Fluorine Anions Research Articles

Theoretical Study of Molecular and Electronic Structures of 51Knot Systems: Two-Layered ONIOM Calculations

In this study we examine the electronic and molecular structures of the [51 knot···(PF6)10]+ pentafoil knot system and report calculated interaction energies that result from halides (X = F, Cl, Br, and I) localized at the center of the [51knot···(PF6)9]X molecular structure. The equilibrium geometries were fully optimized at the ONIOM(M06/6-31G(2d,p):PM6) level of theory, starting from an initial geometry for the pentafoil knot obtained from experimental X-ray data. The molecular systems were divided into two layers, for which the M06/6-31G(2d,p) level of theory was used to describe the high layer ([C4H6]5X- structure) and the PM6 semiempirical method was employed for the low layer. The calculated electronic energies show that the interaction between the fluorine anion and the pentafoil knot produces the most stable structure, whereas an unfavorable interaction is observed for iodide due to the diffuse character of its electronic cloud. Using basis set superposition error (BSSE) correction techniques, the observed values of the interaction are -0.201 hartrees for the fluoride ion and -0.100 hartrees for iodide.

Analyzing excited-state processes and optical signatures of a ratiomeric fluorine anion sensor: a quantum look

Recently, the spectroscopic signatures of a benzoselenadiazole derivative have been investigated in the framework of designing a new ratiometric fluoride sensor (Saravanan et al., Org Lett, 2014, 16: 354–357). It was suggested that this sensor is undergoing excited-state intramolecular proton transfer. In this work, we provide a new look at these experimental data, using a state-of-the-art time-dependent density functional theory approach to mimic the spectroscopic signatures. New insights about the nature of the excited-state processes are obtained.

Preparation of NaY zeolite membranes in fluoride media and their application in dehydration of bio-alcohols

Improved NaY zeolite membranes were prepared in the presence of ammonium fluoride. The crystallization and separation performance of fluoride-derived NaY zeolite membranes were studied in comparison with fluoride-free membranes. The addition of ammonium fluoride in gel influenced the crystallization and the morphologies of NaY zeolite and zeolite layers, and effectively suppressed the formation of the impurity phase of P-type zeolite in NaY zeolite layers. The fluoride-derived NaY zeolite membranes had thinner zeolite layers and displayed both higher fluxes and separation factors for the dehydration of bio-alcohols (ethanol and butanol) than the fluoride-free membranes. The separation factors increased with the increasing kinetic diameters of alcohols for the methanol, ethanol, i-propanol and n-butanol aqueous solutions. Synthesis reproducibility of fluoride-derived membranes and membrane stability during the dehydration process were also investigated. 29Si and 19F MAS NMR results confirmed that fluorine anions were not included in FAU crystals.

Structural investigations, high temperature behavior and phase transition of Na6Ca4(SO4)6F2

Polycrystalline material of a sulfate apatite with chemical composition Na6Ca4(SO4)6F2 or (Na2Ca4)Na4(SO4)6F2 has been synthesized by solid state reactions. Basic crystallographic data are as follows: hexagonal symmetry, a = 9.3976(1) A, c = 6.8956(1) A, V = 527.39(1) A3, Z = 1, space group P63/m. For structural investigations the Rietveld method was employed. Thermal expansion has been studied between 25 and 600 °C. High temperature (HT) powder diffraction data as well as thermal analysis indicate that the apatite-type compound undergoes a reconstructive phase transition in the range between 610 and 630 °C. Single-crystals of the HT-polymorph were directly grown from the melt. Structural investigations based on single-crystal diffraction data of the quenched crystals performed at −100 °C showed orthorhombic symmetry (space group Pna21) with a = 12.7560(8) A, b = 8.6930(4) A, c = 9.8980(5) A, V = 1097.57(10) A3 and Z = 2. Unit cell parameters for a quenched polycrystalline sample of the HT-form obtained at ambient conditions from a LeBail-fit are as follows: a = 12.7875(1) A, b = 8.7255(1) A, c = 9.9261(1) A, V = 1107.53(2) A3. The lattice parameters of both modifications are related by the following approximate relationships: aHT ≈ 2cRT, bHT ≈ -(½aRT + bRT), cHT ≈ aRT. The HT-modification is isotypic with the corresponding potassium compound K6Ca4(SO4)6F2. The pronounced disorder of the sulphate group even at low temperatures has been studied by maximum entropy calculations. Despite the first-order character of the transformation clusters of sulfate groups surrounding the fluorine anions can be identified in both polymorphs. Each of the three next neighbor SO4-tetrahedra within a cluster is in turn surrounded by 8–9 M-cations (M: Na,Ca) defining cage-like units. However, in the apatite structure the corresponding three tricapped trigonal prisms are symmetry equivalent. Furthermore, the central fluorine atom of each cluster is coordinated by three next M-neighbors (FM3-triangles), whereas in the HT-polymorph a four-fold coordination is observed (FM4-tetrahedra).

