Abstract
The preparation, crystal structures, and electric and magnetic properties of (BETS)2MX4 molecular conductors (BETS = bis(ethylenedithio)tetraselenafulvalene; M = Mn2+, Fe3+, Co2+, Ni2+, Cu2+; X = Cl, Br, CN) are reported. Resistivity measurements down to 2 K reveal the coexistence of the BETS π conduction electrons and the localized magnetic moments of the anions in the κ-(BETS)2FeCl4 and κ-(BETS)4(CoCl4)(C2H3Cl3) salts. Another FeCl4 phase, λ-(BETS)2FeCl4, undergoes a sharp metal-insulator (MI) transition around 8 K. At the same temperature, a magnetic transition of the FeCl4-anions takes place cooperatively. A superconducting transition is observed at 4.6 K in λ-(BETS)2(FeCl4)0.5(GaCl4)0.5, where half of the anion sites are occupied by magnetic ions. The crystals prepared from 1,1,2-trichloroethane solutions with the NiCl42- and MnCl42- anions exhibit the behavior of a semimetal down to ≈100 K. The (BETS)4(Cu2Cl6) salt remains metallic down to 4.2 K. ESR studies show that the Fe3+ ions in κ- and λ-(BETS...
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