ABSTRACT
Cubic crystals of tripotassium aluminium (or gallium) nitridotriphosphate, K3 M III(PO3)3N (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 IIIO6] octa-hedra linked together via (PO3)3N groups. The latter are formed from three PO3N tetra-hedra 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 tetra-dentate type of coordination for the latter potassium cations by the (PO3)3N6- anion is observed. These K3 M III(PO3)3N (M III = Al, Ga) compounds are isostructural with the Na3 M III(PO3)3N (M III = Al, V, Ti) compounds.
ABSTRACT
The solid solution KNi(0.93)Fe(II)(0.07)Fe(III)(PO4)2 {potassium [nickel(II)/iron(II)] iron(III) bis(orthophosphate)} has been prepared by the flux method. The compound shows a new type of structure for a phosphate with the general composition M(I)M(II)M(III)(PO4)2. The framework is formed by [(Ni/Fe)O6] polyhedra [Fe site occupancy = 0.069â (14)] linked via shared oxygen vertices forming a cis-like parallel chain stretching along a and [FeO5] polyhedra (located on alternate sides of the chains) connected via two types of PO4 groups into a three-dimensional structure. The K atoms are disordered between two sites, denoted K1A and K1B, with occupancies of 0.930â (9) and 0.070â (9), respectively, and reside inside channels along the a axis. Calculations of the Voronoi-Dirichlet polyhedra of the K atoms give a coordination scheme for K1A of [9â +â 3] and for K1B of [10â +â 2]. The most remarkable feature of the structure is the splitting of the K-atom site and the population of the K1A and K1B positions due to substitution of Ni by Fe in the (Ni/Fe) position.
ABSTRACT
Polycrystalline silver(I) deca-calcium heptakis(orthophos-phate), AgCa10(PO4)7, was obtained by solid-state reaction. It is isotopic with members of the series MCa10(PO4)7 (M = Li, Na, K and Cs), and is closely related to the structure of ß-Ca3(PO4)2. The crystal structure of the title compound is built up from a framework of [CaO9] and two [CaO8] polyhedra, one [CaO6] octa-hedron (site symmetry 3.) and three PO4 tetra-hedra (one with site symmetry 3.). The Ag(+) cation is likewise located on a threefold rotation axis and resides in the cavities of the rigid [Ca10(PO4)7](-) framework. It is surrounded by three O atoms in an almost regular triangular environment.
ABSTRACT
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)O6octa-hedron (site symmetry 3.), with a mixed Mn/Fe occupancy, and a PO4 tetra-hedron (site symmetry .2). The Na⺠cations are distributed over two partially occupied sites in the cavities of the framework. One Na⺠cation (site symmetry -3.) is surrounded by six O atoms, whereas the other Na⺠cation (site symmetry .2) is surrounded by eight O atoms.
ABSTRACT
The double phosphate Cs(3)In(3)(PO(4))(4), prepared by a flux technique, features a fragment of composition In(3)O(16) formed by three corner-sharing InO(6) polyhedra. The central In atom resides on a twofold rotation axis, while the other two In atoms are on general positions. The O atoms in this fragment also belong to PO(4) tetrahedra, which link the structure into an overall three-dimensional anionic In-O-P network that is penetrated by tunnels running along c. Two independent Cs(+) cations reside inside the tunnels, one of which sits on a centre of inversion. In general, the organization of the framework is similar to that of K(3)In(3)(PO(4))(4), which also contains an In(3)O(16) fragment. However, in the latter case the unit consists of one InO(7) polyhedron and one InO(6) polyhedron sharing an edge, with a third InO(6) octahedron connected via a shared corner. Calculations of the Voronoi-Dirichlet polyhedra of the alkali metals give coordination schemes for Cs of [9+2] and [8+4] (1 symmetry), and for K of [8+1], [7+2] and [7+2]. This structural analysis shows that the coordination requirements of the alkali metals residing inside the tunnels cause the difference in the In(3)O(16) geometry.
ABSTRACT
The complex phosphate tricaesium calcium iron bis(diphosphate), Cs(3)CaFe(P(2)O(7))(2), has been prepared by the flux method. Isolated [FeO(5)] and [CaO(6)] polyhedra are linked by two types of P(2)O(7) groups into a three-dimensional framework. The latter is penetrated by hexagonal channels along the a axis where three Cs atoms are located. Calculations of caesium Voronoi-Dirichlet polyhedra give coordination schemes for the three Cs atoms as [8 + 3], [9 + 1] and [9 + 4]. The structure includes features of both two- and three-dimensional frameworks of caesium double pyrophosphates.
ABSTRACT
The title compound, K(0.8)Ca(9.8)Fe(0.2)(PO(4))(7) (potassium deca-calcium iron hepta-phosphate), belongs to the whitlockite family. The structure is built up from several types of metal-oxygen polyhedra: two [CaO(8)], one [CaO(7)] and one [(Ca/Fe)O(6)] polyhedron with a mixed Ca/Fe occupancy in a 0.8:0.2 ratio, as well as three tetra-hedral [PO(4)] 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 [PO(4)] tetra-hedra via edges and corners results in formation of a three-dimensional framework with composition [Ca(9.8)Fe(0.2)(PO(4))(7)](0.8-). The remaining K atoms (site-occupation factor = 0.8) are located in large closed cavities and are nine-coordinated by oxygen.
ABSTRACT
Caesium magnesium orthophosphate is built up from MgO(4) and PO(4) tetra-hedra (both with . m. symmetry) linked together by corners, forming a three-dimensional framework. The Cs atoms have .m. site symmetry and are located in hexa-gonal channels running along the a- and b-axis directions.
