Liquid Anhydrous Hydrogen Fluoride Research Articles

Effects of Hydrogen Bonding on Nuclear Data Development of Liquid Anhydrous HF

Anhydrous Hydrogen Fluoride (HF) at high temperatures and pressures is used to process and manufacture nuclear fuel. As HF is often used directly with uranium, correct neutron thermal scattering cross sections are crucial to criticality safety applications. Classical molecular dynamics (CMD) simulation of the flexible HF system was used to create the thermal scattering law (TSL) and cross sections. The initial 2-site model is used in LAMMPS, and it can not capture the H-bond. To correctly represent the H-bond effects, a second, 3-site model was constructed in GROMACS. The 3-site model handled H-bonds by connecting a massless charge to the molecule. Key model parameters were compared to experimental data to verify the approach and models. To get the normalized VACF, the model was compared using hydrogen and fluorine bond length, density, potential energy, and diffusion coefficient. The phonon DOSs for both models were derived from the normalized VACF. DOSs were used to estimate the TSL (S(α,β)) and neutron thermal scattering cross sections for hydrogen in HF. The TSLs were evaluated using the FLASSH code with the Schofield diffusion model. It was observed that the representation of the hydrogen bonding changes the TSL's diffusional contributions. This is represented in the low energy scattering cross section, where intermolecular binding effects shift the cross section.

Attempted syntheses of new mixed-cation hexafluoridoarsenates(V) in liquid anhydrous HF acidified with AsF5; the crystal structures of A3M(HF)Mn(AsF6)7 (A = H3O, K/H3O; M = Ca, Sr, Ba)

A study of the reactions between the various starting molar ratios of H3OAsF6, and in situ prepared M(AsF6)2 (M = Mg, Ca, Sr, Ba) and Mn(AsF6)2 in liquid anhydrous hydrogen fluoride (aHF) acidified with AsF5 resulted in three novel oxonium salts, i.e. (H3O)3M(HF)Mn(AsF6)7 (M = Ca, Sr) and (H3O)5BaMn(AsF6)9. Reactions between in situ prepared AAsF6 (A = K, NH4), M(AsF6)2 (M = Ca, Sr, Ba) and M’(AsF6)2 (M’ = Mn, Mg, Ni, Co, Zn) in aHF acidified with AsF5 gave mixtures of various products upon crystallization. An attempt to grow single crystals of K3Ba(HF)Mn(AsF6)7 resulted in (H3O/K)3Ba(HF)Mn(AsF6)7 instead, due to moisture penetrating through the reaction vessel walls during long lasting crystallization. The crystal structures of A3M(HF)Mn(AsF6)7 (A = H3O for M = Ca and Sr; A = H3O/K for M = Ba) salts are isotypical and crystallize in the monoclinic space group P21/n (No. 14). The crystal structures consist of a complex three-dimensional framework formed from M2+ (M = Ca, Sr, Ba) and Mn2+ cations interconnected with [AsF6]– anions. The HF molecules are bound directly to alkaline earth metals via the fluorine atom. Single charged cations are located within the cavities. The Mn atoms are found in an octahedral coordination of six fluorine atoms. The Ca atoms are coordinated by eight fluorine atoms, while this number increases to nine for the Sr and Ba atoms.

Syntheses of Dioxygenyl Salts by Photochemical Reactions in Liquid Anhydrous Hydrogen Fluoride: X-ray Crystal Structures of α- and β-O2Sn2F9, O2Sn2F9·0.9HF, O2GeF5·HF, and O2[Hg(HF)]4(SbF6)9.

