crystal of MAImC₁-Na-Mo₈. The sodium cations in MAImC₁-Na-Mo₈ were exchangeable to other monovalent metal cations such as silver or potassium to form hybrid crystals of MAImC₁-Ag-Mo₈ or MAImC₁-K-Mo₈. Their molecular and crystal structures were clearly revealed by single crystal X-ray analyses. The MAImC₁-Na-Mo₈ hybrid crystal worked as the hybrid monomer, and was found polymerizable by a radical polymerization using AIBN as an initiator to obtain inorganic-organic polymers (P-MAImC₁-Na-Mo₈). The conductivities of the hybrid monomer and polymer consisting of MAImC₁-Na-Mo₈ were investigated.

Full text of DOI:10.1039/C8CE01658E

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Controlled introduction of metal cations into
polymerizable ionic liquid-polyoxomolybdate
Cite this: DOI: 10.1039/c8ce01658e
hybrid crystals†
Jun Kobayashi,a Toshiyuki Misawa, a Chihiro Umeda,b Toru Isono,b Seiji Ono,b
Haruo Naruke,c Yosuke Okamura, b Shinichi Koguchi,a Masashi Higuchi,b
a
Yu Nagaseb and Takeru Ito
*
A polymerizable ionic-liquid cation having methacryl group and imidazolium moieties (denoted as MAImC1)
was successfully hybridized with octamolybdate (Mo8O264−, Mo8) to obtain inorganic–organic hybrid crys-
tals containing monovalent metal cations. The hybrid crystals were initially prepared as sodium ion-
containing hybrid crystal of MAImC1–Na–Mo8. The sodium cations in MAImC1–Na–Mo8 were exchangeable
to other monovalent metal cations such as silver or potassium to form hybrid crystals of MAImC1–Ag–Mo8
or MAImC1–K–Mo8. Their molecular and crystal structures were clearly revealed by single crystal X-ray anal-
yses. The MAImC1–Na–Mo8 hybrid crystal worked as the hybrid monomer, and was found polymerizable by
a radical polymerization using AIBN as an initiator to obtain inorganic–organic polymers (P-MAImC1–Na–
Mo8). The conductivities of the hybrid monomer and polymer consisting of MAImC1–Na–Mo8 were
investigated.
Received 28th September 2018,
Accepted 7th December 2018
DOI: 10.1039/c8ce01658e
rsc.li/crystengcomm
amphiphilic ionic-liquids and polymerizable ionic-liquid have
been also utilized to build up hybrid crystals with POMs,30–37
Introduction
Rechargeable batteries such as lithium-ion or sodium-ion bat-
teries are now being applied to power sources.1–5 For the future
usage in motor vehicles working at intermediate temperature
(373 to 573 K), solid electrolytes with high conductivity are
demanded to improve thermal stability and energy efficiency.
Inorganic–organic hybrid materials have potential for the con-
struction of highly conductive solid electrolytes as functional-
ized crystalline materials.6–10 We can expect synergy of the
merits derived from inorganic and organic components as ob-
served in molecular conductors.7 The introduction of metal cat-
ions into such hybrid materials can provide functions such as
ionic conductivity8,9 and ion-exchanging property.10
and some of them exhibit proton conductivities.32–34
The selective introduction of metal cations into the POM
hybrid crystals has to be realized for the emergence of
designed functions such as ionic conduction. A promising
option is to use octamolybdate ([Mo8O26]4−, Mo8) anion. The
Mo8 anion has several isomers represented by β-type and
γ-type (Fig. 1a),38–40 and the β-Mo8 anion tends to coordinate
to coexisting metal cations in the solid states.41–45 The con-
trolled introduction of monovalent metal cations was real-
ized also in POM-surfactant hybrid crystals by utilizing the
Mo8 isomerization reactions.46–48 In this introduction
method of metal cations, the composition can be easily
designed by simply changing the kind of coexisting metal cat-
ion under mild conditions near the room temperature. The
hybrid crystals containing Na+ are applicable to the solid
electrolytes or electrode materials for sodium-ion batteries.
Here we report another successful system of metal cation-
containing inorganic–organic hybrid crystals. The hybrid
crystals were constructed from polymerizable ionic-liquid
(MA-ImC1, Fig. 1) and β- or γ-Mo8 anion for the first time.
