Trifluoromethylsulfonyl-based salts of BEDT-TTF: Crystal and electronic structures and physical properties

Three 2:1 salts of the organic donor molecule bis(ethylene-dithio)tetrathiafulvalene (BEDT-TTF or ET) with trifluoromethylsulfonyl-based anions N(SO2CF3)(2)(-), CH(SO2CF3)(2)(-) and C(SO2CF3)(3)(-) were prepared by electrocrystallization. These salts were characterized by single-crystal X-ray diffraction, electron spin resonance (ESR) spectroscopy, electrical resistivity measurements and electronic band structure calculations. (ET)(2)N(SO2CF3)(2) is a two-dimensional (2D) metal, but its ESR spin susceptibility above 150 K shows a weakly semiconducting behavior, presumably because during ESR measurements the sample cooling rate is slow hence allowing the disordered anions to readjust their positions. (ET)(2)CH (SO2CF3)(2) is a 2D metal and undergoes a metal-to-insulator (MI) transition at 110 K due probably to a geometry change of the donor molecule layers. (ET)(2)C(SO2CF3)(3) is a one-dimensional (1D) metal and undergoes an MI between 180 and 240 K, which is expected to be of charge density wave type. (C) 2002 Elsevier Science (USA).