Positive at last: a pure phosphorus cation

Ever since Hennig Brand’s discovery in 1669, elementary phosphorus has fascinated chemists around the world. It is industrially produced by the tonne and its compounds have numerous applications in materials science and the life sciences. The main known forms of the element are white, red and black phosphorus.

In addition, there are hundreds of compounds in which phosphorus is present as an anion, a negatively charged ion. Some of these compounds have very useful properties. They are suitable for use as electrode materials for lithium-ion batteries, for instance. But all attempts in the past decades to synthesise a positively charged cation as a complement to the known negative ion have failed.

A research team led by Prof Dr Ingo Krossing from the Faculty of Chemistry, Pharmacy, and Earth Sciences of the University of Freiburg has now succeeded in creating a positively charged pure phosphorus compound. The results have been published in the renowned journal Angewandte Chemie.

The team used the stabilising effect of a non-reactive counterion to synthesise sizable quantities of the first ever pure phosphorus cation [P9]+ both in solution and in solid form. In addition, the salt obtained in this way remains stable for weeks at room temperature. It is thus finally possible to perform chemical reactions with this particle, which was previously known only from gas-phase experiments.

Due to its broad availability, the cation can be used in fundamental as well as applied research. One promising possibility is the semiconductor synthesis of the compound gallium phosphide, which is relevant for blue light-emitting diodes (LEDs).