Polymorphism of a New Bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) Based Molecular Conductor; Novel Transformations in Metallic BEDTTTF Layers

The synthesis, structure, anion composition, and physical properties of a new organic conductor (BEDT-TTF)2[(IBr2)0.2 (BrICl)0.1(ICl2)0.7], where BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, are described in detail. This molecular conductor exists as two polymorphs displaying semiconducting ((beta)ʹ-phase) and metallic ((beta)"-phase) transport properties. Complete (beta)" to (beta) and partial (beta)" to (beta)ʹ transformation have been discovered for the first time in conducting BEDT-TTF-based salts and studied by using ESR spectroscopy. Both transformations are irreversible, the (beta)" (right arrow)(beta)one resulting from high-temperature solid-state reactions. The (beta)"- and (beta)-phases are variable in composition.