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

Abstract

The prototypical [Ni(dmit)₂] complex (dmit: 1,3-dithiole-2-thione-4,5-dithiolate) is modified here by combining the N–R substitution found in [Ni(R-thiazdt)₂] complexes (R-thiazdt: N-alkyl-thiazoline-2-thione-4,5-dithiolate) and the selone substitution found in [Ni(dmiSe)₂] complex (dmiSe: 1,3-dithiole-2-selone-4,5-dithiolate) to give a novel N-methyl substituted, radical anionic complex formulated as [Ni(Me-thiazSe-dt)₂]¹⁻ (Me-thiazSe-dt: N-methyl-thiazoline-2-selone-4,5-dithiolate). Both this anionic complex and its mixed-valence Et₄N⁺ salt crystallize with a rare cis arrangement of the two dithiolene ligands around the Ni atom. In the 1 : 2 [Et₄N][Ni(Me-thiazSe-dt)₂]₂ salt, the complexes organize into dimerized chains well isolated from each other, giving the salt a strong one-dimensional character. It shows however a high RT conductivity of 4.6 S cm⁻¹ and small activation energy of 33 meV, indicating a possible Mott insulator behavior, which is not suppressed under pressures up to 10 GPa.