Ionic-liquid-assisted synthesis of the phosphorus interhalides [PBr4][IBr2] and [PBr4][I5Br7].

The phosphorus interhalides [PBr4][IBr2] (1) and [PBr4]2[I5Br7] (2) were prepared by reaction of PBr5 and the interhalogen IBr in the ionic liquid [MeBu3N][N(Tf)2] (N(Tf)2: bis(trifluoromethylsulfonyl)amide). [PBr4][IBr2] (1) consists of tetrahedral [PBr4]+ cations and linear [IBr2]- anions. [PBr4]2[I5Br7] (2) also contains [PBr4]+ cations as well as the iodine bromide anion [I5Br7]2-. The latter represents the yet largest known polyiodinebromide. Moreover, (2) shows remarkable halogen release (IBr and Br2) of 96.8 wt% below 300 °C. For the ternary system P-Br-I, (1) and (2) are the first compounds that were characterized by crystal structure analysis. Composition, bonding situation and properties were further validated by energy dispersive X-ray (EDX) analysis, thermogravimetry (TG) and Raman spectroscopy.