ESR spectra of fluorine-containing radicals of phosphorus and arsenic

ESR spectra observed at 120 K in γ-irradiated solid solutions of PF₅ in neopentane and AsF₅ in SF₆ are ascribed to the radical ions PF₅^? and AsF₅^? in which the unpaired electron interacts strongly with the central nucleus and with four equivalent ¹⁹F nuclei. Hyperfine interaction with the fifth ¹⁹F nucleus was not resolvable in either case. The spectra were quite distinct from those of the tetrafluorides PF₄ and AsF₄, thus eliminating the possibility that they were due to tetrafluoride radicals undergoing rapid intramolecular ¹⁹F exchange.     

Highly conductive meta derivatives of poly(phenylene sulfide)

Changes in the backbone structure of several meta derivatives of polyphenylene sulfide upon doping with AsF₅ have been investigated by IR spectroscopy. Poly(m-phenylene sulfide) does not form a conducting complex with AsF₅ unless reacted under conditions where carbon-carbon bonds form intramolecularly between phenyl rings. This assertion has been verified by comparison of the IR spectra of poly(m-phenylene sulfide) and a newly synthesized derivative, poly(thio-3,7-dibenzothiophendiyl), after doping with AsF₅. This new derivative forms a complex with AsF₅ which exhibits a conductivity of 18.5 S/cm. A sulfone-containing derivative has also been synthesized, poly[thio-3,7-(dibenzothiophene-5,5-dioxide)-diyl]. With this polymer, a much lower conductivity, 10^?3 S/cm, was obtained after exposure to AsF₅.     

Synthesis,Characterization, and Properties of Aligned Polyacetylene Films

Highly aligned polyacetylene films are synthesized by three different methods in which nematic liquid crystals are used as an ordered matrix solvent: Method 1, polymerization of acetylene is carried out in a quiescent nematic solution in which a Ti(OBu)₄-AlEt₃ Ziegler-Natta catalyst is dissolved homogeneously; Method 2, macroscopic alignment is attained by gravity flow of the nematic liquid crystal-catalyst system; and Method 3, the nematic liquid crystal-catalyst solution is aligned under a magnetic field. Characterization of these films is carried out through SEM observation and measurements of polarized visible and infrared absorption spectra. Results indicate that as-prepared films have highly aligned fibrils. Upon doping by I₂ and AsF₅, these films exhibit high electrical condactivity of the order of 10₄ S/cm.     

X-ray crystal structure and raman spectrum of tribromine(1+) hexafluoroarsenate(V), Br3+AsF6−, and raman spectrum of pentabromine(1+) hexafluoroarsenate(V), Br5+AsF6−

A single crystal of Br₃⁺AsF₆^? was isolated from a sample of BrF₂⁺AsF₆^? which had been stored for 20 years. It was characterized by x-ray diffraction and Raman spectroscopy. It is shown that Br₃⁺AsF₆^? (triclinic, a = 7.644(7) Å, b = 5.641(6) Å, c = 9.810(9) Å, α = 99.16(8)°, β = 86.61(6)°, γ = 100.11(7)°, space group P1 R(F) = 0.0608) is isomorphous with I₃⁺AsF₆^?. The structure consists of discrete Br₃⁺ and AsF₆^? ions with some cation-anion interaction causing distortion of the AsF₆^? octahedron. The Br₃⁺ cation is symmetric with a bond distance of 2.270(5) Å and a bond angle of 102.5(2)°. The three fundamental vibrations of Br₃⁺ were observed at 297 (ν₃), 293 (ν₁), and 124 cm^?1 (ν₂). The Raman spectra of Cl₃⁺AsF₆^? and I₃⁺AsF₆^? were reinvestigated and ν₃(B₁) of I₃⁺ was reassigned. General valence force fields are given for the series Cl₃⁺, Br₃⁺, and I₃⁺. Reactions of excess Br₂ with either BrF₂⁺AsF₆^? or O₂⁺AsF₆^? produce mixtures of Br₃⁺AsF₆^? and Br₅⁺AsF₆^?. Based on its Raman spectra, the Br₅⁺ cation possesses a planar, centrosymmetric structure of C_2h symmetry with three semi-ionically bound, collinear, central Br atoms and two more covalently, perpendicularly bound, terminal Br atoms.     

