Phosphorus heptabromide
Phosphorus heptabromide is an inorganic compound with the chemical formula . It is one of the phosphorus bromides. At normal conditions, it forms red prismatic crystals. can be prepared by the sublimation of a mixture of phosphorus pentabromide and bromine. The structure of  consists of a tetrabromophosphonium cation , paired with a tribromide anion , and the tribromide anion is non-symmetric. See also 
 Phosphorus tribromide
 Phosphorus pentabromide

References 

Phosphorus bromides
Polyhalides
Quaternary phosphonium compounds