Bridge Linkage Research Articles

Higher-order structure formation of ultrafine boehmite particles in sols, gels, and dried materials

Higher-order structures formed by ultrafine boehmite particles (diameter = several nm) in the aqueous sol or gel state as well as dried materials have been studied. The sol solutions containing the primary particles of boehmite are optically isotropic, but become optically anisotropic by the addition of a desired amount of electrolytes. A further increase in electrolyte concentration changes the sol solution to a jelly state which exhibits strong optical anisotropy. These phenomena may result from the one-dimensional aggregation of primary particles by edge to edge linkage of the primary particles and network formation by bridge linkage between the above one-dimensional aggregates. Unique slit-shaped or honeycomb-like structures constructed with thin walls of boehmite are observed when the sols and/or gels are frozen or lyophilized. In these structures, the plane (010) of the boehmite primary particle is set parallel to the plane of the thin walls which are composed of stacked layers of the primary particles in the direction of the b-axis.

ChemInform Abstract: Formation and Scission of the Imidazolate Bridge Linkage in Binuclear Copper(II) Complex with Glycylglycine as a Function of pH in Aqueous Solution.

AbstractThe formation and scission of the imidazolate‐bridge linkage in the binuclear Cu(II) complex (I) are studied in aqueous solutions as a function of pH.

Formation and scission of the imidazolate-bridge linkage in binuclear copper(II) complex with glycylglycine as a function of pH in aqueous solution

The formation and scission of the imidazolate- bridge linkage in the binuclear copper(II) complex with glycylglycine ([GlyGlyCu IIIm −Cu IIGlyGly] −, GlyGly = glycylglycinate(2-), Im − = imidazolate- (1-)) were studied in aqueous solutions as a function of pH. Potentiometric titration and electron spin resonance spectroscopy showed that the binuclear complex was formed in the range 9.8 < pH < 11.5. The bridge was broken by protonation at lower pH to give rise to two kinds of mononuclear complexes, [GlyGlyCu IIH 2O] and [GlyGlyCu IIImH] (ImH= imidazole). The equilibrium constant was 7.46 × 10 −5 mol dm −3. Above pH 11.5, the bridge in the binuclear complex was broken by hydroxide ion to give rise to [GlyGlyCu IIOH −] − and [GlyGlyCu II- Im −] −. The coordinated imidazolate of the latter complex was not displaced by hydroxide ion even under conditions of high pH.

Coal liquefaction by the hydrogen produced from methanol, 4. effect of catalyst species

Liquefaction of Taiheiyo Japanese coal by hydrogen generated in situ from the decomposition of methanol was examined using various kinds of methanol decomposition and hydrogenation catalysts with conversion compared. CuO containing methanol decomposition catalysts had maximum activity and the maximum yield of oil distilling up to 600°C was nearly 80 wt.% (daf base). Using model compounds the mechanism was examined. This catalyst has high activity in methanol decomposition, and for the splitting of bridge linkages as well as in hydrogenation of aromatic rings. Hydrogenation catalyst also had a significant contribution on the increase of coal conversion, especially in the yield of oil distilling at lower temperatures. Alumina or silica-alumina supports prevent the conversion because they accelerate the synthesis of dimethyl ether from methanol. In such cases the hydrogen amount generated in situ from the decomposition of methanol decreased.

Structural Characterization of Several Metal(II) 2-Methyl-8-quinolinolato Complexes in Several Organic Solvents

Abstract Bivalent metal complexes of cobalt(II), nickel(II), copper(II), and zinc(II) with 2-methyl-8-quinolinol (2MeHql) were prepared. Their properties, such as those shown by thermogravimetry (TG) and differential thermal analysis (DTA), X-ray diffraction, magnetic susceptibility, and the optical spectra, were measured and compared with those of 8-quinolinolato complexes. All the metal complexes prepared here are monohydrates, whereas their 8-quinolinolato complexes are dihydrates. The methyl group at the 2-position of the quinoline ring caused a shift of about 40–80 °C in the dehydration temperature, and, as a result of the dehydration, a dimer anhydrate was produced. The dimer-formation conditions were established in chloroform and dioxane solutions. However, the addition of such basic solvents as pyridine, water, and methanol cleaved the bridge linkages in complexes and produced a distorted octahedral configuration by solvent-binding in the axial position. The existence of a copper complex with a dimer structure such as has been shown in other metal complexes was not verified in any of the solvents used here.

