Issue 33, 2021

Unusual stoichiometry, band structure and band filling in conducting enantiopure radical cation salts of TM-BEDT-TTF showing helical packing of the donors

Abstract

Electrocrystallization of tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) (1) as pure (S,S,S,S) and (R,R,R,R) enantiomers in the presence of (n-Bu4N)2(Mo6O19) and chloroform or bromoform afforded a series of four isostructural enantiopure radical cation salts [(S/R)-1]9(Mo6O19)5·(CHX3)2 (X = Cl, Br) crystallizing in the trigonal non-centrosymmetric space group R32. In the formula unit there are six donors of type A and three donors of type B showing, respectively, (ax, ax, eq, eq) and all-ax conformations (ax = axial, eq = equatorial) of the methyl substituents. The donors form a hexagonal network in the ab plane with a helical twist between them leading to lateral orbital overlap interactions. Electrocrystallization of the racemic donor provided the compound [(rac)-1]2(Mo6O19) which crystallized in the monoclinic system P21/n. Single crystal resistivity measurements show semiconducting behaviour of the enantiopure materials with a relatively high room temperature conductivity of 0.8–1.2 S cm−1, but rather insensitive to applied pressures of up to 2.3 GPa. Analysis of the electronic structure of the conducting solids through extended Hückel tight-binding band structure calculations indicates a Mott insulator behaviour explaining the semiconducting character and suggests that these compounds are valuable candidates for Dirac cone materials. Further insight into the conducting properties is provided by preliminary field effect transistor measurements.

Graphical abstract: Unusual stoichiometry, band structure and band filling in conducting enantiopure radical cation salts of TM-BEDT-TTF showing helical packing of the donors

Supplementary files

Article information

Article type
Paper
Submitted
09 Mar 2021
Accepted
16 Apr 2021
First published
16 Apr 2021

J. Mater. Chem. C, 2021,9, 10777-10786

Unusual stoichiometry, band structure and band filling in conducting enantiopure radical cation salts of TM-BEDT-TTF showing helical packing of the donors

F. Pop, C. Mézière, M. Allain, P. Auban-Senzier, N. Tajima, D. Hirobe, H. M. Yamamoto, E. Canadell and N. Avarvari, J. Mater. Chem. C, 2021, 9, 10777 DOI: 10.1039/D1TC01112J

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