The 1-6 weberite Na2Te2O7 and some observations on compounds with the weberite structure

The 1-6 weberite Na₂Te₂O₇ (Imm2, a = 7.233 Å, b = 10.104 Å, c = 7.454 Å) has been prepared by high-pressure synthesis. It is shown that $\text{a}$) (the mean unit-cell dimension per formula unit) of oxide weberites A₂B₂O₇ can be represented as a linear function of the effective ionic radii of A and B. The problem of the true space-group symmetry of weberite is discussed.     

Programmed probe thermal analysis and its use in the study of thermal decomposition of some trans-substituted derivatives of zeise's salt

A mass spectrometer equipped with a programmed probe and a total ion monitor may be used to study thermal decompositions by gradually heating the sample in the probe. The ion current is monitored and mass spectra taken at appropriate points permit the identification of decomposition products. Single ion monitoring can also be employed. The method has been used to examine a series of compounds formed by the replacement of the trans-Cl ligand of Zeise's salt. Pathways for the thermal decomposition are postulated.     

The mechanism of the photoinduced hydrogenation of norbornadiene catalyzed by chromium carbonyl complexes

Kinetic, spectrophotometric and actinometric investigations of the hydrogenation of norbornadiene catalyzed by norbornadiene—Cr(CO)₄ show that the photoinduced transients promote thermal catalytic cycles.     

Electrochemical reduction of 4-thienylquinazoline in dimethylformamide

Electrochemical reduction of 4-thienylquinazoline (4-TQ) at the dropping mercury electrode in dimethylformamide solutions containing 0.1 M tetrabutyl ammonium iodide supporting electrolyte gave two well-defined diffusion-controlled waves. The first wave was found to be quasi-reversible and the second irreversible, on the basis of the usual criteria. The controlled potential electrolysis experiments carried out at the limiting regions of the frist and the total waves of 4-TQ yielded the same number of electrons, namely two, in both cases. Mechanisms corresponding to the total wave and the first wave were proposed based on the results obtained.     

Origin of the quadrupole splitting in the Mössbauer 57Fe spectrum of cubic (disordered) LiFeO2

The room-temperature Mössbauer ⁵⁷Fe spectrum of polycrystalline disordered cubic α-LiFeO₂ contains a quadrupole splitting |Δ_obs| of 0.65(2) mm/sec. This value is relatively large for an Fe atom in an essentially Fe³⁺_HS state. To account for its magnitude, the distribution of the electric-field gradient (EFG) values associated with the Fe atoms was investigated by means of exact geometric analysis involving the 12 nearest cation neighbors (model A) as well as large-scale computer simulation involving more distant cations (models B to E). It is found that (1) the major contribution to |Δ_obs| comes from the distribution of +1 and +3 charges among the 12 nearest cation neighbors of a reference Fe atom; (2) this contribution by itself largely accounts for |Δ_obs|; (3) the contribution from cations beyond the seventh-nearest neighbors is marginal; (4) displacing the oxygen atoms from their lattice sites toward adjacent Fe atoms produces a significant effect on the distribution of EFG values at a reference Fe atom, while incipient cation ordering appears to have a relatively small effect; and (5) the contribution of the EFG = 0 component to model |EFG| distributions will be overemphasized unless cations beyond the first-nearest neighbors are included in the EFG summation. The 144 distinct (up to rotation and reflection) Li¹⁺_12?kFe³⁺_k configurations on the coordination cuboctahedron of nearest cation neighbors (required for the examination of model A) are listed, together with their symmetries and multiplicities, and it is shown that the 144 configurations engender only 17 distinct |EFG| values. Observations are also made on various geometric aspects of calculating EFG at ⁵⁷Fe³⁺_HS on cubic lattices.     

Application of phase-titrations for estimation of adulteration of gasoline and high-speed diesel with kerosene

A simple, cheap and quick routine method based on phase-titration has been developed for the estimation of adulteration of gasoline and high-speed diesel with kerosene. Since no instrumentation is required, the method can be used as a field method for analysis at filling stations. Adulteration of gasoline with kerosene can be determined to +/-1%, and of diesel with kerosene to +/-2%. Even non-technical personnel with a few day's training can analyse fuel samples by this method.     

Studies of molecular motions and vibrational relaxation VII. Rotational diffusion model to investigate the band shapes of the ν5 and ν8 ban

Reorientational correlation functions G_rot^(l)(t)) for the degenerate (E) bands of liquid acetonitrile (CH₃CN) have been computed us NMR spin-lattice relaxation data (for CD₃CN) and gas phase Raman band profiles, assuming that the rotational diffusion model is valid. The effects both anisotropic rotational motion and of Coriolis coupling are included. The predicted correlation functions along with those calculated using ther cl “free” rotor equations, have been compared with those obtained from the υ_s (Raman) and υ_s (IR and Raman) experimental band profiles. It shown that, despite the simplicity of the model and obvious (understandable) discrepancies at short times, sensible conclusions may be drawn. This work a starting point for the testing of more complicated models for reorientational motion in dense phases.     

Chemiluminescent reaction of lucigenin with reducing sugars

The chemiluminescent reaction, in alkaline solution, of lucigenin with the reducing sugars sorbose, fructose, lactose, glucose, xylose, galactose, arabinose and mannose has been studied. There is a linear relationship (correlation coefficient = 0.996) between the emission intensity and the second-order rate constant for the alkaline oxidation of these sugars. The emission intensity is linearly related to the sugar concentration; at high sugar concentrations (5mM) it is independent of the lucigenin concentration, but at low concentrations (<0.05mM) is linearly related to the lucigenin concentration. These facts support the view that the rate-limiting step is the tautomerization of the sugars to the 1,2-enediol form; the enediol then undergoes reaction with lucigenin.     

