K6[Mn2O6] und K6[Fe2 O6] - ein Vergleich

K₆[Mn₂O₆] and K₆[Fe₂O₆] - a Comparison K₆[Mn₂O₆] has been prepared (dark-red single crystals). The structure (a = 8.88₆, b = 6.76₀, c = 11.39₄ Å, γ = 132.1°, space group P2₁, Z = 2, 1151 symmetry independent reflections hk0–hk9, R = 0.051) shows Al₂Cl₆-like anions [Mn₂O₆]^6?. By unit-cell transformation to the monoclinic setting P2₁/a (a = 6.76₀, b = 11.39₄, c = 6.63₈ Å, β = 96,9°) the structural similarity to K₆[Fe₂O₆] becomes evident. The Madelung Part of Lattice Energy, MAPLE, is calculated.     

Die KristallStrukturen von K6[Ge2Te6] und K6[Sn2Te6] und ihre kristall-chemische Beziehung zum K6[Si2Te6]-Typ

Crystal Structures of K₆[Ge₂Te₆] and K₆[Sn₂Te₆] and their Relations to the K₆[Si₂Te₆] Type K₆[Ge₂Te₆] and K₆[Sn₂Te₆], the first members of the families of telluro-digermanates and telluro-distannates have been prepared and their structures determined. The space group is C 2/c with cell constants a = 16.010(8), b = 13.619(8), c = 9.713(5) Å, β = 95.19(5)° and Z = 4 for the Ge compound. The Sn compound has space group P 2₁/c, a = 9.590(5), b = 13.654(8), c = 9.606(5) Å, β = 116.84(5) and Z = 2. The structures were established by direct methods, using four-circle diffractometer data. The final R value for 828 (1677) independent reflexions is 0.068 (0.047) for the Ge (Sn) compound. Both structures have discrete X₂Te₆ groups (X = Ge, Sn) in staggered conformation connected by K atoms in distorted octahedral or trigonal prismatic environments and bear direct subgroup relationships to that of K₆[Si₂Te₆]. The average X? Te distance is 2.579 (2.724) Å and the X? X distance 2.492 (2.814) Å.     

Die Systeme K2NaAlF6/Na2SO4 und K2NaAlF6/K2SO4 Phasendiagramme und Alkaliionenleitung

On the Systems K₂NaAlF₆/Na₂SO₄ and K₂NaAlF₆/K₂SO₄: Phase Diagrams and Alkali Ion Conductivity The phase diagrams of the K₂NaAlF₆/Na₂SO₄ and K₂NaAlF₆/K₂SO₄ systems have been determined by means of thermal, x-ray powder and electrochemical methods in the solidus-liquidus and the sub-solidus region, as well. At the optimum combination of parameters, the alkaliion conductivity increased by about three orders of magnitude upon doping K₂NaAlF₆ with Na₂SO₄ and/or K₂SO₄.     

Das Mischkristallsystem K2OsCl6

The Mixed Crystal System K₂OsCl₆? K₂SnCl₆ Homogeneous mixed crystals between K₂OsCl₆ and K₂SnCl₆ have been prepared in any composition ratio by precipitation from concentrated K₂OsCl₆/K₂SnCl₆ solutions with concentrated hydrochloric acid. The lattice constants follow Vegard's rule.     

Rerefinement of K2[TiF6]

Crystals of dipotassium hexa­fluoro­titanate(IV), K₂[TiF₆], were grown from aqueous solution. The crystal structure was refined with anisotropic displacement parameters. Ti⁴⁺ is octahedrally coordinated by F^? (point group m), and K⁺ is 12‐coordinate (point group 3m). The dispersion of birefringence is presented.     

Über Thio-, Selenido- und Telluridogermanate (III): Zur Kenntnis von K6Ge2S6, K6Ge2Se6 und Na6Ge2Te6

On Thio-, Selenido-, and Telluridogermanates (III): K₆Ge₂S₆, K₆Ge₂Se₆, and Na₆Ge₂Te₆ The new compounds K₆Ge₂S₆ and K₆Ge₂Se₆ crystallize in the monoclinic system, space group C2/m (No 12); lattice constants see “Inhaltsübersicht”. The compounds are isotypic and form the K₆Si₂Te₆ structure. Na₆Ge₂Te₆ crystallizes in the K₆Sn₂Te₆ structure, monoclinic, space group P2₁/c (No 14); lattice constants see “Inhaltsübersicht”.     

