Solvent inclusion and disorder effects on an isostructural series of organic conductors

Abstract

Interest in quasi-one-dimensional organic conductors has been renewed by the discovery¹ of superconductivity in (tetra-methyltetraselenafulvalene)₂PF₆, (TMTSF)₂PF₆. At ambient pressure (TMTSF)₂PF₆ undergoes a Peierls distortion at 18 K (ref. 2) whereas under modest pressure the properties remain metallic with the onset of superconductivity at 0.9 K (ref. 1). There is now an incentive to synthesize other organic metals in which the Peierls distortion is suppressed in the hope that these may also superconduct under pressure. So far (DEPE) (TCNQ)₄ (H₂O)_x, is the only example^3,4 to show a monotonic increase in conductivity, characteristic of a metal, on cooling at ambient pressure to below 30 mK. This metallic behaviour has, however, been disputed₅. I verify here the unique temperature dependence of conductivity of (DEPE) (TCNQ)₄ (H₂O)_x and report the electrical and structural properties of the isostruc-tural congeners (DMPP) (TCNQ)₄ (H₂O)_x, and (DRPA) (TCNQ)₄ (H₂O)_x where R = M (methyl) and E (ethyl) (see Table 1 for full names).