Poly- and Interhalogen Anions from Fluorine to Bromine.

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 leading to the formation of polyfluorides, polychlorides, polybromides, and polyinterhalides are also illustrated. The structural diversity of polyhalides has dramatically 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 were examined by sophisticated state-of-the-art quantum-chemical calculations and investigated spectroscopically in rare gas matrix-isolation experiments under cryogenic conditions at 4 K. In addition, the bonding in such polyhalide systems is discussed. The last section deals with applications of such polyhalides in halogenation reactions, electrochemistry as well as their use as reactive ionic liquids, emphasizing the promising future of the field of polyhalogen chemistry.