Ca3Be6B5O16F: the first alkaline-earth beryllium borate with fluorine anions.

The first all-alkaline-earth beryllium borate with fluorine anions, Ca3Be6B5O16F, was synthesized by a spontaneous crystallization flux method using LiF-B2O3 as the flux. The structural framework of Ca3Be6B5O16F is composed of the inter-connected [Be6B3O16] and [BO3] fundamental building blocks, with [CaO7F] distorted polyhedra located in the interstitial sites. The [Be6B3O16] group is discovered for the first time in beryllium borates. The UV-Vis-NIR diffuse-reflectance spectrum demonstrates that its UV cutoff edge is below 200 nm, and this is confirmed by first-principles studies. Thermal analysis reveals an incongruent feature at 1321 K. IR spectroscopy measurements are consistent with the crystallographic study. These data reveal that the crystal could have an application as a deep-ultraviolet optical material.

Anatase TiO2 hollow nanosheets: dual roles of F−, formation mechanism, and thermal stability

Anatase TiO2 hollow nanosheets with a width of 550 nm, a thickness of 100 nm, and a hole diameter of 350 nm were hydrothermally fabricated in an aqueous solution containing NH4VO3, HF, and HCl at an appropriate composition. Structural analyses on the products obtained at different intervals during the synthesis revealed that the formation of the anatase TiO2 hollow nanosheets consisted of three steps: oriented assembly of square-like NH4TiOF3 nanoparticles, topochemical conversion of NH4TiOF3 to anatase TiO2, and selective etching by F− on the flat nanosheets. The fluorine anion was involved in the formation of NH4TiOF3 as the key intermediate, it directed the construction of the nanosheet, and participated in the etching process to generate the hollow structure. The resultant anatase TiO2 hollow nanosheets exhibited a rather high thermal stability, maintaining the anatase crystallite structure and the hollow shape up to 1073 K.

Topological reaction sites – very strong chalcogen bonds

The analysis of interactions in complexes of S(CN)2, Se(CN)2, SFCl and SeFCl with F(-) and Cl(-) anions is performed here. The sulphur and selenium atoms act in these complexes as Lewis acid centres interacting with fluorine and chlorine anions. The arrangement of sub-units in complexes is in agreement with the σ-hole concept; particularly it is a result of contacts between positive and negative electrostatic potential sites. The interactions in complexes analyzed may be classified as very strong charge assisted chalcogen bonds and they possess numerous characteristics typical for covalent bonds. Even in the case of complexes of SFCl and SeFCl, i.e. SFCl2(-) and SeFCl2(-), the trivalency of the chalcogen atom is observed. The calculations were carried out at the MP2(full)/aug-cc-pVTZ level of approximation, the analyses were performed with the use of the Natural Bond Orbital (NBO) method, the Quantum Theory of 'Atoms in Molecules' (QTAIM) and the Electron Localization Function (ELF) approach. The results obtained by these methods are in agreement giving the consistent picture of the complexes' configurations and their electron charge distribution. The QTAIM and ELF approaches allow us to predict for S(CN)2, Se(CN)2, SFCl and SeFCl molecules the directions of nucleophilic attack. They are in line with the prediction based on the σ-hole concept. The Symmetry Adapted Perturbation Theory (SAPT) approach was also applied.

