19F NMR Study of Antimony(III) Fluoride Complexes in Solution

The state of SbF₃, Sb₃O₂F₅, MSb₃F₁₀, MSb₂F₇, M₃Sb₄F₁₅, MSbF₄, and M₂SbF₃, as well as HF and MF (M = Na, K, Rb, Cs, NH₄, and Tl), in a 0.25 M aqueous solution at room temperature was studied by ¹⁹F NMR. It is found that chemical shifts of the ¹⁹F NMR signals (relative to CFCl₃) for the compounds under investigation vary in the 73.3–157.5 ppm range. For the Sb(III) fluoride complexes, chemical shifts in the ¹⁹F NMR spectra vary in the 73.3–85.5 ppm range (relative to CFCl₃). Although the crystals of Sb(III) fluoride complexes contain different polyhedra that are joined in different ways, the NMR spectra of all compounds under study show one narrow signal. The spectra of aqueous solutions of Sb(III) fluoride complexes do not contain signals of free fluoride ions and oxofluoride Sb₃O₂F₅.     

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.     

Dynamic disorder in ammonium oxofluorotungstates (NH4)2WO2F4 and (NH4)3WO3F3

Ammonium oxofluorotungstates, (NH₄)₂WO₂F₄ and (NH₄)₃WO₃F₃, are characterized by vibration spectroscopy and quantum chemistry methods with the use of NMR ¹⁹F and ¹H data. It is shown in the approximation of the density-functional theory that in isolated octahedrons [WO₂F₄]^2? and [WO₃F₃]^3? the mutual arrangement of oxygen atoms in cis-position corresponds to the energy minimum. The presence of intraspheric disorder in [WO₃F₃]^3? (unlike [WO₂F₄]^2?) explains the complex character of vibrational spectra of this anion and eliminates existent in the literature differences in their interpretation (between C _2v and C _3v structure variants). Models of intraspheric dynamics of [WO₃F₃]^3? are discussed.     

Effect of anion doping on mobility of ionic charge carriers in solid solutions based on Ba2In2O5

In the work, mobilities of oxygen and protons are determined for F^?-substituted solid solutions based on brownmillerite Ba₂In₂O₅ and their concentration dependences are analyzed. It is found that small additives of the more mobile anion (F^? ions) promote an increase in oxygen mobility as a result of additional effects of repulsion of ions of different nature in the anion sublattice. Mobility of oxygen at high fluoride concentrations decreases due to the overlapping of migration paths of diffusion, as both anions, fluoride ions and oxygen ions, move via oxygen vacancies. Concentration dependences of mobility of proton carriers have a similar character, which is related to the effect of the oxygen sublattice. The anion doping method used in the work can be recommended as the general method for improvement of the transport characteristics of oxygen-ionic and protonic conductors with a perovskite-like structure.     

Ordre oxygène-flour dans les oxyfluorures Na2WO2F4, LiW3O9F,et NaMoO3F

Crystal structures of complex oxyfluorides Na₂WO₂F₄, LiW₃O₉F, and NaMoO₃F have been previously determined by X-ray diffraction but without assigning the specific position of oxygen or fluorine. Using various techniques such as ¹⁹F nuclear magnetic resonance, Raman spectroscopy, electrostatic energy and site potential calculations, analysis of the local balance between charge of neighboring ions, clear evidence has been given of an ordered oxygen-fluorine distribution within the anionic sublattices which is proposed. The accuracy of each method used has been discussed for each phase.     

