Two new phosphate langbeinites,Rb2YbTi(PO4)3 and Rb2Yb0.32Ti1.68(PO4)3, investigated at 293 and 150 K

The rubidium ytterbium titanium phosphates Rb₂YbTi(PO₄)₃, (I), and Rb₂Yb_0.32Ti_1.68(PO₄)₃, (II), have been structurally characterized from X‐ray data collected at both 293 and 150 K. Compound (II) is blue owing to the presence of mixed‐valence titanium (41% Ti³⁺ + 59% Ti⁴⁺). Both (I) and (II) belong to the langbeinite structure type, with mixed Yb/Ti populations in the two crystallographically independent octahedral sites (of symmetry 3). Ytterbium favours one of these sites, where about two‐thirds of the Yb atoms are found. The O‐atom displacement parameters are large in both compounds at both temperatures.     

Enthalpy of Phase Transitions and Heat Capacity of Stoichiometric Compounds in LaBr3-MBr Systems (M=K,Rb, Cs)

Molar enthalpies of solid-solid and solid-liquid phase transitions of the LaBr₃, K₂LaBr₅, Rb₂LaBr₅, Rb₃LaBr₆ and Cs₃LaBr₆ compounds were determined by differential scanning calorimetry. K₂LaBr₅ and Rb₂LaBr₅ exist at ambient temperature and melt congruently at 875 and 864 K, respectively, with corresponding enthalpies of 81.5 and 77.2 kJ mol^-1. Rb₃LaBr₆ and Cs₃LaBr₆ are the only 3:1 compounds existing in the investigated systems. The first one forms from RbBr and Rb₂LaBr₅ at 700 K with an enthalpy of 44.0 kJ mol^-1 and melts congruently at 940 K with an enthalpy of 46.7 kJ mol^-1. The second one exists at room temperature, undergoes a solid-solid phase transition at 725 K with an enthalpy of 9.0 kJ mol^-1 and melts congruently at 1013 K with an enthalpy of 57.6 kJ mol^-1. Two other compounds existing in the CsBr-based systems (Cs₂LaBr₅ and CsLa₂Br₇) decompose peritectically at 765 and 828 K, respectively. The heat capacities of the above compounds in the solid as well as in the liquid phase were determined by differential scanning calorimetry. A special method - 'step method' developed by SETARAM was applied in these measurements. The heat capacity experimental data were fitted by a polynomial temperature dependence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Darstellung und Strukturbestimmung zweier Salze der Trimetaphosphimsäure,K3(PO2NH)3 und Rb3(PO2NH)3

Synthesis and Structure Determination of Two Salts of the Trimetaphosphimic Acid, K₃(PO₂NH)₃ and Rb₃(PO₂NH)₃ The reaction between P₃N₅ and the corresponding alkalimetal hydroxide monohydrate under ammonothermal conditions (6 kbar, 450 °C after 10 d) in autoclaves leads to the salts of the trimetaphosphimic acid K₃(PO₂NH)₃ resp. Rb₃(PO₂NH)₃. The structure of K₃(PO₂NH)₃ was solved by single crystals X-ray methods. The isotypic structure of Rb₃(PO₂NH)₃ was solved by X-ray powder diffraction methods. K₃(PO₂NH)₃: R3 (No. 148), a = 12.615(3) Å, c = 10.224(2) Å, Z = 6, R₁/wR₂ = 0.0276/0.0726, N(F > 2σ(F)) = 769, N(Var.) = 51.Rb₃(PO₂NH)₃: R3 (No. 148), a = 12.9971(5) Å, c = 10.5485(5), Z = 6, R_Bragg(F) = 0.0626, 289 reflections. K₃(PO₂NH)₃ and Rb₃(PO₂NH)₃ contain six-membered rings P₃N₃ substituted by oxygen which are connected to double molecules by N–H … O bridge bonds. These twinmolecules are stacked in columns which form the motive of close packed rods. K⁺ resp. Rb⁺ are between these columns. They are coordinated by 6 O which belong to 5 different rings.     

