Dimensional Control in Polyoxometalate Crystals Hybridized with Amphiphilic Polymerizable Ionic Liquids

Ionic liquids are an important component for constructing functional materials, and polyxometalate cluster anion is a promising partner for building inorganic–organic hybrid materials comprising ionic liquids. In such hybrid materials, the precise control of the molecular arrangement in the bulk structures is crucial for the emergence of characteristic functions, which can be realized by introducing an amphiphilic moiety into the ionic liquids. Here, an amphiphilic polymerizable imidazolium ionic liquid with a methacryloyl group was firstly hybridized with polyoxometalate anions of octamolybdate ([Mo8O26]4−, Mo8) and silicotungstate ([SiW12O40]4−, SiW12) to obtain inorganic–organic hybrid crystals. The polymerizable ionic liquid with a octyl chain (denoted as MAImC8) resulted in the formation of anisotropic molecular arrangements in the bulk crystal structure, which was compared with the hybrid crystals composed from the polymerizable ionic liquid without a long alkyl chain (denoted as MAIm). Rather densely packed isotropic molecular arrangements were observed in the hybrid crystals of MAIm–Mo8 and MAIm–SiW12 due to the lack of the amphiphilic moiety. On the other hand, using the amphiphilic MAImC8 cation gave rise to a honeycomb-like structure with the Mo8 anion and a layered structure with the SiW12 anion, respectively.


Introduction
Ionic liquid molecules attract extensive attention from researchers owing to their characteristic properties such as conductivity, catalysis, and separation abilities [1][2][3][4][5][6][7][8][9][10][11]. These properties are quite attractive for the construction of functional materials. The hybridization of ionic liquids as organic components with other inorganic counter parts is effective for building up functional inorganic-organic hybrid materials. To select inorganic counter parts for the hybridization is crucial for improving the thermal stability and other properties.
Recently, we designed a polymerizable ionic liquid cation with an imidazolium moiety with a methacryloyl group ([{CH 2 =C(CH 3 )COO(CH 2 ) 2 }C 3 H 3 N 2 (CH 3 )] + , denoted as MAImC 1 , Figure 1a), and successfully synthesized inorganic-organic hybrid monomers and polymers with several POM anions [42][43][44]. These MAImC 1 -POM hybrids were isolated as single crystals with clarified structures, and behaved as monomers of hybrid polymers exhibiting high conductivity as solid electrolytes [44]. In the MAImC 1 -POM hybrid monomers, the POM arrangements in the bulk crystal structures were isotropic due to the small molecular size of the MAImC 1 cation. Introducing an amphiphilic moiety into MAImC 1 will give rise to a more anisotropic molecular arrangement of POM anions derived from the structure-directing ability of the amphiphilic moiety [30][31][32].
Here we report the first syntheses of POM hybrid crystals with amphiphilic polymerizable ionic liquids.
Recently, we designed a polymerizable ionic liquid cation with an imidazolium moiety with a methacryloyl group ([{CH2=C(CH3)COO(CH2)2}C3H3N2(CH3)] + , denoted as MAImC1, Figure 1a), and successfully synthesized inorganic-organic hybrid monomers and polymers with several POM anions [42][43][44]. These MAImC1-POM hybrids were isolated as single crystals with clarified structures, and behaved as monomers of hybrid polymers exhibiting high conductivity as solid electrolytes [44]. In the MAImC1-POM hybrid monomers, the POM arrangements in the bulk crystal structures were isotropic due to the small molecular size of the MAImC1 cation. Introducing an amphiphilic moiety into MAImC1 will give rise to a more anisotropic molecular arrangement of POM anions derived from the structure-directing ability of the amphiphilic moiety [30][31][32].
Here we report the first syntheses of POM hybrid crystals with amphiphilic polymerizable ionic liquids. The amphiphilic polymerizable ionic liquid is a MAImC1 derivative with a long octyl chain instead of a methyl group ( [42,44]. The hybrid crystals with MAImC8 contained anisotropic arrangements of POM anions in their bulk crystal structures due to the presence of an amphiphilic moiety, while hybrid crystals with MAIm exhibited isotropic POM arrangements.
