Interaction in the molten system Rb2O‐P2O5‐TiO2‐NiO. Crystal structure of the langbeinite‐related Rb2Ni0.5Ti1.5(PO4)3

The interaction in the molten system Rb₂O‐P₂O₅‐TiO₂‐NiO was investigated at different molar ratios Rb/P = 0.5‐1.3, fixed Ti/P = 0.15, Ti/Ni = 1.0 at temperature range 1073–953 K. The conditions of formation of complex phosphates RbTi₂(PO₄)₃, Rb₂Ni_0.5Ti_1.5(PO₄)₃ and RbNiPO₄ have been determined. The new phosphate Rb₂Ni_0.5Ti_1.5(PO₄)₃ (space group P2₁3, a = 9.9386(2) Å) has been obtained and investigated by the single crystal X‐ray diffraction and FTIR‐spectroscopy. It has langbeinite‐like structure, that is built up from mixed (Ni/Ti)O₆‐octahedra and РО₄‐tetrahedra. Rubidium atoms are located in closed cavities of 3D‐framework.     

The triple pyrophosphate Cs3CaFe(P2O7)2

The complex phosphate tricaesium calcium iron bis(diphosphate), Cs₃CaFe(P₂O₇)₂, has been prepared by the flux method. Isolated [FeO₅] and [CaO₆] polyhedra are linked by two types of P₂O₇ 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.     

Synthesis and characterization of phosphates in molten systems Cs2O-P2O5-CaO-M2O3 (M—Al, Fe, Cr)

The crystallization of complex phosphates from the melts of Cs₂O-P₂O₅-CaO-M^III₂O₃ (M^III—Al, Fe, Cr) systems have been investigated at fixed value Cs/P molar ratios equal to 0.7, 1.0 and 1.3 and Са/Р=0.2 and Ca/М^III=1. The fields of crystallization of CsCaP₃O₉, β-Ca₂P₂O₇, Cs₂CaP₂O₇, Cs₃CaFe(P₂O₇)₂, Ca₉M^III(PO₄)₇ (M^III—Fe, Cr), Cs_0.63Ca_9.63Fe_0.37(PO₄)₇ and CsCa₁₀(PO₄)₇ were determined. Obtained phosphates were investigated using powder X-ray diffraction and FTIR spectroscopy. Novel whitlockite-related phases CsCa₁₀(PO₄)₇ and Cs_0.63Ca_9.63Fe_0.37(PO₄)₇ have been characterized by single crystal X-ray diffraction: space group R3c, a=10.5536(5) and 10.5221(4) Å, с=37.2283(19) and 37.2405(17) Å, respectively.     

Enthalpies of formation and strain of chlorobenzoic acids from thermochemical measurements and from ab initio calculations

Molar enthalpies of sublimation of 2-chloro-, 3-chloro-, and 4-chlorobenzoic acids were obtained from the temperature dependence of the vapor pressure measured by the transpiration method. Thermochemical investigations of chlorobenzoic acids available in the literature were collected and combined with own experimental results to obtain their reliable standard molar enthalpies of formation at T = 298.15 K in the gaseous state. Ab initio calculations of chlorobenzoic acids have been performed using the G3(MP2) theory, and results from the homodesmic reactions are in excellent agreement with experiment. New results help us to resolve the uncertainty in the available thermochemical data on chlorobenzoic acids. The strain enthalpies of chlorobenzoic acids have been assessed using an isodesmic reaction procedure.     

Synthesis and characterization of phosphates in the pseudo‐ternary melted systems Cs2O‐P2O5‐MIIO (MII – alkaline earth)

