Structures,raman, infrared and electronic absorption spectra of pyridinium trihalides

Vibrational and electronic absorption spectra of PyHI₃, PyHIBr₂, PyHICl₂, PyHBr₃ and PyHBrCl₂ are presented and explained in terms of the vibrations and electronic transitions, respectively, of the pyridinium and trihalide ions. Two compounds, PyHI₃ and PyHBr₃, show charge transfer bands in the absorption spectra of the solids, and the vibrational spectrum of the PyH⁺ ion in solid PyHBr₃ differs from the normal PyH⁺ spectrum. PyHBr₃ as well as PyHI₃ contains asymmetric trihalide ions in the solid state, as can be concluded from the Raman and infrared spectra.