Fluoride Anion Research Articles

Isatin as a simple, highly selective and sensitive colorimetric sensor for fluoride anion

AbstractHerein, we report the fluoride anion sensing properties of a commercially available and inexpensive organic compound, isatin, which is found to be a highly selective and sensitive sensor. In naked-eye experiments, by addition of fluoride anions, isatin shows a dramatic color change from pale yellow to violet at room temperature, while the addition of other anions,i.e.Cl−,$\mathrm{Cl}^-,$Br−,I−,ClO4−,H2PO4−andPF6−,$\mathrm{Br}^-,\mathrm I^-,\mathrm{ClO}_4^-,{\mathrm H}_2\mathrm{PO}_4^-\,\mathrm{and}\,\mathrm{PF}_6^-,$did not induce any colour change. Additionally, recognition and titration studies have also been done through UV/Vis spectroscopy. Isatin displayed a new absorption band at 533 nm after the addition of fluoride anions, which is presumably due to acid-base interaction between isatin and fluoride anions, while other anions did not trigger noticeable spectral changes. The detection limit was observed to be 0.367 ppm. DFT calculations were also performed to further explain the behavior of receptor 1 towards the Fˉ anion. Owing to high sensitivity and selectivity, isatin can be useful in the detection of biologically or environmentally important fluoride anions at very low concentration.

Periodic Tendril Perversion and Helices in the AMoO2F3 (A = K, Rb, NH4, Tl) Family.

Although compounds of the formula AMoO2F3 (A = K, Rb, Cs, NH4, Tl) have been known for decades, crystal structures have only been reported for CsMoO2F3 and NH4MoO2F3. The three compounds (Rb/NH4/Tl)MoO2F3 are isostructural and crystallize in the centrosymmetric space group C2/c (No. 15). The compounds contain the MoO2F3- anionic chain, composed of corner-sharing MoO2F4 octahedra, with Mo6+ coordinated by two cis bridging fluoride anions that are trans to terminal oxide anions. The MoO2F3- chain has a very unusual and complex chain structure; a single chain contains alternating zigzag and helical sections. These helical regions alternate in chirality along the chain, and thus the chains exhibit periodic tendril perversion. To the best of the authors' knowledge, no other materials with a similar chain structure have been reported. On the other hand, KMoO2F3 is noncentrosymmetric and chiral, crystallizing in the enantiomorphic space group P212121 (No. 19). KMoO2F3 also contains the MoO2F3- anionic chain. However, the chain is helical, with only one enantiomer present, resulting in a chiral, noncentrosymmetric structure.

Removal of F− from Water Using Templated Mesoporous Carbon Modified with Hydrated Zirconium Oxide

Three types of MgO-templated mesoporous carbon possessing different specific surface area and pore size distribution were modified with hydrated zirconium oxide (ZrO2·xH2O) to prepare fluoride anion (F−) adsorbents. ZrO2·xH2O was synthesized through the auto-hydrolysis of zirconium oxychloride (ZrOCl2) in water under the coexistence of mesoporous carbon. X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS) indicated that the mesoporous carbon surfaces were coated with mainly amorphous ZrO2·xH2O. Capabilities of aqueous F− removal of the prepared adsorbents and the unmodified mesoporous carbons were compared. The F− uptake by the prepared adsorbents was larger than that observed using unmodified carbons, indicating that the F− adsorption capacity was improved through the ZrO2·xH2O coating. Moreover, the adsorption capability was found to depend on the pore size of the mesoporous carbons. The F− uptake decreased as pH of F− solution increased. Protonation and deprotonation of ZrO2 were found to affect the F− adsorption.

Self-Assembly of Multinuclear Sandwich Silver(I) Complexes by Cooperation of Hexakis(azaheteroaryl)benzene Ligands, Argentophilic Interactions, and Fluoride Inclusion.

