Solubilities in aqueous mixtures oft-butanol andtrans-dichlorotetra(3-alkylpyridine) cobalt(III) hexachlororhenate(IV): Gibbs energies of transfer of the complex cations

The solubilities of the hexachlororhenate(IV) salts of the complex cations trans-[Co(3Mepy)₄Cl₂]⁺ and trans-[Co(3Etpy)₄Cl₂]⁺ have been determined in water+t-butyl alcohol mixtures. By reference to the solubilities of Cs₂ReCl₆ and the Gibbs energies of transfer of Cs⁺ from water into water+t-butyl alcohol mixtures, G _t ^o (Cs⁺), G _t ^o [Co(3Mepy)₄Cl ₂ ⁺ ] and G _t ^o [Co(3Etpy)₄Cl ₂ ⁺ ] are calculated. These latter values, when introduced into the equation for a free energy cycle applied to the process of the initial state going to the transition state for the solvolyses of these two cations, produces values for G _t ^o [Co(3Mepy)₄Cl^2+*] and G _t ^o [Co(3Etpy)₄Cl^2+*] for the Co³⁺ cations in the transition state. These values are compared with (G _t ^o (i) for i=[Co(Rpy)₄Cl₂]⁺, [Co(Rpy)₄Cl]^2+*, [Coen₂XCl]⁺ and [Coen₂X]^2+* to investigate the influence of the hydrophobicity of the surface of the complex on its stability in the mixtures. G _t ^o (i) (solvent sorting) are compared with G _t ^o (i) (TATB).     

High performance liquid chromatographic separation and UV determination of cobalt, copper iron and platinum in pharmaceutical preparations using bis(isovalerylacetone)ethylenediimine as complexing reagent

The reagent bis(isovalerylacetone)ethylenediimine(H₂IVA₂en) has been examined for HPLC separation and UV determination of cobalt, copper, iron and platinum using off-line precolumn derivatization and extraction in chloroform. The complexes of cobalt(II), cobalt(III), iron(II), iron(III) and the reagent have been subsequently separated on a Microsorb C-18 column. The complexes were eluted isocratically using ternary mixtures of methanol/water/acetonitrile. Detection was achieved by UV monitoring. Detection limits for Co(II), Co(III), Fe(II) and Fe(III) were 2.5–5.0 ng/injection, based on 0.5–1.0 g/ml with 5 l/injection. The concentration of cobalt(II) and cobalt(III) in aqueous solution have been determined. The presence of oxovanadium(IV), platinum(II), and nickel(II) did not affect the determinations. The HPLC method developed has been applied to the determination of cobalt, copper, iron and platinum in pharmaceutical preparations at the 30 g/g to 15 mg/g level and the obtained results were compared to those of atomic absorption spectrometry.     

Role of CO2 in dehydrogenation of propane over CrOX/SiO2 catalyst with low Cr content

When ethene alone was contacted with silica supported cobalt catalyst (Co/SiO₂), ethene homologation took place with considerable activity. Moreover, the propene metathesis reaction was suppressed ca. 1/6 fold as much as in the case using MoO_X/SiO₂ catalyst. The possibility of selective homologation with a lower activity for metathesis was suggested for the cobalt-based catalyst system.     

Intercalative reaction of a cobalt(III) cage complex,Co(sep)3+, with magadiite,a layered sodium silicate

The cationic metal cage complex (1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]cicosane)cobalt(III), Co(sep)³⁺ has been investigated as a potential pillaring reagent for Na⁺-magadiite (Na_1.7Si₁₄O_27.9(OH)_1.9 · 7.6 H₂O) a synthetic layered sodium silicate. Reaction of Na⁺-magadiite with aqueous solutions of Co(sep)Cl₃ at 25°C resulted in the binding of Co(sep)³⁺ cations to the external crystalline surface of the layered silicate. In contrast, an intercalated product exhibiting a 17.6 Å basal spacing was generated by reaction at 100°C.²⁹Si MAS NMR and FT-IR spectroscopy indicate that Co(sep)³⁺ intercalated reaction products retain the magadiite layer structure. Moreover, scanning electron micrographs of the reaction products showed retention of the original particle morphology, suggesting a topotactic intercalation. However, during intercalation, some of the Co(sep)³⁺ was found to undergo an unusual demetalation reaction leaving a combination of Co(II) and Co(sep)³⁺ between the layers. Nitrogen surface area analysis showed that only a small amount of microporous surface existed in the Co(sep)³⁺ intercalated derivative, suggesting that most of the interlayer space is stuffed with cobalt species.     

Gaseous complexes of cobalt(II) bromide and pyridine

The stepwise decomposition of CoBr₂py₂(s) has been investigated on a thermobalance by the “modified entrainment” method yielding Δ₁H=88.6 kJ mol¹, Δ₁S=156.6 JK^?1 mol^?1 and Δ₂H=119.0 kJ mol^?1, Δ₂S=211.8 JK^?1 mol^?1 for the dissociation of the first and second pyridine. The evaporation of CoBr₂py₂(l) and the association of gaseous pyridine to CoBr₂py(l) forming CoBr₂py₂(g) has been studied by vis spectroscopy at 250?420°C. By combining the new results with literature values, a complete thermodynamic cycle for the solid-liquid-gas equilibria in the CoBr₂-pyridine system could be established. It shows that in solution the formation of CoBr₂py₂ is not determined by the cobalt-pyridine bond energy but by the solvation energy of the rectants.     

