Electrical conductivity of polyblends of poly(1,4-phenylene vinylene) and poly(2,5-dimethoxy-1,4-phenylene vinylene)

Summary A series of polyblends of poly(1,4-phenylene vinylene), PPV, and poly(2,5-dimethoxy-1,4-phenylene vinylene), PDMPV, were prepared in film form from precursor polyblends of the respective sulfonium salt polymers, which were separately prepared from the respectivebis(sulfonium salt) monomers. The blend films were doped with I₂ at room temperature to obtain a wide range of electrical conductivities (10^–2 to 10²Scm^–1) depending on the blend composition. The higher the content of PDMPV in the blends the higher was the conductivity.     

Synthesis of fluorocyclohexadienes by the electrochemical fluorination of p-difluorobenzenes on a preparative scale

Fluorine containing-cyclohexadienes (FCHDs), 3,3,6,6,-tetrafluoro-1,4-cyclohexadiene (1a), 1-chloro-3,3,6,6-tetrafluoro-1,4-cyclohexadiene (3a) and 1-bromo-3,3,6,6-tetrafluoro-1,4-cyclohexadiene (4a), were isolated in pure states with high yields (ca. 80%) by the preparative scale electrochemical fluorination of 1,4-difluorobenzene (1), 1-chloro-2,5-difluorobenzene (3) and 1-bromo-2,5-difluorobenzene (4), respectively, in Et₄NF · mHF (Et = C₂H₅: m = 4.0, 4.45 and 4.7) at a platinum anode, followed by extraction and fractional distillation. The electrochemical fluorination of 1,2,4-trifluorobenzene (2) yielded both 1,3,3,6,6-pentafluoro-1,4-cyclohexadiene (2a) and 2,5,5,6,6-pentafluoro-1,3-cyclohexadiene (2b) with high yield (ca. 90%). Some of (2a) was also isolated in a pure state by fractional distillation. Each substrate compound (1–4) was fluorinated to the corresponding FCHDs with an almost quantitative yield when 2.0–2.1 faraday (per mol of substrate) of electricity was passed.     

Lithium secondary cells using LiX (X=ClO4, BF4) as electrolyte and poly(2,5-pyrrolylene) and poly(2,5-thienylene) as materials for positive electrodes

Repeated charge-discharge cycles of lithium secondary cells using poly(2,5-pyrrolylene) and poly(2,5-thienylene) on carbon fibre plates as the materials for positive electrodes have been tested. When the Li|LiBF₄|poly(2,5-pyrrolylene) secondary cell is charged and discharged at 0.1 mA cm^–2, it gives 91% current efficiency and 70% energy efficiency with an average discharging voltage of 2.75 V at the 9th charge-discharge cycle. This secondary cell has a theoretical energy density of 135 kW kg^–1 based on the energy stored and the weights of poly(2,5-pyrrolylene) and the active materials. The Li|LiClO₄|poly(2,5-thienylene) secondary cells show somewhat lower current efficiency and energy efficiency at the 9th charge-discharge cycle. The lithium cells using the polymers are rechargeable more than 50 times, but after about 50 cycles considerable lowering of the current efficiency and energy efficiency of the cells is observed, presumably due to degradation of the polymer.     

Catalysis of the oxidation of 1,4-cyclohexadiene to benzene by electroactve binuclear rhodium complexes

Electrochemical oxidation of Rh₂(TMB) ₄ ²⁺ (TMB = 2,5-diisocyano-2,5-dimethylhexane) in the presence of 1,4-cyclohexadiene produces benzene and two protons. It is probable that a key step in the reaction is hydrogen-atom transfer from 1,4-cyclohexadiene to electrochemically generated Rh₂(TMB) ₄ ³⁺ . The H-atom abstraction apparently is facilitated by the presence of a d* hole in the Rh ₂ ³⁺ ₂ complex.     