Neuartige basische Liganden für die homogenkatalvtische Homologisierung von Methanol zu Ethanol, III [1]. Der Einfluß neuartiger P–N-Liganden auf die Selektivität und den Umsatz bei der Ethanolsynthese aus Methanol / Novel Basic Ligands for the Homogeneous Catalytic Homologation of Methanol to Ethanol, III [1]. The Impact of Novel P-N-Ligands on the Selectivity and Conversion for the Synthesis of Ethanol from Methanol

The N -P-N-ligands RP(XC5H4N)2 (1b′, c′, b″, c″) [X = O: R = t-Bu (b′), Me (c′); X = NH: R = t-Bu (b″), Me (c″)] are characterized by their different complex chemical behaviour towards group VI metal carbonyl derivatives. By reaction of 1b′, c′, b″, c″ with (CH3CN)3M(CO)3 the complexes (OC)3M[RP(XC5H4N)2] (2b′, c′, 3b″) and (OC)4W|[CH3P(NHC5H4N)2] (3c″) [M = Mo (2).,W(3)] are formed in which the ligands are tridentate and bidentate, respectively. This difference can be explained with the existence of hydrogen bridge linkages between NH and pyridyl groups in 3c″. Homologation experiments of methanol with 1, CoOAc: and I2 as an activator show high conversions (85%) with about 40% of ethanol selectivity. The lowest selectivities are found with 1c″.

Chemie polyfunktioneller moleküle: LXXIX. Kristall- und molekülstruktur von μ,-carbonyl-μ-chloro-di[μ,-bis(diphenylphosphino)-amin- p, P′]-bis[carbonyl-rhodium(I)]chlorid-methanol (1/1)

The molecular and crystal structure of the compound [Rh 2(μ-CO)(μ-Cl)(μ-Ph 2PNHPPh 2) 2(CO) 2]Cl·CH 3OH (1/1) (II) have been investigated in order to obtain confirmation of the complicated hydrogen bridge linkage system, deduced earlier from vibrational spectroscopy. Crystals of II are triclinic, space group P 1 , with a 1680.6(1.1), b 1380.6(5), c 1190.5(1.1) pm, α 96.30(3), γ 96.00(7), γ 110.75(3)° and Z = 2. On the basis of 3258 unique reflections, the structure was refined by blocked matrix least-squares techniques to a conventional R value of 0.064. The two rhodium atoms of the cation are bridged by two nearly transoid PNP ligands. In the equatorial plane, which is not exactly perpendicular to the waved bridging ligand planes, the two metals are slightly asymmetrically bridged by a Cl and a CO ligand. A terminal CO group on each metal, one nearly colinear with the single RhRh bond (273.7 pm), the other at an angle to die metal-metal distance, completes the rhodium coordination. The geometry of the rhodium atoms can be described as a significant distorted bipyramid. The cations of II are connected together to infinite chains along the b-axis of the crystal by strong ▪ hydrogen-bridging bond systems.

