Mise au point d'un appareillage de preparation et de manipulation de melanges anhydres HFNH3MF (M alcalin) — tension de vapeur totale au-dessus de solutions HFNH3 riches en HF

An apparatus for preparing and handling HFNH₃MF mixtures (M alkali metal) has been designed and constructed. The vacuum line made of plastic materials (PVF₂, PTFCE, PTFE) allows the purification of anhydrous hydrogen fluoride, preparation and analysis of HFNH₃ or HFNH₃MF mixtures and their handling for further study or destruction.Total vapour pressures above HFNH₃ binary mixtures rich in HF have been measured and are described as a function of ammonia concentration and temperature (?10 to +20°C).     

Alkali-metal trifluoromonosulphatomanganates (III) A2[MnF3(SO4)] (A = NH4, Li,Na or K)

Pink-brown crystalline alkali-metal trifluoromonosulphatomanganates(III), A₂[MnF₃(SO₄)] (A = NH₄, Li, Na or K), have been synthesised in high yields by reacting KMnO₄ or MnO(OH) with 40% HF and A₂SO₄ or by the reaction of MnO(OH) with 40% HF and A₂S₂O₈ (A = NH₄ or K). The chemicallly estimated oxidation state of manganese occurs between 2.9 and 3.1, and the room temperature magnetic moments lie in the range 4.0–4.2 BM. (NH₄)₂[MnF₃(SO₄)] on being pyrolysed at 340°C yields MnSO₄.     

An MO-theoretical calculation of solvent effect upon the NH3 + HF = NH4F reaction

An ab initia molecular orbital calculation was done as to a reacting system, NH₃+HF=NH₄F, with the inclusion of the solvent effect as the origin of dipolar field. The reactants were assumed to stay in dimers, (NH₃)₂ and (HF)₂, in advance to the reaction, and the respective partners of two reactants were regarded as point dipoles. The system was stabilized to some extent by two dipoles adopted. A study of configuration analysis on this system was made with and without the dipoles. Their effect was found to be favorable for proceeding of the reaction.     

Determination of impurities in niobium metal by a radiochemical neutron activation analysis

A radiochemical separation method using an anion exchange resin has been applied to 3N grade Nb for determining nine impurity elements. Five elements (Cr, Fe, Co, Zn and Se) were separated in 2M HF, three elements (Mo, W and Hf) in 32M HF, Nb in 0.5M HF/3M HCl, and Ta in 1M NH₄F/4M NH₄CCl. The contents of the elements were calculated by a single comparator method using two monitors of Au and Co. The main impurity was revealed to be Ta with a content of over 160 ppm.     

Investigation of UO4·2NH3·2HF by simultaneous thermogravimetry-differential thermal analysis-mass spectrometry technique

Thermal decomposition of UO₄·2NH₃·2HF was studied under high vacuum and in different gas atmospheres (N₂, O₂, synth. air). Gaseous decomposition products were analyzed and recorded using a quadrupole mass spectrometer.By discussing TG and MS data as well as X-ray analysis of intermediate products an attempt is made, to explain decomposition mechanisms under varied experimental conditions.Thermal decomposition strongly supports the results of X-ray analysis leading to the formula UO₄·2NH₃·2HF.     

Synthese et caracterisation de fluorotellurates IV alcalins et d'ammonium partie II: Etude des fluorotellurates d'ammonium NH4TeF5 et (NH4)2TeF6

New methods of synthesis:

• •reaction of aqueous or anhydrous HF with TeO₂ and NH₄F or NH₄HF₂, with (NH₄)₂TeCl₆
• •reaction of TeF₄ with NH₄F or NH₄HF₂
• •reaction of NH₄HF₂ with TeO₂

have been investigated for NH₄TeF₅ and a new compound (NH₄)₂TeF₆. The resulting compounds have been analysed and characterized.     

Hydrogen bonded complexes and the HF vibrational energy distributions from the reaction of F atoms with NH2 and NH3

