Systematic Approach to the Synthesis of Cobaltocenium Salts with Reduced Forms of TCNQF₄: Two [Cp₂Co](TCNQF₄) Polymorphs and [Cp₂Co]Li(TCNQF₄)

Three new crystallographically characterized compounds were prepared in high yield from reactions between [Cp₂Co]PF₆ (Cp = cyclopentadiene) and lithium salts of the radical anion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF₄^1-) or the dianionic TCNQF₄^2-. The two [Cp₂Co]TCNQF₄ compounds (1 and 2) with 1:1 stoichiometry were found to be polymorphic, α and β. Remarkably, the syntheses only differed by the presence of a small amount of neutral TCNQF₄ in the case of polymorph β (2). The role of the TCNQF₄ has been rationalized on the basis of a transient intermediate, postulated as [Cp₂Co](TCNQF₄)₂. Compound 3 contains TCNQF₄^2- and crystallized as [Cp₂Co]Li(TCNQF₄). This material highlights a novel coordination mode for the Li⁺ cation that participated in the formation of a metal-organic framework accommodating the [Cp₂Co]⁺ cation. All complexes were comprehensively characterized by Fourier transform infrared spectroscopy, UV-vis spectroscopy, and electrochemistry. Polymorph β (2) has a conductivity of 5.8 × 10^-4 S cm^-1, which lies well within the semiconductor range. Previous work in this area employed redox chemistry based on the reaction of cobaltocene or ferrocene with neutral TCNQ. The introduction of metathesis reactions enhances the synthetic flexibility enabling a systematic approach to new materials. ©