Alkaline earth fluorides and their complexes: A sol–gel fluorination study

Sol–gel fluorination of the divalent metal fluorides MgF₂, CaF₂ and BaF₂ and their complex fluorides K₂MgF₄, BaMgF₄, and BaAlF₅ is reported. Structural, optical and surface properties are discussed.     

Impact of Magnesium(II) on Beryllium Fluorides in Solutions Studied by 19F NMR Spectroscopy

Beryllium fluorides are widely used in protein phosphorylation studies to get stable transition state analogs or near attack conformers, which has attracted much attention. BeF₃^? is one of the optimal phosphoryl (PO₃^?) analogs for its identical geometry and charge, and Mg²⁺ naturally participates in the phosphoryl binding in biological systems. In solutions, BeF₃^? coexists with other beryllium fluorides (BeF₄^2?, BeF₂ and BeF⁺) and magnesium fluorides, and there are equilibriums between these species. In this article, ¹⁹F NMR spectroscopy was applied to the investigation of the impact of magnesium(II) on beryllium fluorides. It has been found that when Mg²⁺ was introduced into the solutions, the chemical shifts, the intensities and the line widths of ¹⁹F signals of various beryllium fluoride complexes were changed. After ionic strength correction, these effects were remarkable only for BeF₄^2? and BeF₃^?, especially BeF₄^2?, when the concentration of the fluoride ion is relatively low. Mechanism of the effects is proposed which involves ion pair formation between Mg²⁺ and beryllium fluorides.     

Les fluoronitrures de terres rares

The reaction of rare-earth nitrides with fluorides or the pyrolysis of these fluorides in gaseous ammonia atmosphere leads, in the case of lanthanum, cerium, and gadolinium, to nitride fluorides of general formula LnN_xF_3?3x. They crystallize with a fluorite-type structure which can be described in a consistent manner in terms of a Willis model. The magnetic properties of Gd₃NF₆ have been studied.     

Utilisation de methodes de trempe ultra-rapide pour une nouvelle chimie du fluor

Quick quenching preparation from the melt has been extensively used for new fluoride preparations. Some examples are given for obtaining either non crystalline solids (PbF₂AlF₃; PbF₂ZnF₂; Sb₂O₃SbOF systems) or metastable crystalline fluorides (Li₂ZnF₄; SnF_2+x; Sb(O, F)_2+x). A new quenching method called ‘reactive splat-cooling’ well adapted to fluorides is described.     

Superionic Conduction in Complex Fluorides of Antimony(III) MnSbxFy (M—Cations of an Alkali Metal, Ammonium, or Thallium, n = 1–3, and x = 1–4)

Methods of ¹⁹F NMR and impedance spectroscopy are used to investigate the internal mobility of fluoride (ammonium) ions and electrophysical characteristics of complex trivalent antimony fluorides MSb₄F₁₃, MSb₃F₁₀, MSb₂F₇, M₂Sb₃F₁₁, M₃Sb₄F₁₅, and MSbF₄ (M is an alkali cation, ammonium, thallium). The ion motion types in the cationic and anionic sublattices of the fluorides are determined at 150–500 K. The polymorphous transformations in the fluorides are usually phase transitions to a superionic state and their high ionic (superionic) conductivity (σ ≥ 10⁻⁴ to 10⁻² S cm⁻¹ at 400 K) is due to the diffusion motion of ions of fluoride, ammonium, and possibly sodium, potassium, and thallium. The high polarizability of thallium ions favors the development of high mobility of fluoride ions in the fluorides.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 560–572.Original Russian Text Copyright © 2005 by Kavun, Uvarov, Slobodyuk, Brovkina, Zemnukhova, Sergienko.     

Enhanced Lewis acidity by aliovalent cation doping in metal fluorides

A model regarding the generation of acidity in binary metal fluorides has been proposed and its validity has been examined for several binary fluoride systems with the general compositions MF₃/M′F₃ and MF₂/M′F₃. In accordance with this hypothesis, the binary systems (CrF₃/AlF₃, CrF₃/FeF₃ and AlF₃/VF₃) do not show acidities larger than the sum of the acidities of the component fluorides. The hypothesis predicts the generation of Lewis acidity when MF₂ is the major component (host) and generation of Brønsted acidity when MF₃ acts as the host for the MF₂/M′F₃. The experimental results (surface acidity and catalytic activity) confirmed the predictions made from this hypothesis for binary combinations MgF₂/ M′F₃ (M′=Cr, Al, Fe, V). The application of this model is discussed in terms of other parameters: ionic radii and the fluoride affinity of the metal fluorides involved.     

Oxygen difluoride

The preparation and chemical and physical properties of the oxygen fluorides (OF₂, OF, O₂F₂, OOF and O₄F₂) are reviewed. There has been speculation about the existence of other oxygen fluorides (O₃F₂, O₃F, OSF₂ and O₆F₂) but these have not been well-characterized. The first member, OF₂, is much more stable than the other oxygen fluorides, and is also less-reactive. In addition to acting as a fluorinating agent and oxidizer, OF₂ has been shown to be a source of the OF radical. Dioxygen difluoride is a powerful fluorinating agent, but if reacted under carefully controlled conditions, can be a source of the OOF radical.     

