Novel Low Temperature Modulated Structure of the Ambient Pressure Superconductor (BEDT-TTF)2I3 and a Design Strategy for New Superconducting Polyhalide Phases

The first ambient pressure S-based organic superconductor (BEDT-TTF) 2 I 3 , abbreviated (ET) 2 I 3 , exhibits a novel modulated structure below ∼ 200 K. At 125 K the ET molecules and I 3 − anions exhibit large displacements 0.124 (3) A and 0.281 (1) A, respectively, from their positions in the "average structure." New ambient pressure superconducting polyhalide derivatives such as (ET) 2 IBr 2 are discussed with transition temperatures of 2.7 K, and in one sample, 4.2 K.