Crystal structures and physical properties of new BDA-TTP conductors

The TaF6 and FeBr4 salts of BDA-TTP [2,5-bis(13-dithian-2-ylidene)-l,3,4,6-tetrathiapcntalene] have been prepared and characterized as β-(BDA-TTP)2TaF6 and β-(BDA-TTP)2FeBr4, respectively. The crystal structure of β-(BDA-TTP)2TaF6 is isostructural to those of the ambient-pressure superconductors β-(BDA-TTP)2X (X = SbF6, AsF6 and PF6), but this salt undergoes an MI (metal-to-insulator) transition instead of a superconducting transition at ambient pressure. The β-(BDA-TTP)2FeBr4 salt, which is tsomorphous to the superconductors β-(BDA-TTP)2MCl4 (M = Fe and Ga) under applied pressures, exhibits a phase transition near 170 K and antiferromagnetic ordering with the Néel temperature (TN) of about 9.5 K at ambient pressure.