Polymers oxidation with VO(acac)2 complex

The introduction of epoxy groups in the polymer backbone is one of the most promising methods of modifying polydienes. In this work the performance of the classical catalytic system VO(acac)₂/tert-butylhydroperoxide was evaluated for the epoxidation of polydienes. The polymers investigated were a hydroxylated poly(butadiene), two polybutadienes with high and with low 1,4-content, a poly(isoprene), and a styrene–butadiene copolymer. The epoxidized polymers were characterized by IR, ¹H and ¹³C NMR and GPC techniques. The vanadium system was active for the epoxidation reaction and the reactivity decreases in the order HTPB>PI>1,4-PB>1,2-PBSBR. The occurrence of secondary reactions to low extension could be detected by the presence of hydroxyl, carbonyl and alcohol signals in the spectra of epoxidized polymers. Incomplete mass recovery (70–90%) was observed probably due to the chain degradation or modification of the polymer polarity.     

Preparation and characterization of Cr- and Fe-pillared bentonites by using CrCl3, FeCl3, Cr(acac)3 and Fe(acac)3 as precursors

Four pillared bentonites (Cr-PILB, Cr(acac)₃-PILB, Fe-PILB and Fe(acac)₃-PILB were prepared and characterized by X-ray diffraction (XRD), nitrogen sorption measurements and thermogravimetric (TG) analysis. The surface acidities of the samples and their structures were also investigated in the gas phase adsorption data of pyridine by the aid of FT-IR spectroscopic techniques. The XRD data and FT-IR spectra of the samples reflected mainly the structure of bentonite. The nitrogen adsorption–desorption isotherms of the samples were Type II shaped and showed in general mesoporous structures with pore openings of 4 nm. Two steps mass losses were observed in the TGA thermograms of B, Cr-PILB and Fe-PILB, while three steps mass losses were detected in the case of Cr(acac)₃-PILB and Fe(acac)₃-PILB. IR study by the adsorption of pyridine on the samples showed both Lewis and Brönsted acid sites on their surfaces.     

Mild oxidation of alcohols with periodic acid catalyzed by [Ru(acac)2(CH3CN)2]PF6 in water

A facile [Ru(acac)₂(CH₃CN)₂]PF₆ (Hacac = acetylacetone) (1) catalyzed oxidation of alcohols to aldehydes or ketones using H₅IO₆ as oxidant in water at room temperature is described.     

Synthesis and structure of [{As(NBu)3}2Li6] containing an [As(NBu)3] trianion

Attempts to prepare the [As(N^tBu)₃]³⁻ trianion by the reaction of As(NMe₂)₃ with [^tBuNHLi]_n (1:3 monomer equiv.) proved unsuccessful. However, if the reaction is carried out with an excess of ^tBuNH₂ (3 equiv.) the target complex [{As(N^tBu)₃}₂Li₆] (1) is obtained. This is the first example of a complex containing an [As(NR)₃]³⁻ trianion.     

Self-assembled chloro-bridged metallo-prismatic cations of the general formula [M6(η-C5Me5)6(μ3-tpt)2(μ-Cl)6] (M = Rh, Ir; tpt = 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine)

Two cationic pentamethylcyclopentadienyl metal-based hexanuclear complexes with trigonal prismatic architecture have been synthesised through a two-step strategy. The dinuclear complexes [M(η⁵- C₅Me₅)(μ-Cl)Cl]₂ (M = rhodium and iridium) react with 2,4,6-tri(pyridin-4-yl)-1,3,5-triazine (tpt) in dichloromethane to give the trinuclear complexes [Rh₃(η⁵-C₅Me₅)₃(μ₃-tpt)Cl₆] (1) and [Ir₃(η⁵-C₅Me₅)₃(μ₃-tpt)Cl₆] (2), respectively. Addition of silver triflate to 1 and 2 in dichloromethane connects two identical triangular panels to form the hexanuclear metallo-prismatic cations [Rh₆(η⁵-C₅Me₅)₆(μ₃-tpt)₂(μ-Cl)₆]⁶⁺ (3) and [Ir₆(η⁵-C₅Me₅)₆(μ₃-tpt)₂(μ-Cl)₆]⁶⁺ (4), respectively. Cations 3 and 4 have been isolated as their triflate salts and characterised by ¹H NMR, IR and UV/visible spectroscopy.     

