Molecular Design of Organic Ionic Plastic Crystals Consisting of Tetracyanoborate with Ultralow Phase Transition Temperature

Hongyao Zhou; Shun Sato; Yusuke Nishiyama; Genki Hatakeyama; Xiaohan Wang; Yoichi Murakami; Teppei Yamada

doi:10.1021/acs.jpclett.3c02371

Molecular Design of Organic Ionic Plastic Crystals Consisting of Tetracyanoborate with Ultralow Phase Transition Temperature

J Phys Chem Lett. 2023 Oct 19;14(41):9365-9371. doi: 10.1021/acs.jpclett.3c02371. Epub 2023 Oct 12.

Authors

Hongyao Zhou¹, Shun Sato¹, Yusuke Nishiyama², Genki Hatakeyama¹, Xiaohan Wang³, Yoichi Murakami⁴, Teppei Yamada¹

Affiliations

¹ Department of Chemistry, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033, Japan.
² JEOL Ltd., Musashino, Akishima, Tokyo 196-8558, Japan.
³ Department of Mechanical Engineering, School of Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan.
⁴ Laboratory for Zero-Carbon Energy, Institute of Innovative Research, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.

PMID: 37853708
DOI: 10.1021/acs.jpclett.3c02371

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_p = -55 °C) while maintaining a high melting point (T_m = 242 °C). Replacement of the cation with either tetraalkylammonium or phosphonium and comparing their phase behavior, the high T_m was attributed to the relatively small interionic distance between [spiropyr]⁺ and [TCB]^-. At the same time, the low T_p was realized by the restricted vibrational mode of the spirostructure, allowing the initiation of isotropic rotational motion with less thermal energy input.