Manganese(II) complexes with diethylamine in aqueous solutions

Interaction between MnCl₂ and diethylamine (DEA) in aqueous solutions has been studied by UV, IR, and EPR spectroscopy as part of the design and research program on models of natural photosystems. The composition of the precipitate for comparable concentrations of reagents and solute oxygen has been investigated. Mn(II) was found to be oxidized with oxygen to give MnO₂·H₂O as a precipitate. In the solution over the precipitate, Mn(III) complexes with DEA are formed; the complex molecule has four and six amine molecules in the coordination sphere.     

Structural relationships between dicopper diacetylide (Cu-C≡C-C≡C-Cu) and dicopper acetylide (Cu-C≡C-Cu)

Dicopper diacetylide Cu-C≡C-C≡C-Cu, prepared from butadiyne has been studied by FT-IR spectroscopy in comparison to dicopper acetylide Cu-C≡C-Cu. Upon ageing by exposure to air at room temperature, Cu-C≡C-Cu has been transformed into Cu-C≡C-C≡C-Cu as demonstrated by FT-IR spectroscopy and this compound is further transformed on standing in air. A special kind of solid state oxidative coupling reaction occurs so that polyynes chains are formed in these aged solids. It is shown that the FT-IR spectrum of copper acetylide prepared from ammonia solutions of Cu⁺ and Cu²⁺ ions is comparable to that of air oxidized Cu-C≡C-Cu (and Cu-C≡C-C≡C-Cu) prepared exclusively from Cu⁺ ions in presence of a reducing agent demonstrating that Cu²⁺ ions display the same oxidizing effect as oxygen causing coupling reactions in solution and producing Cu-C≡C-C≡C-Cu.Cu-C≡C-Cu oxidized at 60–70°C with CuCl₂ produces a product which could be formulated as Cu(C≡C)₂₀Cu; FT-IR absorption at 1950 cm⁻¹ could suggest the presence of cumulenic carbon chain although acetylenic carbon chains cannot be excluded completely.     

Radiation-cured polyisoprene/C60 fullerene nanocomposite. Part 1: Synthesis in hexane and in toluene

Fullerene C₆₀ can be grafted onto polyisoprene chains by γ irradiation in n-hexane or in toluene. The resulting polyisoprene/C₆₀ nanocomposites can be easily recovered from the solutions and have been characterized by electronic absorption and Fourier transform-infrared (FT-IR) spectroscopy. The electronic absorption spectroscopy clearly shows that C₆₀ undergoes addition reaction from the polyisoprene macroradicals formed by γ radiolysis. FT-IR spectroscopy supports the grafting reaction of polyisoprene on C₆₀ and additionally it shows that C₆₀ acts as a sensitizer for the partial cis–trans isomerization of the polyisoprene monomeric units. Relatively high levels of C₆₀ lead the polyisoprene-based nanocomposite to a crosslinked gel.The thermal behaviour of the polyisoprene/C₆₀ nanocomposites has been studied by the thermogravimetric analysis (TGA-DTG). It is shown that the radical adducts polyisoprene/C₆₀ are thermally reversible and regenerate free C₆₀ during the pyrolysis under N₂.     

Cross-linking of Polymer of Intrinsic Microporosity (PIM-1) via nitrene reaction and its effect on gas transport property

Polymer of Intrinsic Microporosity (i.e. PIM-1) has been crosslinked thermally via nitrene reaction using polyethylene glycol biazide (PEG-biazide) as a crosslinker. The crosslinking temperature was optimized using TGA coupled with FT-IR spectroscopy. The dense membranes containing different ratios of PIM-1 to PEG-biazide were cast from chloroform solution. Crosslinking of PIM-1 renders it insoluble even in excellent solvents for the uncrosslinked polymer. The resulting crosslinked membranes were characterized by FT-IR spectroscopy, TGA and gel content analysis. The influence of crosslinker content on the gas transport properties of PIM-1, its density and fractional free volume (FFV) were investigated. Compared to the pure PIM-1 membrane, the crosslinked PIM-1 membranes showed better gas separation performance especially for CO₂/N₂, CO₂/CH₄ and propylene/propane (C₃H₆/C₃H₈) gas pairs and as well as suppressed penetrant-induced plasticization under high CO₂ pressure.     

