Showing papers on "Cobalt published in 1968"

Reactions of gases in solution. Part III. Some reactions of nitrous oxide with transition-metal complexes

Abstract: Nitrous oxide reacts rapidly in solution at room temperature and at atmospheric pressure with a number of transition-metal complexes. It reacts with the cobalt(I) corrin, vitamin B12s, in aqueous solution according to the stoicheiometry 2CoI+ N2O → 2CoII+ N2 and with [CoI(Ph2P·CH2·CH2·PPh2)2]Br in benzene or ethanol according to the stoicheiometry 2CoI+ N2O → N2. The cobalt dimethylglyoxime, bipyridyl, and corrin complexes act as catalysts for the reduction of N2O to N2 by borohydride. In contrast to previous reports we find that acidified aqueous solutions of TiCl3 do not reduce N2O.

Pseudomorphic deposits of cobalt on copper

Abstract: Cobalt was deposited in ultra-high vacuum onto (001) copper surfaces prepared inside the vacuum chamber. If the copper substrate was at room temperature during film growth then the cobalt grew approximately as a monolayer. The structure and lattice parameter of the cobalt remained the same as the copper until its thickness reached about 20 A. At this thickness long dislocations to accommodate part of the difference between the lattice parameters of cobalt and copper were generated. Many of these dislocations were unusual in that they were imperfect. The stacking faults associated with them converted a little of the f.c.c. cobalt into the stable h.c.p. structure. If the copper was hot (350°C) during the deposition of cobalt, then film growth began with the formation of three-dimensional nuclei. Nuclei less than about 375 A in radius were f.c.c. and were strained to match the copper lattice.

The Structure of Vitamin B$_{12}$. VII. The X-ray Analysis of the Vitamin B$_{12}$ Coenzyme

Abstract: The three-dimensional molecular structure of coenzyme B 12 (59-deoxyadenosylcobalamin) has been determined by X-ray diffraction. The crystals, as grown from an acetone-water solution and photographed wet, are orthorhombic (space group P 2 1 2 1 2 1 ) with a = 27·93, b = 21·73 and c = 15·34 A. Four coenzyme molecules (C 72 H 100 O 17 N 18 PCo) and about 68 water molecules make up the unit cell. 3068 Bragg reflexions, extending to a spacing of 0·9 A, were measured with the crystals in contact with their mother liquor. The intensities were estimated visually from Weissenberg films taken with Cu Kα radiation. The cobalt atoms were easily located from the Patterson synthesis. The structure was solved in three steps, using first cobalt alone, then cobalt and 53 light atoms, and in the third approximation, 106 atoms, which included nearly the full asymmetric unit, except for water and hydrogen. Refinement of the atomic coordinates was accomplished initially by calculation of difference syntheses and finally by differential synthesis. The atomic positions have standard deviations of about 0·04 A. The conformation of the molecule is very similar to cyanocobalamin. The principal differences are in the orientation of the acetamide and propionamide side chains. Factors which influence the conformation of the corrin nucleus are analysed by comparing several corrinoids of known structure. Features of the molecule which have been examined in detail include the pucker in the pyrroline rings, the bend in the corrin macrocycle, the conformation of the nucleotide and nucleoside moieties and the orientation of the deoxyadenosine moiety with respect to the corrin nucleus. The packing of the molecules and the hydrogen bonding is discussed and compared with that found in the wet and dry vitamin B 12 crystals. Each coenzyme molecule participates in 18 direct intermolecular hydrogen bonds.

Magneto‐optic Properties of Nickel, Iron, and Cobalt

Abstract: The frequency dependence of the real and imaginary parts of the nondiagonal components of the dielectric permeability tensor of iron, cobalt, and nickel is calculated in the region 0.2–6.0 eV from experimental curves of the equatorial Kerr effect. The curves obtained can be reconciled with results from photoemission by assuming that the curve of positive values of e2′ corresponding to transitions in the 3d ↓ subband is pushed down by the curve e2′ with the opposite sign corresponding to transitions in the 3d ↑ subband.

Kinetics of thiophene hydrogenolysis on a cobalt molybdate catalyst

Abstract: The intrinsic kinetics of the hydrogenolysis of thiophene on a cobalt molybdate catalyst were studied in a differential reactor with recirculation, at a total pressure of about 1 atm. and temperatures of 235° to 265°C. Retardation of the reaction by both thiophene and hydrogen sulfide was significant and the rate of thiophene disappearance was correlated by a Langmuir-Hinshelwood type of kinetic equation. Hydrogenation of the butene intermediate was inhibited by both butene and hydrogen sulfide and the rate of this reaction was also described with a Langmuir-Hinshelwood rate equation. The forms of the kinetic expressions obtained imply that the butene is not hydrogenated at the original desulfurization site.

