Syntheses of NF4 salts derived from the lewis acids AlF3 and BeF2

The new salts NF₄Be₂F₅ and NF₄AlF₄ were prepared from concentrated NF₄HF₂ solutions and BeF₂ and AlF₃ respectively.     

Etude catorimetrique de la decomposition thermique des sels de tetraflouroammonium (NF4)2NiF6 et NF4SbF6

The study of the thermal decomposition of the tetrafluoroammonium salts (NF₄)₂NiF₆ and NF₄SbF₆ by differential scanning calorimetry also gave enthalpies of decomposition for (NF₄)₂NiF₆ and NF₄SbF₆ of 134.7 ± 13.0 kJ mol^?1 and 245.6 ± 28.9 kJ mol^?1 respectively. The corresponding standard enthalpies of formation are found to be ?1033 and ?1649 kJ mol^?1 respectively.     

Hydrogendifluorokobaltate(II)

Zusammenfassung Aus Kobalt(II)perchlorat und Piperidiniumhydrogendifluorid entstehen in nichtwäßrigen Lösungsmitteln (L) Komplexe, welche HF₂-Einheiten als Liganden enthalten, nämlich [Co(HF₂)L ₅]⁺, [Co(HF₂)₂ L ₄], [Co(HF₂)₃ L ₃]^–, [Co(HF₂)₄ L ₂]^2– und [Co(HF₂)₆]^4–.

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Hydrogendifluorocobaltates(II)

Cobalt(II)perchlorate and piperidinium hydrogendifluoride in non-aqueous solvents (L) yield complex compounds containing an HF₂-group as ligand, e.g. [Co(HF₂)L ₅]⁺, [Co(HF₂)₂ L ₄], [Co(HF₂)₃ L ₃]^–, [Co(HF₂)₄ L ₂]^2– and [Co(HF₂)₆]^4–.

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Mit 3 Abbildungen     

Mass-spectrometric study of tetrafluorohydrazine and the products resulting from its breakdown under electron impact

Conclusions Electron-impact methods have been used to study positive (NF⁺, NF₂ ⁺, N₂F₂ ⁺) and negative (F^–, F₂ ^–, N₂F^–, NF₂ ^–) ion formation in the mass spectra of tetrafluorohydrazine and its decomposition products.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1306–1311, June, 1978.The authors would like to thank V. Ya. Rosolovskii for a discussion of the results obtained in this work.     

Formation Mechanism of NF4+ Salts and Extraordinary Enhancement of the Oxidizing Power of Fluorine by Strong Lewis Acids

Although the existence of the NF₄⁺ cation has been known for 51 years, and its formation mechanism from NF₃ , F₂ , and a strong Lewis acid in the presence of an activation energy source had been studied extensively, the mechanism had not been established. Experimental evidence had shown that the first step involves the generation of F atoms from F₂ , and also that the NF₃⁺ cation is a key intermediate. However, it was not possible to establish whether the second step involved the reaction of a F atom with either NF₃ or the Lewis acid (LA). To distinguish between these two alternatives, a computational study of the NF₄ , SbF₆ , AsF₆ , and BF₄ radicals was carried out. Whereas the heats of reaction are small and similar for the NF₄ and LAF radicals, at the reaction temperatures, only the LAF radicals possess sufficient thermal stability to be viable species. Most importantly, the ability of the LAF radicals to oxidize NF₃ to NF₃⁺ demonstrates that they are extraordinary oxidizers. This extraordinary enhancement of the oxidizing power of fluorine with strong Lewis acids had previously not been fully recognized.     

Enthalpie de dissolution du fluorure et de l′hydrogenofluorure d'ammonium dans les solutions d'acide fluorhydrique

The standard enthalpies of solution of NH₄F and NH₄HF₂ in aqueous solutions of hydrogen fluoride (in the range of concentration 0–30 mol.1^?1) have been measured and from these results the standard enthalpy of formation of NH₄HF_2(c) has been derived as: δH^o_fNH₄HF_2(c) = ?809.9 ± 0.9 kJ.mol^?1     

Structure and stability of the HFF and FHF radicals

The structure and stability of the HFF and FHF isomers in their two lowest electronic states is studied by means of ab initio SCF and CI calculations employing a double-zeta basis plus various polarization functions. Both complexes can be essentially described by an HF dipole (exhibiting a standard HF bond length) attracting a fluorine atom, with an FF distance of 5.14 bohr calculated for the HF··F ground state and an H··F bond of 4.3 bohr for the most stable FHF species. The HF₂ radical is found to prefer a bent structure in its ²Σ⁺ - ²A' ground state with an extremely flat potential curve, while the first very low-lying excited state of HF₂ as well as both components of the ground (in this case ²Π) state of the FH··F complex are calculated to be linear. The symmetric FHF structure exhibits optimal bond lengths at approximately 2.1 bohr but is considerably less stable than the asymmetrical arrangement of nuclei. With respect to dissociation into HF + F the HF₂ form is found to be stable in both (²Σ⁺ - A') and ²Π states while the conformer FH··F shows a minimum only for the ²Π ground state; the exothermicity of the H + F₂ → HF + F reaction is calculated to be 104.6 kcal mol^?1 in good agreement with the experimental quantity of 102.5 ± 2.8 kcal mol^?1. Comparison with the negative ions HF₂^?and FHF^? is made whenever appropriate.     

