Subtle Steric Differences Impact the Structural and Conducting Properties of Radical Gold Bis(dithiolene) Complexes

Abstract

Among single component molecular conductors, neutral radical gold dithiolene complexes [(R-thiazdt) Au] derived from the N-alkyl-1,3-thiazoline-2-thione-4,5-dithiolate (R-thiazdt) ligand provide an extensive series of conducting, non-dimerized, half-filled band systems. Analogues of the known R=isopropyl (iPr) derivative were investigated here with R=NMe , cyclopropyl (cPr) and n-propyl (nPr), aiming at rationalizing the different solid state structures adopted by these compounds despite very closely related substituents on the heterocyclic nitrogen atom. An original crisscross organization within dimerized chains is observed with R=NMe , differing however from the analogous iPr derivative by a 180° rotation of the heterocyclic nitrogen substituent. On the other hand, the cyclopropyl and n-propyl substituents lead to robust, uniform, non-dimerized chains with a strongly 1 D electronic structure and a formal half-filled electronic structure. The semiconducting behaviour of these two radical complexes is characteristic of a Mott insulator, whose sensitivity to external pressure has been evaluated up to 2.5 GPa.

High Ambipolar Mobility in a Neutral Radical Gold Dithiolene Complex

“…The susceptibility (χ p ) of 2 is low, only 4 × 10 −4 emu mol −1 at room temperature, far lower than expected for isolated S = 1/2 molecules. This kind of Pauli‐like, small paramagnetic susceptibility with weak temperature dependence is reported in other neutral gold dithiolene complexes with a thermally‐activated conductivity . The decrease below 60 K could be ascribed to a transition to a nonmagnetic ground state, a suggestion supported by solid state 1 H NMR data, which show no critical divergence of T 1 −1 and almost temperature independent signal shapes (Figure S8, Supporting Information), unlike that seen in antiferromagnetic transitions .…”

“…In particular, neutral nickel and gold bis(1,2‐dithiolene) complexes have been studied as single component conductors, due to attractive features such as their square planar geometry and delocalized electronic structure, which leads to favorable intermolecular stacking interactions (a requirement for solid state conductivity) and reversible and tunable redox chemistry. Additionally, neutral gold dithiolene complexes can behave as Mott insulators, with one radical per site, resulting in an activation barrier for conductivity behavior that can be overcome with pressure . Since the first molecular superconductor based on a metal dithiolene complex was reported, a charge transfer salt (TTF)[Ni(dmit) 2 ] 2 , a large number of neutral complexes containing dithiolene ligands with a TTF backbone have been synthesized, such as Au(ptdt) 2 , and Au(tmdt) 2 , showing metallic or near metallic behavior at ambient temperature and pressure.…”

“…Neutral gold dithiolene complexes without TTF containing ligands have also been reported, such as Au(α‐tpdt) 2 and Au(bdt) 2 , showing a wide variety of conductive properties, from semiconductor to metallic . Several complexes in the thiazole dithiolate family have been reported showing activated conductivity under ambient conditions, with some showing metal‐like conductivity under pressure, and one showing metallic behavior under ambient conditions …”

Electrochemical deposition of a semiconducting gold dithiolene complex with NIR absorption

“…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.…”

Stable Metallic State of a Neutral-Radical Single-Component Conductor at Ambient Pressure

“…20 It is worth mentioning that when the substituent on the nitrogen atom is bigger than a methyl group no disorder was observed and the trans isomer was obtained. 15,17,18,19 Figure 3. Upon cooling, a metallic behavior is observed in the whole temperature range from 300 to 4 K with a ratio of 5 between these two temperatures.…”