Abstract

A new organic conductor, β″-(BEDT-TTF)₂SF₅CHFCF₂SO₃ [BEDT-TTF, hereafter abbreviated ET, refers to bis(ethylenedithio)tetrathiafulvalene], was prepared by electrocrystallization. The crystal structure of this salt was determined by single crystal X-ray diffraction at 298 and 150 K, its physical properties were examined by electrical resistivity, Raman spectroscopy and EPR measurements, and its electronic structure was calculated and compared with that of the analogous salt β″-(ET)₂SF₅CH₂CF₂SO₃. Whereas β″-(ET)₂SF₅CHFCF₂SO₃ has disordered anions and undergoes a metal-to-insulator transition at ∼190 K, β″-(ET)₂SF₅CH₂CF₂SO₃ has ordered anions and is semiconducting down to ∼100 K, metallic below ∼100 K, and superconducting below 5 K. At room temperature both β″-(ET)₂SF₅CHFCF₂SO₃ and β″-(ET)₂SF₅CH₂CF₂SO₃ have similar electronic band structures and physical properties. When the temperature is lowered, each donor molecule stack becomes dimerized in both salts. However, the interdimer interaction within each donor stack nearly vanishes in β″-(ET)₂SF₅CHFCF₂SO₃, but remains substantial in β″-(ET)₂SF₅CH₂CF₂SO₃.