Yamamoto Kaichi, Kanematsu Yusuke, Nagashima Umpei, Ueda Akira, Mori Hatsumi, Tachikawa Masanori
Graduate School of Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama-City, Kanagawa, 236-0027, Japan.
Faculty of Information Sciences, Hiroshima City University, 3-4-1, Ozuka-Higashi, Asa-Minami-Ku, Hiroshima, 731-3194, Japan.
Phys Chem Chem Phys. 2016 Nov 2;18(43):29673-29680. doi: 10.1039/c6cp05414e.
κ-H(Cat-EDT-TTF) (H-TTF) is a hydrogen-bonded π-electron system which was found to reveal C2/c symmetry at 50-293 K, while its isotopologue, κ-D(Cat-EDT-TTF) (D-TTF), showed the phase transition at 185 K from C2/c to P1[combining macron]. To elucidate the origin of such a difference, we calculated the potential energy curves (PECs) for the hydrogen transfer along the H-bonds in these conductors. We found that both the π-stacking and the hydrogen nuclear quantum effect drastically affected the hydrogen transfer energy. By taking account of both effects, we obtained a symmetric single-well effective PEC for H-TTF, which indicated that the hydrogen was always located at the center of the H-bond. By contrast, the effective PEC of D-TTF was a low-barrier double-well, indicating that the position of the H-bonded deuterium would change according to the temperature. We concluded that the π-stacking and the nuclear quantum effect were the key factors for the appearance of phase transition only in D-TTF.
κ-H（Cat-EDT-TTF）（H-TTF）是一种氢键π电子体系，发现在50 - 293 K时具有C2/c对称性，而其同位素类似物κ-D（Cat-EDT-TTF）（D-TTF）在185 K时显示出从C2/c到P1[上加一横]的相变。为了阐明这种差异的起源，我们计算了这些导体中沿氢键的氢转移的势能曲线（PEC）。我们发现π堆积和氢核量子效应都极大地影响了氢转移能量。综合考虑这两种效应，我们得到了H-TTF的对称单阱有效PEC，这表明氢总是位于氢键的中心。相比之下，D-TTF的有效PEC是一个低势垒双阱，表明氢键合氘的位置会随温度变化。我们得出结论，π堆积和核量子效应是仅在D-TTF中出现相变的关键因素。