A kinetic analysis on the gas phase polymerization of ethylene over polymer supported (CH3)2Si[Ind]2ZrCl2 catalyst

Kinetics of the gas phase polymerization of ethylene over polymer supported (CH₃)₂Si[Ind]₂ZrCl₂ catalyst is examined. It requires a two-site model to adequately describe the experimental results. The active sites seem to follow a first-order deactivation. The number of sites activated is dependent upon the cocatalyst (MAO) concentration level as well as temperature. It was observed that the decrease of activity at higher temperatures resulted from a strong dependency of the first-order decay rate constant on temperature. On the other hand, the propagation rate constants of two active sites show similar dependency on temperature.     

Synthesis and X-ray crystal structure determination of monomeric cis-Pd(2,2′-bipyridine)(NO3)2

Complex cis-Pd(2,2′-bipyridine)(NO₃)₂ was synthesized by the reaction of cis-Pd(2,2′-bipyridine)Cl₂ with AgNO₃ in water and crystallized by vapor diffusion of diethyl ether into an acetonitrile solution of the complex. The crystal structure obtained shows that each of the two nitrate ligands are coordinated through oxygen atoms to the Pd(2,2′-bipyridine)²⁺ center in unidentate fashion. IR and ¹H NMR spectral data were also obtained.     

The structural characterization and hydroformylation activity of the tri-rhodium complex [Rh3(μ2-dppm)2(μ2-CO)3(K-CO)3]BF4

Rh₂(cod)₂(μ₂-dppm)(μ₂-Cl)]BF₄ (1) rearranges under carbon monoxide to give [Rh₃(μ₂-dppm)₂(μ₂-CO)₃(K¹-CO)₃]BF₄ (2). Complex 2 has been structurally characterized by single crystal X-ray crystallography. The hydroformylation activities of 1 and 2 were compared for substrates styrene and 1-hexene and the activity of 2 found to be unexpectedly high.     

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.     

Solution and solid phase electrochemical behaviour of [Os(bpy)3]3[P2W18O62]

[Os(bpy)₃]₃[P₂W₁₈O₆₂] has been synthesised and characterised by elemental analysis, spectroscopic (UV-vis, IR spectroscopy) and electrochemical techniques. In 0.1 M Bu₄NPF₆ DMSO the complex shows a series of redox couples associated with the Os^3+/2+ and bipyridine ligands of the cationic [Os(bpy)₃]²⁺ moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion, [P₂W₁₈O₆₂]⁶⁻. At this electrolyte concentration, the Os³⁺ redox form of the complex was seen to adsorb onto the electrode surface. When the electrolyte concentration is lowered to 0.01 M Bu₄NPF₆ in addition to the Os^3+/2+ redox couple, the redox process associated with the [P₂W₁₈O₆₂]^8−/7− couple also exhibited properties indicating surface based processes were present. Electroactive films of the complex were formed on carbon macroelectrodes by the redox switching of the transition metal within the complex. Voltammetric investigations into the film's behaviour in a range of buffer solutions (pH 2.0, 4.5 and 7.0) were performed. The films were found to possess better stability in acidic pH and the same pH dependence for the tungsten-oxo framework of the heteropolyanions as in solution. Solid state electrochemical measurements on mechanically attached microparticles of the complex were performed, with the effect of both the nature and concentration of the aqueous electrolyte on this behaviour being investigated. Upon redox switching between the Os^2+/3+ redox states, there is an associated insertion/expulsion of anions from/to the solution phase. Scanning electron micrographs of these solid state films were attained before and after redox cycling.     