Röntgenstrukturuntersuchungen an den polymorphen Elpasolithen K2LiAlF6 und Rb2LiGaF6

X-Ray Structural Studies of the Polymorphic Elpasolites K₂LiAlF₆ and Rb₂LiGaF₆ At single crystals of low (LT) and high temperature (HT) modifications of K₂LiAlF₆ and of Rb₂LiGaF₆, synthesized at normal pressure (NP), the crystal structures were refined. LT-K₂LiAlF₆ is a cubic elpasolite (Fm3m, Z = 4, a = 784.2(1) pm; Al–F: 181.2(1) pm), HT-K₂LiAlF₆ and NP-Rb₂LiGaF₆ are isostructural with the hexagonal-rhombohedral type of Cs₂NaCrF₆ (R3m, Z = 6, a = 561.7(1) resp. 586.3(1), c = 2757.6(6) resp. 2856.3(5) pm; mean values Al–F: 180.5 resp. Ga–F: 189.3 pm). A cubic high pressure modification (HP) of Rb₂LiGaF₆ was obtainable as a powder only (a = 820.8(2) pm). The relations of distances between LT/HT and HP/NP polymorphs of elpasolites are compared and discussed.     

Zur Kenntnis der Hexafluororhodate(III): Über Cs2K[RhF6], Rb2K[RhF6], K2Na[RhF6], Rb2Na[RhF6] und Tl2Na[RhF6]

On the Knowledge of Hexafluororhodates(III): Cs₂K[RhF₆], Rb₂K[RhF₆], K₂Na[RhF₆], Rb₂Na[RhF₆] and Tl₂Na[RhF₆]. New prepared are the compounds Cs₂KRhF₆ (a = 9.04₉ Å), Rb₂NaRhF₆ (a = 8.49₂ Å), Rb₂KRhF₆ (a = 8.87₆ Å), K₂NaRhF₆ (a = 8.36₂ Å) and Tl₂NaRhF₆ (a = 8.52₆ Å), all cubic Elpasoliths of pink colour. The Madelung-Part of lattice energy, MAPLE, is calculated and discussed.     

Neubestimmung der Kristallstrukturen der Hexahydroxometallate Na2Sn(OH)6, K2Sn(OH)6 und K2Pb(OH)6

Redetermination of the Crystal Structures of the Hexahydroxometallates Na₂Sn(OH)₆, K₂Sn(OH)₆, and K₂Pb(OH)₆ Slow cooling down of hot saturated hydroxo stannate‐ resp. ‐plumbate solutions gives crystals of Na₂Sn(OH)₆, K₂Sn(OH)₆, and K₂Pb(OH)₆ well suited for an X‐ray structure determination. With these crystals the so far known crystal data were verified, determined more precisely and H‐positions found for the first time. The compounds crystallize rhombohedral in the space group R 3. The hexagonal unit cells contain three formula units with Na₂Sn(OH)₆: a = 5.951(1) Å, c = 14.191(2) Å, c/a = 2.384 K₂Sn(OH)₆: a = 6.541(1) Å, c = 12.813(4) Å, c/a = 1.959 K₂Pb(OH)₆: a = 6.625(1) Å, c = 12.998(2) Å, c/a = 1.962 The compounds are not isotypic whereas the atoms occupy in all three cases the same Wyckoff positions. Na₂Sn(OH)₆ has with an hcp packing of O a CdI₂ like superstructure with Na and Sn in octahedral interstices. Hydrogen bonds O–H…O–H play a role in solid K₂Sn(OH)₆ and K₂Pb(OH)₆. In these compounds the potassium ions are shifted from an octahedral coordination in an hcp packing of O. They have nine nearest O‐neighbours. The hydrogen bonds are investigated by Raman spectroscopy.     