Optical Gas Sensing Properties of Silica Film Doped with Cobalt Oxide Nanocrystals

SiO₂ sol-gel films doped with cobalt oxide nanocrystals have been fabricated. The nanocrystals precipitate in the glass film at 500_°C, while the film is still porous. The nanocomposite films showed a reversible change in the optical transmittance when exposed to CO in the 250 < < 850 nm range. The effects of the residual porosity and testing temperature have been studied. The gas sensing properties of the cobalt oxide nanocrystals doped films are compared with those of nickel oxide nanocrystals doped silica film, previously reported.     

二次锂电池正极材料Li_xNi_（0．3）Co_（0．7）O_2的XPS与XRD

结果表明，ＬｉｘＮｉ０．３Ｃｏ０．７Ｏ２具有六方晶系Ｒ３－ｍ空间群结构。当Ｘ＝１，０．３１５时，其晶胞参数分别为ａ＝２．８２６ｎｍ，ｃ＝１４．１３０ｎｍ和ａ＝０．２８０８ｎｍ，ｃ＝１．４２５３ｎｍ；ＭＯ６（Ｍ＝Ｎｉ，Ｃｏ）八面体中Ｍ－Ｏ平均距离分别为０．１９４１ｎｍ和０．１９３３ｎｍ。ＸＰＳ分析结果表明ＬＩｘＮｉ０．３ＣＯ０．７Ｏ２表面存在Ｌｉ２Ｏ，同时探讨了其中过渡金属离子的３ｄ电子结构变化。     

Synthesis of nanosize metallic and alloyed particles in ordered phases

Functionalized reverse micelles have been used to synthesize Copper and Cobalt nanoparticles differing by their size and shape. They can be also used to synthesize Fe–Cu alloy (at 30% Fe) and composite (at 70% Fe) particles. In the case of Fe–Cu system, the magnetic properties are presented.     

Stabilization of CoI by ZnII in pure acetonitrile and its reaction with aryl halides

The study of the electrochemical behavior of cobalt(II) bromide (CoBr(2)) in pure acetonitrile allowed us to demonstrate that Co(2+) is the catalyst precursor involved in the electrochemical and chemical conversions of arylhalides, ArX, to arylzinc compounds in that solvent. The reduction of Co(2+) leads to the Co(+) species, which disproportionates too rapidly to react further with aryl halides. However, the presence of zinc(II) bromide allows us to stabilize the electrogenerated cobalt(I) and to observe it on the timescale of slow cyclic voltammetry. Under such conditions, the Co(I) species has time to react with aryl halides and produce [Co(III)ArX](+) complexes that are reduced into [Co(II)ArX] by a single electron uptake at the same potential at which Co(2+) is reduced. Rate constants for the oxidative addition of ArX to Co(I) have been determined for various aryl halides and compared to the values obtained in an acetonitrile (ACN)/pyridine (9:1, v/v) mixture. It is shown that Co(I) is stabilized more by ZnBr(2) than by pyridine. A transmetallation reaction between [Co(II)ArX] and ZnBr(2) has also been observed. We finally propose a mechanism for the cobalt-catalyzed electrochemical conversion of aryl bromides into organozinc species in pure acetonitrile.     

The phenomenon of conglomerate crystallization in coordination compounds. XXIII: The crystallization behavior of [cis-Co(en)2(N3)(SO3)] · 2H2O (I) and of [cis-Co(en)2(NO2)(SO3)] · H2O (II)

A room temperature water solution of (I) crystallizes as a racemate, space groupP2 ₁/n with lattice constantsa=7.737(6),b=10.694(5),c=15.097(6) Å, and=102.83(5)°;V=1218.05 ų andd (calc; M.W.=337.24, Z=4) = 1.642 g cm^–3. A total of 2381 data were collected over the range 4° 2 < 50°; of these, 1452 (independent and withI 3(I)) were used in the structural analysis. Data were corrected for absorption ( = 15.76 cm^–1), and the relative transmission coefficients ranged from 0.8976 to 0.9984. Refinement led to the finalR(F) andR _w(F) residuals of 0.0858 and 0.1116. A room temperature water solution of (II) crystallizes as a racemate in space group P2₁/c with lattice constantsa=6.638(3),b=11.425(8),c=15.147(16) Å, and=93.27(6)°; F=1146.8 Å andd (calc; M.W.=323.2,Z=4) = 1.872 g cm^–3. A total of 2200 data were collected over the range 4° 2 < 50°; of these, 1918 (independent and withI 3(I)) were used in the structural analysis. Data were corrected for absorption (=16.94 cm^–1), and the relative transmission coefficients ranged from 0.9049 to 0.9967. Refinement led to the finalR(F) andR _w(F) residuals of 0.0231 and 0.0279. The chirality symbol for the particular enantiomer of (I) refined here is (), while for (II) the chirality symbol is (), which means that in the latter compound one of the en rings is in a higher energy conformation. We attribute this result to competitive intramolecular hydrogen-bonded interactions between the — NH₂ hydrogens of the en ligands and the oxygens of the -NO₂ and -SO₃ ligands, strengths which are enhanced by coercing a change in sign of the torsional angle of one en ringa motion which permits both oxo ligands to form stronger hydrogen bonds while retaining proper O O contacts. This phenomenon is not observed in (I) since the azide ligand does not compete with -SO₃ for such hydrogen-bonded interactions, and nonbonded pair repulsions can be minimized without affecting the ability of — SO₃ oxygens to form strong intramolecular hydrogen bonds.