Pulsed NMR study of NH4+ β-alumina

Proton NMR relaxation times T₂, T₁, and T_1? are reported for NH₄⁺ β-alumina powder in the temperature range 77 K < T < 500 K at 16 MHz. The measurements show that the NH₄⁺ ions both reorient and translate. The translational process can be characterized by the parameters E = 20 kJ mole^?1 and τ⁰_d = 3 × 10^?11 sec. Relaxation at high temperatures is dominated by dipolar coupling to paramagnetic impurities. Reasons for the different activation energies measured using NMR and other techniques for β-alumina compounds are discussed.     

Evidence for proton pairs in γ-AIOOH (boehmite) from NMR absorption spectra

Continuous-wave and Fourier transform NMR absorption spectra have been recorded for pure γ-AIOOH at room temperature and 130K. The well-resolved doublet lineshape shows that there are proton pairs (intrapair separation $\text{R ? 1.7}$ Å), the presence of which has not previously been recognized. A structural model based on the occupation of two sites consistent with the space group Cmcm is proposed.     

A simple,reliable model of the bending mode of water

A simple, reliable model of the bending mode vibration of the water molecule based on the Morse oscillator is presented. The model yields accurate predictions of the rotation—vibration level structure in the various ν₂ bands as well as the geometric structure of the ground state.     

The structure of a cubic hydrogen rhenium bronze,H1.36ReO3

The structure of D_1.36ReO₃ has been determined by a room temperature powder neutron diffraction study. The unit cell is body centered cubic (space group Im3) and contains eight formula weights (a = 7.497 ± 0.001Å). A least squares method based on peak intensities was used to refine the structure. The rhenium atoms lie on the special perovskite sites and are surrounded by distorted octahedra of oxygen atoms which are displaced towards the vacant perovskite A sites. The deuterium atoms are statistically distributed over 72 possible sites in the unit cell, as OD bonds.     

NMR study of water reorientation in molybdic acids: MoO3 · 2H2O and yellow MoO3 · H2O

Proton NMR relaxation times (T₂, T₁, T_1?) are reported for powder samples of MoO₃ · 2H₂O and yellow MoO₃ · H₂O in the temperature range 150–325 K and at 20 and 60 MHz. No translation of hydrogen atoms is detected but the spin-lattice relaxation behavior indicates reorientation of H₂O molecules. The waters coordinated to Mo atoms undergo 180° flips (about their C₂ axes) with similar motional parameters in both compounds. The interlayer waters in MoO₃ · 2H₂O undergo 180° flips with different parameters. An assumed Arrhenius-type temperature dependence of correlation times leads to preexponential factors which are “anomalously” low. The possible involvement of temperature-dependent activation barriers is discussed.     

The protonation and hydrogen transfer processes in alkene and alkyne derivatives of Os3 and H2Os3(CO)10

The complexes H₃O_s3(CO)₉CMe, H₂O_s3(CO)₁₀, H₂O_s3(CO)₉L (L = PEt₃, PPh₃ or AsPh₃), HO_s3(CO)₁₀CHC(H)Ph, and O_s3(CO)₁₀HC₂Me undergo protonation in acid to yield [H₄O_s3(CO)₉CMe]⁺ and [H₄O_s3(CO)₁₀]²⁺, [H₃O_s3(CO)₉L]⁺, [H₂O_s3(CO)₁₀CHC(H)Ph]⁺ and [HO_s3(CO)₁₀HC₂Me]⁺, respectively. The structure of these ions and their hydrido-ligand transfer reactions are described.     

Spectrophotometric study and analytical applications of the ternary complex Nb-Snazox-H2O2

The possible equilibria of formation for the colored ternary complex of Nb(V), Snazox (azoderivative of 8-hydroxyquinoline), and H₂O₂ are studied. It is shown that an unsaturated coordination complex is formed with a stoichiometric ratio of 1:1:2 and a relatively high conditional stability constant (pK′_d = 13.05 ± 0.55).A detailed account of the optimal experimental conditions for full color development i.e., pH, buffer solutions, ionic strength, rate of color development, order of addition of reagents, etc., is given.Beer's law is obeyed for a final concentration of Nb(V) in the range 1–10 ppm with a precision of about 1%.     

