Anhydrous HF Research Articles

Mechanochemical Synthesis and Magnetic Properties of the Mixed-Valent Binary Silver(I,II) Fluorides, AgI2AgIIF4 and AgIAgIIF3.

Fluoridoargentates(II) represent a fascinating class of silver(II) compounds with structural and magnetic similarities to cuprate superconductors. However, their synthesis is challenging, leaving their properties largely underexplored and hindering the discovery of new phases. This study introduces mechanochemistry as a novel approach for the synthesis of fluoridoargentates(II), avoiding the use of anhydrous HF or elemental fluorine and employing readily available equipment. Notably, ball milling of commercially available precursors successfully produced the long-sought-after first two examples of binary mixed-valent silver(I,II) phases, AgI2AgIIF4 (Ag3F4) and AgIAgIIF3 (Ag2F3). While the AgI2AgIIF4 phase was obtained at room temperature, the AgIAgIIF3 phase is metastable and required milling under cryogenic conditions. Characterization by synchrotron powder X-ray and neutron diffraction revealed that AgI2AgIIF4 crystallizes in the P21/c space group and is isostructural to β-K2AgF4. In this crystal structure, [AgIIF2F4/2]2- distorted octahedral units with 4 + 2 coordination, extend parallel to a-crystallographic axis giving a quasi-one-dimensional canted antiferromagnetic character, as shown by magnetic susceptibility. The triclinic perovskite AgIAgIIF3 phase adopts the P1̅ space group, is isostructural to AgCuF3 and also shows features of a one-dimensional antiferromagnet. This mechanochemical approach, also successfully applied to synthesize β-K2AgF4, is expected to expand the field of silver(II) chemistry, accelerating the search for silver analogs to cuprate superconductors and potentially extending to other cations in unusual oxidation states.

Synthesis, Characterization, and Polymorphism of [H3O][NbF6]: A Polar and Possibly Ferroelectric Oxonium Salt

Abstract[H3O][NbF6] was obtained from the controlled hydrolysis of NbF5 in anhydrous liquid HF. It adopts a polar, orthorhombic crystal structure with space group Iba2 (no. 45, oI88) at room temperature. A first‐order phase transition at 137 K leads to a cubic non‐centrosymmetric polymorph in space group I213 (no. 199, cI88). This low‐temperature modification results from a distinct rotation of the [H3O]+ cations canceling their polar orientation in the room temperature phase. Quantum‐chemical calculations estimate a rotational barrier between 5.8 to 6.4 kJ/mol. At a temperature of 363 K, the compound adopts a centrosymmetric, cubic crystal structure in space group Pm m (no. 221, cP11) that shows rotational disorder of cations and anions. The transition from the polar phase at room temperature to the centrosymmetric phase at high temperature not only reveals the plastic nature of the high‐temperature structure but also hints at potential ferroelectric properties, underscoring the multifaceted behavior of [H3O][NbF6] across different temperature regimes.

Further Insights into the Chemical Synthesis of F2 and on Drying moist HF.

It is well established that solid K2MnF6 reacts with excess SbF5 forming elemental F2. However, if the reaction is carried out in anhydrous HF (aHF) as a solvent, this is surprisingly not the case. Instead, the green Mn(IV) compound K3[(MnIVF)(SbF6)5]F is obtained. The reductive elimination of F2 was not observed under the applied conditions. The compound was characterized by its crystal structure, by Raman spectroscopy, and by quantum-chemical solid-state calculations. It crystallizes in the monoclinic space group P21/c, mP164, with the lattice parameters a = 12.2393(13), b = 12.167(2), c = 20.115(5) Å, β = 110.805(8)°, V = 2800.1(9) Å3, Z = 4 at T = 200 K. As the use of strictly anhydrous HF is crucial in this and other similar reactions, methods for drying moist HF are discussed.

