Fluoride Affinities Research Articles

Development of magnetic La doped Al2O3 core-shell nanoparticle loaded hydrogel for selective recovery of fluoride from aquatic medium

The selective removal of pollutants from water bodies is regarded as a conciliation between the rapid expansion of industrial activities and need of clean water for sustainability. Fluoride is one such geogenic pollutant, and various materials have already been reported. Developing an efficient field employable material is however a challenge. Herein, we report the synthesis and competencies of strategically designed magnetic La-doped Al2O3 core-shell nanoparticle loaded polymeric nanohybrid as a benchmark fluoride sorbent. A facile synthesis strategy involved fabrication of Fe3O4 magnetic core followed by growth of La doped Al2O3 shell using sol-gel method. Doping of La2O3 into Al2O3 structure was optimised (6%), resulting in Fe3O4-Al0.94 La0.06O1.5 core-shell particles which provided exceptional fluoride affinity. The obtained magnetic Fe3O4-Al0.94La0.06O1.5 core-shell nanoparticles were then loaded (22%) into alginate to form cross-linked hydrogel beads (Fe3O4-Al0.94 La0.06 O1.5-Ca-ALG). These prepared hydrogel beads were characterised and utilized for selective recovery of fluoride under different ambient conditions. Driving forces for enhanced fluoride uptake by La doped Al2O3 were investigated and explained with the help of both experimental observation and theoretical simulation. Density functional theory calculations indicated significant expansion in the cell volume of Al2O3 due to La doping which favoured the fluoride sorption. The calculated defect formation energy for the incorporation of F into Al2O3 was found to decrease in the presence of La. XPS analysis suggested direct interaction of fluoride with Al, forming Al-F bond and breaking Al-O bond. Different vital parameters for uptake were optimised. Also, kinetics, isotherm and diffusion models were evaluated. Developed hydrogel beads attained record sorption capacity of 132.3mgg-1 for fluoride. Overall, excellent stability, no leaching of constituents, effectiveness for selective fluoride recovery from groundwater, brand it a perfect epitome of sustainable water treatment application.

Diiminium Nucleophile Adducts Are Stable and Convenient Strong Lewis Acids.

Strong Lewis acids are essential tools for manifold chemical procedures, but their scalable deployment is limited by their costs and safety concerns. We report a scalable, convenient, and inexpensive synthesis of stable diiminium-based reagents with a Lewis acidic carbon centre. Coordination with pyridine donors stabilises these centres; the 2,2'-bipyridine adduct shows a chelation effect at carbon. Due to high fluoride, hydride, and oxide affinities, the diiminium pyridine adducts are promising soft and hard Lewis acids. They effectively produce acylpyridinium salts from carboxylates that can acylate amines to give amides and imides even from electronically intractable coupling partners.

The Effect of Carborane Substituents on the Lewis Acidity of Boranes.

The Lewis acidity of primary, secondary, and tertiary boranes with phenyl, pentafluorophenyl, and all three isomers of the C-substituted icosahedral carboranes (ortho, meta, and para) was investigated by computing their fluoride, hydride, and ammonia affinities as well as their global electrophilicity indices and LUMO energies. From these calculations, it was determined that the substituent effects on the Lewis acidity of these boranes follow the trend of ortho-carborane > meta-carborane > para-carborane > C6F5 > C6H5.

Chemical Adsorption of HF, HCl, and H2O onto YF3 and Isostructural HoF3 Surfaces by First Principles

The two elements, yttrium and holmium, form a geochemical twin pair as their cations possess equivalent ratios of charge to radius. However, despite their equal electrostatics, a subtle difference in their fluoride or chloride affinity is known within solutions. In this work, we investigated whether this affinity gap is also present within the solid phase and how it depends on the surface configuration. We modeled adsorptions onto β-YF3 (waimirite) and isostructural β-HoF3 by periodic density functional theory. To draw conclusions on the affinity toward fluoride and chloride vs. water, adsorbates of HF, HCl, or H2O onto any of the four highly abundant surfaces of (010), (100), (011), and (101) were studied. Among others, the conformational landscape was explored by 200 ps of ab initio molecular dynamics. For stoichiometric surfaces of both MF3, we indeed found stronger adsorptions for HF than HCl. All (hkl)·H2O showed slightly stronger adsorption energies for HoF3, while for HF and HCl, the metal preferences varied by the surface. While (100) showed the strongest preference for HoF3, (101) preferred YF3 by the same magnitude.

