Rietveld refinement of langbeinite-type K2YHf(PO4)3

Potassium yttrium hafnium tris­(orthophosphate) belongs to the langbeinite-family and is built up from [MO6] octa­hedra [in which the positions of the two independent M sites are mutually occupied by Y and Hf in a 0.605 (10):0.395 (10) ratio] and [PO4] tetra­hedra connected via vertices into a three-dimensional framework. This framework is penetrated by large closed cavities in which the two independent K atoms are located; one of the K atoms is nine-coordinated and the other is 12-coordinated by surrounding O atoms. The K, Y and Hf atoms lie on threefold rotation axes, whereas the P and O atoms are located in general positions

KMg0.09Fe1.91(PO4)2

KMg0.09Fe1.91(PO4)2, potassium [iron(II)/magnesium] iron(III) bis(orthophosphate), is a solid solution derived from compounds with general formula KM IIFe(PO4)2 (M II = Fe, Cu), in which the Mg atoms substitute Fe atoms only in the octa­hedrally surrounded sites. The framework of the structure is built up from [FeO5] trigonal bipyramids and [MO6] (M = (Fe, Mg) octa­hedra sharing corners and edges and connected by two types of bridging PO4 tetra­hedra. The K+ cations are nine-coordinated and are situated in channels running along [101]

Redetermination of AgPO3

Single crystals of silver(I) polyphosphate(V), AgPO3, were prepared via a phospho­ric acid melt method using a solution of Ag3PO4 in H3PO4. In comparison with the previous study based on single-crystal Weissenberg photographs [Jost (1961 ▶). Acta Cryst. 14, 779–784], the results were mainly confirmed, but with much higher precision and with all displacement parameters refined anisotropically. The structure is built up from two types of distorted edge- and corner-sharing [AgO5] polyhedra, giving rise to multidirectional ribbons, and from two types of PO4 tetra­hedra linked into meandering chains (PO3)n spreading parallel to the b axis with a repeat unit of four tetra­hedra. The calculated bond-valence sum value of one of the two AgI ions indicates a significant strain of the structure

Synthesis, Structure and Magnetic Characterization of a New Phosphate K 1.84 Fe 1.42 Nb 0.58 (PO 4 ) 3 with the Lang- beinite-type Structure

A new complex phosphate K 1.84 Fe 1.42 Nb 0.58 (PO 4 ) 3 has been synthesized by the self-flux technique. The X-ray single crystal structure and magnetic properties were studied. The compound crystallizes in the cubic system with space group P2 1 3 (a = 9.9404(10)Å) and belongs to the langbeinite structure type. The structure contains [M 2 P 3 O 18 ] building units. "Closed" fragments [M 8 P 9 O 60 ] provide space for location of two potassium atoms. Antiferromagnetic interactions were detected at low temperatures which originate from superexchange through a M(1)-O-P-O-M(2) pathway with corresponding J = −5.5(1) cm −1 . The relationship between the UV/vis absorption and the structure is discussed

Rietveld refinement of whitlockite-related K0.8Ca9.8Fe0.2(PO4)7

The title compound, K0.8Ca9.8Fe0.2(PO4)7 (potassium decacalcium iron heptaphosphate), belongs to the whitlockite family. The structure is built up from several types of metal–oxygen polyhedra: two [CaO8], one [CaO7] and one [(Ca/Fe)O6] polyhedron with a mixed Ca/Fe occupancy in a 0.8:0.2 ratio, as well as three tetrahedral [PO4] units. Of the 18 sites in the asymmetric unit, the site with the mixed Ca/Fe occupation, the K site, one P and one O site are on special positions 6a with 3 symmetry, whereas all other sites are on general positions 18b. The linkage of metal–oxygen polyhedra and [PO4] tetrahedra via edges and corners results in formation of a three-dimensional framework with composition [Ca9.8Fe0.2(PO4)7]0.8−. The remaining K atoms (site-occupation factor = 0.8) are located in large closed cavities and are nine-coordinated by oxygen

NASICON-related Na3.4Mn0.4Fe1.6(PO4)3

The solid solution, sodium [iron(III)/manganese(II)] tris(orthophosphate), Na3.4Mn0.4Fe1.6(PO4)3, was obtained using a flux method. Its crystal structure is related to that of NASICON-type compounds. The [(Mn/Fe)2(PO4)3] framework is built up from an (Mn/Fe)O6 octahedron (site symmetry 3.), with a mixed Mn/Fe occupancy, and a PO4 tetrahedron (site symmetry .2). The Na+ cations are distributed over two partially occupied sites in the cavities of the framework. One Na+ cation (site symmetry -3.) is surrounded by six O atoms, whereas the other Na+ cation (site symmetry .2) is surrounded by eight O atoms

The solid solution K3.84Ni0.78Fe3.19(PO4)5

The title compound, tetrapotassium tetra[nickel(II)/iron(III)] pentakis(orthophosphate), K3.84Ni0.78Fe3.19(PO4)5, has been obtained from a flux. The structure is isotypic with that of K4MgFe3(PO4)5. The three-dimensional framework is built up from (Ni/Fe)O5 trigonal bipyramids with a mixed Fe:Ni occupancy of 0.799 (8):0.196 (10) and isolated PO4 tetrahedra, one of which is on a general position and one of which has -4.. site symmetry. Two K+ cations are statistically occupied and are distributed over two positions in hexagonally shaped channels that run parallel to [001]. One K+ cation [occupancy 0.73 (3)] is surrounded by nine O atoms, while the other K+ cation [occupancy 0.23 (3)] is surrounded by eight O atoms

K₂M^III₂(M^VIO₄)(PO₄)₂ (M^III = Fe, Sc; M^VI = Mo, W), Novel Members of the Lagbeinite-Related Family: Synthesis, Structure, and Magnetic Properties

The possibility of PO₄^3– for MoO₄^2– partial substitution in the langbeinite framework has been studied by exploration of the K–Fe­(Sc)–Mo­(W)–P–O systems using the high-temperature solution method. It was shown that 1/3PO₄^3– for MoO₄^2– substitution leads to formation of three novel compounds K₂Fe­(MoO₄)­(PO₄)₂, K₂Sc­(MoO₄)­(PO₄)₂, and K₂Sc­(WO₄)­(PO₄)₂ with slightly increased lattice parameters and significant distortion of the anion tetrahedra without structure changes. In contrast, the antiferromagnetic structure is modified by substitution in the low-temperature region. The structural peculiarities are discussed in light of bond-valence sums calculations