By treating gaseous, liquid, or solid fluorides with UV-photolyzed O2/F2 mixtures and by treating solid oxides with UV-photolyzed F2 (or O2/F2 mixtures) in liquid anhydrous HF at ambient temperature, we investigated the possibility of the preparation of O2MIIIF4 (M = B, Fe, Co, Ag), O2MIVF5 (M = Ti, Sn, Pb), (O2)2MIVF6 (M = Ti, Ge, Sn, Pb, Pd, Ni, Mn), O2MIV2F9 (M = Sn), O2MVF6 (M = As, Sb, Au, Pt), O2MV2F11 (M = Pt), O2MVIF7 (M = Se), (O2)2MVIF8 (M = Mo, W), and O2MVIIF8 (M = I). The approach has been successful in the case of previously known O2BF4, O2MF6 (M = As, Sb, Au; Pt), O2GeF5, and (O2)2(Ti7F30). Novel compounds O2GeF5·HF, α-O2Sn2F9 (1-D), and the HF-solvated and nonsolvated forms of β-O2Sn2F9 (2-D) were synthesized and their crystal structures determined using single-crystal X-ray diffraction. The crystal structures of all of these materials arise from the condensation of octahedral MF6 (M = Ge, Sn) units. The anion in the crystal structure of O2GeF5·HF is comprised of infinite ([GeF5]−)∞ chains of GeF6 octahedra that share common vertices. The HF molecules and O2+ cations are located between the chains. The crystal structure of α-O2SnF9 (1-D) is constructed from [O2]+ cations and polymeric ([Sn2F9]−)∞ anions which appear as two parallel infinite chains comprised of SnF6 units, where each SnF6 unit of one chain is connected to a SnF6 unit of the second chain through a shared fluorine vertex. The single-crystal structure determination of [O2][Sn2F9]·0.9HF reveals that it is comprised of two-dimensional ([Sn2F9]−)∞ grids with [O2]+ cations and HF molecules located between them. The 2-D grids have a wavelike conformation. The ([Sn2F9]−)∞ layer contains both six- and seven-coordinated Sn(IV) atoms that are interconnected by bridging fluorine atoms. A new, more complex [O2]+ salt, O2[Hg(HF)]4[SbF6]9, was prepared. In its crystal structure, the Hg atoms bridge to SbF6 units to form a 3-D framework. The O2+ cations are located inside the voids while the HF molecules are bound to Hg atoms through the F atom. Attempts to prepare several chlorine analogues of O2+ fluorine salts (i.e., O2TiCl5 and O2MCl6 (M = Nb, Sb)) failed.

Anhydrous Hydrogen Fluoride Cleavage in Boc Solid Phase Peptide Synthesis.

Solid phase peptide synthesis using tert-butyloxycarbonyl/benzyl chemistry (Boc-SPPS) is important for producing peptides for fundamental research as well as for clinical use. During Boc-SPPS, liquid anhydrous hydrogen fluoride (HF) is used to remove the side chain protecting groups of the assembled peptide and to release it from the resin. Here, we provide a detailed protocol for "HF cleavage," aiming to improve accessibility and the use of this valuable and well-validated technique.

Preparative Electrosynthesis of Strong Oxidizers at Boron-Doped Diamond Electrode in Anhydrous HF.

The use of the boron-doped diamond electrode as a sufficiently stable electrode for electrochemical measurements/synthesis in liquid anhydrous hydrogen fluoride medium is reported. Electrooxidation of silver(I) has been studied in this solvent by using classical transient electrochemical methods and impedance spectroscopy. It has been found that faradaic currents related to silver(I) oxidation and the fluorine evolution reaction are reasonably separated at the potential scale, which allows efficient electrosynthesis of AgII F2 , a powerful oxidizer. Impedance spectroscopy measurements provide insight into complex mechanism of AgF2 formation. The procedure for electrosynthesis is provided for the first time in both galvanostatic and potentiostatic condition.

Syntheses and the crystal chemistry of the perfluoridotitanate(IV) compounds templated with ethylenediamine and melamine