Bond Dissociation Energies of Carbene-Carbene and Carbene-Main Group Adducts.

A range of carbene structures and their adducts with one another and with a selection of small-molecule electrophiles and nucleophiles were examined at the composite correlated molecular orbital theory G3MP2 level to explore ground-state "carbenic" structures, their stabilities, and reactivities. Differences between carbene general classification as a singlet electrophilic carbene or singlet nucleophilic carbene and their given reactivity are discussed. A key quantity is the carbon-carbon bond dissociation energy for carbene dimers or the carbene-adduct dissociation energy for other species. The carbene dimer bond dissociation energies span a wide range from 10 to 170 kcal/mol. The hydrogenation energies and singlet-triplet splitting were found to correlate best with the carbene's self-dimerization energy, whereas other descriptors do not. The proton and fluoride affinities of the carbenes alone prove inadequate for classifying reactivity among classes of carbenes. The self-dimerization bond dissociation energy, hydrogenation energy, and singlet-triplet splitting of various carbenes, despite sometimes large differences in proton affinity and other indicators of reactivity, provide usable metrics to correlate substantial amounts of thermodynamic and kinetic (reactivity) information regarding these structures.

Hemoglobin and myoglobin stabilization by heme-fluoride complexes

Under physiological conditions, hemoglobin (Hb) and myoglobin (Mb) are subject to autoxidation, leading to the formation of ferric heme proteins with weakened globular structures and resulting in the loss of the heme cofactor. To gain further insights into the role of the heme pocket in the stabilization of the heme-containing proteins (holo-Mb and holo-Hb), the relative stabilities of heme-bound fluoride complexes (Mb-F and Hb-F) were examined under denaturing conditions. The electronic spectra of the heme proteins were followed upon addition of guanidine hydrochloride (GuHCl) and under denaturation-induced acidification. In the presence of ~ 2 M GuHCl, the heme-bound fluoride complexes are 27 – 46% more stable than metaquo Mb and Hb and about 50% more stable under acidic conditions. Mb and Hb denaturation equilibria at 25 and 40 °C were analyzed by using two-state and three-state models, respectively. Under GuHCl-induced and acid-induced denaturations, Mb-F and Hb-F behave as a two-state process. In addition, the affinity for fluoride under these denaturing conditions were determined. The dissociation constants (Kd) for fluoride binding in Hb and Mb under 1.5 M GuHCl are slightly greater than the measured Kd without GuHCl, which we attribute to the presence of molten-globular holo protein intermediates that are not favorable for fluoride binding. This study shows that the measured fluoride affinities in the presence of GuHCl at various temperatures and the effects of pH on the Kd can provide additional thermodynamic properties of Mb and Hb denaturation processes at low pH.

Hemoglobin and Myoglobin Stabilization by Heme-Fluoride Complexes

Under physiological conditions, hemoglobin (Hb) and myoglobin (Mb) are subject to autoxidation, leading to the formation of ferric heme proteins with weakened globular structures and resulting in the loss of the heme cofactor. To gain further insights into the role of the heme pocket in the stabilization of the heme-containing proteins (holo-Mb and holo-Hb), the relative stabilities of heme-bound fluoride complexes (Mb-F and Hb-F) were examined under denaturing conditions. The electronic spectra of the heme proteins were followed upon addition of guanidine hydrochloride (GuHCl) and under denaturation-induced acidification. In the presence of ~2M GuHCl, the heme-bound fluoride complexes are 27 – 46% more stable than ferric Hb and Mb. In addition, the affinity for fluoride under these denaturing conditions were determined. The dissociation constants ( K d ) for fluoride binding in Hb and Mb under 1.5 M GuHCl are slightly greater than the measured K d without GuHCl, which we attribute to the presence of molten-globular holo protein intermediates that are not favorable for fluoride binding. Under acidic denaturation, the acid-induced denaturing curves of Mb-F and Hb-F are -0.3 and -0.5 pH units shifted relative to ferric Hb and Mb, which show that the heme-bound fluoride proteins are more resistant to acid denaturation. This study shows that the measured fluoride affinities in the presence of GuHCl at various temperatures and the effects of pH on the K d can provide additional thermodynamic properties of Hb and Mb denaturation processes at low pH, where interactions between the heme pocket and the heme-bound fluoride are much stronger.