The gas phase reactions of fluorine atoms with amino radicals and ammonia molecules: F(²P)+NH₂(²B₁) → HF(¹Σ⁺)+NH(³Σ⁻) and F(²P)+NH₃(¹A₁) → HF(¹Σ⁺)+NH₂(²B₁) produce hydrogen fluoride with very different primary vibrational energy distributions as determined by low-pressure chemiluminescence studies. The reaction with NH₂ yields HF with an inverted primary vibrational energy distribution, P(v′=1:2:3:4)=0.23:0.68:0.08:0.01. The HF from the reaction with ammonia is cold (non-inverted), P(v′=1:2)=0.60:0.40. Recent experimental work on these reactions is critically assessed and some discrepancies between low-pressure chemiluminescence results and fast-flowing afterglow studies are resolved. The results of high-level ab initio calculations (up to 6–311G^** CISD) on reactants, products, and the hydrogen bonded complexes FH … NH and FH … NH₂ in the exit channels are reported. The most reliable of the computations predict that FH … NH₂ is significantly more bound than FH … NH (8.1 versus 4.1 kcal mol⁻¹ in comparison with products at the 6-311G^** MP2 level).Also, the calculated vibrational frequencies for the two hydrogen bonded complexes indicate that the FH stretch and NH₂ asymmetric stretch are much closer in frequency in FH … NH₂ than are the FH and NH stretches in FH … NH. The strong interaction and the close match of vibrational frequencies in the FH … NH₂ case both will lead to fast internal vibrational relaxation (IVR) of the reaction exoergicity from the FHN bonds, where it is released, to the NH₂ fragment in the F/NH₃ reaction. Thus, the HF produced in this reaction is expected to have less vibrational excitation than that created in the F/NH₂ reaction, for which these IVR mechanisms are not as important, and simple direct abstraction dynamics are expected.     

Rotational and translation distributions of HF and NH3 subliming from solid NH4F

Infrared laser spectroscopy and time-of-flight mass spectrometry have been used to measure the rotational and translational distributions of HF and NH₃ subliming from a polycrystalline sample of NH₄F. The results of this study are compared with thermal desorption and gas-surface scattering experiments.     

Theoretical studies on the structure of M+BF−4 ion pairs M = Li+, NH+4: the role of electrostatics and electron correlation

A systematic investigation of the M⁺BF₄ ⁻ (M = Li or NH₄) ion-pair conformers has been carried out using an electrostatic docking model based on the molecular electrostatic potential topography of the free anion. This method provides a guideline for the subsequent ab initio molecular orbital calculations at the Hartree-Fock (HF) and second-order M?ller-Plesset perturbation theory (MP2) levels. It has been demonstrated that the model presented here yields more than 75% of the HF interaction energy when Li⁺ is the cation involved and more than 90% for the case of NH₄ ⁺. Inclusion of MP2 correlation in the HF-optimized geometries leads to stationary point geometries with different numbers of imaginary frequencies and in some places where the energies of two adjacent conformers are very close, the energy rank order is altered. The HF lowest-energy minima for the Li⁺BF₄ ⁻ and NH₄ ⁺BF₄ ⁻ show a bidentate and tridentate coordinating cation, respectively, whereas at the MP2 level, this ordering is reversed. Received: 9 September 1997 / Accepted: 5 November 1997     

Ammonium and potassium fluoromonooxalatomanganates(II), A[MnF(C2O4)] (A = NH4 or K) and sodium fluoromonooxalatomanganate(II) dihydrate,Na[MnF(C2O4)] · 2H2O

Summary Light pink-white microcrystalline ammonium and potassium fluoromonooxalatomanganates(II), A[MnF(C₂O₄)] (A = NH₄ or K), and sodium fluoromonooxalatomanganate(II) dihydrate, Na[MnF(C₂O₄)] · 2H₂O, have been synthesized by two different methods. Either KMnO₄ is reduced in the presence of 40% HF and alkali metal oxalate, A₂C₂O₄ (A = NH₄, Na or K), or MnO(OH) in 40% HF reacts with A₂C₂O₄. Characterisation was made by elemental analyses, determination of oxidation states, magnetic susceptibility measurements and infrared spectral studies.     

Non-convertional hydrogen bonding interaction of BH3NH3 complexes: a comparative theoretical study