Fabrication and characterization of TiO2-ZrO2-ZrTiO4 nanotubes on TiZr alloy manufactured via anodization.

Titanium and its alloys are able to grow a stable oxide layer on their surfaces and have been used frequently as substrates for anodization in an electrochemical surface treatment. A nanotubular oxide layer is formed in the presence of fluorine anion (F-) via anodization due to the competition between oxide formation and solvatization. In this study, a highly ordered titania-zirconia-zirconium titanate (TiO2-ZrO2-ZrTiO4) nanotubular layer was formed on the surface of Ti50Zr alloy via anodic oxidation in an F- containing electrolyte. The sizes of the nanotubes (i.e., the inner and outer diameters, and wall thicknesses), morphology, crystal structure, hydrophilic properties and components of the TiO2-ZrO2-ZrTiO4 nanotubular layer before and after annealing were examined by scanning electron microscopy (SEM), thin film X-ray diffraction, X-ray photoelectron spectroscopy (XPS) analysis and water contact angle measurements. The results indicated that the inner diameter, outer diameter and wall thickness of the as-formed TiO2-ZrO2-ZrTiO4 nanotubes were distributed in the ranges of 3-120 nm, 12-165 nm and 3-32 nm, respectively, and depended on the F- concentration of the electrolyte and the applied potential during anodization. The number of smaller nanotubes increased with increasing F- concentration and the mean nanotube inner and outer diameters increased with increasing applied potential. The as-formed TiO2 and ZrTiO4 nanotubes exhibited an amorphous structure and the as-formed ZrO2 nanotubes displayed an orthorhombic structure. These phases transformed into anatase TiO2 and orthorhombic ZrO2 and ZrTiO4 after annealing. The hydrophilic properties of the TiO2-ZrO2-ZrTiO4 nanotubular layer were affected by the size distribution of the nanotubes. The surface roughnesses and the nanotubular character transformed the nanotubes to exhibit superhydrophilic properties after annealing. The TiO2-ZrO2-ZrTiO4 nanotubular surface on Ti50Zr alloy exhibited higher surface energy than that of the TiO2 nanotubular surface on commercially pure (CP) titanium.

A simple approach to the fabrication of fluorine-doped zinc oxide thin films by atomic layer deposition at low temperatures and an investigation into the growth mode

A simple low-temperature fabrication of fluorine-doped ZnO (ZnO:F) thin films by atomic layer deposition (ALD) was investigated and the growth mode of the films was analyzed. A novel method for fluorine doping into a ZnO matrix was successfully developed that uses ALD with a home-made fluorine source at a low deposition temperature of 140 °C, which is low enough for films to be applied to a plastic substrate. The fluorine doping concentration was controlled from 0 at.% to 1.2 at.% by manipulating the pulse sequence ratio of the oxygen source (deionized water) and the home-made fluorine source. Structural and morphological properties were investigated by X-ray diffraction and field emission scanning electron microscopy. The growth mode of the films was studied by grazing-incidence wide-angle X-ray diffraction. The grain growth orientation was found to change significantly as the fluorine concentration was increased due to the characteristics of fluorine doping in the oxygen sites of ZnO. This phenomenon could be explained by a perturbation and passivation effect resulting from the fluorine doping mechanism, with the fluorine anions filling oxygen-related defect sites in the ZnO lattice. A photoluminescence study confirmed the diminishment of defect sites and showed that, due to the Burstein–Moss effect, the optical transmittance in the visible region increased significantly with an increase in the fluorine doping concentration from 80.87% to 83.02%. The lowest resistivity was 1.876 × 10−3 Ω cm for ZnO thin films doped with 1.0 at.% fluorine when the carrier concentration and mobility were 1.375 × 1020 cm−3 and 24.20 cm2 V−1 s−1, respectively.

