Phosphonium
Phosphonium is an ion. It is rare. Its chemical formula is PH4+. It is similar to ammonium. It is almost never found outside of an organic compound. Its molar mass is 35.01 g/mol.
Phosphonium Media
Structure of solid "phosphorus pentachloride", illustrating its autoionization to tetrachlorophosphonium.
Tetrakis(hydroxymethyl)phosphonium chloride is used in production of textiles.