Infrared (IR) spectra were recorded on a Jasco FT/IR-4200ST spectrometer (JASCO Corporation, Tokyo, Japan) by the KBr pellet method. Powder X-ray diffraction (XRD) patterns were measured with a Rigaku MiniFlex300 diffractometer (Rigaku Corporation, Tokyo, Japan) by using Cu Kα radiation (λ = 1.54056 Å) at ambient temperature. CHN (carbon, hydrogen, and nitrogen) elemental analyses were performed with a PerkinElmer 2400II elemental analyzer (PerkinElmer, Waltham, MA, USA). As-prepared MAIm-Mo 8 (denoted as 1) was initially precipitated by a cation exchange reaction. Na 2 MoO 4 ·2H 2 O (1.0 g, 4.1 mmol) was dissolved in 10 mL of H 2 O, and then the pH was adjusted to 3.8 by 6 M HCl. To the obtained homogeneous solution was added an ethanol solution (10 mL) of MAIm-N (0.28 g, 1.6 mmol) neutralized by 1 M HCl (2.0 mL). The resulting suspension was filtered to obtain colorless precipitates, which was dried under ambient atmosphere to obtain colorless precipitates (0.73 g, yield: 48%). An acetonitrile/ethanol solution (20 mL, 1:1 (v/v)) of as-prepared 1 (0.03 g) was heated at ca. 343 K for 3 h, and then the supernatant was slowly evaporated at room temperature to obtain colorless plates of 1.

Synthesis of MAImC 8 -Mo 8
As-prepared MAImC 8 -Mo 8 (denoted as 2) was synthesized and recrystallized by a similar procedure to 1. Na 2 MoO 4 ·2H 2 O (0.51 g, 2.1 mmol) dissolved in 10 mL of H 2 O was adjusted to pH 3.8 by 6 M HCl, and then an ethanol solution (10 mL) of MAImC 8 ·Br (0.30 g, 0.80 mmol) was added. The resulting suspension was filtered and dried to obtain colorless precipitates (0.38 g, yield: 47%). An acetonitrile/ethanol solution (20 mL, 1:1 (v/v)) of as-prepared 2 (0.03 g) was heated at ca. 343 K for 3 hours, and the supernatant was slowly evaporated at room temperature to obtain colorless plates of 2. CHN elemental analysis: Calcd for C 51

X-ray Crystallography
Single crystal X-ray diffraction measurements for 1-3 were performed with an ADSC Q210 CCD area detector by using synchrotron radiation (λ = 0.60000-0.80000 Å, Table 1) at 2D beamline in the Pohang Accelerator Laboratory (PAL, a synchrotron radiation facility in Pohang, Republic of Korea). The processing of both diffraction images and absorption correction were performed with HKL3000 [45]. The diffraction measurements for 4 were made on a Rigaku XtaLAB P200 diffractometer (Rigaku Corporation, Tokyo, Japan) using graphite monochromated Mo Kα radiation, and the data were collected and processed using CrysAlisPro [46]. The structures were solved by the dual-space algorithm using SHELXT Version 2014/5 [47] or SHELXS Version 2013/1 [48], and refined by the full-matrix least-squares method on F 2 using SHELXL Version 2014/7 [48]. All calculations were performed using the CrystalStructure software package [49]. Most non-hydrogen atoms were refined anisotropically, and the hydrogen atoms of organic moieties were refined using the riding model. Further details of the crystal structure investigation may be obtained free of charge from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or E-Mail: deposit@ccdc.cam.ac.uk (CCDC 1934917-1934920).
Both as-prepared precipitates of 1 and 2 were successfully recrystallized by using acetonitrile/ethanol solution to obtain single crystals. The IR spectra of recrystallized 1 (Figure 2b) were almost identical to that of the as-prepared 1 (Figure 2a), indicating that the molecular structures were retained before and after the recrystallization. The molecular structures of 2 were also the same before and after the recrystallization as observed in the IR spectra of hybrid crystal 2 (Figure 2c,d).
