The synthesis, crystal structures and band electronic structures of BEDT‐TTF based synmetals are discussed, where BEDT‐TTF is bis(ethylenedithio)‐tetrathiofulvalene here abbreviated to “ET”. The electrical properties of ET:X salts above their phase transitions are either 1D [for (ET)2X, where X− = ICl2−, AuBr2−, Au(CN)2− and Ag(CN)2−], 2D metallic [for (ET)2X, where X− = I3−, AuI2−, IBr2− and I2Br−] or 3D metallic [for (ET)Ag4(CN)5]. The β‐(ET)2X (X− = I3−, AuI2− and IBr2−) salts become ambient pressure organic superconductors at 1,4 K (or ∼ 8 K under pressure), 5.0 K, and 2.8 K, respectively. The variation of critical temperatures of this series of β‐(ET)2X salts are correlated to the respective changes in unit cell volume or in the density of electronic states at the Fermi level.
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