From alternate routes to fluorspar (CaF2) or anhydrous HF (aHF) to conversion of fluorspar into a nucleophilic fluorinating agent

From alternate routes to fluorspar (CaF2) or anhydrous HF (aHF) to conversion of fluorspar into a nucleophilic fluorinating agent

Global potential energy surface survey of pentanitrogen cation

We reported hitherto the most extensive isomeric, interconversion and decomposition landscape of the pentanitrogen cation (N5 +) at the CCSD(T)_CBS//MP2/cc-pVTZ, CBS-QB3 and CCSD(T)_CBS//CCSD/cc-pVTZ levels. A maximum number of eleven isomers and fourteen transition states were located, among which three and eight were reported for the first time. Moreover, the counterion stabilisation effect by the model BF4 − anion as well as the solvation effect in anhydrous HF solvent at different temperatures were investigated. Notably, although 01 is rather well known, a new type of N2-extrusion process for the 01 salt (with BF4 − counterion) was identified.

Chromium(VI) Oxyfluoride Dianions, [Cr2 O4 F6 ]2- and [CrO2 F4 ]2- ; Syntheses and Structures of [XeF5 ]2 [Cr2 O4 F6 ], [XeF5 ]2 [Cr2 O4 F6 ] ⋅ nX (X=HF, n=4; X=XeOF4 , n=2), and [XeF5 ][Xe2 F11 ][CrO2 F4

The fluorobasic character of the strong oxidative fluorinator, XeF6 , and the oxidative resistance of the [XeF5 ]+ and [Xe2 F11 ]+ cations have been exploited for the syntheses of several novel Cr(VI) dianion salts. The reactions of XeF6 and CrO2 F2 in anhydrous HF and by direct fusion of the reactants in melts have yielded the first dinuclear Cr(VI) oxyfluoro-dianion salts, [XeF5 ]2 [Cr2 O4 F6 ], [XeF5 ]2 [Cr2 O4 F6 ] ⋅ 4HF, [XeF5 ]2 [Cr2 O4 F6 ] ⋅ 2XeOF4 , and mononuclear Cr(VI) oxyfluoro-dianion salt, [XeF5 ][Xe2 F11 ][CrO2 F4 ]. The salts were structurally characterized by low-temperature (LT) single-crystal X-ray diffraction (SCXRD) and LT Raman spectroscopy. The [CrO2 F4 ]2- and [Cr2 O4 F6 ]2- dianions have distorted octahedral cis-dioxo Cr(VI) coordination spheres in which two F-atoms are trans to one another and two F-atoms are trans to O-atoms, where the [Cr2 O4 F6 ]2- dianion is the fluorine-bridged dimer of the [CrO2 F3 ]- anion. Quantum-chemical calculations were used to obtain the energy-minimized, gas-phase geometries, and the calculated vibrational spectra of the gas-phase dianions and their ion-pairs, which were used to aid in the vibrational frequency assignments of the crystalline salts. NBO and MEPS analyses and SCXRD show these salts are comprised of intimate ion-pairs in which their cations and anions interact through primarily electrostatic Xe- - -F σ-hole bonds.

Molecular Additive-Assisted Tellurium Homogenization in ZnSeTe Quantum Dots.

The addition of aqueous hydrohalic acids (HX, X = F, Cl, Br) during the synthesis of colloidal quantum dots (QDs) is now widely employed to achieve high-quality QDs. However, this reliance on the use of aqueous solutions is incompatible with oxygen- and water-sensitive precursors such as those used in the synthesis of Te-alloyed ZnSe QDs. Herein, we show this incompatibility, leads to phase segregation into Te-rich and Te-poor regions, causing spectral broadening and luminescence peak shifting under high laser irradiation and applied electrical bias. Here we report a synthetic strategy to produce anhydrous-HF in-situ by using benzenecarbonyl fluoride (BF) as a chemical additive. Through in-situ 19 F nuclear magnetic resonance spectroscopy, we find that BF reacts with surfactants in tandem, ultimately producing intermediary F···H···trioctylamine adducts. These act as a pseudo-HF source that releases anhydrous HF. The controlled release of HF during the nucleation and growth steps homogenizes the Te distribution in the ZnSeTe lattice, leading to spectrally-stable blue-emitting QDs under increasing laser flux from ∼3 μW to ∼12mW and applied bias from 2.6 to 10V. Single-dot photoluminescence (PL) spectroscopy and analyses of the absorption, PL and transient absorption spectra together with density functional theory point to the role of anhydrous HF as a Te homogenizer. This article is protected by copyright. All rights reserved.

