Synthesis and Properties of 2-Alkylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene Derivatives and Crystal Structures of Their Cation Radical Salts

Abstract: Tetrathiafulvalene derivatives condensed with 2-alkylidene-1,3-dithiole moiety, MeDTES (2-isopropylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene), EtDTES (2-(pentan-3-ylidene)-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene), and CPDTES (2-cyclopentanylidene-1,3-dithiolo[4,5-d]-4,5-ethylenediselenotetrathiafulvalene) have been synthesized. Crystal structure analysis of MeDTES salts with Au(CN)₄⁻, ReO₄⁻, and I₃⁻ and a CPDTES salt with I₃⁻ reveals that the donor−anion ratios of all salts are 1:1. Band calculation of (MeDTES)[Au(CN)₄] suggests a quasi-one-dimensional Fermi surface that could be the result of the uniform stack of donor molecules. In spite of this stacking, the salt is a Mott insulator because of a large on-site Coulomb interaction U. (MeDTES)(ReO₄)(H₂O)_0.5 possesses Fermi points and exhibits semiconducting behavior with small activation energy (E_a = 0.058 eV). I₃⁻ ions form disordered infinite chain in (MeDTES)(I₃)(DCE)_0.25, but those in (CPDTES)(I₃) exist as discrete ions. They show low conductivity (10⁻⁴−10⁻² S cm⁻¹) at room temperature and the band calculation suggests that they are band insulator.