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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
Highly conductive plastic crystals based on fluorohydrogenate anions
Ryosuke Taniki1, Kazuhiko Matsumoto, Rika Hagiwara
1Graduate School of Energy Science, Kyoto University, Kyoto 606-8501, Japan.
The Journal of Physical Chemistry. B
|December 29, 2012
Summary
New ionic plastic crystals, N,N-dimethylpyrrolidinium fluorohydrogenate [DMPyr(FH)(2)F] and N-ethyl-N-methylpyrrolidinium fluorohydrogenate [EMPyr(FH)(2)F], show promising ionic conductivity. These materials exhibit anion-dominated charge transport in their plastic crystal phases.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Electrochemistry
Background:
- Ionic plastic crystals are a class of materials exhibiting unique solid-state properties.
- Understanding their structural and transport characteristics is crucial for developing advanced ionic conductors.
Purpose of the Study:
- To synthesize and characterize novel ionic plastic crystals: N,N-dimethylpyrrolidinium fluorohydrogenate [DMPyr(FH)(2)F] and N-ethyl-N-methylpyrrolidinium fluorohydrogenate [EMPyr(FH)(2)F].
- To investigate their physicochemical, structural, and electrochemical properties, focusing on ionic conductivity and charge transport mechanisms.
Main Methods:
- Synthesis of DMPyr(FH)(2)F and EMPyr(FH)(2)F salts.
- Differential scanning calorimetry to determine melting entropy and phase transitions.
- X-ray diffraction to analyze crystal structures and lattice parameters.
- Ionic conductivity measurements.
- Pulsed-field gradient spin-echo NMR spectroscopy to study ion mobility and diffusion coefficients.
Main Results:
- Both DMPyr(FH)(2)F and EMPyr(FH)(2)F exhibit low melting entropy changes (4.1 and 2.0 J K(-1) mol(-1), respectively).
- Ionic plastic crystal phases were observed in the temperature ranges of 258-325 K for DMPyr(FH)(2)F and 236-303 K for EMPyr(FH)(2)F.
- These phases adopt NaCl-type structures with lattice constants of 9.90 Å (DMPyr(FH)(2)F) and 10.18 Å (EMPyr(FH)(2)F).
- Ionic conductivities in the plastic crystal phases ranged from 10(0) to 10(1) mS cm(-1), with specific values of 10.3 mS cm(-1) at 298 K for DMPyr(FH)(2)F and 14.4 mS cm(-1) at 288 K for EMPyr(FH)(2)F.
- NMR studies indicated that charge transport is primarily due to anion mobility (diffusion coefficient ~10(-7) cm(2) s(-1)), with limited cation mobility.
Conclusions:
- The synthesized ionic plastic crystals possess favorable properties for ionic conduction.
- Anion mobility is the dominant charge transport mechanism in the ionic plastic crystal phases of DMPyr(FH)(2)F and EMPyr(FH)(2)F.
- These findings contribute to the development of new solid electrolytes with tunable properties.
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