Search results for "Vanadium"
showing 10 items of 260 documents
Four-, five- and six-coordinated Zn-II complexes of OH-containing ligands: Syntheses, structure and reactivity
2002
Four-, five- and six-coordinated complexes of Zn-II with OH-rich molecules possessing an ONO binding core were synthesized, characterized and their structures were established by single-crystal X-ray diffraction, The corresponding metal ion geometries were found to be distorted tetrahedral, square pyramidal and octahedral, respectively. The complexes exhibit interesting lattice structures such as layered and corrugated sheets owing to the presence of a number of weak intermolecular interactions. The five-coordinated, water-bound Zn-II complex was studied because of its putative hydrolysis property towards p-nitrophenyl acetate. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
New intermediates for the synthesis of olefin polymerization catalysts: the complexes [M2(µ-Cl)2Cl4(thf)4](M = Ti or V, thf = tetrahydrofuran); Cryst…
1993
The dimeric titanium(III) and vanadium(III) complexes [M2(µ-Cl)2Cl4(thf)4](M = Ti 1 or V 2, thf = tetrahydrofuran) have been prepared by recrystallization of [MCl3(thf)3] from dichloromethane. In the dimers, composed of slightly distorted edge-sharing octahedra, the metal atoms separated by Ti ⋯ Ti and V ⋯ V distances of 3.711 (3) and 3.619(1)A, respectively, are surrounded by two terminal Cl atoms, two oxygen atoms of thf molecules and are linked by two bridging Cl atoms. The geometry around the titanium atoms differs from that around vanadium because the thf molecules and the terminal chlorine atoms are differently located with respect to the bridging chlorine atoms of the M2(µ-Cl)2 unit.…
Influence of titanium-vanadium alloys on cell morphology: electron microscopy and ESCA studies
2000
Titanium and its alloys provide optimum metallurgical properties for implants. The formation of an oxide layer favours compatibility with the adjacent hard and soft tissues. Research focuses on further optimizing the passive layer, particularly with respect to minimizing metal ion migration into the tissues. The present study concentrates on two alloys (Ti6A14V and Til.5A125V) coated with oxide layers generated by different techniques: thermal oxidation, anodic oxidation and sol-gel treatment. Only thermal oxidation fails to reduce surface and subsurface concentrations of vanadium, whereas other treatments avoid the element in the outermost surface areas of the alloys. Additionally, the the…
A tris-oxovanadium pyrogallate complex: synthesis, structure, and magnetic and electronic properties
2021
International audience; With the aim of identifying new cation-phenolate complexes, we herein investigated the reactivity of pyrogallol (H(3)pgal) with vanadium salts. A trimetallic anionic complex was identified, and found to be formed under a broad set of reaction conditions. This complex, with the formula V3O3(pgal)(3)(3-), consists of three oxovanadium(iv) units connected together by three pyrogallate ligands to afford a bowl-shaped species presenting a pseudo 3-fold symmetry axis. Its crystal structure is reported, as well as its characterisation by a broad set of techniques, including powder X-ray diffraction, thermogravimetric analysis, infrared and Raman spectroscopy, and solid stat…
Synthesis of new vanadium–chromium and chromium–molybdenum oxynitrides by direct ammonolysis of freeze-dried precursors
2000
Interstitial vanadium–chromium and chromium–molybdenum oxynitrides in the solid solution series V1 − zCrz(OxNy) and Cr1 − zMoz(OxNy) (z = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) have been obtained by direct ammonolysis of precursors resulting from the freeze-drying of aqueous solutions of the appropriate metal salts. A study of the influence of the preparative variables on the outcomes of this procedure is presented. Compounds in the V1 − zCrz(OxNy) series are prepared as single phases by nitridation at 1073 K, followed by fast cooling of the samples. Compounds in the Cr1 − zMoz(OxNy) series are prepared as nearly single phases by nitridation at different temperatures, optimized for each composi…
