A. Pron

Electron spin resonance studies of magnetic soliton defects in polyacetylene

We present electron spin resonance studies of the magnetic defect in undoped polyacetylene. Temperature dependences of the absorption spectra of (CD)x and (CH)x over the range 2–295 K have been obtained. The properties of the magnetic defect in fully isomerized trans samples and in cis‐rich samples are compared. The data are consistent with a description in terms of a mobile neutral magnetic defect in the trans polymer and a stationary one in the cis‐rich polymer. The spin resonance linewidths are determined by unresolved hyperfine splittings resulting from interaction of the electron spin with many nuclear spins within the envelope of the spatially extended magnetic defect. The results of analyses of the detailed line shapes and linewidths are discussed in terms of the bond alternation domain wall (soliton) model of the magnetic defect.

Specific heats of pure and doped polyacetylene

The temperature dependences (0.8 K ⩽ T < 7 K) of the specific heats of pure polyacetylene (both cis and trans isomers) and heavily doped metallic [CH(AsF5)0.12]X are reported. Results for undoped cis-(CH)X indicate behavior typical of crystalline polymers, whereas isomerization to the trans-form leads to a small term linear in temperature signifying increased disorder. Comparison of the data from cis and trans starting material indicates that isomerization is induced during doping. The increased coefficient of the linear term in the metallic polymer is discussed in terms of two contributions; an electronic term expected for a metal, and the increased effect of disorder in the doped polymer.

Electrical resistivity and X-ray spacings of graphite tetrafluoroborate, hexafluorophosphate and hexafluoroantimonate compounds synthesized from nitronium salts

Abstract The action on graphite of the nitronium salts NO2BF4, NO2PF6, and NO2SbF6 dissolved in dry nitromethane has led to the formation of novel intercalation compounds. These compounds have been synthesized in a wide variety of states and characterized with respect to X-ray identity period along the c - axis , electrical resistivity normal to the c - axis , and thickness and weight change.

Intercalation of pyrographite by NO2+ and NO+ salts

Abstract BF 4 − , PF 6 − and SbF 6 − ions have been intercalated into pyrographite HOPG by chemical oxidation. The graphite is oxidized by NO 2 + (or NO + in certain experiments) coming from NO 2 BF 4 , NO 2 PF 6 and NO 2 SbF 6 (or NOSbF 6 ) salts dissolved in dry nitromethane. X-ray diffraction allows us to determine the identity period along the c axis leading to the stage n and the interpianar distance d I . Relative weight change leads us to believe that the MF x − anions are solvated by the solvent. Chemical analyses confirm this hypothesis allowing us to give to these compounds the ideal formula C + 23n MF − x (CH 3 NO 2 ) y .

‘Organic metals.’ Reaction of FeCl3 with polyacetylene, (CH)x, and poly-(p-phenylene), (p-C6H4)x

Films of the polymer semiconductor polyacetylene, (CH)x and powders of the polymer semiconductor poly-(pphenylene), (pC6H4)x, when treated with FeCL3(dissolved in dry nitromethane), are converted into organic metals which exhibit high p-type conductivity due to the oxidation of the π-system of the polymers, with the concomitant complete reducation of Fe3+ to Fe2+, as evidenced by Mossbauer spectroscopy.

‘Organic metals’. New classes of p-type dopants for converting polyacetylene, (CH)x into the ‘metallic’ state

When ca. 85%cis films of the semiconducting polymer, ‘polyacetylene,’(CH)x, are treated with H2SO4, HClO4, (NO2)(SbF6), (NO)(SbCl6), and (NO2)(BF4) two new classes of dopants are introduced to give golden, flexible films exhibiting high conductivities characteristic of the metallic state.

Identification of intercalated species in AsF5NO2SbF6 intercalated graphite using 19F N.m.r.; fluorine exchange between the various species

Abstract An intercalated graphite was prepared by reaction of polycrystalline graphite with AsF 5 followed by reaction with NO 2 SbF 6 . At −73%, four narrow lines are found in the 19 F n.m.r. spectrum at +124.1, +112.7, +66.7, and +46.8 ppm (relative to CFCl 3 ). These lines are attributed to SbF 6 − , SbF 5 , AsF 6 − in rapid chemical exchange with AsF 5 , and AsF 3 , respectively. This demonstrates the use of n.m.r. for the qualitative analysis of the chemical species present in the interlamellar space. As the temperature is increased, the lines broaden (except for that of AsF 3 ) and subsequently narrow, indicating, further, that chemical exchange of fluorine is occurring among SbF 6 − , SbF 5 , AsF 6 − and AsF 5 . At 22 °C the exchange rate is ∼ 10 3 s −1 for SbF 6 − and >3 × 10 3 s −1 for the other species. The data are interpreted in terms of a model in which fluorine exchange between SbF 6 − and the fluoro-arsenic species occurs via SbF 5 .

Transport and optical properties of graphiteMF6 compounds prepared from nitronium salts

Abstract The action of nitronium salts NO 2 + X − (X − ≡ PF 6 − , SbF 6 − ) dissolved in dry nitromethane (CH 3 NO 2 ) with graphite leads to the formation of graphite salts of ideal composition C 23n + X − (CH 3 NO 2 ) 1.7 . Since these compounds possess high electrical conductivities, they were characterized by the following in situ measurements: metallic reflectance spectra, basal plane conductivity and its temperature dependence, and X-ray diffraction. The properties related to the above measurements present differences according as the compounds are more or less “charged”. Anomalies in resistivity versus temperature are ascribed in part to the freezing of solvent molecules.

NMR determination of the ordering of CH3NO2 co-intercalated with PF6−, AsF6−, or SbF6− in graphite

Abstract Comparison of the intensities of the 19 F and 1 H NMR spectra of the graphite intercalation compound prepared by reaction of highly-oriented pyrolytic graphite with NO 2 PF 6 dissolved in CH 3 NO 2 showed that the number of CH 3 NO 2 molecules present per PF 6 − ion varied from 1.64 to 1.14 depending upon sample preparation. The 1 H NMR spectra of CH 3 NO 2 in single pieces of HOPG intercalated with PF 6 − , AsF 6 − , or SbF 6 − show 1:2:1 triplets due to dipolar splittings resulting from partial ordering of the CH 3 NO 2 molecules with the molecular symmetry axis parallel to the graphite planes.

Arsenic pentafluoride-doped polyacetylene: Chemical composition of the dopant species

Abstract Elemental analyses have been performed on seventeen different samples of cis -rich (CH) x film treated with AsF 5 vapor in order to gain an understanding of the doping reaction and the nature of the dopant species. The bulk composition of the doped film is extremely sensitive to relatively minor variations in doping procedure and/or purity of the AsF 5 . Fourteen of the samples contained only carbon, hydrogen, arsenic and fluorine, resulting in an empirical formula of [CH(AsF q ) y ] x . The As:F ratio varied in different samples from 1:5.02 to 1:6.00. Three samples contained oxygen, their composition being consistent with the empirical formula [CH(HAsF 5 OH) y ] x . The nature of the dopant species is discussed.