α‐Tris(2,4‐pentanedionato‐κ2O,O′)aluminium(III) at 240, 210, 180, 150 and 110 K: a new δ phase at 110 K

The crystal structure of the title compound, [Al(C₅H₇O₂)₃], has been investigated by a multi‐temperature measurement to provide information on thermal vibrations and disorder in the structure. At 110 K, the structure of a new δ polymorph could be determined. A disorder–order phase transition takes place between 150 and 110 K and is klassengleich. The unit‐cell volume increases by a factor of three and the diffraction pattern shows weak supercell reflections.     

α‐Tris(2,4‐pentanedionato‐κ2O,O′)chromium(III) at 290 and 110 K: a new δ phase at 110 K

The crystal structure of the title compound, [Cr(C₅H₇O₂)₃], has been determined at 290 and 110 K to provide information on thermal vibrations and disorder. The α polymorph at room temperature has been reported [Morosin (1965). Acta Cryst. 19 , 131–137]. The reinvestigation of this structure, presented here, indicates the presence of weak uninterpretable supercell reflections together with disorder streaks. The discussed structure can thus be considered as an average structure. After cooling to 110 K, a new δ polymorph was found, which is a superstructure of the α polymorph. The space group remains P2₁/c and the phase transition can therefore be considered as klassengleich. The unit‐cell volume increases by a factor of six, resulting in six independent molecules in the asymmetric unit.     

4,4′‐Di­bromo­benzo­phenone at 293 and 103 K

The structure of 4,4′‐di­bromo­benzo­phenone, C₁₃H₈Br₂O, was determined at two different temperatures (293 and 103 K). A phase transition was not detected in this temperature range. Its crystal structure was found to be isostructural with that of the di­iodo analogue, but not with the structure of the di­chloro derivative.     

Synchrotron‐radiation study of the two‐leg spin‐ladder (VO)2P2O7 at 120 K

The crystal structure of the ambient‐pressure phase of vanadyl pyrophosphate, (VO)₂P₂O₇, has been precisely determined at 120 K from synchrotron X‐ray diffraction data measured on a high‐quality single crystal. The structure refinement unambiguously establishes the orthorhombic space group Pca2₁ as the true crystallographic symmetry. Moreover, it improves the accuracy of previously published atomic coordinates by one order of magnitude, and provides reliable anisotropic displacement parameters for all atoms. Along the a axis, the structure consists of infinite two‐leg ladders of vanadyl cations, (VO)²⁺, which are separated by pyrophosphate anions, (P₂O₇)^4?. Parallel to the c axis, the unit cell comprises two alternating crystallographically inequivalent chains of edge‐sharing VO₅ square pyramids bridged by PO₄ double tetrahedra. No structural phase transition has been observed in the temperature range between 300 and 120 K.     

Powder neutron diffraction of Tl2BeF4 at six temperatures from room temperature to 1.5 K

The structure of thallium fluoro­beryllate, Tl₂BeF₄, has been analysed by the Rietveld method on neutron diffraction patterns collected at 1.5, 50, 100, 150, 200 and 300 K, with the aim of detecting low‐temperature instabilities. Atomic parameters based on the isomorphic β‐K₂SO₄ crystal in the paraelectric phase were used as the starting model at room temperature; no evidence for any phase transition has been detected at lower temperature. The structure was determined in the ortho­rhom­bic space group Pnma. All the atoms (except one F atom) occupy sites with m symmetry. We have compared the structure with those of other compounds of the β‐K₂SO₄ family, at room temperature, in order to gain insight into their observed instabilities. The irregular coordination of the cations may indicate stereochemical activity of the Tl^I lone pair but does not indicate a possible structural instability.     

Structure cristalline de (NH4)2PO3H,H2O: Stereochimie de l'Ion PO3H2− et ses relations avec PO3F2− et SO32−

(NH₄)₂PO₃H, H₂O crystallizes in the monoclinic system, space group P2₁/c, with a = 6.322(1) Å, b = 8.323(1) Å, c = 12.676(1) Å, β = 98.84(1) and Z = 4. The structure was refined to R = 0.022 based on 853 independent X-Rays intensities. Improved dimensions of the tetrahedral PO₃H^2? ion have been obtained: P?H = 1.34(2) and P?O = 1.514(2) Å. The geometry of this ion is compared with that of PO₃F^2? and SO₃^2? ions and we find a decrease of the volume: V_F? > V_H+ > V_{lone pair}.     