Na+, Ag+, and K+ were introduced into the MAImC1–Mo8 hy-
brid crystals (MAImC1–Na–Mo8 (1), MAImC1–Ag–Mo8 (2),
MAImC1–K–Mo8 (3)) in a controlled manner by changing the
coexisting monovalent cation under the mild synthetic condi-
tions. The metal cations formed one- or two-dimensional net-
work with the Mo8 anions, the dimensionality of which
Polyoxometalate (POM) cluster anions are promising candi-
dates as inorganic components to construct functional hybrid
materials.11–24 Hybridizing POMs with ionic-liquids25–29 is ad-
vantageous for the emergence of conductive properties. The
a Department of Chemistry, School of Science, Tokai University, Hiratsuka 259-
1292, Japan. E-mail: takeito@keyaki.cc.u-tokai.ac.jp; Fax: +81 463 58 9543;
Tel: +81 463 58 1211 ex. 3737
b Department of Applied Chemistry, School of Engineering, Tokai University,
Hiratsuka 259-1292, Japan
c Chemical Resources Laboratory, Tokyo Institute of Technology, Midori-ku,
Yokohama 226-8503, Japan
† CCDC 1870335–1870337. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c8ce01658e
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the range of 400–1000 cm−1 together with peaks derived from
MAImC1 (methylene groups in 2800–3000 cm−1 and
methacryl group in 1200–1800 cm−1). This indicates the suc-
cessful formation of MAImC1–Na–Mo8 (1). The presence of
Na+ cation in 1 was revealed by X-ray structure analysis (see
below), and confirmed by EDX spectroscopy. IR spectrum of
the single crystals of 1 (Fig. 2b) obtained by recrystallization
was almost the same as that of the as-prepared 1 (Fig. 2a).
The powder X-ray diffraction (XRD) pattern of the as-
prepared 1 (Fig. 3a) was almost the same in the peak posi-
tions as the pattern calculated from the single crystal struc-
ture of 1 (Fig. 3b). These results demonstrate that both mo-
lecular and crystal structures of 1 were retained before and
after the recrystallization process.
Single crystal X-ray structure analysis clarified the molecu-
lar structure of 1 (Table 1 and Fig. 4a). The chemical formula
Fig. 1 Molecular structure of components. a) Octamolybdate (Mo8)
anions in ball and stick (green: Mo, red: O) and polyhedral
representations (left), and polymerizable ionic-liquid (MAImC1) cation
(right). b) Synthetic route of MAImC1-I.
was
[{CH2C(CH3)COOIJCH2)2}C3H3N2IJCH3)]3Naijβ-Mo8O26]
(denoted as MAImC1–Na–Mo8), in which three MAImC1 cat-
ions (1+ charge) were associated with one β-Mo8 anion
(4− charge) and one Na+ cation due to the charge compensa-
tion. One Na+ cation was sandwiched by two β-Mo8 anions to
possess eight-fold coordination environment (Na–O distance:
2.53–2.67 Å) to form one-dimensional (1D) infinite chain
(Fig. 4a and 5a). The 1D chain structure was similar to those
observed in Na+-containing pyridinium surfactant crystals of
β-Mo8.46,47
depended on the size of metal cations. Na+-containing hybrid
crystal of 1 was successfully polymerized by a radical poly-
merization as the inorganic–organic hybrid “monomer”, and
the conductivities of the inorganic–organic hybrid monomer
and polymer were evaluated.
This is the first example of the hybrid crystal constructed
from polymerizable ionic-liquid of MAImC1 and poly-
oxomolybdate. The hybrid crystal of 1, the hybrid
“monomer”, was successfully polymerized to form inorganic–
organic hybrid polymer as described below.
Results and discussion
Synthesis and structure of MAImC1–Na–Mo8 (1) hybrid
crystal
Starting polymerizable ionic-liquid of MAImC1 was synthe-
sized as iodide salt according to the procedure previously
reported (Fig. 1b, see Experimental section).34 Pale-yellow
precipitate was obtained from acidified molybdate solution
by adding MAImC1. The IR spectrum of the precipitate
(Fig. 2a) exhibited characteristic peaks of β-Mo8 anion38–40 in
Fig. 3 Powder X-ray diffraction patterns of hybrid crystals composed
of MAImC1 and Mo8. Calculated patterns were obtained from the
structure by single-crystal X-ray diffraction. a) As-prepared MAImC1–
Na–Mo8 (1). b) Calculated pattern of MAImC1–Na–Mo8 (1). c) Single
crystal of MAImC1–Ag–Mo8 (2). d) Calculated pattern of MAImC1–Ag–
Mo8 (2). e) Single crystal of MAImC1–K–Mo8 (3). f) Calculated pattern of
MAImC1–K–Mo8 (3).
