Theoretical study of the H/D isotope effect on phase transition of hydrogen-bonded organic conductor κ-H3(Cat-EDT-TTF)2. Issue 43 (24th October 2016)

• Record Type: Journal Article
• Authors: Yamamoto, Kaichi; Kanematsu, Yusuke; Nagashima, Umpei; Ueda, Akira; Mori, Hatsumi; Tachikawa, Masanori
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 43(2016)
• Page Start: 29673
• Page End: 29680
• Publication Date: 2016-10-24
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp05414e
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : κ-H3 (Cat-EDT-TTF)2 (H-TTF) is a hydrogen-bonded π-electron system. Only its isotopologue, D-TTF, shows the phase transition. We obtained a symmetric single-well effective-PEC for H-TTF and low-barrier effective-PEC for D-TTF. Abstract : κ-H3 (Cat-EDT-TTF)2 (H-TTF) is a hydrogen-bonded π-electron system which was found to reveal C 2/ c symmetry at 50–293 K, while its isotopologue, κ-D3 (Cat-EDT-TTF)2 (D-TTF), showed the phase transition at 185 K from C 2/ c to P 1̄. 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.