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

Abstract

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.

Mixed-Valence Conductors from Ni Bis(diselenolene) Complexes with a Thiazoline Backbone

“…This Bu 4 N + salt is isostructural with the Et 4 N + one, but the limited increase of the unit cell volume (from 971 to 1016 Å 3 ) indicates a sub-stoichiometry in the Bu 4 N + cation, hence the formulation [Bu 4 N] x [Ni­(Me-thiazds) 2 ] 2 with 0 < x < 1 (see below for details). The obtention of mixed-valence salts comes here in strong contrast with N -ethyl dithiolene and diselenolene, [Ni­(Et-thiazdt) 2 ] 0 and [Ni­(Et-thiazds) 2 ] 0 , as well as N -methyl dithiolene [Ni­(Me-thiazdt) 2 ] 0 , all isolated as neutral, single-component species. ,, …”

“…The obtention of mixed-valence salts comes here in strong contrast with N-ethyl dithiolene and diselenolene, [Ni(Et-thiazdt) 2 ] 0 and [Ni(Et-thiazds) 2 ] 0 , as well as N-methyl dithiolene [Ni(Me-thiazdt) 2 ] 0 , all isolated as neutral, singlecomponent species. 10,11,18 Molecular Structures. In the three mixed-valence salts, the nickel complexes are organized in the form of highly dimerized, for 3).…”

“…17 We have shown that the oxidation of [Ni(Et-thiazds) 2 ] −1 salts afforded the neutral [Ni(Etthiazds) 2 ] 0 , which exhibits an essentially 1D electronic structure with large band dispersion and small highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) gap and a semiconducting behavior, with σ RT = 8 × 10 −3 S cm −1 and E act = 0.12 eV. 18 By analogy with our recent results on gold diselenolene complexes with the less sterically demanding R = Me analogue [Au(Me-thiazds) 2 ] −1 , 19,20 we investigate here the oxidation of the corresponding monoanionic N-methyl substituted nickel diselenolene analogue, which is to say [Ni(Me-thiazds) 2 ] −1 (Chart 1f), in order to see whether this complex during electrocrystallization would generate the unknown singlecomponent conductor [Ni(Me-thiazds) 2 ] 0 or a rare mixedvalence salt. Herein, we describe the synthesis of three monoanionic nickel complexes of the Me-thiazds diselenolene ligand with different counterions, [C][Ni(Me-thiazds)] with C = Bu 4 N + , Et 4 N + , and Ph 4 P + , and the outcome of their electrocrystallization, providing rare examples of mixed-valence salts of nickel diselenolene complexes, further blessed with high conductivities.…”

“…Besides, one should mention the dsise analogues (Chart e) with only one mention of a mixed-valence conducting salt (Bu 4 N)­[Ni­(dsise) 2 ] 2 . We have shown that the oxidation of [Ni­(Et-thiazds) 2 ] −1 salts afforded the neutral [Ni­(Et-thiazds) 2 ] 0 , which exhibits an essentially 1D electronic structure with large band dispersion and small highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap and a semiconducting behavior, with σ RT = 8 × 10 –3 S cm –1 and E act = 0.12 eV . By analogy with our recent results on gold diselenolene complexes with the less sterically demanding R = Me analogue [Au­(Me-thiazds) 2 ] −1 , , we investigate here the oxidation of the corresponding monoanionic N-methyl substituted nickel diselenolene analogue, which is to say [Ni­(Me-thiazds) 2 ] −1 (Chart f), in order to see whether this complex during electrocrystallization would generate the unknown single-component conductor [Ni­(Me-thiazds) 2 ] 0 or a rare mixed-valence salt.…”

A highly conducting mixed-valence nickel bis(dithiolene) salt [Et4N][Ni(Me-thiazSe-dt)2]2 with selone substitution

“…As other monoanionic nickel complex, [Ni(Me-thiazSe-dt) 2 ] 1− exhibits a strong absorption in the NIR range, observed here at 1306 nm (ε = 25 000 M −1 cm −1 ), identical to that reported for the N-ethyl analog (λ max = 1308 nm, ε = 26 900 M −1 cm −1 ). 26 Redox properties were evaluated by cyclic voltammetry (Fig. S1 in ESI †) and results are collected in Table 1.…”