Fig. 2 IR spectra of hybrid crystals composed of MAImC1 and Mo8. a)
As-prepared MAImC1–Na–Mo8 (1). b) Single crystal of MAImC1–Na–Mo8
(1). c) Single crystal of MAImC1–Ag–Mo8 (2). d) Single crystal of
MAImC1–K–Mo8 (3).
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Table 1 Crystallographic data
Compound
1
2
3
Chemical formula
Formula weight
C30H45N6NaMo8O32
1792.22
C32H56N6Ag2Mo8O32
2020.07
C24H36N6K2Mo8O30
1734.29
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Triclinic
P1
Triclinic
P1
Triclinic
P1
¯
¯
¯
12.4487(7)
14.0216(8)
17.0849(9)
112.2762IJ14)
93.2135IJ15)
105.0974IJ15)
2624.1(3)
2
9.5969(7)
10.9992IJ12)
14.5293IJ12)
87.894(12)
72.005(9)
75.7836IJ10)
1412.7(2)
1
9.822(3)
10.107(4)
12.444(4)
85.67(3)
86.14(3)
78.71(3)
1206.2(7)
1
α (°)
β (°)
γ (°)
V (Å3)
Z
ρcalcd (g cm−3
T (K)
)
2.268
193
1.951
2.374
93
2.478
2.387
93
2.276
μ(Mo Kα) (mm−1
)
No. of reflections measured
No. of independent reflections
Rint
No. of parameters
R1 (I > 2σ(I))
41 831
11 944
0.0712
700
0.0768
0.1742
25 493
6479
0.0470
365
0.0246
0.0577
15 617
5482
0.2095
295
0.0622
0.1874
wR2 (all data)
Fig. 4 Crystal structure of hybrid crystals composed of MAImC1 and Mo8 (C: gray, N: blue, O: red, Na: yellow, Ag: green, K: orange; Mo8 anions in
polyhedral representations). a) MAImC1–Na–Mo8 (1). b) MAImC1–Ag–Mo8 (2). c) MAImC1–K–Mo8 (3).
Synthesis and structure of MAImC1–Ag–Mo8 (2) hybrid crystal
H5)4]·2CH3CN (MAImC1–Ag–Mo8, Table 1). The crystal packing
is shown in Fig. 4b. The Mo8 anion in 2 was γ-Mo8 coordinated
by four ethoxo ligands.31 The dissolved β-Mo8 from 1 reacted
with ethanol to isomerize into ethoxo-grafted γ-Mo8 anions,
which reprecipitated as the crystals of 2. Two MAImC1 cat-
ions (1+ charge) and two Ag+ were associated with one γ-Mo8
anion (4− charge) to form 1D infinite chain structure (Fig. 5b).
One acetonitrile molecule of crystallization was bonded to
each Ag+ cation. Each Ag+ cation possessed six-fold coordina-
tion environment consisting of five Ag–O bonds (distance:
2.41–2.67 Å) and one Ag–N bond with a distance of 2.37 Å.
The Ag–Ag bond distance was 3.08 Å. The 1D chain structure
was similar to those observed in Na+-containing ionic-liquid
surfactant crystals of the ethoxo-grafted γ-Mo8 anions.31
The Na+ cation in 1 was successfully exchanged by other
monovalent metal cations. By the recrystallization process un-
der the presence of AgNO3, Ag+-introduced hybrid crystal of
MAImC1–Ag–Mo8 (2) was isolated as single crystals. The IR
spectra (Fig. 2c) of 2 suggested the presence of β-Mo8 anion,
but the single crystal X-ray structure analysis unveiled that 2
contained γ-type Mo8 (see below). The γ-Mo8 was coordinated
ethoxo ligands, and the Mo atoms possessed only six-fold co-
ordination environment. Therefore, to distinguish the ethoxo-
grafted γ-Mo8 and β-Mo8 by IR spectra was quite difficult. The
powder XRD pattern of 2 (Fig. 3c) was almost the same in the
peak positions as the pattern calculated from the single crys-
tal structure of 2 (Fig. 3d), suggesting the same molecular and
crystal structures at ambient temperature and 93 K. Slight dif-
ferences in the peak intensity and position of the patterns
may be due to the difference in the measurement temperature
(powder: ambient temperature, single crystal: 93 K).
