Diagnosis of the Redox Levels of TCNQF4 Compounds Using Vibrational Spectroscopy

The vibrational spectroscopy of TCNQF(4)(0), TCNQF(4)(1-) and TCNQF(4)(2-) 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 TCNQF(4) compounds. In the C=C stretching region (1460-1600 cm(-1)), TCNQF(4)(0) and TCNQF(4)(1-) show two bands, with the more energetic being at 1600 cm(-1) in TCNQF(4)(0) and at approximately 1535 cm(-1) in TCNQF(4)(1-); in TCNQF(4)(2-) both modes absorb below 1500 cm(-1), often merging to give a single band. In the C-F and endocyclic C-C stretching region (1290 and 1360 cm(-1)), TCNQF(4)(0) and TCNQF(4)(1-) show strong bands, whereas TCNQF(4)(2-) 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 TCNQF(4)(2-). This sensitivity to coordination is likely to affect the spectra of many organic molecular ions.