Mixed-valence gold bis(diselenolene) complex turning metallic under pressure

Abstract

While oxidation of d⁸ anionic gold bis(dithiolene) complexes most often affords the corresponding neutral radical single-component conductor, an original gold bis(diselenolene) complex isolated as a Ph₄P⁺ salt affords upon electrocrystallization a mixed-valence 1 : 2 salt, [Ph₄P][Au(Me-thiazds)₂]₂ (Me-thiazds: 2-methyl-1,3-thiazoline-2-thione-4,5-diselenolate). This salt exhibits a rare charge alternation associated with the simultaneous presence of both cis and trans isomers of the gold complex in the conducting layers. The salt is semiconducting (σ_RT = 3 × 10⁻² S cm⁻¹, E_act = 0.137 eV) but, in contrast with other 1 : 2 gold bis(dithiolene) salts, turns metallic under pressure (>10 GPa). [Ph₄P][Au(Me-thiazds)₂]₂ is thus the first metallic, fully characterized, 1 : 2 mixed-valence gold complex, opening the door for the preparation of highly conducting solids of this type.