σ,π-acetylido complexes via P---C bond cleavage of phosphinoacetylenes: X-ray structure of Fe2(CO)6(CCPh)(PPh2)

Solutions of Co^II salts of organic acids in primary amines absorb molecular oxygen rapidly and irreversibly forming μ-dioxygen—cobalt complexes. Thermolysis leads to a homopolar cleavage of the OO bond with subsequent radical reactions involving ligand amine. After thermolysis the capacity of oxygen uptake is reestablished (catalysis).     

Photoelectron core levels for enargite,Cu3AsS4

The mineral chemistry of enargite surfaces and near‐surfaces prepared by fracture within an ultrahigh vacuum are investigated using XPS and synchrotron radiation XPS (SRXPS). The purpose of the study is to identify surface core‐level line positions in high‐resolution photoelectron spectra. The XPS spectra obtained using monochromatic Al Kα radiation show that there are near‐identical monosulphide line positions in S 2p spectra for the As–S and Cu–S bonds in enargite. The SRXPS spectra for sulphur are remarkably similar to the XPS spectra for sulphur, showing that there is minimal difference in the chemical environment between sulphur atoms at the surface and in the mineral matrix. The Cu 2p XPS data have only cuprous contributions and a minor surface contribution. The surface Cu contribution is observed as a high‐binding‐energy tail in the Cu 2p_3/2 spectrum. The As 3d data for both XPS and SRXPS show contributions from arsenic atoms at the surface and in the bulk mineral matrix. The surface contribution is distinct and is found 1 eV below the bulk contribution. The results of the study suggest that, following fracture, the enargite surface is reorganized in such a manner that the surface is characterized by protrusions of individual arsenic atoms. Copyright © 2004 John Wiley & Sons, Ltd.     

Potentiometric studies of dithiooxamide with a sulphide-selective membrane electrode

The sulphide-selective electrode is applicable to the determination of dithiooxamide by titration with silver nitrate. The effect of the alkali content of the solutions on the reaction has been studied. The reaction products are silver sulphide, oxalic acid, and nitric acid. If the alkali concentration of the solution is lower than that equivalent to the acid formed during the titration, the amount of sulphide produced by hydrolysis decreases and the equilibrium potential is established more slowly.The determination is rapid and accurate in the presence of 1 M sodium hydroxide.     

γ-sets and other singular sets of real numbers

A family of $\text{J}$ of open subsets of the real line is called an ω-cover of a set X iff every finite subset of X is contained in an element of $\text{J}$. A set of reals X is a γ-set iff for every ω-cover $\text{J}$ of X there exists $\text{〈D}{}_{\mathrm{n}}\text{: n < ω〉?}\text{J}{}^{\mathrm{\omega }}$ such that

In this paper we show that assuming Martin's axiom there is a γ-set X of cardinality the continuum.     

Reaction of η5-cyclopentadienylbis(triphenylphosphine)cobalt(I) with alkadiynes. Preparation and reactions of bicyclic cobalt metallocycles and a stable trimethylsilyl-substituted mono-complexed alkadiyne. Comments on the mechanism of cobalt-catalyzed alkyne cooligomerization

Reactions of η⁵-cyclopentadienylbis(triphenylphosphine)cobalt(I) (5) with several 2,n-alkadiynes (2) were investigated. Each of these reactions leads initially to a material in which one of the acetylene functional groups is π-coordinated to cobalt; this complex then undergoes conversion to a metallocycle. In cases where the two acetylene functions are connected by three- and four-carbon bridges (2b, 2c), metallocycles formed by intramolecular reaction of two acetylene functions in the same molecule may be isolated. In cases where the acetylene functions are joined by larger or smaller bridges, the reactions are more complex, and both inter- and intramolecular metallocycles are formed. Reactions of 5 with 1,8-bis(trimethylsilyl)-1,7-octadiyne (16) gives an isolable crystalline mono-acetylene complex (17), this material is stable in the solid state but undergoes conversion to metallocycle (18) in benzene solution. The relationship of these results to the mechanism of the CpCo(CO)₂-catalyzed benzocycloalkene synthesis is discussed; it is suggested that intramolecular metallocycles are intermediates in reactions leading to benzocyclopentanes and -cyclohexenes, but intermolecular metallocycles are probably involved in reactions leading to benzocyclobutenes.     