The preparation of copper(II) and copper(I) salts in acetonitrile using group VA and VB pentafluorides

Copper(II) fluorine reacts with the pentafluorides, TaF₅, PF₅, and AsF₅, in acetonitrile to give solvated Cu^II, hexafluoroanion salts. These react with copper metal to give the corresponding Cu^I compounds. Similar reactions occur between AsF₅ and silver(I) or thallium(I) fluorides, but silver(II) fluoride reacts with MeCN, and Ag^I hexafluoroarsenate is formed. PF₅ oxidises Cu slowly in MeCN to give Cu^I hexafluorophosphate, but AsF₅ has no oxidising ability towards metals in MeCN. Spectroscopic data for Cu(MF₆)₂·5MeCN and Cu(MF₆)·4MeCN (M = Ta or P) are discussed.     

Effect of chain aggregation on the conductivity and ESR spectra of polyaniline

Solutions of polyaniline in m-cresol with and without camphorsulfonic acid (CSA), as well as films cast from these solutions were studied by ESR spectroscopy at 133–423 K and by optical spectroscopy in the range λ = 350–1100 nm. An analysis of the optical and ESR spectra shows that in the solutions and films without CSA polyaniline is fully doped but the conductivity of these films is low (∼10⁻⁸ S cm⁻¹; cf. 100 S cm⁻¹ for the films with CSA). Compared with the CSA-containing samples, the samples without CSA are characterized by broader ESR lines and higher contribution of the Curie spins to the magnetic susceptibility. These facts indicate a weak aggregation of polyaniline chains without CSA, which leads to low conductivity. A formula was proposed, which describes the temperature dependence of the polyaniline ESR linewidth and allows the interchain distance and the mobility of electrons moving along polymer chains to be determined. The conductivity of polyaniline films is affected by moderate heating (363–388 K) of the films and solutions from which the films were cast. It was found that the interchain distances correlate with the conductivity of the films and with the broadening of their ESR lines caused by the effect of O₂. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2701–2711, December, 2005.     

The relationship of graphite/AsF5 intercalation compounds to Cx+AsF6− salts

Graphite intercalated by AsF₅ has been reported to give compounds of formula C_8nAsF₅ where n is the stage. It is doubtful however if materials of exact composition C_8nAsF₅ have ever been obtained. The intercalation of graphite by AsF₅ is associated with electron oxidation of the graphite according to the equation: 3AsF₅ + 2e^? → 2AsF₆^? + AsF₃. Because of the easy removal or displacement of AsF₃ the As:F ratio is readily increased beyond 5. By treating graphite with excess AsF₅, removing volatiles under vacuum and repeating the cycle seven times a first stage salt C₁₀⁺AsF₆^? (C_o = 7.96 ā) is made. Interaction of graphite with AsFs in the molar ratio 8:1, within a small volume reactor, yields a material of approximate composition C₈AsF₅. The major component of the volatiles at the onset of their removal is AsF₅,, but, at a composition close to C₁₀AsF₅, is AsF₃. ‘Graphite AsF₅’ can be prepared by adding AsF₃ to C_xAsF₆ salts. The electrical conductivities of ‘AsF₅’ and AsF₆ relatives will be compared and discussed.     

Temperature dependence of the ESR line width of C60 − in C60 crystals doped with sodium, potassium, zinc, and indium

The ESR line width of the C₆₀ ⁻ anion in samples of fullerides (Na, K, Zn, and In) with low metal content (0.01%) is ∼0.1 mT at 77 K and ∼1 mT at 300 K. The line shape is fitted better by the Lorentzian function than by the Gaussian function. The spin-lattice relaxation likely makes some contribution to the line width. Time-dependent changes in the ESR spectra were observed: they are related to diffusion of cations to defects of the crystalline lattice. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 669–672, April, 1998.     

