Si trova su / Altri legami
© 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···Se contacts (81% of the van der Waals contact distance). Limited interactions between dimers leads to a large semiconducting gap and low conductivity (σRT = 1.7 × 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.
