Synthesis,characterization and ethylene polymerization activity of titanium,zirconium and hafnium compounds derivatives from symmetric oxamide

New non-metallocene polymerization catalysts derived from 1,2-bis(3,5-di-tert-butyl-2-hydroxiphenyl)oxamide (L) and transition metals (Ti, Zr, Hf) were synthesized and tested for ethylene polymerization reactions. The syntheses were carried out from various bases and solvents (triethylamine/toluene, NaH/THF and NaOH/methanol). The zirconium compound (5) showed the highest catalytic activity (the polyethylene molecular weight was 98,000 Da) and polydispersity index (1.8–2.0) when n-heptane was used as solvent. In terms of T_m and crystallinity, this catalyst produced the highest density linear polyethylene.     

Synthetic studies for the preparation of phosphorus carbonyl rhenacycles with the selenoimidodiphosphinate ligand [N(SePPh2)2]

The synthesis of the rhenacycles [Re(CO)₃(PR₃){Ph₂P(Se)NP(Se)Ph₂-κ²Se}], PR₃ = PPh₃ (1), PMePh₂ (2), and PMe₂Ph (3) by a straightforward high yield procedure is described. Attempts at the preparation of the spiro [Re(CO)₂(Ph₂PCH₂CH₂PPh₂-κ²P){Ph₂P(Se)NP(Se)Ph₂-κ²Se}] resulted in the formation of complexes [Re₂(CO)₆{Ph₂P(Se)NP(Se)Ph₂-κ²Se}₂(μ-Ph₂PCH₂CH₂PPh₂)] (4) and [Re(CO)₃(Ph₂PCH₂CH₂PPh₂-κ²P){Ph₂P(Se)NP(Se)Ph₂-κSe}] (5). All new inorganic rhenacycles 1-5 were characterized in solution and in solid state. The X-ray diffraction analysis of [Re(CO)₃PPh₃{Ph₂P(Se)NP(Se)Ph₂-κ²Se}] showed that its MnSePNPSe ring conformation is sensitive to temperature.     

Neutral carbon chain free energies

The structures and energies of singlet and triplet neutral carbon linear chains up to 22 atoms – and frequencies of vibrations for chains up to 17 atoms – are obtained using density functional theory (B3LYP) with a polarized split-valence basis set (6-31G*). Analytical expressions for the dependence of the energy with the number of atoms in the chains are presented with an explicit identification of the electrostatic contribution. The addition reaction free energies of two linear chains allow to visualize the reaction pathways of formation of chains up to 17 carbon atoms and to establish their dissociation temperatures. Free energy calculations show that odd chains of more than 15 atoms have triplet ground states at experimental accessible temperatures. Cycling characteristics of linear chains are discussed.     

The electrodeposition of high-density,ordered arrays of Bi1-xSbx nanowires

Here we report the synthesis of dense arrays of Bi1-xSbx nanowires with >5 x 1010 nanowires/cm2. The individual wires are crystalline, relatively homogeneous, and highly textured in a 110 direction, with diameters of 40 nm and a composition of x = 12-15 atom % Sb. By tuning the solution concentrations and controlling the growth rate by controlling the potential, the composition, crystallinity, and morphology of the nanowires can be varied.     

Determination of mineral balances in sheep offered feed with added cadmium and zinc

The optimum conditions for microwave digestion of herbage and faeces to determine mineral concentrations were obtained by varying sample mass, reagent and heating programme, and it was confirmed that the resulting element concentrations were the same as for certified reference material. The effects of feeding cadmium to sheep at a level that is typical of polluted regions (1 mg/kg) for ten days were investigated, as well as the possible amelioration of cadmium effects by adding 30 mg/kg Zn to the diet. Cadmium in the feed increased the cadmium balance and produced several mineral disturbances, in particular a reduction in sodium balance which is typical of renal tubular disorders. Including zinc in the diet as well as cadmium reduced the cadmium balance to a level similar to that of sheep that did not receive cadmium or zinc, which suggests that the zinc status is critical in determining whether cadmium in feed increases the cadmium balance in sheep.     

Formation of carbonylrhenium cryptates with alkali metal cations: Coordination chemistry studies of [Ph2P(E)NP(E)Ph2], E = O,S, Se towards ReBr(CO)5

Reaction of ReBr(CO)₅ with Li[Ph₂P(O)NP(O)Ph₂] afforded the cryptate Li[Re₂(CO)₆{μ-Ph₂P(O)NP(O)Ph₂-κ²O,O’}₃]; whereas K[Ph₂P(O)NP(O)Ph₂] reacted with ReBr(CO)₅ to give K[Re₂(CO)₆{μ-Ph₂P(O)NP(O)Ph₂-κ²O,O′}{Ph₂P(O)NP(O)Ph₂-κ²O,O′}₂]. Other chalcogen ligands’ salts M[Ph₂P(E)NP(E)Ph₂], E = Se and S, M = K and Li gave dirhenium carbonyls with bromido and Ph₂P(E)NP(E)Ph₂, E = Se or S bridges upon reaction with ReBr(CO)₅.     

Catalysis of the water gas shift reaction by cis -[Rh(CO)2(AMINE)2](PF6) complexes in an aqueous tetrabutylammonium hydrogensulfate solution

Rhodium(I) complexes, cis-[Rh(CO)₂(amine)₂](PF₆) (amine = 4-picoline, 3-picoline, 2-picoline, pyridine, 3,5-lutidine or 2,6-lutidine) dissolved in an aqueous solution of tetrabutylammonium hydrogensulfate (N(C₄H₉)₄HSO₄), catalyze the water-gas shift reaction (WGSR). The role of the coordinated amine on the catalytic activity was examined.     

Avalanches and scaling in plastic deformation

Plastic deformation of crystalline materials is a complex nonhomogeneous process characterized by avalanches in the motion of dislocations. We study the evolution of dislocation loops using an analytically solvable phase-field model of dislocations for ductile single crystals during monotonic loading. The distribution of dislocation loop sizes is given by P(A) approximately A-sigma, with sigma=1.8+/-0.1. The exponent is in agreement with those found in acoustic emission experiments. This model also predicts a range of macroscopic behaviors in agreement with observation, including hardening with monotonic loading, and a maximum in the acoustic emission signal at the onset of yielding.