Fluoride Anion Research Articles

Glasses and Glass–Ceramics from Li2O-KF-TiO2-SiO2 System Doped with SiC

Unfamiliar invert host silicate glass from the system SiO2-TiO2-KF-Li2O was prepared together with SiC doped samples by traditional melt-quenching technique. Collective characterization of the prepared glasses through FTIR, optical, thermal and microhardness properties were measured to justify the effect of silicon carbide (SiC) on the resultant data. Silicon carbide is selected because its known high mechanical and thermal properties and extended applications of SiC- containing candidates in several domains. Structural FTIR characterization of the prepared glasses reveals familiar silicate network in spite of their invert percent together with the suggested sharing of Si-Ti or Ti-Ti or fluoride units. Optical spectra show only distinct UV absorption with additional small peaks at 380–420 nm in high percent of SiC. Such UV spectra are assumed to originate from unavoidable traces of ferric ions contaminated within the raw materials used for the preparation of glasses. The known high thermal and mechanical properties of silicon carbide are identified to be reflected on the measured thermal expansion and Vickers microhardness data. Samples from the parent glasses were thermally heated to produce their corresponding glass-ceramic derivatives. X-ray diffraction analysis indicate the formation of the peculiar orlovite crystalline phase as a major one due to the presence of all the constituents within the chemical composition of the invert glass. Also, some minor crystalline phases of lithium silicate or lithium titanium silicate are identified. It is assumed that the presence of self-nucleation Li2O and high negatively charged fluoride anions beside the conditional oxide of TiO2 facilitate the ease of nucleation and crystallization of the formed crystalline phase. SEM results confirm the x-ray data showing different crystalline features with the addition of SiC.

Where Are Sodium Ions in AOT Reverse Micelles? Fluoride Anion Probes Nanoconfined Ions by 19F Nuclear Magnetic Resonance Spectroscopy.

Confining water to nanosized spaces creates a unique environment that can change water's structural and dynamic properties. When ions are present in these nanoscopic spaces, the limited number of water molecules and short screening length can dramatically affect how ions are distributed compared to the homogeneous distribution assumed in bulk aqueous solution. Here, we demonstrate that the chemical shift observed in 19F NMR spectroscopy of fluoride anion, F-, probes the location of sodium ions, Na+, confined in reverse micelles prepared from AOT (sodium dioctyl sulfosuccinate) surfactants. Our measurements show that the nanoconfined environment of reverse micelles can lead to extremely high apparent ion concentrations and ionic strength, beyond the limit in bulk aqueous solutions. Most notably, the 19F NMR chemical shift trends we observe for F- in the reverse micelles indicate that the AOT sodium counterions remain at or near the interior interface between surfactant and water, thus providing the first experimental support for this hypothesis.

Tailoring basic and acidic properties of MgAl hydrotalcite by fluoride anions: Effect on glycerol oligomerisation

In this work, two families of catalysts based on mixed metal oxides derived from MgAl hydrotalcites were synthesized with a Mg/Al molar ratio of 3. On the one hand, in the first family, the fluoride anion was incorporated in the interlayer space by using ammonium fluoride, exploiting the “memory effect” characteristic of hydrotalcites. In the second family, fluoride anions substituted oxides anions in the layer, incorporating directly them during the precipitation of hydroxides, by using cryolite as a precursor for both fluorine and aluminium. The hydrotalcites were transformed into mixed metal oxides by thermal treatment and tested in the glycerol etherification reaction at 230 ºC, in a batch reactor at atmospheric pressure. The hydrotalcites and the corresponding mixed metal oxides were characterized by different experimental techniques, such as X-ray diffraction (XRD), elemental analysis (CHF), N2 sorption at − 196 ºC, thermogravimetric analysis (ATD-TG), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of CO2 and NH3 (CO2-TPD and NH3-DTP) and solid state nuclear magnetic resonace (ssNMR) of 19F. It was found that the mixed metal oxides prepared from hydrotalcites, where fluorine was incorporated in the synthesis step using cryolite, achieved the maximum conversion values and complete selectivity towards diglycerol. Diglycerols were the unique detected products and, in some cases, the formation of triglycerols was also detected.

