Protic Organic Ionic Plastic Crystals

Transcription

1 Structure and Ion Dynamics in Imidazolium-based Protic Organic Ionic Plastic Crystals Haijin Zhu *,1,2, Xiaoen Wang 1,2, R. Vijayaraghavan 3, Yundong Zhou 1, Douglas R. MacFarlane 3, Maria Forsyth *,1,2 1 Institute for Frontier Materials, Deakin University, Geelong, Victoria 3216, Australia. 2 ARC Centre of Excellence for Electromaterials Science, Deakin University, 221 Burwood Highway, Burwood, Victoria 3125, Australia. 3 School of Chemistry, Monash University, Clayton, Victoria 3169, Australia Corresponding Author *Tel: h.zhu@deakin.edu.au (H Zhu); maria.forsyth@deakin.edu.au (M Forsyth). 1

2 1. Material Synthesis 1.1 Synthesis of 1-methyl-3H-imidazolium triflate (HMIM Tf) Aqueous solution of triflic acid (6.5g, 0.043moles) was slowly added to aqueous solution of 1-methyl imidazole (3.5 g, moles) in an ice bath and the contents were stirred for 1h. Then water was distilled using rotary evaporator under vacuum to give white solid (9.85 g, yield 98.5%). The product was dried at room temperature in a vacuum desiccator for a couple of days to remove traces of water. The stoichiometry was confirmed by determining the ph of a 0.1 M aqueous solution of the material and found to be in satisfactory agreement with a control aqueous sample. It was then characterized by Electrospray Mass Spectrometry to detect the respective cations and anions of the ionic liquid. Electrospray mass spectroscopy analysis, (cone ±25V) : HMIM Tf MS [ES] + =83.0; MS [ES] - = Synthesis of Imidazolium triflate (H 2 IM Tf) Aqueous solution of triflic acid (6.9g, 0.046moles) was slowly added to aqueous solution of imidazole (3.1 g, moles) in an ice bath and the contents were stirred for 1h. Then water was removed under reduced pressure to get white solid (9.8 g, yield 98%). The product was further dried at room temperature in a vacuum desiccator to ensure removal of traces of water. The stoichiometry was confirmed by determining the ph of a 0.1 M aqueous solution 2

3 of the material and found to be in satisfactory agreement with a control aqueous sample. Electrospray Mass Spectrometry was then employed to characterize the product. Electrospray mass spectroscopy analysis, (cone ±25V) : H 2 IM Tf MS [ES] + =69.0; MS [ES] - = Experimental 2.1 Solid state NMR All the NMR experiments were performed on a Bruker Avance III 500 MHz wide-bore NMR spectrometer operating at 1 H Lamor Frequency of MHz. A 5 mm double resonance static probe head was used for all the static 1 H, 19 F and 13 C variable temperature NMR experiments. A 4 mm double resonance DVT MAS probe was used for the 1 H 13 C and 19 F 13 C CP-static/MAS experiments. A 1.3 mm double resonance probe was used to run the 1H NMR at 62.5 khz at 0 oc and 50 o C, to gain a higher 1 H NMR resolution. The sample temperatures for all the static and MAS experiments were calibrated separately with the isotropic chemical shifts of lead nitrate at different temperatures using the method described in literature. 1 3

4 2.2 Synchrotron X-ray Diffraction Synchrotron X-ray diffraction patterns of the solid powder samples were collected on the Powder Diffraction beamline at the Australian Synchrotron (Clayton, Melbourne) at a wavelength of = (2) A (Calibrated using a LaB6 reference). Samples were filled into a 300 µm diameter glass capillary tube in the glovebox and sealed with flame for data collection. Unit cell indexing and refinement of the diffraction data were carried out using the software GSAS-II 2 based on the least square theory. 2.3 DSC measurements DSC experiments were performed on a TA-Q100 instrument. The samples were first cooled down to -100 o C, and then three temperature cycles between -100 ~ 250 o C were scanned and recorded. The heating and cooling rates were 10 o C/min for both samples. Thermograms of the cooling and the second heating scan were presented. 2.4 AC impedance spectroscopy The ionic conductivity was measured using a solartron SI1260 impedance/gain phase analyzer, which is connected to a solartron 1296 dielectric interface with the frequency range from 1 Hz to 1 MHz. A pair of gold coated stainless steel blocking electrodes was used to avoid the reactions with electrodes. The whitish powder samples were pressed into pellets and then sandwiched between the electrodes. Both samples were packed and air-tightly sealed into a testing cell in an argon atmosphere. Sample temperature was controlled with a Eurotherm controller (model 2204), and measured with a type T thermal couple attached to one electrode. An equilibration time of 15 mins was applied to each temperature before measurements. 4

