High Ambipolar Mobility In A Neutral Radical Gold Dithiolene Complex

A new anionic gold dithiolene complex NBu4 center dot[1] is synthesized from the (1-((1,1-biphenyl)-4-yl-)-ethylene-1,2-dithiolene ligand 1, and the cis and trans isomers are separated by recrystallization. The trans isomer is oxidized via electrocrystallisation to the neutral gold dithiolene complex 2. Complex 2 crystalizes in 1D chains, held together by short (3.30-3.37 angstrom) S-S contacts, which are packed in a herringbone arrangement in the ab-plane. The complex exhibits semiconductor behavior (sigma(RT) = 1.5 x 10(-4) S cm(-1)) at room temperature with a small activation energy (E-a = 0.11 eV), with greater conductivity along the stacking direction. The charge transport behavior of complex 2 is further investigated in single-crystal field-effect transistor (FET) measurements, the first such measurements reported for gold dithiolene complexes. Complex 2 shows incredibly balanced ambipolar behavior in the single-crystal field-effect transistor (SC-FET), with high charge-carrier mobilities of 0.078 cm(2) V-1 s(-1), the highest ambipolar mobilities reported for metal dithiolene complexes. This well-balanced behavior, along with the activated conductivity and band structure calculations, suggests that 2 behaves as a Mott insulator. The magnetic properties are also studied by superconducting quantum interference device (SQUID) magnetometry and solid state H-1 NMR, with evidence of a nonmagnetic ground state at low temperature.