Facile formation of molybdenum(VI) monooxo aryloxides MoO(OAr)4-nCln from molybdenum dioxo dichloride

Molybdenum monooxo compoundsMoO(OAr)4-nCln (n=0-2, Ar=2,6-Me2C6H3 or 2,6-i-Pr2C6H3) have been synthesized starting from the dioxo precursor MoO2Cl2. The complexes are characterized spectroscopically and by X-ray diffraction. The formation mechanism likely involves phenol precoordination followed by addition across the Mo=O bond.     

Inside or outside a ligand cleft? Synthetic, structural, and kinetic inertness studies of zinc, cadmium, and mercury complexes of cross-bridged cyclam and cyclen

Ethylene cross-bridging of the popular tetraazamacrocyclic ligand cyclam has led to metal complexes with enhanced kinetic inertness. The synthesis and spectral characterization of zinc(II), cadmium(II), and mercury(II) complexes of cross-bridged cyclam (L1) as well as cross-bridged cyclen (L2) are reported along with the details of our synthetic route to L2. X-ray structural studies revealed that all Zn(II) and Cd(II) cations are fully kappa(4)N-coordinated inside the respective ligand's molecular cleft with L1 providing the better fit for Zn(II). While Hg(II) is similarly coordinated to L2, it has been found to complex L1 outside the ligand cleft in a novel exo-kappa(2)N-mode. Solution NMR data of the kappa(4)N complexes are consistent with the presence of only a single cis-folded isomer in each case. Ligand (1)H and (13)C coupling to both (111,113)Cd and (199)Hg in their complexes can be clearly discerned. The relative kinetic inertness of representative cross-bridged complexes in acidic aqueous solution has been assessed and found to be in the following order: Zn(II) > Cd(II)[dbl greater-than] Hg(II). The data also reaffirm that cross-bridged cyclam ligand L1 forms a substantially more inert complex with zinc(II) than either the smaller cyclen analogue L2 or the unbridged 1,4,8,11-tetramethyl-cyclam L3.     

Magnetic propulsion of intense lithium streams in a tokamak magnetic field

This paper describes the effect and gives the theory of magnetic propulsion which allows driving free surface plasma facing liquid lithium streams in tokamaks. In the approximation of a thin flowing layer the MHD equations are reduced to one integrodifferential equation which takes into account the propulsion effect, viscosity, and the drag force due to magnetic pumping and other interactions with the magnetic field. A stability criterion is obtained for stabilization of the "sausage" instability of the streams by centrifugal force.     

Chemical Bond in Metal Azides and Their Reactivity

Results of experimental investigations into the processes of slow and explosive decomposition of metal azides and the corresponding phenomenological models are analyzed. The energy-band structure and the valence electron density for actual crystallographic planes as well as the hypothetical electron density of the first unoccupied band of KN₃ and AgN₃ are calculated by the density functional method with the use of pseudopotentials. It is demonstrated that the anion-cation chemical bond in KN₃ is predominantly ionic in character, whereas a significant covalent component in AgN₃ is caused by Ag d-states. From the character of distribution of the valence and hypothetical electron densities it follows that the exciton and vibron decomposition mechanisms are improbable. The chain process is also improbable for alkali metal azides, because the gap energy for them is E _g 8 eV, which is close to the energy of azide ion decomposition Q 9–12 eV; the chain process is probable for AgN₃, because E _g(AgN₃) 3 eV. The chain process in AgN₃ is also favored by intense delocalization of the valence electron density through the hybridization of the Ag d-state and the N p-state, which causes a relatively high hole mobility.     

Structure and Reactivity of Glycosides: IV. Koenigs-Knorr Synthesis of Aryl β-D-Glucopyranosides Using Phase-Transfer Catalysts

A series of acetylated aryl -D-glucopyranosides were prepared in 12-63% yields from tetra-O- acetyl--D-glycopyranosyl bromide and phenols containing acyl, formyl, and hydroxy substituents, and also from sterically hindered phenols in the two-phase system chloroform-aqueous alkali in the presence of triethylbenzylammonium chloride. Hydroxyethylated sucrose and dibenzo-18-crown-6 do not behave as phasetransfer catalysts in glycosylation of phenols.     

Raising the Coefficient of Turbulent Diffusion in the Reaction Zone as Means To Improve Technical and Economical Parameters of Polymer Production

Use of a new type of apparatus, high-output small-size tubular turbulent reactors of mainly dif- fuser-confuser design, in very fast processes, including polymerization, is considered. The turbulent diffusion coefficient D _t and its distribution over the apparatus volume were calculated as functions of the confuser divergence angle . The calculations were confirmed by experimental data. New reactor designs for a number of processes of large-tonnage polymer production were proposed and put into practice.     

X-ray study of structural features of GaSb(Si) single crystals grown using a set of diffraction methods under various heat and mass transfer conditions

Structural features of GaSb(Si) single crystals grown under various heat and mass transfer conditions were studied by x-ray topography and by double- and triple-crystal diffractometry. It was shown that a decrease in the convective flow intensity during crystal growth by the vertical Bridgman method with axisymmetric upper heat supply in comparison with the Czochralski method eliminates growth striations (caused by microsegregation) and improves the uniformity of electrical parameters of materials. According to triple-crystal x-ray diffractometry data, the increased density of structural defects observed in some crystal regions causes significant lattice distortions, which makes an additional contribution to crystal inhomogeneity. Some specific features in x-ray topography images of growth striations, caused by a high silicon concentration and a dopant state deviation from an ideal substitutional solid solution, were revealed.     

The compression of chemically inert gases in a closed volume and their equation of state

The totality of processes that occur when gases are compressed in a closed volume were studied. An equation describing the removal of molecules from the gas phase undergoing compression was suggested. The solution to this equation predicted the existence of two modes in the development of this process and the possibility of the transition from one mode to another at a point. The influence of the size of gas molecules on the form of the suggested equation and, accordingly, on the removal of molecules from the gas phase was analyzed. The case of the equisignificance of the effective volume of molecules in the gas and liquid phases and the situation which allowed us to ignore this parameter for particles in the gas phase were studied. The predicted differences in condensation for these models were substantial and could likely be checked experimentally. The results obtained were used to suggest an equation of state of real gases, which physically correctly described the regions of their compression and condensation and the compression of condensed liquids. The influence of liquid compressibility on the form of the equation of state and the corresponding isotherms was studied.