Polyhalogen and Polyinterhalogen Anions from Fluorine to Iodine

This Review deals with the evolving field of polyhalogen chemistry, specifically polyhalogen anions (polyhalides). In addition to a historical outline, current progress in synthetic approaches towards the formation of polyfluorides, polychlorides, polybromides, and polyinterhalides is also illustrated. The structural diversity of polyhalides has substantially increased in the past decade, especially for polychlorides and polybromides, which are commonly characterized by single-crystal X-ray diffraction, Raman spectroscopy, and quantum-chemical calculations. Polyfluorides have been examined by sophisticated state-of-the-art quantum-chemical calculations and investigated spectroscopically in noble gas matrix-isolation experiments under cryogenic conditions at 4 K. The bonding in such polyhalide systems is also discussed. The last Section deals with applications of polyhalides in halogenation reactions and electrochemistry as well as their use as reactive ionic liquids, emphasizing the promising future of polyhalogen chemistry.