Etudes stereochimiques dans la serie du silacyclopentane: synthese de dimethyl-1,2 alcoxy-1 silacyclopentanes a stereoisomere preferentiel

The stereoselective alcoholysis of 1,2-dimethyl-1-chlorosilacyclopentane and the catalytic alcoholysis of 1,2-dimethylsilacyclopentane are described.     

Reactions of methylniobium(V) and methyltantalum(V) chlorides with ketones

The chlorides Me_xMCl_5-x, M = Nb, Ta, x = 1, 2, 3 react with carbodiimides RNCNR (R = isopropyl, cyclohexyl, p-tolyl) to give products of the types MCl₄[NR-C(Me)=NR], MeMCl₃[NR-C(Me)=NR], MCl₃[NR-C(Me)=NR]₂, Me₂MCl₂[NR-C(Me)=NR], MeMCl₂[NR-C(Me)=NR]₂, which cóntain bidentate acetamidine groups arising from insertion of the carbodiimide into the metal-carbon bond. The products have been characterised by elemental analysis IR and proton NMR spectra.     

Synthese und struktur von dicyclopentadienyl(trimethylsilyl)titanchlorid

Dicyclopentadienyl(trimethylsilyl)titanium chloride, a stable trimethylsilyltitanium compound, is synthesized by reaction of dicyclopentadienyltitanium dichloride and tris(trimethylsilyl)aluminium, coordinated with diethyl ether, or lithium tetarakis(trimethylsilyl)aluminate. The IR and NMR spectra are reported. The crystal structure of the title compound has been determined. It shows a distorted tetrahedral surrounding of the titanium atom; the Ti–Si distance is 267 pm.     

Microdetermination of secondary aliphatic amines using a copper ion-selective electrode

A simple, accurate, and selective method is described for the microdetermination of aliphatic secondary amines. The method is based on their reaction with carbon disulfide and ammoniacal copper sulfate at 40 °C for 30 min to yield copper dialkyldithiocarbamate. The excess copper is then measured by titration with EDTA or NaDDC using a copper ion-selective electrode. A mean recovery of 98.2% with a standard deviation of 0.8% is obtained for aliphatic secondary amines and their salts having a wide range of pK_a.     

Behaviour of membrane graphite electrodes in potentiometric titrations of reducing substances with bromine in acetic acid

A platinum electrode, a Radelkis OP-C-7111D graphite electrode and a laboratory-prepared silicone-rubber-based membrane graphite electrode were used in potentiometric titrations of reducing substances with bromine in acetic acid. In determinations of hydroquinone, 2-methylhydroquinone, 2-chlorohydroquinone and ascorbic acid, the Radelkis electrode showed the greatest sensitivity. The advantage of the laboratory-prepared membrane graphite electrode lay in its rapid attainment of stable potential values. Titrations were improved by addition of potassium acetate to the solutions analysed. The effects of water and acetic anhydride on the results were also investigated.     

Energy transfer between Eu2+ ions in RbMgF3 crystals

Time-resolved spectroscopy after pulsed nitrogen laser excitation was used to characterize the energy transfer between Eu²⁺ ions in different crystal field sites in RbMgF₃ crystals. The results are consistent with electric dipole—dipole interaction and indicate that the Eu²⁺ ions are forming clusters in this host. As temperature is raised, the upper crystal field components of the metastable states of the ions become thermally populated and this changes the characteristics of the transfer process.     

The formation of dimetallocycles from reactions of alkynes with (η-C5Me5)2Rh2(CO)2; X-ray structure of [(η-C5Me5)2Rh2(η-CO) {μ-η2,η2-C(O)C2-(CF3)2}]

The complexes (η-C₅Me₅)₂Rh₂(μ-CO) {μ-η²,η²-C(O)CRCR} are obtained from reactions between (η-C₅Me₅)₂Rh₂(CO)₂ and the alkynes RCCR (R  CF₃, CO₂Me, or Ph) at 25°C. The molecular geometry of the complex with R  CF₃ has been established by X-ray diffraction; the bridging 'ene-one' unit adopts a μ-η²,η² conformation. Other complexes isolated from these reactions include (η-C₅Me₅)Rh(C₆R₆) (R  CF₃, CO₂Me), (η-C₅Me)₂Rh₂(C₄R₄) (R  CO₂Me) and (η-C₅Me₅)₂Rh₂(CO₂C₂R₂) (R  Ph). The reaction between (η-C₅Me₅)₂Rh₂(CO)₂ and C₆F₅CCC₆F₅ gives (η-C₅Me₅)₂Rh₂(CO)₂(C₆F₅C₂C₆F₅). Mononuclear complexes such as (η-C₅Me₅)Co(C₄R₄CO) are the major products isolated from reactions between (η-C₅Me₅)₂CO₂(CO)₂ and alkynes at 25°C.     

Studies of Ziegler-type catalysts for the polymerization of ethylene and propylene—III the polymerization of propylene with TiCl4-MgCl2-based catalysts

It has been confirmed that a reaction product of TiCl₄ and MgCl₂ is an extremely active catalyst for the polymerization of propylene. This catalyst is markedly different from the usual Ziegler-Natta TiCl₃ catalyst in the dependence of its reactivity on additions of aluminium alkyl co-catalyst and Lewis base.     

Viscosities and activation energies of flow of mixtures containing 1,2-dibromoethane

The viscosities of the mixtures of 1,2-dibromoethane + cyclohexane, + benzene, +toluene, +o-xylene, +m-xylene, and +p-xylene have been measured at 298.15 and 308.15 K as a function of composition. The viscosity data have been analysed in the light of approaches developed by Hind and Grunberg . Using Eyring kine- matic scheme the viscosity data have been employed to calculate activation energies of flow.