X-ray structure analyses together with CHN elemental analyses revealed that the  Figure 3). Both hybrid crystals contained three MAIm (1+ charge) or MAImC 8 (1+ charge) and one Na + associated with one β-type Mo 8 anion (4− charge), being similar to other hybrid crystals consisting of β-type Mo 8 anions [42,53,54]. Both crystal structures contained a one-dimensional (1D) infinite chain composed of the Na + cation and Mo 8 anion (Mo 8 -Na + 1D chain) as shown in Figure 3a,b, while the coordination environments of Na + were different. The Na + cation in 1 was surrounded by O atoms of two Mo 8 anions and two MAIm cations, and located in a six-fold coordination environment (Na-O distance: 2.28-2.43 Å, mean value: 2.36 Å) to form a zig-zag chain structure (Figure 3a, right). On the other hand, the Na + cation in 2 was sandwiched by only two β-Mo 8 anions to possess an eight-fold coordination environment (Na-O distance: 2.40−2.90 Å, mean value: 2.60 Å), resulting in a more straight chain structure (Figure 3b, right).  Figure 3). Both hybrid crystals contained three MAIm (1+ charge) or MAImC8 (1+ charge) and one Na + associated with one β-type Mo8 anion (4-charge), being similar to other hybrid crystals consisting of β-type Mo8 anions [42,53,54]. Both crystal structures contained a one-dimensional (1D) infinite chain composed of the Na + cation and Mo8 anion (Mo8-Na + 1D chain) as shown in Figure 3a,b, while the coordination environments of Na + were different. The Na + cation in 1 was surrounded by O atoms of two Mo8 anions and two MAIm cations, and located in a six-fold coordination environment (Na-O distance: 2.28-2.43 Å , mean value: 2.36 Å ) to form a zig-zag chain structure (Figure 3a, right). On the other hand, the Na + cation in 2 was sandwiched by only two β-Mo8 anions to possess an eight-fold coordination environment (Na-O distance: 2.40−2.90 Å , mean value: 2.60 Å), resulting in a more straight chain structure (Figure 3b, right).
In addition, the packing manners of the Mo8-Na + 1D chains in the crystal structures of 1 and 2 were different. The Mo8-Na + 1D chains in 1 were rather densely packed in the crystal structure (Figure 3a, left), while the Mo8-Na + 1D chains in 2 were located more separately, to exhibit a honeycomb-like structure along the a-axis direction (Figure 3b, left). Namely, 1 had a rather isotropic arrangement of the Mo8-Na + 1D chains, while 2 possessed a more anisotropic arrangement of the Mo8-Na + 1D chains in the bulk crystal structure. This difference in the arrangements of the Mo8-Na + 1D chains between 1 and 2 will be due to the presence of the amphiphilic moiety in the polymerizable ionic liquid cations. The MAImC8 had a long alkyl chain, which interacted with itself to control the arrangement of the Mo8-Na + 1D chain in the crystal structures of 2 [30][31][32]. As shown in Figure 3c, several C-C bonds in the methylene groups of MAImC8 had a gauche conformation, which forced both octyl and methacryloyl groups to locate to the same side against the charged and hydrophilic imidazolium ring. These molecular conformations of MAImC8 caused the segregation of hydrophilic and hydrophobic parts in the crystal structure of 2, resulting in the anisotropic honeycomb-like arrangement of the Mo8-Na + 1D chains (Figure 3b, left). The octyl chains were not interdigitated in a straight manner.   Powder XRD patterns of as-prepared 1 and 2 (Figure 4a,c) were quite similar in the peak positions to the patterns calculated from the single crystal structure of 1 and 2 (Figure 4b,d), indicating that the crystal structures of 1 and 2 were retained before and after the recrystallization. Slight differences in the peak intensity and position of the patterns may be derived from the difference in the measurement temperature (powder: ambient temperature, single crystal: 100 K). This suggests that the Mo8-Na + 1D chains were already formed in the as-prepared precipitates due to their stable and rigid structures. The amphiphilic moiety of MAImC8 in 2 also contributed to the formation of a stable and rigid crystal structure derived from the van der Waals interactions between the octyl chains. In addition, the packing manners of the Mo 8 -Na + 1D chains in the crystal structures of 1 and 2 were different. The Mo 8 -Na + 1D chains in 1 were rather densely packed in the crystal structure (Figure 3a, left), while the Mo 8 -Na + 1D chains in 2 were located more separately, to exhibit a honeycomb-like structure along the a-axis direction (Figure 3b, left). Namely, 1 had a rather isotropic arrangement of the Mo 8 -Na + 1D chains, while 2 possessed a more anisotropic arrangement of the Mo 8 -Na + 1D chains in the bulk crystal structure. This difference in the arrangements of the Mo 8 -Na + 1D chains between 1 and 2 will be due to the presence of the amphiphilic moiety in the polymerizable ionic liquid cations. The MAImC 8 had a long alkyl chain, which interacted with itself to control the arrangement of the Mo 8 -Na + 1D chain in the crystal structures of 2 [30][31][32]. As shown in Figure 3c, several C-C bonds in the methylene groups of MAImC 8 had a gauche conformation, which forced both octyl and methacryloyl groups to locate to the same side against the charged and hydrophilic imidazolium ring. These molecular conformations of MAImC 8 caused the segregation of hydrophilic and hydrophobic parts in the crystal structure of 2, resulting in the anisotropic honeycomb-like arrangement of the Mo 8 -Na + 1D chains (Figure 3b, left). The octyl chains were not interdigitated in a straight manner.