Pyridylpyrrolido ligand in Ge(II) and Sn(II) chemistry: synthesis, reactivity and catalytic application.

In our previous communication, we have reported the synthesis of a new chlorogermylene (B) featuring a pyridylpyrrolido ligand. This study details the preparation of a series of new germylenes and stannylenes starting from B. A transmetallation reaction between B and SnCl2 led to the analogous chlorostannylene (1) with the simultaneous elimination of GeCl2. This is a very unusual example of transmetallation between two elements of the same group. The preparation of 1via lithiation led to the formation of 2 as a side product, where the ortho C-H bond of the pyridine ring was activated and functionalized with a nBu moiety. Subsequently, B and 1 were used as precursors to generate germylene (4) and stannylene (5) featuring tris(trimethylsilyl)silyl (hypersilyl) moieties. We also prepared tetrafluoropyridyl germylene (6) by reacting 4 with C5F5N with the simultaneous elimination of (Me3Si)3SiF by utilizing the fluoride affinity of the silicon atom. As there is scarcity of Sn(II) compounds as single-site catalysts, we investigated 5 as a catalyst towards the hydroboration of aldehydes, ketones, alkenes and alkynes. All the compounds have been characterized by single-crystal X-ray diffraction and by state of the art spectroscopic studies.

Borolan-2-yl involving anion acceptors for organic liquid electrolyte-based fluoride shuttle batteries

Boron-based anion acceptors (AAs) have been used to dissociate MF salt (CsF) in organic liquid electrolyte-based fluoride shuttle batteries (FSBs). Here, two boron-based compounds, 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine (DiOB-Py) and N,N-diethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline) (DiOB-An), were examined as electrolyte additives for G4 containing CsF. DiOB-Py and DiOB-An are structurally similar except that the former is functionalized with pyridine whereas the latter with aniline. Since pyridine in DiOB-Py withdraws an electron pair on the phenyl ring via the resonance effect, the Lewis acidity of borate increases. On the other hand, since lone pair electrons of aniline are donated to the phenyl ring through the resonance effect, the acidity of borate in DiOB-An decreases. AAs are known to have a moderately strong fluoride affinity to provide sufficient dissolution of CsF in the electrolyte solvent. Thus, the effects of the acidity strength of the borates on the electrochemical compatibility of BiF3 were investigated. DiOB-Py imparted relatively high fluoride ion conductivity and CsF solubility, thereby allowing enhanced FSB performance.

Anion receptors with 1,3,5‐triazacyclohexane and 1,4,7,10‐tetraazacyclododecane scaffolds

AbstractFluoride, chloride, and bromide affinities of 1,3,5‐triazacyclohexane (TACH) and 1,4,7,10‐tetraazacyclododecane (Cyclen) were studied theoretically using ωB97XD and B3LYP functionals and 6‐311++G(d,p) basis set. To enhance and modify the anion affinities of TACH and Cyclen, several anion receptors with –(CH2)nOH and –(CH2)nNH2 (n = 1–3) substituents were designed and investigated. These anion receptors are attached to the halides (X−) via formation of NH … X and OH … X hydrogen bonds. The anion affinities calculated by ωB97XD were larger than those obtained by B3LYP indicating the dispersion contribution to the anion affinities. It was found that the anion affinities of these compounds depend on both the alkyl chain length and nature of the interaction, NH … X or OH … X. The ωB97XD‐calculated fluoride affinities of TACH and Cyclen were 149.5 and 207.2 kJ mol−1, respectively. By substitution of –(CH2)nOH groups, anion receptors with F− affinities of 277 and 326 kJ mol−1 were obtained, which can be classified among the strongest organic anion receptors. The affinity of all TACH and Cyclen toward the halides was as F− > Cl− > Br−, while substitution of –(CH2)3OH and –(CH2)3NH2 into Cyclen changed the trend to F− > Br− > Cl−.

Lewis Acidity and Basicity: Another Measure of Carbene Reactivity.