Carbon nanotubes and onions from carbon monoxide using Ni(acac)2 and Cu(acac)2 as catalyst precursors

New catalyst precursors (copper and nickel acetylacetonates) have been used successfully for the synthesis of carbon nanotubes and onion particles from carbon monoxide. Catalyst nanoparticles and carbon products were produced by metal-organic precursor vapour decomposition and catalytic disproportionation of carbon monoxide in a laminar flow reactor at temperatures between 705 and 1216 °C. Carbon nanotubes (CNTs) were formed in the presence of nickel particles at 923-1216 °C. The CNTs were single-walled, 1-3 nm in diameter and up to 90 nm long. Hollow carbon onion particles (COPs) were produced in the presence of copper particles at 1216 °C. The COPs were from 5 to 30 nm in diameter and consisted of several concentric carbon layers surrounding a hollow core. The results of computational fluid dynamics calculations to determine the temperature and velocity profiles and mixing conditions of the species in the reactor are presented. The mechanisms for the formation of both CNTs and COPs are discussed on the basis of the experimental and computational results.     

Direct fluorination of poly(p-phenylene)

Because of its good chemical and thermal stability due to the π-delocalization along the polymer chain, poly(p-phenylene) was used as starting material for fluorination to obtain new carbon fluoride. A complete characterization of both the virgin polymer, in order to define parameters such as the chain length and the degree of crystallinity, and the fluorinated materials was performed by complementary techniques (¹⁹F, ¹H and ¹³C NMR, XRD, FT-IR and EPR). From these data, possible fluorination mechanisms are discussed. Finally, tribological properties have been also studied for the fluorinated samples and compared to those of conventional graphite fluorides.     

First X-ray structure of discrete anion [HgBr5]: Synthesis, characterization and single crystal X-ray structure determination of [Co(NH3)6][HgBr5]

A new cobalt(III) complex salt, [Co(NH₃)₆][HgBr₅](1) was crystallized from a solution of hexaamminecobalt(III)bromide and potassium tetrabromomercurate(II) in aqueous medium in 1:1 molar ratio. This complex salt has been characterized by elemental analyses, spectroscopic techniques (e.g. UV/Visible, IR), solubility product and conductance measurements. The complex salt crystallizes in Orthorhombic crystal system with space group Pnma. Single crystal X-ray structure determination revealed the presence of discrete ions: [Co(NH₃)₆]³⁺ cation and a new anion [HgBr₅]³⁻. This is the first structural report of a complex salt containing this new anion. The structure consists of stacks of cations and anions demonstrating supramolecular arrangements through N–HBr hydrogen-bond interactions. The crystal lattice is stabilized by these non-covalent interactions besides electrostatic interaction.     

Synthesis, structural characterization and third-order non-linear optical property of new three-dimensional metal-organic polymer [Fe2(μ10-btc)0.5(μ2-ox)0.5(μ2-O)1.5]n

One new metal-organic polymer formulated as [Fe₂(μ₁₀-btc)_0.5(μ₂-ox)_0.5(μ₂-O)_1.5]_n 1 (btc = 1,2,4,5-benzenetetracarboxylate, pyramellitate; ox = oxalate) has been synthesized by low-temperature solid-state reaction and characterized by single-crystal X-ray diffraction, elemental analyses, TGA, IR spectra and UV–visible spectra. Complex 1 presents the first 3D coordination network structure constructed by bridging btc, ox and O mixed ligands. In 1, carboxyl groups of btc are all deprotonated and they have a new type of μ₁₀-btc coordination mode. The third-order non-linear optical (NLO) properties of the title compound 1 were also investigated and they exhibit the reverse saturable absorption and self-defocusing performance with modulus of the hyperpolarizability (γ) 5.98 × 10⁻³⁰ esu for 1 in a 7.45 × 10⁻⁴ mol dm⁻³ DMF solution.     

Diplatinum(III) [Cl2(μ2-amidinate)4] compound derived from air oxidation of mononuclear cis-[Pt(NH3)2(amidine-κ)2] complex

The dinuclear platinum(III) complex [Pt₂Cl₂{μ₂-N(H)C(Et)N(H)}₄] (2) has been prepared by heating cis-[Pt(NH₃)₂{NHC(NH₂)Et}₂](Cl)₂ (cis-1) under aeration conditions in an EtOH/H₂O mixture at 70 °C for 2 d and it was characterized by elemental analyses (C, H, N), ESI⁺-MS, IR, ¹H and ¹³C NMR spectroscopies and also by X-ray diffraction. Complex 2 represents the second Pt^III dimer stabilized by the amidinate ligand ever known and it has a lantern-type structure with four amidinate ligands bridging two Pt^III centers with Pt–Pt distance of 2.4809(2) Å.     