Powder XRD patterns of as-prepared 1 and 2 (Figure 4a,c) were quite similar in the peak positions to the patterns calculated from the single crystal structure of 1 and 2 (Figure 4b,d), indicating that the crystal structures of 1 and 2 were retained before and after the recrystallization. Slight differences in the peak intensity and position of the patterns may be derived from the difference in the measurement temperature (powder: ambient temperature, single crystal: 100 K). This suggests that the Mo 8 -Na + 1D chains were already formed in the as-prepared precipitates due to their stable and rigid structures. The amphiphilic moiety of MAImC 8 in 2 also contributed to the formation of a stable and rigid crystal structure derived from the van der Waals interactions between the octyl chains.  (b) calculated pattern of 1 using the structure obtained by single-crystal X-ray diffraction; (c) as-prepared 2; (d) calculated pattern of 2 using the structure obtained by single-crystal X-ray diffraction.

SiW12 Hybrids with Polymerizable Ionic Liquids
Dodecatungstosilicate (SiW12) hybrids with the polymerizable ionic liquids were obtained as colorless precipitates in ca. 50% yield for MAIm-SiW12 (3) and ca. 70% yield for MAImC8-SiW12 (4), respectively. The characteristic peaks of SiW12 [17,44,55] were observed for as-prepared 3 ( Figure  5a) and 4 (Figure 5c) in the range of 400-1100 cm −1 of IR spectra. The presence of the polymerizable ionic liquids were confirmed by the IR spectra (in the range of 2800-3000 cm −1 for methylene groups and 1200-1800 cm −1 for methacryloyl group), which showed successful formation of the hybrid crystals comprising SiW12 and the polymerizable ionic liquids.
Single crystals of 3 were obtained from 1,4-dioxane (C4H4O2) solution, while single crystals of 4 were grown from 1,4-dioxane/ethanol solution. As-prepared 3 (Figure 5a) and recrystallized 3 (Figure 5b) were almost the same in the IR spectra, indicating the retention of the molecular structures before and after the recrystallization. A slight difference in the peaks in the range of 1500-1700 cm −1 may be derived from the difference in the crystal structures of as-prepared 3 and recrystallized 3 (see below). The retention of the molecular structures of 4 was also verified by the IR spectra measured before and after the recrystallization (Figure 5c,d).

SiW 12 Hybrids with Polymerizable Ionic Liquids
Dodecatungstosilicate (SiW 12 ) hybrids with the polymerizable ionic liquids were obtained as colorless precipitates in ca. 50% yield for MAIm-SiW 12 (3) and ca. 70% yield for MAImC 8 -SiW 12 (4), respectively. The characteristic peaks of SiW 12 [17,44,55] were observed for as-prepared 3 (Figure 5a) and 4 (Figure 5c) in the range of 400-1100 cm −1 of IR spectra. The presence of the polymerizable ionic liquids were confirmed by the IR spectra (in the range of 2800-3000 cm −1 for methylene groups and 1200-1800 cm −1 for methacryloyl group), which showed successful formation of the hybrid crystals comprising SiW 12 and the polymerizable ionic liquids.  (Table  1). These hybrid crystals contained four polymerizable ionic liquid cations (1+ charge) associated with one SiW12 anion (4-charge). All of the protons of the starting H-SiW12 were replaced by ion-exchange reactions without remaining counter cations after the hybridization [44,[56][57][58], which was different from the cases of Mo8 hybrid crystals of 1 and 2. Both recrystallized SiW12 hybrid crystals of 3 and 4 contained the solvents of crystallization (1,4-dioxane utilized in the recrystallization process for 3; 1,4-dioxane and water for 4), which also contrasts with the Mo8 hybrid crystals of 1 and 2. Figure 6 depicts crystal structures of 3 ( Figure 6a) and 4 (Figure 6b). In both crystals, each SiW12 anion was isolated by the imidazolium moieties of the polymerizable ionic liquids (Figure 6a, right for 3; Figure 6b, right for 4).