Selective Oxidation of Glycerol with O<sub>2</sub> Catalyzed by Fluorine-Modified CuNiAl Hydrotalcite

A fluorine anion modified CuNiAl hydrotalcite (CuNiAl-LDH (F-)) was prepared for the selective oxidation of glycerol (GLY) using O2 as oxidant. It was found that the obtained catalyst with typical layer structures of hydrotalcite compounds was an effective heterogeneous catalyst in GLY oxidation. Under the present conditions, the main product was the C3 oxygenated products of primary alcohol glyceric acid (GLYAC). The highest conversion of GLY reached 32.0% with 58.1% of the selectivity to GLYAC.

Synthesis and Characterization of a Novel Sodium Transition Metal Oxyfluoride: NaMnMoO3F3·H2O

NaMnMoO3F3·H2O was precipitated at low temperature from aqueous dissolutions of Na2MoO4·2H2O in aqueous HF (or NaHF2) using either Mn(CH3COO)2·4H2O or MnF2 as manganese precursors. Chemical analysis, IR spectra, and effective paramagnetic moment are in agreement with the proposed formula. Electron microscopy studies indicate that the sample is constituted of very thin plate-like microcrystals. The average crystal structure (a = 3.5947(1), b = 21.246(1), and c = 7.3893(2) Å and Cmcm (No. 63) SG) has been elucidated through powder diffraction methods (synchrotron and neutron). Tiny superstructure peaks are observed that can be indexed with the space group Pbca and cell parameters a = 7.1894(2), b = 21.246(1), and c = 7.3893(2) Å. Electron diffraction confirms the doubling of a parameter. Ordering of O and F is proposed in agreement with Pauling's second crystal rule and bond strength sums for each anionic position. The structure that is formed has a layered stacking arrangement along the b-axis of the MnO4F2 octahedra layers that share corners along a- and c-directions. The large interlayer space contains MoO4F2 octahedra (connected to the layer) together with sodium ions and water molecules, tentatively forming hydrogen bonding with fluorine anions. The origin of the superstructure could not be fully elucidated, but it is presumably related to slight distortions within the MnO4F2 octahedra.

Formation and crystallization of chlorine- and bromine-containing hafnium fluoride-based glasses

We have studied glass-forming regions for ZBLAN-type hafnium fluoride-based glasses with the compositions (63–53)HfF4 · 20BaF2 · 4LaF3 · (1–3)InF3 · (0–20)NaF in which fluorine anions are partially replaced by chlorine and bromine anions. The crystallization mechanism of the glasses has been investigated by differential thermal analysis and X-ray diffraction. The results demonstrate that characteristic features of the glasses are a significant decrease in glass transition temperature (t g) and the precipitation of fine-particle crystalline chloride and bromide phases at temperatures well below the crystallization temperature (t x) of their fluoride analogs. We have studied the effect of the Cl/F and Cl/Br ratios in the glass batch and the melt cooling rate after glass preparation on the crystallization behavior of the glasses and determined the heat treatment temperature and time for the formation of transparent glass-ceramic samples upon heat treatment in the temperature range where chloride and bromide phases precipitate. Doping of the glasses with 1 at % or smaller amounts of rare-earth metals is found to have no significant effect on the phase segregation process during heat treatment.

X-ray diffraction study of the NaF-LiF-NdF3 eutectic in the liquid and solid states

The ternary eutectic alloy with the composition 33 mol % NaF + 53 mol % LiF + 14 mol % NdF3 has been studied in the liquid and crystalline states using differential thermal analysis and X-ray diffraction at room and high temperatures. The results demonstrate that the alloy undergoes no phase transformations below its melting point: the only phases identified with certainty are NaF, LiF, and NaNdF4. The melt contains complex microgroups differing in cation composition. Analysis of structural models for the melt indicates that there is no dense noncrystalline packing of the fluorine anions, in contrast to what was observed previously in the eutectic NaF-LiF-LaF3 melt.

