Synthesis of (C5H5)2Zr(O2C)CH3 and (C5H5)2Zr(O2C)CH2CH3 for olefin polymerization

Summary (C₅H₅)₂Zr(O₂C)CH₃ and (C₅H₅)₂Zr(O₂C)CH₂CH₃ complexes were synthesized, characterized and activated with MAO for ethylene polymerization. The highest catalytic activity was achieved at Al/Zr molar ratio of 3000 for both systems. The effects of the size of the R group in the carboxylate ligands, the Al/Zr molar ratio and reaction temperature on the catalytic activity and polymer properties were studied and discussed.     

Organometallics in ethylene polymerization with a catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2: 1. Suspension polymerization process

Suspension polymerization of ethylene with the catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂, at different molar ratios Mg/Ti and Al/Ti, was studied. The transition metal compounds in the catalyst complex formed in this system were found to consist only of Ti(II) and Ti(III), without free Ti(IV); but even with a Ti(II) content of 30% the catalyst was highly active. The influence of the molar ratio cocatalyst/catalyst (Al/Ti and Mg/Ti) on the catalyst activity and on the polyethylene molecular weight was studied, together with the reduction of TiCl₄ by Al(C₂H₅)₂Cl and Mg(C₆H₅)₂ in the reduction step. The polymer yield increased to some limiting molar ratio Mg/Ti and to some limit ratio Al/Ti and further increase of organometal concentration in the system has practically no influence on the catalyst productivity. Dependence of the polyethylene molecular weight on the molar ratios Mg/Ti and Al/Ti was observed, proving the presence of chain transfer reactions with organometallics.     

Kinetics of Polyurethane Formation in Polymerization Reactions Using the Organometallic Diol (η5-C5H4CH2CH2OH)2Mo2(CO)6

Summary The kinetics of the dibutyltin diacetate (DBTA) – catalyzed polymerization reactions of (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ with Hypol 2000 (an isocyanate-terminated polyether prepolymer) and with 1,4-butanediol were studied, as were the kinetics of a copolymerization involving (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ and PEG-1000 (a poly(ethylene glycol)) with Hypol 2000. The purpose was to determine if (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ appreciably affected the overall rate of the polymerization reaction and if it changed the mechanism of the reaction. The kinetics were analyzed with a fitting program, which allowed extraction of the rate constants for the individual elementary steps in the mechanism. The results showed that (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ does not significantly alter the timescale of the reaction and that the same reaction mechanism is likely used as with the 1,4-butanediol and PEG-1000. There are some differences in the rate constants of the elementary steps, but these differences can be attributed to the increased steric crowding caused by the bulkier (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ diol. The effect of the (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ on the polymers’ physical properties was also investigated. As is the case with other segmented polyurethanes, the hydrogen bonding index (HBI) and the relative amount of soft segments of the (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆-containing polyurethane correlate in a general way with the physical properties of the polymer.     

Calorimetric investigation of nanotubular hydrosilicates in the Mg3Si2O5(OH)4-Ni3Si2O5(OH)4 system

A calorimetric investigation of the synthesized nanotubular hydrosilicates based on compounds of the variable composition (Mg,Ni)₃Si₂O₅(OH)₄ with a chrysotile structure is performed on a Tian-Calvet high-temperature heat-flux microcalorimeter. The enthalpies of formation of the hydrosilicates from elements at a temperature of 298.15 K are determined using oxide melt solution calorimetry. Original Russian Text ? L.P. Ogorodova, I.A. Kiseleva, E.N. Korytkova, V.V. Gusarov, 2007, published in Fizika i Khimiya Stekla.     

Synthesis and characterisation of tetraosmium carbonyl clusters bearing an azo type ligand: crystal and molecular structures of [Os4(μ-H)4(CO)11(NC5H4N=NPh)] and [Os4(μ-H)4(CO)10(MeCN)(NC5H4N=NPh)]

Reaction of [Os₄(μ-H)₄(CO)₁₀(MeCN)₂] with one equivalent of 4-phenylazopyridine (4-PAP) in CH₂Cl₂ at ambient conditions afforded two new tetraosmium clusters [Os₄(μ-H)₄(CO)₁₁(NC₅H₄N=NPh)] (1) and [Os₄(μ-H)₄(CO)₁₀(MeCN)(NC₅H₄N=NPh)] (2) in moderate yields. Compound 1 exists as a pair of isomers in solution, which differ in the location of the bridging hydride ligands. The molecular structures of clusters 1 and 2 consist of a highly distorted tetrahedral metal skeleton, with the azo ligand terminally bonded to an osmium atom.     