Polyynes and cyanopolyynes synthesis from the submerged electric arc: about the role played by the electrodes and solvents in polyynes formation

The products of the electric arc between graphite electrodes have been investigated by high performance liquid chromatography-diode-array detector (HPLC-DAD) analysis in various media: distilled water, liquid nitrogen, methanol, ethanol, n-hexane and benzene. In distilled water, hydrogen capped polyynes H-(CC)_n-H were the unique products demonstrating that carbon is supplied by the graphite electrodes while hydrogen is supplied by the solvent plasmalysis (in this case water plasmalysis). Arcing graphite electrodes in liquid nitrogen produces cyanopolyynes: NC-(CC)_n-CN demonstrating that in this case the end groups of the polyyne chains are supplied by molecular nitrogen plasmalysis caused by the electric arc. Graphite arcing in methanol and ethanol produces very clean solutions (by-products negligible or absent) of hydrogen-capped polyynes with C₈H₂ as the main product accounting for more than 70 mol percent of the total polyyne concentration. By replacing graphite electrodes with titanium electrodes in methanol or in ethanol, polyynes are not formed at all; only trace amounts of polycyclic aromatic hydrocarbons (PAHs) were detected. When arcing with graphite electrodes is conducted in n-hexane or in benzene, polyyne formation is accompanied by a significant production of PAH, especially in benzene. These results have been rationalized in terms of carbonization or coking tendency of a given solvent. The effect of using titanium electrodes in place of graphite electrodes has been investigated also in n-hexane and in benzene as well as the effects of very high electric current intensity employed to ignite and sustain the submerged electric arc.     

Chemical processes on active carbon surface: A new example of nitrogen fixation

The behavior of activated carbon fibers (ACF) and activated carbon (AC) in water and aqueous solutions of H₂O₂, NaOH, NaCN and KI₃ in the presence of atmospheric air is studied by physicochemical methods: X-ray photoelectron spectroscopy (XPS), ESR, and attenuated total reflectance IR (ATR-IR) and Fourier Transform IR (FT-IR) spectroscopy. The superoxide radical anion O ₂ ^?· is shown to exist on the ACF surface in aqueous solutions, whose formation is explained by reaction of molecular oxygen with radical active centers of surface defects. It is found that in aqueous solutions of inorganic compounds, both possessing (H₂O₂, KI₃) and not possessing (NaOH, NaCN) pronounced oxidative properties, the ACF surface is oxidized more rapidly than on aging in air. Evidence for fixation of atmospheric nitrogen on contact of ACF and AC with H₂O or aqueous solutions of NaOH, NaCN, and KI₃ is obtained. Possible conjugate redox reactions resulting in fixation of N₂ molecules and oxidation of the surface of carbon materials are discussed.     

γ Radiolysis of C60 fullerene in water and water/ammonia mixtures: relevance of fullerene fate in ices of interstellar medium

The γ radiolysis of fullerene C₆₀ dispersed in H₂O, H₂O/NH₃, H₂O/methanol and H₂O/NH₃/methanol was studied at 250 and 500 kGy. It was found that C₆₀ originally insoluble in the above mentioned hosting matrix became soluble as a consequence of multiple hydroxylation and oxidation reaction produced by the free radicals generated by the radiolysis of the hosting matrix. The changes undergone by C₆₀ were studied by infrared spectroscopy (FT-IR) and by electronic absorption spectroscopy. The astrochemical consequences of the present study are that C₆₀ ejected in the interstellar medium for instance from protoplanetary and planetary nebulae can condense together with water and other ices in dense molecular clouds. Under the action of high energy radiation C₆₀ reacts with the free radicals generated from the matrix where it is embedded it is solubilized and consequently its carbon content becomes available for further abiotic processes of synthesis of molecules of astrobiological interest. The behavior of C₆₀ appears comparable to that of common PAHs which are also hydroxylated and oxidized under similar conditions.     