Effect of air oxidation on coal hydrogenation

Japanese Taiheiyo coal (75.9%C) was oxidized with air at 250 °C for 3–40 h and at 300 °C for 3–10 h. The weight decreased from 16.3 to 46.5% at 250 °C and from 21.7 to 41.3% at 300 °C. Carbon loss and yield of NaOH soluble were obtained. The resultant oxidation products were hydrogenated at 370 °C for 1 h under 10 MPa hydrogen pressure using red mud with sulphur as catalyst and wash oil as solvent. Conversion to pyridine, benzene and n-hexane soluble fraction shows a minimum for the coal oxidized 10 h at 250 °C and for the coal oxidized for 3 h at 300 °C. Initial oxidation makes a network structure which contributes to a reduction in conversion, but in later stages of oxidation, splitting of bridge linkages and/or ring opening of aromatic structures, contribute to increases in conversion.

A neutron-diffraction study of hemimorphite

The hydrogen atoms in hemimorphite, Zn4Si207(OH)2' H20, have been located and its crystal structure refined using 415 three-dimensional singlecrystal neutron-diffraction data. The mineral is orthorhombic, space group Imm2, with a = 8.367(5), b = 10.730(6), c = 5.115(3) A, and Z = 2. The structure consists of three-membered rings of corner-sharing Zn(OH)Oa (X 2) and Si04 tetrahedra arranged in compact sheets parallel to (010). Three oxygen atoms in each tetrahedron are bonded to two zinc atoms and one silicon atom, while a fourth oxygen atom forms a bridging bond to an equivalent cation in an adjacent sheet. The water molecules are oriented parallel to (010) inside large cavities between the tetrahedral sheets and are held in place by hydrogen bonds to and from the hydroxyl groups of the Zn - OH - Zn bridging linkages. Mul. liken population analyses calculated using constant bond lengths and the ob. served angles within and between the tetrahedra allow a rationalization of the bond-length variations in the Si04 group, but are less successful in the case of Zn(OH)Oa. Detailed analysis of observed bond length and calculated overlappopulation variations in a variety of tetrahedral oxyanions suggests that the poorer agreement in the case of the Zn tetrahedron is more a function of the larger overall size of the group than of the relative ionic character of the bonds.

Zur Frage der Bildung von Dimethylnitrosamin aus Tetracyclin-Derivaten bei der Nitrosierung in saurer Lösung / On the Problem of Dim ethylnitrosamine Form ation from Tetracycline-Derivatives by Nitrosation Reaction in Acidic Medium

The hydrochlorides from tetracycline and six tetracycline derivatives -- 7-dimethylamino-6-des-methyl-6-desoxytetracycline [minocycline], 7-chlorotetracycline [chlorotetracycline], 7-chloro-anhydrotetracycline [anhydrochlorotetracycline, 7-chloro-6-desmethyltetracycline [demethylchlorotetracycline], 5-hydroxytetracycline [oxytetracycline] and 6-desoxy-5-hydroxytetracycline [doxycycline] -- were reacted with different amounts of sodium nitrite at 37 degrees C for two hours in aqueous buffer solutions at pH 2 and 4. Dimethylnitrosamine formation was confirmed by gas-liquid chromatography and by combined gas-liquid chromatography/mass-spectrometry from minocycline, doxycycline, oxytetracycline and anhydrochlorotetracycline. Dimethylnitrosamine formation from minocycline and doxycycline was blocked by ascorbic acid. The catalytic effect of sodium thiocyanate for the dimethylnitrosamine formation from minocycline and nitrite was investigated. The different reactivity of the investigated tetracycline derivatives towards nitrite in acidic solutions is discussed by stereochemical considerations in connection with the formation of hydrogen bridge linkages. This hypothesis was confirmed by dimethylnitrosamine formation from anhydrochlorotetracycline and sodium nitrite at pH 2.

