On the Use of Raman Spectroscopy in the Characterization of Iodine in Charge-Transfer Complexes

FT-Raman spectra of some polyiodides and of a series of D · I2 charge-transfer complexes (where D is a molecule containing the thione or selone groups as donors), all characterized by x-ray diffraction, are reported. For the adducts with the thione compounds, which can be considered weak or medium-weak complexes, an empirical linear correlation between the frequency of the v(I-I) stretching vibrations and the d(I-I) bond distances has been found. Some polyiodides show FT-Raman spectra that are indistinguishable with respect to those displayed by the neutral complexes of weak or medium-weak strength; in such cases, the polyiodide can be regarded as a diiodine molecule, perturbed by an I n (n = 1,3,…) donor. Polyiodides of this type show Raman absorptions falling in the linear correlation.