Tunable Diode Laser Diagnostic Studies of H2-Ar-O2 Microwave Plasmas Containing Methane or Methanol

Tunable infrared diode laser absorption spectroscopy has been used to detect the methyl radical and ten stable molecules in H₂-Ar-O₂ microwave plasmas containing up to 7.2% of methane or methanol, under both flowing and static conditions. The degree of dissociation of the hydrocarbons varied between 30 and 90% and the methyl radical concentration was found to be in the range 10 ¹⁰ –10 ¹² molecules cm ^–3 . The methyl radical concentration and the concentrations of the stable C-2 hydrocarbons C ₂ H ₂ , C ₂ H ₄ , and C ₂ H ₆ , produced in the plasma decayed exponentially when increasing amounts of O ₂ were added at fixed methane or methanol partial pressures. In addition to detecting the hydrocarbon species, the major products CO, CO ₂ , and H ₂ O were also monitored. For the first time, formaldehyde, formic acid, and methane were detected in methanol microwave plasmas, formaldehyde was detected in methane microwave plasmas. Chemical modeling with 57 reactions was used to successfully predict the concentrations in methane plasmas in the absence of oxygen and the trends for the major chemical product species as oxygen was added.     

Atmospheric pressure chemical vapour deposition of selenium and tellurium films by UV laser photolysis of diethyl selenium and diethyl tellurium

Excimer laser‐induced photolysis of gaseous diethyl selenium and diethyl tellurium (C₂H₅)₂M (M = Se, Te) is controlled by cleavage of both M? C bonds, it yields C₁–C₄ hydrocarbons (ethene as major product) and results in chemical vapour deposition of selenium films and nanosized tellurium powder. The selenium and tellurium properties were characterized by X‐ray photoelectron spectroscopy and Scanning electron Microscopy techniques. Copyright © 2001 John Wiley & Sons, Ltd.     

Combined Reforming and Partial Oxidation of CO<Subscript>2</Subscript>-Containing Natural Gas Using an AC Multistage Gliding Arc Discharge System: Effect of Stage Number of Plasma Reactors

The effect of stage number of multistage AC gliding arc discharge reactors on the process performance of the combined reforming and partial oxidation of simulated CO₂-containing natural gas having a CH₄:C₂H₆:C₃H₈:CO₂ molar ratio of 70:5:5:20 was investigated. For the experiments with partial oxidation, either pure oxygen or air was used as the oxygen source with a fixed hydrocarbon-to-oxygen molar ratio of 2/1. Without partial oxidation at a constant feed flow rate, all conversions of hydrocarbons, except CO₂, greatly increased with increasing number of stages from 1 to 3; but beyond 3 stages, the reactant conversions remained almost unchanged. However, for a constant residence time, only C₃H₈ conversion gradually increased, whereas the conversions of the other reactants remained almost unchanged. The addition of oxygen was found to significantly enhance the process performance of natural gas reforming. The utilization of air as an oxygen source showed a superior process performance to pure oxygen in terms of reactant conversion and desired product selectivity. The optimum energy consumption of 12.05 × 10²⁴ eV per mole of reactants converted and 9.65 × 10²⁴ eV per mole of hydrogen produced was obtained using air as an oxygen source and 3 stages of plasma reactors at a constant residence time of 4.38 s.     