The crystal structure of hydrogen cerium(III) sulfate hydrate, [H3O][Ce(SO4)2] · H2O

[H₃O][Ce(SO₄)₂] · H₂O crystallizes in the monoclinic system with unit-cell dimensions (from single-crystal data) a = 9.359(4), b = 9.926(4), c = 8.444(3) Å, β = 96.53(9)° and space group P2₁/n, z = 4. The structure was solved by conventional heavy-atom methods using 1787 counter-measured reflections (MoKα radiation), and refined using full-matrix least-squares techniques to an R of 0.0465 (ωR = 0.0413). The structure consists of cerium(III) ions in irregular nine-coordination to oxygen atoms from two bidentate sulfate ions, four monodentate sulfate oxygen atoms, and one water molecule. The oxonium ions are present as isolated ions in the structure and take par in the hydrogen bonding network. The Ce-O bond lengths range from 2.454(7) to 2.626(6) Å.     

Laser-induced fluorescence in N2 and N+2 by multiple-photon excitation at 266 nm

The fluorescence transitions corresponding to the second positive system of N₂ (C³Π_u → B³Π_g) for Δv = 0, 1 and the first negative system of N⁺₂(B²Σ⁺_u → X²Σ⁺_g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N₂.     

Products of the reaction of H2Os3(CO)10 with cyclonona-1,2diene

Treatment of H₂Os₃(CO)₁₀ with cyclonona-l,2-diene produced HOs₃(CO)₉C₉H₁₃ and Os₂(CO)₆(C₉H₄)₂. Single crystal X ray analysis has shown that the latter is not isostructural with Fe₂(CO)₆(C₉H₁₄)₂.     

High-pressure syntheses of TaS3, NbS3, TaSe3, and NbSe3 with NbSe3-type crystal structure

Transition metal trichalcogenides TaSe₃, TaS₃, NbSe₃ and NbS₃ were prepared under the reaction conditions of 2 GPa, 700°C, 30 min. NbSe₃ is exactly the same as that obtained in the usual sealed-tube method. The other products are modifications of each usual phase. They have crystal structures very similar to that of NbSe₃. The lattice parameters are a = 10.02Å, b = 3.48 Å, c = 15.56 Å, β = 109.6° for TaSe₃, a = 9.52 Å, b = 3.35 Å, c = 14.92 Å, β = 110.0° for TaS₃, and a = 9.68 Å, b = 3.37 Å, c = 14.83 Å, β = 109.9° for NbS₃. In spite of the similarity in their crystal structures, these high-pressure phases show a variety of electrical transport properties. TaSe₃ is a superconductor having T_c at 1.9 K. TaS₃ is a semiconductor with two transitions at 200 and 250 K. NbS₃ is a semiconductor with E_a = 180 MeV.     

Detection of the quadruple point in the CuSO4·5H2O and BaCl2·2H2O systems: effect of experimental parameters

The effects of sample mass, particle size, and furnace heating rate were studied for the detection of the quadruple point in the CuSO₄·5H₂O system using the simultaneous differential thermal analysis—electrical conductivity (DTA—EC) technique. As the sample mass decreased, both the DTA and EC peak amplitudes decreased. Increasing the furnace heating rate caused an increase in the peak splitting for the first DTA peak. In the case of particle size, an optimum size of about 80 mesh was found to give a maximum in the EC curve peak. The simultaneous DTA—EC curves for BaCl₂·2H₂O are also given.     

Synthesis and crystal chemistry of NH3(MoO3)3

NH₃(MoO₃)₃ crystallizes with hexagonal symmetry, space group $\text{P6}{}_3\text{m}$, lattice constants a = 10.568 Å, c = 3.726 Å, and Z = 2. The crystal structure has been determined by Patterson synthesis and refined assuming isotropic temperature factors to a final conventional R value of 0.085. The structure shows a three-dimensional arrangement built up of double chains of distorted MoO₆ octahedra, parallel to the [001] direction. The octahedral double chains are linked among each other through common oxygen atoms. In addition to the shared oxygen atoms, each molybdenum is coordinated to one terminal oxygen. MoO distances range from 1.645 to 2.378 Å and OMoO angles from 74.3 to 114.3°. These results are consistent with the fact that molybdenum in high-valence states shows octahedral coordination with terminal oxygens.     

