New organic metal with the mixed anion, β-(ET)2(IBr2)0.7(I3)0.3: Synthesis, structure and properties

The crystals of the stable organic metal β-(ET)2(IBr2)0.7(I3)0.3 have been obtained by chemical oxidation of the concentrated solution of bis (ethylenedithio) tetrathiafulvalene by IBr in nitrobenzene. The total yield of the reaction is about 80%. The room-temperature conductivity of the single crystals in the conducting ab plane amounts to 10–50Ω−1 cm−1 and the ratio R293 K/R4 K = 300–400. The unit cell crystallographic parameters for β-(ET)2(IBr2)0.7(I3)0.3: a = 6.603(2), b = 8.996(2), c = 15.152(4) Å, α = 94.05(2), β = 95.15(3), γ = 110.22(3)°, V = 836.2 Å3 at 293 K and a = 6.608(2), b = 8.834(2), c = 15.038(3) Å, α = 95.64(2), β = 95.01(2), γ = 109.91(2)°, V = 814.5 Å3 at 130 K, space group P1¯, Z = 1. The orientation disordering of one of the ET ethylene groups (ET molecules are in staggered and eclipsed conformations) at room temperature, as well as complete ordering of the ones at 130 K (ET molecules are in eclipsed conformation only) was found. Differential scanning calorimetry (DSC) data show that order—disorder phase transition (ΔH=3.3 ± 0.1 J/g) takes place at 125–148 K.