Synthesis, structure and physical properties of the organic metal ([2H8]BEDT-TTF)4Cl2·6D2O

Abstract

([²H₈]BEDT-TTF)₄Cl₂·6D₂O [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene] has been obtained as long black needles by electrocrystallisation of [²H₈]BEDT-TTF in CH₂Cl₂ in the presence of [(C₂H₅)₄N]Cl·D₂O. It crystallises in the orthorhombic space group Pcca, a= 32.575(2)Å, b= 6.709(1)Å, c= 14.854(2)Å, V= 3246(1)ų and Z= 2. The structure consists of twisted (dihedral angle of 29°) pairs of crystallographically equivalent BEDT-TTF cations forming stacks parallel to c with close intermolecular S ⋯ S contacts along b, resulting in layers. A layered network of chlorine and water molecules linked by weak hydrogen bonds alternates with the layers of organic donor molecules. The conductivity parallel to b is 40 S cm^–1 at 300 K, almost constant with decreasing temperature to ca. 160 K. Below 150 K the conductivity shows a temperature-dependent activation energy, ranging from 14 meV at 140 K to 6 meV at 10 K. It increases linearly by a factor of 3 by applying a pressure up to 24 kbar; the transition temperature decreases from 160 to 20 K. The anisotropy of the microwave conductivity is 0.5:240:3.6 S cm^–1. The spin and static susceptibilities measured, respectively, by electron paramagnetic resonance (EPR) and Faraday magnetometry are temperature independent between 70 and 300 K, and obey a Curie–Weiss law below 50 K with θ=–4 K. The calculated band structure and Fermi surface show twodimensional character of both electron and hole pockets, with the possibility of 2k_F nesting.