Two distinct lithium diffusive species for polymer gel electrolytes containing LiBF4, propylene carbonate (PC) and PVDF

Polymer gel electrolytes have been prepared using lithium tetrafluoroborate (LiBF4), propylene carbonate (PC) and polyvinylidene fluoride (PVDF) at 20% and 30% concentration by mass. Self diffusion coefficients have been measured using pulse field gradient nuclear magnetic resonance (PFG-NMR) for the cation and anion using 7Li and 19F resonant frequencies respectively. It was found that lithium ion diffusion was slow compared to the much larger fluorine anion likely resulting from a large solvation shell of the lithium. Lithium ion diffusion measurements exhibited two distinct diffusive species, whereas the fluorine ions exhibited only a single diffusive species.

Fluorine intercalation in the n = 1 and n = 2 layered manganites Sr2MnO3.5+x and Sr3Mn2O6

Fluorine insertion into the oxygen defect superstructure manganite Sr2MnO3.5+x has been shown by transmission electron microscopy (TEM) to result in two levels of fluorination. In the higher fluorine content sections, the fluorine anions displace oxygen anions from their apical positions into the equatorial vacancies, thus destroying the superstructure and reverting to a K2NiF4-type structure (a=3.8210(1)Å and c=12.686(1)Å). Conversely, lower fluorine content sections retain the Sr2MnO3.5+x defect superstructure, crystallising in the P21/c space group. Fluorine intercalation into the reduced double-layer manganite Sr3Mn2O6 occurs in a step-wise fashion according to the general formula Sr3Mn2O6Fy with y=1, 2, and 3. It is proposed that the y=1 phase (a=3.815(1)Å, c=20.29(2)Å) is produced by the filling of all the equatorial oxygen vacancies by fluorine atoms whilst the y=2 phase (a=3.8222(2)Å, c=21.2435(3)Å) has a random distribution of fluorine anions throughout both interstitial rocksalt and equatorial sites. Neutron powder diffraction data suggest that the fully fluorinated y=3 phase (a=3.8157(6)Å, c=23.666(4)Å) corresponds to the complete occupation of all the equatorial oxygen vacancies and the interstitial sites by intercalated fluorine.

Synthesis and Characterization of Imidazolium Salts Bearing Fluorinated Anions

AbstractThe reaction of 1‐methylimidazole and α,α‐dibromo‐p‐xylene was followed by a metathesis reaction with fluorinated anion sources, which yielded new fluorinated imidazolium salts [C6H4(CH2(C4H6N2)2]2+ 2[A]– where A = BF4 (2), PF6 (3), CF3SO3 (4), and CF3COO (5). The compounds were characterized by 1H‐, 13C‐, 19F‐, 31P NMR, and IR spectroscopy. Single crystal X‐ray diffraction data of compounds 2, 3, and 4 were also reported, whereas compound 5 was found to be a liquid. The solid compounds crystallized in the monoclinic P21/c space group and have similar crystallographic parameters. The study revealed that the different fluorinated anions affected the spatial arrangement of atoms and the extent of cation–anion interactions, hence, influenced the stability and coordination properties of the imidazolium salts. A trend was observed which related the strength of cation–anion interaction to physical properties such as melting point.

