Synthesis and crystal structure of the hydrogen polyphosphide bis(tetraphenylphosphonium) hydrogenheptaphosphide-ammonia(1/3) (PPh4)(2)HP7 center dot 3NH(3)

(PPh4)(2)HP7 . 3NH(3) was prepared by the reaction of K3P7 with a proton-charged ion exchange resin in the presence of (PPh4)Br in liquid ammonia.. and characterized by low temperature X-ray structure analysis. The thermally very unstable compound contains the hydrogenheptaphosphide anion HP2-, the nortricy-clane-like cage of which is slightly distorted by the attachment of the hydrogen atom.