Chemical reactions between ethane-1,2-diamine [C2H4(NH2)2; ethylenediamine, abbr. en] and 1,3,5-triazine-2,4,6-triamine [C3H6N6; melamine, abbr. mel], with titanium tetrafluoride (TiF4) were carried out in liquid anhydrous hydrogen fluoride (aHF). The latter acted in a dual role: as a reagent and as a solvent. The n(en): n(TiF4) = 2:1, 1:1, 1:3, 1:4, and n(mel): n(TiF4) = 2:1, 1:1, 1:2, 1:3, 1:4 M ratios were studied. Crystallizations of the products from the saturated HF solutions yielded single crystals of [enH2]F2·2HF, previously known [enH2][TiF6] and three new perfluoridotitanate(IV) salts, i.e., [enH2][TiF6]·HF, [enH2]0.5[TiF5] and [melH2][TiF6]·HF. Their crystal structures were determined including the crystal structure of the low-temperature modification of [enH2][TiF6]. The [enH2]0.5[TiF5] phase represents the first example of a structurally characterized perfluoridotitanate(IV) compound with a double charged cation, where instead of the usual octahedral [TiF6]2− monomer, another kind of anion is present, i.e., polymeric chain-like ([TiF5]−)∞ anion. The reactions in en/TiF4/HF and mel/TiF4/aHF systems are not selective enough to enable syntheses of individual [enH2]2+ and [melH2]2+ perfluoridotitanates(IV) in large quantities.

Impedance of Nickel and Platinum Anodic Dissolution in Anhydrous Hydrogen Fluoride

Liquid anhydrous hydrogen fluoride (aHF) is a widely used solvent for the anodic fluorination of organic and inorganic molecules, electrosynthesis of fluorine containing compounds and electrolytic generation of fluorine. Anhydrous hydrogen fluoride is also used on the industrial scale for the production of most fluorine compounds. In this research we intended to use aHF in electrosynthesis of divalent silver fluoride, AgIIF2, which is the most stable and commonly used divalent silver compound. Currently, the chemical methods of AgIIF2 synthesis involve several steps performed in aHF leading to the formation of a fine graded powders contaminated with amorphous impurities. Strongly aggressive nature and high toxicity of aHF makes this synthesis difficult and time consuming, however by using electrochemical methods one may reduce the number of necessary steps and complexity of the synthesis. It should be noted that in general electrosynthesis is inexpensive, safe and effective method of high purity chemicals preparation. Electrochemical methods usually lead also to the formation of more crystalline products as we have recently observed for silver(II) sulfate obtained in the form of compact crystallites with a few tens of micrometers in size [1]. Electrochemical studies in aHF are seldom reported, Hackerman et al. reported kinetic measurements of anodic dissolution of 24 different materials in aHF [2]. All investigated electrodes have undergone corrosion in aHF particularly during anodic polarization. To date no stable working electrode material has been reported for electrochemical studies in aHF. The most promising materials with the slowest anodic dissolution are platinum and nickel [2]. Here we report the mechanistic studies of platinum and nickel corrosion during anodic polarization in aHF carried out by using Electrochemical Impedance Spectroscopy (EIS). It should be noted that although this method is the most suitable for mechanistic studies it has not been previously reported for electrochemical processes in anhydrous HF. The stability of individual electrodes during anode polarization in aHF was determined. Based on the impedance analysis we report strong passivation of nickel electrode and we discuss the mechanism of platinum oxidation. Pt undergo anodic dissolution with the formation of adsorbed intermediates, furthermore the electrode processes are coupled with chemical reactions leading to the fluorine evolution. The electrosynthesis of AgIIF2 in aHF containing AgF was attempted and possible reaction mechanism will be also discussed. [1] P. Połczyński, T.E. Gilewski, J. Gawraczyński, M. Derzsi, P.J. Leszczyński, W. Gadomski, Z. Mazej, R. Jurczakowski, W. Grochala, Efficient Electrosynthesis of AgIISO4: A Powerful Oxidizer and Narrow Band Gap Semiconductor, European Journal of Inorganic Chemistry, 2016 (2016) 5401-5404. [2] N. Hackerman, E. Snavely, L. Fiel, The anodic polarization behaviour of metals in hydrogen fluoride, Corrosion Science, 7 (1967) 39-50.

