Fluoride Systems Research Articles

Glass formation in the fluoride system ZrF4-BiF3-BaF2

The glass formation in the system ZrF4-BiF3-BaF2 has been investigated in the composition range (75–30)ZrF4-(0–60)BiF3-(0–40)BaF2, mol %. The synthesis and thermal and optical properties of bismuth-barium-fluorozirconate glass were described. As was shown by the DSC (differential scanning calorimetry) method, at the BiF3 content of 20–35 mol %, glass with the highest stability against crystallization was formed. Further stabilization of the vitreous state can be attained using additives of alkali metals and trifluorides.

Polarons in Magnetoelectric Fluorides

The complex dielectric constant/ac electrical conductivity was investigated as a function of the frequency and temperature in four fluorides systems, K3Fe5F15, K3Fe2Cr3F15, (NH4)2FeF6, and Pb5Cr3F19. All studied fluorides systems undergo ferroelectric (or antiferroelectric) phase transition at higher temperatures, and ferromagnetic (or antiferromagnetic) transition at low temperatures. At lower temperatures, in all studied systems, the real part of the complex ac electric conductivity was found to follow the universal dielectric response σ′ ∝ ν s , being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that, at low temperatures, this mechanism governs the charge transport in all studied fluoride systems.

Growth of Self Organized Eutectic Fibers from LiF─Rare Earth Fluoride Systems

ABSTRACTEutectic fibers consisting of an ordered arrangement of LiF fibrils inside a LiREF4 matrix (RE = Y, Gd) can be grown with the micro-pulling-down method at sufficiently large pulling rate exceeding 120 mm/h. The distance between individual fibrils could be scaled down to 1 µm at 300 mm/h pulling. LiF-LiYF4 has stronger tendency to form facetted eutectic colonies than LiF-LiGdF4, explained by the larger entropy of melting of the former.

Spectroscopic fingerprints of valence and spin states in manganese oxides and fluorides

We performed a systematic study of soft X-ray absorption spectroscopy in various manganese oxides and fluorides. Both Mn L-edges and ligand (O and F) K-edges are presented and compared with each other. Despite the distinct crystal structure and covalent/ionic nature in different systems, the Mn-L spectra fingerprint the Mn valence and spin states through spectral lineshape and energy position consistently and evidently. The clear O- and F-K pre-edge features in our high resolution spectra enable a quantitative definition of the molecular orbital diagram with different Mn valence. In addition, while the binding energy difference of the O-1s core electrons leads to a small shift of the O-K leading edges between trivalent and quadrivalent manganese oxides, a significant edge shift, with an order of magnitude larger in energy, was found between divalent and trivalent compounds, which is attributed to the spin exchange stabilization of half-filled 3d system. This shift is much enhanced in the ionic fluoride system. This work provides the spectroscopic foundation for further studies of complicated Mn compounds.

Hydrothermal synthesis, phase evolution, and optical properties of Eu3+-doped KF–YF3 system materials

Abstract

A molecular receptor based on the 2,3,7,8,12,13,17,18-octaethyl-21,23-dimethylporphyrin for detection of fluoride ions: Synthesis, spectral and complexation properties

2,3,7,8,12,13,17,18-Octaethyl-21-methylporphyrin and 2,3,7,8,12,13,17,18-octaethyl-22,23-dimethylporphyrin monotriflate based on the former were synthesized. Basic and complexing properties of these compounds were studied by the method of spectrophotometric titration in acetonitrile-perchloric acid and acetonitrile-tetrabutylammonium fluoride systems at 298 K. It was established that in the system of acetonitrile-perchloric acid the cationic forms of 2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin do not form complexes with fluoride ions, whereas 2,3,7, 8,12,13,17,18-octaethyl-22,23-dimethylporphyrin monotriflate forms complexes of 1:1 composition with the fluoride ions. The protonation constant of 2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin and the stability constant of the complex of 2,3,7,8,12,13,17,18-octaethyl-22,23-dimethylporphyrin with fluoride ions in acetonitrile at the standard temperature were determined.

ChemInform Abstract: Spatial Inhomogeneity in Crystalline Materials and Saddle‐type Congruent Melting Points in Ternary Systems

AbstractReview: 104 refs.