Sr0.5Zr2(PO4)3陶瓷的力学性能研究

用共沉淀法和低分子有机溶剂分散获得SZP粉体,经干压成型和烧结得到SZP陶瓷.研究了其力学性能与烧结温度烧结时间和添加剂用量的关系.最佳工艺条件为添加MgO6wt%,1300℃或ZnO3wt%,1200℃均烧结1.5小时,SZP陶瓷的抗压强度分别可达244.0MPa和226.2MPa.     

The doping concentration dependent tunable yellow luminescence of Sr5(PO4)2(SiO4):Eu

Color tunable yellow-emitting phosphors of Sr_5−5xEu_5x(PO₄)₂SiO₄ (x = 0.05-0.15) were prepared by conventional solid-state reaction method. The X-ray powder diffraction patterns, the photoluminescence excitation and emission spectra were measured. The main excitation bands of the phosphors locate at a broad band extending from 300 to 500 nm, which can match the emission of ultraviolet- and blue-emitting diode chips. The tunable luminescence color was realized by the changing Eu²⁺ doping in Sr₅(PO₄)₂SiO₄. The structure and luminescence properties were investigated. Sr_5−5x(PO₄)₂SiO₄:Eu_5x displays two typical luminescence centers, which originate from two different Sr²⁺ (Eu²⁺) sites in the host. The site-occupation, the luminescence intensity and energy transfer between the Eu²⁺ ions occupying two different crystallographic Sr²⁺ sites were discussed on the base of the luminescence spectra and crystal structure. This is helpful to improve this phosphor for a potential application as a white light emitting diode phosphor.     

The metal-chain complexes (X)[Os(CO)3(CNBu)]3Mn(CO)5 (X=Cl, Br, I)

In what is a new metal-chain forming reaction, (X)[Os(CO)₃(CNBu^t)]₃Mn(CO)₅ (X=Cl, Br, I) complexes have been prepared by the successive addition of Os(CO)₄(CNBu^t) to Mn(CO)₅(X) in hexane. The crystal structure of the iodo derivative reveals it to contain an approximately linear Os₃ Mn chain of metal atoms.     

Synthesis, structure and photoluminescence of a novel palladium(I) compound: [Pd3(μ3-Cl)2(dppp)3][Pd2(μ2-Cl)3(PPh3)2](PPh3)2

Pd(PPh₃)₂Cl₂ reacts with PdCl₂ and 1,3-bis(diphenylphosphine)propane (dppp) in ethanol–DMF–pyridine mixed solvent to yield a novel palladium(I) compound [Pd₃(μ₃-Cl)₂(dppp)₃][Pd₂(μ₂-Cl)₃(PPh₃)₂](PPh₃)₂. It features an isolated structure based on [Pd₃(μ₃-Cl)₂(dppp)₃]⁺ cations having triangulo-palladium clusters and [Pd₂(μ₂-Cl)₃(PPh₃)₂]⁻ anions in which the coordination environment of palladium is an unusual tetrahedral geometry. Its photoluminescence is measured.     

Organometallics in ethylene polymerization with a catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2: 2. Polymerization process in pseudo-solution

A study has been made of ethylene polymerization in pseudo-solution with a catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂ in the presence of hydrogen as a regulator of polyethylene molecular weight. The polymerization process in pseudo-solution by adjustment of hydrogen makes it possible to produce polyethylene having a wide range of molecular weights. For this purpose melt indices between 0°–50°C/min are desirable and these values are not reached with a suspension type of ethylene polymerization with a catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂. The effect of the molar ratio cocatalyst/catalyst (Al/Ti and Mg/Ti) on the catalyst activity and on the polyethylene molecular weight was studied, together with the content of hydrogen as a regulator of the molecular weight. The catalyst productivity increased to some limiting molar ratio Mg/Ti and Al/Ti and further increase of organometallics in the catalyst system did not influence the polymer molecular weight. In the case of ethylene polymerization with this catalyst combination in the presence of hydrogen, some activation of the catalyst was observed. Two mechanisms, which may account for the activation effect of the hydrogen are discussed.     

