Characterization of TcCl4 and β-TcCl3 by X-ray absorption fine structure spectroscopy

Technetium tetrachloride and β-TcCl₃, synthesized from the reaction of Tc metal and Cl_2(g) in sealed tubes, were characterized by X-ray absorption fine structure spectroscopy. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements are in good agreement with the X-ray diffraction structures of the two compounds. For TcCl₄, the absorbing Tc atom is surrounded by Cl atoms at 2.34(2) Å and Tc atoms at 3.66(4) Å. For β-TcCl₃, the absorbing Tc atom is surrounded by Cl atoms at 2.40(2) Å and Tc atoms at 2.81(3), 3.66(4) and 5.71(6) Å. EXAFS spectroscopy indicates that the TcCl₄ and β-TcCl₃ samples obtained by sealed tube reactions are single phase. The X-ray absorption near edge structure spectra of TcCl₄ and β-TcCl₃ were recorded; the positions of the Tc K-edges of β-TcCl₃ (21,050.5 eV) and TcCl₄ (21,053.0 eV) are compared to the ones measured for α-TcCl₃ (21,051.0 eV) and TcCl₂ (21,048.8 eV). A correlation between the positions of the Tc K-edges and the oxidation state of the Tc atom in technetium binary chlorides was determined.     

A computer controlled continuous dilution dilatometer for the determination of solute molar volumes and direct measurement of reaction volumes in solution

The design and operation of a computer controlled continuous dilution dilatometer utilizing a diode array detection system is presented. To test the accuracy and reproducibility of the technique, apparent molar volumes of dilute aqueous solutions of potassium ferricyanide and potassium ferrocyanide have been measured. To provide supporting data for high pressure studies of reaction volumes and molar volume change in solutions of high ionic strength, study of these electrolytes was extended by dilution into 0.1M and 1.0M potassium nitrate solutions rather than extrapolation to zero ionic strength as is normal. In addition, the system has been used to determine reaction volumes of some acid-base reactions by direct measurement, using the equipment as an automatic titration dilatometer.     

Rapid catalytic transfer reduction of aromatic nitro compounds to hydroxylamines

A general method has been developed for the rapid, metal-catalysed transfer reduction of nitro compounds to N-substituted hydroxylamines.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Gas phase thermal diffusivities by a thermal lens technique

A simplified design of thermal lens apparatus is presented in which a chopped cw argon laser beam produces a transient thermal lens in a cylindrical gas cell. The axial intensity variation of a cw helium-neon laser probing this lens is analysed to yield the thermal diffusivities and thus the thermal conductivity coefficients of Kr, CO₂, CH₄, C₂H₆, C₃H₈, C₃H₆ and C₄H₁₀ as 9.4 × 10^?3 ± 4%, 1.6 × 10^?2 ± 3%, 2.98 × 10^?2 ± 4%, 2.03 × 10^?2 ± 4%, 2.05 × 10^?2 ± 7%, 1.6 × 10^?2 ± 8% and 1.9 × 10^?2 ± 8% respectively in W m^?1 K^?1 at 300 K. The method is rapid, requiring only that the sample be transparent at both laser frequencies used. A simplified mathematical analysis is shown to be adequate for this system. For the conditions specified, self-lensing of the argon laser beam is shown to be compensated by using an effective laser beam diameter.