Synthesis of racemic and chiral BEDT-TTF derivatives possessing hydroxy groups and their achiral and chiral charge transfer complexes

Sara Jane Krivickas; Chiho Hashimoto; Junya Yoshida; Akira Ueda; Kazuyuki Takahashi; John D Wallis; Hatsumi Mori

doi:10.3762/bjoc.11.172

Synthesis of racemic and chiral BEDT-TTF derivatives possessing hydroxy groups and their achiral and chiral charge transfer complexes

Beilstein J Org Chem. 2015 Sep 8:11:1561-9. doi: 10.3762/bjoc.11.172. eCollection 2015.

Authors

Sara Jane Krivickas¹, Chiho Hashimoto², Junya Yoshida², Akira Ueda², Kazuyuki Takahashi³, John D Wallis⁴, Hatsumi Mori²

Affiliations

¹ The Institute for Solid State Physics, the University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan ; The University of Adelaide, Adelaide, South Australia, 5005 Australia.
² The Institute for Solid State Physics, the University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan.
³ The Institute for Solid State Physics, the University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan ; Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Hyogo 657-8501, Japan.
⁴ School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK.

Abstract

Chiral molecular crystals built up by chiral molecules without inversion centers have attracted much interest owing to their versatile functionalities related to optical, magnetic, and electrical properties. However, there is a difficulty in chiral crystal growth due to the lack of symmetry. Therefore, we made the molecular design to introduce intermolecular hydrogen bonds in chiral crystals. Racemic and enantiopure bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) derivatives possessing hydroxymethyl groups as the source of hydrogen bonds were designed. The novel racemic trans-vic-(hydroxymethyl)(methyl)-BEDT-TTF 1, and racemic and enantiopure trans-vic-bis(hydroxymethyl)-BEDT-TTF 2 were synthesized. Moreover, the preparations, crystal structure analyses, and electrical resistivity measurements of the novel achiral charge transfer salt θ(21)-[(S,S)-2]3[(R,R)-2]3(ClO4)2 and the chiral salt α'-[(R,R)-2]ClO4(H2O) were carried out. In the former θ(21)-[(S,S)-2]3[(R,R)-2]3(ClO4)2, there are two sets of three crystallographically independent donor molecules [(S,S)-2]2[(R,R)-2] in a unit cell, where the two sets are related by an inversion center. The latter α'-[(R,R)-2]ClO4(H2O) is the chiral salt with included solvent H2O, which is not isostructural with the reported chiral salt α'-[(S,S)-2]ClO4 without H2O, but has a similar donor arrangement. According to the molecular design by introduction of hydroxy groups and a ClO4 (-) anion, many intermediate-strength intermolecular hydrogen bonds (2.6-3.0 Å) were observed in these crystals between electron donor molecules, anions, and included H2O solvent, which improve the crystallinity and facilitate the extraction of physical properties. Both salts are semiconductors with relatively low resistivities at room temperature and activation energies of 1.2 ohm cm with E a = 86 meV for θ(21)-[(S,S)-2]3[(R,R)-2]3(ClO4)2 and 0.6 ohm cm with E a = 140 meV for α'-[(R,R)-2]2ClO4(H2O), respectively. The variety of donor arrangements, θ(21) and two kinds of α'-types, and their electrical conductivities of charge transfer complexes based upon the racemic and enantiopure (S,S)-2, and (R,R)-2 donors originates not only from the chirality, but also the introduced intermolecular hydrogen bonds involving the hydroxymethyl groups, perchlorate anion, and the included solvent H2O.

Keywords: BEDT-TTF; chiral molecular crystal; hydrogen bonding; hydroxy group; molecular conductors.