Evidence for the net addition of arene C-H bonds across a Ru(II)-hydroxide bond

TpRu(PMe3)2(OH) (1) reacts with C6D6 to initiate H/D exchange between the hydroxide ligand and the deuterated benzene. In addition, complex 1 catalyzes H/D exchange between H2O and C6D6. Mechanistic and computational studies suggest that a likely reaction pathway for the H/D exchange involves loss of PMe3 to produce {TpRu(PMe3)(OH)}, followed by the net addition of a benzene C-H(D) bond across the Ru-OH bond to form the putative complex TpRu(PMe3)(OH2)(Ph).     

Sintering and magnetic properties of Co-Nb ferrites

A series of samples of the system Co Nb_x Fe_2-x O₄ (x=0, 0.2, 0.4, 0.6 and 0.8) are prepared by the usual ceramic technique. X-ray analysis shows that they are cubic spinel (single phase). The lattice parameter, theoretical densityD _x, bulk densityD and the porosityP are measured for the samples. The magnetic susceptibility is measured and conducted with the additions of niobia. Results were evaluated on the bases of the exchange electrons at the octahedral sites.

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Zusammenfassung Mittels herkömmlicher keramischer Verfahren wurde eine Reihe von Proben des Systemes Co Nb_xFe_2-xO₄ (mitx=0, 0.2, 0.4, 0.6 und 0.8) gefertigt. Röntgenographische Untersuchungen zeigen ein kubisches Spinell (single-phase). Gitterkonstanten, theoretische Dichte D_x, Raumdichte D und das relative Porenvolumen der einzelnen Proben wurden bestimmt. Die magnetische Suszeptibilität wurde bestimmt. Die Ergebnisse wurden auf der Grundlage von Elektronenübergängen an den oktaedrischen Stellen gewertet.

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The author is indebted to Prof. Dr. A. Tawfik and Dr. G. Gaballa for their helpful discussions and cooperation during this work.     

Extreme value modeling under power normalization

In this paper the mathematical modeling of extremes under power normalization is developed. An estimate of the shape parameter within the generalized extreme value distribution under power normalization is suggested. The statistical inference about the upper tail of a distribution function by using the power normalization is studied. Two models for generalized Pareto distribution under power normalization (GPDP) are given. Estimates for the shape and scale parameters within these GPDP’s are obtained. Finally, a simulation study illustrates and corroborates theoretical results.     

1,1'-(3-methyl-4-phenylthieno[2,3-b]thiophene-2,5-diyl)diethanone as a building block in heterocyclic synthesis. Novel synthesis of some pyrazole and pyrimidine derivatives

A series of new bis(heterocycles) featuring thieno[2,3-b]thiophene rings was synthesized in a combinatorial manner. Intramolecular cyclization of enaminone derivatives with appropriate N-nucleophiles afforded the target compounds. All compounds were characterized by 1H-, 13C-NMR, GCMS, IR, and UV-Vis spectrometry. These compounds represent a new class of sulfur- and nitrogen-containing heterocycles that should also be of interest as new materials.     

Utilization of anion exchange resin Spectra/Gel for separation of arsenic from water

Arsenic in drinking water is one of the most challenging health hazards facing mankind today. Arsenic is a naturally occurring carcinogen and creates epidemiological problems through chronic ingestion from drinking water. Arsenic is present in water primarily as As(III) or As(V). Removal of both As(III) and As(V) from water by adsorption on strong base anion-chloride has been studied. Arsenic concentration was measured by Inductively Coupled Argon Plasma (ICP) analysis. The resin was regenerated and the adsorbed arsenic fractions were eluted by using 2 M NaCl. The effect of different parameters that influence adsorption process, such as relative arsenic and resin concentrations, retention time, and pH, were investigated. Results obtained revealed that As(III) was poorly adsorbed, whereas As(V) was successfully retained on the resin. The adsorption process was optimized by using 1 g resin for 16 ppm As(V) at pH 9 for 30 min. The removal efficiency of As(V) was 99.2%.     

Disproportionation of Gold(II) complexes. A density functional study of ligand and solvent effects

A computational study of gold(II) disproportionation is presented for the atomic ion as well as complexes with chloride and neutral ligands. The Au2+ atomic ion is stable to disproportionation, but the barrier is more than halved to 119 kcal/mol in an aqueous environment vs 283 kcal/mol in the gas phase. For dissociative disproportionation of chloride complexes, the loss of chlorine, either as an atom (Delta G(aq) = +20 kcal/mol) or as an anion (Delta G(aq) = +15 kcal/mol) represents the largest calculated barrier. The calculated transition state for associative disproportionation is only 9 kcal/mol above separated Au(II)Cl3(-) anions. For the disproportionation of Au(II)L3 complexes with neutral ligands, disproportionation is highly endergonic in the gas phase. Calculations imply that for synthesis of a monometallic Au(II) complex, a nonpolar solvent is preferred. With the exception of [Au(CO)3]2+, disproportionation of Au(II)L3 complexes to Au(I)L and Au(III)L3 is exergonic in solution phase for the ligands investigated. The driving force is provided by the very favorable solvation free energy of the trivalent gold complex. The solvation free energy contribution to the reaction (Delta G(solv)) is very large for small and polar ligands such as ammonia and water. Furthermore, calculations imply that choosing ligands that would yield neutral species upon disproportionation may provide an effective route to thwart this decomposition pathway for Au(II) complexes. Likewise, bulkier ligands that yield larger, more weakly solvated complex ions would appear to be desirable.     

Multivariate order statistics based on dependent and nonidentically distributed random variables

In this paper some identities and inequalities which involve the joint distribution of order statistics in a set of dependent and nonidentically distributed random variables are derived. These identities and inequalities provide a unified way to handle the joint distribution of order statistics in a set of univariate or bivariate observations.     

Flow-injection extraction-spectrophotometric determination of permanganate with the triphenylsulphonium cation

Summary Permanganate can be determined spectrophotometrically at 548 nm after flow-injection extraction into chloroform of the ion-associate triphenylsulphonium permanganate. The carrier stream was a pH 6 buffer containing 10% (w/v) ammonium fluoride and the reagent stream was 0.10% (w/v) triphenylsulphonium chloride. The injection rate was 20 h^–1. The calibration graph is linear up to 40 g ml^–1 and the detection limit is 1.10 g ml^–1 Mn(VII), based on injection volumes of 250 l. The system has been applied to the determination of manganese in steels and a cupro-nickel alloy.     

Gamma induced changes in Makrofol/CdSe nanocomposite films

We applied an ex-situ casting procedure to prepare a nanocomposite (NCP) from Makrofol polycarbonate (PC) and CdSe nanoparticles. The CdSe nanoparticles were prepared by a thermolysis procedure in the presence of N₂ gas flow. Rietveld refinement of x-ray data illustrated that the CdSe adopts a cubic zinc blend structure of 6.057 Å lattice parameter and 2 nm typical grain size. Samples from the prepared NCP were exposed to γ dosages (20 kGy-250 kGy). The modifications induced in the NCP films owing to γ dosages have been studied. The γ irradiation (50 kGy-250 kGy) causes crosslinks that reduce the optical bandgap from 4.15 eV to 3.81 eV, associated with an increase in dielectric parameters and refractive index. This is attributed to an increase in the mass fraction of the disordered regions as specified by x-ray diffraction. The PC-CdSe NCP was found to have a reaction to color modification which makes it suitable for saleable reproduction on a printing press.