Selective CO2-to-C2H4 Photoconversion Enabled by Oxygen-Mediated Triatomic Sites in Partially Oxidized Bimetallic Sulfide

Selective CO₂ photoreduction into C₂ fuels under mild conditions suffers from low product yield and poor selectivity owing to the kinetic challenge of C−C coupling. Here, triatomic sites are introduced into bimetallic sulfide to promote C−C coupling for selectively forming C₂ products. As an example, FeCoS₂ atomic layers with different oxidation degrees are first synthesized, demonstrated by X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy spectra. Both experiment and theoretical calculation verify more charges aggregate around the introduced oxygen atom, which enables the original Co−Fe dual sites to turn into Co−O−Fe triatomic sites, thus promoting C−C coupling of double *COOH intermediates. Accordingly, the mildly oxidized FeCoS₂ atomic layers exhibit C₂H₄ formation rate of 20.1 μmol g⁻¹ h⁻¹, with the product selectivity and electron selectivity of 82.9 % and 96.7 %, outperforming most previously reported photocatalysts under similar conditions.     

Quantum-chemical study of the effect of oxygen on the formation of active sites of silver clusters during the selective adsorption of hydrocarbons

Density functional theory (PBE with a modified Dirac-Coulomb-Breit Hamiltonian) is used to simulate the adsorption of hydrocarbons (C₂H₂, C₂H₄, C₂H₆) on the surface of a sorbent containing Ag⁰, Ag^δ+, and AgO sites. The dynamics of change in the structural characteristics of Ag _n (n ≤ 10) is analyzed and the adsorption of oxygen on Ag₈ and Ag₁₀ is studied to select the adsorption site model. Studying the interaction of hydrocarbons with Ag₈, Ag₁₀, Ag ₁₀ ⁺ , Ag₁₀O, and Ag₁₀O₂ clusters reveals that the presence of oxygen leads to an increase in the activation of unsaturated hydrocarbons, and the adsorption energy of C₂H₂ increases tenfold. It is found that the role of adsorbed oxygen is not only to form adsorption sites of hydrocarbons (Ag^δ+) but also to bind C₂H₂ and C₂H₄ directly to the sorbent’s surface.     

Pure cubic ZrO2 nanoparticles by thermolysis of a new precursor

Zirconia (ZrO₂) nanoparticles have been synthesized through the thermolysis of bis-aqua, tris-2-hydroxyacetophenato zirconium (IV) nitrate, [Zr(HAP)₃(H₂O)₂](NO₃), as a precursor in oleylamine (C₁₈H₃₇N) and triphenylphosphine (C₁₈H₁₅P). The combination of C₁₈H₃₇N and C₁₈H₁₅P was added to act as surfactants to control the particle size. C₁₈H₃₇N and C₁₈H₁₅P play an important role in preventing aggregation of ZrO₂ nanoparticles. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and Fourier transform infrared (FT-IR) spectroscopy to depict the phase and morphology. The synthesized ZrO₂ nanoparticles have a cubic structure. The FT-IR spectrum showed the purity of obtained cubic phase ZrO₂ nanocrystals.     

The first bis(orotato–N,O) complex: Synthesis,crystal structure,spectroscopic and thermal characterization of (chaH)2[Cu(HOr–N,O)2(cha)] · 2H2O (cha = cyclohexylamine and HOr = orotate(2−))

The novel bis(cyclohexylaminium) cyclohexylaminebis(orotate–N,O)cuprate(II) dihydrate, (C₆H₁₅N)₂[Cu(C₅H₂N₂O₄)₂(C₆H₁₄N)] · 2H₂O, has been prepared and characterized by elemental analysis, magnetic measurements, FT-IR and UV–Vis spectroscopy, thermal analysis and X-ray diffraction. The Cu(II) complex crystallizes in the monoclinic space group P2₁/c. The copper atom in the five-coordinated (chaH)₂[Cu(HOr–N,O)₂(cha)] · 2H₂O is chelated by a deprotonated pyrimidine nitrogen atom and carboxylate oxygen atom as a bis(bidentate) ligand and the cyclohexylamine ligand completes the square-pyramidal coordination. The thermal decomposition of the complex has been predicted by the help of thermal analysis (TG, DTG and DTA).     

