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

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          Summary

          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(ClO 4) 2 and the chiral salt α’-[( R,R)- 2]ClO 4(H 2O) were carried out. In the former θ 21-[( S,S)- 2] 3[( R,R)- 2] 3(ClO 4) 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]ClO 4(H 2O) is the chiral salt with included solvent H 2O, which is not isostructural with the reported chiral salt α’-[( S,S)- 2]ClO 4 without H 2O, but has a similar donor arrangement. According to the molecular design by introduction of hydroxy groups and a ClO 4 anion, many intermediate-strength intermolecular hydrogen bonds (2.6–3.0 Å) were observed in these crystals between electron donor molecules, anions, and included H 2O 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(ClO 4) 2 and 0.6 ohm cm with E a = 140 meV for α'-[( R,R)- 2] 2ClO 4(H 2O), 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 H 2O.

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          Electrical magnetochiral anisotropy.

          Electrical conductors can be chiral, i.e., can exist in two forms where one is the other's mirror image. Thus far, no effect of chirality on magnetotransport has been observed. We argue that the electrical resistance of any chiral conductor should depend linearly both on the external magnetic field and the current through the conductor and on its handedness. We suggest two mechanisms to carry this effect and show experimentally on model systems that both are effective.
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            Structural Genealogy of BEDT-TTF-Based Organic Conductors II. Inclined Molecules:θ,α, andκPhases

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              Electrical magnetochiral anisotropy in a bulk chiral molecular conductor

              So far, no effect of chirality on the electrical properties of bulk chiral conductors has been observed. Introduction of chiral information in tetrathiafulvalene precursors represents a powerful strategy towards the preparation of crystalline materials in which the combination of chirality and conducting properties might allow the observation of the electrical magnetochiral anisotropy effect. Here we report the synthesis by electrocrystallization of both enantiomers of a bulk chiral organic conductor based on an enantiopure tetrathiafulvalene derivative. The enantiomeric salts crystallize in enantiomorphic hexagonal space groups. Single crystal resistivity measurements show metallic behaviour for the enantiopure salts down to 40 K, in agreement with band structure calculations. We describe here the first experimental evidence of electrical magnetochiral anisotropy in these crystals, confirming the chiral character of charge transport in our molecular materials.
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                Author and article information

                Contributors
                Role: Guest Editor
                Journal
                Beilstein J Org Chem
                Beilstein J Org Chem
                Beilstein Journal of Organic Chemistry
                Beilstein-Institut (Trakehner Str. 7-9, 60487 Frankfurt am Main, Germany )
                1860-5397
                2015
                8 September 2015
                : 11
                : 1561-1569
                Affiliations
                [1 ]The Institute for Solid State Physics, the University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba, 277-8581, Japan
                [2 ]The University of Adelaide, Adelaide, South Australia, 5005 Australia
                [3 ]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
                Article
                10.3762/bjoc.11.172
                4660918
                26664576
                e0b73ccd-fef6-4df8-b688-1fed991730ce
                Copyright © 2015, Krivickas et al; licensee Beilstein-Institut.

                This is an Open Access article under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                The license is subject to the Beilstein Journal of Organic Chemistry terms and conditions: ( http://www.beilstein-journals.org/bjoc)

                History
                : 8 June 2015
                : 21 August 2015
                Categories
                Full Research Paper
                Chemistry
                Organic Chemistry

                Organic & Biomolecular chemistry
                bedt-ttf,chiral molecular crystal,hydrogen bonding,hydroxy group,molecular conductors

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