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
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 1273-953â 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] octa-hedra (site symmetry 3) connected via three bridging PO4 tetra-hedra. 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
Polycrystalline potassium nickel(II) hafnium(IV) tris-(orthophosphate), a langbeinite-type phosphate, was synthesized by a solid-state method. The three-dimensional framework of the title compound is built up from two types of [MO6] octa-hedra [the M sites are occupied by Hf:Ni in ratios of 0.754â (8):0.246â (8) and 0.746â (8):0.254â (8), respectively] and [PO4] tetra-hedra 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
Herein, the peculiarities of complex phosphate formation in self-fluxes of Cs-MII-Bi-P-O (MII = Ca, Sr, Ba and Pb) systems with Cs/P = 0.7-1.3 at fixed ratios of Bi/P = 0.2 and Bi/MII = 1.0 were studied and discussed. Three novel isostructural diphosphates with the general composition Cs3MIIBi(P2O7)2 (MII = Ca, Sr and Pb) and the original framework topology were synthesized and characterized via single-crystal and powder X-ray diffraction, SEM, DTA, and FTIR- and UV-VIS-spectroscopy. In addition, electronic structure (DFT) and Voronoi-Dirichlet polyhedra (VDP) characteristics calculations and crystallochemical analysis were performed. In the structure of the new compounds, the MIIO7 and BiO6 polyhedra are connected via common oxygen vertices forming infinite helical-like chains, which are linked by P2O7 groups into a 3D-framework with pentagonal tunnels, where the Cs+ cations are located. The structural peculiarities are discussed considering perspectives for the creation of new luminescent materials. The dielectric bandgaps, Eg, of the Cs3MIIBi(P2O7)2 crystals reveal an â¼0.2 eV low-energy shift in the Ca-Sr-Pb sequence of MII cations, which reveals the possibility to tune the optical absorbance spectra of the crystals via the synthesis of solid solutions with various contents of MII cations. The glass-ceramic synthetic approach is also proposed as a convenient method for the creation of new diphosphates, and the applicability of this method is verified for Cs3CaBi(P2O7)2.
ABSTRACT
Potassium rubidium cobalt(II)/titanium(IV) tris-(orthophosphate), Rb0.743K0.845Co0.293Ti1.707(PO4)3, has been obtained using a high-temperature crystallization method. The obtained compound has a langbeinite-type structure. The three-dimensional framework is built up from mixed-occupied (Co/Ti(IV))O6 octa-hedra (point group symmetry .3.) and PO4 tetra-hedra. The K(+) and Rb(+) cations are statistically distributed over two distinct sites (both with site symmetry .3.) in the large cavities of the framework. They are surrounded by 12 O atoms.
ABSTRACT
The title compound, tetra-potassium tetra-[nickel(II)/iron(III)] penta-kis-(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 0.799â (8):0.196â (10) and isolated PO4 tetra-hedra, 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 hexa-gonally shaped channels that run parallel to [001]. One K(+) cation [occupancy 0.73â (3)] is surrounded by nine O atoms, while the other K(+) cation [occupancy 0.23â (3)] is surrounded by eight O atoms.
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
KMg(0.09)Fe(1.91)(PO(4))(2), potassium [iron(II)/magnesium] iron(III) bis(orthophosphate), is a solid solution derived from compounds with general formula KM(II)Fe(PO(4))(2) (M(II) = Fe, Cu), in which the Mg atoms substitute Fe atoms only in the octa-hedrally surrounded sites. The framework of the structure is built up from [FeO(5)] trigonal bipyramids and [MO(6)] (M = (Fe, Mg) octa-hedra sharing corners and edges and connected by two types of bridging PO(4) tetra-hedra. The K(+) cations are nine-coordinated and are situated in channels running along [101].
ABSTRACT
The possibility of PO(4)(3-) for MoO(4)(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 1/3PO(4)(3-) for MoO(4)(2-) substitution leads to formation of three novel compounds K(2)Fe(MoO(4))(PO(4))(2), K(2)Sc(MoO(4))(PO(4))(2), and K(2)Sc(WO(4))(PO(4))(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.
ABSTRACT
Single crystals of silver(I) polyphosphate(V), AgPO(3), were prepared via a phospho-ric acid melt method using a solution of Ag(3)PO(4) in H(3)PO(4). In comparison with the previous study based on single-crystal Weissenberg photographs [Jost (1961 â¶). 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 [AgO(5)] polyhedra, giving rise to multidirectional ribbons, and from two types of PO(4) tetra-hedra linked into meandering chains (PO(3))(n) spreading parallel to the b axis with a repeat unit of four tetra-hedra. The calculated bond-valence sum value of one of the two Ag(I) ions indicates a significant strain of the structure.
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
Potassium yttrium hafnium tris-(orthophosphate) belongs to the langbeinite-family and is built up from [MO(6)] octa-hedra [in which the positions of the two independent M sites are mutually occupied by Y and Hf in a 0.605â (10):0.395â (10) ratio] and [PO(4)] tetra-hedra 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.
ABSTRACT
Nine novel phosphates, based upon a combination of caesium, zirconium and lanthanide ions, were obtained from fluoride-containing fluxes using high-temperature crystallization. The structures of Cs(1.80)Eu(0.80)Zr(1.20)(PO(4))(3) (CsEuZrP), Cs(1.79)Gd(0.79)Zr(1.21)(PO(4))(3) (CsGdZrP), Cs(1.87)Tb(0.87)Zr(1.13)(PO(4))(3) (CsTbZrP), Cs(1.67)Dy(0.67)Zr(1.33)(PO(4))(3) (CsDyZrP), Cs(1.75)Ho(0.75)Zr(1.25)(PO(4))(3) (CsHoZrP), Cs(1.78)Er(0.78)Zr(1.22)(PO(4))(3) (CsErZrP), Cs(1.70)Tm(0.70)Zr(1.30)(PO(4))(3) (CsTmZrP), Cs(1.52)Yb(0.52)Zr(1.48)(PO(4))(3) (CsYbZrP) and Cs(1.63)Lu(0.63)Zr(1.37)(PO(4))(3) (CsLuZrP) were solved using single-crystal X-ray diffraction. All compounds are isostructural to the mineral langbeinite (cubic system, space group P2(1)3). Their framework structures originate from the cross-linking of metal octahedra [MO(6)] (M = Zr, Ln) by phosphate tetrahedra. Cs(+) cations are located in the closed cavities of the framework and preferentially occupy one of the two available sites. The principles of crystallization of the equilibrium langbeinite-related phosphates in the fluxes of the system Cs(2)O-P(2)O(5)-LnF(3)-ZrF(4) (Ln = La-Nd, Sm-Lu) are discussed based on their crystal structures.
ABSTRACT
Tetrapotassium cerium(IV) zirconium tetrakis(monophosphate) crystallizes in the tetragonal system (space group I4(1)/amd). A complex disorder in K4CeZr(PO4)4 involves the mixing of Ce and Zr atoms on a single site with -4m2 symmetry and the splitting of P- and O-atom positions, equivalent to a rotation of the phosphate groups, to yield eight- and sixfold coordination environments around Ce and Zr, respectively. The K atoms are located in tunnels running parallel to the a and b axes.