Surface alteration of (VO)2P2O7 by α-Sb2O4 as a route to control the n-butane selective oxidation

The catalytic properties of (VO)₂P₂O₇/α-Sb₂O₄ mixed oxides system for n-butane mild oxidation have been investigated on two mechanical mixtures (M1 and M2) of the same well crystallized (VO)₂P₂O₇ (reference vanadyl pyrophosphate) with two different morphologies of α-Sb₂O₄.The M1 mixture of (VO)₂P₂O₇ with α-Sb₂O₄ (1), prepared by oxidation of Sb₂O₃, leads to the oxidative dehydrogenation (ODH) of n-butane, whereas the M2 mixture of (VO)₂P₂O₇ with a commercial α-Sb₂O₄ (2) (Aldrich) with a different morphology improves the maleic anhydride selectivity as compared to the reference (VO)₂P₂O₇ catalyst (synergetic effect). After reaction, no ternary VPSbO phase is detected by XRD and DTA and it was controlled that the two α-Sb₂O₄ oxides are catalytically inactive.The (VO)₂P₂O₇ reference catalyst which produced only maleic anhydride as mild oxidation product shows by XPS a slightly oxidized surface (14% V⁵⁺–86% V⁴⁺).Contamination of the (VO)₂P₂O₇ phase by migration of Sb species occurs after catalytic reaction in the case of the M1 mixture as shown by XPS, LEIS and TEM–EDX analysis. XPS showed that (VO)₂P₂O₇ is partially superficially reduced (86% V⁴⁺–14% V³⁺). This feature is consistent with the decrease of acidity as observed by pyridine adsorption–desorption.In opposition with the M1 mixture, no contamination of the (VO)₂P₂O₇ phase is observed after catalytic reaction in the case of the M2 mixture. The XPS study shows, in this case, that (VO)₂P₂O₇ is partially oxidized (30% V⁵⁺–70% V⁴⁺) at a higher level than for the reference (VO)₂P₂O₇ catalyst. This situation is associated with the increase of selectivity observed for maleic anhydride (synergetic effect).The difference in the catalytic results for the two M1 and M2 mixtures, as compared to the (VO)₂P₂O₇ reference catalyst, can be explained by the alteration of the surface composition of (VO)₂P₂O₇ and the distribution of vanadium oxidation state due to different interaction between Sb₂O₄and (VO)₂P₂O₇, depending on the orientation of the α-Sb₂O₄ crystals.     

A new approach for synthesis of electroactive phenol based polymer: 4-(2,5-Di(thiophen-2-yl)-1H-pyrrol-1-yl)phenol and its oxidative polymer

In this study, the 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)phenol (4-DTPP) was synthesized by the reaction of 1,4-di(2-thienyl)-1,4-butanedione and 4-aminophenol. This monomer was electrochemically polymerized in the presence of LiClO₄ as the supporting electrolyte in acetonitrile (AN). The copolymerization were achieved in the presence of thiophene (Th) with 3,4-ethylenedioxythiophene (EDOT) in 0.1 M LiClO₄/AN electrolyte-solvent couple. The polymer of 4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)phenol was synthesized by oxidative polycondensation reaction in an aqueous alkaline medium using NaOCl (30%) as oxidant. The structures of compounds were confirmed by FT-IR, UV–vis, and ¹H-NMR techniques. The characterizations of compounds were made by TG–DTA, DSC, gel permeation chromatography (GPC) and solubility tests. Electrical conductivities of the synthesized monomer and polymer were measured by four-point probe technique using a Keithley 2400 electrometer. Fluorescence measurements were carried out in various solvents.     

Solvothermal synthesis of 1D and 2D cobalt(II) and nickel(II) coordination polymers with 2,5-dihydroxy-p-benzenediacetic acid

1D cobalt(II) and nickel(II) coordination polymers {[Co(dba)(H₂O)₄] · H₂O}_n (1) and {[Ni(dba)(H₂O)₄] · H₂O}_n (2) (H₂dba = 2,5-dihydroxy-p-benzenediacetic acid) were synthesized under low temperature solvothermal condition. When 4,4′-bipyridine (bpy) was introduced to the synthetic systems of 1 and 2, respectively, two novel 2D coordination polymers {[Co(dba)(bpy)] · 0.5H₂O}_n (3) and [Ni(dba)(bpy)(H₂O)₂]_n (4) with different structures were obtained. All of the compounds were characterized by elemental analysis, FT-IR, UV–Vis spectra and single crystal X-ray diffraction.     

