Old Donors For New Molecular Conductors: Combining Tmtsf And Bedt-Ttf With Anionic (Taf6)(1-X)/(Pf6)(X) Alloys

Tetramethyl-tetraselenafulvalene (TMTSF) and bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) are flagship precursors in the field of molecular (super)conductors. The electrocrystallization of these donors in the presence of (n-Bu4N)TaF6 or mixtures of (n-Bu4N)TaF6 and (n-Bu4N)PF6 provided Bechgaard salts formulated as (TMTSF)(2)(TaF6)(0.84)(PF6)(0.16), (TMTSF)(2)(TaF6)(0.56)(PF6)(0.44), (TMTSF)(2)(TaF6)(0.44)(PF6)(0.56) and (TMTSF)(2)(TaF6)(0.12)(PF6)(0.88), together with the monoclinic and orthorhombic phases delta(m)-(BEDT-TTF)(2)(TaF6)(0.94)(PF6)(0.06) and delta(o)-(BEDT-TTF)(2)(TaF6)(0.43)(PF6)(0.57), respectively. The use of BEDT-TTF and a mixture of (n-Bu4N)TaF6/TaF5 afforded the 1:1 phase (BEDT-TTF)(2)(TaF6)(2)center dot CH2Cl2. The precise Ta/P ratio in the alloys has been determined by an accurate single crystal X-ray data analysis and was corroborated with solution F-19 NMR measurements. In the previously unknown crystalline phase (BEDT-TTF)(2)(TaF6)(2)center dot CH2Cl2 the donors organize in dimers interacting laterally yet no organic-inorganic segregation is observed. Single crystal resistivity measurements on the TMTSF based materials show typical behavior of the Bechgaard phases with room temperature conductivity sigma approximate to 100 S/cm and localization below 12 K indicative of a spin density wave transition. The orthorhombic phase delta(o)-(BEDT-TTF)(2)(TaF6)(0.43)(PF6)(0.57) is semiconducting with the room temperature conductivity estimated to be sigma approximate to 0.16-0.5 S/cm while the compound (BEDT-TTF)(2)(TaF6)(2)center dot CH2Cl2 is also a semiconductor, yet with a much lower room temperature conductivity value of 0.001 to 0.0025 S/cm, in agreement with the +1 oxidation state and strong dimerization of the donors.