Chiral, radical, gold bis(dithiolene) complexes

Abstract

In the search for single component conductors, eventually blessed with chirality, we have prepared three novel Au(III) bis(dithiolene) complexes of the 6,7-dihydro-5H-1,4-dithiepine-2,3-bis(thiolate) ligand exhibiting a fused seven-membered ring. The unsubstituted ligand as well as two chiral enantiopure derivatives, with methyl groups in 5,7 positions or a ketal moiety in 6 position, were used to provide the corresponding anionic d⁸ Au(III) bis(dithiolene) complexes (1, 2 and 3) as Bu₄N⁺ salts. The anions adopt a square planar geometry around the gold atom with a pseudo centrosymmetric chair conformation of the outer seven-membered rings. Cyclic voltammetry experiments demonstrate that they can be easily oxidized to the neutral radical state in a 0.40–0.50 V range (vs. SCE). Their electrocrystallization afforded neutral radical species for two of them, which were structurally characterized. An original transformation of the unsubstituted complex 1 upon oxidation is observed in its oxidation product, leading to an unexpected radical complex 1′′, with two different dithiolene ligands. Its peculiar electronic structure and the formation of alternated stacks in the solid state explains its semiconducting character with direct gap. On the other hand, the radical complex 3′ derived from the chiral ketal derivative 3 is organized into face-to-face dimers, isolated from each other in the crystal.