Bis(tetraethylammonium) hydrogensulfate dihydrogenphosphate at 292 and 150 K

The title compound, 2C₈H₂₀N⁺·HSO₄⁻·H₂PO₄⁻, was crystallized in a desiccator over P₄O₁₀ from a water solution of stoichiometric amounts of tetraethyl­ammonium hydroxide and sulfuric and phosphoric acids. The compound is deliquescent. The structure contains two symmetry‐independent cations in nearly the same conformation, as well as two symmetry‐independent anions, the central atoms of which are equally occupied by P and S. The anions are interconnected by short O⃛O hydrogen bonds into one‐dimensional chains. The distances and angles between some of the methyl or methyl­ene groups and anionic O atoms indicate the presence of C—H⃛O hydrogen bonds. The structure was determined from data at 292 (2) and 150 (2) K. These room‐ and low‐temperature structures are virtually the same, with the exception of the localization of the H atoms that participate in the symmetry‐restricted O⃛O hydrogen bonds. A differential scanning calorimetry experiment indicated no phase transition below the temperature at which the compound started to decompose (353 K), down to 93 K.     

Raman spectra of Sr3(PO4)2 and Ba3(PO4)2 orthophosphates at various temperatures

The Raman spectra for Sr₃(PO₄)₂ and Ba₃(PO₄)₂ were investigated in the temperature range from 80 to 1623 K at atmospheric pressure. An unexpected melting of each sample was observed around 1573–1583 K in this study. In the temperature range from 80 to 1323 K, the Raman wavenumbers of all observed bands for Sr₃(PO₄)₂ and Ba₃(PO₄)₂ continuously decrease with increasing temperature. A quantitative analysis on the wavenumbers of Raman bands for both samples reveals that the ν₃ antisymmetric stretching vibrations show the strongest temperature dependence and the ν₂ symmetric bending vibration displays the weakest temperature dependence. The effects of cations on Raman bands are discussed. The reason for the unexpected melting of both samples is mainly attributed to the significant contribution from excess surface energy and the grain-boundary energy that has apparently lowered the melting points of the small samples, i.e., Gibbs–Thomson effect.     

Synthesis of Ammonium‐ and 4‐Dimethylaminopyridinium Amidofluorophosphates and Crystal Structure of [DMAPH][PO2F(NH2)]

NH₄[PO₂F(NH₂)] has been prepared by the reaction of a betaine py·PO₂F with excess ammonia in acetonitrile solution, while the ammonolysis of DMAP·PO₂F with a stoichiometric amount of NH₃ yields [DMAPH][PO₂F(NH₂)]. The crystal structure of the latter was determined by single‐crystal X‐ray diffraction, which revealed that the anions [PO₂F(NH₂)]^— are linked to infinite chains by double N—H···O bridges. Additional strong N—H···O bridging bonds connect each anion with its [DMAPH]⁺ counterion. The formation of a new betaine NH₃·PO₂F in the solution of py·PO₂F in liquid ammonia was proved by ³¹P NMR spectroscopy and by identification of its hydrolysis products.     

Struktur und Magnetismus von Fluoriden Cs2MCu3F10 (M = Mg,Mn, Co,Ni), Varianten des CsCu2F5‐Typs