Synthesis and electrical properties of poly[2-(2-(4-trifluoromethyl)phenyl)ethenyl-1,4-phenylenevinylene] and PPV copolymers

Summary Poly[2-(2-(4-(trifluoromethyl)phenyl)ethenyl)-5-methoxy-1,4-phenylenevinylene] (PFEMPV) and a series of PPV copolymers containing 1,4-phenylenevinylene (PV) units were synthesized through a water-soluble precursor route, and their electrical and third-order nonlinear optical properties were studied. The PFEMPV films could not be doped with I₂, but FeCl₃-doped films showed an electrical conductivity of 5.0x10^-4 S/cm. The conductivities of FeCl₃-doped copolymer films ranged from 2.0x10^-3 to 2.0 S/cm depending on their copolymer compositions. The third-order nonlinear optical susceptibility, ⁽³⁾(–;,,–), was also investigated by the degenerate four wave mixing technique at 602 nm. The ⁽³⁾ value of PFEMPV was 6.9x10^-11 esu. The photoluminescence spectrum of PFEMPV shows its emission maximum at 550 nm.     

面包酵母No.6催化不对称合成(2S,5S)-2,5-已二醇反应特性

Baker’s yeast number 6 was selected by screening. It showed good catalytic activity and enantioselectivity for asymmetric reduction of 2,5-hexanedione to produce (2S,5S)-2,5-hexanediol. Gas chromatography-mass spectrometry (GC-MS) revealed that the intermediate was (S)-5-hydroxyhexane-2-one. Reduction of 2,5-hexanedione proceeded in a two-step reaction. The hydroxyketone was initially formed, and this intermediate was further re-duced to the diol. Factors influencing the product yield and the enantiomeric excess of the reduction of 2,5-hexandione catalyzed by baker’s yeast number 6 were investigated. Higher concentration (≤100 mmol•L－1) of 2,5-hexandione did not influence 5-hydroxyhexane-2-one production, but 2,5-hexanediol production was inhibited by excess accumulation (＞30 mmol•L－1) of intermediate. The optimal conditions were glucose as the co-substrate at an initial glucose concentration of 20 g•L－1, 34C, pH 7.0 and cell concentration 60 g•L－1 (cell dry mass). Under the optimal condition and an initial substrate concentration of 30 mmol•L－1, the yield of 2,5-hexandiol was 78.7% and the enantiomeric excess of (2S,5S)-2,5-hexandiol was 94.4% for 24-h reduction.     

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.     

Synthesis and electrical conductivity of AsF5-doped poly(arylene vinylenes)

Summary A series of polymers containing 2,5-disubstituted phenylene vinylene units, and the polymer containing 1,4-naphthalene vinylene units, were prepared by polymerization of their bis(sulfonium salts) through a base elimination reaction in solution. Films of these polymers were cast from aqueous solution and chemically treated (doped) with AsF₅ vapor. The electrically conductivities of the doped films varied greatly with changes in polymer structure, with the highest value obtained of 1.8 ohm^–1 cm^–1 for poly (2,5-dimethoxyphenylene vinylene).     

The oxidative coupling of methane and the activation of molecular O2 on CeO2/BaF2

CeO₂/BaF₂ was used as the catalyst for the oxidative coupling of methane (OCM). At 800°C and CH₄O₂=2.71,CH₄ conversion of 34% with C₂ hydrocarbon selectivity of 54.3% was obtained. XRD measurement showed that partial anion (O^2–,F^–) and/or cation (Ce⁴⁺,Ba²⁺) exchange between CeO₂ and BaF₂ lattices occurred. ESR study showed that O^– species existed on degassed catalyst. XPS study revealed that, when BaF₂ was added to CeO₂, the binding energy of Be 3d_5/2 was 2.2 eV lower than that in CeO₂, and the electron-enriched lattice oxygen species was detected. XPS, ESR and Raman study showed that, under O₂ adsorbing conditions, O ₂ ^2– and O _– ² species were detected on CeO₂/BaF₂.This work was supported by the State Key Laboratory for Physical Chemistry of the solid surface and the National Science Foundation of China.     

