CRYSTAL AND ELECTRONIC STRUCTURES OF MOLECULAR CONDUCTORS BASED ON THE MULTI-SULFUR pi -DONOR MOLECULES.

The electronic structures and electrical resistivities of molecular conductors based on multi-sulfur pi -donor molecules such as BEDT-TTF(ET) and BMDT-TTF(MT) are examined. A new charge distribution rule due to the necessity of the reduction of Coulomb repulsion appears in two-dimensional (2D) conductors. The beta double prime -ET//2(AuBr//2)//1// minus //x(A)//x(A equals IBr//2, I//3) is a new molecular metal with the 1D and 2D Fermi surfaces. The stepwise drops of the resistivity were observed in beta -ET//2 (AuI//2)//1// minus //x(I//3)//x(x congruent 0. 1), indicating the existence of the high-Tc and low-Tc states. A new layered molecular superconductor, theta -ET//2(I//3)//1// minus //x(Aul//2)//x (x less than 0. 02) is also presented. Tc is 3. 6 K. The system has an ideally 2D electronic structure.