Discrete Mono-, Di-, and Trinuclear Anions [MoOF5]-, [MoVOF5]2-, [MoO2F4]2-, [Mo2O2F9]-, [Mo3O3F13]-, and the Infinite Chain Anion [MoO2F3]- Obtained from Reactions of MoOF4: Synthesis and Analysis of the Structure-Chemical Relations of the Compounds.

The herein-reported oxyfluoridometallate salts were synthesized and structurally characterized during the studies of the Lewis acidity of MOF4 (M = Mo, W) with various fluoride ion donors (RbF, CsF, TlF, AgF, SrF2, BaF2, PbF2) in different solvents (aqHF 48%, aHF, BrF3, ClF3). Phase-pure MoOF4 was either synthesized by hydrolysis of MoF6 with SiO2 in anhydrous HF (aHF) or by reactions of BrF3 with MoO2 or MoO3, respectively. The compound was characterized by infrared and Raman spectroscopy, solid-state quantum-chemical calculations, as well as powder and single-crystal X-ray diffraction. MoOF4 reacted with PbF2 in aHF forming Pb[MoOF5]2, while under comparable conditions, WOF4 formed Pb3[WOF5]4F2, containing the [WOF5]- anion. Salts containing such [MoOF5]- anions were also directly obtained from reactions of BrF3, MoO3, and AF2 (A = Sr, Ba), while with AgF, the compound Ag[Mo2O2F9] was observed. ClF3 reacted with MoO3 to form [ClOF2][Mo3O3F13]. Carrying out similar reactions in aqueous HF (aqHF) in autoclaves under hydrofluorothermal conditions leads to O-richer compounds with the composition A[MoO2F4] (A = Sr, Ba). With RbF or Tl2(CO3), the compounds A[MoO2F3] (A = Rb, Tl) were obtained. With CsF reduction to Mo(V) occurred as Cs2[MoVOF5] was formed. We report on similarities and differences within the respective anions and within the crystal structures of these compounds.

Structural Characterization and Bonding Analysis of [Hg{Fe(CO)5}2]2+ [SbF6]-2.

The non-classical carbonyl complex [Hg{Fe(CO)5}2]2+ [SbF6]-2 is prepared by reaction of Hg(SbF6)2 and excess Fe(CO)5 in anhydrous HF. The single-crystal X-ray structure reveals a linear Fe-Hg-Fe moiety as well as an eclipsed conformation of the eight basal CO ligands. Interestingly, the Hg-Fe bond length of 2.5745(7) Å is relatively similar to the corresponding Hg-Fe bonds in literature-known [Hg{Fe(CO)4}2]2- dianions (2.52-2.55 Å), which intrigued us to analyze the bonding situation in both the dications and dianions with the energy decomposition analysis with natural orbitals for chemical valence (EDA-NOCV) method. Both species are best described as Hg(0) compounds, which are also confirmed by the shape of the HOMO-4 and HOMO-5 of the dication and dianion, respectively, in which the electron pair is located mainly at the Hg. Furthermore, for the dication and the dianion, the σ back-donation from Hg into the [Fe(CO)5]22+ or the [Fe(CO)4]22- fragment is the most dominant orbital interaction and surprisingly these interaction energies are also very similar even in absolute values. The fact that both iron-based fragments are missing two electrons explains their prominent σ-acceptor properties.

Atomic layer deposition of calcium fluoride for barrier coating applications

We report on the development of an atomic layer deposition (ALD) process for calcium fluoride thin films using bis(N,N-di-i-propylformamidinato)calcium(II) and anhydrous HF as reactants. Deposition rates were observed to be linear versus the number of ALD cycles performed, varying between 0.4 and 0.3 Å/cycle at substrate temperatures ranging from 175 to 250 °C, respectively. The optical properties of the resulting nanocrystalline CaF2 films were characterized by spectroscopic ellipsometry and show good transparency down to a UV wavelength of 193 nm, and good agreement with reference refractive index parameters. One motivation for the development of this ALD process is for chemical barrier applications in fluorine-containing chemistries. The robustness of the coating was tested by reactive ion etching of CaF2 films deposited on silicon in an SF6 plasma, yielding an Si:CaF2 etch ratio of greater than 2000:1 at a plasma power of 300 W.

XeF2 Coordination Complexes of the [BrO2]+ Cation, [O2Br(FXeF)n][AsF6] (n = 1, 2) and [O2Br(FXeF)2][SbF6]; Their Syntheses and Structural Characterizations.

