A weakly coupled molecular spin-ladder (BEDT-TTF)Zn(SCN)3

The title compound, (BEDT-TTF)Zn(SCN)3, has two uniform-stacks of BEDT-TTF+. The extended-Hückel calculation reveals that the dominant magnetic interaction is in the stack direction, while it is about 1/10 between the stacks. Thus the title compound is a weakly-coupled spin-ladder. The existence of spin-gap (340 K) is for the first time confirmed for the weak-coupling limit, by measuring static magnetization. The tight-binding band calculation reveals that, if a metallic state is realized by a carrier-doping, it will be stable against penodic lattice distortions.