Synthesis and structure of MAImC1–K–Mo8 (3) hybrid crystal
K+ cation was also successfully introduced into the hybrid
crystals consisting of MAImC1 and β-Mo8. The recrystalliza-
tion under the presence of KCl led the formation of the hybrid
crystal of MAImC1–K–Mo8 (3). The IR spectrum (Fig. 2d) of 3
The formula of 2 was ambiguously determined to be
[{CH2C(CH3)COOIJCH2)2}C3H3N2IJCH3)]2Ag2ijγ-Mo8O24IJOC2-
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“monomer” of 1 was evaluated under anhydrous atmosphere
(dry N2, 438 K). The Nyquist spectrum showed a suppressed
half circle in the high- and medium-frequency regions and
an inclined line in the low-frequency region (Fig. 6). The
equivalent circuit employed here is shown in the inset of
Fig. 6. It consists of bulk resistance and capacitance (Rb and
Cb), grain boundary resistance and capacitance (Rgb and Cgb),
and charge transfer resistance (Rct) along with double layer
capacitance (Cdl). ZW represents the Warburg impedance. The
red line in Fig. 6 represents simulated data with the equiva-
lent circuit successfully reproducing the measured spectrum.
The estimated value of Rb was 9.8 × 103 Ω, from which the
conductivity of 1 was calculated to be 7.8 × 10−6 S cm−1. The
carrier in the hybrid monomer of 1 is plausibly considered to
be Na+ cation.
The inorganic–organic hybrid polymer was successfully
synthesized by the radical polymerization of 1 by using 2,2′-
azobisIJisobutyronitrile) (AIBN) as an initiator. The resulting
polymer (P-MAImC1–Na–Mo8) was obtained as colourless pre-
cipitates derived from polymerizable cation,24,34 while several
POM hybrid polymers have been prepared with POMs having
covalently-grafted polymerizable group or with cationic
polymers.23,50–61 IR spectrum of hybrid polymer of P-MAImC1–
Na–Mo8 (Fig. 7a) exhibited characteristic peaks of the β-Mo8
anion in the range of 400–1000 cm−1, the same as that of the
hybrid monomer of 1 (Fig. 2a and b). This confirmed success-
ful polymerization of the hybrid monomer of 1 with the mo-
lecular structures retained. Fig. 7b shows powder XRD pat-
terns of the hybrid monomer and polymer consisting of
MAImC1–Na–Mo8. XRD patterns of P-MAImC1–Na–Mo8 hybrid
polymer did not show distinct peak except for halo patterns
typical for amorphous polymer phase, supporting the suc-
cessful polymerization of the hybrid monomer of 1. Some
weak peaks in the XRD patterns of P-MAImC1–Na–Mo8 were
different from those of 1 in their positions, and may be de-
rived from rather ordered structure of P-MAImC1–Na–Mo8. In
addition, solid-state 13C-magic angle spinning (MAS) NMR
Fig. 5 Molecular arrangements of Mo8 anions in the hybrid crystals
composed of MAImC1 and Mo8 (C: gray, N: blue, O: red, Na: yellow,
Ag: green, K: orange; Mo8 anions in polyhedral representations). a)
MAImC1–Na–Mo8 (1). b) MAImC1–Ag–Mo8 (2). c) MAImC1–K–Mo8 (3).
indicated that the β-Mo8 anions were hybridized in 3, being
confirmed by the single crystal X-ray structure analysis. The
powder XRD pattern of 3 (Fig. 3e) was different from that cal-
culated from the single crystal structure of 3 (Fig. 3f), which
suggests the change in the bulk structures owing to the re-
moval of the solvent of crystallization (acetonitrile, see below).
