Introducing Selenium in Single-Component Molecular Conductors Based on Nickel Bis(dithiolene) Complexes

Two selenated analogues of the all-sulfur single-component molecular conductor [Ni(Et-thiazdt)(2)] (Et-thiazdt = N-ethylthiazoline-2-thione-4,5-dithiolate) have been prepared from their precursor radical-anion complexes. Replacement of the thione by a selenone moiety gives the neutral [Ni(Et-thiazSedt)(2)] complex. It adopts an unprecedented solid-state organization (for neutral nickel complexes), with the formation of perfectly eclipsed dimers and very short intermolecular Se center dot center dot center dot Se contacts (81% of the van der Waals contact distance). Limited interactions between dimers leads to a large semiconducting gap and low conductivity (sigma(RT) = 1.7 x 10(-5) S cm(-1)). On the other hand, going from the neutral [Ni(Et-thiazdt)(2)] dithiolene complex to the corresponding [Ni(Et-thiazds)(2)] diselenolene complex gives rise to a more conventional layered structure built out of uniform stacks of the diselenolene complexes, different, however, from the all-sulfur analogue [Ni(Et-thiazdt)(2)]. Band structure calculations show an essentially 1D electronic structure with large band dispersion and a small HOMO-LUMO gap. Under high pressures (up to 19 GPa), the conductivity increases by 4 orders of magnitude and the activation energy is decreased from 120 meV to only 13 meV, with an abrupt change observed around 10 GPa, suggesting a structural phase transition under pressure.

Automated summary

Two selenated analogues of a sulfur-containing nickel complex have been synthesized, showing different solid-state structures and electrical properties. One exhibits a large semiconducting gap and low conductivity, while the other has a conventional layered structure with a smaller HOMO-LUMO gap.