The strength of metal/alumina interfaces

Abstract: The room-temperature strengths of interfaces formed by melting aluminium, cobalt, gold, iron, nickel, palladium, silver, and uranium in contact with alumina have been measured. Correlations were sought between the strengths and the physical properties of the systems. Metals which formed void-free interfaces and were not subject to martensitic transformations bonded well to alumina. Metals subject to martensitic transformations (cobalt and uranium) were virtually non-adherent at room temperature.

Cobalt–molybdenum–alumina hydrodesulphurisation catalysts. Part I. A spectroscopic and magnetic study of the fresh catalyst and model compounds

Abstract: The u.v., visible, and i.r. spectra of the following compounds containing cobalt, molybdenum, and aluminium in tetrahedral and octahedral co-ordination in oxide lattices, and the magnetic susceptibilities over the temperature range 80–380°K of the first four compounds are reported: hydrated cobalt molybdate, calcined cobalt molybdate (CoMoO4), cobalt(II) molybdenum(IV) oxide (Co2Mo3O8), cobalt aluminate, cobalt(II) oxide, cobalt(II,III) oxide (Co3O4), sodium molybdate, ammonium paramolybdate, molybdenum trioxide, and γ-alumina. The spectroscopic and magnetic properties of a fresh (i.e., unsulphided) cobalt–molybdenum–alumina hydrodesulphurisation catalyst are reported and compared with the properties of the above compounds in order to determine the chemical and structural environment of cobalt and molybdenum in the catalyst. Cobalt is present as cobalt(II), approximately 50% in octahedral co-ordination and 50% in tetrahedral co-ordination by oxide. There is very little magnetic interaction between the cobalt ions which are well dispersed in the catalyst. Molybdenum is present as molybdenum(VI) in tetrahedral co-ordination by oxide. There is no evidence for the presence in the catalyst of Co3O4 or any well defined compound of cobalt, molybdenum, or aluminium. The relevance of the results to the preparation of the catalyst is discussed.

Cobalt(II), nickel(II), and copper(II) complexes of 2-methylimidazole

Abstract: The preparation and spectral and magnetic properties are reported for complexes of cobalt(II), nickel(II), and copper(II) with 2-methylimidazole (Mlz). The complexes (Mlz)2CoX2(X = Cl, Br, or I), (Mlz)2NiX2(X = Br or I), and (Mlz)2CuX2(X = Cl or Br) have tetrahedral structures whereas (Mlz)2NiCl2 has a polymeric octahedral structure. The structures of the ‘inner’ complexes (Mlz′)2N (Mlz′= C4H5N2; N = Ni, Co, or Cu) together with that of (Mlz)4CuCl2 are described. The complexes are compared with those of 2-methylpyridine and the differences discussed in terms of steric hindrance and basicity.

Anhydrous metal trifluoroacetates

Abstract: Anhydrous chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), copper(II), and zinc(II) trifluoroacetates have been prepared from solutions in nitromethane resulting from metathesis between the appropriate metal chloride and silver trifluoroacetate. The electronic spectra and magnetic susceptibilities suggest that the metal atoms are in octahedral co-ordination. The i.r. spectra of these and potassium, caesium, and silver trifluoroacetates have been recorded and assignments made for all observed bands. The effect of heat on the metal trifluoroacetates has been studied and the solubilities in diethyl ether and benzene have been examined.

Permanent magnetic materials

Abstract: THE SPECIFICATION DESCRIBES MAGNETIC COMPOSITIONS OF THE TERNARY SYSTEM CO-CU-RARE EARTH AND RELATED COMPOSITIONS WHEREIN THE COBALT MAY BE PARTIALLY OR COMPLETELY SUBSTITUTED WITH IRON, ALUMINUM OR NICKEL. CERTAIN OF THE INCLUDED COMPOSITIONS HAVE COERCIVITIES OF MANY THOUSANDS OF OERSTEDS.

Polarographic Behavior of Tris(2,2′-bipyridine)cobalt(II) and Tris(2,2′-bipyridine)cobalt(III) in Acetonitrile Solutions

Abstract: The electrode processes of tris(2,2′-bipyridine)cobalt(II) and tris(2,2′-bipyridine)cobalt(III) complexes at the dropping mercury electrode in acetonitrile solutions have been investigated by the measurement of direct current, alternating current and Kalousek polarograms. The cobalt(II) complex gave a one-step oxidation and a four-step reduction wave and the cobalt (III) complex, a five-step reduction wave, when tetraethylammonium perchlorate was used as supporting electrolyte. The solution containing the cobalt(II) and the cobalt(III) complexes gave a reversible composite wave. The limiting currents of the first two steps named from positive to negative potentials of the reduction wave of the cobalt(II) complex were diffusion-controlled, the first step being of a one-electron reduction process and the second step, of a two-electron reduction process. From the effect of free 2,2′-bipyridine and water on the reduction wave of the cobalt(II) complex and from the Kalousek polarograms, the electrode processes...