Superconductivity at 2. 8 K and 1. 5 kbar in. kappa. -(BEDT-TTF) sub 2 Cu sub 2 (CN) sub 3 : The first organic superconductor containing a polymeric copper cyanide anion

Attempts to synthesize new k-phase superconductors have concentrated on ET salts with complex anions composed of Cu(I) or Ag(I) metal ions and pseudohalide anions. The targeted anion approach', by use of a preformed anion found in KCu{sub 2}(CN){sub 3}.H{sub 2}O and the presence of trace amounts of water, led to the discovery of the first copper-cyanide containing superconductor, K-(ET){sub 2}Cu{sub 2}(CN){sub 3}. The crystal structure, superconducting properties, and band electronic structure are described in this article. The complex k-(ET){sub 2}Cu{sub 2}(CN){sub 3} is in many ways similar to the superconductor K-(ET){sub 2}Cu(N(CN){sub 2})Cl, the superconductor with the highest T{sub c} reported to date. 28 refs., 3 figs.