Fluorine insertion reactions of the brownmillerite materials Sr2Fe2O5, Sr2CoFeO5, and Sr2Co2O5

The brownmillerite structure provides an ordered vacancy lattice into which fluorine anions should easily be accommodated, with full occupation of the vacant sites resulting in a simple perovskite structure. Low-temperature fluorine insertion reactions with the brownmillerite Sr2Co2O5 and related materials Sr2CoFeO5 and Sr2Fe2O5 have been investigated with a view to using fluorine insertion reactions to fill the oxygen vacancies in these materials, thus forming cubic perovskite-type phases with mixed 3+/4+ B cation oxidation states. The synthesis and magnetic properties of the new perovskite materials SrCoO2.5F0.5 and SrCo0.5Fe0.5O2.5F0.5 are presented here, supplemented by a consideration of Madelung energy calculations in order to explain the dissimilar fluorination behaviour of Sr2Fe2O5.

Preparation and microstructural analysis of high-performance mordenite membranes in fluoride media

High-performance mordenite membranes were prepared in fluoride media on porous tubular mullite supports by a single hydrothermal synthesis. Mordenite membranes and powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), magic-angle spinning nuclear magnetic resonance (MAS NMR) and contact angle with water droplets. The microstructure (i.e. hydrophilicity and crystal morphology) and pervaporation (PV) performance were influenced by the fluoride source and synthesis temperature. The 19F MAS NMR evidence shows the fluorine anion is present in channels of the mordenite crystal as a counterion of cations. Eight mordenite membranes (M-3 serial) prepared using NH4F-modified gels exhibited high fluxes of 1.50±0.25kgm−2h−1 together with high separation factors of 1380±110 for a water/ethanol (10/90wt.%) mixture at 75°C. The membranes also displayed good water-selective for the water/i-propanol mixture. The high performance is attributed to the thin zeolite layer and good surface hydrophilicity of mordenite membranes prepared in fluoride media.

3,5-Diferrocenylpyridine: Synthesis, characterisation, palladium(II) dichloride complex and electrochemistry

3,5-Diferrocenylpyridine was synthesised from 3,5-dibromopyridine and ferroceneboronic acid, in respectable yield (48%), using a microwave-enhanced Suzuki cross-coupling reaction. This novel ligand and its palladium(II) dichloride complex have been fully characterised using elemental analysis, HR–ESI-MS, IR, UV and NMR spectroscopy. Additionally, the molecular structures of 3,5-diferrocenylpyridine and [Pd(3,5-diferrocenylpyridine)2Cl2] were confirmed by X-ray crystallography. A comprehensive study of the electrochemistry of 3-ferrocenylpyridine, 3,5-diferrocenylpyridine and their palladium(II) dichloride complexes was performed using traditional hexafluorophosphate and weakly-coordinating fluorinated aryl borate anions. Electronic communication between the two proximal ferrocenyl centres of 3,5-diferrocenylpyridine and its palladium complex is only observed when the weakly-coordinating fluorinated aryl borate anions are used as the supporting electrolyte.

Molecular Engineering Design to Resolve the Layering Habit and Polymorphism Problems in Deep UV NLO Crystals: New Structures in MM′Be2B2O6F (M═Na, M′═Ca; M═ K, M′═Ca, Sr)

A novel series of alkali and alkaline earth metal combined fluorine beryllium borates NaCaBe2B2O6F, KCaBe2B2O6F, and KSrBe2B2O6F were successfully synthesized through molecular engineering design and grown in crystals by spontaneous nucleation technique from self-flux systems. The idea, introduction of relatively small alkali and alkaline earth metal cations and the fluorine anion, successfully resulted in the novel UV NLO crystal NaCaBe2B2O6F, the following substitution of cations directed to two centrosymmetric compounds KCaBe2B2O6F and KSrBe2B2O6F. In all of their structures, the a–b plane is the infinite lattice layer (Be3B3O6F3)∞ made up of BO3 and BeO3F anionic groups, and for the first time, it was found that the adjacent layers are connected with fluorine bridge atoms to form (Be6B6O12F3)∞ double layers, instead of oxygen bridge atoms usually occurred in other oxides. This structural characteristic is greatly beneficial to improve the layering-growth habit and eliminate polymorphism of a crystal. ...