A new type of hydrogen bond, called a dihydrogen bond, has recently been introduced. In this bond hydrogen is donated to (hydridic) hydrogen. In this paper, ab initio HF, MP2 and DFT(B3LYP) levels of theory with different basis sets in combination with counterpoise procedure for basis set superposition error correction have been applied to BH₃NH₃ dimer and BH₃NH₃ complexes of methane, hydrogen cyanide, ammonia, water, methanol and hydrogen fluoride to understand the features of dihydrogen bond. The optimized geometric parameters and interaction energies for various isomers at different levels are estimated. The structures obtained at different computational levels are in agreement with each other. Dihydrogen bond does not occur in both BH₃NH₃⋯CH₄ and BH₃NH₃⋯NH₃ complexes. Apart from the B–H⋯H–N dihydrogen bond found in the BH₃NH₃ crystal and dimmer, the B–H⋯H–X (XC, O, F) dihydrogen bonds have been observed in the BH₃NH₃⋯HCN, BH₃NH₃⋯H₂O, BH₃NH₃⋯CH₃OH and BH₃NH₃⋯HF complexes, while the classic H bonds also exist in the last three complexes. As for the complexes in which only dihydrogen bonds appear the strength of dihydrogen bonds ranges from 17.9 to 18.9 kJ mol⁻¹ at B3LYP/6-311++g(d,p) level. Binding energies obtained from the MP2 and B3LYP optimized structures are more sensitive to basis sets than those from the HF method. Larger basis functions generally tend to produce slightly longer intermolecular distances, and the B3LYP and MP2 methods generate shorter intermolecular distances though they usually produce longer bond lengths compared with those at the HF level. The infrared spectrum frequencies, IR intensities and the vibrational frequency shifts are reported. Finally the solution phase studies on BH₃NH₃⋯HF complex are also carried out using the Onsager reaction field model with a range of dielectric constants from 2 to 80 at B3LYP/6-311++g(d,p) level.     

Ab initio models for multiple-hydrogen exchange: Comparison of cyclic four- and six-center systems

High-level ab initio calculations {QCISD(T)/6-311 +G**//MP2(fu)/6-31 +G**, with corrections for higher polarization [evaluated at MP2/6-311 +G(3df,2p)] and ΔZPE//MP2(fu)/6-31 +G**, i.e., comparable to Gaussian-2 theory} indicate concerted mechanisms for double- and triple-hydrogen exchange reactions in HF and HCl dimers and trimers, in mixed dimers and trimers containing one NH₃, and in mixed dimers of HF, HCl, and NH₃ with formic acid. All these reactions proceed via cyclic four- or six-center transition structures, the latter being generally more favorable. Calculated activation barriers (ΔH^d? at 0 K, kcal/mol) are 42.3 for (HF)₂, 20.3 for (HF)₃, 41.2 for (HCl)₂, 25.6 for (HCl)₃, 36.0 for NH₃-HF, 10.6 for NH₃(HF)₂, 19.9 for NH₃-HCl, 2.3 for NH₃(HCl)₂, 9.7 for HCO₂H-HF, 7.0 for HCO₂H-HCl, and 11.3, for HCO₂H-NH₃. The barriers are lower for the more ionic systems and when more ion pair character is present. © John Wiley & Sons, Inc.     

Zur Struktur und Reaktivität des Diammoniumhexafluoromanganats(IV)

About the Structure and Reactivity of Diammonium Hexafluoromanganate(IV) Electrolytic oxidation of an aqueous suspension of MnF₂ containing NH₄F, and subsequent crystallization in 40% HF yields yellow crystals of (NH₄)₂MnF₆. It crystallizes in the hexagonal K₂MnF₆ type structure with the space group P6₃mc and a = 5.903; c = 9.565 Å; Z = 2. With in situ powder diffraction studies it is shown, that (NH₄)₂MnF₆ is gradually reduced in a NH₃ atmosphere between 30 and 230 °C to afford (NH₄)₃MnF₆, (NH₄)₂MnF₅, and finally NH₄MnF₃. (NH₄)₃MnF₆, thereby, forms a hitherto unknown cubic (a = 9.082 Å) high temperature modification with the cryolite type structure. Under N₂ the thermal decomposition of (NH₄)₂MnF₆ proceeds via NH₄MnF₄ to yield MnF₂.     

The complexes of phenyl acetylene with HF,H2O,and NH3: An ab initio study

Phenyl acetylene complexes with HF, H₂O, and NH₃ are investigated with ab initio molecular orbital calculations using the 6-31G Gaussian basis set. HF is found to form a π complex, whereas H₂O and NH₃ form σ complexes. Observations of experimental spectroscopic shifts are rationalized.     

Reactions of photogenerated fluorine atoms with molecules trapped in solid argon

Isolated radicals^.NH₂ and radical-molecule complexes^.NH₂−HF, which are products of the reactions of mobile fluorine atoms with NH₃ molecules in solid argon, were identified by EPR spectroscopy. The isotropic HFC constants of the complex (a _N=1.20,a _H=2.40, anda _F=0.70 mT) were determined experimentally. The constant of isotropic HFC with the nucleus of hydrogen atom of the HF molecule is less than 0.1 mT. This assignment was confirmed in the experiments on isotope substitution of atoms (H→D),¹⁴N→¹⁵N) in the NH₃ molecule. According to quantum-chemical calculations, the free complex^.NH₂−HF has a planar structure withC ₂, summetry and a binding energy of 12 kcal mol⁻¹. Optimization of the arrangement of the complex in the crystal showed that its structure is only slightly distorted in the Ar lattice so that the equilibrium configuration is close to that obtained from gas-phase calculations. Different ratios of relative intensities of the proton triplet lines in the EPR spectra of isolated^.NH₂ radicals and^.NH₂−HF complexes were qualitatively explained by different heights of the barriers to rotation of the NH₂ fragment in the Ar lattice.     