5 3. Supplementary Results Table S1. The space group and unit cell parameters including a, b, c, α, β, γ, and unit cell volume of HMIM. Phase Space group a(å) b(å) c(å) a( ) β( ) Y( ) Unit cell volume(å 3 ) I P4/mmm (Tetragonal) II III (- 10 ) P1 (Triclinic) P1 (Triclinic) Table S2. The space group and unit cell parameters including a, b, c, α, β, γ, and unit cell volume of H 2 IM. Phase Space group a(å) b(å) c(å) a( ) β( ) Y( ) Unit cell volume(å 3 ) I R3-H (Trigonal) II P1 (Triclinic) III P1 (Triclinic)

6 IV C2/m (Monoclinic)

7 Figure S1. Solution-state 1 H NMR spectra of the H 2 IM and HMIM samples. 1 mol/l D2O solution were prepared for the NMR measurements, and the spectra were recorded at 22 o C. Figure S2. 1 H Magic-angle spinning NMR spectra of the HMIM and H 2 IM sample measured at 62.5 khz. Close inspection may find a shoulder in the peak of N-H group (at about 12 ppm) of the H 2 IM sample 50 o C spectrum. This may indicate a slightly different environment for the two N-H protons in the imidazolium cation in solid Phase III. 7

8 (a) (b) Figure S3. Static 13 C NMR spectra of the (a) HMIM and (b) H 2 IM samples measured at different temperatures. The spectra of Phase I and the melt of the HMIM were measured using single pulse excitation, the rest of spectra were recorded using 1 H 13 C CP at static condition. The 1-methly-imidazlium cation exhibit sharp (liquid-like) 13 C line at 95 o C in solid phase I; whereas the more symmetric imidazolium cation shows a partially averaged chemical shift anisotropy (CSA) pattern at 145 o C in phase II, suggesting a anisotropic rotation/reorientation of the imidazolium ring about a certain preferable axis. Figure S4. A comparison of the 19 F static NMR spectra of the HMIM and H 2 IM samples measured at room temperature (22 o C). The HMIM clearly exhibits a narrow component whereas the H 2 IM doesn t. 8

9 Figure S5. A comparison of the static 19 F 13 C cross polarization NMR spectra of the HMIM and H 2 IM samples measured at room temperature (22 o C). The static 13 C NMR lineshape of an organic solid, is usually dominated by the chemical shift distribution and/or chemical shift anisotropy, whereas the other factors such as dipole-dipole interactions are negligible (in the 1 H decoupled spectra). Therefore, the broader lineshape of the HMIM sample is most likely originated from a broader distribution of 13 C environment, which implies more disordered environment for the triflate anion in HMIM sample. Figure S6. 19 F 13 C CP-MAS NMR spectra of the HMIM and H 2 IM samples measured at room temperature (22 o C). A small peak at about 35 ppm is seen for the HMIM sample. This peak is attributed to the methyl group from the cation. The cross polarization transfer from the triflate anion to the methyl group suggests the spatial proximity between two groups. Comparison between the 1 H 13 C and 19 F 13 C CP spectra clearly show that the CF 3 group 9

10 of the triflate anion is overlapped with the peak of carbon position 4 and 5 in the imidazolium cation. T (K) Phase IV III FWHM (Hz) 10k Phase III II /T (K -1 ) Figure S7. Arrhenius plot of the full width at half maximum (FWHM) of 1 H static spectra against 1000/T for the H 2 IM sample. Animation S1. 1H and 19F NMR spectra_vt.swf 10

11 1. Bielecki, A.; Burum, D. P. Temperature Dependence of207pb MAS Spectra of Solid Lead Nitrate. An Accurate, Sensitive Thermometer for Variable-Temperature MAS. Journal of Magnetic Resonance, Series A 1995, 116, Toby, B. H.; Von Dreele, R. B. GSAS-II: the genesis of a modern open-source all purpose crystallography software package. Journal of Applied Crystallography 2013, 46,