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.