The electrochemical reduction of CO2 to CH4 and C2H4 at Cu/Nafion electrodes (solid polymer electrolyte structures)

The construction of copper/Nafion electrodes (solid polymer electrolyte structures) by an electroless plating method is described. These electrodes were used for the gas phase electrochemical reduction of CO₂ to hydrocarbon products, including CH₄ and C₂H₄. The faradaic efficiencies of the electrodes under ambient conditions with a counter solution of 1 mM H₂SO₄ at a potential of –2.00 V vs. SCE reached a steady-state value of about 20% after 30 min of electrolysis. This corresponded to a rate of total hydrocarbon production of approximately 9.8×10^–7 mole h^–1 cm^–2. Increasing the potential of the electrode to more negative potentials, or increasing the proton concentration of the counter solution, caused a decrease in the faradaic efficiencies due to a relative increase in the rate of proton reduction vs. that of CO₂ reduction. If the proton concentration of the counter solution was decreased to an alkaline pH, hydrocarbon production quickly ceased because of proton starvation.     

Redox chemistry of H2S oxidation by the British Gas Stretford process part IV: V-S-H2O thermodynamics and aqueous vanadium (v) reduction in alkaline solutions

The thermodynamics of V-H₂O and V-S-H₂O systems at 298 K are summarized in the form of potential-pH and activity-pH diagrams calculated from recently published critically assessed standard Gibbs energies of formation. At pH 9, as used in Stretford Processes, V-H₂O potential-pH diagrams predicted that the V(v)/V(iv) couple involves HV₂O₇ ^3–/V₄O₉ ^2– ions. However, in neutral and alkaline solutions there is difficulty in discriminating between kinetic intermediates and thermodynamically stable solution species, some with V(v)/V(iv) mixed oxidation states. Hence, V₁₈O₄₂ ^12– ions may be the stable V(iv) species, depending on the concentration, though no thermodynamic data are available to enable them to be included in potential-pH calculations. Potential-pH diagrams for V-S-H₂O systems predicted an area of stability for VS₄ in the pH range 2–8 and over a restricted potential range; neither VS nor VS₂ were predicted to be stable under any conditions considered. In cyclic voltammetric experiments at Hg, Au and vitreous carbon electrodes, reduction of vanadium (v) species (probably HV₂O₇ ^3– ions) was found to be irreversible on a variety of electrode surfaces and, at lower potentials, led predominantly to the formation of solid oxide films (V₃O₅, V₂O₃ and VO) rather than to V(iv) solution species, of which V₁₈O₄₂ ^12– ions probably predominate at equilibrium. In the presence of the large excess of HS^– ions required to form VS₄ ^3– ions, the electrochemical behaviour of a gold electrode was dominated by the former species.     

Electrochemical reduction of Pt(CN) 4 2− ions in molten sodium-potassium cyanide eutectic

The reduction of Pt(CN) ₄ ^2– ions was studied in a NaCN-KCN eutectic melt by means of chronopotentiometry and cyclic voltammetry over the temperature range 510–580° C. The reduction to Pt(CN) ₄ ^4– was shown to be a reversible process. The density of the NaCN-KCN eutectic melt was determined as a function of temperature.     

Konfigurative Zuordnung über sterisch definierte Epoxidringe. VIII. Glycidonitrile. I. Synthese von 4-Aryl-1-oxaspiro(2,5)octan-2-nitrilen und 4-Aryl-1-oxaspiro(2,5)octan-2-carbonsäureestern

Determination of Configurations by the Aid of Sterically Corresponding Epoxides. VIII. Glycidic Nitriles. I. Synthesis of 4-Aryl-1-oxaspiro(2,5)octane-2-nitriles and 4-Aryl-1-oxaspiro(2,5)octane-2-carboxylic Acid Methyl Esters The condensation of 2-aryl-cyclohexan-1-ones ( 1–5 ) with ClCH₂CN or ClCH₂CO₂CH₃ at 80°C in the presence of NaH and in dimethoxyethane yields the corresponding glycidic nitriles and the glycidic esters, respectively. The configuration and the preferred conformation of the two isomeric 1-oxaspiro-[2,5]octane derivatives ( 12 A and 12 B ) formed have been determined by ¹H-n.m.r. spectroscopy. Some earlier results from BOEKELHEIDE and SCHILLING and from SCHWARTZMAN and WOODS have been corrected.     