Aluminabenzene-based Lewis superacids and weakly coordinating anions.

Quantum-chemical calculations were used to describe both the acidity of aluminabenzene-based Lewis acids and stability of aluminabenzene-based anions. Aluminabenzene itself was found to exhibit greater acidity than antimony pentaflouride, and thus can be qualified as a Lewis superacid. Substitution of the heterocyclic ring with electron withdrawing groups results in formation of extremely strong Lewis superacids. Two of them, namely AlC5 Cl5 and AlC5 (CN)5 are the strongest Lewis acids described in the literature so far. Whereas, anions formed after the addition of fluoride anion to substituted aluminabenzene-based Lewis acids, while characterized by somewhat lower electronic stability than the least coordinating anions hitherto known, are considerably more stable in terms of thermodynamic stability (measured by the propensity to electrophile attack). On this account they are expected to act as counterions for the most reactive cations. The proposed Lewis acids may be prone to the isomerization and dimerization, whereas studied anions are expected to be stable with regard to such processes.

Regeneration Analysis of Bone Char Used in Water Defluoridation: Chemical Desorption Route, Surface Chemistry Analysis and Modeling

High concentrations of fluoride (F−) in drinking water represent a public health threat, and consequently, effective and sustainable methods are required to improve the water quality, mainly in developing and low-income countries. This study focused on the thermodynamics of fluoride adsorption on bone char regenerated with NaOH for water defluoridation. A detailed analysis of the number of fluoride adsorption/desorption cycles, their impact on the performance and surface chemistry of bone char using different NaOH concentrations, and modeling of the adsorption mechanism using statistical physics theory was carried out. The results showed that 0.075 mol/L NaOH was effective in recuperating the defluoridation properties of bone char with a regeneration efficiency higher than 90% during five adsorption/desorption cycles. Bone char regeneration efficiency decreased up to 64% after ten adsorption/desorption cycles with a maximum fluoride adsorption capacity of 0.18 mmol/g. NaOH restored the bone char surface properties for ligand exchange of the fluoride anions via the hydroxyapatite functionalities contained in this adsorbent. It was calculated that around 0.25–0.46 mmol/g hydroxyapatite ligand exchange sites of regenerated bone char samples could be involved in the fluoride adsorption, which was also expected to be a mono-ligand mechanism. The reduction in defluoridation properties of bone char during the regeneration cycles was attributed to the decrease in the ligand exchange capacity as well as the deactivation and blocking of some functional groups of hydroxyapatite, which limited their participation in consecutive adsorption processes. This study contributes to the optimization of the recycling and reuse of bone char for fluoride removal from water to reduce the operating defluoridation costs, thus enhancing the application of this technology in low-income areas where fluorinated water represents a threat to public health.

Caesium manganese fluoride cubic-perovskite nanoparticles – synthesis, luminescence and magnetic properties

Lead halide perovskite materials have outstanding optical properties such as color purity and efficient fluorescence in the visible spectrum. However, the toxicity of lead makes the synthesis, processing, use and disposal of such materials hazardous for humans and the environment. Therefore, the exploration of different perovskite materials containing the transition metal Mn(II) and fluoride anions might lead to more appealing alternatives towards more sustainable and environmentally friendly functional materials. Nanocrystals primarily consisting of cubic CsMnF3 – a polymorph so far only reported at pressures of 3 × 104 bar – were synthesized from manganese(II) acetate and caesium fluoride precursors using a heating-up approach in high boiling organic solvents. The concentration of defects could be tuned by changing the amount of fluorinating precursor CsF, with more defects produced when an excess of CsF was used in the synthesis. The structure, morphology, optical and magnetic properties of the product nanoparticles were studied. Due to their X-ray sensitized fluorescence, likely caused by defects in the crystal structure, these materials are promising for potential applications in dosimetry.Graphical CsMnF3 nanocrystals were synthesized by a heating-up method using stoichiometric or excess quantities of the fluoride precursor CsF to control the concentration of defects (CMF and CMF-d). The obtained nanoparticles exhibited X-ray sensitized luminescence, enhanced by a factor of up to 3.75 after irradiation with X-rays for 2 h.

