Oxynitrides and Nitridophosphates

It has become apparent that N atoms can be substituted for O atoms in many condensed phosphates to give isostructural atomic arrangements. NMR spectra of these P/N/0 compounds have indicated the existence of [PN3O], [PN2O2] and [PNO3] tetrahedral units. Examples of complete replacement of O by N have already been given (4.188), (4.194). 

The oxynitride PON has been obtained in the amorphous state and in at least three different crystalline forms. One of these is isostructural with a quartz and the other is isostructural with 6 cristobalite which in turn are isostructural with corresponding varieties of AIPO4. 

With simple ionic formulations, charge balances are easily obtained  

In the quartz and cristobalite forms of PON there is a random distribution of O and N atoms in the corners of [P(0/N)4] tetrahedra which share their comers with other tetrahedra. Another oxynitride, P40Ng, has been identified and has a structure built from comer- and edge-shared [PON3] and [PN4] tetrahedra [187]. Preparations can be based on melamine. 

4NH4H2PO4 + C3N3(NH2)3 4PON + 3CO2 -E 6H2O -1- 6NH3 PON (P cristobalite) +NH3 — 

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