The reaction of aluminum fluoride solution with cryolite

The title reaction was investigated kinetically and the products obtained were analyzed and examined by physicochemical methods. The reaction was found to result in the formation of NaAlF₄.H₂O and its solid solutions with aluminum fluoride with compositions down to Na_0.5AlF_3.5.1.3H₂O, except in the presence of chiolite seed crystals, which cause the reaction to give it as the final product.It was suggested that the solid solution are brought about by coprecipitation of approximately monohydrated hexagonal ° -AlF₃ direct from solution, both compounds being presumably isostructural each other.Differences in the infrared spectra of Na₂AlF₆, Na₅Al₃F₁₄ and NaAlF₄.H₂O were indicated.Homogenous mixtures of Na₃AlF₆ and NaAlF₄.H₂O are found to react exothermally at 350°C to give Na₅Al₃F₁₄, while NaAlF₄.H₂O alone decomposes into Na₅Al₃F₁₄ and AlF₃.     

Calorimetric Investigations of Some Phases in the System Sodium Fluoride - Aluminium Fluoride

Beside the two well-known minerals cryolite, Na₃AlF₆, and chiolite, Na₅Al₃F₁₄, the binary system NaF-AlF₃ also contains a third compound, NaAlF₄, sodium tetrafluoroaluminate. Solid NaAlF₄ has been prepared from its vapour under controlled conditions. The stability of NaAlF₄ has been investigated by differential scanning calorimetry. It is shown that the disproportionation of the compound: 5NaAlF_4(s)=Na₅Al₃F_14(s)+2AlF_3(s) takes place at considerable rate between 700 and 900 K. The enthalpy of this reaction is calculated and found to be -66.9 kJ. Enthalpies of the two solid state transitions α-Na₃AlF₆ → β-Na₃AlF₆ and α-AlF₃ → β-AlF₃ have also been measured and new values are reported. The enthalpy of formation of chiolite, Na₅Al₃F₁₄, at 900 K has been recalculated from enthalpy increment data obtained by drop calorimetry. A value of ΔH₉₀₀ ^o = -7513.6±12.0 kJ mol^-1 has been obtained. This value is in disagreement with the recommended value given in JANAF Thermochemical Tables given at 900 K ΔH_f ^o = -7559.2 kJ mol^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chemistry of the CARBOFTOREX process. Identification of the absorption bands of the ligands in the electronic spectra of aqueous solutions of U(VI) fluoride carbonate complexes

The electronic absorption bands of U(VI) fluoride carbonate and fluoride hydroxide complexes were assigned taking account of dissociation, hydration, association, and ligand exchange. The absorption in the range of 190–400 nm was found to be related to the formation of neutral and dissociated anionic U(VI) fluoride carbonate and fluoride hydroxide complexes and the polynuclear Na_2n [(UO₂–O–UO₂)F₄(OH)_2n–1 ? kH₂O] complex.     

High temperature crystallization of aluminum fluoride. Course,hydrolysis, solid phases.

A study for AlF₃ crystallization from water solution was performed in the temperature range 100 to 200°C.Four solid phases were found to be precipitated, AlF₃.3H₂O (up to ca.120°C, cubic α-AlF₃.H₂O (decomposition of AlF₃.3H₂O in suspension), hexagonal β -AlF₃.H₂O (direct from solution) and the hydroxyfluoride Al(OH,F)₃.H₂O with an F/Al ratio of ca. 2.5 (hydrolysis of AlF₃). The extent of hydrolysis was established as a function of the initial AlF₃ concentration.X-ray diffraction and thermogravimetric data for the monohydrates were given and differences between the two indicated.     

Mechanism of fluoride loss from fluoropolytungstates possessing the keggin structure

The fluoropolytungstates [H₂W₁₂F₂O₃₈]^4? and [HW₁₂F₃O₃₇]^4?, which are of the metatungstate type with the fluoride ions occupying inner sites, lose fluoride ion and form more higly charged species [H₂W₁₂FO₃₉]^5? and [HW₁₂F₂O₃₈]^5? in aqueous solution about pH 3 in media of suitable ionic strength. Kinetic results are presented here consistent with a mechanism involving less condensed species containing 11 tungsten and 1, 2 or 3 fluoride atoms. Involvement of such species is supported by the isolation of the aluminotungstates [HW₁₁AlF₃O₃₆(H₂O)] (TMA)₅², 30H₂O and [H₂W₁₁AlF₂O₃₇(H₂O)](TMA)₅, 17H₂O.     