Alignment of acentric MoO3F3 anions in a polar material: (Ag3MoO3F3)(Ag3MoO4)Cl

(Ag₃MoO₃F₃)(Ag₃MoO₄)Cl was synthesized by hydro(solvato)thermal methods and characterized by single-crystal X-ray diffraction (P3m1, No. 156, Z=1, a=7.4488(6)Å, c=5.9190(7) Å). The transparent colorless crystals are comprised of chains of distorted fac-MoO₃F₃³⁻ octahedra and MoO₄²⁻ tetrahedra anions, as suggested by the formulas Ag₃MoO₃F₃ and Ag₃MoO₄⁺, and are connected through Ag⁺ cations in a polar alignment along the c-axis. One Cl⁻ anion per formula unit serves as a charge balance and connects the two types of chains in a staggered fashion, offset by . In MoO₄²⁻, the Mo atom displaces towards a single oxide vertex, and in MoO₃F₃³⁻, the Mo displaces towards the three oxide ligands. The ordered oxide-fluoride ligands on the MoO₃F₃³⁻ anion is important to prevent local inversion centers, while the polar organization is directed by the Cl⁻ anion and interchain dipole-dipole interactions. The dipole moments of MoO₃F₃³⁻ and MoO₄²⁻ align in the negative c-axis direction, to give a polar structure with no cancellation of the individual moments. The direction and magnitude of the dipole moments for MoO₃F₃³⁻ and MoO₄²⁻ were calculated from bond valence analyses and are 6.1 and 1.9 debye (10⁻¹⁸ esu cm) respectively, compared to 4.4 debye for polar NbO₆ octahedra in LiNbO₃, and 4.5 debye for polar TiO₆ octahedra in KTiOPO₄ (KTP).     

Struktur‐ und magnetochemische Untersuchungen an Ba5Mn3F19 und verwandten Verbindungen AII5MIII3F19

Structural and Magnetochemical Studies of Ba₅Mn₃F₁₉ and Related Compounds A^II₅M^III₃F₁₉ Single crystal structure determinations by X‐ray methods were performed at the following compounds, crystallizing tetragonally body‐centred (Z = 4): Sr₅V₃F₁₉ (a = 1423.4(2), c = 728.9(1) pm), Sr₅Cr₃F₁₉ (a = 1423.5(2), c = 728.1(1) pm), Ba₅Mn₃F₁₉ (a = 1468.9(1), c = 770.3(1) pm, Ba₅Fe₃F₁₉ (a = 1483.5(1), c = 766.7(1) pm), and Ba₅Ga₃F₁₉ (a = 1466.0(2), c = 760.1(2) pm). Only Ba₅Mn₃F₁₉ was refined in space group I4cm (mean distances for elongated octahedra Mn1–F: 185/207 pm equatorial/axial; for compressed octahedra Mn2–F: 199/182 pm), the remaining compounds in space group I4/m. In all cases the octahedral ligand spheres of the M1 atoms showed disorder, the [M1F₆] octahedra being connected into chains in one part of the compounds and into dimers in the other. The magnetic properties of the V, Cr and Mn compounds named above and of Pb₅Mn₃F₁₉ and Sr₅Fe₃F₁₉ as well were studied; the results are discussed in context with the in part problematic structures.     

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.     

A new layered perovskite,KSrNb2O6F,by powder neutron diffraction

The structure of a new layered oxyfluoride, viz. potassium strontium diniobium hexaoxide fluoride, KSrNb₂O₆F, was refined from powder neutron diffraction data in the orthorhombic space group Immm. The oxyfluoride compound is an n = 2 member of the Dion–Jacobson‐type family of general formula A[A′_n−1B_nX_3n+1], which consists of double layered perovskite slabs, [SrNb₂O₆F]⁻, between which K⁺ ions are located. Within the perovskite slabs, the NbO₅F octahedra are significantly distorted and tilted about the a axis. A bond‐valence‐sum calculation gives evidence for O/F ordering in KSrNb₂O₆F, with the F⁻ ions located in the central sites of the corner‐sharing NbO₅F octahedra along the b axis. All atoms lie on special positions, namely Nb on m, Sr on mmm, K on m2m, F on mm2, and O on sites of symmetry m and m2m.     

Coupled Li/Nb and O/F ordering on the Na and Cl sites of the average NaCl structure of Li4NbO4F

The average, as well as the cation and anion ‘disordered’, crystal structure of Li₄NbO₄F has been carefully investigated via coupled neutron and X-ray powder diffraction studies as well as via electron diffraction studies. The existence of a spectacular highly structured diffuse intensity distribution in the latter provides strong evidence for coupled Li¹⁺/Nb⁵⁺ and O²⁻/F⁻ ordering on the Na and Cl sites of the average NaCl structure of Li₄NbO₄F. Bond valence sum calculations have been used to investigate local crystal chemistry as well as to suggest plausible local crystal chemical constraints while ab initio DFT based theoretical calculations of a 2×2×2 supercell have been carried out in order to provide additional insight into the local crystal chemistry of this compound.     

