Chemical state analysis of fluorine in various compounds using X-ray fluorescence spectra

F Kα X-ray fluorescence (XRF) spectra of various fluorides were measured and to investigate the chemical state of fluorine in xHoF₃-20BaF₂-10AlF₃-(70 − x)GeO₂ (mol%, x = 10-50) glass. The main peak (Kα_1,2) position and the relative intensity of the satellite peak attributable to Kα_3,4 were discussed relating to the M-F bond covalency. Results showed that the fluorine in xHoF₃-20BaF₂-10AlF₃-(70 − x)GeO₂ (mol%, x = 10-50) glass had a completely different chemical state from that of starting materials. Quantitative analyses of the glasses were also undertaken using XRF measurements for each component. These results suggest that 30% fluorine in the 50HoF₃-20BaF₂-10AlF₃-20GeO₂ system is substituted by oxygen through pyrohydrolysis of the fluorides.     

Mechanochemical synthesis,structure, and properties of solid solutions of alkaline earth metal fluorides: Ma1−xMbxF2 (M: Ca,Sr, Ba)

The capability of mechanochemical synthesis for the formation of solid solutions of alkaline earth metal fluorides M^a_1−xM^b_xF₂ (M: Ca, Sr, Ba) was tested by fluorination of metal acetates and metal hydroxides with ammonium fluoride directly at milling. Evidence was found for a mutual substitution of cations on their lattice positions in Ca_1−xSr_xF₂ and Ba_1−xSr_xF₂ samples. For the Ba/Ca-system this synthesis route is only partially successful. X-ray diffraction and ¹⁹F MAS NMR spectroscopy were used to characterize all samples concerning their crystal structure and local fluorine coordination. Calculations of ¹⁹F chemical shifts with the superposition model along with probability calculations for the intensity of the individual ¹⁹F lines, performed in dependence on the molar composition of the samples, perfectly agree with the experimental findings. The fluoride ion conductivity of as-prepared samples, determined by temperature dependent DC conductivity measurements, is significantly higher than those of crystalline binary fluorides. Moreover, a higher F⁻ ion conductivity is observed for samples with higher mixing grade in the Ca/Sr-and the Ba/Sr-systems.     

Crystalline aluminium hydroxy fluorides—Suitable reference compounds for F chemical shift trend analysis of related amorphous solids

On the basis of MAS NMR-data for crystalline AlF_x(OH)_3−x·H₂O samples in the pyrochlore structure, ¹⁹F chemical shifts correlate with the average chemical composition of the octahedral environment, given by AlF_xO_6−x in these compounds.The attribution of local structures in sol-gel derived amorphous AlF_x(OX)_3−x·XOH (X = H, R (alkyl)) compounds is of special interest as these or consecutively prepared solids exhibit remarkable features, for example, a high surface (HS) area accompanied by a high Lewis acidity.By transferring this scale of a ¹⁹F chemical shift trend analysis to such compounds a prediction of the chemical nature of the average Al coordination becomes possible.A new synthetic approach to crystalline aluminium hydroxy fluorides involving a sol gel fluorination as the first reaction step and an aluminium alkoxide as precursor compound is presented. Varying the amount of HF leads to different F-OH-ratios in the AlF_x(OH)_3−x compounds.     

Hydrurofluorures ioniques MF2−xHx (M = Sr,Ba): Synthèse et étude structurale par diffraction des neutrons

The study of the substitution of H^? for F^? ions in SrF₂ and BaF₂ has shown the existence of the cubic hydride fluorides MF_2?xH_x (M = Sr, Ba). The variation of the lattice parameter with hydrogen replacement is stronger than it is in the case of CaF_2?xH_x. The upper limit of substitution diminishes for the series calcium, strontium, barium. Neutron diffraction confirms the simple structural model, already proposed for calcium hydride fluoride: a fluorine cubic structure with a statistical distribution of H^? and F^? on 8(c) sites.     

The theoretical study for the perovskite-type manganese fluorides of KMnF3, RbMnF3 and K1−xLixMnF3

We performed the hybrid-density functional theory (DFT) calculations for the strongly correlated perovskite-type manganese fluorides of KMnF₃, RbMnF₃ and K_1?xLi_xMnF₃ In both solids, UBHHLYP, which contains 50% Hartree–Fock exchange term, provided the reasonable effective exchange integral (J_ab) values, in comparison with the experimental ones. In order to investigate the intrinsic roles of counter cations precisely, we examined the variations of the total energy and J_ab value, assuming the displacement of counter cation toward <1 0 0> direction. In KMnF₃ (RbMnF₃), it was found that the steric repulsion between potassium (rubidium) and bottleneck is large, while that between lithium and bottleneck is negligible in K_1?xLi_xMnF₃. Finally, we also showed the possibility of the lithium ion conduction in the antiferromagnetic K_1?xLi_xMnF₃. It was concluded that the lithium ion conduction in RMnF₃ is possible, if the vacancy at R site exists.     