Self-assembly of AgOTf and AgF with the hexatopic ligands hexakis(pyridin-2-yl)benzene (2) and 2,4,6-tris(pyridin-2-yl)-1,3,5-tris(quinolin-2-yl)benzene (3) affords the discrete sandwich-shaped complexes [Ag4F(2)2](OTf)3, [Ag4F(3)2](OTf)3, and [Ag5F(2)2](OTf)4. The solid-state structures of the complexes were characterized by single-crystal X-ray diffraction analysis, which revealed that the fluoride anion is coordinated in the center of the Ag4-square or Ag5-pentagon units which are positioned between two molecules of the hexakis(azaheteroaryl)benzene. The generation of complexes is dictated by a unique cooperation of ligand coordination, argentophilicity, and fluoride anion inclusion. All three complexes adopt highly symmetrical structures in solution, as evidenced by appearance of one set of proton resonances for the two ligands arranged face to face.

Topochemical anion insertion into one-dimensional Bi channels in Bi2PdO4

We show anion intercalation reaction to ternary palladate Bi2PdO4 (P4/ncc) with one-dimensional (1D) channels comprised of Bi3+ ions. By low-temperature treatment with XeF2, fluoride anions are inserted in the 1D pores (4b site), giving Bi2PdO4Fx (x ​< ​0.5) where only Pd2+ cations are oxidized. This F– insertion causes anisotropic lattice evolution with expansion on the ab plane and contraction along the c axis, and thus 1D pore flexibly changes the size depending on the F– density. The 1D channels are also able to capture O2− anions to form Bi2PdO4+δ (δ ​~ ​0.1) when heated under an O3 gas flow.

A near-infrared fluorescent probe for selective detection of fluorion

Abstract In this work, we have designed and synthesized the fluorescent probe 1, which was capable to selectively detect fluoride anion (F−). More importantly, the probe 1 possessed near-infrared excitation and emission wavelengths (excitation at 650 nm and emission at 695), and the probe solution had changed dramatically from yellow to cyan with the addition of F–. In addition, the fluorescence intensity exhibited perfectly positive correlation with concentration of F− concentration from 0 to 40 μM (R2 = 0.9972), which offered the important condition for quantitative analysis. The probe 1 owned detection limit of 46 nM. Therefore, this near-infrared probe can be of great benefit for detecting F− in practical application.

Understanding the conversion mechanism and performance of monodisperse FeF2 nanocrystal cathodes.

The application of transition metal fluorides as energy-dense cathode materials for lithium ion batteries has been hindered by inadequate understanding of their electrochemical capabilities and limitations. Here, we present an ideal system for mechanistic study through the colloidal synthesis of single-crystalline, monodisperse iron(II) fluoride nanorods. Near theoretical capacity (570 mA h g-1) and extraordinary cycling stability (>90% capacity retention after 50 cycles at C/20) is achieved solely through the use of an ionic liquid electrolyte (1 m LiFSI/Pyr1,3FSI), which forms a stable solid electrolyte interphase and prevents the fusing of particles. This stability extends over 200 cycles at much higher rates (C/2) and temperatures (50 °C). High-resolution analytical transmission electron microscopy reveals intricate morphological features, lattice orientation relationships and oxidation state changes that comprehensively describe the conversion mechanism. Phase evolution, diffusion kinetics and cell failure are critically influenced by surface-specific reactions. The reversibility of the conversion reaction is governed by topotactic cation diffusion through an invariant lattice of fluoride anions and the nucleation of metallic particles on semicoherent interfaces. This new understanding is used to showcase the inherently high discharge rate capability of FeF2.

Phosphonium Boranes for the Selective Transport of Fluoride Anions across Artificial Phospholipid Membranes.

With the view of developing selective transmembrane anion transporters, a series of phosphonium boranes of general formula [p-RPh2 P(C6 H4 )BMes2 ]+ have been synthesized and evaluated. The results demonstrate that variation of the R group appended to the phosphorus atom informs the lipophilicity of these compounds, their Lewis acidity, as well as their transport activity. Anion transport experiments in POPC-based large unilamellar vesicles show that these main-group cations are highly selective for the fluoride anion, which is transported more than 20 times faster than the chloride anion. Finally, this work shows that the anion transport properties of these compounds are extremely sensitive to the steric crowding about the boron atom, pointing to the crucial involvement of the Group 13 element as the anion binding site.