Gas‐phase reactions of XH3+ (X = C,Si, Ge) with NF3: a comparative investigation on the detailed mechanistic aspects

The gas‐phase reaction of CH₃⁺ with NF₃ was investigated by ion trap mass spectrometry (ITMS). The observed products include NF₂⁺ and CH₂F⁺. Under the same experimental conditions, SiH₃⁺ reacts with NF₃ and forms up to six ionic products, namely (in order of decreasing efficiency) NF₂⁺, SiH₂F⁺, SiHF₂⁺, SiF⁺, SiHF⁺, and NHF⁺. The GeH₃⁺ cation is instead totally unreactive toward NF₃. The different reactivity of XH₃⁺ (X = C, Si, Ge) toward NF₃ has been rationalized by ab initio calculations performed at the MP2 and coupled cluster level of theory. In the reaction of both CH₃⁺ and SiH₃⁺, the kinetically relevant intermediate is the fluorine‐coordinated isomer H₃X‐F‐NF₂⁺ (X = C, Si). This species forms from the exoergic attack of XH₃⁺ to one of the F atoms of NF₃ and undergoes dissociation and isomerization processes which eventually result in the experimentally observed products. The nitrogen‐coordinated isomers H₃X‐NF₃⁺ (X = C, Si) were located as minimum‐energy structures but do not play an active role in the reaction mechanism. The inertness of GeH₃⁺ toward NF₃ is also explained by the endoergic character of the dissociation processes involving the H₃Ge‐F‐NF₂⁺ isomer. Copyright © 2009 John Wiley & Sons, Ltd.     

Gas‐phase reactions of SiHn+ (n = 1,2) with NF3: A computational investigation on the detailed mechanistic aspects

The mechanism of the gas‐phase reactions of SiH_n⁺ (n = 1,2) with NF₃ were investigated by ab initio calculations at the MP2 and CAS‐MCSCF level of theory. In the reaction of SiH⁺, the kinetically relevant intermediates are the two isomeric forms of fluorine‐coordinated intermediate HSi‐F‐NF₂⁺. These species arise from the exoergic attack of SiH⁺ to one of the F atoms of NF₃ and undergo two competitive processes, namely an isomerization and subsequent dissociation into SiF⁺ + HNF₂, and a singlet‐triplet crossing so to form the spin‐forbidden products HSiF⁺ + NF₂. The reaction of SiH₂⁺ with NF₃ involves instead the concomitant formation of the nitrogen‐coordinated complex H₂Si‐NF₃⁺ and of the fluorine‐coordinated complex H₂Si‐F‐NF₂⁺. The latter isomer directly dissociates into NF₂⁺ + H₂SiF, whereas the former species preferably undergoes the passage through a conical intersection point so to form a H₂SiF‐NF₂⁺ isomer, which eventually dissociates into H₂SiF⁺ and NF₂. © 2012 Wiley Periodicals, Inc.     

Vibrational spectra of AuF5 complexes with nitrogen fluorides and oxofluorides

Vibrational spectra and structural features of AuF₅ complexes with nitrogen fluorides (NF₃, N₂F₄) and oxofluorides (FNO, NF₃O) are investigated. Vibrational frequency assignment in the solid phase and in solution of anhydrous HF was made. Distinctive features of vibrational spectra of X⁺AuF₆ ^? (X = NF₄ ⁺, N₂F₃ ⁺, NO⁺, NOF₂ ⁺) related to structural transformations of cations and hexafluoroaurate anion due to the influence of the crystal field and cation-anion interactions are discussed.     

Exchange studies with NF4AsF6

Isotopic exchange experiments have been conducted with the salt NF₄AsF₆ and gaseous ⁷⁶AsF₅, As¹⁸F₅, ¹⁸F₂, ¹⁵NF₃ and N¹⁸F₃. Exchange of the fluorine atoms of AsF₅ is believed to occur via the less volatile complex salt NF₄As₂F₁₁. Evidence for the existence of this salt is presented in the form of pressure composition data.     

A comparison of enthalpies of tetrafluoroammonium salts and other fluoro-nitrogen species

It is shown that enthalpies of nitrogen fluorides and oxo fluorides deviate markedly from enthalpies of corresponding hydroxo compounds, whereas there is good agreement (circa 2%) between carbon mono, di and trifluoro compounds and their hydroxo analogues. The extent of deviation correlates with the extra number of lone pair repulsions of fluoro over oxo compounds. The enthalpy of NF₄⁺(g) can be extrapolated from the other (N,F) and (N,O,F) compounds. The enthalpies of solid NF₄⁺ salts are close to those of corresponding NO₂⁺ salts and from this an exothermic heat of formation for NF₄⁺F^? is predicted.     