A neutron-diffraction study of hemimorphite

Abstract The hydrogen atoms in hemimorphite, Zn4Si2O7(OH)2 · H2O, have been located and its crystal structure refined using 415 three-dimensional singlecrystal neutron-diffraction data. The mineral is orthorhombic, space group Imm2, with a = 8.367(5), b = 10.730(6), c = 5.115(3) Å, and Z = 2. The structure consists of three-membered rings of corner-sharing Zn(OH)O3 ( × 2) and SiO4 tetrahedra arranged in compact sheets parallel to (010). Three oxygen atoms in each tetrahedron are bonded to two zinc atoms and one silicon atom, while a fourth oxygen atom forms a bridging bond to an equivalent cation in an adjacent sheet. The water molecules are oriented parallel to (010) inside large cavities between the tetrahedral sheets and are held in place by hydrogen bonds to and from the hydroxyl groups of the Zn – OH – Zn bridging linkages. Mulliken population analyses calculated using constant bond lengths and the observed angles within and between the tetrahedra allow a rationalization of the bond-length variations in the SiO4 group, but are less successful in the case of Zn(OH)O3. Detailed analysis of observed bond length and calculated overlappopulation variations in a variety of tetrahedral oxyanions suggests that the poorer agreement in the case of the Zn tetrahedron is more a function of the larger overall size of the group than of the relative ionic character of the bonds.

Five co-ordinate complexes of bivalent iron, cobalt, nickel, copper, and zinc halides with terdentate Schiff base and azo-ligands containing tertiary nitrogen donor atoms

The ligands N-(β-N′N′-dimethylaminoethyl)pyridinaldimine (paenMe2), N-(2′-N′N′-dimethylaminophenyl)-pyridinaldimine (paphen–NMe2), N-(2′-N″N″-dimethylaminophenyl)-2-N′N′-dimethylaminobenzylideneimine (Me2N–baphen–NMe2) and 2,2′-bis-(NN-dimethylamino)azobenzene (Me2N–ab–NMe2) form complexes with the chlorides or bromides of bivalent iron, cobalt, nickel, copper, and zinc having the general formula MLX2. The stereochemistry of these complexes has been studied by means of magnetic and spectrophotometric measurements. With the exception of Cu(Me2N–baphen–NMe2)Cl2 and Cu(Me2N–ab–NMe2)Cl2, which attain six-co-ordination through chlorine bridging linkages, all are five-co-ordinate complexes.

High-spin five-co-ordinate nickel(II) and cobalt(II) complexes with 2,6-diacetylpyridinebis(imines)

The Schiff bases obtained from 2,6-diacetylpyridine and various aliphatic amines behave as tridentate ligands with set of donor atoms NNN in nickel(II) and cobalt(II) complexes. The complexes have the general formula MLX2(M = Ni or Co; L = 2,6-diacetylpyridinebisimine; and X = halogen or pseudohalogen) and are all of the high-spin type. The nickel and cobalt halide complexes are five-co-ordinate both in the solid state and in solution, while the nickel and cobalt nitrate complexes are octahedral. The cobalt thiocyanate complexes are monomeric and five-co-ordinate, while the nickel thiocyanate complexes achieve a polymeric octahedral structure, presumably through intermolecular bridging linkages of the thiocyanate groups.

A study of the oxidative degradation of phenol-formaldehyde polycondensates using infrared spectroscopy

An infrared spectrophotometric examination of the oxidative degradation of acid- and base-catalyzed phenol-formaldehyde polycondensates, novolaks and resoles, respectively, has been carried out in the temperature range form 100–200°C. The existence of structural moieties such as quinone methides and dibenzyl ethers in the cured phenolic resins systems could not be substantiated. The oxidation of phenolic resins was shown to be a stepwise degradation. Attack of oxygen, a surface reaction, was shown to be at the doubly activated methylene bridge linkage to form a substituted dihydroxybenzophenone system. This species was substantiated by the synthesis of polymers containing the ketonic linkage and their spectral identity to the degrading resin. The initial oxidation was shown to continue through the formation of quinone structures and secondary oxidation was shown to continue through the formation of quinone structures and secondary oxidation at these functional linkages to produce carboxylic acids as one of the fragments during chain scission. This degradation mechanism is in good agreement with other supporting experimental data concerning phenolic resin degradation.