Laser-induced free-carrier absorption in Si single crystal

The transmitted energy density in thin single Si crystal, wafers is measured at=1.06 m as a function of the incident energy density for a Nd laser pulse of 30 ns duration. Non-linear effects begin to become important at about 0.3 J/cm². The contribution due to free-carriers is separated from the interband one by using measurements made at low energy density and at different sample temperatures in the 20°–150 °C range. The time dependence of the free-carrier concentration and of the lattice temperature is computed for different values of the Auger constant. The experimental data in the 0.2–2.5 J/cm² energy density range are fitted with an Auger constant of 10^–30 cm⁶s^–1.Work supported in part by M.P.I. and G.N.S.M.-C.N.R.     

Isocyanide addition to MN2(CO)5(Ph2PCH2PPh2)2 and the formation of a four-electron doubly-bridging isocyanide

The reactions of Fe(CO)₅, Fe(CO)₄P(C₆H₅)₃, M(CO)₆ (M  W, Mo, Cr), and (CH₃C₅H₄Mn(CO)₃ with KH and several boron and aluminium hydrides were investigated. Iron pentacarbonyl was converted quantitatively to K⁺Fe(CO)₄-(CHO) by hydride transfer from KBH(OCH₃)₃ allowing isolation of [P(C₆H₅)₃]₂-Nⁿ⁺Fe(CO)₄(CHO)^? in 50% yield. Lower yields were obtained with LiBH(C₂H₅)₃, and other hydride sources gave little or no formyl product. The stability of Fe(CO)₄(CHO)^? in THP was found to depend on the cation, decreasing in the order [P(C₆H₅)₃]₂N⁺ > K⁺ > Na⁺ > Li⁺. No formyl complexes were isolated and no spectroscopic evidence for formyl formation was observed in the reactions of the other transition metal carbonyls with several hydride sources. Fe(CO)₄-P(C₆H₅)₃ gave K₂Fe(CO)₄ when treated with KHB(OCH₃)₃. When treated with LiBH(C₂H₅)₃, W(CO)₆ gave a mixture of HW₂(CO)₁₀^?and (OC)₅W(COC₂H₅)^?; the latter was methylated to give the carbene complex (OC)₅WC(OCH₃)C₂H₅.     

On the electronic states of macrocycles of the extended porphyrin family and their coordination compounds

The electronic absorption spectra of Ni, Zn and Mg hemiporphyrazine derivatives are presented and discussed together with theoretical results obtained by INDO/S computations. The absorption spectra of all the metal derivatives show marked red shifts of the lowest energy absorption bands with respect to those of the metal free hemiporphyrazine. The possible explanation that in metal derivatives low lying excited states with a fully conjugated π electron system are present is supported by theoretical computations.     

Infrared investigation of aluminum- and chromium-substituted magnetites and of the lacunar spinels resulting from their oxidation

When Fe³⁺ ions are substituted by aluminum or chromium on magnetite octahedral sites, the ir spectrum shows the conversion of an inverse spinel to a normal spinel. Both broad bands of magnetite are gradually replaced by the four characteristic bands of normal spinels II–III. They are also observed for solid solutions, FeCr₂O₄FeAl₂O₄, with, however, a further band at 780 cm^?1 which may be assigned to Al³⁺ ions on tetrahedral sites. Low-temperature (<400°C) oxidation of these compounds whose sizes are less than 2000 Å results in lacunar spinels III–III. The ir spectrum of these solids is characterized by two absorption bands (as for inverse spinels II–III) except for compounds close to pure γFe₂O₃ in which an order of vacancies could be put in evidence.