Formation of Ni(CO)4 during the Interaction between CO and Silica-Supported Nickel Catalyst: an FTIR Spectroscopic Study

The formation of Ni(CO)₄ during interaction of CO with silica-supported highly dispersed nickel metal (d _av4 nm) was investigated by FTIR spectroscopy. At temperatures below 145 K, in addition to linear and bridged nickel carbonyls, CO adsorption on Ni⁰/SiO₂ leads to the formation of Ni(CO) _x (x=2, 3) subcarbonyls (band at ca. 2090 cm^–1) and negligible amounts of Ni(CO)₄ adsorbed on SiO₂ (band at 2048 cm^–1). Up to this temperature CO causes no detectable erosion of the metal surface. Above 145 K the rate of interaction between CO and the nickel particles significantly increases. Until 235 K Ni(CO)₄ mainly remains in the adsorbed state, while at still higher temperatures the equilibrium between adsorbed and gaseous Ni(CO)₄ (band at 2058 cm^–1) is shifted towards the latter. It is assumed that subcarbonyls formed on defect sites of the metal surface are precursors of the nickel tetracarbonyl. Successive adsorption–evacuation cycles of CO at room temperature result in a decrease in the amount of the Ni(CO)₄ formed, probably due to a reduction of the number of defect metal sites. On the basis of ¹²CO and ¹³CO coadsorption, an alternative interpretation of the band at 2048 cm^–1 to species containing isolated Ni(CO)₃ groups is proposed.     

Synthesis and two-photon absorption properties of 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles

Two symmetrical 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on “push-core-pull-core-push” molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig–Horner reaction. Pumped by nanosecond laser at 800 nm, strong up-conversion emissions with the central wavelength at 507 nm (green) of 2,5-bis[4-(2-N,N-diphenylaminostyryl)phenyl]-1,3,4-oxadiazole and 475 nm (blue) of 2,5-bis[4-{2-(3-N-ethylcarbazolyl)vinyl}phenyl]-1,3,4-oxadiazole in the solution of CHCl₃ have been observed. Their two-photon absorption cross-sections obtained by nonlinear transmission method are 107 × 10⁻⁴⁸ cm⁴ s photon⁻¹ and 66 × 10⁻⁴⁸ cm⁴ s photon⁻¹. A very effective energy transfer from the excited terminal units to the π-conjugated bridging units of the 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles is the dominant contribution to the two-photon absorption.     

Bis(4′-phenyl-2,2′:6′,2″-terpyridine)ruthenium(II): Holding the {Ru(tpy)2} embraces at bay

The solid state structure of [Ru(Phtpy)₂][PF₆]₂ · 4MeCN has been determined (Phtpy = 4′-phenyl-2,2′:6′,2″-terpyridine); [Ru(Phtpy)₂]²⁺ cations pack into sheets by virtue of {M(tpy)₂}₂ embraces, and the MeCN solvent molecules are involved in NH–C interactions which prevent the efficient packing of adjacent sheets. Comparisons with related structures lead to some generalizations about packing motifs in salts containing [M(Phtpy)₂]²⁺ or [M(pytpy)₂]²⁺ cations (pytpy = 4′-pyridyl-2,2′:6′,2″-terpyridine).     

A manganese(III) complex that exhibits spin crossover behavior

A novel Mn^III(d⁴) complex, which exhibit spin crossover (SCO) phenomenon arising from the spin transition of LS ↔ HS state, was characterized structurally as well as magnetically. Single crystal X-ray diffraction methods structurally determined the compound as [Mn^III(OL1)₂]Cl · 3H₂O. Two facially coordinating tridentate ligands are bound to the manganese(III) ion, resulting in an MnN₄O₂ chromophore with an axially-compressed octahedral geometry. The nitrogen donors are all in the equatorial plane with Mn–N distances ranging from 2.14 to 2.19 Å, the two oxygen donors occupy the axial positions at 1.86 Å. Magnetic susceptibilities were measured between 77 and 300 K. At 77 K, the magnetic moment converges close to the expected low spin (LS) value of 2.8 μB, whereas at 300 K the high spin (HS) limit is entropically inaccessible, as this is a one-electron SCO.