Gold bis(dithiolene) radical turning metallic under pressure: fusing pyrazine and dithiine rings on a dithiolene ligand†

Abstract

Conducting molecular materials built on dithiolene complexes −as mixed-valence salts or single component materials− are most often based of planar structures which efficiently stack on top of each other. We report here an original dithiolene ligand, namely [1,4]dithiino[2,3-b]pyrazine-2,3-bis(thiolate) (hereafter noted as pzdtdt) which associates an electron-withdrawing pyrazine ring and a folded (by 40-50°) dithiine ring. While such strong distortions from planarity has hindered up to now the isolation of highly conducting materials from such dithiine-containing dithiolene complexes, we show here that the radical gold complex [Au(pzdtdt)2]•, obtained by electrocrystallization from the 1e− oxidation of [Ph4P][Au(pzdtdt)2], organizes in the solid-state into regular, non-dimerized chains, with a semi-conducting behavior at ambient pressure, turning metallic upon application of pressures above 4 GPa. The electronic structure of [Au(pzdtdt)2]• is discussed in terms of electron localization effects, through spin-polarized band-structure calculations.