Copper(I) Hexafluoroantimonate — An Example of a Compound with CuI in a Solely Fluorine Environment.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Copper(I) hexafluoroantimonate – an example of a compound with Cu I in a solely fluorine environment

Yellow–orange single crystals of CuSbF 6, were prepared by reacting Cu wire (∼10 mmol) with SbF 5 (∼3 mmol) in liquid anhydrous hydrogen fluoride (aHF) and by reduction of Cu(SbF 6) 2 with Cu metal in aHF. CuSbF 6 crystallizes rhombohedral at 296 K with the LiSbF 6 structure type, with a = 530.4(4) pm, c = 1453(1) pm and Z = 3, space group R 3 ¯ (no. 148). The structure is dominated by isolated layers of regular [SbF 6] − octahedra and Cu + cations. An attempt to prepare CuF by reaction between CuSbF 6 and CsF in aHF at ∼190 K failed. Instead of CuF, a mixture of Cu and CuF 2 was obtained.

Preparation of Lithium Hexafluorophosphate from LiF and P in Fluorine Atmosphere

Abstract Pure lithium hexafluorophosphate (LiPF6) has been successfully prepared by the reaction between the elemental fluorine and the equi-molar mixture of LiF and P (F2 direct method). The product was pure enough to be used as an electrolyte salt of lithium secondary battery. Especially, the stepwise introducing of fluorine gas into a reaction system was effective to prepare LiPF6 in a high yield. The results of Rietveld refinement of XRD data revealed that the structure of LiPF6 was trigonal (, Z = 3, a0 = 0.4932(2), c0 = 1.2641(5) nm, cell volume; 2.663(2) × 10−28 m3). The cell constants of LiPF6 prepared by the F2 direct method were almost the same as those of LiPF6 prepared by the reaction between LiF and PF5 in a liquid anhydrous hydrogen fluoride (L-AHF method).

Room temperature syntheses of lanthanoid tetrafluorides (LnF 4, Ln = Ce, Pr, Tb)

CeF 3 is oxidised to CeF 4 at room temperature by elemental fluorine in liquid anhydrous hydrogen fluoride (aHF) as a solvent. The reactions of ultraviolet photolysed F 2 with Pr 6O 11 or Tb 4O 7 in aHF at room temperature produce PrF 4 or TbF 4, respectively, in quantitative yield. The synthesis described of PrF 4 represents a convenient approach requiring only commercially available reactants.

Room temperature preparations of second and third transition series tetrafluorides and a possible novel structure type for OsF 4 and RhF 4

The polymeric tetrafluorides, MF 4 (M=Mo, Ru, Pd, Re, and Os) have been precipitated from their MF 6 2− salts in liquid anhydrous hydrogen fluoride (aHF) at ∼20 °C. For M=Ru, Os and Pd, AsF 5 can be used to displace the tetrafluoride, but this strong F − acceptor is too strongly oxidizing for use in making MoF 4 and ReF 4, for which SbF 5 is effective. X-ray powder diffraction photograph (XRDP) show the MF 4 to have the same structures as those from higher temperature preparations, when previously known. XRDP of OsF 4 are very like those of RhF 4 and indicate a close structural relationship of the pair, and a significant structural difference from the PdF 4 type structure adopted by M=Pd, Pt, Ir, and Re. A new, two-dimensional, ‘raft’ structure is proposed for OsF 4 and RhF 4.

Disproportionation of Ag(II) to Ag(I) and Ag(III) in Fluoride Systems and Syntheses and Structures of (AgF+)2AgF4-MF6- Salts (M = As, Sb, Pt, Au, Ru)