Mechanochemical reactions of fluorides with hemin

Hemin has two potential sites to react with fluorides, the peripheral acid groups and the central Fe^III cation. The mechanochemical reactions of hemin with fluorides (LiF, NaF, KF, CsF, NH₄F and AgF) were monitored using X-ray diffraction (XRD), and IR and Mössbauer spectroscopies. LiF and NaF were found inert when milled with hemin, however KF, CsF, NH₄F and AgF react at both hemin sites. At the iron site Cl⁻ is replaced by F⁻ with formation of KCl, CsCl, NH₄Cl, and AgCl, as detected by XRD, while with the peripheral acid groups, fluorides collect the acidic protons to form KHF₂, CsHF₂, NH₄HF and AgHF₂. The reactions of hemin with the reactive fluorides take place first at the iron site and then at the propionic acid groups.     

On the dichotomy of the SN2/ET reaction pathways: an apparent SN2 reactivity in the reaction of naphthalene dianion with alkyl fluorides

Dilithium naphthalene (Li₂C₁₀H₈) displays a S_N2 reactivity profile in its reaction with alkyl fluorides (n-, s- and t-octyl fluoride). S_N2 seems to be the dominant mechanism operating with primary alkyl fluorides, which presumably turns into competition with ET as we move to secondary and tertiary alkyl fluorides. Significantly, lithium naphthalene (LiC₁₀H₈) seems to have also an important nucleophilic component when reacting with alkyl fluorides, in contrast to the previously proposed general ET process valid for all alkyl halides. These results explain the observed distribution of products and are reinforced by a complete analysis of the products originated by the reaction with 6-halohexenyl radical probes, whose main alkylation products are described here for the first time.     

Platinum fluorides beyond PtF6?

Quantum-chemical calculations at DFT B3LYP and ab initio MP2, CCSD, and CCSD(T) levels have been performed on various binary fluorides of platinum up to formal oxidation state +VIII, to evaluate the stability of these species. The calculations indicate clearly that elimination of F₂ from PtF₈ is a strongly exothermic reaction, with a moderate activation barrier. An exothermic decay is also observed for the homolytic bond breaking. Furthermore, our investigations suggest that both decomposition channels of PtF₇ are exothermic. The existence of platinum fluorides higher than PtF₆ is therefore highly unlikely.     

A comparison of enthalpies of tetrafluoroammonium salts and other fluoro-nitrogen species

It is shown that enthalpies of nitrogen fluorides and oxo fluorides deviate markedly from enthalpies of corresponding hydroxo compounds, whereas there is good agreement (circa 2%) between carbon mono, di and trifluoro compounds and their hydroxo analogues. The extent of deviation correlates with the extra number of lone pair repulsions of fluoro over oxo compounds. The enthalpy of NF₄⁺(g) can be extrapolated from the other (N,F) and (N,O,F) compounds. The enthalpies of solid NF₄⁺ salts are close to those of corresponding NO₂⁺ salts and from this an exothermic heat of formation for NF₄⁺F^? is predicted.     

Über Bodenkörper des Systems K+/Na+/Cr3+/F−/H2O

For the use of water-soluble wood preservations based on fluorides and chromates of alkaline metals which contain potassium and sodium, the fluoride is fixed particularly well in wood because there is formed the least soluble phase of all possible fluorochromates(III) of the system, K₂Na[CrF₆]. It develops from an aqueous solution always in a grossly disordered state because ions of alkaline metals and of fluorides are partly replaced by water molecules.     

Interaction of sulphur hexafluoride with metals and oxides

The interaction of SF₆ with metals and oxides has been studied by thermal analysis techniques. It has been shown that sulphur hexafluoride is an active fluorinating agent. It reacts both with oxides at temperatures about 600–700° and with metals at about 500–600°, to produce fluorides with the former and fluorides as well as sulphides with the latter. Higher temperatures bring about transformation of metals and their sulphides into pure fluorides.Thermodynamic evaluation of possible processes taking place in the fluorination of metals and oxides has been carried out.X-Ray diffraction and chemical analyses were used to identify final products for such metals and oxides as Zn, Cd, La₂O₃, Nd₂O₃ and Pr₆O₁₁.     

The determination of fluorine in rare earth fluorides by high temperature hydrolysis

The technique of pyrohydrolysis has been applied to the determination of fluorine in the fluorides of scandium, yttrium, and the lanthanons. These fluorides have been divided into two classes according to their rate of hydrolysis. Lutetium, ytterbium, cerium(III), scandium, gadolinium, terbium, dysprosium, holmium, erbium, and thulium florides can be hydrolyzed in 30 min or less. Yttrium, lanthanum, praseodymium, neodymium, samarium, and europium fluorides require from 45 to 150 min for complete hydrolysis. Accelerators, such as uranium oxide (U₃O₈), chromium(III) oxide, and a mixture of these oxides have been used successfully to reduce the tune required for quantitative hydrolysis of the fluorides in the latter group. The use of the correct accelerator reduces the hydrolysis time to 30 min or less for all these fluorides except lanthanum, praseodymium and neodymium.     