The π-electron delocalization of phenol–fluoride system in explicit solvent conditions

The hybrid quantum chemical (QM/MM) model of the environment was used for characteristics of π-electron delocalization in aromatic ring of phenol–fluoride complex. The inductive effect of approaching fluoride on aromaticity of phenol was quantified by 27 aromaticity indices in the presence of explicit first hydration layer. Observed changes in aromaticity of the phenol aromatic ring cannot be described by a single aromaticity index and a vector of eight contributions was proved to be indispensible. The selection of these the most representative aromaticity measures was performed by means of Principal Component Analysis (PCA). It was demonstrated that significant and subtle role of explicit water molecules on extend of π-electron delocalization. The values of indices such as hardness (η), ATI, NICS(1) and DRE are sensitive to approaching fluoride and increase their values in polar conditions. On the other hand, such indices as BAC, Lagrangian form of kinetic energy density estimated at ring critical points and Shanon-like entropy are mostly dependent on the conformation of the first solvation layer and are less susceptible to the separation distance of fluoride. Thus, multidimensional nature of aromaticity is even more complex if direct intermolecular interactions are taken into account in water solutions.

X-ray photoelectron spectroscopy as detection tool for coordinated or uncoordinated fluorine atoms demonstrated on fluoride systems NaF, K2TaF7, K3TaF8, K2ZrF6, Na7Zr6F31 and K3ZrF7

While systems K3TaF8 and K3ZrF7 were prepared by modified molten salt method modified wet pathway was used for reproducible preparation of Na7Zr6F31. Its congruently melting character was demonstrated on simultaneous TG/DSC measurements and XRD patterns. X-ray photoelectron spectroscopy was applied for identification of differently bonded fluorine atoms in series of compounds NaF, K2TaF7, K3TaF8, K2ZrF6, Na7Zr6F31 and K3ZrF7. Three different types of fluorine atoms were described qualitatively and quantitatively. Uncoordinated fluorine atoms (F−) provide signals at lowest binding energies, followed by signals from terminally coordinated fluorine atoms (M–F) and then bridging fluorine atoms (M–F–M) at highest energy. Based on XPS F 1s signals assigned to fluorine atoms in compounds with correctly determined structure it was suggested that fluorine atoms in K3ZrF7 have partially bridging character.

Tb3+-Yb3+ cooperative down and up conversion processes in Tb0.81Ca0.19F2.81:Yb3+ single crystals

The energy transfer processes between Tb3+ and Yb3+ ions are studied in Tb-based fluoride single crystals. These are very transparent from the UV to the IR wavelength regions, except for the characteristic absorption lines of the rare-earth ions under study. In contrast with previously reported Tb3+-doped glasses and oxide powders, these crystals containing a high Tb3+ concentration present two major advantages for the study of the energy transfer processes in the Tb3+-Yb3+ ion pair. Firstly, the adverse influence of host defects is minimized with the use of high quality crystals. Secondly, the high Tb3+ concentration guarantees a much higher absorption cross-section of UV light, and consequently these crystals have real potential for practical applications. Photoluminescence spectra in the visible-IR wavelength region demonstrate the existence of efficient down and up conversion processes by crossed excitation and emission characteristics of Tb3+ and Yb3+ ions. In the down conversion process, Tb3+(5D4) → 2Yb3+(2F5/2), two IR photons are emitted for each Tb3+ ion deexcited by second-order energy transfer to two Yb3+ ions. The total quantum efficiency of the down conversion process in the fluoride system is shown to increase linearly with the Yb3+ concentration, reaching its maximum at the Yb3+ solubility limit in the fluoride host. Further, efficient up conversion by two- and three-IR photon absorption is observed.

DFT and Experimental Studies on the PtX2/X–-Catalyzed Olefin Hydroamination: Effect of Halogen, Amine Basicity, and Olefin on Activity, Regioselectivity, and Catalyst Deactivation

