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A number of layered conducting BEDT-TTF, bis(ethylenedithio)tetrathiafulvalene, salts with heavily fluorinated organosulfonate anions have been prepared and characterized. Of particular interest are the salts containing SF 5 R SO 3 − anions, where R is a partially fluorinated aliphatic backbone. While structurally similar —the β″ packing type predominates—the ground state of these salts varies from superconducting in the case of β″-(BEDT-TTF) 2 SF 5 CH 2 CF 2 SO 3 [1] to insulating. Many of the salts with insulating ground states are metallic at room temperature, but charge localization and disproportionation over crystallographically non-equivalent sites occurs at low temperature. The organosulfonate group exhibits a propensity to bind to lithium ions, thus ternary salts incorporating Li + into the complex anion layer are often found. The fluorophilic effect in organofluorine compounds may be exploited to form salts where the conducting BEDT-TTF layers are separated by extremely bulky anion bilayers. The crystal structure of one such system, (BEDT-TTF) 3 [(CF 3 ) 2 CFC 2 H 4 SO 3 ] 4 (H 5 O 2 ) 2 , is described here.

The inverse deuterium isotope effect, previously found in κ-(BEDT-TTF) 2 Cu(NCS) 2 , is also found in two other BEDT-TTF based superconductors with different packing motifs and different types of anions. Remarkably, the magnitude of the isotope shift is essentially identical in all three superconductors, ca. +0.26 ±0.06 K. These results, when taken together with the recent results of Lang et al. on the uniaxial pressure derivatives of T c , suggest that the inverse isotope effect may not have a direct relationship to the pairing mechanism but instead is a reflection of the change in the internal lattice pressure.