Electrical properties and electronic states of molecular conductors based on unsymmetrical organometallic-dithiolene gold(III) complexes

The electronic properties of cation radical salts derived from organometallic mixed-ligand complexes [(ppy)Au(S-S)] (ppy^- = C-dehydro-2-phenylpyridine(-); S-S^2- = dithiolene ligand) with Au(III)-C σ-bond were investigated. A 2:1 salt complex [(ppy)Au(C ₈H₄S₈)]₂[PF₆] (C ₈H₄S₈^2- = 2-{(4,5-ethylenedithio)-1, 3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithiolate(2-)) exhibited semiconductive behavior under ambient pressure (ρ_rt = 2.6 Ω cm, E _a = 0.03 eV). Magnetic measurements show that it is a Mott insulator close to the metal-insulator boundary. Raman and infrared spectra have revealed that the complex has a quasi-one-dimensional dimeric structure consisting of uniformly charged donor molecules. The complex exhibits metallic behavior at pressures above 0.8 GPa. In contrast, a similar compound [(ppy)Au(C ₈H₄S₆O₂)]₂[BF ₄] (C₈H₄S₆O₂^2- = 2-{(4,5-ethylenedioxy)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithiolate(2- )) is a band insulator.