Structures of phosphonitrides in light of the extended Zintl-Klemm concept.

The extended Zintl-Klemm concept (EZKC) is applied to explain the crystalline structures of phosphonitrides (also known as nitridophosphates in the chemical literature). The examples of (AE)AlPN(NH) (AE = Ca, Sr, Ba), GePN and MPN (M = Be, Ca, Sr, Ba, Ge) are mainly discussed, although the examples of LiGaGe and LiGaGeO have been also commented on due to their relation with BePN. It is shown that the EZKC provides a better understanding of the structures of these compounds than in previous descriptions. In most of these nitrides, P atoms behave as pseudo-Si atoms and N atoms behave as pseudo-O atoms, so providing a good explanation for the four-connectivity of P atoms forming PN units, which behave as pseudo-SiO units like the SiO units in many polymorphs of SiO. In addition, the EZKC shows that the notation of these compounds as phosphonitrides is more appropriate than as nitridophosphates because N atoms act as the anions in these compounds.