Optimisation des facteurs influencant la conductivité anionique dans quelques fluorures de structure fluorine

The large influence in the M_1?xM′_xF_2+x solid solutions (M = Sr, Pb, M′ = Y, In, Sb, Bi) of the covalency of the MF₂ “starting lattice” on the electrical properties of fluorides of fluorite-type structure is clearly shown in a comparative investigation. The influence of the polarizability of the substituting trivalent ion is only significant as far as the starting lattice contains a weakly polarizable cation. Enhancement of the electrical performances of β-PbF₂ by substitution of Pb²⁺ by trivalent cations seems to be due mainly to increasing disordering within the anionic sublattice and hence the role of cationic polarizability is apparently a second-order effect.     

Hydrolysis of ZrF 6 2− anions in solutions of copper(II) ammine and synthesis of Cu x Zr(OH) y F z nanolayers by the ionic layering method

The possibility to synthesize M_1x M₂(OH) _y F _z nanolayers by the ionic layering method with the use of soluble anionic complexes of metal fluorides was demonstrated. The influence of the concentration and pH of reagent solutions and of the number of ionic layering cycles on the kinetics of layer growth was studied using the example of Cu _x Zr(OH) _y F _z layers. The composition of the synthesized layers was studied by X-ray photoelectron (XPE) spectroscopy, ellipsometry, and electronic and Fourier transform IR (FT-IR) transmission spectroscopy.     

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.     

Etude par effet Mössbauer des composés de type “bronzes fluorés” MxFeF3 (M = K,Rb, Cs,NH4)

The hexagonal, tetragonal and pyrochlore-type nonstoichiometric iron fluorides M_xFeF₃ (M = K, Rb, Cs, NH₄) have been studied by Mössbauer spectroscopy over the temperature range 4.2 to 295 K. The magnetic transition temperatures have been determined. The ferrous and ferric ions remain in discrete oxidation states indicating the absence of charge hopping. The broadened lines of the spectra of the hexagonal and tetragonal phases are consistent with the disordering of Fe²⁺ and Fe³⁺ in the structure. By contrast, the narrow linewidths of the spectra of the pyrochlore-type phases characterize a structural ordering between the ferrous and ferric ions.     

Phase relation studies in Pb1−xM′xF2+x systems (0.0⩽x⩽1.0; M′=Nd3+, Eu3+ and Er3+)

In this communication we report the synthesis and characterization of a series of compounds with the general composition Pb_1−xM′_xF_2+x, (0.0⩽x⩽1.0; M′=Nd³⁺, Eu³⁺ and Er³⁺) to elucidate the detailed phase relations between PbF₂ and M′F₃. These three rare-earth fluorides were selected so as to delineate the effect of ionic size on the phase relations. In all the three systems, fluorite-type solid solutions are formed at the PbF₂ rich end. The solid solubility limits of NdF₃, EuF₃ and ErF₃ in the PbF₂ lattice, as observed from this study, are 30, 25 and 15 mol%, respectively. In PbF₂–NdF₃ system, beyond the fluorite-type solid solutions, NdF₃ phase is observed. However, in both PbF₂–EuF₃ and PbF₂–ErF₃ systems, certain fluorite related ordered phases, namely, a rhombohedral phase with about 40 mol% of EuF₃ or ErF₃ in PbF₂, and a tetragonal phase with 45–50 mol% of ErF₃ in PbF₂, are observed. In all the three systems, no solubility of the PbF₂ in the hexagonal or orthorhombic rare-earth fluoride lattice is observed. This is the first report on phase relation in these three systems under short annealed and slow cooled condition.     

Self-diffusion coefficient measurements at high temperature by PFG NMR

We have developed a new experimental setup for the measurement of self-diffusion coefficients at high temperature (up to 1500 K) in corrosive liquids. It is based on pulsed field gradient NMR using a 10 mm liquid probe with two channels F-H/X modified and coupled with laser heating. The values obtained thanks to this setup are in good agreement with the available data obtained using the reference method, i.e., the capillary method. We present here results on ¹⁹F, ⁷Li, ²³Na, ²⁷Al in molten fluorides. In alkali fluoride mixtures, the self-diffusion coefficients depend weakly on the composition (nature and concentration of the different alkali) but mainly on temperature. In cryolite (Na₃AlF₆), the diffusion evidences AlF_x^3 ? x species.     

Boron trifluoride-catalyzed reaction of alkyl fluoride with silyl enolate, allylsilane, and hydrosilane

Alkylation of silyl enolates with tert-alkyl or allylic fluorides proceeds smoothly in the presence of a catalytic amount of boron trifluoride to afford the corresponding carbonyl compounds. Allylation and reduction of alkyl fluorides with allylsilane and hydrosilane, respectively, occur under BF₃ catalysis.     

Thermal investiongation of metal fluoberyllate hydrates and metal fluoride hydrates

The thermal decompositions of MBeF₄ · H₂O and MF₂ · x H₂O, where M = Ni(II), Co(II) or Cu(II) and x = 0–6, have been carried out using a MOM derivatograph. Dehydration takes place in multiple steps. Anhydrous fluoberyllates dissociate first to MF₂ and BeF₂ and then decompose to MO and BeO in two steps. Metal fluorides give ultimately oxyfluoride in one step. None of the intermediate hydrates is thermally stable, except CuF₂ · 2 H₂O. The probable mechanisms of thermal decomposition have been reported. Pyrolysed products are characterised by elemental analysis and X-ray powder patterns. The value of enthalpy change is reported for each decomposition step.     

