Structural Transitions from Triangular to Square Molecular Arrangements in the Quasi-One-Dimensional Molecular Conductors (DMEDO-TTF)2XF6 (X = P, As, and Sb)

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• 作者：Takashi Shirahata ; Keita Shiratori ; Shouhei Kumeta ; Tadashi Kawamoto ; Tadahiko Ishikawa ; Shin-ya Koshihara ; Yoshiaki Nakano ; Hideki Yamochi ; Yohji Misaki ; Takehiko Mori
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：August 15, 2012
• 年：2012
• 卷：134
• 期：32
• 页码：13330-13340
• 全文大小：601K
• 年卷期：v.134,no.32(August 15, 2012)
• ISSN：1520-5126

文摘

A series of quasi-one-dimensional molecular conductors (DMEDO-TTF)₂XF₆ (X = P, As, and Sb), where DMEDO-TTF is dimethyl(ethylenedioxy)tetrathiafulvalene, undergo characteristic structural transitions in the range of 130鈥?95 K for the PF₆ salt and 222鈥?42 K for the AsF₆ salt. The dramatic structural transition is induced by the order of the ethylenedioxy moiety, and the resulting anion rotation leads to the reconstruction of the H路路路F interaction between the methyl groups and the anions. The unique hydrogen bonds play a crucial role in the transition. As a result, the molecular packing is rearranged entirely; the high-temperature molecular stacks with an ordinary quasi-triangular molecular network transforms to a quasi-square-like network, which has never been observed among organic conductors. Nonetheless, the low-temperature phase exhibits a good metallic conductivity as well, so the transition is a metal鈥搈etal (MM) transition. The resistivity measured along the perpendicular direction to the conducting ac-plane (蟻) and the calculation of the Fermi surface demonstrate that the high-temperature metal phase is a one-dimensional metal, whereas the low-temperature metal phase has considerable interchain interaction. In the SbF₆ salt, a similar structural transition takes place around 370 K, so that the quasi-square-like lattice is realized even at room temperature. Despite the largely different MM transition temperatures, all these salts undergo metal鈥搃nsulator (MI) transitions approximately at the same temperature of 50 K. The low-temperature insulator phase is nonmagnetic, and the reflectance spectra suggest the presence of charge disproportionation with small charge difference (0.14).