The crystallization of alkali‐earth phosphates in the melts of Cs₂O‐P₂O₅‐M^IIO (M^II – Ca, Sr, Ba) pseudo‐ternary systems have been investigated at various Cs/P molar ratios and at fixed value of M^II/P equal to 0.15. Type of the phosphate which crystallizes in melts depends on the Cs/P initial ratio. Crystallization fields of CsM^IIP₃O₉, M^II₂P₂O₇ and Cs₂M^IIP₂O₇ were briefly investigated and characterized. The new diphosphate Cs₂CaP₂O₇ has been obtained and investigated by the single crystal and powder X‐ray diffraction and FTIR‐ spectroscopy. It crystallizes in C 2/m space group, with the following parameters of the monoclinic cell: a = 10.261(2), b = 5.9316(12), c = 7.2404(14) Å, β = 118.54(3)°. The architecture of [CaP₂O₇]^2‐ anionic sublattice, which is built up from [CaO₆] octahedra and [P₂O₇] bitetrahedra, interlinked via the common oxygen vertices, gives rise to formation of hexagonal tunnels along crystallographic direction b, where caesium atoms are located. One of the most remarkable features of the structure is specific positional disorder of the diphosphate group, which is connected with the existence of two equiprobable half‐occupied sites of the bridging oxygen. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase formation in molten system (Na/K)2O‐TiO2‐P2O5. Crystal structures of NASICON and langbeinite‐related phosphates (K/Na)1+xTi2(PO4)3 (x = 0 and 0.357)

Crystallization of high temperature self‐flux of system Na₂O‐K₂O‐TiO₂‐P₂O₅ was investigated at different molar ratios (Na+K)/P = 0.9; 1.0 or 1.2 and Na/K = 1.0 or 2.0 over the temperature range 1000–650°C. The conditions of formation of complex phosphates K_0.10Na_0.90Ti₂(PO₄)₃ (NASICON‐related) and K_0.877Na_0.48Ti^ІІІ_0.357Ti^ІV_1.643(PO₄)₃ (langbeinite‐related) have been established. The new obtained compounds were investigated using FTIR‐spectroscopy, powder and single crystal X‐ray diffraction and optical microscopy methods. The influence of alkaline metal nature on the structure formation of complex phosphates in the high temperature self‐fluxes is discussed.     

A novel In3O16 fragment in Cs3In3(PO4)4

The double phosphate Cs₃In₃(PO₄)₄, prepared by a flux technique, features a fragment of composition In₃O₁₆ formed by three corner‐sharing InO₆ 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 PO₄ 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 K₃In₃(PO₄)₄, which also contains an In₃O₁₆ fragment. However, in the latter case the unit consists of one InO₇ polyhedron and one InO₆ polyhedron sharing an edge, with a third InO₆ 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] ( 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 In₃O₁₆ geometry.     

Interaction between Co2P4O12 and alkali metal nitrate (chloride) melts

Reactions between Co₂P₄O₁₂ and alkali metal nitrate (chloride) melts was studied in the temperature range 350–400°C (800–850°C) at different phosphate/melt ratios. The effect of the nature of an alkali metal and the ratio between the components in the Co₂P₄O₁₂-M^INO₃ (M^ICl) system on composition of the reaction products was established. The resulting crystalline phases (NaCoPO₄, Na₄Co₃(PO₄)₂P₂O₇, Na₉Co₃(PO₄)₅ and KCoPO₄) were studied by X-ray powder diffraction, IR and electron spectroscopy, and scanning electron microscopy. The features of transformation of the Co₂P₄O₁₂ framework into KCoPO₄ under the effect of excessive alkali metal ions in the melt are discussed.     

The double phosphates MIMIIPO4 (MI – Na,K; MII – Mg,Mn, Co,Ni, Zn) – synthesis from chloride melts and characterization

The particularities of the chemical interaction in systems M^IPO₃‐M^IIO(or Mn₂O₃)‐M^ICl (M^I – Na, K; M^II – Mg, Co, Ni, Zn) have been investigated at the temperature 1073 K and molar ratios P/M^x = 1 or 2 and M^ICl/(M^IPO₃ + M^IIO(or Mn₂O₃)) = 30. The conditions of formation of complex phosphates M^ІM^IIPO₄ and Na₄Ni₃(PO₄)₂P₂O₇ have been found. Influences of the nature of alkali and bivalent metals on the products composition were discussed. The advantages of chloride melts using (synthesis time reduction and temperature reducing) for preparing of complex phosphates were shown. The synthesized compounds have been characterized using the powder X‐ray diffraction, Fourier transform infrared and diffuse reflectance spectroscopies.