The crystal of 3 had a composition of [{CH2C(CH3)COO-
IJCH2)2}C3H3N2IJCH3)]2K2ijβ-Mo8O26]·2CH3CN (MAImC1–K–Mo8,
Table 1, Fig. 4c). Two MAImC1 cations (1+ charge) and two K+
were associated with one β-Mo8 anion (4− charge). In 3, the
β-Mo8 anions and K+ cations formed two-dimensional (2D)
layered structures (Fig. 5c), being different from 1 and 2.
There were two crystallographically independent K+ cations
as shown in Fig. 5c: one K+ cation was sandwiched by two
β-Mo8 anions to possess eight-fold coordination environment
(K–O distance: 2.72–2.89 Å). The other K+ cation was in the
six-fold coordination environment by four O atoms from
β-Mo8 (K–O distance: 2.70–2.82 Å) and two crystallographi-
cally equivalent N atoms from the acetonitrile molecules of
crystallization with a distance of 2.87 Å.
The changes in the arrangement of the β-Mo8 or γ-Mo8 an-
ion and metal cation will be owing to the size of metal cat-
ion. The larger size of metal cations led to an increase in the
dimensionality from 1D to 2D. Smaller metal cations of Na+
(1.18 Å in ionic radius)49 and Ag+ (1.15 Å)49 formed 1D chain
structure, while larger K+ cation (1.38 Å in 6-fold coordina-
tion; 1.51 Å in 8-fold coordination)49 resulted in 2D layered
structure. This connectivity between the Mo8 anions and
metal cations was relevant to other β-Mo8 hybrids.45,48
Fig. 6 Nyquist spectrum (open circles) of as-prepared hybrid mono-
mer of MAImC1–Na–Mo8 (1) at 438 K under anhydrous atmosphere and
simulated spectrum (red line) based on an equivalent electronic circuit
in the figure. The parameters obtained by the fitting are as follows: Rb
= 9.8 × 103 Ω, Rgb = 9.3 × 103 Ω, Rct = 1.5 × 103 Ω, Cb = 2.6 × 10−8 F,
Conductivity of MAImC1–Na–Mo8 (1) hybrid monomer and polymer
Cgb
=
8.2
×
10−9 F, Cdl 10−6 F, 104 s−1/2
= 1.0 × σ = 1.4 × Ω
Conductivity of 1 was investigated by alternate current (AC)
impedance spectroscopy. At first, the as-prepared hybrid
.
Z
 1 j  / 




w
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ered to be Na+ cations, while the detailed feature is under
investigation.
Experimental
Materials and methods
Materials. All chemical reagents except for the ionic-liquid
imidazolium (MAImC1) cation were purchased from Wako
Pure Chemical Industries, Ltd. (Wako) and Tokyo Chemical
Industry Co., Ltd. (TCI). 2,2′-AzobisIJisobutyronitrile) (AIBN,
Wako) was purified by recrystallization from ethanol before
use, and the other reagents were employed as received.
MAImC1 was prepared as iodide salt (MAImC1-I) according to
the previously described procedures.34
Methods. IR spectra (as KBr pellet) were recorded on a
Jasco FT/IR-4200ST spectrometer. Powder X-ray diffraction
(XRD) patterns were measured with a Rigaku MiniFlex300 dif-
fractometer by using Cu Kα radiation (λ = 1.54056 Å) at ambi-
ent temperature. CHN elemental analyses were performed
with a PerkinElmer 2400II elemental analyser. Energy disper-
sive X-ray spectroscopy (EDS) was performed on a Hitachi
Miniscope TM3030. Solution 1H NMR spectroscopy was
conducted with a Bruker AVANCE-500 NMR spectrometer
(500 MHz) at room temperature. Solid-state 13C-magic angle
spinning (MAS) NMR spectra (MAS rare 8 kHz) were recorded
with a Bruker AVANCE III 400WB spectrometer by using cross
polarization.
Conductivity measurements were carried out by alternat-
ing current (AC) impedance method. Pelletized powder sam-
ples sandwiched with Pt electrodes were employed. Anhy-
drous conductivities were measured in a frequency range
from 20 to 1.0 × 107 Hz using a Wayne Kerr 6510P induc-
tance–capacitance–resistance (LCR) meter under dry nitrogen
atmosphere. Conductivities under ambient atmosphere of rel-
ative humidity (RH) ∼30% and fully humidified conditions
of RH 95% were measured in a frequency range from 20 to
1.0 × 106 Hz using an Agilent technologies 4284A or a HIOKI
3532-50 LCR meter coupled with an Espec SH-641 bench-top
type temperature and humidity chamber.