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.     

The missing hydrate AlF3·6H2O [Al(H2O)6]F3: Ionothermal synthesis,crystal structure and characterization of aluminum fluoride hexahydrate

AlF₃ is a strong Lewis acid and several hydrates of it are known, namely the monohydrate, the trihydrate (of which two polymorphs have been described) and the nonohydrate, which forms in the abundance of water, as well as a more complex fluoride of composition Al_0.82□_0.18F_2.46(H₂O)_0.54 whose structure has been related to the ReO₃ type. The monohydrate features edge connected [AlF₆] octahedra, in the tri- and nonahydrate mixed F/O coordination of aluminum is observed. Here we report on a new aluminium fluoride hydrate, AlF₃·6H₂O, which could be obtained via ionothermal synthesis in the ionic liquid n-hexyl-pyridinium tetrafluoroborate. The ionic liquid serves in the synthesis of AlF₃·6H₂O as the reaction partner (fluoride source) and solvent. Overmore it controls the water activity allowing access to the missing AlF₃·6H₂O. Single-crystal X-ray diffraction analysis of AlF₃·6H₂O shows that it crystallizes in the anti-Li₃Bi-type of structure according to F₃[Al(H₂O)₆] (Fm-3m, a = 893.1(2) pm, Z = 4) featuring hexaaqua aluminium(III) cations and isolated fluoride anions. The compound was further characterized by powder X-ray diffraction, TG/DTA, IR analyses.     

The hydrothermal decomposition of aluminum fluoride trihydrate. Kinetics and mechanism

The hydrothermal decomposition of AlF₃.3H₂O in water suspension was investigated by chemical and X-ray analyses at temperatures ranging from 114 to ca. 143°C. It was found that this process runs from a trihydrate to a monohydrate composition according to a zero order rate equation to give subsequently Al(OH,F)₃.H₂O and β -AlF₃.H₂O direct from solution and α -AlF₃.H₂O by conversion of solid trihydrate. Reactions involved in the process are discussed in detail.     

NaAlF4: Preparation, crystal structure and thermal stability

The compound NaAlF₄ has been obtained in the form of thin fibrous crystals or fine colorless powder by condensation at 18 °C of vapors arising over chiolite Na₅Al₃F₁₄ or NaCaAlF₆, heated up to 800 °C. Thermal stability has been investigated by the methods of thermal analysis and high temperature X-ray diffraction. When heated in air, NaAlF₄ is stable up to 390-400 °C, then there is an exothermal solid state decay into Na₅Al₃F₁₄(s) and AlF₃(s). At higher temperature Na₅Al₃F₁₄(s) decays into Na₃AlF₆(s) and NaAlF₄(g). The crystal structure (space group Cmcm, a=3.6124(1) Å, b=14.9469(7) Å, c=5.2617(3) Å, V=284.10 Å³) has been determined by X-ray powder diffraction method. In the crystal structure of NaAlF₄ the octahedrons [AlF₆] are joined through vertices and form corrugated layers, sodium ion layers being located between them. The distances between the atoms of Al-F are in the range 1.791-1.814 Å, and those for Na…F are in the range 2.297-2.439 Å. In spite of limited thermal stability of the crystal form, the compound NaAlF₄ is the main component of the gas mixture over solid and molten salts in the ternary system NaF-AlF₃-CaF₂ and participates in chemical transformations between the phases at high temperature.     

The fluorination of methane and related compounds by copper(II) fluoride and other metal fluorides