Arenesulfonyl Fluoride Synthesis via Copper‐free Sandmeyer‐type Fluorosulfonylation of Arenediazonium Salts

The limited availability of highly valuable arenesulfonyl fluorides seriously hinders their further application in many research fields including medicinal chemistry and chemical biological, organic synthesis, polymer preparation, etc. We report herein a mild and efficient copper‐free Sandmeyer‐type fluorosulfonylation reaction of various arenediazonium salts to prepare valuable arenesulfonyl fluorides using K₂S₂O₅ as both a reductant and a practical sulfonyl source in combination with N‐fluorobenzenesulfonimide as an effective fluorine source. This methodology provides an attractive route to diverse important arenesulfonyl fluorides given the overall practicality and scope.     

The Binary System BaF2/AlF3

The system BaF₂/AlF₃ is investigated by X-ray and D.T.A., and the liquid-solid phase diagram is established. Five ternary fluorides are disclosed: trimorphic BaAlF₅, Ba₃Al₂F₁₂, Ba₅AlF₁₉, polymorphic Ba₃AlF₉ and Ba₅AlF₁₃. Neutron thermodiffractometry experiments are performed to specify some parts of the diagram. The cell parameters of the fluorides are given and the results are discussed and compared with those of the previous works.     

Contribution a l'etude des composes fluores ternaires du vanadium + II

Very few vanadium (+ II) fluorides are known and some difficulty is experienced in preparing them. In accordance with previous results, only three ternary fluorides, NaVF₃, KVF₃ and RbVF₃, may be prepared in the systems MF-VF₂, where M is an alkali element. Whatever MF/VF₂ ratio a partial or a total disproportionation of vanadium + II accurs. The structures of NaVF₃, KVF₃, and RbVF₃ have been defined. The ternary compounds of MVF₃ formulation have been compared with those of other 3d elements.     

Fast Ion Conducting Nanocrystalline Alkaline Earth Fluorides Simply Prepared by Mixing or Manual Shaking

Simple mixing or shaking of alkaline earth hydroxides with ammonium fluoride results in nanocrystalline phase pure metal fluorides MF₂ (M: Ca, Sr, Ba). The formation of the alkaline earth fluorides was investigated by varying the reaction conditions. Evidence was found that just the contact between the starting materials is sufficient for the reaction to take place. X‐ray diffraction, elemental analysis, ¹⁹F MAS NMR spectroscopy, and measurements of DC conductivities were used to characterize the fluorides regarding properties like crystal structure, crystallite sizes, local fluorine coordination, and fluorine ion conductivity. The ¹⁹F MAS NMR spectra of the phase pure fluorides prepared showed several signals, which were assigned to defects, impurities, or geometric distortions. The fluorides prepared by mixing or shaking revealed fluorine ion conductivities several orders of magnitude higher than observed for the respective microcrystalline alkaline earth fluorides. Therefore, the synthesis routine presented in this study may open a path to a very quick and simple synthesis of nanocrystalline fast fluorine ion conductors.     

Recent developments in the preparation of high surface area metal fluorides

An overview of the main procedures for the preparation of fluorides with very high surface areas is given. Three processes are outlined: (i) plasma fluorination, (ii) sol–gel route and (iii) oxidative decomposition of inorganic precursors. From all three processes nanostructured metal fluorides with 100–400 m² g⁻¹ can be obtained. Prevention of the local overheating during fluorination seems to be the key factor to obtain the high surface area fluorides. TEM investigations of AlF₃ and CrF₃ obtained by oxidative decomposition revealed considerable differences in their morphologies and crystallinity. CrF₃ is completely amorphous and unstable under beam. AlF₃ contains an amorphous phase and nanocrystalline phases of α-AlF₃ and β-AlF₃. Nanocrystals are uniformly distributed within the amorphous phase. Also present are the rod-like nanostructures that consist of β-AlF₃ and are 5–10 nm wide.     

Synthesis of Alkyl-Aryl Ethers by Copper-catalyzed Etherization Reactions of Aryl Fluorides with Tetraalkylammonium Bromides and H2O

Synthesis of alkyl aryl ethers via copper‐catalyzed etherizations of electron‐deficient aryl fluorides with quaternary ammonium bromides and water has been developed. In the presence of Cu(OAc)₂, POPh₃ ( L4 ) and Cs₂CO₃, a variety of electron‐deficient aryl fluorides underwent the reaction with quaternary ammonium bromides and H₂O in moderate to good yields. The mechanism was also discussed.