High Ambipolar Mobility in a Neutral Radical Gold Dithiolene Complex

A new anionic gold dithiolene complex NBu4·[1] has been synthesised from the (1-((1,1 biphenyl)-4-yl-)-ethylene-1,2-dithiolene ligand 1, and the cis and trans isomers separated by recrystallization. The trans isomer is oxidised via electrocrystallisation to the neutral gold dithiolene complex 2. Complex 2 crystallises in one-dimensional chains, held together by short (3.30-3.37 Å) S-S contacts, which are packed in a herringbone arrangement in the ab-plane. The complex exhibits semiconductor behaviour (σRT = 1.5 × 10−4 S cm−1) at room temperature with a small activation energy (Ea = 0.11 eV), with greater conductivity along the stacking direction. The charge transport behaviour of complex 2 was further investigated in single crystal FET measurements, the first such measurements reported for gold dithiolene complexes. Complex 2 showed incredibly balanced ambipolar behaviour in the SC-FET, with high charge carrier mobilities of 0.078 cm2 V–1 s–1, the highest ambipolar mobilities reported for metal dithiolene complexes. This well-balanced behaviour, along with the activated conductivity and band structure calculations, suggests that 2 behaves as a Mott insulator. The magnetic properties were also studied by SQUID magnetometry and solid state 1H NMR, with evidence of a non magnetic ground state at low temperature.