The molecular arrangements of the SiW12 anions in the bulk crystal structures of 3 and 4 were quite different. The SiW12 anions are arranged rather densely and isotropically in 3 (Figure 6a, left). On the contrary, the SiW12 anions in 4 formed the inorganic monolayers sandwiched by the MAImC8 organic layers with an interlayer distance of 20.2 Å (Figure 6b, left), and exhibited much more anisotropic structure than 3. Such anisotropic molecular arrangement will be induced by the amphiphilic moiety of the MAImC8 cations. The MAImC8 in 4 had similar conformations to those observed in 2 (Figure 3c). The octyl chains in 4 were not interdigitated in a straight manner as in the crystals of 2. Single crystals of 3 were obtained from 1,4-dioxane (C 4 H 4 O 2 ) solution, while single crystals of 4 were grown from 1,4-dioxane/ethanol solution. As-prepared 3 (Figure 5a) and recrystallized 3 (Figure 5b) were almost the same in the IR spectra, indicating the retention of the molecular structures before and after the recrystallization. A slight difference in the peaks in the range of 1500-1700 cm −1 may be derived from the difference in the crystal structures of as-prepared 3 and recrystallized 3 (see below). The retention of the molecular structures of 4 was also verified by the IR spectra measured before and after the recrystallization (Figure 5c,d).
Chemical  (Table 1). These hybrid crystals contained four polymerizable ionic liquid cations (1+ charge) associated with one SiW 12 anion (4− charge). All of the protons of the starting H-SiW 12 were replaced by ion-exchange reactions without remaining counter cations after the hybridization [44,[56][57][58], which was different from the cases of Mo 8 hybrid crystals of 1 and 2. Both recrystallized SiW 12 hybrid crystals of 3 and 4 contained the solvents of crystallization (1,4-dioxane utilized in the recrystallization process for 3; 1,4-dioxane and water for 4), which also contrasts with the Mo 8 hybrid crystals of 1 and 2. Figure 6 depicts crystal structures of 3 ( Figure 6a) and 4 ( Figure 6b). In both crystals, each SiW 12 anion was isolated by the imidazolium moieties of the polymerizable ionic liquids (Figure 6a, right for 3; Figure 6b, right for 4). The powder XRD pattern of as-prepared 3 (Figure 7a) was different from that calculated from the single crystal structure of 3 (Figure 7b). This demonstrates that the crystal structures of 3 changed after the recrystallization, probably because of desolvation of solvent molecules of the crystals under the ambient atmosphere. On the other hand, powder XRD patterns of as-prepared 4 ( Figure 7c) were essentially similar to the patterns calculated from the single crystal structure of 4 ( Figure 7d), indicating that the crystal structures of 4 were retained before and after the recrystallization. These results suggest that the amphiphilic moiety of the polymerizable ionic liquid enabled formation of the stable crystal structures of 4 owing to the van der Waals interactions between the octyl chains. The powder XRD pattern of as-prepared 3 (Figure 7a) was different from that calculated from the single crystal structure of 3 ( Figure 7b). This demonstrates that the crystal structures of 3 changed after the recrystallization, probably because of desolvation of solvent molecules of the crystals under the ambient atmosphere. On the other hand, powder XRD patterns of as-prepared 4 ( Figure 7c) were essentially similar to the patterns calculated from the single crystal structure of 4 (Figure 7d), indicating that the crystal structures of 4 were retained before and after the recrystallization. These results suggest that the amphiphilic moiety of the polymerizable ionic liquid enabled formation of the stable crystal structures of 4 owing to the van der Waals interactions between the octyl chains.

Discussion
As observed in the crystal structures of 2 and 4, introducing the amphiphilic moiety into the polymerizable ionic liquid enabled the construction of the anisotropic molecular arrangements of POM inorganic clusters in the bulk crystal structures. The amphiphilic MAImC8 cation behaved as a structure-directing reagent, like typical surfactants [30][31][32], owing to the van der Waals interactions between the octyl chains of MAImC8. The presence of a long alkyl chain in the polymerized ionic liquids induced the segregation of hydrophilic parts (charged POM and imidazolium ring) and a hydrophobic moiety (alkyl chain and methacryloyl group), which led to the formation of the anisotropic POM arrangements in the crystal structures of 2 and 4. Introducing the amphiphilic moiety into the polymerizable ionic liquid also realized stable crystal structures. The crystal structures of 2 and 4 were retained before and after the recrystallization process, although the crystal structures of the hybrid crystal of 3 without the amphiphilic moiety changed in their crystal structures through the recrystallizations procedures.
