A Single-Component Conductor Based on a Radical Gold Dithiolene Complex with Alkyl-Substituted Thiophene-2,3-dithiolate Ligand.

Alkyl-substituted thiophene-2,3-dithiolate ligands are prepared through a Thio-Claisen rearrangement of 4,5-bis(propargylthio)-1,3-dithiole-2-thione derivatives. The two novel dithiolate ligands, namely, 4,5-dimethyl-thiophene-2,3-dithiolate (α-Me2tpdt) and 4-ethyl-5-methyl-thiophene-2,3-dithiolate (α-EtMetpdt), are engaged in anionic Au(III) square planar complexes formulated as Au(α-Me2tpdt)2 and Au(α-EtMetpdt)2, isolated as Ph4P(+) salts. Monoelectronic oxidation gives the neutral radical complexes Au(α-Me2tpdt)2 and Au(α-EtMetpdt)2. The latter crystallizes into uniform stacks with limited interstack interactions, giving rise to a calculated half-filled band structure. It exhibits a semiconducting behavior with room temperature conductivity of 3 × 10(-3) S cm(-1), indicating that this single-component conductor can be described as a Mott insulator. The different structures observed in Au(α-EtMetpdt)2 and the known Au(Et-thiazdt)2 complex (Et-thiazdt: N-ethyl-thiazoline-2-thione-4,5-dithiolate), despite their very similar shapes, are tentatively attributed to differences in the electronic structures of the ligand skeleton.