Crystal structure, physical properties and electronic structure of a new organic conductor beta ''-(BEDT-TTF)(2)SF5CHFCF2SO3

A new organic conductor, beta-(BEDT-TTF)(2)SF5CHFCF2SO3 [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 beta-(ET)(2)SF5CH2CF2SO3. Whereas beta-(ET)(2)SF5CHFCF2SO3 has disordered anions and undergoes a metal-to-insulator transition at similar to 190 K, beta-(ET)(2)SF5CH2CF2SO3 has ordered anions and is semiconducting down to similar to 100 K, metallic below similar to 100 K, and superconducting below 5 K. At room temperature both beta-(ET)(2)SF5CHFCF2SO3 and beta-(ET)(2)SF5CH2CF2SO3 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 beta-(ET)(2)SF5CHFCF2SO3, but remains substantial in beta-(ET)(2)SF5CH2CF2SO3.