Photocatalytic Reduction of NO with C2H6 on a Hollandite-Type Catalyst

The photocatalytic reduction of nitrogen monoxide (NO) with ethane on the hollandite type catalyst (K₂Ga₂Sn₆O₁₆KGSO) was investigated. Using a closed-gas circulating system equipped with a Q-MASS detector and in-situ diffuse reflectance FT-IR spectroscopy. The reactant gases of NO and ¹³C₂H₆ decreased with the increasing irradiation time. In contrast, the N₂ yield increased proportionally to the conversion of ¹³C₂H₆. Nitrogen oxides such as N₂O did not reach their detectable levels. The NO adsorbed on KGSO was found to change to its activated species by UV irradiation. The oxidized products of C₂H₆ such as CH₃CHO increased in proportion to the reaction time. The present results strongly suggest that KGSO has remarkable photocatalytic activity for the reduction of NO with C₂H₆.     

Kinetics and modeling of the thermal reaction of propene at 800 K. Part iii. Propene in the presence of small amounts of oxygen

The thermal reaction of propene was examined around 800 K in the presence of less than 20% oxygen. At initial time, the production of H₂, CH₄, C₂H₄, C₂H₆, allene, C₃H₈, 1,3-butadiene, butenes, 3- and 4-methylcyclopentene, a mixture of 1,4- and 1,5-hexadienes, methylcyclopentane (or dimethylcyclobutane), 4-methylpent-1-ene, and hex-1-ene, was observed along with hydrogen peroxide, CO, and small quantities of ethanal and CO₂. Oxygen increases the initial production of hydrogen and of most hydrocarbons and, particularly, that of C₆ dienes and of cyclenes. However, the production of allene, methylcyclopentane (or dimethylcyclobutane), and 4-methylpent-1-ene is practically not affected. A kinetic study confirms the mechanism proposed for the thermal reaction of propene. Formation of allene, thus, involves a four-center-unimolecular dehydrogenation of propene, that of 4-methylpent-1-ene is explained by an ene bimolecular reaction while methylcyclopentane (or dimethylcyclobutane) probably arises from a bimolecular process involving a biradical intermediate. Other products arise from a conventional chain radical mechanism. A kinetic scheme is proposed in which chains are primarily initiated by the bimolecular step: C₃H₆+O₂→HO₂·+C₃H₅· which competes with the second-order initiation of propene pyrolysis. Since allene production is not affected by oxygen, it is concluded that allyl radicals are not dehydrogenated by oxygen; but they oxidize in a branching step involving allylperoxyl radicals; r. radicals other than methyl, and allyl are dehydrogenated according to the conventional process: r·+O₂→unsaturated+HO₂· and account for the production of a large excess of C₆ diolefins, methylcyclopentenes, and hydrogen peroxide, when r. stands for C₆H₁₁, the allyl adduct. Hydrogen peroxide gives rise to a degenerate branching of chains. Based on the proposed scheme, a modeling of the reaction is shown to account fairly well for the concentration-time profiles. Rate constants of many steps are evaluated and discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 503–522, 1998     

Hexamethylenetetrammonium dodecahydro-<Emphasis Type="Italic">closo</Emphasis>-dodecaborate: Synthesis and study

The reaction of dodecahydro-closo-dodecaboric acid with hexamethylenetetramine (urotropin) was studied by potentiometric titration, chemical and X-ray diffraction analyses, thermogravimetry, and IR and X-ray photoelectron spectroscopy. The donor-acceptor bond with acid H⁺ cations involves only one of the nitrogen donor atoms of hexamethylenetetramine. The product (C₆H₁₂N₄H)₂B₁₂H₁₂ is isolated as a finely crystalline, easily filterable, and poorly soluble precipitate. A saturated solution of the product contains no more than 0.4 g of the salt per 100 g.     