Structure and Magnetism of Fluorides Cs₂MCu₃F₁₀ (M = Mg, Mn, Co, Ni), Variants of the CsCu₂F₅ Type X‐ray structure determinations of single crystals showed that compounds Cs₂MCu₃F₁₀ crystallize with Z = 2 in space group P2₁/n (No.14) (M = Mn) of the CsCu₂F₅ type resp. in its supergroup I2/m (No.12) (M = Mg, Co, Ni). Cs₂MgCu₃F₁₀: a = 714.9(1), b = 736.8(1), c = 940.4(1) pm, b = 96.29(1)°, (Mg‐F: 199.2 pm); Cs₂MnCu₃F₁₀: a = 725.1(1), b = 742.7(1), c = 951.0(2) pm, b = 97.28(3)°, (Mn‐F: 209.1 pm); Cs₂CoCu₃F₁₀: a = 717.8(3), b = 739.1(2), c = 939.4(4) pm, b = 97.49(2)°, (Co‐F: 203.1 pm); Cs₂NiCu₃F₁₀: a = 716.3(1), b = 737.7(1), c = 938.2(2) pm, b = 97.09(1)°, (Ni‐F: 201.0 pm). As determined directly for the Mg compound and generally concluded from the average distances M‐F noted, M substitution concerns mainly the octahedrally coordinated position of the CsCu₂F₅ structure, the distortion of which is very much reduced thereby. Within the remaining [CuF₄] and [CuF₅] coordinations, in contrast to CsCu₂F₅, one F ligand is disordered, in case of the Mn compound the pyramidally coordinated Cu atom, too. The magnetic properties are complex and point to frustration and spin glass effects. Only at the diamagnetically substituted variants with M = Mg, Zn no Néel point appears, which is reached at 27, 23, 36 and 55 K for M = Mn, Co, Ni and Cu, resp. At lower temperatures ferri‐ resp. weak ferromagnetism and hysteresis is observed.     

K3BiSe3, Rb3BiSe3 und Cs3BiSe3 – Substitutionsvarianten des Th3P4-Typs

K₃BiSe₃, Rb₃BiSe₃, and Cs₃BiSe₃ – Derivatives of the Th₃P₄ Structure Type The compounds K₃BiSe₃, Rb₃BiSe₃, and Cs₃BiSe₃ were synthesized by heating mixtures of Bi₂O₃ and the respective alkalicarbonate in a stream of hydrogen saturated by selenium at 850°C. Thin crystals of the compounds appear red in transmitted light. They crystallize isostructural with Na₃AsS₃, space group P2₁3, lattice constants a = 9.771(5) Å, a = 10.161(3) Å, and a = 10.587(5) Å for K₃BiSe₃, Rb₃BiSe₃, and Cs₃BiSe₃, respectively. The Na₃AsS₃ structure type is a derivative of the Th₃P₄ structure type.     

Syntheses,Crystal Structures,and Properties of New Ternary Chalcogenides of Group 4 Metals: Rb4Ti3S14, Cs4Zr3S14, K4Hf3Se14, and K4ZrHf2Se14

The new ternary compounds Rb₄Ti₃S₁₄, Cs₄Zr₃S₁₄, K₄Hf₃Se₁₄, and K₄ZrHf₂Se₁₄ were prepared by reacting the respective transition metals in alkali metal polychalcogenide melts. Two crystallographically independent transition metal cations are present that are coordinated by eight chalcogen atoms (Q) in an irregular fashion or by seven chalcogen atoms yielding a distorted pentagonal bipyramid. The M(1)Q₈ and M(2)Q₇ polyhedra are connected by sharing common edges or trigonal faces leading to the formation of infinite linear one‐dimensional anionic chains running parallel to the [101] direction. The chains are separated by alkali metal cations. The optical band gaps determined are 1.59 eV for Rb₄Ti₃S₁₄, 2.35 eV for Cs₄Zr₃S₁₄, and 2.02 eV for K₄Hf₃Se₁₄. In‐situ X‐ray powder diffractometry demonstrates that Rb₄Ti₃S₁₄ decomposes at 430 °C into Rb₂S₅ and TiS. During the cooling cycle the re‐formation of the polysulfide is observed. According to this result the polysulfide could be prepared using TiS instead of metallic Ti as well.     

Solid solutions between β-Ca3(PO4)2 and sodium-containing whitlockite

Mixtures of CaHPO₄, CaCO₃, and Na₂CO₃ were heated at 870°C under steam or under dry CO₂ until phase composition and weight were constant. According to chemical analysis and X-ray diffractometry the stability field of the β-Ca₃(PO₄)₂ phase is limited by the molar P/Ca ratio of 0.664 ± 0.003 and 0.675 ± 0.010 irrespective of the partial water vapour pressure. A continuous series of solid solutions was found between β-Ca₃(PO₄)₂ and a new whitlockite with the composition Ca₁₀Na(PO₄)₇. The IR spectrum of these solid solutions shows that the point symmetry of the PO₄ groups and their environment increases with increasing sodium content. This is in agreement with data published about the structure of β-Ca₃(PO₄)₂ and whitlockite. The composition of these solid solutions suggests that Na⁺ ions can replace H⁺ ions in the whitlockite structure. Carbonate and pyrophosphate ions are not incorporated in these whitlockites.     