Synthese und Untersuchung von Hydroxylammonium‐fluorohafnaten(IV)

Synthesis and Characterization of Hydroxylammonium Fluorohafnates(IV) Two new hydroxylammonium compounds, (NH₃OH)₂HfF₆ and (NH₃OH)₃HfF₇ were isolated from the system NH₂OH/HF/HfF₄/H₂O. The compounds were prepared by dissolving Hf‐foil in aqueous hydrofluoric acid (40 % or 20 %) followed by adding of NH₂OH in ethanolic solution. The characterization was carried out by chemical, thermal, and structural analyses. The compounds are isomorphic with the hydroxylammonium fluorozirconates. Thermal analysis of (NH₃OH)₂HfF₆ and (NH₃OH)₃HfF₇ showed that they decompose in three or two steps with HfF₄ as final product.     

Theoretical study of reaction channels for the weakly bound complex systems created with HF,CO2, and various amines

This investigation conducted reaction channels of weakly bound complexes CO₂…HF, CO₂…HF…NH₃, CO₂…HF…NH₂CH₃, CO₂…HF…NH(CH₃)₂, and CO₂…HF…N(CH₃)₃ systems, using the Gaussian 98 package at the B3LYP/6‐311++G(3df,2pd) level. The syn‐fluoroformic acid or syn‐fluoroformic acid plus NH₃ or amine conformers are more stable than the related anti‐fluoroformic acid or anti‐fluoroformic acid plus NH₃ or amine conformers. However, the above‐mentioned weakly bound complexes are more stable than both the related syn‐ and anti‐type fluoroformic acid or acid plus NH₃ or amine conformers and their related decomposed into CO₂ + HF or CO₂ + NHR₃F (R?H, CH₃) combined molecular systems. Five reaction channels of the weakly bound complexes exist. Each channel includes weakly bound complexes and their related above‐mentioned systems. Moreover, each reaction channel contains two transition states. The transition state between the weakly bound complex and anti‐fluoroformic acid type structure (T₁₃) is significantly higher than that of internal rotation (T₂₃) between syn‐ and anti‐FCO₂H (or FCO₂H…NR₃) structures. However, the above‐mentioned T₁₃ can significantly decrease its energy by adding the third molecule NH₃ or NR₃ (R?H or CH₃). The more CH₃ that is substituted in NR₃ of the reaction channel, the lower the activation energy of the transition state in the system is affected. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Density functional theory of chemical reactivity indices in some ion—molecule reaction systems

Three isoelectronic reactions, proton transfer (PT ), hydrogen abstraction (HA ), and electron transfer (ET ), of NH⁺₃ with NH,₃ H₂O, and HF have been studied using ab initio molecular orbital calculations. For the reaction of NH⁺₃ + H₂O, the energy of the transition state (TS) is higher than that of the reactants. This is consistent with the experimental observation that the rate constant is less than the average dipole orientation (ADO) rate constant. It seems reasonable that the reaction rate for the reaction NH⁺₃ + H₂O would hardly depend on the v₂ mode of NH⁺₃ at least for low-lying excited states (E_int≤ 0.714 eV) of the v₂ mode, because the v₂ mode contributes mainly to the normal mode orthogonal to the reaction coordinate at the TS . This is consistent with experimental observation. A similar prediction can be made for the NH⁺₃ + HF reaction. The electron-transfer processes for the HA reactions have been examined in terms of the intrinsic reaction coordinate (IRC ). The order of reactivity with NH⁺₃ is NH₃ > H₂O > HF. It is found that the degree of the electron transfer and the reactivity are correlated with the absolute hardness (η) of NH₃, H₂O, and HF. This is in accord with the softness as the chemical reactivity index in the density functional theory. © 1996 John Wiley & Sons, Inc.     

Limits on the localized interpretation of molecular orbital wavefunctions

A new measure of orbital localizability is proposed. The actual improvement in classical electrostatic interpretations of electronic energy contributions on localization of CH₄, NH₃, H₂O, HF and Ne LCAO wavefunctions is computed to be small. Substantial valence LMO spatial overlapping remains.