The β-type Mo8 anion tends to coordinate metal cations to form a 1D chain or two-dimensional (2D) layered structures [42,54]. The smaller metal cations such as Na + or Ag + preferred the 1D chain structure, while the larger cations such as K + or Cs + gave rise to a 2D layered structure. In the case of 1 and 2, the Na + cation of the starting material (Na2MoO4·2H2O) remained to form the Mo8-Na + 1D chain structures in the crystal structures. Furthermore, 1 and 2 kept their molecular and crystal structures before and after the recrystallization (Figures 2 and 4), suggesting the retention of the Mo8-Na + 1D chain structures. These stable Mo8-Na + 1D chain structures could be beneficial to the Na + -conducting materials. On the other hand, the typical Keggin-type SiW12 anion exhibits Td symmetry, which is higher than the C2h symmetry of the β-Mo8 anion (Figure 1b) [59,60]. The more spherical SiW12 anion tends to be surrounded by the heterocyclic moiety of the polymerizable ionic liquid or surfactant [44,56], resulting in the isolated arrangement of SiW12 without the coordination by metal cations.
As described here, introducing the amphiphilic moiety into the polymerizable ionic liquid is an effective way to control the POM arrangements in the hybrid single crystals. Such controlled arrangement of POM anions will have beneficial emergent functions such as conductive properties [12,13,29]. In principle, these POM hybrid crystals of 1-4 behave as inorganic-organic hybrid

Discussion
As observed in the crystal structures of 2 and 4, introducing the amphiphilic moiety into the polymerizable ionic liquid enabled the construction of the anisotropic molecular arrangements of POM inorganic clusters in the bulk crystal structures. The amphiphilic MAImC 8 cation behaved as a structure-directing reagent, like typical surfactants [30][31][32], owing to the van der Waals interactions between the octyl chains of MAImC 8 . The presence of a long alkyl chain in the polymerized ionic liquids induced the segregation of hydrophilic parts (charged POM and imidazolium ring) and a hydrophobic moiety (alkyl chain and methacryloyl group), which led to the formation of the anisotropic POM arrangements in the crystal structures of 2 and 4. Introducing the amphiphilic moiety into the polymerizable ionic liquid also realized stable crystal structures. The crystal structures of 2 and 4 were retained before and after the recrystallization process, although the crystal structures of the hybrid crystal of 3 without the amphiphilic moiety changed in their crystal structures through the recrystallizations procedures.
The β-type Mo 8 anion tends to coordinate metal cations to form a 1D chain or two-dimensional (2D) layered structures [42,54]. The smaller metal cations such as Na + or Ag + preferred the 1D chain structure, while the larger cations such as K + or Cs + gave rise to a 2D layered structure. In the case of 1 and 2, the Na + cation of the starting material (Na 2 MoO 4 ·2H 2 O) remained to form the Mo 8 -Na + 1D chain structures in the crystal structures. Furthermore, 1 and 2 kept their molecular and crystal structures before and after the recrystallization (Figures 2 and 4), suggesting the retention of the Mo 8 -Na + 1D chain structures. These stable Mo 8 -Na + 1D chain structures could be beneficial to the Na + -conducting materials. On the other hand, the typical Keggin-type SiW 12 anion exhibits T d symmetry, which is higher than the C 2h symmetry of the β-Mo 8 anion (Figure 1b) [59,60]. The more spherical SiW 12 anion tends to be surrounded by the heterocyclic moiety of the polymerizable ionic liquid or surfactant [44,56], resulting in the isolated arrangement of SiW 12 without the coordination by metal cations.
As described here, introducing the amphiphilic moiety into the polymerizable ionic liquid is an effective way to control the POM arrangements in the hybrid single crystals. Such controlled arrangement of POM anions will have beneficial emergent functions such as conductive properties [12,13,29]. In principle, these POM hybrid crystals of 1-4 behave as inorganic-organic hybrid monomers to construct hybrid polymers [20,[42][43][44], which could pave the way to another category of conductive materials. The polymerization of these hybrids and investigation of conductivities are in progress.