Metallic Properties of 1:1 Charge-Transfer Salt, Dimethyltetraselenoanthracene-Tetrafluoroborate (DMTSA-BF₄)

Pseudo-one-dimensional charge-transfer salt DMTSA-BF₄ shows high electrical conductivity (σ_RT ≈ 500 Scm^-1) and metallic temperature dependence down to ca. 160K, in contrast to the conventional half-filled organic conductors which are regarded as Mott insulators. The pseudo-one-dimensionality is evidenced by the polarized reflectance spectra. The electrical resistivity, thermopower magnetic susceptibility, and polarized reflectance spectrum suggest that DMTSA-BF₄ is a metal above ca. 150K. This compound is the first metal among the 1:1 organic charge-transfer salts The low-temperature reflectance spectrum suggests that the glide plane symmetry is broken below 150K and the fluctuation of this broken symmetry is already observed at room temperature The metal-insulator transition around 150K is regarded as Peierls transition. The Hubbard parameter U/W is estimated to be <0.8, which may be the possible reason for the metallic nature in high-temperature phase.