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Single crystals of the langbeinite-type phosphates K1.65Na0.35TiFe(PO4)3 and K0.97Na1.03Ti1.26Fe0.74(PO4)3 were grown by crystallization from high-temperature self-fluxes in the system Na2O–K2O–P2O5–TiO2–Fe2O3 using fixed molar ratios of (Na+K):P = 1.0, Ti:P = 0.20 and Na:K = 1.0 or 2.0 over the temperature range 1273–953 K. The three-dimensional framework of the two isotypic phosphates are built up from [(Ti/Fe)2(PO4)3] structure units containing two mixed [(Ti/Fe)O6] octa­hedra (site symmetry 3) connected via three bridging PO4 tetra­hedra. The potassium and sodium cations share two different sites in the structure that are located in the cavities of the framework. One of these sites has nine and the other twelve surrounding O atoms. [ABSTRACT FROM AUTHOR]

Cubic crystals of tripotassium aluminium (or gallium) nitridotriphosphate, K3MIII(PO3)3N (MIII = 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 [MIIIO6] octa­hedra linked together via (PO3)3N groups. The latter are formed from three PO3N tetra­hedra sharing a common N atom. The coordination environments of the three potassium cations are represented by two types of polyhedra, viz. KO9 for one and KO9N for the other two cations. An unusual tetra­dentate type of coordination for the latter potassium cations by the (PO3)3N6– anion is observed. These K3MIII(PO3)3N (MIII = Al, Ga) compounds are isostructural with the Na3MIII(PO3)3N (MIII = Al, V, Ti) compounds. [ABSTRACT FROM AUTHOR]

Polycrystalline potassium nickel(II) hafnium(IV) tris(orthophosphate), a langbeinite-type phosphate, was synthesized by a solid-state method and refers to langbeinite-type phosphates. The three-dimensional framework of the title compound is built up from two types of [MO6] octahedra [the M sites are occupied by Hf:Ni in ratios of 0.754 (8):0.246 (8) and 0.746 (8):0.254 (8), respectively] and [PO4] tetrahedra are connected via O vertices. The K+ cations are located in two positions within large cavities of the framework, having coordination numbers of 9 and 12. The Hf, Ni and K sites lie on threefold rotation axes, while the P and O atoms are situated in general positions. [ABSTRACT FROM AUTHOR]