Ba3(BO3)(CO3)F: The First Borate Carbonate Fluoride Synthesized by the High-Temperature Solution Method

In contrast to the well-investigated halogen-containing borates and carbonates, very few halogen-containing borate carbonate compounds have been reported. Specifically, no example of borate carbonate fluoride has been synthesized successfully until now. Herein, the planar π-conjugated units [BO₃]³⁻ and [CO₃]²⁻ and the F⁻ ions are introduced simultaneously into one crystal structure resulting in the first borate carbonate fluoride, Ba₃(BO₃)(CO₃)F, by the high-temperature solution method in the atmosphere. Its structure features a hexagonal channel formed by the [BO₃]³⁻ and [CO₃]²⁻ units with the [F₃Ba₈]¹³⁺ trimers filled in the channel. Various characterizations including single crystal- and powder-XRD, EDX, IR, UV-vis-NIR, and TG-DSC, together with the first principles calculation have been carried out to verify the structure and fully understand the structure–property relationships.     

The substitution of germanium for silicon in AST-type zeolite

The substitution of silicon by germanium in the AST zeolite framework type, [Si_nGe_40−nO₈₀]*4(SDA⁺F⁻) expressed as unit cell content in its cubic F-centered symmetry, has been studied. Three different kinds of templates, dimethyldiethylammonium, dimethyldiisopropylammonium and isopropyltrimethylammonium cations, were used in the hydrothermal synthesis process in fluoride medium. The products were identified with XRD, MAS NMR, SEM and thermal analysis. The analysis of the X-ray powder diagrams shows that AST crystallizes in different space group symmetries depending on the nature of the SDA and the degree of Ge-substitution. The resonance signals of ¹⁹F in MAS NMR experiments for the pure Si- and Ge-end members are at −38.2 and −15 ppm, respectively, indicating that the F⁻-anion is located as co-template in the double-four-ring (D4R) of the tetrahedral framework. This is confirmed by Rietveld analysis of powder diffraction data of the pure Ge-end member. The peak splitting of the ¹⁹F NMR signal in pure GeO₂AST-type material is related to the displacement of F⁻ location inside the D4R. Two more distinct signals at −8 and −19 ppm, respectively, are observed for X-ray pure AST-samples of intermediate compositions and assigned to fluoride in D4R built of 4[GeO₄]- and 4[SiO₄]-tetrahedra (4Ge, 4Si) and to (2Ge, 6Si)-D4R, respectively. An ordered distribution of Ge in the AST-framework is proposed for cubic AST with compositions around Si/Ge=1.5–1 by correlating the intensities of ¹⁹F NMR signals and the results from chemical analysis. This model is further confirmed by the quantitative analyses of the corresponding ²⁹Si MAS NMR spectra.     

123Sb NQR and 19F NMR study of potassium,rubidium, and cesium heptafluorodiantimonates(iii)

The dynamics of crystal lattices of potassium, rubidium, and cesium heptafluorodiantimonates(iii) and specific features of internal rotations of the Sb₂F₇ fluoride groups in these compounds were studied using ¹²³Sb NQR in the temperature interval from 77 to 325 K and ¹⁹F NMR in the temperature interval from 240 to 470 K in combination with X-ray diffraction and thermogravimetric analyses. The distinctions in the dynamic behavior of the fluoride ions with changing the size (polarizability) of outer-sphere cations are discussed. The structural phase transition in CsSb₂F₇ was revealed at 425—430 K accompanied by the appearance of a high ion conductivity ( 1.3·10^–3 S cm^–1 at 450 K). A second type phase change can exist at 220—270 K.     

New anion-conducting fluorite-like solid solution Bi1 − x Te x (O,F)2 + δ (0.28 < x < 0.43) in the BiF3-BiOF-TeO2 system

A new fluorite-like solid solution, II-Bi_{1 ? x} Te _x (O,F)_{2 + δ}, was produced by solid-phase synthesis at 873 K with subsequent annealing, its concentration boundaries were determined, and a scheme of an isothermal (873 K) section of the BiF₃-BiOF-TeO₂ system was proposed. The new phase was characterized by X-ray powder diffraction, electron microscopy, and impedance spectroscopy. Making heterovalent substitutions simultaneously in the cation and anion sublattices, Te⁴⁺ ? Bi³⁺ and O^2? ? F^? allowed one to vary the tellurium cation content x (at constant anion nonstoichiometry δ) or the anion nonstoichiometry δ (at constant tellurium cation content x or constant fluoride ion content), which enabled one to describe the effect of these parameters on the properties of the solid solution. The anion excess δ was found to dominate the unit cell parameter of the solid solution and its ionic conductivity. The conduction within the studied temperature range was proven to be mainly by fluoride ions. It was assumed that the ordering of superstoichiometric anions, or clustering, can manifest itself as the structural modulations of the phase II-Bi_{1 ? x} Te _x (O,F)_{2 + δ} that were detected in this work.     

