Doping of (CH)x films to the metallic state with metal hexafluorides

When polyacetylene films, (CH)_x, are exposed to the vapours of hexafluorides, the resistances of the films drop rapidly. The following hexafluorides were shown to dope (CM)_x to the metallic state: SeF₆, TeF₆, WF₆, ReF₆, OsF₆, IrF₆, MoF₆, UF₆ and XeF₆. Conductivity $\text{vs}$ degree of doping curves obtained for WF₆, MoF₆ and UF₆ exhibit a shape similar to that observed for AsF₅; namely, an increase in electrical conductivity of several orders of magnitude at low concentrations until a point when additional doping has little further effect. Parallel e.s.r. line-shape measurements confirm metallic behaviour above a critical transition. The highest conductivity observed in the series is 350 Ω^?1 cm^?1 for [CH(WF₆)_0.087]_x. The maximum observed for the XeF₆ doped polyacetylene was about 0.1 Ω^?1 cm^?1. The other hexafluorides gave materials which show intermediate conductivities. The XeF₆ doped polyacetylene is not stable, presumably because of internal fluorination of the (CH)_x by the dopant.     

Redox reactions involving molybdenum,tungsten and uranium hexafluorides in acetonitrile

The redox properties of molybdenum, tungsten and uranium hexafluorides in acetonitrile at 298 K have been compared with other redox couples using cyclic voltammetry, and by carrying out appropriate redox reactions under carefully controlled conditions. The order of oxidizing ability established is UF₆ > MoF₆ > NO⁺¹ > solvated Cu²⁺ ? WF₆. The position of the solvated Tl³⁺ cation probably lies between MoF₆ and Cu²⁺ Reactions which occur in the Cu metal/solvated Cuⁿ⁺ (n = 1 or 2)/WF₆ system are accounted for by redox and fluoride-ion-transfer equilibria.     

Collisional ionization of atomic cesium by UF6 and WF6

Collisional ionization of Cs by UF₆ and WF₆ has been studied in crossed-beam geometry. Product UF^?₆ and WF^?₆ contain ≈3 eV of internal excitation energy even at the lowest Cs laboratory impact energy of 7 eV.     

The Oxidizing Properties of the Third Transition Series Hexafluorides and Related Compounds

Some of the transition metal hexafluorides demonstrate an astonishing oxidizing power. In particular may be mentioned PtF₆, which is capable of oxidizing molecular oxygen or xenon, a process requiring an electron affinity, E(PtF₆), > ?156 kcal·mole^?1. From a comparative study of all of the hexafluorides of the third transition series the electron affinity is seen to increase regularly in the sequence WF₆ < ReF₆ < OsF₆ < IrF₆ < PtF₆. The increase in E with unit increase in atomic number of M appears to be ≈ ?20 kcal·mole^?1. On the other hand the ability of the hexafluorides to accept F^? decreases along this series. This effect enables IrF₆ to be more effective than PtF₆ in the generation of nitrogen oxide trifluoride, ONF₃, by the oxidative fluorination of nitrosyl fluoride, ONF. Both PtF₆ and IrF₆ interact spontaneously with ONF or O₂NF to generate fluorine, at or below room temperature. The decrease in F^? -acceptor ability along the series, which stands in sharp contrast to the increase in electron affinity, suggests that ligand crowding increases sharply across the series from WF₆ to PtF₆. This accords with the observed decrease in molecular volume along the series, both in the hexafluorides and in the MF₆^? salts. It is clear from this comparison that the species IrF₆ and PtF₆ are close to a minimum volume for this series. The oxide pentafluorides ReOF₅ and OsOF₅ are similar in oxidizing ability to their respective hexafluorides but are poorer F^? acceptors. Evidently the ligand crowding in MOF₅ molecules is greater than in MF₆.     

A [205T1]-thallium NMR study of thallium(I) and thallium(III) fluorometalates in acetonitrile

The concentration-dependent behavior observed for ²⁰⁵T1 n.m.r. resonances from thallium(I) fluorometalates, PF₆^-, WF₇^-, MoF₆^- and UF₆^-, in acetonitrile indicates that some degree of ion-pairing is present in these solutions. The paramagnetic anion, UF₆^-, has a pronounced effect on ²⁰⁵T1 resonance in the T1⁺ salt, but its effect on T1³⁺ is very small. It is suggested that T1³⁺ is effectively solvated by MeCN and that direct ion-pairing is unimportant. The ²⁰⁵T1 shielding of T1³⁺ is decreased by the presence of T1⁺ in solution, possibly as a result of the increase in asymmetry of the T1³⁺ environment.     

