A NEW FAMILY OF MOLECULAR-METALS BASED OIL BIS(ETHYLENETHIO)TETRATHIAFULVALENE (BET-TTF) AND OCTAHEDRAL COUNTERIONS

The electrochemical synthesis and physical characterization of a series of new bis(ethylenethio)tetrathiafulvalene (BET-TTF) based salts, (BET-TTF)PF6, and (BET-TTF)(2) X (X = PF6, AsF6, and SbF6), are reported. In all X-ray crystal structures, only the E isomer of BET-TTF is present. The (BET-TTF)PF6 (2) salt crystallizes in the centrosymmetric group P21/a, in which donors stack uniformly along the b crystallographic axis in a herringbone pattern with a crystal packing similar to alpha-phases of BEDT-TTF. The three 2:1 salts crystallize in the triclinic P-1 space group and are isostructural, being the crystal packing motif very similar to the beta-phases of BEDT-TTF. In salts (BET-TTF)(2)AsF6 (4) and (BET-TTF)(2)SbF6 (5) a structural disorder due to the external sulfur positions of BET-TTF is observed. Band electronic calculations on these structures indicate a quasi-2D electronic character for salts 4 and 5. All 2:1 salts show metallic character down to similar to 100 K, where a very broad transition toward an activated conductivity is observed. The relationships between the crystal structures, physical properties, and electronic structures are discussed.