Phosphonium Boranes for the Selective Transport of Fluoride Anions across Artificial Phospholipid Membranes

AbstractWith the view of developing selective transmembrane anion transporters, a series of phosphonium boranes of general formula [p‐RPh2P(C6H4)BMes2]+ have been synthesized and evaluated. The results demonstrate that variation of the R group appended to the phosphorus atom informs the lipophilicity of these compounds, their Lewis acidity, as well as their transport activity. Anion transport experiments in POPC‐based large unilamellar vesicles show that these main‐group cations are highly selective for the fluoride anion, which is transported more than 20 times faster than the chloride anion. Finally, this work shows that the anion transport properties of these compounds are extremely sensitive to the steric crowding about the boron atom, pointing to the crucial involvement of the Group 13 element as the anion binding site.

TBAF‐Catalyzed Cyclization Reactions of o‐(Alkynyl)phenyl Propargyl Alcohols with Malonate Esters: A Possible Cation–π Interaction as The Activation Approach

An efficient method has been devised for the synthesis of dihydroisobenzofuran derivatives through the reaction of in situ generated ynones with potentially C‐nucleophilic malonate esters. All the products are capable to be prepared by applying the tandem strategy at room temperature. The reaction was realized through a combination of the pivotal TBAF‐catalyzed conjugate addition and selective O‐nucleophilic cyclization. As revealed by the control experiments, both the basicity of fluoride anion and ammonium cation–π interaction with alkyne unit might play crucial roles in the cyclization reaction.

Synthesis and Luminescence and Ionochromic Properties of 9-Hydroxy-1-methyl-3-oxo-3H-benzo[f]chromene8-carbaldehyde Imines and Hydrazones

Formylation of 9-hydroxy-1-methyl-3H-benzo[f]chromen-3-one with hexamethylenetetramine in acetic acid afforded 9-hydroxy-1-methyl-3-oxo-3H-benzo[f]chromene-8-carbaldehyde which was converted to the corresponding aldehyde imines and aroylhydrazones. According to the 1H NMR and UV spectral data, 9-hydroxy-1-methyl-3-oxo-3H-benzo[f]chromene-8-carbaldehyde imines in solution exist as ketone tautomers, whereas its aroylhydrazones have enol structure. 9-Hydroxy-1-methyl-3-oxo-3H-benzo[f]chromene-8-carbaldehyde aroylhydrazones are multifunctional ionochromic compounds capable of forming colored complexes with d metal cations, as well as with fluoride, cyanide, and acetate anions. The complexation leads to switching of the absorption and fluorescence properties of the initial compounds. Metal cations cause naked-eye visible change of the solution color from colorless to bright orange and fluorescence quenching, whereas in the presence of anions the color changes to red in combination with a red shift and increase in the emission intensity.

Low cost, high sensitivity detection of waterborne Al3+ cations and F− anions via the fluorescence response of a morin derivative dye

Morin dye is known as a cheap and readily available selective ‘off → on’ fluorescent sensitiser when immobilised in a phase transfer membrane for the detection of Al3+ ions. Here, a morin derivative, NaMSA, which readily dissolves in water with good long-term stability is used in conjunction with a fibre optic transducer with lock-in detection to detect Al3+ in drinking water below the potability limit. The combination of a water soluble dye and the fibre optic transducer require neither membrane preparation nor a fluorescence spectrometer yet still display a high figure-of- merit. The known ability to recover morin-based Al3+ cation sensors selectively by exposure to fluoride (F−) anions is further developed enabling a complementary sensing of either fluoride anions, or aluminium cations, using the same dye with a sub-micromolar limit-of-detection for both ions. The sensor performance parameters compare favourably to prior reports on both aqueous aluminium and fluoride ion sensing.