Room-Temperature Synthesis of Zeolite Membranes toward Optimized Microstructure and Enhanced Butane Isomer Separation Performance.

Room temperature (RT) synthesis of high-performance zeolite membranes, which is profound from techno-economic and eco-friendly perspectives, remains a grand challenge. In this work, we pioneered the RT preparation of well-intergrown pure-silica MFI zeolite (Si-MFI) membranes, which was realized through adopting highly reactive NH4F-mediated gel as nutrient during epitaxial growth. Benefiting from the introduction of fluoride anions as mineralizing agent as well as precisely tuned nucleation and growth kinetics at RT, both their grain boundary structure and thickness could be deliberately controlled, resulting in the formation of Si-MFI membranes showing unprecedented n-/i-butane separation factor (96.7) and n-butane permeance (5.16 × 10-7 mol m-2 s-1 Pa-1) in the case of a feed molar ratio of 10/90, which well transcended the state-of-the-art membranes reported in the literature. This RT synthetic protocol was also proven effective for preparing highly b-oriented Si-MFI film, thus showing great promise for the preparation of diverse zeolite membranes with optimized microstructure and superior performance.

Accelerated Crystallization of LTA Zeolite Using a Combination of High-Silica FAU Zeolite with Low Crystallinity and Additional Al Sources

Synthesis methods and crystallization mechanisms of LTA zeolites have been studied by various approaches such as using alkali metal hydroxides, organic structure-directing agent cations, or fluoride anions, so that the understanding of the crystallization pathway is one of particular interest. As a fundamental research, we succeeded in synthesizing a highly crystalline LTA zeolite by combining dealuminated FAU with low crystallinity and an additional aluminum source (Al(OH)3). The crystallization rate of the LTA zeolite was higher than that from conventional colloidal silica (Ludox HS-40) and Al(OH)3. In addition, there was a large difference in the particle size distribution of the as-made LTA zeolites. Furthermore, when using dealuminated FAU and Al(OH)3, Al-rich aluminosilicate species with four-ring structures were observed in the initial induction period, after which the gradual incorporation of TMA+ cations into sod cages of the LTA zeolite was found. Based on the obtained results, a crystallization scheme for LTA zeolites synthesized using zeolitic sources of dealuminated FAU as starting materials is proposed, which deepens the understanding of the crystallization pathway of LTA zeolite.

Photo- And Ionochromic Diarylethenes with Receptor Fragments in The Thiazole Bridge

Diarylethenes containing coumarin and thiophene substituents in the thiazole bridge and quinoline receptor fragments were synthesized. 2-Chloroquinoline diarylethenes form colored cyclic hexadiene forms under UV light, which undergo reverse isomerization when exposed to visible light. 2-Hydroxyquinoline diarylethenes are nonphotochromic. The ionochromic effects of interaction with fluoride anions and copper(II) and nickel(II) cations were studied.

Tuning Emission Color and Efficiency of 1,2,5-Triaryl-3,4-cycloalka[c]arsoles

Abstract A variety of 1,2,5-triaryl-3,4-cycloalka[c]arsoles were synthesized in this study to control emission color and efficiency. The torsion between the arsole center and the aryl groups at the 2,5-positions was dependent on the size of the fused cycloalkane, resulting in different absorption maxima. In addition, structural relaxation was affected by the fused cycloalkane, which changed the emission color and efficiency. Notably, the cyclopentane-fused arsole showed aggregation-caused quenching (ACQ) in the solid state, while cyclohexane and cycloheptane offered aggregation-induced emission enhancement (AIEE). This trend was also seen in heterocycle-fused arsoles; five- and six-membered rings offered ACQ and AIEE, respectively. The p-(dimethylamino)phenyl and p-(dimesitylboryl)phenyl groups at the 2,5-positions exhibited red-shifted emission owing to the charge transfer character, and they could detect ions such as protons and fluoride anions, respectively.