A comparative study on the polymerization of 1-octene promoted by vanadium and titanium complexes supported by phenoxyimine and salen type ligands
2013
Polymerizations of 1-octene were carried out in the presence of vanadium and titanium complexes bearing salen-type or phenoxyimine ligands activated with various co-catalysts. Vanadium complexes turned out active only in conjunction with MAO, whereas the titanium ones were active in combination with Al(i-Bu)3/Ph3CB(C6F5)4. The activity of all catalysts was moderate or low and it was dependent on the ligand type: bis(phenoxyimine) complexes were more active than the salen ones. Both vanadium and titanium catalytic systems produced poly(1-octene)s possessing atactic structures with [mmmm] sequences in the range from 12 to 56 % at room temperature. A temperature decrease to 0.5 °C for the reac…
Chemical fingerprint of outdoor PM2.5 in Malta
2015
Intro: RESPIRA (EU Funded - Italia-Malta 07-13) indicated that living in Malta is a risk factor for asthma. Aim: To determine the chemical profile of PM2.5 in Malta, and compare with reference values. Methods: Using FAI pumps at 10l/min/48hr, samples were collected on Teflon and Quartz filters from 6 schools and 46 homes in Malta. Total ICP-MS measurement (Residual+extracted), X ray Fluorescence, and thermo-optical methods(TO) were used for analysis by CNR in Rome. Aeroqual IQM60 counters were used for total PM2.5 mass. All data in ng/m3, Mean, (1st to 3rd quartile) of all 48 hour measurements.
Tri-alkenyl polyhedral oligomeric silsesquioxanes as comonomers and active center modifiers in ethylene copolymerization catalyzed by bis(phenoxy-imi…
2018
Abstract In copolymerization of ethylene (E) with tri-alkenyl-silsesquioxanes (POSS-6-3 and POSS-10-3) were used bis(phenoxy-imine) titanium, zirconium and vanadium catalysts, as well as salen-type vanadium catalysts. There were obtained copolymers with POSS-R-3 units as side branches of polymer chains. The type of employed bis(phenoxy-imine) titanium, zirconium and vanadium catalysts and salen-type catalyst of vanadium determined the copolymer chain termination reactions, as well as the mechanism of modification of the active species by the POSS-R-3 comonomer. POSS-R-3 comonomers caused selective poisoning of bis(phenoxy-imine) zirconium catalyst and they provided protection against tight …
Intermediate valencies of vanadium cations appearing during oxidation of vanadium–iron spinels
2000
Abstract The oxidation state of vanadium cations in nanosized vanadium–iron spinels at stoichiometry and at oxidative nonstoichiometry has been investigated by associating X-ray diffraction, thermal analysis (DSC), infrared and X-ray photoelectron spectroscopies. It has been established that, during oxidation, the V3+ cations present several intermediate valencies before to realize the final oxidation state +5. A comparison was made with the oxidation of V2O3.
Synthesis, structural studies and reactivity of vanadium complexes with tridentate (OSO) ligand
2007
The direct reaction between [VCl(3)(thf)3] or [VO(OEt)3] and 2,2'-thiobis{4-(1,1,3,3-tetramethyl-butyl)phenol (tbopH(2)) leads to the formation of [V(2)(micro-tbop-kappa(3)O,S,O)2Cl(2)(CH(3)CN)(2)] (1).4CH(3)CN or [V(2)(micro-OEt)2(O)2(tbop-kappa(3)O,S,O)2] (2), respectively, in high yield. Compounds 1 and 2 were characterized by chemical and physical techniques including X-ray crystallography and variable temperature magnetic susceptibility studies (J = -29.1 cm(-1)) for 1. Complexes 1 and 2 were supported on MgCl2 and when activated with aluminium alkyls, were found to effectively polymerize ethene to produce polyethylene with a narrow molecular weight distribution M(w)/M(n) approximately…