Structure and thermal stability of difluoroamino compounds in the liquid state

The kinetics of decomposition of 15 difluoroamino compounds with NF₂ groups at primary, secondary, and tertiary carbon atoms in the liquid state was investigated. Activation energies (E _a) for all of the compounds were in the interval 100–120 kJ · mol^–1. The reaction rate does not depend on the electronic effects of the substituents and decreases only in the case of steric shielding of the NF₂ group. ForN-difluorobenzylamine it was shown that the gas-phase elimination of HF is characterized byE = 176 kJ·mole^–1, while the rate of decomposition in a solution depends on the dielectric constant of the medium. Based on the results obtained, a mechanism for liquid-phase decomposition, which involves heterolysis of the N-F bonds, is suggested.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 336–338, February, 1994.     

Determination of the difference in the zero point energies of gauche- and trans-N2F4 from the equilibrium constant of NF2 radical dimerization

Experimental equilibrium constants of the dimerization process 2 NF₂(g) = N₂F₄(g) were used for the determination of the energy difference in the ground states of gauche- and trans-N₂F₄(g) molecules. The equilibrium studied was taken as a result of two partial processes, viz. 2 NF₂(g) = trans-N₂F₄(g) and 2 NF₂(g) = gauche-N₂F₄(g). The treatment used represents a generalization of the “third law analysis”, leading to a non-linear problem which was solved by the “variable metric method” iteration technique. After treatment of all the experimental data available in the literature the value 2.39 kJ.mol^-1 was found. The applicability of quantum chemistry methods for this kind of calculation is discussed.     

On the synthesis of the N2F+5 cation. A critical comment on the paper by Toy and Stringham.

Toy and Stringham recently reported [1] the synthesis of N₂F⁺₅ (CF₃)₃CO^-, a salt containing the novel pentafluorohydrazinium cation. This cation would be of significant academic and practical interest [2] since it would constitute the first known example of a substituted NF⁺₄ cation, i.e. an NF⁺₄ cation in which a fluorine ligand is replaced by an NF₂ group. According to the authors of [1], N₂F⁺₅(CF₃)₃CO^- was formed in a very unusual reaction involving the transfer of a fluorine cation from (CF₃)₃COF to N₂F₄ according to:

     

An AB initio molecular orbital study of the NF2 and N2F4 molecules,and ESR hyperfine coupling constants in NF2

In this publication, we present the results of gaussian type orbital calculations of ESR hyperfine coupling constants in NF₂. We also present electron density maps for the molecule, and the results of a calculation of ΔH⁰₂₉₈ for the reaction N₂F₄ → 2NF₂.     

Thermal decomposition of α-(difluoroamino)polynitroalkanes

The compounds RC(NO₂)₂NF₂ differ little from their nitro analogs, RC(NO₂)₃, in stability. They decompose in the gas and liquid phases at identical rates and the decomposition is controlled by cleavage of a C-NO₂ bond. For R=NO₂, F, and Me the Arrhenius parameters, E (kJ mol^–1) and log (A/s), are: 161.3 and 16.00; 180.2 and 16.20; 168.4 and 16.00, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 649–651, April, 1995.The authors are grateful to A. A. Fainzil'berg and S. A. Shevelev for providing the compounds for the study.     

Effective modification of MgO with surface transition metal oxides for NF3 decomposition

NF3 decomposition over transition metal oxides coated MgO reagents in the absence of water is investigated. The results show that NF3 can be decomposed completely over pure MgO but the time of NF3 steady full conversion kept as short as 80 min, while the reactivities of coated MgO reagents were remarkably enhanced by transition metal oxides, for example the time of NF3 complete conversion over 12%Fe/MgO extended to 380 min. It is suggested that not only an increase in surface area but also a significant enhancement in the fluorination of MgO substrate caused by the surface transition metal oxides result in an improved reactivity of coated MgO reagents for NF3 decomposition.     

Equilibrium constants of HF,F-, HF-2 and H2F2 species in formic acid.

Equilibrium constants for the fluorinated species HF, F^-, HF^-₂ and H₂F₂ in formic acid and in a 1M potassium formate solution in formic acid have been studied by ¹⁹F NMR. The chemical shifts of these species have been determined from measurements of the shifts for various initial mixtures of differing concentrations of dissolved HF, F^- and HF^-₂. From these values, relative concentrations of HF, F^-, and HF^-₂ and H₂F₂ in each solution have been calculated through a numerical method. The following constants were obtained: K₁ = [H⁺][F^-]/[HF] = 1.1 x 10^-5M; K_D = [HF][F^-]/[HF^-₂] = 0.5 M; K′₁ = [H⁺][HF^-₂]/[H₂F₂]= 1.1 x 10^-5 M; K′_D = [HF]²/[H₂F₂]=0.5 M.