NEW BETS SUPERCONDUCTORS AND METALS WITH TETRAHEDRAL NONMAGNETIC AND MAGNETIC ANIONS (BETS EQUALS BIS(ETHYLENEDITHIO)TETRASELENAFULVALENE)

Two types of BETS conductors are reported. Needle crystals of lambda-B ETS(2)GaX(x)Y(4-x) gave a series of new superconductors: lambda-BETS(2 )GaCl(4) (T-c=7 K), lambda-BETS(2)GaBrCl(3) (8 K), lambda-BETS(2)GaCl( 3)F (3.5 K), lambda-BETS(2)GaBr(0.5)Cl(3.5) (6.5 K). lambda-BETS(2)GaB r(1.5)Cl(2.5), which is a semiconductor at 1 bar, exhibited a supercon ducting transition at 8 K and ca. 1 kbar. Pressure and temperature dep endencies of the resistivities of lambda-BETS(2)GaX(x)Y(4-x) closely r esemble those of kappa-type BEDT-TTF superconductors. Many BETS metals with magnetic ions (Fe3+, Mn2+, Co2+, Cu2+) were prepared. Among them , kappa-type MX(4) (M=Fe, Co; X=Cl, Br) salts and theta-type Cu2Cl6 sa lts are metallic down to at least 4 K. The static susceptibility of la mbda-BETS(2)FeCl(4) shows a characteristic magnetic field dependence b elow its metal-insulator transition temperature.