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Electrical resistivity measurements of bulk samples of carbon nanotubes show that the resistivity behaviour of nanotubes is comparable to that of graphite. Thermopower behaviour of nanotubes is similar to that of certain pyrolytic graphites. Tunneling conductance measurements on isolated tubes however show the existence of a conductance gap which increases with the inverse diameter of the tube.
No abstract is provided for this article.
Ab initio molecular orbital calculations on fluoro- and chloro-methanes, CH4—n X n , predict the correct trends in the photoelectron spectra except in the case of the C(2s) bands of fluoromethanes. Thus, the calculated energies corresponding to the lone pair, σ (CX) and C(1s) bands increase with increasing n as found experimentally; the C(2s) energy in chloromethanes decreases with increasing n, again, in agreement with experiment.
When the Cu(1) site in orthorhombic YBaSrCu3O7−δ (Tc = 80 K), is partly substituted by the carbonate ion (upto 50%), the crystal structure becomes tetragonal and the electron diffraction pattern shows evidence for 2a × 2c superstructure; the material however is not superconducting. The same is true when Y is partly replaced by Ca as in YCaBa2Sr2Cu5(CO3)Oy. When the CO3 group is partly replaced by NO3 group as in the YCaBa2Sr2Cu5(CO3)1−x(NO3)xOy, the structure remains the same but superconductivity is retained. IR spectroscopic studies show that both CO3 and NO3 coordinate strongly and are not present as free ions in these oxyanion cuprate derivatives. Cu K-EXAFS studies on the carbonate and carbonato-nitrate derivatives confirm the presence of the oxyanions in the place of CuO4 units in the CuO chains.
(NH4)2MoS4 and (NH4)2WS4 form solid solutions over the entire composition range. Nanotubes of Mo1−x W x S2 solid solutions have been prepared by employing these solid solutions precursors. Thus, the thermal decomposition of (NH4)2Mo1−x W x S4 in an inert or a hydrogen atmosphere yields Mo1−x W x S2 nanotubes, those with x<0.1 being more readily obtained. The nanotubes exhibit novel tip architectures and defects. Single-walled nanotubes have also been observed in some samples.
No abstract is provided for this article.
In situ resonance Raman scattering of single-walled carbon nanotubes investigated under electrochemical biasing demonstrates that the intensity of the radial breathing mode varies significantly in a nonmonotonic manner as a function of the cathodic bias voltage, but does not change appreciably under anodic bias. The tangential mode is, however, not affected. These results can be quantitatively understood in terms of the changes in the energy gaps between the one-dimensional van Hove singularities in the electron density of states arising possibly due to the alterations in the overlap integral of π bonds between the p orbitals of the adjacent carbon atoms.
The addition reaction of alcohols to substituted phenylisothiocyanates is found to be a second-order reaction. The reaction is catalysed by triethylamine. First-order rate constants of the addition reaction have been determined in excess of ethanol, for a number of substituted phenylisothiocyanates and the rate data give a satisfactory linear correlation with Hammett σ constants of groups. While the energies of activation vary randomly with substitution, the entropies of activation bear a linear relationship to the energies of activation. Infra-red spectra indicate that the thiourethanes which are the products of the addition reaction exist in the thioamide form. The most prominent resonance form which can satisfactorily explain both the kinetic and infrared data, has been suggested.
Electrical conductivity measurements show that Ln1-x Sr x CoO3, (Ln = Pr or Nd) undergoes a non-metal-metal transition when x≈0 3. The d.c. conductivity of compositions with 0<x<0.l obeys the T−1/4law up to 400 K and the a.c. conductivity data follow the ωδ law with δ in the range 0.6–0.8. Surprisingly, however, δ seems to increase with increasing temperature. Thermopower measurements show clear evidence for a change in the mechanism of conduction (around 350 K) from variable range hopping to transport at E c. All these transport properties suggest that Co4+ ions in Ln1-x Sr x CoO3 (0<x<0.1), considered as moving in a lattice of Co3+, form a degenerate gas and that the states at the Fermi energy are Anderson localized.
Interaction of alkali and alkaline earth metal ions is of significance to the biophysical chemistry of proteins and polypeptides. Effect of salts are now known to involve binding with specific sites rather than general effects or alteration of water (solvent)...
No abstract is provided for this article.
The addition reactions of alcohols, ROH (R = CH3, C2H5 n-C3H7, i-C3H7 and t-C4H9), to p-bromophenylisothiocyanate show that the rates decrease in the order, CH3OH > C2H5OH > n-C3H7OH > i-C3H7OH > t-C4H9OH, although the basicities of the alcohols vary in the reverse order. The results indicate the greater importance of steric factors as compared with polar factors. Evidence is also presented for the formation of a complex between the isothiocyanate and the alcohol in the first stage of the addition reaction. In the addition of aniline to substituted phenylisothiocyanates the rate data give a satisfactory linear correlation with Hammett σ constants and the results clearly show that electron-withdrawing groups favour the addition reaction. The addition of aniline to alkyl isothiocyanates have been studied in order to find out the nature of alkyl group interaction in these derivatives. Kinetic studies on the addition of substituted anilines to phenylisothiocyanate show that the rate of reaction increases with the electron-donating ability of the substituents on the aniline as also the basicity of the aniline.
An organically templated cadmium selenate of the formula [enH2][Cd(H2O)2(SeO4)2], I , has been synthesized by carrying out the reaction between CdO and H2SeO4 in the presence of the amine in aqueous medium at 80°C. The structure of I involves isolated infinite [Cd(H2O)2(SeO4)2]2− chains running along the c-axis, with the protonated ethylenediamine molecules between them. Crystal data for I are as follows: Monoclinic, space group=C2/c, a=10.5059(7), b=10.3605(7), c=10.6028(7) A ̊ , β=94.666(2)°, V=1150.25(13) A ̊ 3 , z=8, R 1=0.0237, wR 2=0.0500 (for all data).