Darstellung und Kristallstruktur von K6[Al2O6] und Rb6[Al2O6]

Preparation of Crystal Structure of K₆[Al₂O₆] and Rb₆[Al₂O₆] Colourless single crystals of K₆[Al₂O₆] have been prepared from intimate mixtures of KAlO₂ and K₂O (550°C, 90 d). The structure determination from four-circle diffractometer data (MoKα , 742 I_o(hkl), R = 2.2%, R_w = 2.1%) confirms the space group C2/m with Z = 2; a = 698.25 pm, b = 1 103.54 pm, c = 646.49 pm, β = 102.49°. Colourless single crystals of hitherto unknown Rb₆[Al₂O₆] have been prepared from intimate mixtures of RbAlO₂ and Rb₂O (520°C, 120 d). The structure determination from four-circle diffractometer data (MoKα , 1 240 I_o(hkl)) results in the residual values R = 7.2%, R_w = 4.9%; space group C2/m; a = 725.92 pm, b = 1 143.33 pm, c = 678.06 pm, β = 104.05°; Z = 2. K₆[Al₂O₆] and Rb₆[Al₂O₆] are isostructural with K₆[Fe₂O₆]. A characteristic structure unit is the anion [Al₂O₆]^6? consisting of two edge-sharing [AlO₄] tetrahedra. Effective Coordination Numbers (ECoN), Mean Fictive Ionic Radii (MEFIR), the Madelung Part of Lattice Energy (MAPLE) and the Charge Distribution (CHARDI) are calculated and discussed.     

Das erste quinquinäre Oxoaurat(I) K6Na[IO6][AuO]2 = K6[NaIO6][AuO2/2]2 [1]

Inhaltsübersicht. Bei Versuchen zur Darstellung unbekannter Phasen im System A/Au/I/O (mit A = Alkalimetall) entstanden durch Erhitzen eines Gemenges (2,2 K₂O + 1,0 NaIO₄; Au-Rohr; 700°C, 59 d) farblose, transparente Einkristalle von K₆NaAu₂IO₈, das nach Einkristalldaten (Vierkreisdiffraktometerdaten, 2465 I_o(hkl), AgKα, R = 6,8% und R_w = 5,6%) monoklin in P2/c mit a = 707,4 pm; b = 977,3 pm; c = 1199,4 pm; β = 122,9°; Z = 2 kristallisiert. Charakteristisch sind die hier erstmals gefundenen, HgO-analogen Zickzackketten [AuO_2/2] längs [001]. Daneben prägen, den NaIO₆-Teil der Struktur betreffend, Ketten aus [IO₆]-Oktaeder, über Na in prismatischer Koordination verknüpft, den Aufbau. The First Quinquinary Oxoaurate(I). K₆Na[IO₆][AuO]₂ = K₆[NaIO₆][AuO_2/2]₂ Attempting to synthesize unknown phases in the system A/Au/I/O by heating a mixture of K₂O and NaIO₄ (K: Na = 2.2:1.0, sealed gold tube, 700°C) we obtained colourless, transparent single crystals of K₆NaAu₂IO₆, a new type of Oxoaurate(I). According to single crystal data K₆NaAu₂IO₈ crystallizes in a monoclinic form with a = 707.4 pm, b = 977.3 pm, c = 1199.4 pm β = 122.9° (Z = 2, space group P2/c). Essential part of the structure are chains NaIO₆ and zigzag chains AuO_2/2, both along [001]. The Madelung part of the lattice energy, MAPLE, and effective coordination numbers, ECoN, are calculated and discussed.     

Potassium silver tin selenide,K2Ag2Sn2Se6

The title compound was synthesized by a reactive salt reaction at 773 K over a period of 5 d. It has a one-dimensional chain structure consisting of K⁺ cations and one-dimensional [Ag₂Sn₂Se₆]²⁻ anions. The chain is constructed by edge-sharing bitetrahedral [Sn₂Se₆] units connected in a 1:2 ratio via linear Ag⁺ ions.     

