Organic Molecular Conductors Based on Tetramethyl-TTP: Structural and Electrical Properties Modulated by the Anion Size and Shape

Takashi Shirahata; Shuhei Kohno; Keisuke Furuta; Shogo Katayama; Kento Suzuki; Tadashi Kawamoto; Takehiko Mori; Yohji Misaki

doi:10.1021/acs.inorgchem.1c04004

Organic Molecular Conductors Based on Tetramethyl-TTP: Structural and Electrical Properties Modulated by the Anion Size and Shape

Inorg Chem. 2022 May 23;61(20):7754-7764. doi: 10.1021/acs.inorgchem.1c04004. Epub 2022 May 12.

Authors

Takashi Shirahata^{1

2}, Shuhei Kohno¹, Keisuke Furuta¹, Shogo Katayama¹, Kento Suzuki¹, Tadashi Kawamoto³, Takehiko Mori³, Yohji Misaki^{1

2}

Affiliations

¹ Department of Applied Chemistry, Graduate School of Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
² Research Unit for Development of Organic Superconductors, and Research Unit for Power Generation and Storage Materials, Ehime University, Matsuyama, Ehime 790-8577, Japan.
³ Department of Materials Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan.

PMID: 35549245
DOI: 10.1021/acs.inorgchem.1c04004

Abstract

The tetramethyl derivative of bis-fused tetrathiafulvalene, 2,5-bis(4,5-dimethyl-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (TMTTP), has been successfully synthesized. Most of the radical cation salts consisting of TMTTP feature a high electrical conductivity of σ_rt = 10¹ to 10² S cm^-1 on a single crystal. The anion shape and size of TMTTP conductors modulate the electrical properties. The PF₆^- and AsF₆^- salts exhibit metallic conductivity down to 10 K, while the ReO₄^- and AuI₂^- salts show metal-to-insulator (MI) transition at 126 and 11 K, respectively. Single-crystal X-ray structure analysis of (TMTTP)₂X (X = PF₆, AsF₆, BF₄, and ReO₄) and (TMTTP)₃AuI₂ reveals that the donor packing motif is categorized as the so-called β-type. The tight-binding band calculations of (TMTTP)₂X (X = ReO₄, BF₄, PF₆, and AsF₆) suggest these salts are characterized by quasi-one-dimensional Fermi surfaces. The band calculation based on X-ray structure analysis of (TMTTP)₂ReO₄ at 100 K demonstrates that the MI transition of this salt is associated with the charge ordering with the zigzag stripe pattern.