Structural features of the oxidonitridophosphates K (PO)N ( = Al, Ga).

Cubic crystals of tripotassium aluminium (or gallium) nitridotriphosphate, K (PO)N ( = Al, Ga), were grown by application of the self-flux method. In their isostructural crystal structures, all metal cations and the N atom occupy special positions with site symmetry 3, while the P and O atoms are situated in general positions. The three-dimensional framework of these oxidonitridophosphates is built up from [ O] octa-hedra linked together (PO)N groups. The latter are formed from three PON tetra-hedra sharing a common N atom. The coordination environments of the three potassium cations are represented by two types of polyhedra, . KO for one and KON for the other two cations. An unusual tetra-dentate type of coordination for the latter potassium cations by the (PO)N anion is observed. These K (PO)N ( = Al, Ga) compounds are isostructural with the Na (PO)N ( = Al, V, Ti) compounds.