A test of superconductivity vs. molecular disorder in (BEDT-TTF)2X synthetic metals: synthesis, structure (298, 120 K), and microwave/ESR conductivity of (BEDT-TTF)2I2Br

Two ambient-pressure synthetic metal superconductors, ..beta..-bis(ethylenedithio)tetrathiafulvalene triiodide and ..beta..-bis(ethylenedithio)tetrathiafulvalene iododibromide, in a single organic radical-cation donor system are reported. Low field electron spin resonance (ESR) measurements were performed, and no evidence of superconductivity (complete disappearance of ESR signal) was observed down to a temperature of 1.07 K at both ambient pressure and at a pressure of 5 kbar. Transition temperatures for the two compounds are reported as 1.2-1.6K and 2.3-2.8K, respectively. The molecular structure of the compounds are discussed in detail.