Darstellung und Kristallstruktur der Dialkalimetalltrichalkogenide Rb2S3, Rb2Se3, Cs2S3 und Cs2Se3

Preparation and Crystal Structure of the Dialkali Metal Trichalcogenides Rb₂S₃, Rb₂Se₃, Cs₂S₃, and Cs₂Se₃ Crystalline products were obtained by the reaction of the pure alkali metals with the chalcogens in the molar ratio 2:3 in liquid ammonia at pressures up to 3000 bar and temperatures around 600 K. The substances crystallize in the K₂S₃ type structure (space group Cmc2₁(NO. 36)). Unit cell constants see ?Inhaltsübersicht”?. The characteristic feature of this structure are bent polyanions X₃^2?:(X = S,Se). The new described compounds are compared with the other known alkali metal trichalcogenides.     

Crystal structure and proton conductivity of a new Cs3(H2PO4)(HPO4)·2H2O phase in the caesium di‐ and monohydrogen orthophosphate system

The M_x H_y (A O₄)_z acid salts (M = Cs, Rb, K, Na, Li, NH₄; A = S, Se, As, P) exhibit ferroelectric properties. The solid acids have low conductivity values and are of interest with regard to their thermal properties and proton conductivity. The crystal structure of caesium dihydrogen orthophosphate monohydrogen orthophosphate dihydrate, Cs₃(H_1.5PO₄)₂·2H₂O, has been solved. The compound crystallizes in the space group Pbca and forms a structure with strong hydrogen bonds connecting phosphate tetrahedra that agrees well with the IR spectra. The dehydration of Cs₃(H_1.5PO₄)₂·2H₂O with the loss of two water molecules occurs at 348–433 K. Anhydrous Cs₃(H_1.5PO₄)₂ is stable up to 548 K and is then converted completely into caesium pyrophosphate (Cs₄P₂O₇) and CsPO₃. Anhydrous Cs₃(H_1.5PO₄)₂ crystallizes in the monoclinic C 2 space group, with the unit‐cell parameters a = 11.1693 (4), b = 6.4682 (2), c = 7.7442 (3) Å and β = 71.822 (2)°. The conductivities of both compounds have been measured. In contrast to crystal hydrate Cs₃(H_1.5PO₄)₂·2H₂O, the dehydrated form has rather low conductivity values of ∼6 × 10⁻⁶–10⁻⁸ S cm⁻¹ at 373–493 K, with an activation energy of 0.91 eV.     

Zur Kenntnis der Dialkalimetalldichalkogenide β-Na2S2, K2S2, α-Rb2S2, β-Rb2S2, K2Se2, Rb2Se2, α-K2Te2, β-K2Te2 und Rb2Te2

On Dialkali Metal Dichalcogenides β-Na₂S₂, K₂S₂, α-Rb₂S₂, β-Rb₂S₂, K₂Se₂, Rb₂Se₂, α-K₂Te₂, β-K₂Te₂ and Rb₂Te₂ The first presentation of pure samples of α- and β-Rb₂S₂, α- and β-K₂Te₂, and Rb₂Te₂ is described. Using single crystals of K₂S₂ and K₂Se₂, received by ammonothermal synthesis, the structure of the Na₂O₂ type and by using single crystals of β-Na₂S₂ and β-K₂Te₂ the Li₂O₂ type structure will be refined. By combined investigations with temperature-dependent Guinier-, neutron diffraction-, thermal analysis, and Raman-spectroscopy the nature of the monotropic phase transition from the Na₂O₂ type to the Li₂O₂ type will be explained by means of the examples α-/β-Na₂S₂ and α-/β-K₂Te₂. A further case of dimorphic condition as well as the monotropic phase transition of α- and β-Rb₂S₂ is presented. The existing areas of the structure fields of the dialkali metal dichalcogenides are limited by the model of the polar covalence.