The ESR spectrum of arsenic tetrafluoride

The ESR spectrum of AsF₄, generated by γ-radiolysis of a solid solution of AsF₃ in SF₆, is reported. The ⁷⁵As hyperfine interaction is 1576 G, and the two kinds of ¹⁹F nuclei have interactions of 49 G (equatorial) and 238 G (apical). These data are compared with those from the well-known PF₄ radical.     

Electron spin resonance study of γ-irradiated poly(acrylic acid)

Electron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ-irradiated in air at room temperature and recorded at room temperature and at liquid-nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least-squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10-line spectra are assigned to the chain radicals CH₃? CH? CH₂ ～ and/or ～ CH₂? CH? CH₂ ～. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the C_α? C_β bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption.     

Synthesis and electrical conductivity of poly(arylene vinylene). I. Poly(2,5-dimethoxyphenylene vinylene) and poly(2,5-dimethylphenylene vinylene)

The highly conjugated aromatic polymers, poly(2,5-dimethoxyphenylene vinylene) and poly(2,5-dimethylphenylene vinylene), were obtained from their water soluble, sulfonium salt precursor polymers. Films of these polymers were reacted with either AsF₅ or I₂ vapor. Poly(2,5-dimethoxyphenylene vinylene) showed increases in electrical conductivity of up to 14 to 15 orders of magnitude for these two dopants, while an 8 to 9 order of magnitude increase was observed for poly(2,5-dimethylphenylene vinylene) with the same dopants. The synthesis of the precursor polymers, the properties and elimination reactions of films of the precursors, the doping reactions, and the conductivities of the resulting phenylene vinylene films are discussed.     

Poly(P-phenylene sulfide) hexafluoroarsenate: A novel conducting polymer

Poly(p-phenylene sulfide) (PPS) is a melt- and solution-processible polymer which on treatment with AsF₅ forms a blue-black material with a conductivity of 1–10 Ω^?1 cm^?1. Thermopower measurements indicate that the resulting polymer is p type, consistent with partial oxidation of the PPS by the AsF₅. The rate and extent of this doping process prove to be particularly sensitive to the degree of crystallinity of the starting polymer. There is also evidence of crosslinking of the polymer chains during the reaction with AsF₅. The details of both the chemistry and physics of the doping of PPS and several of its derivatives are presented.     

ESR of Gd<Superscript>3+</Superscript> ions in potassium yttrium tungstate

The software in MATHLAB medium has been developed to model ESR spectra of paramagnetic centers in single crystals. By means of this program, the angular dependences of ESR spectra found in KY(WO₄)₂, potassium yttrium tungstate, doped with gadolinium were analyzed. The spectra analysis indicates that they are determined by the presence of Gd³⁺ ions with the electron spin S = 7/2 occupying the structural position of Y³⁺ ions in the crystal structure. Parameters of spin Hamiltonian were defined for the analyzed ESR spectrum of Gd³⁺. Unusual features of the analyzed ESR spectra have been discovered in the region of 9.5 GHz which remind by appearance SHF line. The researches made show the position of this line to correspond to the region of quasi-intersection of energetic levels, and along with the line shape it is most likely to reflect the peculiarities of the region in whose interval wave functions of the energetic levels undergo substantial modifications.     

Study on the Mechanism of the Radiation-Induced Chain Oxidation of N,N,N,N-Tetramethyl-4,4′-diaminodiphenylmethane by Tetrabromomethane in Poly(vinyl chloride) Films

Kinetics and mechanism of the radiation-induced chain oxidation of N,N,N,N-tetramethyl-4,4-diaminodiphenylmethane (Am) by tetrabromomethane in poly(vinyl chloride) (PVC) films were studied by ESR and optical spectroscopy. The quantitative analysis of the ESR spectra of PVC films containing Am and CBr₄ irradiated with -rays at 77 K was performed. The nature of radical species involved in the chain process was established. It was shown that the heating of the films after their irradiation at 77 K resulted in the formation of free radicals Am^·, which initiated the chain oxidation of amine with a chain length of 100. The kinetic features of the chain oxidation–reduction reactions occurring in vacuum and in the presence of oxygen were compared.     

