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Diagnosis of the Redox Levels of TCNQF4 Compounds Using Vibrational Spectroscopy


  • TCNQF4=2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane


The vibrational spectroscopy of TCNQF40, TCNQF41− and TCNQF42− has been investigated by means of density functional theory. Band assignments in infrared and Raman spectra have been clarified and a series of diagnostics developed for redox level characterisation of TCNQF4 compounds. In the C[DOUBLE BOND]C stretching region (1460–1600 cm−1), TCNQF40 and TCNQF41− show two bands, with the more energetic being at 1600 cm−1 in TCNQF40 and at approximately 1535 cm−1 in TCNQF41−; in TCNQF42− both modes absorb below 1500 cm−1, often merging to give a single band. In the C[BOND]F and endocyclic C[BOND]C stretching region (1290 and 1360 cm−1), TCNQF40 and TCNQF41− show strong bands, whereas TCNQF42− absorbs weakly or not at all. (Additional bands, e.g. from co-crystallised solvent molecules, may complicate this region.) In the nitrile stretching region (2000–2250 cm−1), modes are highly sensitive to nitrile coordination by metal cations. All three redox levels can produce bands above 2200 cm−1, however bands below 2150 cm−1 are usually due to TCNQF42−. This sensitivity to coordination is likely to affect the spectra of many organic molecular ions.