Defluorinative Transformation of (2,2,2-Trifluoroethyl)arenes Catalyzed by the Phosphazene Baset-Bu-P2

In this study, we demonstrated that 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene) (t-Bu-P2) catalyzes the defluorinative functionalization reactions of (2,2,2-trifluoroethyl)arenes with alkanenitriles to produce monofluoroalkene products. The reaction proceeds through HF elimination from a (2,2,2-trifluoroethyl)arene to form a gem-difluorostyrene intermediate, which is followed by nucleophilic addition of an alkanenitrile and elimination of a fluoride anion. The catalysis is compatible with a variety of functional groups.

The selective turn-on recognition of fluoride ions using 5-aryl-rhodanines: Colorimetric & fluorescent detection

The main goal of this study is to obtain 5-Ar-Rhs by Knoevenagel condensation without using any catalyst as an ion-sensing organic ligand and investigate their sensing abilities. The 5-Ar-Rhs were obtained as the main product from the no-catalyst reactions carried out at high temperatures. Following synthesis, the anion-sensing properties of 5-Ar-Rhs were studied using colorimetric detection, and spectroscopic methods. The results showed that the 5-Ar-Rhs is only selective for F¯¯ion in the presence of different ions. The binding ratios of 5-Ar-Rhs to F¯ were found to be 1:1 according to Job's plot experiments. The binding constant of 3A and 3B were calculated and found to be 7.05 × 105 M−1 and 1.45 × 104 M−1 for F¯, respectively. The LOD values of 3A and 3B were calculated and found to be 22.4 µM and 27.3 µM, respectively. In addition, theoretical studies by DFT methods were also carried out to optimize the structure and explained the fluoride anion binding mechanism of 5-Ar-Rhs 3A and 3B. As a result, temperature and solvent-controlled Knoevenagel condensation reactions of the 3-NH2-Rh (1), which has a reactive amino group, were examined. Additionally, we can understand that 3A and 3B are good selective candidate sensors that can be used for fluoride detection from sensing studies.

Origin of Vanadium Site Sequential Oxidation in KxVPO4F1–yOy

M-ion batteries (M = Li, Na, K ...) positive electrode materials most often operate through the reversible oxidation of transition-metal ions. In complex materials involving many transition metals or many redox centers, understanding the sequence in which they participate to the reaction is not trivial but is often necessary to explain the electrochemical properties. Mixed anion vanadium phosphates, such as KVPO4F0.5O0.5, are known to contain two different redox entities that are V3+O4F2 and V3+O5F “ionic” entities on the one hand and {V4+═O}O5 and {V4+═O}O4F “covalent” vanadyl-type units on the other hand. However, their participation to the redox mechanism occurring during the charge of this material has never been studied. Here, we use V K-edge X-ray absorption spectroscopy to unveil the redox mechanism of KVPO4F1–yOy (y = 0, 0.5, 1), performing data analysis via a chemometric approach. With XAS being very sensitive to the oxidation state and bond length, it was found that the ionic V3+–F units oxidize at a lower potential than the covalent {V4+═O} ones, which is surprising considering the high electronegativity of fluoride anions but is consistent with the redox potential observed for KVPO4F and KVOPO4. Further, ab initio calculations and ex situ X-ray diffraction analyses allowed an atomistic description of the redox mechanism with the sequential oxidation of the cis V site before the trans V site in KVPO4F upon charge. Finally, the complete atomically resolved redox mechanism of KVPO4F0.5O0.5 is proposed.

Gold nanoshells with magnetic cores and a urea-based receptor for SERS sensing of fluoride anions: experimental and computational study.

