Gold bis(dithiolene) radical with fused pyrazine and dithiine rings on dithiolene ligand turns metallic under pressure

Abstract

Conducting molecular materials built on dithiolene complexes, as mixed-valence salts or single component materials, are most often based on planar structures which efficiently stack on top of each other. Herein, we report an original dithiolene ligand, namely, [1,4]dithiino[2,3-b]pyrazine-2,3-bis(thiolate) (hereafter noted as pzdtdt), which combines an electron-withdrawing pyrazine ring and a folded (by 40–50°) dithiine ring. Until now, such strong distortions from planarity have been hindering the isolation of highly conducting materials from dithiine-containing dithiolene complexes. However, in this study, we showed that the gold complex radical [Au(pzdtdt)₂]˙ obtained via electrocrystallization from the 1e⁻ oxidation of [Ph₄P][Au(pzdtdt)₂] organized into regular, non-dimerized chains in the solid state. Interestingly, [Au(pzdtdt)₂]˙ exhibited a semi-conducting behaviour at ambient pressure and turned metallic upon application of pressures above 4 GPa. The electronic structure of [Au(pzdtdt)₂]˙ was investigated in terms of electron localization effects through spin-polarized band-structure calculations.