Lanthanide thermodynamic predictions

For the plus-two and plus-three lanthanide ions, ΔH_f is inversely related to the sums of the ionic radii by ΔH°_f = Q_n + A/(r_Ln³⁺+ r_xn?) + B. This equation reproduces the known values for the plus-three oxides and the halides, and predicts the absolute hydration energies of the aqueous lanthanide(III) ions. The model is also used to calculate ΔH_f of the lanthanide(II) oxides and fluorides. Based upon the enthalpies of disproportionation, EuO, YbO, SmF₂, EuF₂ and YbF₂ are predicted to be stable.     

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.     

A new method for making acyl fluorides using BrF3

While many carboxylic acids could be converted directly to acyl fluorides by using BrF₃, the reaction with acyl chlorides was found to be of a more general nature and yields better results. Surprisingly, reacting t-butyl esters with bromine trifluoride also resulted in acyl fluorides in reasonable yields. The reactions were completed in a few seconds at 0 °C.     

Relations structurales entre U3O8 et quelques fluorures mixtes de formules M2M′3F11, MM′2F7 et MM′3F10

U₃O₈ oxide, as well as M₂M′₃F₁₁, MM′₂F₇ and MM′₃F₁₀ fluorides, with M = Rb, Tl, Cs, NH₄ and M′ = In, Lu, Yb, Tm, is described as the regular repetition according to the … A-A-A … sequence of identical and parallel sheets of edge-and corner-sharing M′F₇ or UO₇ pentagonal bipyramids and M′F₆ octahedra. M′ and U atoms are systematically located at the lattice points of a pseudohexagonal network, but in the fluorides some of these lattice points are vacant, producing hexagonal tunnels in which M atoms are located. It is shown that in the two kinds of compounds the same linear chains and M′₃X₁₇ groups of pentagonal bipyramids are present, and that the transformation of the U₃O₈ structure into the fluorides can be achieved by an ordered substitution of some linear … UOUO … chains by … M-M-M … chains. All these structures can be described with the same structural model based on the chemical twinning principle.     

Complex copper(II) fluorides. XV. The Ternary System BaF2?CuF2?ScF3

The liquid-solid phase diagram of the binary system BaF₂? ScF₃ is established by D.T.A. and radiocrystallography. Three fluorides are disclosed: Ba₃Sc₂F₁₂, Ba₅Sc₃F₁₉ and a cubic high temperature phase Ba_1?xSc_xF_2+x (x = 0.17), the structure of which derives from that of BaF₂. A solid solution between BaF₂ and ScF₃ is also evidenced at high temperature. The ternary system BaF₂? CuF₂? ScF₃ is investigated by radiocrystallography and an isothermal section at 670°C is given. It shows the existence of four phases: a complex quaternary fluoride Ba₁₀Cu₁₂ScF₄₇, two “polytypic” phases the structure of which derives from that of BaCuF₄ and a tetragonal solid solution Ba₅Sc_3?xCu_xF_19?x with 0 ≤ x ≤ 1.     

Structural studies of magnesium nitride fluorides by powder neutron diffraction

Samples of ternary nitride fluorides, Mg₃NF₃ and Mg₂NF have been prepared by solid state reaction of Mg₃N₂ and MgF₂ at 1323–1423 K and investigated by powder X-ray and powder neutron diffraction techniques. Mg₃NF₃ is cubic (space group: Pm3m) and has a structure related to rock-salt MgO, but with one cation site vacant. Mg₂NF is tetragonal (space group: I4₁/amd) and has an anti-LiFeO₂ related structure. Both compounds are essentially ionic and form structures in which nitride and fluoride anions are crystallographically ordered. The nitride fluorides show temperature independent paramagnetic behaviour between 5 and 300 K.     

Mechanochemical synthesis,structure and properties of lead containing alkaline earth metal fluoride solid solutions MxPb1-xF2 (M = Ca,Sr, Ba)

The paper deals with the mechanochemical synthesis of lead containing alkaline earth metal fluoride solid solutions M_xPb_1-xF₂ (M = Ca, Sr, Ba) by high-energy ball milling. Several metal precursors and fluorinating agents were tested for synthesizing M_0.5Pb_0.5F₂. Metal acetates and ammonium fluoride as precursors show the most promising results and were therefore used for the formation of M_xPb_1-xF₂ with different metal cationic ratios. The characterization of the local fluorine coordination and the crystal structure was performed by ¹⁹F MAS NMR spectroscopy and X-ray diffraction. Additional calculations of ¹⁹F chemical shifts using the superposition model allow a deeper insight into the local structure of the compounds. The fluoride ion conductivity was followed by temperature dependent DC conductivity measurements. Significantly higher conductivities were found in comparison with those of the corresponding binary fluorides. The highest values were observed for samples with high lead content M_0.25Pb_0.75F₂, bearing in mind the much higher conductivity of PbF₂ compared to MF₂.