Structural features of the oxidonitridophosphates K(3) M (III)(PO(3))(3)N (M (III) = Al, Ga)

Cubic crystals of tripotassium aluminium (or gallium) nitridotriphosphate, K(3) M (III)(PO(3))(3)N (M (III) = 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 [M (III)O(6)] octa­hedra linked together via (PO(3))(3)N groups. The latter are formed from three PO(3)N tetra­hedra sharing a common N atom. The coordination environments of the three potassium cations are represented by two types of polyhedra, viz. KO(9) for one and KO(9)N for the other two cations. An unusual tetra­dentate type of coordination for the latter potassium cations by the (PO(3))(3)N(6–) anion is observed. These K(3) M (III)(PO(3))(3)N (M (III) = Al, Ga) compounds are isostructural with the Na(3) M (III)(PO(3))(3)N (M (III) = Al, V, Ti) compounds.