Interaction of Ag(+) salts in anhydrous liquid hydrogen fluoride, aHF, with AgF(4)(-) salts gives amorphous red-brown diamagnetic Ag(I)Ag(III)F(4), which transforms exothermally to brown, paramagnetic, microcrystalline Ag(II)F(2) below 0 degrees C. Ag(I)Au(III)F(4) prepared from Ag(+) and AuF(4)(-) in aHF has a tetragonal unit cell and a KBrF(4) type lattice, with a = 5.788(1) Å, c = 10.806(2) Å, and Z = 4. Blue-green Ag(II)FAsF(6) disproportionates in aHF (in the absence of F(-) acceptors) to colorless Ag(I)AsF(6) and a black pseudotrifluoride, (Ag(II)F(+))(2)Ag(III)F(4)(-)AsF(6)(-). The latter and other (AgF)(2)AgF(4)MF(6) salts are also generated by oxidation of AgF(2) or AgF(+) salts in aHF with F(2) or in solutions of O(2)(+)MF(6)(-) salts (M = As, Sb, Pt, Au, Ru). Single crystals of (AgF)(2)AgF(4)AsF(6) were grown from an AgFAsF(6)/AsF(5) solution in aHF standing over AgF(2) or AgFBF(4), with F(2) as the oxidant. They are monoclinic, P2/c, at 20 degrees C, with a = 5.6045(6) Å, b = 5.2567(6) Å, c = 7.8061(8) Å, beta = 96.594(9) degrees, and Z = 1. The structure consists of (AgF)(n)()(n)()(+) chains (F-Ag-F = 180 degrees, Ag-F-Ag = 153.9(11) degrees, Ag-F = 2.003(4) Å), parallel to c, that enclose stacks of alternating AgF(4)(-) and AsF(6)(-), each anion making bridging contact with four Ag(II) cations of the four surrounding chains "caging" them. There is no registry between the ordered array in one "cage" and that in any neighboring "cage". The F-ligand anion bridges between the anions and, with the Ag(II) of the chains, generates a trifluoride-like structure. (AgF)(2)AgF(4)AsF(6) [like other (AgF)(n)()(n)()(+) salts] is a temperature-independent paramagnet except for a Curie "tail" below 50 K.

Room Temperature Syntheses of AuF6- and PtF6- Salts, Ag+AuF6-, Ag2+PtF62-, and Ag2+PdF62-, and an Estimate for E(MF6-) [M = Pt, Pd

Solutions of AuF4- or PtF62- salts, prepared from the metals at ∼20 °C, in liquid anhydrous hydrogen fluoride (aHF), made basic with alkali fluorides, are further oxidized by photodissociated F2 (visible or near-UV light) to give AuF6- or PtF6- salts, including O2+AuF6- (with O2 in the F2). Similar photochemical oxidation of PdF62- salts does not occur. This new synthetic approach has provided LiAuF6 and LiPtF6 for the first time, each of which has the LiSbF6 type (R3̄) structure with (hexagonal cell): LiAuF6, a = 4.9953(9) Å, c = 13.704(3) Å, V/Z = 98.71(6) Å3; LiPtF6, a = 5.0236(7) Å, c = 13.623(2) Å, V/Z = 99.25(5) Å3. Interaction of AuF6- with Ag+ gives Ag+AuF6- (R3̄, a = 5.283(3) Å, c = 15.053(6) Å, V/Z = 121.3(2) Å3), whereas PtF62- or PdF62- stabilize Ag2+ as Ag2+Pt(Pd)F62- (R3̄; AgPtF6: a = 5.049(8) Å, c = 14.46(2) Å, V/Z = 106.4(5) Å3; and AgPdF6, a = 5.00(4) Å, c = 14.6(2) Å, V/Z = 105(3) Å3). New cubic modifications (probable space group Ia3) have been found for AgMF6 (M, a value, Å): Ru, 9.653(10); Os, 9.7318(9); Ir, 9.704(2). The preference for Ag2+Pt(Pd)F62- over Ag+Pt(Pd)F6- is attributed to a second electron affinity of Pt(Pd)F6, E(Pt(Pd)F6-)> 60 kcal mol-1.

Facile Routes to NiF(6)(2)(-), AgF(4)(-), AuF(6)(-), and PtF(6)(-) Salts Using O(2)(+) as a Source of O(2)F in Anhydrous HF.

O(2)(+) salts dissolved in liquid anhydrous hydrogen fluoride (aHF) at 20 degrees C or below oxidize aHF solutions of PtF(6)(2)(-) to PtF(6)(-). The parent base of O(2)(+) salts in aHF (O(2)F((solv))) generated with alkali fluoride is long-lived below -50 degrees C. An aHF solution of O(2)F((solv)) oxidizes Au(III) to Au(V) below -50 degrees C (2O(2)F((solv)) + AuF(4)(-)((solv)) --> AuF(6)(-)((solv)) +2O(2(g))). In situ generation of O(2)F((solv)) (O(2)(+)((solv)) + F(-)((solv)) --> O(2)F((solv))) with AgF(2) or NiF(2) in suspension in the aHF made basic with alkali fluoride gives AgF(4)(-) and NiF(6)(2)(-)salts. Low solubility of AAsF(6)(A = Cs, K) in aHF provides for the metathetical preparation of (O(2))(2)PdF(6) solutions in aHF. Removal of aHF, even at -60 degrees C, results in some O(2) and F(2) loss, to a composition approaching (O(2))PdF(5).