New Quaternary Chalcogenides BaLnMQ3 (Ln = Rare Earth or Sc; M = Cu, Ag; Q= S, Se): II. Structure and Property Variation vs Rare-Earth Element

Some new quaternary compounds of the type BaLnMQ₃ (Ln = rare earth or Sc; M = Cu, Ag; Q = S, Se) have been synthesized by the reaction of the constituent binary chalcogenides and elements at 1000°C. The crystal structures of two of these compounds have been determined by single-crystal X-ray diffraction techniques and are isostructural. Crystal data: BaErCuS₃—space group D¹⁷_2h —Cmcm, M= 464.32, Z = 4 , a = 3.987(1), b = 13.377(3), c = 10.101(2) Å (T = 115 K), V = 538.7(4) ų, R_w (F²) = 0.095 for 848 observations and 24 variables, R(F) = 0.037 for 840 observations having F²₀ > 2σ (F²₀); BaYAgSe—space group D¹⁷_2h —Cmcm, M = 571.0, Z = 4, a = 4.239(1), b = 14.030(2), c = 10.636(2) Å (T = 115 K), V = 632.6(2) ų, R_w (F²) = 0.057 for 645 observations and 24 variables, R(F) = 0.023 for 595 observations having F²₀ > 2σ(F²₀). These two compounds adopt the layered KZrCuS₃ structure type. The layers, which are separated by Ba²⁺ ions, consist of edge-sharing octahedral chains and corner-sharing tetrahedral chains. The other compounds synthesized crystallize either with this same structure or with that of β-BaLaCuSe₃, a slightly distorted variation, which is isostructural with Eu₂CuS₃. The diffuse reflective UV-visible spectra of several of these compounds have been measured. From magnetic susceptibility measurements, both BaNdCuS₃ and BaGdCuS₃ show Curie-Weiss behavior, whereas BaCeCuS₃ and BaCeCuSe₃ show in addition temperature-independent paramagnetism.     

Organoboron compounds as Lewis acid receptors of fluoride ions in polymeric membranes

Newly synthesized organoboron compounds – 4-octyloxyphenylboronic acid (OPBA) and pinacol ester of 2,4,6-trifluorophenylboronic acid (PE-PBA) – were applied as Lewis acid receptors of fluoride anions. Despite enhanced selectivity, the polymer membrane electrodes containing the lipophilic receptor OPBA exhibited non-Nernstian slopes of the responses toward fluoride ions in acidic conditions. Such behavior was explained by the lability of the B–O bond in the boronic acids, and the OH⁻/F⁻ exchange at higher fluoride content in the sample solution. In consequence, the stoichiometry of the OPBA–fluoride complexes in the membrane could vary during the calibration, changing the equilibrium concentration of the primary anion in membrane and providing super-Nernstian responses. The proposed mechanism was supported by ¹⁹F NMR studies, which indicated that the fluoride complexation proceeds more effectively in acidic solution leading mainly to PhBF₃⁻ species. Finally, the performances of the membranes based on the phenylboronic acid pinacol ester, with a more stable B–O bond, were tested. As it was expected, Nernstian fluoride responses were recorded for such membranes with worsened fluoride selectivity.     

Synthesis,structure, ion mobility,phase transitions,and ion transport in rubidium ammonium hexafluorozirconates

Rubidium ammonium hexafluorozirconates Rb_2?x (NH₄)_x ZrF₆ (1.5 < x < 2.0) have been synthesized, and their structure, ion mobility (180–480 K), and electrophysical properties have been studied by X-ray crystallography, ¹H and ¹⁹F NMR, DTA, and impedance methods. Compounds with x > 1.5 are isostructural with (NH₄)₂ZrF₆. Rubidium cations are isomorphously substituted for the ammonium cations. The high-temperature modifications of the compounds, which form upon the phase transitions at 413–418 K, are characterized by translational diffusion of ions in the fluoride and ammonium sublattices. The ¹⁹F NMR spectra are characterized by uniaxial ¹⁹F magnetic shift anisotropy. The electrophysical properties of this series of compounds are studied in the temperature range 300–480 K.     