A DFT/B3LYP study with inclusion of solvent and temperature effects has probed the olefin activation mechanism for the intermolecular hydroamination of ethylene and 1-hexene by aniline derivatives catalyzed by the PtX2/X– system on the basis of a variety of experimental results, including new experiments on catalyst deactivation. For ethylene and aniline, the calculated ΔG‡cycle between the resting state [PtX3(C2H4)]−, 1X, and the TOF-determining transition state of the C–H reductive elimination from [PtX3(H)(CH2CH2NHPh)]−, TS2X, is slightly smaller for X = Br than for Cl or I. The ΔG‡cycle decreases as the aniline basicity decreases. For the slightly less efficient hydroamination of 1-hexene, ΔG‡cycle is greater than that for the hydroamination of ethylene, with a preference for the Markovnikov addition, in agreement with experiment and with essentially equivalent ΔG‡cycle values for the Br and I systems. In general, the results of the calculations are in agreement with the experimental observation. A clear-cut comparison of trends is hampered by the small energy differences and by the possibility, proven in certain cases, that the reaction parameters under investigation affect the catalyst degradation rate in addition to its intrinsic activity. Extrapolation of the computational study to the fluoride system suggests that this should be even more active. However, experimental studies show that this is not the case. The reason for this anomaly has been traced to the basicity of the fluoride ion, which triggers more rapid catalyst decomposition. A bonding analysis of 1X indicates a significant push–pull π interaction between the C2H4 and the trans-F ligand.

Partition of the Li,Cs‖F,Cl,Br quaternary mutual system into simplexes and investigation of the LiF-CsF-CsCl-CsBr tetrahedron

A quaternary mutual system of fluorides, chlorides, and bromides of lithium and cesium was partitioned into simplexes by a geometric method and by a graph method. Phase transformations and chemical reactions in the bordering ternary mutual systems were described. A conversion line was experimentally studied, and information on crystallizing phases within the composition prism of the Li,Cs‖F,Cl,Br system was obtained and confirmed by X-ray powder diffraction data. The characteristics of the minimum in the LiF-CsF-CsCl-CsBr tetrahedron were determined.

Polarons in low temperature phase of (NH4)3FeF6

The frequency and temperature dependence of the dielectric constant and the ac electrical conductivity in (NH4)3FeF6 was investigated. The temperature dependence of the dielectric constant reveals the phase transition from tetragonal to cubic phase at 270 K. At temperatures below 225 K, the ac conductivity and dielectric constant follow the universal dielectric response (UDR), being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 225 K this mechanism governs the charge transport in this fluoride system.

Tetrapyrrole cation receptor for selective binding fluoride ion

The 5,10,15,20-tetraphenyl-2,3,7,8,12,13,17,18,21,22,23,24-dodecamethylporphyrin ditriflate was synthesized and its complexing properties toward fluoride ion were investigated by spectrophotometric titration in the acetonitrile-tetrabutylammonium fluoride system. We found that at the complexation the two triflate counterions are replaced by the fluoride ions. The stability constants of the complexes and the concentration ranges of their existence were determined.

In situ remineralisation of eroded enamel lesions by NaF rinses

ObjectiveThe purpose of this pilot study was to evaluate the remineralisation of eroded enamel by NaF rinses in an intra-oral model. MethodsServing as their own control, subjects (N=80) participated in a randomised, four-leg (20 subjects/leg), 28-day, parallel design study. In each leg, each participant wore a customised orthodontic bracket attached to a mandibular molar that contained one tooth block having an initial erosive lesion (0.3% citric acid, pH 3.75, 2h). Within the 28-day period, participants engaged in twice-daily brushing for 1min with a fluoride-free dentifrice followed by 1-min rinsing with one of the following aqueous rinses: fluoride-free (0ppm F), 225ppm F, 225ppm F plus functionalised β-tricalcium phosphate (fTCP), and 450ppm F. Following intra-oral exposure, appliances were removed and specimens were analysed using surface microhardness (SMH) and transverse microradiography (TMR). ResultsStatistically significant (p<0.05) remineralisation, as determined by SMH and TMR, of the eroded enamel relative to baseline occurred for each fluoride system. No significant differences in SMH were observed amongst the fluoride groups (p>0.05), however, 225ppm plus fTCP produced 27% and 7% SMH indent length reduction relative to 225ppm F and 450ppm F, respectively. No significant differences in TMR were observed amongst the fluoride groups (p>0.05), however, 225ppm F plus fTCP and 450ppm F produced significant (p<0.05) mineral gains relative to the fluoride-free control, whilst 225ppm F did not (p>0.05). Relative to the 225ppm F group, the 450ppm F and 225ppm F plus fTCP groups produced 65% and 61% greater mineral change, respectively. ConclusionsThese pilot results demonstrate this model is sensitive to fluoride and that addition of fTCP to an aqueous rinse containing 225ppm F may provide significant remineralisation benefits. Therefore, the combination of relatively low levels of fluoride and fTCP might be an effective alternative to a high fluoride treatment for anti-erosion benefits.

