Molecular conductors from bis(ethylenedithio) tetrathiafulvalene with tris(oxalato)rhodate

This article reports a family of new radical-cation salts of bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF) with tris(oxalato) rhodate: three salts with the formula beta''-(BEDT-TTF)(4)[(cation)Rh(C2O4)(3)]center dot solvent (solvent = fluorobenzene, chlorobenzene, or bromobenzene) and one with the formula pseudo-kappa-(BEDT-TTF)(4)[(NH4)Rh(C2O4)(3)]center dot benzonitrile. We report here the syntheses, crystal structures, electrical properties and Raman spectroscopy of these new molecular conductors. The bromobenzene salt shows a decrease in resistivity below 2.5 K indicative of a superconducting transition and a Shubnikov-de Haas oscillation with a frequency of 232 T and effective mass m* of 1.27m(e).