The study demonstrates that a combination of plasmonic nanostructures and artificial receptors can be applied for sensing small molecular species. Gold nanoshells containing magnetic cores are used as the SERS-active substrates, which opens the way for the development of multimodal contrast agents with applicability extended to sensing or for the separation of analytes by magnetic solid-phase extraction. Disubstituted ureas forming hydrogen-bonded complexes with certain anions can be employed as molecular sensors. In this case study, gold nanoshells with silica-coated Mn-Zn ferrite cores were prepared by a multistep procedure. The nanoshells were co-functionalized with an N-(4-mercaptophenyl)-N'-(4-nitrophenyl)urea sensor synthesized directly on the gold surface, and with 4-nitrothiophenol, which is adopted as an internal standard. SERS measurements were carried out with acetonitrile solutions of tetrabutylammonium fluoride (Bu4NF) over a concentration range of 10-10-10-1 mol L-1. The spectral response of the sensor is dependent on the fluoride concentration in the range of 10-5-10-1 mol L-1. To investigate further the SERS mechanism, a model sensor, N-(4-bromophenyl)-N'-(4-nitrophenyl)urea, was synthesized and used in Raman spectroscopy with solutions of Bu4NF, up to a molar ratio of 1 : 20. The spectra and the interactions between the sensors and fluoride anions were also studied by extensive DFT computations.

Tailoring Basic and Acidic Properties of Mgal Hydrotalcite by Fluoride Anions: Effect on Glycerol Oligomerisation

Tailoring Basic and Acidic Properties of Mgal Hydrotalcite by Fluoride Anions: Effect on Glycerol Oligomerisation

Anion-assisted supramolecular polymerization of luminescent organic π-conjugated chromophores in a moderately polar solvent: tunable nanostructures and their corresponding effects on electronic properties.

Supramolecular polymers of π-conjugated organic chromophores have emerged as promising candidates in organic electronics because of their dynamic and highly ordered molecular organization. Herein, we demonstrate the formation of luminescent, highly conducting supramolecular polymers of a functionalized naphthalimide π-chromophore-based organic semiconductor in a moderately polar organic solvent (tetrahydrofuran) by overcoming solute-solvent H-bonding via assistance from fluoride anions. The polymerization is exclusively guided by the synergistic effects of cascade H-bonding (F-⋯H-N- of primary amines, followed by -CO⋯H-N- of amides), π-π stacking and hydrophobic interactions. An increasing molar equivalent of anions leads to a morphology transition from 1D nanowires to 2D nanosheets via nanotubes and nanorings, but above a particular threshold of the same anion, depolymerization-mediated disruption of long-range order and formation of non-luminescent spherical particles was observed. Such significant impacts of anions in supramolecular polymerization-depolymerization were utilized in modulating the electronic properties of this naphthalimide-based organic semiconductor.

Transmembrane fluoride anion transport by meso-3,5-bis(trifluoromethyl)phenyl picket calix[4]pyrrole.

Meso-3,5-bis(trifluoromethyl)phenyl picket calix[4]pyrrole 1 displays excellent fluoride anion transport activity across artificial lipid bilayers showing EC50 = 2.15 μM (at 450 s in EYPC vesicle) with high fluoride over chloride ion selectivity. The high fluoride selectivity of 1 was ascribed to the formation of a sandwich type π-anion-π interaction complex.

Shining light on fluoride detection: a comprehensive study exploring the potential of coumarin precursors as selective turn-on fluorescent chemosensors.

In this study, we report a fluoride chemosensor based on the use of a non-fluorescent pre-coumarin, compound 1. This compound undergoes selective fluoride-triggered formation of coumarin 2, with a concomitant turn-on fluorescence signal. Although compound 1 exists as a mixture of alkene isomers (2 : 1 in favor of the E isomer), only the minor Z-isomer undergoes cyclization. Nonetheless, comprehensive computational and experimental studies provide evidence that in situ isomerization of E-1 to Z-1, followed by fluoride-triggered phenolate evolution and intramolecular cyclization, facilitates the generation of coumarin 2 in high yield. Moreover, this system is an effective turn-on fluorescence sensor for fluoride anions, which displays outstanding selectivity (limited response to other commonly occurring analytes), sensitivity (lowest reported limits of detection for this sensor class), and practicality (works in solution and on paper to generate both fluorometric and colorimetric responses). Ongoing efforts are focused on expanding this paradigm to other pre-coumarin scaffolds, which also undergo analyte-specific coumarin formation accompanied by turn-on fluorescence.

