Synthetic Precursors for TCNQF₄^2– Compounds: Synthesis, Characterization, and Electrochemical Studies of (Pr₄N)₂TCNQF₄ and Li₂TCNQF₄

Careful control of the reaction stoichiometry and conditions enables the synthesis of both LiTCNQF₄ and Li₂TCNQF₄ to be achieved. Reaction of LiI with TCNQF₄, in a 4:1 molar ratio, in boiling acetonitrile yields Li₂TCNQF₄. However, deviation from this ratio or the reaction temperature gives either LiTCNQF₄ or a mixture of Li₂TCNQF₄ and LiTCNQF₄. This is the first report of the large-scale chemical synthesis of Li₂TCNQF₄. Attempts to prepare a single crystal of Li₂TCNQF₄ have been unsuccessful, although air-stable (Pr₄N)₂TCNQF₄ was obtained by mixing Pr₄NBr with Li₂TCNQF₄ in aqueous solution. Pr₄NTCNQF₄ was also obtained by reaction of LiTCNQF₄ with Pr₄NBr in water. Li₂TCNQF₄, (Pr₄N)₂TCNQF₄, and Pr₄NTCNQF₄ have been characterized by UV–vis, FT-IR, Raman, and NMR spectroscopy, high resolution electrospray ionization mass spectrometry, and electrochemistry. The structures of single crystals of (Pr₄N)₂TCNQF₄ and Pr₄NTCNQF₄ have been determined by X-ray crystallography. These TCNQF₄^2– salts will provide useful precursors for the synthesis of derivatives of the dianions.