Cation radical salts of ethylenedisulfanyl-bridged dimeric ethylenedithiotetrathiafulvalene with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF4), PF6−, AsF6−and BF4−: synthesis, structure and conducting properties

Abstract

Single crystals of four cation radical salts based on an ethylenedisulfanyl linked tetrathiafulvalene (bis(ethylenedithiotetrathiafulvalenylsulfanyl)ethane, 1), 1·[TCNQF₄]₂, 1·PF₆(CH₂Cl₂)_0.5, 1·AsF₆(CH₂Cl₂)_0.5 and 1·BF₄, were prepared by chemical oxidation and electrocrystallization. The crystal structures of these salts are described, along with their electrical conducting behaviors. For comparison, the crystal structure of the neutral donor is also reported. In the crystal of the 1·[TCNQF₄]₂ salt the donor molecules adopt a Z-shaped conformation with the two TTF moieties located at the trans-position of the bridge, which resembles what is observed in its neutral crystals. The charge on each TTF moiety is +1, and there is no continuous π–π overlap in this crystal, leading to insulator behavior in this salt with σ_rt < 10⁻⁷ S cm⁻¹. The two salts with PF₆ and AsF₆ as the counter anion are isostructural, and in these salts the donor molecules adopt a U-shaped conformation with the two TTF moieties located at the cis-position of the bridge. The donor molecules are packed into two-dimensional layers, which serve as the conducting path. The stacking pattern in the crystal of 1·BF₄ is similar to that in 1·PF₆(CH₂Cl₂)_0.5 and 1·AsF₆(CH₂Cl₂)_0.5. The crystals of salts 1·PF₆(CH₂Cl₂)_0.5, 1·AsF₆(CH₂Cl₂)_0.5 and 1·BF₄ display semi-conducting properties from room temperature down to 60 K.