Crystal Structures and Electrical Resistivities of Three-Component Organic Conductors: (BEDT-TTF)2MM′(SCN)4 [M = K, Rb, Cs; M′ = Co, Zn, Cd]

New three-component organic conductors, (BEDT-TTF)2MM′(SCN)4 [M = K, Rb, Cs; M′ = Co, Zn, Cd], are prepared. The crystal structure analyses of α-ET2CsCo(SCN)4, ETZn(SCN)3, α-ET2RbZn(SCN)4, α-ET2CsZn(SCN)4, α-ETCd0.66(SCN)2, and ET2CsCd(SCN)4 are carried out. Most of salts have the α-type donor arrangement and the polymer sheet like [···M′2+···(SCN)−···M+···] in a thick anion layer. Especially α-(BEDT-TTF)2CsM′(SCN)4 [M′ = Co and Zn] are metallic down to 20 K.