Processing Gray Selenium in Phosphonium-Based Ionic Liquids.

The dissolution of gray selenium in tetraalkylphosphonium acetate ionic liquids was investigated by UV-vis, NMR, and Raman spectroscopy as well as quantum chemical calculations and electrochemical methods. Acetate anions and tetraalkylphosphonium cations facilitate the formation and stabilization of oligoselenides Se and cationic Se species in the ionic liquid phase. Chemical exchange of selenium atoms was demonstrated by variable-temperature Se NMR experiments. Additionally, uncharged cycloselenium molecules exist at high selenium concentrations. Upon dilution with ethanol, amorphous red selenium precipitates from the solution. Moreover, crystalline SeTe solid solutions precipitate when elemental tellurium is added to the mixture as confirmed by powder X-ray diffraction and Raman spectroscopy.