Nitridophosphate

A nitridophosphate is an inorganic compound that contains nitrogen bound to a phosphorus atom, considered as replacing oxygen in a phosphate.

Anions include NPN PN3 P3N6. Related compounds include the oxonitridophosphates imidonitridophosphates, nitridoborophosphates, and nitridosilicatephosphates. By changing the phosphorus, related materials include nitridovanadates and nitridorhenates.

Nitridophosphate compounds include elements from the alkali metals, alkaline earths, first row transition metals, rare earth elements, and some other main group elements.

Characteristics
Nitridophosphate compounds nearly always contain phosphorus in tetrahedral configuration. They can be characterised by the condensation index K which is the ratio of numbers of phosphorus tetrahedral centres to nitrogen vertices. As more nitrogen atoms are shared between phosphorus, condensation increases. The maximum is for P3N5 which no longer has any capacity for cations. For K of 1/2 three dimensional frameworks are produced. For 2/7 or 3/7 layered arrangements of tetrahedra are produced. For 1/3 chains or ring structures are prominent. 1/4 is for uncondensed PN4 compounds. Tow PN4 tetrahedra can also share an edge: P2N6, as the P-N bond is not very polarised, so there is less electrostatic repulsion. Uncondensed compounds are sensitive to air and water but highly condensed compounds are water or acid stable.

Nitridophosphate compounds are usually insulators and are transparent to light.

Formation
Heating P3N5 with a metal nitride at gigapascal pressure and a temperatures of over 1000 °C forms nitridophosphates. P3N5 decomposes over 850°C at ambient pressure. However there are a few nitridophosphates that do no require such high temperatures to form.

Heating ammonia under pressure with red phosphorus, and metals, metal nitrides or metal azides is a method called ammonothermal synthesis.

Use
Nitridophosphates are under investigation as luminescent materials, that can covert blue light into red.