Structural Variety in ET Radical Cation Salts with Gold(I) Cyanide Anions

We report the synthesis and characterization of four new charge-transfer salts based on bis(ethylenedithio)tetrathiafulvalene (ET) and Au–CN-based anions: (ET)[Au2(CN)3] (1), (ET)3[Au(CN)2]3(TCE) (TCE: 1,1,2-trichloroethane) (2), (ET)5[Cu2{μ-Au(CN)2}2{Au(CN)2}2(CN)][Au(CN)2] (3), and (ET)4[Au(CN)2]3(EtOH)0.5 (4). Despite the structural richness and electronic versatility of ET-based materials, Au–CN-containing ET salts have remained largely unexplored. In this study, we developed new types of Au–CN-containing ET salts with a variety of unique anion species, including mononuclear, dinuclear, and polynuclear anions, by means of single-crystal X-ray diffraction measurements. Raman spectroscopy measurements were performed to evaluate the charge states of ET molecules, such as the fully oxidized (salt 1, 2) and charge separated (salt 3, 4) states. Transport measurements revealed semiconducting behavior in these salts. The experimental findings were consistent with our band structure calculations, which clarified the dimensionality and filling of the frontier bands. These results highlight the diverse structural and electronic properties in Au–CN-based organic conductors and provide valuable insights for further investigations into the physical properties of radical cation salts with less-explored anion components.