Synthesis,Structure and High Thermal Stability of a Novel Three‐dimensional Zinc(II) Complex with an Unsymmetrical Rigid‐flexible Ligand

A novel metal‐organic framework, [Zn(C₁₀H₈O₅)]_n ( 1 ) (C₁₀H₈O₅ = 2‐(4‐carboxylatophenoxy)propionate), was synthesized and characterized by elemental analysis, IR spectroscopy, X‐ray crystallography and thermogravimetric analysis. The crystal structure study reveals that each zinc atom is coordinated by four oxygen atoms from four different ligands to obtain a distorted tetrahedron. The rigid carboxyl group bridges two adjacent zinc atoms to form a dimer of eight‐membered rings, whereas the flexible carboxyl group bridges two adjacent dimers to form 1D chains along the a axis. Two adjacent 1D chains are interconnected by the ligands to produce 2D layers. These layers are further stabilized by intermolecular hydrogen bonds to construct a 3D framework showing high thermal stability (445 °C).     

Solution ozonolysis of C<Subscript>70</Subscript>: stable products and chemiluminescence

For the first time the total and relative contents of the stable ozonolysis products of fullerene C₇₀ solutions were identified by IR spectroscopy and elemental and chemical analyses. At the 100% conversion of C₇₀ a mixture of products corresponding to the empirical formula C₇₀O_14.3H_0.21 (epoxides: polyketones: polyesters: secondary fullerene ozonides (SFOZ): acids = 1.07: 6: 6: 0.21: 1.02) is formed. The content of polyketones, polyesters, acids, and SFOZ increases during the whole ozonolysis time (1 h). The number of oxygen atoms in epoxides C₇₀O _n (n = 1–4) is lower than that in epoxides C₆₀O _n (n = 1–6) formed by the ozonolysis of fullerene C₆₀. The kinetic curve of accumulation of epoxides C₇₀O _n (n = 1–4) passes through a maximum, which is observed 0.5 min after the beginning of ozonolysis. No epoxides were identified among the products 3.5 min after the ozonolysis. The photoluminescence (PL) (λ_max = 645 and 685 nm) of fullerene polyketones in glassy EtO₂/EtOH solutions frozen at 77 K was observed. This PL is much brighter, than that of polyketones formed upon the ozonolysis of fullerenes C₆₀. For the first time the chemiluminescence (CL) was detected and studied upon the ozonolysis of C₇₀ solutions at 300 K. The CL emitters are excited states of fullerene polyketones. The CL spectrum is partially overlapped with the known CL spectrum appeared upon the ozonolysis of C₆₀ (λ_max = 685 nm) but contains the greater number of maxima (λ_max = 645 and 685 nm), which is related to a lower symmetry of the C₇₀ oxidation products.     

Synthesis and Characterization of Single-Phase Cubic ZrO2 Spherical Nanocrystals by Decomposition Route

A simple thermal decomposition route has been developed to prepare single-phase cubic ZrO₂ nanospheres by [Zr(sal)₃(H₂O)₂](NO₃) as the new precursor. The ZrO₂ nanocrystals have been prepared by bis-aqua, tris-salicylaldehydato zirconium(IV) nitrate; [Zr(sal)₃(H₂O)₂](NO₃), as precursor in oleylamine (C₁₈H₃₇N) and triphenylphosphine (C₁₈H₁₅P). To control the particle size, combination of C₁₈H₃₇N and C₁₈H₁₅P were applied as surfactants. The C₁₈H₃₇N and C₁₈H₁₅P play an important role in preventing aggregation of ZrO₂ nanocrystals. The products were characterized by X-ray diffraction, transmission electron microscopy, photoluminescence spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy to depict the phase and morphology. The FT-IR spectrum showed the purity of obtained ZrO₂ nanocrystals with cubic phase.