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-S2- = dithiolene ligand) with Au(III)-C sigma-bond were investigated. A 2:1 salt complex [(ppy)Au(C8H4S8)](2)[PF6] (C8H4S82- = 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene)-1,3-dithiole-4,5-dithiolate(2-)) exhibited semiconductive behavior under ambient pressure (rho(rt) = 2.6 Omega 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(C8H4S6O2)](2)[BF4] (C8S6O22- = 2-{(4,5-ethylenedioxy)-1,3-dithiole-2-ylidenel-1,3-dithiole-4,5-dithiolate(2-)) is a band insulator.