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Updated: Jul 13, 2025

From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding
Published on: March 24, 2018
Molecular Design of Organic Ionic Plastic Crystals Consisting of Tetracyanoborate with Ultralow Phase Transition
Hongyao Zhou1, Shun Sato1, Yusuke Nishiyama2
1Department of Chemistry, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.
Abstract:
Organic ionic plastic crystals (OIPCs) are a ductile soft material where the composing ions are in isotropic free rotation, while their positions are aligned in order. The rotational motion in its plastic phase promotes ion conduction by decreasing the activation energy. Here, we report novel OIPCs comprised of tetracyanoborate ([TCB]-) and various organic cations. In particular, the OIPC composed of [TCB]- and spiro-(1,1')-bipyrrolidinium ([spiropyr]+) cations can transform into its plastic phase at ultralow temperature (T = -55 °C) while maintaining a high melting point (T = 242 °C). Replacement of the cation with either tetraalkylammonium or phosphonium and comparing their phase behavior, the high T was attributed to the relatively small interionic distance between [spiropyr]+ and [TCB]-. At the same time, the low T was realized by the restricted vibrational mode of the spirostructure, allowing the initiation of isotropic rotational motion with less thermal energy input.
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