Methane reacted with MnF₃ between 350-650°C affording hydrogen fluoride, MnF₂, the fluoromethanes CH₃F, CH₂F₂, CHF₃ and CF₄ and a complex mixture of less volatile fluorocarbons.Methane reacted with FeF₃ between 650-950°C giving the fluoromethenes CH₃F, CH₂F₂ and CHF₃, C₂H₄ and carbon, as well as hydrogen fluoride and FeF₂.A more detailed study of the CuF₂-CH₄ reaction between 600-850°C showed that copper metal, hydrogen fluoride and CH₃F were always obtained, other products including CH₂F₂, CHF₃, CF₄, C₂H₄, C₂H₆, C₂F₆ and carbon. Yields of the fluoromethanes were enhanced by using relatively large amount of CuF₂ and by adding CaF₂ as an inert support. A nearly constant reaction rate occurred at a fixed temperature. Dilution of methane with nitrogen decreased yields of carbon and CH₃F but increased yields of C₂H₄ and C₂H₆.A brief study of the reactions with CuF₂ and some of the CH₄-CuF₂ reaction products was also made. Ethane and ethene both afforded traces of trifluoromethane and relatively large yields of carbon and hydrogen fluoride. That the fluorination of methane to tetrafluoromethane could take place sequentially was demonstrated by reactions with CH₃F, CH₂F₂ and CHF₃. Some pyrolysis of CH₂F₂ and CHF₃ also occurred under the chosen reaction conditions.The CH₄-CuF₂ reaction was made part of a cyclic process in which generation of the CuF₂ in situ from copper metal by successive reaction with oxygen at 400°C and hydrogen fluoride at temperatures rising to 600°C was followed by reaction with methane; 68% coversion to fluorinated products occurred. The cycle was completed by re-conversion of the copper metal residue back to CuF₂ and further reaction with methane when almost identical yields of fluorocarbons and hydrogen fluoride were obtained.     

Thermal transformation of quaternary compounds in NaF–CaF2–AlF3 system

Details of quaternary compounds formation in the system NaF–CaF₂–AlF₃ are specified. To achieve this aim, the samples of phases NaCaAlF₆ and Na₂Ca₃Al₂F₁₄ have been obtained by high-temperature solid-phase synthesis. Their thermal behavior when heated up to 800 °C has been studied using the methods of high-temperature X-ray diffraction (XRD) and thermal analysis (TA). The system under consideration can be regarded as a quasibinary section CaF₂–NaAlF₄, where at T=745–750 °C invariant equilibrium is implemented with the phases CaF₂–NaCaAlF₆–Na₂Ca₃Al₂F₁₄–(liquid melt)–(NaAlF₄). The peculiarity of the equilibrium is NaAlF₄ metastability at normal pressure. Below the equilibrium temperature the quaternary phase Na₂Ca₃Al₂F₁₄ is stable and NaCaAlF₆ above this temperature. The phase NaCaAlF₆ fixed by rapid quenching from high temperatures and when heated up to 640 °C decomposes, yielding Na₂Ca₃Al₂F₁₄. Further heating in vacuum at temperature up to 740 °C results in decomposition of Na₂Ca₃Al₂F₁₄ into CaF₂ and Na₃AlF₆. The expected reverse transformation of Na₂Ca₃Al₂F₁₄ into NaCaAlF₆ has not been observed under experimental conditions. Transformations in bulk samples reveal direct and reverse transformation of quaternary phases.

Synopsis

Thermal transformation of the quaternary compounds in system (NaF–CaF₂–AlF₃) was investigated using high-temperature X-ray diffraction (XRD) and thermal analysis (TA). In the system the invariant equilibrium is implemented with the phases CaF₂–NaCaAlF₆–Na₂Ca₃Al₂F₁₄–(liquid melt)–(NaAlF₄) at T=745–750 °C.     

Controlling Complexation Behavior of Early Lanthanides via the Subtle Interplay of their Lewis Acidity with the Chemical Stability of 5,5'-(Azobis)tetrazolide

Two novel nitrogen-rich lanthanide compounds of 5,5'-(azo bis)tetrazolide (ZT) were synthesized and structurally characterized. The dinuclear, isostructural compounds [Ce₂(ZT)₂CO₃(H₂O)₁₂] · 4 H₂O ( 1 ) and [Pr₂(ZT)₂CO₃(H₂O)₁₂] · 4H₂O ( 2 ) were synthesized via two independent routes. Compound 1 was obtained after partial Lewis acidic decomposition of ZT by Ce^IV in aqueous solution of (NH₄)₂Ce(NO₃)₆ and Na₂ZT. Compound 2 was obtained by crystallization from aqueous solutions of Pr(NO₃)₃, Na₂ZT, and Na₂CO₃. By X-ray diffraction analysis at 200 K, it was found that the trivalent lanthanide cations are bridged by a bidentate carbonato ligand and each cation is further coordinated by six H₂O ligands and one ZT ligand thus being ninefold coordinated.     