Synthesis and structure of the tetradeca-iron(III) oxide–alkoxide cluster [Bu4N]2[Fe14O8(OCH2CH3)20Cl8]

The iron(III) oxide–alkoxide cluster, di-tetra-n-butylammonium octachloro-tetra(μ₃-oxo)-tetra(μ₄-oxo)- icosa(μ₂-ethoxo)-tetradeca-iron(III), has been isolated and its X-ray crystal structure determined.     

A novel (3,4,8)-connected 3D topology framework based on [Gd2(bpdc)3(H2O)3] second building units

A new 3D coordination polymer {[Gd₂(bpdc)₃(H₂O)₃]·H₂O}_n(1) has been isolated from the reaction of 2,2′-bipyridine-4,4′-dicarboxylic acid (H₂bpdc) and Gd(III) salts under hydrothermal conditions. Single-crystal X-ray diffraction study shows that compound 1 is constructed from Gd₂-based second building units (SBUs) [Gd₂(bpdc)₃(H₂O)₃] and displays a 3D (3,4,8)-connected net with (4²·6)(3²·4²·5²)(3²·4⁵·5⁴·6¹¹·7⁶) topology. A thermogravimetric analysis of 1 shows a high thermal stability. The magnetic behavior of 1 reveals a weak antiferromagnetic interaction between Gd(III) ions.     

Solid solution between Al-ettringite and Fe-ettringite (Ca6[Al1 − xFex(OH)6]2(SO4)3·26H2O)

The solid solution between Al- and Fe-ettringite Ca₆[Al_1 − xFe_x(OH)₆]₂(SO₄)₃·26H₂O was investigated. Ettringite phases were synthesized at different Al/(Al + Fe)-ratios (= X_Al,total), so that X_Al increased from 0.0 to 1.0 in 0.1 unit steps. After 8 months of equilibration, the solid phases were analyzed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the aqueous solutions were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analyses of the solid phases indicated the existence of a miscibility gap between X_Al,total = 0.3-0.6. Some of the XRD reflections showed two overlapping peaks at these molar ratios. The composition of the aqueous solutions, however, would have been in agreement with both, the existence of a miscibility gap or a continuous solid solution between Al- and Fe-ettringite, based on thermodynamic modeling, simulating the experimental conditions.     

Synthesis, crystal structure and magnetic properties of a new three-dimensional porous framework: [Gd2(BDA)3(DMF)2(H2O)4] · 2DMF

The open framework compound of [Gd₂(BDA)₃(DMF)₂(H₂O)₄] · 2DMF (1), prepared by heating GdCl₃ with 2,2′-bipyridyl-4,4′-dicarboxylatic acid (BDA) in mixed solvent, is constructed from BDA linking up polymeric [GdO₅(DMF)(H₂O)₂]_n tethers. The 1D channels are filled with coordinated and uncoordinated DMF molecules hydrogen bonding to terminal aqua ligands. The study of the temperature dependent magnetic susceptibilities revealed that there are ferromagnetic interactions between intra-chain Gd^III atoms and weak antiferromagnetic interactions between inter-chain Gd^III atoms.     

Ionic association equilibria in the dimethyl sulphoxide solutions of Mn(CF3COO)2, Co(CF3COO)2 and Ni(CF3COO)2

The molar conductivity curves have been determined for Mn(CFR₃COO)₂, Co(CF₃COO)₂ and Ni(CF₃COO)₂ in dimethyl sulphoxide at 25°C. The first step association constants are derived. Auxiliary measurements of the visible absorption spectra and the nmr chemical shifts of the solvent protons indicate lack of coordination¹ of the anion in the solutions of Ni(CF₃COO)₂. On the other hand, bidentate coordination of the anion, taking place to a small extent in addition to the outer-sphere association, is inferred for Co(CF₃COO)₂. On the assumption that the outer-sphere association constants are approximately the same for the three metal trifluoroacetates, the highest extent of the inner-sphere association is inferred for Mn(CF₃COO)₂.