WHAT MAKES BEDT-TTF CONSTRUCT THE KAPPA-TYPE SALTS

The new two ambient pressure organic superconductors, kappa-(BEDT-TTF) 2Cu(CN) [N(CN)2] (Tc=11.2K) and kappa'-(BEDT-TTF)2Cu2(CN)3 (Tc=3.8K) s how the typical donor packing motives for the kappa-type BEDT-TTF salt . Comparing the crystal structures to those of the other BEDT-TTF salt s, the following general feature has become apparent for the ambient p ressure superconducting salts with the planar anion layers. (1) The pa cking pattern of the donor molecules is governed by the pattern of the openings in the anion layer, and (2) Tc is roughly proportional to V( mes2), the volume of the space in which the carriers can mainly move a round in the two-dimensional conducting layer.