Systematic Approach to the Synthesis of Cobaltocenium Salts with

Article Cite This: Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Systematic Approach to the Synthesis of Cobaltocenium Salts with Reduced Forms of TCNQF4: Two [Cp2Co](TCNQF4) Polymorphs and [Cp2Co]Li(TCNQF4) Jinzhen Lu,† Ruchika Ojha,† Alan M. Bond,* and Lisandra L. Martin* School of Chemistry, Monash University, Clayton, 3800, Victoria, Australia

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ABSTRACT: 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 (TCNQF41−) or the dianionic TCNQF42−. 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 TCNQF42− 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.

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compounds of this moiety.9 The presence of the four electron withdrawing fluorines on TCNQF4 shifts the reversible potentials of the TCNQF40/1− and TCNQF41−/2− processes to considerably more positive values.24 Thus, TCNQF42− is far less sensitive to oxidation than TCNQ2−,25 thereby giving rise to increased stability of TCNQF42−-based materials.9 The combination of factors surveyed suggests that stoichiometric and nonstoichiometric ratios of cations/anions could be used to create a systematic series of materials based on TCNQ(F)1−, TCNQ(F)2−, or fractionally reduced TCNQ(F)0