Molecular design for high Tc organic superconductors

Materialized candidates of the conducting components for high-Tc organic superconductors are described. To design molecules, we applied the empirical rules which had been derived from the structure-property relationship in ambient pressure BEDT-TTF superconductors. The rules reveal that (1) the anion structure governs the donor packing motif, (2) Tc is nearly proportional to the volume of the space in which charge carriers delocalize effectively, and (3) the increased interaction between the conducting layers raises Tc. Although the strategy has not afforded superconductors yet, the first concept gave a new BEDT-TTF salt, (BEDT-TTF)2(NO3)(H2O)2 which shows a kind of a-type packing motif. This salt is semiconducting and exhibits a semiconductor-semiconductor transition at 245–250 K and is suspected to be a rare example of BEDT-TTF based Mott semiconductors. Also the attempts to satisfy the third concept are described.