Bi2WO6量子点(QDs)修饰Bi2MoO6-xF2x异质结的构筑及其催化活性增强机理

采用简单沉积-沉淀法合成了Bi_2WO_6@Bi_2MoO_(6-x)F_(2x)(BWO/BMO_(6-x)F_(2x))异质结,借助XRD、XPS、TEM、SEM、EDS、UV-Vis-DRS、PC和EIS等测试技术对其组成、形貌、光吸收特性和光电化学性能等进行系统表征,并以模型污染物罗丹明B(Rh B)的光催化降解作为探针反应来评价Bi_2WO_6@Bi_2MoO_(6-x)F_(2x)异质结的光催化活性增强机制。形貌分析表明,所得Bi_2MoO_6微球由大量厚度为20~50 nm的纳米片组成;FE-SEM和HR-TEM分析表明,尺寸约为10 nm的Bi_2WO_6量子点均匀沉积在Bi_2MoO_(6-x)F_(2x)微球表面,形成新颖的Bi_2WO_6@Bi_2MoO_(6-x)F_(2x)异质结;与纯Bi_2MoO_6或者Bi_2WO_6相比,1∶1Bi_2WO_6@Bi_2MoO_(6-x)F_(2x)异质结表现出更好的光催化活性和光电流性质,其对RhB光催化降解的表观速率常数分别为纯BMO和BWO的6.4和11.6倍。PC和EIS图谱分析表明,Bi_2WO_6量子点表面沉积显著提高Bi_2MoO_(6-x)F_(2x)光生电子/空穴的分离效率和迁移速率;活性物种捕获实验证明了·O_2~-和h~+是主要的活性物种。根据实验结果,探讨了F-掺杂和Bi_2WO_6量子点之间的协同效应对Bi_2MoO_6的光催化活性的影响机制。     

A study of the hydrolysis of ZrF<Stack><Subscript>6</Subscript><Superscript>2−</Superscript></Stack> and the structure of intermediate hydrolysis products by <Superscript>19</Superscript>F and <Superscript>91</Superscript>Zr NMR in the 9.4 T field

The high-field ¹⁹F and ⁹¹Zr NMR method is used to study the hydrolysis and polycondensation of hexafluorozirconate ZrF₆²⁻ in aqueous and water-peroxide solutions. During hydrolysis in aqueous solutions only ZrF₆²⁻ and F⁻ ions were observed by NMR, however, in the water-peroxide medium, an intermediate product of hydrolysis ([F₅Zr-OO-ZrF₅]⁴⁻ dimer) was detected. The dimer structure is confirmed by ¹⁹F and ⁹¹Zr NMR. In high fields (¹⁹F NMR frequency > 200 MHz), the fluorine exchange between ZrF₆²⁻ and F⁻ is slow in the ¹⁹F NMR scale and has a multisite character.     

A study of the anion mobility in mixed fluorides with the tysonite structure

Summary From the studies which have been carried out it follows that in Berthollide solid solutions with the tysonite structure there is intensive diffusion of fluoride ions in the vacancies, and this is responsible for the electrical conductivity of the crystals. It follows from an analysis of the NMR data obtained that the fluorine vacancies are produced in the positions corresponding to fluorine atoms of low mobility, confirming structural studies which indicate the preferential formation of vacancies in the F_III positions. At low temperatures, the movement of the highly mobile F_I fluorine atoms shows practically no association with the low-mobility F_III positions. Thus in spite of the high concentration of anion vacancies in the specimens studied, the mobility of fluorine at low temperatures does not increase, compared with the ideal tysonite structure. It follows from the temperature dependence of the¹⁹F NMR spectra, however, that the presence of vacancies increases the mobility in the subsystems of fluorine atoms with low mobility and increases the exchange between the fluorine atoms with high and low mobilities.L. V. Kirenskii Institute of Physics, Siberian Branch, Academy of Sciences of the USSR. Institute of Crystallography, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 20, No. 4, pp. 622–626, July–August, 1979.