Kernresonanzuntersuchungen an Hexafluoriden

N.M.R. Measurements on Hexafluorides ¹⁹F n.m.r. spectra of natural and ¹²⁹Xe enriched XeF₆, ²³⁸UF₆, ²³⁵UF₆, PtF₆, IrF₆, OsF₆ and AuF₆^? were measured and interpretated. The tetramerisation of XeF₆ at low temperatures can be confirmed.     

Preparation and adsorption performance of a NiO/MgF2 composite adsorbent

Fluoride adsorbents have been applied for the purification of UF₆ product from fluorination process. A MgF₂-based adsorbent, NiO/MgF₂, was prepared using NiF₂ as doping agent. The specific surface area of NiO/MgF₂ was 5 times larger than that of MgF₂, its porosity was also larger than that of MgF₂. The saturated adsorption capacity of NiO/MgF₂ for MoF₆ was 21.4?±?1.9 mg g^?1. The desorption behavior was examined by thermogravimetric analysis (TG). The NiO/MgF₂ with adsorbed MoF₆ was investigated using extended X-ray absorption fine structure spectroscopy (EXAFS), which showed no bonding interactions between NiO and MoF₆, while the adsorption of MoF₆ on NiO/MgF₂ was chemisorption via a Mo–F–Mg bond.

     

AB initio Calculations of the structure and spectra of chromium, molybdenum, and tungsten tetrafluorides. nontetrahedral molecular structure of WF4

The properties of MF₄ molecules (M = Cr, Mo, W) are investigated by the restricted Hartree-Fock method using Möller-Plesset second-order perturbation theory and by the second-order configuration interaction method using the multiconfigumtion wave function derived in a complete active space approximation, in wide bases complemented with polarization d and f functions. Relativistic effective potentials are used to describe the core electrons. For CrF₄ and MoF₄, the tetrahedral configuration of nuclei in the electronic state of³k₂ symmetry is energetically most favorable. In the WF4 molecule, the least-energy structure is a D_2h structure in the singlet state ¹A₁. The D_4h,(¹ A_1g) and T_d ( ³A₂) configurations in the WF₄ molecule are higher on the energy scale than the ground state by 4 and 6305 cm’1 and are saddle points. For all of the analyzed configurations of MF₄ molecules, the geometrical parameters, the vibrational spectra, and the energies of vertical electronic transitions are found. The chemical bonding is analyzed and a simple model is proposed to explain the variation of the relative energies of states in the series CrF₄→MoF₄→WF₄.     

Hydrolysis reactions of transition metal hexafluorides in liquid hydrogen fluoride: oxonium salts with Pt,Ir and Ru.

The hydrolysis reactions of OsF₆, IrF₆, PtF₆, RuF₆ and RhF₆ in hydrogen fluoride have been studied. Hydrolysis of OsF₆ in HF leads to an improved synthesis of OsOF₄. Hydrolyses of IrF₆, PtF₆ and RuF₆ yield oxonium salts, H₃O⁺MF^-₆, having rhombohedral cells with nearly identical dimensions. If excess water is used, the salt (H₃O⁺)₂PtF⁼₆ can also be isolated. Hydrolysis of RhF₆ leads to an unstable product which could not be further characterized.     

Electron affinities of higher molybdenum fluorides as determined by the effusion technique

The effusion technique with mass spectral recording of ions was employed to investigate the ionic component of molybdenum trifluoride saturated vapour. The equilibrium constants of ion—molecular reactions involving MoF₅^?, MoF₆^? and MoOF₄^? were measured. The following thermodynamic values were obtained from experimental data: MoF₄(g) + F^?(g) = MoF₅^?(g),ΔH₂₉₈⁰ = ?382.0 ± 20.1 kJ/mole; MoF₅(g) + F^?(g) = MoF₆^?(g), ΔH₂₉₈⁰ = ?413.4 ± 20.1 kJ/mole; MoOF₃(g) + F^?(g) = MoOF₄^?, ΔH₂₉₈⁰ = ?418.0 ± 20.5 kJ/mole; EA(MoF₅ = 3.6 ± 0.2 eV, EA(MoF₆) = 3.6 ± 0.2 eV, EA(MoOF₄) = 4.0 ± 0.4 eV. Reported as well as estimated molecular constants were used to calculate thermodynamic functions of some participants of ion—molecular reactions. For MoOF₃, BeF₃^? and Be₂F₅^? vibration frequencies were calculated from the estimated force field.     