The syntheses and structural characterizations of the first XeF2 coordination complexes of the [BrO2]+ cation are described. The reactions of [BrO2][PnF6] (Pn = As, Sb) with XeF2 in anhydrous HF solvent yield the salts [O2Br(FXeF)n][AsF6] (n = 1, 2) and [O2Br(FXeF)2][SbF6], which were characterized by low-temperature (LT) Raman spectroscopy and single-crystal X-ray diffraction (SCXRD). The XeF2 ligands and [PnF6]- coordinate to the Lewis acidic [BrO2]+ cation through primarily electrostatic BrV---FXe σ-hole bonds that result from coordination of the F atoms into regions of high positive electrostatic potential on the Br(V) atom and have bond trajectories that avoid the stereoactive valence electron lone-pair of Br(V). The complexes and their structural characterizations by LT Raman spectroscopy and SCXRD significantly extend the coordination chemistry of Br(V) and provide rare examples of a noble-gas difluoride coordinated to a strong oxidant main-group Lewis acid center.

Photochemical preparation of Cs[MF6] salts (M = Ru, Rh, Os, Ir, Pt); crystal structures and Raman spectra

Attempts to prepare Cs[MVIF7] and Cs2[MVIF8] salts by photochemical reactions between CsF, noble metal M (M = Ru, Rh, Os, Ir, Pt) and UV-irradiated F2 in anhydrous HF failed. The main products were Cs[MVF6] salts. The formation of MF6 (M = Rh, Os, Ir) was also observed. The reaction between PtF6 and a solution of CsF in anhydrous HF resulted in the formation of CsPtF6 and the release of elemental F2. The crystal structures of the Cs[MVF6] salts (M = Ru, Rh, Os, Ir, Pt) were determined on single crystals. They are isotypic and crystallize in the trigonal space group R ̅3 (No. 148), belonging to the KAsF6 (KOsF6) family of crystal structures. The Raman spectra of Cs[MF6] salts (M = Ru, Rh, Os, Ir, Pt) are also described.

On pyridine chloronium cations.

We present the first solid-state structural evidence of mono- and bis(pyridine)chloronium cations. The latter was synthesized from a mixture of pyridine, elemental chlorine and sodium tetrafluoroborate in propionitrile at low temperatures. The mono(pyridine) chloronium cation was realized with the less reactive pentafluoropyridine, using ClF, AsF5, and C5F5N in anhydrous HF. During the course of this study, we also investigated pyridine dichlorine adducts and found a surprising disproportionation reaction of chlorine that depended on the substitutional pattern of the pyridine. Electron richer dimethylpyridine (lutidine) derivatives favor full disproportionation into a positively and a negatively charged chlorine atom which forms a trichloride monoanion, while unsubstituted pyridine forms a 1 : 1 py·Cl2 adduct.

From cyclic (alkyl)(amino)carbene (CAAC) precursors to fluorinating reagents. Experimental and theoretical study.

Addition of anhydrous HF to the hydrochloride [MeCAACH][Cl(HCl)0.5] resulted in the formation of salts with high HF content. By stepwise removal of HF in vacuo, we selectively prepared [MeCAACH][F(HF)2] (3) and [MeCAACH][F(HF)3] (4). We also characterised a salt with [F(HF)4]- anions within the structure of [MeCAACH][F(HF)3.5] (5). Compounds with a lower content of HF were not accessible under vacuum conditions. MeCAAC(H)F (1) was selectively prepared by abstraction of HF from 3 with CsF or KF, while [MeCAACH][F(HF)] (2) was prepared by mixing 3 and 1 in a 1 : 1 ratio. Compound 2 proved to be quite unstable as it tends to disproportionate into 1 and 3. This observation triggered our computational study, in which the structural relationships between CAAC-based fluoropyrrolidines and dihydropyrrolium fluorides were investigated using different DFT methods. The study showed that the results were very sensitive to the computational method used. For a correct description, the quality of the triple-ζ basis set was crucial. Surprisingly, the isodesmic reaction of [MeCAACH][F] + [MeCAACH][F(HF)2] → [MeCAACH][F(HF)] + [MeCAACH][F(HF)] did not confirm the low thermodynamic stability of 2. Furthermore, the use of 3 as a nucleophilic fluorinating reagent was tested on a range of organic substrates, as it is the most stable compound in this series. It was found to have the potential to fluorinate benzyl bromides, 1- and 2-alkyl bromides, silanes and sulfonyls with good to excellent yields of the target fluorides.