Enhanced photo-catalytic activity of TiO2 nanostructured thin films under solar light by Sn and Nb co-doping

In this study, preparation of Sn and Nb co-doped TiO₂ dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of co-doping content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), field emission SEM (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and UV–Vis absorption spectroscopy. Surface chemical state of thin films was examined by atomic X-ray photoelectron spectroscopy (XPS). XRD results suggest that adding impurities has a great effect on the crystallinity and particle size of TiO₂. Titania Rutile phase formation in thin film was promoted by Sn⁴⁺ addition but was inhibited by Nb⁵⁺ doping. The prepared co-doped TiO₂ photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue (MB) solution under solar irradiation. Comparison with undoped and Sn or Nb-doped TiO₂, codoped TiO₂ shows an obviously higher catalytic activity under solar irradiation.     

Über die Matrixisolation von AsCl4F

Matrix Isolation of AsCl₄F The gasphase components during the sublimation of [AsCl₄]⁺[AsF₆]^? are characterized by means of mass and IR matrixisolation spectroscopy. The primary vaporization products are AsF₅ and the new halide AsCl₄F. The IR spectra of AsCl₄F and PCl₄F are compared and the calculated force constants are discussed. Other mixed halides of arsenic are formed under suitable conditions.     

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.     

Die Reaktionen von CF3IOF2 mit Fluoridionenakzeptoren: ein Neues Darstellungsverfahren für Iodosylverbindungen

Reactions of CF₃IOF₂ with Fluoride Ion Acceptors: A New Method for the Preparation of Iodosyl Compounds CF₃IOF₂ reacts with the Lewis acids BF₃, AsF₅ and SbF₅ to form the iodosyl compounds IO[BF₄], IO[AsF₆], IO[SbF₆], and IO[Sb₂F₁₁]. The conditions of the preparation, the ¹⁹F-n.m.r. spectra, the Raman spectra and the thermal decomposition of the new compounds are described.     

Photo-induced radical formation in cellulose

The characteristics of cellulose radicals produced by photo-irradiation were studied from their ESR spectra. All spectra of the irradiated samples contained a singlet spectrum with a line width of 28 gauss. Spectra consisting mainly of a single absorption line were observed in the initial stage of irradiation. With the elapse of irradiation time, two absorption lines with a line width of 8 gauss were added to the original singlet spectrum, leading to the three absorption lines widths of 8, 28, and 8 gauss, respectively, of which the middle line with a line width of 28 gauss showed the maximum intensity. This three-line spectrum was easily produced when hydrogen peroxide or metallic ions such as Fe³⁺, Ag⁺, Fe²⁺, and Ce⁴⁺ were used as sensitizers. The observed ESR spectra consisted of a singlet with a line width of 28 gauss and a triplet with a line width of 8 gauss and a splitting factor of 28 gauss. The triplet component was more unstable toward warming, as compared with the singlet component. Based on the experimental results, it was suggested that cellulose radicals due to the scissions of cellulose chains corresponding to the ESR spectra with a single line could be the most important factor for the initiation of graft copolymerization.     

The electrical conductivity of doped oligo[aromatic diimidoselenide]

DC electrical conductivity of oligo[aromatic diimidoselenide] is studied in the temperature range 300-500 K after doping. The dopants used are I₂, FeCl₃, ZnCl₂, NaClO₄ and CuSO₄. Doping is done by mixing with 10% of the dopant, and by chemical doping. The DC electrical conductivity of the two types of doped materials is measured, compared and results interpreted. A trend of high DC electrical conductivity in the case of chemical doping especially with I₂ has been noticed. A conduction of 10⁻⁷ S cm⁻¹ is obtained at ambient or higher temperatures. This is related to a charge transfer complex formation between the oligomers and I₂. The complexation is confirmed from the electronic spectra of the chemically doped materials which showed a decrease in the π-π^* energy absorption bands and an increase in the n-π^* energy absorption bands.