Fig. 7 a) IR spectra of hybrid monomer of MAImC1–Na–Mo8 (1) (upper)
and P-MAImC1–Na–Mo8 hybrid polymer (bottom). b) Powder X-ray dif-
fraction patterns of hybrid monomer of MAImC1–Na–Mo8 (1) (upper)
and P-MAImC1–Na–Mo8 hybrid polymer (bottom). c) 13C MASNMR
spectra of hybrid monomer of MAImC1–Na–Mo8 (1) (bottom) and
P-MAImC1–Na–Mo8 hybrid polymer (upper).
spectra were compared before and after the polymerization of
1. After the polymerization (Fig. 7c, upper), two peaks at 36.4
and 44.4 ppm assigned to the methylene group newly
appeared, and peaks between 118 and 140 ppm assigned to
the carbon–carbon double bond (Fig. 7c, peaks b, c and g) in
methacryloyl and imidazolium groups changed to the broad
two peaks at 123.7 ppm and 137.4 ppm (Fig. 7c, upper),
which would be carbon peaks derived from only imidazolium
group. Furthermore, it was obvious that the carbonyl carbon
peak of methacryloyl group (Fig. 7c, peak d) was shifted from
166.3 ppm to 177.3 ppm (Fig. 7c, upper) after the polymeriza-
tion. Therefore, it was found from these 13C-NMR spectra
that methacryloyl groups of the monomer, 1, completely
converted to methylene structure in the polymer, P-MAImC1–
Na–Mo8. These changes indicated the successful polymeriza-
tion of the hybrid monomer of 1 by the radical coupling reac-
tion between the methacryloyl groups in MAImC1 cations of
each monomer component, although the molecular weight of
P-MAImC1–Na–Mo8 could not be measured by gel permeation
chromatography (GPC) owing to the low solubility of
P-MAImC1–Na–Mo8. The presence of Na+ cations in the hy-
brid polymer of P-MAImC1–Na–Mo8 was confirmed by EDS
spectroscopy.
Fig. 8 Nyquist spectra (open circles) of hybrid polymer of MAImC1–
Na–Mo8 (P-MAImC1–Na–Mo8) and simulated spectrum (red line) based
on an equivalent electronic circuit in the figure. a) Measured at 363 K
without additional humidity (RH ∼30%). The parameters obtained by
the fitting are as follows: Rb = 3.8 × 108 Ω, Rgb = 4.0 × 108 Ω, Rct = 7.0
× 106 Ω, Cb = 1.5 × 10−9 F, Cgb = 1.5 × 10−9 F, Cdl = 2.0 × 10−8 F. b)
Measured at 363 K with additional humidity (RH 95%). The parameters
obtained by the fitting are as follows: Rb = 3.4 × 103 Ω, Rgb = 3.5 × 103
Ω, Rct = 7.5 × 102 Ω, Cb = 9.5 × 10−8 F, Cgb = 1.8 × 10−8 F, Cdl = 4.0 ×
The hybrid polymer of P-MAImC1–Na–Mo8 exhibited a
conductivity of 5.0 × 10−10 S cm−1 at 363 K without addi-
tional humidity (relative humidity (RH) ∼30%) (Fig. 8a).
On the other hand, the conductivity of P-MAImC1–Na–Mo8
increased by five orders of magnitude to reach 5.1 × 10−5
S cm−1 at 363 K under additional humidity (RH 95%)
(Fig. 8b). The carrier of the conduction is plausibly consid-
10−6 F, σ = 4.0 × 102 Ω s−1/2
.
Z
 1 j  / 




w
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Synthetic procedures
MAImC1–Ag–Mo8 hybrid monomer (2)
An acetonitrile/ethanol solution (15 mL, 1 : 1 (v/v)) containing
as-prepared 1 (0.03 g) and solid AgNO3 (0.02 g) was heated at
348 K for 3 hours, and then the supernatant was kept at 303
MAImC1-I
Synthesis of 1-(2-chloroethyl)-1H-imidazole. The solution of
imidazole 2.04 g (30 mmol) in 1,2-dichloroethane (30 mL) was
added to tetrabutylammonium bromide 0.20 g (0.6 mmol) and
K2CO3 0.82 g (6 mmol). The result mixture was stirred at 358 K
for 5 h. The mixture was extracted with CHCl3, and the organic
layer was washed with water, dried (MgSO4) and evaporated.