Synthese,Kristallstruktur und Eigenschaften von Tetranatrium‐bis(trimetaphosphimato)cuprat(II)‐Decahydrat,Na4{Cu[(PO2NH)3]2} · 10 H2O

Synthesis, Crystal Structure, and Properties of Tetrasodium Bis(trimetaphosphimato)cuprate(II) Decahydrate, Na₄{Cu[(PO₂NH)₃]₂} · 10 H₂O Tetrasodium bis(trimetaphosphimato)cuprate(II) decahydrate, Na₄{Cu[(PO₂NH)₃]₂} · 10 H₂O, was obtained by the reaction of an aqueous solution of Na₃(PO₂NH)₃ · 4 H₂O with Cu(NO₃)₂ · 3 H₂O (molar ratio 2 : 1). The structure of Na₄{Cu[(PO₂NH)₃]₂} · 10 H₂O ( 1 ) was solved by single‐crystal X‐ray methods (P 1, a = 912.51(6), b = 932.14(6), c = 966.10(6) pm, α = 94.840(5), β = 108.652(6), γ = 118.588(6)°, Z = 1). The P₃N₃ rings of the trimetaphosphimate ions exhibit a slightly distorted sofa conformation. The conformation of the anions have been analysed using torsion angles, displacement asymmetry parameters, and puckering parameters. The trimetaphosphimate ions act as bidentate ligands of Cu²⁺. With additionally coordinated water molecules, anionic complexes {Cu[(PO₂NH)₃]₂ · 2 H₂O}^4– are formed. In the crystal these complexes are interconnected by N–H…O und O–H…O hydrogen bonds and they coordinate the Na⁺. Thus, a three‐dimensional network is formed.     

Li＋, Na＋//SO42－, CO32－-H2O交互四元体系288 K介稳相平衡研究

采用等温蒸发法研究了四元体系Li^＋, Na^＋// SO₄^2－, CO₃^2－-H₂O 288 K介稳相平衡及平衡液相的密度、电导率、折光率、粘度和pH值, 测定了该四元体系288 K条件下介稳平衡溶液溶解度及物化性质. 根据实验数据绘制了相应的介稳相图. 研究发现: 该体系介稳平衡中有复盐Na₃Li(SO₄)₂•6H₂O形成. 其介稳相图中有3个共饱点, 7条单变量曲线, 平衡固相为: Li₂SO₄•H₂O, Na₂SO₄, Na₃Li(SO₄)₂•6H₂O, Li₂CO₃, Na₂CO₃•10H₂O. 复盐Na₃Li(SO₄)₂•6H₂O和一水硫酸锂(Li₂SO₄•H₂O)的结晶区较小, 而Li₂CO₃的结晶区最大; 该四元体系介稳平衡条件下未发现Na₂SO₄•10H₂O的结晶区.     

Benzylation of cellulose in the solvent dimethylsulfoxide/tetrabutylammonium fluoride trihydrate

The cellulose solvent dimethylsulfoxide/tetrabutylammonium fluoride trihydrate (TBAF·3 H₂O) was studied as reaction medium for the synthesis of benzyl cellulose (BC) by treating the dissolved polymer with benzyl chloride in the presence of solid NaOH or aqueous NaOH solution. BC samples with degree of substitution (DS) between 0.40 and 2.85 were accessible applying different molar ratios. The studies show that both the TBAF·3 H₂O concentration and the molar ratio of the reagents to repeating unit influence the DS. The solubility of the BC synthesized in a different way, however, of comparable DS is different. Structural analyses were carried out by means of FTIR-, ¹H- and ¹³C NMR spectroscopy. SEC measurements revealed polymer aggregation in samples of low DS synthesized in a solvent containing 9.0% TBAF·3 H₂O. At higher concentration of TBAF·3 H₂O in the solvent, the BC samples obtained do not form aggregates. BC of high DS is crystalline and shows thermotropic liquid crystalline behavior as analyzed by means of DSC. Melting point and degradation temperature are not related to the DS.     

