High Ambipolar Mobility in a Neutral Radical Gold Dithiolene Complex

Abstract

A new anionic gold dithiolene complex NBu 4 ·[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 Å) S-S contacts, which are packed in a herringbone arrangement in the ab-plane. The complex exhibits semiconductor behavior (σ RT = 1.5 × 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 1 H NMR, with evidence of a nonmagnetic ground state at low temperature.

Electrochemical deposition of a semiconducting gold dithiolene complex with NIR absorption

“…As the dithiolone is asymmetric, the salt was initially obtained as a mixture of the cis and trans isomers, distinguishable by a small (0.01 ppm) difference between the dithiolene protons in the 1 H NMR. As reported for other gold dithiolene complexes, 8,24,[25][26][27][28][29][30][31][32][33][34][35][36][37] the two isomers do not appear to interconvert in solution, and thus a pure isomer Fig. S1 †) was isolated via selective precipitation/crystallization in reasonable yield (40%).…”

“…In the case of 2, an intense transition is observed at 1425 nm, charac-teristic of neutral gold dithiolene complexes and has previously been assigned to a SOMO−1 to SOMO transition. 28,[36][37][38] Infrared spectroscopy…”

“…This peak is related to the CvS stretch and its increase in intensity upon oxidation could indicate an increase in dithioketone-like character upon oxidation, something that has previously been observed through changes in the C-S bond length from single crystal diffraction data. 28 The most significant difference in the spectra is the presence of a significant absorption tailing into the high energy region of the spectrum for 2. This absorp-…”

“…The first oxidation and reduction peaks show a strong similarity with structurally related gold dithiolene complexes. 28,39,40 During the electrochemical studies, it was observed that dark green films were depositing on the working electrode. As neutral gold dithiolene complexes are known to be insoluble it was assumed that this deposition occurred during the first oxidation; as a result the first oxidation process was then studied in further detail.…”

“…Similar behaviour has been observed for other gold dithiolene complexes, and has been attributed to strong electron correlation. 9,24,[26][27][28][29]43 Conductive properties Ambient. The temperature dependence of the conductivity of 2 was investigated on a compressed pellet in the 190-300 K range.…”