First-Principle Investigation of Hypothetical NiF4 Crystal Structures

An important synthetic route for the fluorinated organic compounds is electrochemical fluorination (ECF). This is a process taking place on a nickel anode immersed in anhydrous HF. Even though the mechanism is not fully resolved, it is believed that it involves higher valent nickel fluorides formed on the anode. One such compound could be NiF4. Its synthesis and existence have been reported in the literature. However, its crystal structure has so far remained unknown. In this paper, we present, for the first time, the theoretical study of the possible crystal structure of NiF4. We investigated six crystal structures of known metal tetrafluorides as possible candidates for NiF4 by periodic DFT, with the PBE+U method. Of the investigated structures, the most stable polymorph of NiF4 was found to be of the same crystal structure as RuF4. The unit cell parameters were calculated to be a = 4.80 Å, b = 5.14 Å, c = 5.18 Å and β = 105.26∘. All but one of the investigated structures feature octahedrally coordinated nickel centers with two non-bridging fluorine atoms. In the structure originating from ZrF4, all six fluorine atoms around the nickel centers are bridging and two are located in the vacancies around the nickel skeleton, not directly bound to nickel. The overall magnetic arrangement in all the investigated structures is antiferromagnetic. A comparison with other binary nickel fluorides supports the experimental findings that NiF4 is thermodynamically the least stable.

Bi(III) stable in the coordination compounds with XeF2 as a ligand

AbstractMain group trivalent metal canter is added to the diverse family of coordination compounds with XeF2 as a ligand for the first time. [Bi(XeF2)3](BiF6)3 can be prepared by the direct reaction between BiF3, BiF5 and XeF2 in anhydrous HF as solvent. The compound is stable at room temperature under inert conditions. In the compound, the same metal is found in two oxidation states: Bi(III) and Bi(V). [Bi(XeF2)3](BiF6)3 crystalizes in hexagonal space group P 2 c at 150 K with a=10.3296(5) Å, b=10.3296(5) Å, c=12.1775(7) Å. The metal centre Bi(III) is coordinated with nine F atoms. Six F atoms from BiF6 units are located in the corners of the trigonal prism, while the rectangular faces of the trigonal prism are capped with F atoms from three XeF2 ligands. The Bi(III) centres are connected via Bi(V)F6 units into the three dimensional network. All three XeF2 ligands are non‐bridging.

Mixed cation [H3O]+/[XeF5]+/M2+ (M=Ca, Cd), [O2]+/[XeF5]+/Sr2+ and [H3O]+/Sr2+ fluoridoantimonate(V) salts

AbstractThe reaction between H3OSbF6, XeF5SbF6, and M(SbF6)2 (M=Ca, Cd) in anhydrous HF gave (H3O)(XeF5)2M2(SbF6)7 ⋅ nHF salts (n=3.95 for M=Ca and n=3.21 for M=Cd) upon crystallization. Their crystal structures consist of SbF6 units connecting M2+ centers located in the same plane. In this way, slabs are formed, each slab containing a layer of M2+ cations. The [XeF5]+ and [H3O]+ cations are located between adjacent slabs. Single crystals of (O2)(XeF5)2Sr4(SbF6)11 ⋅ 8HF were grown from aHF solution prepared by reaction between O2SbF6, XeF2, SrF2, SbF3 and UV‐irradiated F2. Attempts to grow single crystals of the fluoridoantimonate(V) salt containing simultaneously the cation [H3O]+ and XeF2 coordinated to an M2+ metal center failed. Instead, only a few single crystals of the H3O[Sr(HF)2]3(SbF6)6(Sb2F11) salt were observed. An attempt to grow single crystals of NH4XeF5MnF6 from aHF solution yielded only a mixture of (XeF5)2MnF6 and (NH4)2MnF6.

Crystal Growth from Anhydrous HF Solutions of M2+ (M = Ca, Sr, Ba) and [AuF6]-, Not Only Simple M(AuF6)2 Salts.