The product was isolated by silica gel column chromatography
to give the title compound (1.47 g, 37%) as a colourless liquid.
1H NMR (500 MHz, CDCl3) δ 3.76 (t, J = 10 Hz, 2H), 4.28 (t, J =
10 Hz, 2H), 6.98 (s, 1H), 7.10 (s, 1H), 7.54 (s, 1H).
K
to obtain colourless plates of 2. Anal. calcd for
C22H36N4Ag2Mo8O31 (%): C, 14.39; H, 1.98; N, 3.05. Found: C,
14.74; H, 2.00; N, 3.27. IR (KBr, ν/cm−1): 3147w, 3110w,
3085w, 2971w, 2928w, 1717 m, 1635w, 1572w, 1455w, 1402w,
1376w, 1317w, 1295w, 1168 m, 1092w, 1049w, 1023w, 938s,
915s, 884 m, 844m, 717s, 671m, 622w, 557w, 525w cm−1.
MAImC1–K–Mo8 hybrid monomer (3)
Colourless needles of 3 were obtained by a similar procedure
for 2. Solid KCl (0.02 g) was employed instead of AgNO3.
Anal. calcd for C20H30N4K2Mo8O30 (%): C, 14.54; H, 1.83; N,
3.39. Found: C, 14.46; H, 1.96; N, 3.41. IR (KBr, ν/cm−1):
3146w, 3112w, 2984w, 2954w, 2926w, 1716m, 1634w, 1561w,
1455w, 1404w, 1362w, 1320w, 1299w, 1167m, 1045w, 938s,
916s, 843m, 817w, 721s, 667m, 634w, 558w, 518w cm−1.
Synthesis of 2-(1H-imidazol-1-yl) ethyl methacrylate. The
solution of 1-(2-chloroethyl)-1H-imidazole 1.13 g (13.2 mmol)
in THF (25 mL) was added to methacrylic acid 1.47 g (11.2
mmol) and K2CO3 3.58 g (25.9 mmol). The resulting mixture
was stirred at 339 K overnight. The mixture was extracted with
CHCl3, and the organic layer was washed with water, dried
(MgSO4), and evaporated. The product was isolated by silica
gel column chromatography to give 1.70 g (84%) of the title
1
P-MAImC1–Na–Mo8 hybrid polymer
compound as a colourless liquid. H NMR (500 MHz, CDCl3)
δ 1.93 (s, 3H), 4.25 (t, J = 5 Hz, 3H), 4.40 (t, J = 5 Hz, 3H), 5.61
(s, 1H), 6.10 (s, 1H), 6.96 (s, 1H), 7.08 (s, 1H), 7.51 (s, 1H).
Synthesis of 1-(2-(methacryloyloxy) ethyl)-3-methyl-1H-
imidazol-3-ium iodide (MAImC1-I). The solution of 2-(1H-
imidazol-1-yl) ethyl methacrylate 10 g (55.6 mmol) in 39.4 g
(278 mmol) iodomethane was stirred at 333 overnight. The
product was isolated by silica gel column chromatography to
In a 50 mL eggplant flask, 0.407 g (0.227 mmol) of MAImC1–
Na–Mo8 (1) and 16.0 mg (0.097 mmol) of 2,2′-
azobisIJisobutyronitrile) (AIBN) were dissolved in 1.8 mL of
DMF. After degassing the flask, it was sealed by a three-way
stopcock, and the mixture was stirred at 353 K for 20 h.
Then, the reaction mixture was poured into an excess amount
of ethyl acetate to precipitate the polymer. The obtained poly-
mer was washed with methanol and dried in vacuo to afford
0.352 g of P-MAImC1–Na–Mo8 (yield: 86.5%), which was insol-
uble in any solvent, such as chloroform, THF, DMSO, DMF
and NMP.