The structural and energetic reactivities of various carbenes are evaluated against a standard electrophile (proton) and a standard nucleophile (fluoride). The proton and fluoride affinities of the carbenes studied provide an increased understanding of reactivity modes and mechanisms. General classification of carbenic reactivity as a singlet nucleophilic carbene or a singlet electrophilic carbene is facilitated by this present study, and a need for further classification means along the border between electrophilic and nucleophilic reactivity is considered. The results are based on electronic structure calculations at the composite correlated molecular orbital theory G3MP2 level.

Dihalides of Sterically Constrained Tricyclic Phosphines, Lewis Acidity and Fluoride Affinity, Chloride Abstraction, and a Phosphonium Cation, Dimethylphosphorane

Treatment of the trilithium compounds 3 with PCl3 afforded sterically constrained tricyclic phosphines with annulated five‐ (2 ×) and six‐membered rings and the P atoms in the bridgehead positions (2a, vinylic SiMe2Ph; 2b, vinylic SiMe3 groups). Their AuCl complexes (4) were used for an estimation of the buried volumes (4b: %V = 46 %). Reactions of 2b with XeF2 or SO2Cl2 afforded PX2 derivatives [X = F (5b), Cl (6b)]. Crystal structure determinations including the recently reported difluorides and diiodides of 2a (5a and 7) allow a systematic comparison of structural details. The P atoms have trigonal bipyramidal to square pyramidal surroundings. The PF2 phosphorane 5a behaves as a Lewis acid and coordinates F– to yield a phosphate anion (8) with a PF3C3 molecular centre, while Cl– abstraction from 3a afforded an unstable phosphonium cation (9). Unusual methylphosphoranes with one or two methyl groups attached to phosphorus were obtained by reactions of the dihalides 5a or 6a with methyllithium.

A Simple and Effective Method of Determining Lewis Acidity by Using Fluorescence

Summary The strength of a Lewis acid is an important parameter in establishing its utility for practical applications. Here, we report a universal fluorescence-based method for accurately determining the strength of a range of Lewis acids. Utilizing a fluorescent dithienophosphole oxide architecture, we are able to emulate the structural motif of the widely employed Gutmann-Beckett method. This allows us to precisely correlate the optical response to the strength of a Lewis acid. In comparison to commonly used methods that employ 31P NMR chemical shifts or quantum-chemical calculations, our method strongly suggests that using fluorescent Lewis acid-base adducts (FLAs) is more reliable. Moreover, our method provides a direct measure of the Lewis acidity of a given solution, independent of the Lewis base, with direct implications to the overall utility of a Lewis acid in practical applications.

Electronic Structure Predictions of the Energetic Properties of Tellurium Fluorides.

The heats of formation, bond dissociation energies (BDEs), fluoride affinities (FA), fluorocation affinities (FCA), electron affinities (EA), and ionization energies (IP) of TeF n ( n = 1-6) have been predicted using the Feller-Peterson-Dixon (FPD) approach. To benchmark the approach, the bond dissociation energies of Te2 and TeO, the heats of formation of Te2, TeH2, TeO, and TeO2, and the electron affinity for TeO and TeO2 were calculated as there are experimental thermodynamic data available for these tellurium compounds, which allow confirmation of the heat of formation of Te gas as Δ Hf,0K(Te) = 50.7 ± 0.6 kcal/mol. Spin-orbit corrections are required for good results and cannot be ignored. A comparison among fluoride affinities, fluorocation affinities, electron affinities, and ionization energies of TeF n and SeF n is reported.

Unimolecular reactivity of organotrifluoroborate anions, RBF3- , and their alkali metal cluster ions, M(RBF3 )2- (M = Na, K; R = CH3 , CH3 CH2 , CH3 (CH2 )3 , CH3 (CH2 )5 , c-C3 H5 , C6 H5 , C6 H5 CH2 , CH2 CHCH2 , CH2 CH, C6 H5 CO).

