CRYSTAL AND ELECTRONIC-STRUCTURES OF THE ORGANIC SUPERCONDUCTORS, KAPPA-(BEDT-TTF)2CU(CN)[N(CN)2] AND KAPPA'-(BEDT-TTF)2CU2(CN)3

The crystal structures of the newly obtained two BEDT-TTF superconductors prepared by the electrocrystallization in the presence of Cu, CN, and N(CN)2 were analyzed. The compositions of the "high Tc salt (Tc = 11.2 K)" and the "low Tc salt (Tc = 3.8 K)" are (BEDT-TTF)2 Cu(CN)[N(CN)2] and (BEDT-TTF)2Cu2(CN)3, respectively. The donor packing patterns of them are classified into the K-type salt. The band electronic calculations show the two-dimensional Fermi surfaces in both salts. The crystal structure of the "low Tc salt" is essentially identical to that of the reported K-(BEDT-TTF)2Cu2(CN)3 salt, however, the conducting properties are completely different. The differences may arise from the slight differences of the crystal structures.