Tailor‐Made MgF2‐Based Catalysts by Sol–Gel Synthesis

AbstractIn this paper, recent developments in the field of catalysts based on nanosized metal fluorides are presented with special focus on the exciting and promising magnesium fluoride systems. The majority of these new catalyst systems originate from the work of the authors based on the fluorolytic sol–gel synthesis of metal fluorides, which was developed by this group. They are selected in a way as to highlight the principles and prospects of this new approach to high‐surface‐area, strongly distorted metal fluorides. This new fluorolytic sol–gel route to metal fluorides opens, in the opinion of the authors, a very broad range of scientific and technical applications of the accessible high‐surface‐area metal fluorides. By combining fluorolytic and hydrolytic sol–gel synthesis, this approach can be further extended, also providing access to metal hydroxide fluorides or metal oxide fluorides. The different synthesis strategies as well as the catalytic applications of various MgF2‐based materials are described in detail in this review.

Formation of lithium fluoride/metal nanocomposites for energy storage through solid state reduction of metal fluorides

In order to utilize high energy metal fluoride electrode materials as direct replacement electrode materials for lithium ion batteries in the future, a methodology to prelithiate the cathode or anode must be developed. Herein, we introduce the use of a solid state Li 3N route to achieve the lithiation and mechanoreduction of metal fluoride based nanocomposites. The resulting prelithiation was found to be effective with the formation of xLiF:Me structures of very fine nanodimensions analogous to what is found by electrochemical lithiation. Physical and electrochemical properties of these nanocomposites for the bismuth and iron lithium fluoride systems are reported.

Alizarin complexone–lanthanide(III)–fluoride system: Revised speciation and the origin of the analytical signal

Potentiometric titrations of alizarin complexone (ALC) in the presence of La(III), Eu(III) and Y(III) in 50% vol. DMSO reveal formation of mostly binuclear complexes with monoprotonated (LH) and completely deprotonated (L) forms of the ligand of the type M 2L 2H 2, M 2L 2H and M 2L 2. Only for La(III) a single mononuclear complex LaLH is observed in acidic media. Titrations of the same mixtures with added fluoride show that with Eu(III) and Y(III), fluoride forms ternary complexes without shifting the distribution profile of complexes with differently protonated forms of bound ALC, but with La(III) a strong shift in distribution in favor of complexes with the deprotonated ligand occurs, which explains the appearance of blue colored species in acidic medium giving rise to the analytical signal employed for quantitative determination of fluoride. Detailed analysis of the spectral properties of La(III)–ALC–fluoride system on the basis of the established species distribution diagrams demonstrate the following factors to be involved: (1) fluoride-induced conversion of LaLH to La 2L 2HF around pH 3; (2) anomalously high affinity of La(III)–ALC complexes to fluoride and (3) some sort of mutual effect of fluoride and ALC ligands in ternary La(III) complexes, probably involving change in the metal coordination number, leading to enhanced absorptivity of La 2L 2HF as compared to La 2L 2H.

Thermal stability and crystallization behavior of TiO2 doped ZBLAN glasses

ZBLAN glasses with the composition (in mol%) of (100−x)(53 ZrF4+19 BaF2+5LaF3+3AlF3+20NaF)+xTiO2 (x=0, 1.0 and 2.0mol%) were prepared using a conventional melting technique in dry nitrogen atmosphere. The thermal stability, glass-forming ability, and crystallization kinetics of the ZBLAN system as a function of the TiO2 concentrations were investigated by Differential Scanning Calorimetry (DSC). Also, the crystalline phases were determined by X-ray Diffraction (XRD). Our study indicates that adding TiO2 in a fluoride system improves the thermal parameters of the glass, which is interesting for applications as optical fiber.

Partition of the Li,K‖F,Cl,Br quaternary reciprocal system into simplexes and investigation of components of the LiF-KCl-KBr stable triangle

A quaternary reciprocal system of fluorides, chlorides, and bromides of lithium and potassium was partitioned into simplexes by a geometric method and by a graph method. Phase transformations and chemical reactions in the boundary ternary reciprocal systems were described. A conversion line was experimentally studied, and information on crystallizing phases within the composition prism of the Li,K‖F,Cl,Br system was obtained and confirmed by X-ray powder diffraction data. An immiscibility region in the LiF-KCl-KBr stable triangle was outlined.