Structural and physical properties of BEDO-TTF charge-transfer salts: κ-phase with CF3SO3–

The synthesis, X-ray crystal structures, electron paramagnetic resonance (EPR) studies, conductivity measurements and electronic-band calculations for two new charge-transfer salts κ-(BEDO-TTF)2CF3SO3(I) and (BEDO-TTF)2CF3SO3(C4H8O)0.5(II), are described. Most of the discussion concerns the former which is the first κ-phase obtained with BEDO-TTF. This salt is metallic at room temperature (RT)(σRT= 100 S cm–1) and undergoes a slow change towards semiconducting behaviour at low temperature. Simultaneously, the EPR linewidth of the κ-phase decreases with T from ca. 60 G at 300 K, unlike the behaviour of classical κ-phase superconductors. However, the calculated band structure of I is quite similar to those previously reported for classical κ-phase salts. Comparison of magnetic and conductivity data allows the classification of κ-salts into two groups: (i) classical superconducting salts and (ii) the present salt and related materials. The properties of salts in the latter group are discussed in relation to the role of the anions.