Ni(dmit)2 salts with chiral stilbazolium- and ferrocenyl-based chromophores as countercations

Four 1:1, two-component salts combining the [Ni(dmit)₂]⁻ anion (dmit²⁻ = 2-thioxo-1,3-dithiole-4,5-dithiolato) and chiral stilbazolium-based countercations (HPMS⁺ = 4′-[2-(hydroxymethyl)pyrrolidinyl]-1-methylstilbazolium and MPMS⁺ = 4′-[2-(methoxy-methyl)pyrrolidinyl]-1-methylstilbazolium), or chiral ferrocenyl-based countercations (2⁺ = (E)-1-((R)-2-methylferrocenyl)-2-(1-methyl-4-pyridiniumyl)ethene; 3⁺ = (E)-1-((S)-2-trimethylsilylferrocenyl)-2-(1-methyl-4-pyridiniumyl)ethene) were prepared. Semiconducting behaviour (2·10⁻⁴ S·cm⁻¹ measured on compressed pellets for [Ni(dmit)₂] (MPMS), for example) is secured by the presence of the [Ni(dmit)₂]⁻ anions. The chiral nature of the countercations ensures non-centrosymmetry of the structures (space group P1 for [Ni(dmit)₂](2) and [Ni(dmit)₂](3), for example). A ubiquitous antiparallel arrangement of the cations, which are thus packed in a pseudo-centrosymmetrical environment, results in almost vanishing second-order susceptibilities χ⁽²⁾, and therefore zero efficiencies in second harmonic generation.