BEDT-TTF Salts with Square-Planar Gold(III) Complex Anions: β-(ET)2AuCl4and (ET)2Au(CN)2Cl2

We report the synthesis, crystal structures, and band electronic structures of the first 2:1 salts of the organic donor radical cation bis(ethylene-dithio) tetrathiafulvalene (BEDT-TTF or ET) with square-planar anions, i. e., β-(ET)2AuCl4(1) and (ET)2Au(CN)2Cl2 (2). The crystal and the band electronic structures of 1 are related to the β-phase superconductors, β-(ET)2 X (X ˭ I3, IBr2, AuI2). However, β-(ET)2AuCl4 undergoes a destructive phase transition after prolonged cooling to 120 K and is non-superconducting. Temperature-dependent ESR measurements of 2 indicate a very broad metal- to-insulator phase transition between 250 and 300 K. The band electronic structure of 2 indicates 1-d metallic behavior at room temperature with a well nested open Fermi surface. Crystal parameters: β-(ET)2Au(CN)2Cl2: triclinic, P1, a = 6.590(2) Å, b = 8.561(2) Å. c = 18.319(5)°, α = 93.19(2)°, β = 105.52(2)°, γ = 119.47(2)°, Vc = 845.1(3) Å3, Z = 1. (ET)2Au(CN)2Cl2: monoclinic, P2/c, a = 17.726(8) Å, b = 6.690(4) Å, c = 15.284(10) Å, β = 108.19(5)°, Vc = 1722(2) Å3, Z = 2.