Reaktionen von MoNCl3 und WNCl3 mit elementarem Fluor. Kristallstrukturen von [MoO2F2(THF)2] und [WF4(NCl)(CH3CN)]

Reactions of MoNCl₃ and WNCl₃ with Elemental Fluorine. Crystal Structures of [MoO₂F₂(THF)₂] and [WF₄(NCl)(CH₃CN)] The nitrido chlorides MoNCl₃ and WNCl₃ as well as WCl₄(NCl) react with elemental fluorine forming the N-chloro imido complexes MoF₄(NCl) and WF₄(NCl), which were characterized by IR spectroscopy. With tetrahydrofurane MoF₄(NCl) reacts to give [MoF₄(NCl)(THF)], which in THF solution slowly converts into [MoO₂F₂(THF)₂]. From WF₄(NCl) with acetonitrile the complex [WF₄(NCl)(CH₃CN)] is obtained. Both donor acceptor complexes were characterized by crystal structure determinations. [MoO₂F₂(THF)₂] : Space group P2₁/n, Z = 4, structure solution with 1823 unique reflections, R = 0.033 for reflections with I > 2σ(I). Lattice dimensions at ?40°C: a = 636.2, b = 1119.5, c = 1625.2 pm; β = 93.92(1)º. The compound has a monomeric molecular structure with the fluorine atoms in trans-position to one another and with the oxygen atoms of the THF molecules in trans to the oxo ligands. [WF₄(NCl)(CH₃CN)] : Space group P2₁/m, Z = 2, structure solution with 1119 unique reflections, R = 0.038 for reflections with I > 2σ(I). Lattice dimensions at 20°C: a = 511.7, b = 714.9, c = 1002.5 pm; β = 102.59(10)º. The compound has a monomeric molecular structure in which the nitrogen atom of the acetonitrile molecule coordinates in trans-position to the N-chloro imido group W?N? Cl. The structural parameters of this group are WN = 172.2 pm, NCl = 161.1 pm, WNCl = 178.6º.     

Complex formation of polymeric niobium and tantalum pentafluorides in non-aqueous solvents

¹⁹F NMR and i.r. spectroscopy were employed to study complex formation of niobium and tantalum pentafluorides with triphenylphosphine oxide, ethyl diphenylphosphinate and S-ethyl diphenylthiophosphinate in methylene chloride and in acetonitrile. In methylene chloride solution MF₅L, M₂F_IOL, MF₄L₂⁺ and M₂F_II^? complexes were found (M=Nb, Ta;L- phosphoryl-containing Ligand). I.r. frequencies are assigned. Solvent properties (electric conductivity and donor capacity) affect the relative stability of complexes. The dependence of ¹⁹F NMR parameters on the donor capacity of the ligands is discussed.     

Darstellung der Iminiumsalze CF3?NXCF2+MF6− (X = CH3, F und M = As,Sb) und CF3?NCl = CF2+ AsF6−

Preparation of the Iminium Salts CF₃? NX?CF₂⁺MF₆^? (X = CH₃, F and M = As, Sb) and CF₃? NCl?CF₂⁺ AsF₆^? The preparation of the iminiumsalts CF₃? NX?CF₂⁺ MF₆^? (X = CH₃, F and M = As, Sb) and CF₃? NCl?CF₂⁺ AsF₆^? is reported. The salts were characterized by NMR and infrared spectroscopy. CF₃? NCH₃?CF₂⁺MF₆^? decompose into MF₅ and (CF₃)₂NCH₃.     

Vibrational spectra of transition metal hexafluoride crystals. I. Orthorhombic MoF6, WF6, and UF6 neat crystals

Neat crystal Raman spectra of orthorhombic MoF₆, WF₆, and UF₆ are presented and discussed. This work lays the foundation for presentation of two-particle and total band structures in the two following papers. The neat crystal spectra are interpreted in terms of an internal-external mode separation and a conventional factor group analysis. In general, these data lead to four essential conclusions concerning hexafluoride crystals: (a) Fermi resonance plays an important role in producing the observed energy and intensity differences in this series; (b) k = 0 exciton structures are remarkably similar in the three crystals; (c) similarities and differences between these solids can be directly correlated with molecular parameters such as dipole derivatives, polarizabilities, etc.; and (d) phonons (external modes) can be neatly separated into rotational and translational normal modes.     