Hydrogen bonding interactions induced excited state proton transfer and fluoride anion sensing mechanism for 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐5‐carboxylicacid

AbstractThe present work explores and reports photo‐induced behavior and excited state intramolecular proton transfer (ESIPT) process for the novel 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐5‐carboxylicacid (DICH) compound. Our theoretical investigation implies that two intramolecular hydrogen bonds (O1─H2···N3 or O4─H5···O6) of DICH form are strengthening in the first excited state by comparing bond lengths, bond angles, and infrared (IR) spectra, which may facilitate the ESIPT process effectively. Particularly, the changes of O1─H2···N3 are bigger than O4─H5···O6, which demonstrates that the ESIPT is more likely to happen along with O1─H2···N3. Within the framework of MOs analysis, intramolecular charge transfer phenomenon can be found, which could be a reasonable evidence for confirming the occurrence of the ESPT process in the S1 state. We theoretically construct the potential energy curves for DICH system based on fixing both O1─H2 and O4─H5 bond lengths and optimizing structures in both S0 and S1 states. Through the comparisons of potential barriers among stable configurations, we confirm the S1‐state DICH‐PT1 (proton‐transfer tautomer along with O1─H2···N3) should be the most reasonable configuration ascribed to previous experimental emission peak. Furthermore, we also predict and explain the fluoride‐sensing mechanism for DICH system that the deprotonation reaction bringing from fluoride anion inhibits the initial ESIPT process of DICH, which results in the novel changes of ultraviolet‐visible (UV‐Vis) spectra that plays the roles in fluorescence response. We sincerely hope this work could provide essential insights into the design and function of ESIPT as well as florescence sensor for optoelectronic applications.

Layered Rare-Earth Hydroxide Unilameller Nanosheets: Synthesis, Characterization, and Adsorption

Unilameller nanosheets with a lateral dimension of one nanometer have been isolated from a colloidal solution of europium-containing layered rare-earth hydroxide (LRH) material by the flocculation method. The nanosheets were achieved by changing pH of the colloidal solution from 6.7 to 11.5. The resultant flocculated nanosheets show high efficiency in sorption of fluoride anions from aqueous media (40 mmol/g), providing a potentially useful sorbent material for water purification technology. The sorbent material is demonstrated to be reusable for at least ten times without a significant loss of adsorption efficiency. And the results fit the Langmuir adsorption curve, indicating the chemisorption nature of the nanosheets. Most importantly, the isolated nanosheets are expected to widen the applicability and flexibility in material synthesis using two-dimensional nanomaterials.

Cleft‐Induced Ditopic Binding of Spherical Halides with a Hexaurea Receptor

AbstractA tripodal‐based hexaurea receptor with two clefts (inner cleft and outer cleft) has been studied for spherical halides by 1H NMR, UV‐Vis titrations, and theoretical calculations using density functional theory (DFT). As demonstrated from experimental and computational results, the receptor exhibits cleft‐induced binding for halides in a 1 : 2 binding mode, showing the binding strength in the order of fluoride &gt; chloride &gt; bromide &gt; iodide. The strongest affinity for fluoride is attributed due to the best fit of two fluoride anions at the two clefts within the host‘s cavity. This is also supported by DFT calculations, suggesting that each anion is stabilized by six NH⋅⋅⋅F bonds ‐ one at the inner cleft and other at the outer cleft. In addition, the synthesized receptor, as examined on HeLa cells, has been found to show good biocompatibility.

A naked-eye visible colorimetric and fluorescent chemosensor for rapid detection of fluoride anions: Implication for toxic fluorine-containing pesticides detection

A dual-modal colorimetric and fluorescent probe based on 1,8-naphthalimide, 4-(2,2-dichloroacetamide)-N-n-butyl-naphthalimide (CNA), has been designed and synthesized for the detection of fluoride anion (F−) in CH3CN. CNA exhibited highly sensitivity and selectivity for F− over the other anions, such as Cl−, Br−, I−, NO3−, ClO4−, HSO4−, NO2− and SCN−. The evident colorless to yellow color change of the solution of CNA was observed with the naked eyes only in the presence of F− among the other anions, together with drastically fluorescence quenched. The Job's plot analysis revealed that the binding between the CNA with F− was in 1:1 stoichiometry. The detection limits of the CNA for F− from fluorescence and ratiometric absorption spectra were 0.52, 1.41 μM, respectively. The 1H NMR titration indicated that F− induced the deprotonation of the CNA through hydrogen bonding interaction between amino group of the CNA and F−. Based on this detection system, an IMPLICATION logic gate could be constructed. Furthermore, it could be successfully employed as a selective fluoride anion probe to the fluorescence detection of fluorine containing pesticides (oxyfluorfen).