Potassium organotrifluoroborates (RBF3 K) are important reagents used in organic synthesis. Although mass spectrometry is commonly used to confirm their molecular formulae, the gas-phase fragmentation reactions of organotrifluoroborates and their alkali metal cluster ions have not been previously reported. Negative-ion mode electrospray ionization (ESI) together with collision-induced dissociation (CID) using a triple quadrupole mass spectrometer were used to examine the fragmentation pathways for RBF3- (where R=CH3 , CH3 CH2 , CH3 (CH2 )3 , CH3 (CH2 )5 , c-C3 H5 , C6 H5 , C6 H5 CH2 , CH2 CHCH2 , CH2 CH, C6 H5 CO) and M(RBF3 )2- (M=Na, K), while density functional theory (DFT) calculations at the M06/def2-TZVP level were used to examine the structures and energies associated with fragmentation reactions for R=Me and Ph. Upon CID, preferentially elimination of HF occurs for RBF3- ions for systems where R=an alkyl anion, whereas R- formation is favoured when R=a stabilized anion. At higher collision energies loss of F- and additional HF losses are sometimes observed. Upon CID of M(RBF3 )2- , formation of RBF3- is the preferred pathway with some fluoride transfer observed only when M=Na. The DFT-calculated relative thermochemistry for competing fragmentation pathways is consistent with the experiments. The main fragmentation pathways of RBF3- are HF elimination and/or R- loss. This contrasts with the fragmentation reactions of other organometallate anions, where reductive elimination, beta hydride transfer and bond homolysis are often observed. The presence of fluoride transfer upon CID of Na(RBF3 )2- but not K(RBF3 )2- is in agreement with the known fluoride affinities of Na+ and K+ and can be rationalized by Pearson's HSAB theory.

Structures and Heats of Formation of Simple Alkaline Earth Metal Compounds II: Fluorides, Chlorides, Oxides, and Hydroxides for Ba, Sr, and Ra.

Geometry parameters, vibrational frequencies, heats of formation, bond dissociation energies, cohesive energies, and selected fluoride affinities (difluorides) are predicted for the late alkaline earth (Sr, Ba, and Ra) oxides, fluorides, chlorides, and hydroxides at the coupled cluster theory CCSD(T) level. Additional corrections (scalar relativistic and pseudopotential corrections, vibrational zero-point energies, and atomic spin-orbit effects) were included to accurately calculate the total atomization energies and heats of formation following the Feller-Peterson-Dixon methodology. The calculated values are compared to the experimental data where available. In some cases, especially for Ra compounds, there are no experimental results, or the experimental energetics and geometries are not reliable or have very large error bars. All of the Sr, Ba, and Ra difluorides, dichlorides, and dihydroxides are bent structures with the OMO bond angles decreasing going down the group. The cohesive energies of bulk Be dihalides are predicted to be quite low, while those of Ra are relatively large. The fluoride affinities show that the difluorides are moderately strong Lewis acids and that such trifluorides may form under the appropriate experimental conditions.

Reaction of CO2 with Groups 4 and 6 Transition Metal Oxide Clusters.

Density functional theory (DFT) and coupled cluster theory (CCSD(T)) were used to study the addition of CO2 to group 4 (MO2)n and group 6 (MO3)n (n = 1, 2, 3) nanoclusters. The structures and energetics arising from Lewis acid-base addition (physisorption) and formation of CO32- (chemisorption) of CO2 to these clusters were predicted. Physisorption and chemisorption of CO2 are predicted to be thermodynamically allowed for group 4 (MO2)n clusters, with chemisorption being more favored energetically. Correlations of the ligand binding energies (LBEs) for the group 4 clusters are made with the fluoride affinities and M-O and M═O bond strengths of the clusters. The LBEs for chemisorption on the Zr and Ti clusters are consistent with published experimental and computational studies of bulk solids. Physisorption LBEs for the Ti and Zr clusters are more exothermic than the bulk values, as the cluster models allow for better relaxation at the metal sites. Chemisorption is not predicted to occur with group 6 (MO3)n clusters, as the larger chemisorbed structures were all found to be metastable. CO2 is predicted to weakly physisorb to (WO3)n with physisorption correlating with the Lewis acidity of the metal site.

Electronic Structures of Small (RuO2)n (n = 1-4) Nanoclusters and Their Anions and the Hydrolysis Reactions with Water.