Rapid preparation and electrochemical behavior of carbon-coated Li3V2(PO4)3 from wet coordination

An improved solid-state coordination method namely wet coordination has been developed to synthesize carbon-coated monoclinic Li₃V₂(PO₄)₃ rapidly at a low temperature of 600 °C in 1 h. The structure of the sample was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and energy dispersive analysis of X-rays (EDAX). The diffusion coefficient of the lithium ions was measured by cyclic voltammetry (CV). The electrochemical behavior of the sample exhibits a high initial discharge capacity of 130 mAh g⁻¹, which is very close to its theoretical capacity of 132 mAh g⁻¹ under 95 mA g⁻¹ (0.67 C) in the range of 3.3-4.3 V (vs. Li/Li⁺). These results suggest that wet coordination is a promising method for large-scale production of carbon-coated Li₃V₂(PO₄)₃.     

Structure and physicochemical properties of the (AsSI)1? x (As2S3) x and (AsSeI)1? x (As2Se3) x glasses

The structure and physicochemical properties of glasses in the (AsSI)_1−x (As₂S₃) _x and (AsSeI)_1−x (As₂Se₃) _x systems are investigated. It is demonstrated using ¹²⁷I M?ssbauer spectroscopy that the structure of the glasses under study is built up of the structural units AsS_3/2 (AsSe_3/2), which correspond to the compounds As₂S₃ (As₂Se₃), and the ternary structural units, which correspond to the compounds AsSI (AsSeI). In turn, these structural units are connected into a three-dimensional network. The proposed model accounts for the observed linear dependences of the physicochemical properties (density, microhardness, glass transition temperature) of the glasses on the composition. Original Russian Text ? V.A. Bordovskii, R.A. Castro, A.V. Marchenko, P.P. Seregin, 2007, published in Fizika i Khimiya Stekla.     

Organically templated Np(IV) coordination polymer with in situ formed oxalate anion (ImidazoleH)[Np(C2O4)(CH3SO3)3(H2O)2]

The reaction of Np(V) methanesulfonate solution with imidazole led to the in situ formation of oxalic acid and the reduction of Np(V) to Np(IV). As a result, the novel organically templated organic polymer, (ImidazoleH)[Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂], was formed. The structure consists of infinite chains of [Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂]⁻ and imidazolium cations. The crystal structure is confirmed by IR and UV–vis spectroscopic data. This complex is the first example of structurally characterized 1:1 An(IV) oxalate.     

Ca3(PO4)2 coating of spherical Ni(OH)2 cathode materials for Ni-MH batteries at elevated temperature

Calcium phosphate was used for surface modification of spherical nickel hydroxide to improve its high temperature performance at the first time due to its low cost. The Ca₃(PO₄)₂ and Co(OH)₂ coated nickel hydroxides were prepared by precipitation of Ca₃(PO₄)₂ on the surface of spherical nickel hydroxide, followed by precipitation of Co(OH)₂ on its surface. The optimum coating content of calcium was around 2% (atomic concentration) to obtain high discharge capacity both at 25 and 60 °C. It was shown that the discharge capacity of nickel hydroxide at higher temperatures was improved by coating of Ca₃(PO₄)₂ and cobalt hydroxide. The high temperature performances of the sealed AA-sized nickel-metal hydride (Ni-MH) batteries using Ca/Co coated nickel hydroxide as positive electrodes were carried out, showing much better than those using uncoated or only Co(OH)₂ coated nickel hydroxide electrodes. The charge acceptance of the battery using 2% Ca and 2% Co coated nickel hydroxide reached 81% at 60 °C, where the charge acceptances for uncoated and only Co(OH)₂ coated nickel hydroxide were only 42 and 48%, respectively. It has shown that the Ca/Co coating is an effective way to improve the high temperature performance of nickel hydroxide for nickel-metal hydride batteries. It is a promising cathode material of Ni-MH batteries for EV applications due to the cost.     