Reactions of dioxygen difluoride with neptunium oxides and fluorides

Neptunium dioxide and tetrafluoride are converted in essentially quantitative yield to volatile neptunium hexafluoride by dioxygen difluoride (O 2F 2), both in gas–solid reactions at ambient temperatures and in liquid anhydrous hydrogen fluoride at −78°C. Neptunium dioxydifluoride was identified by Raman spectroscopy as a dominant reaction intermediate in the neptunium dioxide reaction. Direct reaction of NpF 4 with liquid O 2F 2 resulted in violent decomposition of O 2F 2 with little or no conversion to NpF 6. These reaction temperatures contrast markedly with the elevated temperatures (above 200°C) required for NpF 6 generation using elemental fluorine or halogen fluorides.

High yield room temperature syntheses of KAgF 4 and AgF 3 and the preparation and unit cell of LiAgF 4

AgF 2 dissolves at ∼ 20°C in liquid anhydrous hydrogen fluoride (aHF), containing either LiF or KF, with sunlight or ultraviolet (UV)-irradiated F 2. Concentrated KF-aHF solutions quickly give a nearly quantitative conversion to KAgF 4. Preparation of LiAgF 4 is less efficient, but it can be prepared in high purity. It is isomorphous with LiAuF 4, and has a monoclinic unit cell: a = 4.87 (1)_; b = 5.93 (1) ; c = 10.08 (1) Å; β = 93.0(1)°; V = 291 (1) Å 3; z = 4. KHF 2 impurity in KAgF 4 can be removed as KPF 6 with PF s at 0°C. Preparation of AgF 3, with minimum contamination by Ag 3F 8, is achieved at 0°C using GeF 4 as F − acceptor. The high solubility of the salt K 2GeF 6 makes this possible.

Fluorination of deltahedral closo-borane and -carborane anions with N-fluoro reagents

The treatment of cesium salts of CB 11H 12, CB 9H 10, B 12H 2, and B 10H 10 2− with the commercially available N-fluoro reagent 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (F-TEDA) resulted in the formation of fluorinated derivatives of these 10- and 12-vertex borane and carborane anions. This is the first reported use of an N-fluoro reagent to fluorinate BH bonds of any type. The effects of changing the solvent, temperature, and reagent stoichiometry were studied. The derivatives 1-B 10H 9F 2-,2-B 10H 9 F 2, and 1,10-B 10H 8F 2 2 are the first fluorinated derivatives of the parent B 10H 10 2 cluster. For the other three parent anions, reactions with F-TEDA resulted in a higher degree of fluorination than reactions with liquid anhydrous hydrogen fluoride (LAHF) at the same temperature. However, F-TEDA was found to be less regioselective than LAHF for BH → BF transformations.

The room temperature conversion of nickel difluoride to hexafluoronickelate(IV) salts of alkali cations

NiF 2 was oxidized at ~20 °C, to NiF 6 2− by sunlight or ultraviolet light-irradiated F 2 in liquid anhydrous hydrogen fluoride (aHF) containing alkali hydrofluorides AF(HF) x . Quantitative formation of NiF 6 2 can be achieved with strongly basic solutions (e.g., KF:HF molar ratio ~ 1:4). Li 2NiF 6, which was previously unknown, is the least aHF soluble of the alkali NiF 6 2 salts, and was prepared in high purity.

Synthesis of fluorine-graphite intercalation compounds in anhydrous liquid hydrogen fluoride containing a Lewis acid

Synthesis of fluorine-graphite intercalation compounds in anhydrous liquid hydrogen fluoride containing a Lewis acid