1
give 8.45 g (52%) of the title compound as a brown liquid. H
NMR (500 MHz, CDCl3) δ 1.85 (s, 3H), 3.86 (s, 3H), 4.43 (t, J =
5.5 Hz, 3H), 4.52 (t, J = 5.5 Hz, 3H), 5.72 (s, 1H), 6.04 (s, 1H),
7.71 (s, 1H), 7.79 (s, 1H), 9.15 (s, 1H).
Crystallography
MAImC1–Na–Mo8 hybrid monomer (1)
Single crystal X-ray diffraction measurements were
performed on a Rigaku R-AXIS RAPID diffractometer for 1
and a XtaLAB P200 diffractometer for 2 and 3 using graphite
monochromated Mo Kα radiation (λ = 0.71075 Å). Diffraction
data were collected and processed with PROCESS-AUTO62 for
1 and CrystalClear63 for 2 and 3. The structures were solved
by Superflip64 for 1 and 2 or SHELXS Version 2013/1IJref. 65)
for 3 and sequentially expanded using Fourier techniques.
The refinement procedure was performed by the full-matrix
least-squares using SHELXL Version 2014/7 (ref. 65) through
CrystalStructure software package.66 In the refinement pro-
cedure, most non-hydrogen atoms were refined anisotropi-
cally, and some non-hydrogen atoms in 3 were refined iso-
tropically. The hydrogen atoms on C atoms were located in
calculated positions.
As-prepared 1 was precipitated by a cation exchange reaction.
Na2MoO4·2H2O (1.0 g, 4.13 mmol) was dissolved in 10 mL of
H2O, and the pH was adjusted to 4.0 by 6 M HCl. To the
obtained clear colourless solution was added an ethanol solu-
tion (10 mL) of MAImC1-I (0.52 g, 1.55 mmol) to form
colourless suspension. The precipitates were isolated by fil-
tration, and dried in the ambient atmosphere to obtain pale-
yellow powder of as-prepared 1 (yield: 36%). An acetonitrile/
ethanol solution (15 mL, 1 : 1 (v/v)) of as-prepared 1 (0.05 g)
was heated at 348 K for 3 hours, and then the supernatant
was stored at 303 K or slowly evaporated at room temperature
to obtain colourless plates of 1. Anal. calcd for
C30H45N6NaMo8O32 (%): C, 20.10; H, 2.53; N, 4.69. Found: C,
19.87; H, 2.52; N, 4.71. IR (KBr, ν/cm−1): 3149w, 3115w,
2960w, 2925w, 1719w, 1637w, 1562w, 1450w, 1319w, 1296w,
1166w, 1012w, 971m, 920s, 884w, 795s, 649w, 622w, 537w.
3151w, 3090w, 3014w, 2959w, 2926w, 1719s, 1632w, 1559w,
1445w, 1403w, 1380w, 1362w, 1317w, 1294m, 1254w, 1169s,
1043w, 939s, 915s, 841m, 814w, 764w, 717s, 653m, 624w,
553w, 523w cm−1.
Conclusions
Polymerizable ionic-liquid (MAImC1) was utilized to construct
the inorganic–organic hybrid crystals of octamolybdate (Mo8)
anions. The hybrid crystals contained metal cations such as
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Na+, Ag+, and K+, which were successfully introduced by the
well-controlled synthetic manner. Each metal cation was
connected to Mo8 anions, while the dimensionality changed
depending on the size of metal cations. In addition, the Na+
cation-containing hybrid crystal (MAImC1–Na–Mo8) worked as
the inorganic–organic hybrid “monomer”. The radical poly-
merization of MAImC1–Na–Mo8 with AIBN led to successful
formation of the inorganic–organic hybrid polymer of
P-MAImC1–Na–Mo8 without any compositional change. These
hybrid monomer and polymer of MAImC1–Na–Mo8 are prom-
ising as unconventional solid electrolyte or electrode material
for sodium-ion batteries due to the conductive property of
ionic-liquids and redox characteristics of POMs.
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
Dr. Yoshiki Oda and Dr. Tsubasa Kawaguchi (Technology Joint
Management Office, Tokai University) were gratefully acknowl-
edged for the solid-state NMR measurements. This work was
financially supported in part by JSPS KAKENHI Grant Number
JP26410245, and Research and Study Project of Tokai Univer-
sity Educational System General Research Organization.
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