Poly(propylene imine) dendrimer complexes as catalysts for oxidation of alkenes

Complexes of poly(propylene imine) dendrimers D8[DAB-dendr-(NH₂)₈] and D32 [DAB-dendr-(NH₂)₃₂] were prepared by interaction of the dendrimers with transition metal salts such as FeCl₃.6H₂O; CoCl₂.6H₂O; CuCl₂.2H₂O; VOSO₄.5H₂O; Na₂MoO₄.2H₂O and Na₂WO₄.2H₂O at room temperature in aqueous solutions. The content of metal ions in the complexes was found to be from 8.2 to 69.6 mg metal ion/g polymer carrier. The complexes were characterized by using IR, UV-VIS, Moessbauer spectroscopy and EPR. The anticipated co-ordination structure of the compounds was suggested. It was found that the order of the catalytic activity of the complexes of poly(propylene imine) dendrimers D8 and D32 in the reaction of epoxidation of cyclohexene with organic hydroperoxides such as tert-butyl hydroperoxide (t-BHP), ethylbenzene hydroperoxide (EBHP) and cumene hydroperoxide (CHP) was as follows: D32-MoО₂²⁺>D32-VО²⁺>D32-WО₂²⁺ > D32-Co²⁺ > D32-Cu²⁺>D32-Fe³⁺. The order of reactivity of organic hydroperoxides in the reaction studied was: t-BHP > EBHP > CHP.     

Phase formation in the ZrO(NO3)2-NaF(HF)-H3PO4-H2O system at 20°C

Phase formation in the ZrO(NO₃)₂-NaF(HF)-H₃PO₄-H₂O system was studied at 20°C and 2.0–14.5 wt % ZrO₂ in the initial solution along sections with molar ratios PO ₄ ^3? /Zr = 0.5 and 1.5 and also in the presence of hydrogen fluoride at Na/Zr = 1 and PO ₄ ^3? /Zr = 0.5, 1.0, and 1.5. Crystalline zirconium hydrophosphate Zr(HPO₄)₂ · H₂O, fluorozirconates Na₅Zr₂F₁₃ and Na₇Zr₆F₃₁ · 12H₂O, fluorophosphatozirconates NaH₂Zr₃F₃(PO₄)₄ · 3H₂O and NaZr₂F₆(PO₄) · 4H₂O, and amorphous NaZrO_0.5F(PO₄) · 4H₂O (provisional composition) were separated at room temperature. NaH₂Zr₃F₃(PO₄)₄ · 3H₂O and NaZr₂F₆(PO₄) · 4H₂O were prepared for the first time and were studied by crystal-optical, elemental, and thermal analyses, X-ray powder diffraction, IR spectroscopy, scanning electron microscopy (SEM), and X-ray microanalysis. Na₇Hf₆F₃₁ · 12H₂O was found to exist in a mixture with the hydrophosphate.     

A study of the thermodynamic properties and dehydration reaction kinetics of some salt-hydrates

Correlations were determined between heat capacity and temperature and phase change enthalpy of Ba(OH)₂·8H₂O. The phase diagram and DSC curve of the binary system Na₂CO₃·10H₂O?Na₂HPO₄·12H₂O were determined The kinetics of the dehydrating reaction of Ba(OH)₂·8H₂O, Na₂CO₃·10H₂O and Na₂HPO₄·12H₂O were measured and theoretically analyzed by TG.     

Unusual hydrogen bonding in L‐cysteine hydrogen fluoride

L‐Cysteine hydrogen fluoride, or bis(L‐cysteinium) difluoride–L‐cysteine–hydrogen fluoride (1/1/1), 2C₃H₈NO₂S⁺·2F⁻·C₃H₇NO₂S·HF or L‐Cys⁺(L‐Cys...L‐Cys⁺)F⁻(F⁻...H—F), provides the first example of a structure with cations of the `triglycine sulfate' type, i.e.A⁺(A...A⁺) (where A and A⁺ are the zwitterionic and cationic states of an amino acid, respectively), without a doubly charged counter‐ion. The salt crystallizes in the monoclinic system with the space group P2₁. The dimeric (L‐Cys...L‐Cys⁺) cation and the dimeric (F⁻...H—F) anion are formed via strong O—H...O or F—H...F hydrogen bonds, respectively, with very short O...O [2.4438 (19) Å] and F...F distances [2.2676 (17) Å]. The F...F distance is significantly shorter than in solid hydrogen fluoride. Additionally, there is another very short hydrogen bond, of O—H...F type, formed by a L‐cysteinium cation and a fluoride ion. The corresponding O...F distance of 2.3412 (19) Å seems to be the shortest among O—H...F and F—H...O hydrogen bonds known to date. The single‐crystal X‐ray diffraction study was complemented by IR spectroscopy. Of special interest was the spectral region of vibrations related to the above‐mentioned hydrogen bonds.