Group 8 (RuO2)n (n = 1-4) nanoclusters, their anions, and the hydrolysis reactions of the neutral clusters have been studied with the density functional theory (DFT) as well as coupled cluster CCSD(T) theory. The ground state is predicted to be a singlet and a doublet for the neutral RuO2 clusters and anionic clusters, respectively. The CCSD(T) method is required to predict the correct ground state. The calculated singlet-triplet gaps (<15 kcal/mol) and fluoride affinities (<95 kcal/mol) are smaller than those of the group 4 (MO2)n and group 6 (MO3)n metal oxide clusters. The electron affinities range from 2.2 to 3.4 eV, showing that the RuO2 clusters are quite reducible. Clustering energies and heats of formation are calculated. The water physisorption energies are predicted to be -10 to -20 kcal/mol with the adsorption energy for the singlet being generally more exothermic than that for the triplet. The hydrolysis reactions are exothermic for the monomer and dimer clusters and are slightly endothermic or neutral for the trimer and tetramer. H2O is readily dissociated on the monomer and dimer but not on the trimer and tetramer. The physisorption and chemisorption energies are less exothermic, and the barriers for the hydrolysis reactions are larger for RuO2 nanoclusters than for the corresponding group 4 ZrO2 nanoclusters.

Thiourea grafted PVDF affinity membrane with narrow pore size distribution for Au (III) adsorption: Preparation, characterization, performance investigation and modeling

Thick and hydrophilic microporous poly(vinylidene fluoride) (PVDF) affinity membranes were prepared for low-concentration gold separation by grafting thiourea on alkali treated PVDF resin. The modified polymer was easily cast into membranes by non-solvent induced phase separation through two coagulation processes, and the addition of N-methyl-2pyrrolidone into the second coagulation bath improved the pore size distribution effectively. The grafted polymer and membrane were characterized by FTIR, Raman, 1H NMR, XPS, SEM and pore size distribution measurement. Static adsorption of Au (III) with the membranes followed pseudo-second order kinetics and Langmuir isotherm. Dynamic adsorption was investigated by using stacked membranes in the form of a membrane chromatography. The results showed that increasing the number of membrane layers improved the membrane bed utilization, which was attributed to the increased adsorption sites and a combined effect of reduced average membrane pore size and narrowed pore size distribution (PSD). The effect of PSD on performance of the membrane chromatography was further separated from that of the mean pore size, and it was shown that narrower PSD indeed was favorable. A new mathematical model based on dispersive mass transfer through the membrane pores and incorporating PSD was established. The model was found to be able to predict the membrane breakthrough behavior very well. Finally, the elution performance of gold laden membrane was studied, and an optimized formulation of the eluent consisting of thiourea and HCl was determined.

Benchmark Calculations of Energetic Properties of Groups 4 and 6 Transition Metal Oxide Nanoclusters Including Comparison to Density Functional Theory.

The heats of formation and the normalized clustering energies (NCEs) for the group 4 and group 6 transition metal oxide (TMO) trimers and tetramers have been calculated by the Feller-Peterson-Dixon (FPD) method. The heats of formation predicted by the FPD method do not differ much from those previously derived from the NCEs at the CCSD(T)/aT level except for the CrO3 nanoclusters. New and improved heats of formation for Cr3O9 and Cr4O12 were obtained using PW91 orbitals instead of Hartree-Fock (HF) orbitals. Diffuse functions are necessary to predict accurate heats of formation. The fluoride affinities (FAs) are calculated with the CCSD(T) method. The relative energies (REs) of different isomers, NCEs, electron affinities (EAs), and FAs of (MO2)n (M = Ti, Zr, Hf, n = 1-4) and (MO3)n (M = Cr, Mo, W, n = 1-3) clusters have been benchmarked with 55 exchange-correlation density functional theory (DFT) functionals including both pure and hybrid types. The absolute errors of the DFT results are mostly less than ±10 kcal/mol for the NCEs and the EAs and less than ±15 kcal/mol for the FAs. Hybrid functionals usually perform better than the pure functionals for the REs and NCEs. The performance of the two types of functionals in predicting EAs and FAs is comparable. The B1B95 and PBE1PBE functionals provide reliable energetic properties for most isomers. Long range corrected pure functionals usually give poor FAs. The standard deviation of the absolute error is always close to the mean errors, and the probability distributions of the DFT errors are often not Gaussian (normal). The breadth of the distribution of errors and the maximum probability are dependent on the energy property and the isomer.