The use of neat BrCl in organic and inorganic chemistry is limited due to its gaseous aggregate state and especially its decomposition into Cl 2 andB r 2 .T he stabilization of BrCl in form of reactive ionic liquidsv ia an ovel in situ synthesis route shifts this equilibrium drastically to the BrCl side, which leads to safer and easier-to-handle interha-logenation reagents. Furthermore, the crystallined erivatives of the hitherto unknown [Cl(BrCl) 2 ] À and [Cl(BrCl) 4 ] À anions were synthesized and characterized by single-crystal X-ray diffraction (XRD), Ramana nd IR spectroscopy,a sw ell as quantum chemical calculations.