A density‐functional theory approach to the separation of K2ZrF6 and K2HfF6 via fractional crystallization

Because of the low absorption cross‐section for thermal neutrons of zirconium (Zr) as opposed to hafnium (Hf), Zr‐metal must essentially be Hf‐free (<100 ppm Hf) to be suitable for use in nuclear reactors. However, Zr and Hf always occur together in nature, and due to very similar chemical and physical properties, their separation is particularly difficult. Separation can be achieved by traditional liquid–liquid extraction or extractive distillation processes, using Zr(Hf)Cl₄ as feedstock. However, the production of K₂Zr(Hf)F₆ via the plasma dissociation route, developed by the South African Nuclear Energy Corporation Limited (Necsa), could facilitate the development of an alternative separation process. In this theoretical study, the results of density‐functional theory (DFT) simulations of K₂Zr_(1‐z)Hf_zF₆ solid solutions [using Cambridge Serial Total Energy Package (CASTEP)] are presented, for which the supercell approach was applied in an attempt to determine whether solid solution formation during crystallization from aqueous solutions (fractional crystallization) is thermodynamically possible, which would hinder the separation efficiency of this method. Consequently, the calculated thermodynamic properties of mixing were used to evaluate the separation efficiency of Zr and Hf by fractional crystallization using a thermodynamic model to calculate the relative distribution coefficients. The small mixing enthalpies that were calculated from the DFT results, indicates that lattice substitution of Zr(IV) by Hf(IV) in K₂ZrF₆ could occur with relative ease. This is not surprising, considering the close similarities between Zr and Hf, and it was therefore concluded that K₂Zr_(1‐z)Hf_zF₆ solid solution formation might well restrict the separation efficiency of Zr and Hf by fractional crystallization of K₂Zr(Hf)F₆. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Über neue Verbindungen Cs2NaMF6 und K2NaMF6 sowie über Cs2KMnF6

Newly prepared are the cubic derivatives of the perovskite type of structure: K₂NaInF₆ (a = 8.56₀ Å), K₂NaTlF₆ (8.66₈), K₂NaScF₆ (8.48₂), K₂NaYF₆ (8.71₁), Cs₂NaInF₆ (8.90₅), Cs₂NaTiF₆ (8.99₅), Cs₂NaScF₆ (8.85₃), all colourless, as well as K₂NaCuF₆ (8.20₃ Å, green) and Cs₂KMnF₆ (tetragonal, a = 8.93₃; c = 9.26₅ Å, violett). K₂NaCuF₆ [μ = 2.8₇ μ_B, θ = ?17°] and Cs₂KMnF₆ [;μ = 4.8₈ μ_B, θ = ?5°] obey the Curie-Weiss law. The volume chemistry of the compounds is discussed in detail.     

Kristallstruktur und Schwingungsspektren der Caesium- und Kalium-Hexathiometadiphosphate Cs2P2S6 und K2P2S6

Crystal Structure and Vibration Spectra of Cs₂P₂S₆ and K₂P₂S₆ . Cs₂P₂S₆ and K₂P₂S₆ crystallize in the orthorhombic system, space group Immm, Z = 2 with the lattice constants . The compounds are isotypic to Tl₂P₂S₆. In the structure there are discrete P₂S₆^2? anions. Two PS₄ tetrahedra are connected by a common edge to hexathiometadiphosphate groups. The far infrared, infrared, and Raman spectra of these compounds are assigned on the basis of P₂S₆^2? units with D_2h symmetry in analogy to the isoelectronic Al₂Cl₆. The melting points are 440 ± 10°C for Cs₂P₂S₆ and 508 ± 10°C for K₂P₂S₆.     

Aquation of K2 TcBr6 in dilute acid solutions

The photochemical aquation of K₂ TcBr₆ in 2M HRr, 1M HClO₄ and 1M H₂SO₄ has been studied. The absorption spectra of the various Tc(IV) species were measured after the electrophoretic separation. The spectrophotometric changes and the yield of each species as a function of the UV irradiation time were determined. After 25 hours of irradiation of HBr and HClO₄ solutions the main species were the cationic ones (80%) but in H₂SO₄ solution the neutral species reached a yield of 90%. The oxidation of Tc(IV) species to TcO ₄ ^– proceeded more rapidly and extensively in HClO₄ than in HBr and H₂SO₄.