Potassium Fluoride‐Catalyzed Hydroboration of Aldehydes and Ketones: Facile Reduction to Primary and Secondary Alcohols

A catalytic hydroboration of various ketones and aldehydes can be achieved in the presence of inexpensive and commercially available inorganic salts containing fluoride anion. As a result, the reduction of carbonyl moieties to the corresponding primary and secondary alcohols can be achieved at room temperature under mild conditions.

4-Functionalized terpyridine derivative as dual responsive chemosensor for biologically important inorganic cations and fluoride anion

A dual responsive sensor molecule, 2-(4-(2,2′:6′,2″-terpyridin)-4′-yl-phenyl)-N-methyl-3-thiosemicarbazone, has been synthesized and characterized using standard analytical and spectroscopic techniques. The dual binding properties of the sensor molecule were investigated using biologically important inorganic cations (Mn2+, Fe2+, Ni2+, Cu2+, Zn2+, Pb2+ and Hg2+) and anions (F¯, Cl¯, Br¯, I¯, HSO4¯ and H2PO4¯). The sensor molecule is equipped with analyte coordinating donor sites displaying charge transfer controlled spectroscopic properties and shows analyte–receptor interactions. Sensing mechanism involving host–guest interactions was confirmed by spectral and cyclic voltammetry techniques. The receptor shows colorimetric signalling in solution for cations such as Mn2+, Ni2+ and Cu2+ as evidenced by instant colour changes even at 2 μL aliquots of manganese and copper cations, and 4 μL aliquot for nickel cation, among the studied cations. Fluoride anion was detected by naked eye even at 2 μL of aliquot, signalled by the development of yellowish brown colour, through hydrogen bonding, deprotonation of N–H fragment and formation of HF2¯. Thus, the receptor shows dual sensing ability towards selected cations and F¯ anion. Further, paper strip experiments on receptor were also employed for the detection of cations and fluoride anion in solution.

Donor-Acceptor-Appended Triarylboron Lewis Acids: Ratiometric or Time-Resolved Turn-On Fluorescence Response toward Fluoride Binding.

Triarylboron Lewis acid compounds (CzmBoT (1c) and DPAmBoT (2c)), in which carbazole (Cz) or diphenylamine (DPA) donors are linked with a triazine acceptor in the ortho position of the phenylene ring are prepared and characterized. The treatment of 1c and 2c with the fluoride anion produces the corresponding fluoride adducts [1cF]- and [2cF]- as a tetraethylammonium salt. An X-ray diffraction study of [1cF]- reveals a twisted conformation between the Cz and phenylene rings. The Cz-containing 1c shows a ratiometric fluorescence change upon fluoride binding, while the DPA-containing 2c exhibits a turn-on fluorescence response in tetrahydrofuran. In particular, both fluoride adducts exhibit thermally activated delayed fluorescence (TADF) properties with microsecond-range lifetimes. Electrochemical and theoretical analysis suggests that the intramolecular charge-transfer transition from the donor to a conjugated acceptor fragment is switched to the donor to a triazine transition after fluoride binding. Theoretical analysis further demonstrates the twisted structure, effective highest occupied molecular orbital-lowest unoccupied molecular orbital separation, and the small energy splitting between the excited singlet and triplet states for the fluoride adducts, with all supporting the observed TADF. The time-resolved fluorescence measurements of 2c in the presence of both fluoride and a competitive fluorescent dye (Coumarin 6) effectively eliminate the short-lived fluorescence of a dye, retaining long-lived fluorescence signals originating only from [2cF]-.

Application of Boroisoquinoline Fluorophores as Chemodosimeters for Fluoride Ion and Pd (0).

The development of novel chemodosimeters is currently a prosperous field in organic chemistry. Recently, a new family of fluorophores, the boroisoquinolines, were introduced with satisfying photophysical properties. As a continuation of this research, the application of boroisoquinolines is presented as chemodosimeters for fluoride anion and Pd (0). The new tools showed good selectivity for the detection of the analytes. Moreover, the mechanism of action was investigated experimentally.