Crystal growth from anhydrous HF solutions of M2+ (M = Ca, Sr, Ba) and [AuF6]− (molar ratio 1:2) gave [Ca(HF)2](AuF6)2, [Sr(HF)](AuF6)2, and Ba[Ba(HF)]6(AuF6)14. [Ca(HF)2](AuF6)2 exhibits a layered structure in which [Ca(HF)2]2+ cations are connected by AuF6 units, while the crystal structure of Ba[Ba(HF)]6(AuF6)14 exhibits a complex three-dimensional (3-D) network consisting of Ba2+ and [Ba(HF)2]2+ cations bridged by AuF6 groups. These results indicate that the previously reported M(AuF6)2 (M = Ca, Sr, Ba) compounds, prepared in the anhydrous HF, do not in fact correspond to this chemical formula. When the initial M2+/[AuF6]− ratio was 1:1, single crystals of [M(HF)](H3F4)(AuF6) were grown for M = Sr. The crystal structure consists of a 3-D framework formed by [Sr(HF)]2+ cations associated with [AuF6]− and [H3F4]− anions. The latter exhibits a Z-shaped conformation, which has not been observed before. Single crystals of M(BF4)(AuF6) (M = Sr, Ba) were grown when a small amount of BF3 was present during crystallization. Sr(BF4)(AuF6) crystallizes in two modifications. A high-temperature α-phase (293 K) crystallized in an orthorhombic unit cell, and a low-temperature β-phase (150 K) crystallized in a monoclinic unit cell. For Ba(BF4)(AuF6), only an orthorhombic modification was observed in the range 80–230 K. An attempt to grow crystals of Ca(BF4)(AuF6) failed. Instead, crystals of [Ca(HF)](BF4)2 were grown and the crystal structure was determined. During prolonged crystallization of [AuF]6– salts, moisture can penetrate through the walls of the crystallization vessel. This can lead to partial reduction of Au(V) to A(III) and the formation of [AuF4]− byproducts, as shown by the single-crystal growth of [Ba(HF)]4(AuF4)(AuF6)7. Its crystal structure consists of [Ba(HF)]2+ cations connected by AuF6 octahedra and square-planar AuF4 units. The crystal structure of the minor product [O2]2[Sr(HF)]5[AuF6]12·HF was also determined.

Prediction of a model crystal structure for Ni2F5 by first-principles calculations

Abstract Electrochemical fluorination in anhydrous HF, also known as the Simons process, is a widely used industrial method for fluorination of organic compounds. Its mechanism, being not so well understood, has long been debated and is believed to involve higher valent nickel fluorides formed on the nickel-plated anode during the process. One of these is speculated to be Ni2F5, which was previously reported in the literature and assigned via infrared spectroscopy, but its crystal structure is not yet known. We have identified known crystal structures of compounds with similar stoichiometries as Ni2F5 and utilized them as a starting point for our periodic DFT investigations, applying the PBE+U method. Ni2F5 as the most stable polymorph was found to be of the same crystal structure as another mixed valent fluoride, Cr2F5. The calculated lattice parameters are a = 7.24 Å, b = 7.40 Å, c = 7.08 Å and β = 118.9° with an antiferromagnetic ordering of the nickel magnetic moments.

Biobased Linear Alkyl-Benzene Production by Hydrodeoxygenation of Cardanol Under Ambient Pressure

An innovative and green method for 1-phenyl pentadecane production is presented by that utilizes the hydrogenation of cardanol (unsaturated 3-n-pentadecylphenol) under ambient pressure. Different from the common production of branched alkylbenzenes from Friedel–Crafts alkylation method, in which expensive long chain α-olefins and anhydrous HF or AlCl3 acid are used, 1-phenyl pentadecane has better biodegradability and can be used in the production of high-value chemicals or biofuels, such as surfactant detergents, lubricants and diesel fuel additives. The reaction under ambient pressure is milder than high pressure HDO reaction that can avoid excessive H2 consumption and reduce the reaction cost. The 20 MT catalyst used in this research can be reused in five cycles, and the conversion rates remained greater than 90%. This reusable property allows this hydrodeoxygenation reaction process to be conducted in a fluidized bed reactor. The hydrodeoxygenation of cardanol under ambient pressure provides a new method for linear alkylbenzene production that results in a high yield from a bio-based raw material, cardanol.