Stabilization of [WF5]+ by Bidentate N‐Donor Ligands

Transition‐metal hexafluorides do not exhibit fluoride‐ion donor properties in the absence of donor ligands. We report the first synthesis of donor‐stabilized [MF₅]⁺ derived from a transition‐metal hexafluoride via fluoride‐ion abstraction using WF₆(L) (L=2,2′‐bipy, 1,10‐phen) and SbF₅(OSO) in SO₂. The [WF₅(L)][Sb₂F₁₁] salts and [WF₅(1,10‐phen)][SbF₆]?SO₂ have been characterized by X‐ray crystallography, Raman spectroscopy, and multinuclear NMR spectroscopy. The reaction of WF₆(2,2′‐bipy) with an equimolar amount of SbF₅(OSO) reveals an equilibrium between [WF₅(2,2′‐bipy)]⁺ and the [WF₄(2,2′‐bipy)₂]²⁺ dication, as determined by ¹⁹F NMR spectroscopy. The geometries of the cations in the solid state are reproduced by gas‐phase geometry optimizations (DFT‐B3LYP), and NBO analyses reveal that the positive charges of the cations are stabilized primarily by compensatory σ‐electron donation from the N‐donor ligands.     

Fluorination reactions of UF6

Uranium hexafluoride is known to be an oxidative fluorinating agent, frequently breaking CC bonds and oxidizing many elements to a higher oxidation state. This work will compare the behavior of UF₆ to that of two other fluorinating agents, WF₆ and SF₄, which are for the most part non-oxidative.The reactions of UF₆ with a number of quite simple organic compounds have been studied; alcohols, aldehydes, ketones, acids, acid halides, ethers, olefins, and alkanes are included. The reactions of WF₆ and SF₄ with these compounds were investigated also when no data existed in the literature. The primary tool was ¹⁹F NMR, assisted by ¹H NMR, infrared, powder diffraction, thermogravimetry and elemental analysis when needed.The differences in behavior of the three agents with respect to the same compounds will be emphasized.     

Darstellung der Dichlormethyleniminium-Salze Cl2CNClH+ MF6− und Cl2CNClCH3+ MF6− (M = As,Sb) und Kristallstruktur von Dichlormethyleniminiumhexachloroantimonat Cl2CNH2+SbCl6−

Synthesis of the Dichloromethyleneiminium Salts Cl₂C?NClH⁺MF₆^? and Cl₂C?NClCH₃⁺ MF₆^? (M = As, Sb) and Crystal Structure of Dichloromethyleneiminium-hyxachloroantimonate Cl₂C?NH₂⁺SbCl₆^? The N-chloro-dichloromethyleneiminium salts Cl₂C=NCIH⁺MF₆^? (M = As, Sb) are prepared by protonationof trichloromethyleneimine in the superacide system HF/MF5 at 195 K. The synthesis of the N-chloro-N-methyl-dichloromethyleneiminium salts Cl₂C?NClCH₃⁺MF₆^? (M = As, Sb) is proceeded by methylation of perchloromethylenimine by CH₃OSO⁺MF₆^? in SO₂ also at low temperature. All salts are characterized by vibrational and NMR spectra. The dichloromethyleneiminiumhexachloroantimonate crystallizes in the space group P2₁/c with a = 971.3(4)pm, b = 1134.0(4)pm, c = 2154.2(7)pm β = 102.04(3)° and Z = 8.     

Redox reactions of uranium hexafluoride. Comparison with phosphorus pentafluoride and preparation of copper(I) hexafluorouranate(V) [1]

Molecular iodine is oxidised by phosphorus pentafluoride in iodine pentafluoride at room temperature giving I₂⁺, PF₆^?, and PF₃. I₂⁺ is formed from uranium hexafluoride under similar conditions, but further oxidation occurs depending on the reaction stoicheiometry used. In all cases uranium pentafluoride is formed. Copper(II) fluoride reacts with UF₅ in acetonitrile at room temperature to give copper(II) hexafluorouranate(V), which is reduced by copper metal to give the copper(I) salt. The latter compound is formed from UF₆ and Cu metal, via the Cu^II salt, only if a fresh Cu surface is used for the reduction step.     

Thermisch induzierte Bewegungsvorgänge in kristallinen Guanidiniumhexafluorometallaten, (C(NH2)3)3MF6 (M = Al,Ga, In) — eine in situ ESR-Untersuchung

Thermally Induced Mobility in Crystalline Guanidinium Hexafluorometallates, (C(NH₂)₃)₃MF₆ (M = Al, Ga, In) — an in situ E.S.R. Study . The e.s.r. spectroscopic investigation of the title compounds was carried out most successfully by doping them with Cr^III ions. The metal ions in the centres of the MF₆ octahedra are substituted by the Cr^III ions. The zero field splitting parameter | D |, being a measure of the axial distortion of the CrF₆ octahedra, has been determined by fitting the calculated to the experimental resonant field values using a computer program. | D | decreases with increasing temperature. This process is completely reversible in the investigated temperature range of ? 190°C to 270°C. It is explained in terms of the thermally induced movability of the N? H … F network.