Question: why pbr5 does not exist?
Answer: Originally Answered: Why do molecules, such as PBR5 and PI5, not exist? ... In case of PI5 ,phosphorus is smaller in size and iodine has large atomic size,hence fact is,that phosphorus can not form bonds with five iodine atoms due to steric repulsion. Thus PI5 does not exist. hence phosphorus prefer to form PI₃with iodine.