Genuine quadruple bonds between two main-group atoms. Chemical bonding in AeF- (Ae = Be-Ba) and isoelectronic EF (E = B-Tl) and the particular role of d orbitals in covalent interactions of heavier alkaline-earth atoms.

Quantum chemical calculations of anions AeF- (Ae = Be-Ba) and isoelectronic group-13 molecules EF (E = B-Tl) have been carried out using ab initio methods at the CCSD(T)/def2-TZVPP level and density functional theory employing BP86 various basis sets. The equilibrium distances, bond dissociation energies and vibrational frequencies are reported. The alkali earth fluoride anions AeF- exhibit strong bonds between the closed-shell species Ae and F- with bond dissociation energies between 68.8 kcal mol-1 for MgF- and 87.5 kcal mol-1 for BeF- and they show an unusual increasing trend MgF- < CaF- < SrF- < BaF-. This is in contrast to the isoelectronic group-13 fluorides EF where the BDE continuously decreases from BF to TlF. The calculated dipole moments of AeF- are very large between 5.97 D for BeF- and 1.78 D for BaF- with the negative end always at the Ae atom (Ae→F-). This is explained by the location of the electronic charge of the lone pair at Ae, which is rather distant from the nucleus. The analysis of the electronic structure of AeF- suggests significant charge donation Ae←F- into the vacant valence orbitals of Ae. A bonding analysis with the EDA-NOCV method suggests that the molecules are mainly covalently bonded. The strongest orbital interaction in the anions comes from the inductive polarization of the 2pσ electrons of F-, which leads to a hybridization of the (n)s and (n)pσ AOs at Ae. There are two degenerate π donor interactions Ae←F- in all anions AeF-, which provide 25-30% to the covalent bonding. There is another σ orbital interaction in the anions, which is very weak in BeF- and MgF-. In contrast, the second stabilizing σ orbital interaction in CaF-, SrF- and BaF- yields a strongly stabilizing σ orbital, because the Ae atoms use their (n - 1)dσ AOs for bonding. The energy lowering of the second σ interaction in the latter anions is even stronger than the π bonding. The EDA-NOCV results suggest that BeF- and MgF- have three strongly polarized bonds, whereas CaF-, SrF- and BaF- have four bonding orbitals. The quadruple bonds in the heavier alkaline earth species are made possible because they use s/d valence orbitals like transition metals for covalent bonding. The EDA-NOCV analysis of the group-13 fluorides EF gives a conventional picture with one very strong σ bond and two rather weak π interactions.

Solid-state mechanochemical cross-coupling of insoluble substrates into insoluble products by removable solubilizing silyl groups: uniform synthesis of nonsubstituted linear oligothiophenes.

Conventional solution-based organic reactions that involve insoluble substrates are challenging and inefficient. Furthermore, even if the reaction is successful, the corresponding products are insoluble in most cases, making their isolation and subsequent transformations difficult. Hence, the conversion of insoluble compounds into insoluble products remains a challenge in practical synthetic chemistry. In this study, we showcase a potential solution to address these solubility issues by combining a mechanochemical cross-coupling approach with removable solubilizing silyl groups. Our strategy involves solid-state Suzuki-Miyaura cross-coupling reactions between organoboron nucleophiles bearing a silyl group with long alkyl chains and insoluble polyaromatic halides. The silyl group on the nucleophile can act as a solubilizing group that enables product isolation via silica gel column chromatography and can be easily removed by the addition of fluoride anions to form the desired insoluble coupling products with sufficient purity. Furthermore, we demonstrate that after aromatic electrophilic bromination of the desilylated products, sequential solid-state cross-coupling of the obtained insoluble brominated substrates, followed by desilylation, afforded further π-extended functional molecules. Using this conceptually new protocol, we achieved the first uniform synthesis of the longest nonsubstituted linear insoluble 9-mer oligothiophene.