The formation and thermal stability of spurrite,Ca5(SiO4)2CO3

The reversible equilibrium: 2Ca₂SiO₄ + CaO + CO₂ ? Ca₅(SiO₄)₂CO₃ has been studied using F^? and C?^? ions as mineralizers. A pressure-temperature curve is given for the reaction in the range of CO₂ pressures between 0.08 and 1 atmosphere. At these pressures, the decomposition temperatures of spurrite are 790 ± 5°C and 912 ± 5°C respectively. At a given CO₂ pressure the thermal stability of spurrite is greater than that of CaCO₃.     

Ferromagnetic coupling in a novel dicyanamide-bridged dinuclear gadolinium(III) complex [Gd2(dca)4(OH)2 (NITpPy)4] (NITpPy = 4-pyridyl-nitronyl nitroxide radical)

The novel six-coordinated gadolinium(III) complex of formula [Gd₂(dca)₄(OH)₂(NITpPy)₄] (1) (dca = dicyanamide, NITpPy = 4-pyridyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-oxy-3-oxide) has been prepared and characterized by X-ray crystallography. Compound 1 is a dimer structure made up of double μ_1,5-dca-bridged gadolinium(III) ions and one terminal dca ligand; variable-temperature magnetic susceptibility measurements reveal the occurrence of a significant ferromagnetic interaction directly spin polarization through the NITpPy–Gd(III)–NITpPy pathway with J = 11.56 cm⁻¹.     

A CO and CO2 tolerating (La0.9Ca0.1)2(Ni0.75Cu0.25)O4+d Ruddlesden-Popper membrane for oxygen separation

A series of novel dense mixed conducting ceramic membranes based on K₂NiF₄-type (La_1–xCa_x)₂ (Ni_0.75Cu_0.25)O_4+δ was successfully prepared through a sol-gel route. Their chemical compatibility, oxygen permeability, CO and CO₂ tolerance, and long-term CO₂ resistance regarding phase composition and crystal structure at different atmospheres were studied. The results show that higher Ca contents in the material lead to the formation of CaCO₃. A constant oxygen permeation flux of about 0.63 mL·min⁻¹·cm⁻² at 1173 K through a 0.65 mm thick membrane was measured for (La_0.9Ca_0.1)₂ (Ni_0.75Cu_0.25)O_4+δ, using either helium or pure CO₂ as sweep gas. Steady oxygen fluxes with no sign of deterioration of this membrane were observed with increasing CO₂ concentration. The membrane showed excellent chemical stability towards CO₂ for more than 1360 h and phase stability in presence of CO for 4 h at high temperature. In addition, this membrane did not deteriorate in a high-energy CO₂ plasma. The present work demonstrates that this (La_0.9Ca_0.1)₂(Ni_0.75Cu_0.25)O_4+δ membrane is a promising chemically robust candidate for oxygen separation applications.     

New ferrocene-derived hydroxymethylphosphines: FcP(CH2OH)2 [Fc=(η-C5H5)Fe(η-C5H4)] and the dppf analogue 1,1-Fc[P(CH2OH)2]2 [Fc=Fe(η-C5H4)2]

Reactions of the ferrocene-phosphines FcPH₂ and 1,1^′-Fc^′(PH₂)₂ with excess formaldehyde gives the new hydroxymethylphosphines FcP(CH₂OH)₂ 1 and 1,1^′-Fc^′[P(CH₂OH)₂]₂ 2, respectively. Phosphine 1 is an air-stable crystalline solid, whereas 2 is isolated as an oil. Reaction of 1 with H₂O₂, S₈ or Se gives the chalcogenide derivatives FcP(E)(CH₂OH)₂ (E=O, S or Se), whilst reaction of 2 with S₈ gives 1,1^′-Fc^′[P(S)(CH₂OH)₂]₂, which were fully characterised. Phosphine 1 was also characterised by an X-ray crystal structure determination.