On the reduction of platinum oxide layers by hydrogen in aqueous H2SO4 under open circuit conditions

This paper reports investigations on the mechanism of the open circuit (OC) reduction of platinum oxide layers by hydrogen in aqueous sulfuric acid. Special attention was given to the conditions of the oxide layer formation and the anodic oxidation of hydrogen thereupon. A twin-cell technique was developed which allows the instantaneous rate of the OC reduction to be determined. The experimental results show that the dissociative adsorption of hydrogen is the rate-determining step of the process and that the OC reduction follows, an island mechanism. Because of the time-dependent alteration of the oxide layer structure, the formation conditions affect the instantaneous rate of the OC reduction as well as the duration of the total reduction of the oxide layer.     

Vibrational study of the unusual phase sequence in Tl3Cr(SO4)3: A compound containing [Cr(SO43−3]∞ columns

The polarized Raman spectra of small single crystals of Tl₃Cr(SO₄)₃ have been recorded using the Raman microprobe technique in the temperature range 295–660 K. The behavior of the external modes is analyzed on polycrystalline samples with conventional Raman spectrometer from 100 K to the decompositon temperature 660 K. Analysis of the spectra, in connection with dielectric measurements and X-ray data show that Tl₃Cr(SO₄)₃ undergoes the following space group phase sequence

$\text{P2}{}_1\text{c}\text{→}\text{340}\text{K}\text{R}\text{3}\text{→}\text{450}\text{K}\text{R3c}\text{→}\text{630}\text{K}\text{R}\text{3}\text{c}$

in accordance with the point group relationship

$\text{2}\text{m}\text{→}\text{3}\text{→3m→}\text{3}\text{m}$

     

Infrared spectra of Ag2BrNO3 and Ag2ClNO3

The infrared spectra of Ag₂BrNO₃ and Ag₂ClNO₃ are reported. Vibration assignments are proposed on the basis of the group theoretical analysis and D_2h symmetry. Factor group, site and TO-LO splittings are observed. The internal and external mode frequencies are correlated with those of AgNO₃ and KNO₃(II).     

High-temperature lithiation of α-Fe2O3: A mechanistic study

The reaction mechanism for the lithiation of α-Fe₂O₃ has been studied at 420°C in electrochemical cells of the type $\text{LiAl}\text{LiCl}\text{,}\text{KCl}\text{α-}\text{Fe}{}_2\text{O}{}_3$. Initially the hexagonally close-packed oxide lattice transforms to cubic close-packed stacking. Electrochemical and structural data indicate that the discharge reaction proceeds via insertion of lithium into, and iron extrusion from, the cubic close-packed lattice to yield the final discharge products Li₂O and α-Fe. Previous reports have shown that this process is reversible and that high coulombic efficiencies can be obtained from this type of cell, provided that the electrode is not discharged to its full compositional limits.     

Transport of Eu2+ in a H2OCHCl3H2O liquid membrane system containing the macrocyclic polyether 18-crown-6

Macrocyclic polyethers transport alkali and alkaline earth, but not trivalent lanthanide cations in H₂OCHCl₃H₂O liquid membrane systems. We report here the use of 18-crown-6 to transport europium after first reducing it to the bivalent oxidation state. In this oxidation state, the Eu(NO₃)₂ flux is comparable to that of Sr(NO₃)₂.     

Intensities of wagging and rocking bands of water in MnCl2 · 2H2O and CoCl2 · 2H2O

IR relative integrated intensities and half-widths of rocking (R) and wagging (W) bands of water in MnCl₂ · 2H₂O and CoCl₂ · 2H₂O are presented at 300 K and 120 K. Departure of observed intensity into D_W/D_R from those predicted by the fixed dipole model is attributed to anisotropic dynamic changes in dipole during these oscillations. A quantity representing the variation of this anisotropy between W and R oscillations is computed and its origin is discussed. An increase by 20% to 50% in both D_W and D_R on lowering the temperature has also been discussed.     

A kinetic study of the system γ-AlOOHAl2O3

A time-temperature study has been made of the system: $\text{γ-}\text{AlOOH (boehmite)}\text{Al}{}_2\text{O}{}_3$. The isothermal TTT diagram produced demonstrates the course of the transformation sequence, which involves a number of metastable transition alumina intermediate phases. This type of treatment allows calculation of kinetic parameters for the various transformation processes, and these may be correlated with the mechanisms operating. Kinetic aspects of variations in microstructure and crystal structure have also been studied. In particular, the progress of cation migration processes involved in the transformation γ → δ-Al₂O₃ has been followed in terms of the continuous variation of the spinel subcell parameters.