Electrochemical investigation of uranium β-diketonates for all-uranium redox flow battery

The redox flow battery using uranium as the negative and the positive active materials in polar aprotic solvents was proposed. In order to establish the guiding principle for the uranium compounds as the active materials, the investigation of uranium β-diketonate complexes was conducted on (i) the solubility of active materials, (ii) the electrode reaction of U(VI) and U(IV) β-diketonate complexes and (iii) the estimation of the open circuit voltage of the battery. The solubilities of higher than 0.8 mol dm⁻³ of U(VI) complexes and higher than 0.4 mol dm⁻³ of a U(IV) complex were obtained in the solvents. The electrode reactions of U(pta)₄, UO₂(dpm)₂, UO₂(fod)₂ and UO₂(pta)₂ were first studied and the redox potentials of uranium β-diketonates were thermodynamically discussed. The open circuit voltage is estimated more than 1 V by using Hacac or Hdpm. The larger open circuit voltage is expected when a ligand with the larger basicity is used.     

Light-stimulated oxidation reactions of tris(1,10-phenanthroline), tris (2,2′-dipyridine) and bis(2,2′,2″-tripyridine)iron(II) complexes

The oxidation reactions of Fe(phen)²⁺₃, Fe(dipy)²⁺₂ were investigated electrochemically under the irradiation of visible light and in the dark. Two arrests in current were observed at 0.5 and 0.9 V (vs sce) in the anodic polarization curves of these complexes. The initial and the second arrests were ascribed to the oxidations of the aquo-ferrous ion and FeL²⁺_n, respectively. The oxidation of these complexes was stimulated by irradiation with light. It was concluded that d electrons were excited to antibonding ligand orbitals, on absorbing visible light and then the electrochemical oxidation of these complexes proceeded more favourably under the irradiation of light than in the dark.     

The Redox Chemistry of Manganese(III) and -(IV) Complexes

The oxidation-reduction thermodynamics for the manganese(III), -(IV), and -(II) ions, and their various complexes, are reviewed for both aqueous and aprotic media. In aqueous solutions the reduction potential for the manganese(III)/(II) couple has values that range from +1.51 V vs. NHE (hydrate at pH 0) to −0.95 V (glucarate complex at pH 13.5). The Mn(IV)/(III) couple has values that range from +1.0 V (solid Mn^IVO₃ at pH 0) to −0.04 V (tris gluconate complex at pH 13.5). With anhydrous media the propensity for the Mn(III) ion to disproportionate to solid Mn^IVO₂ and Mn(II) ion is avoided. For aprotic systems the range of redox potentials for various manganese complexes is from +2.01 V and +1.30 for the Mn(IV)/(III) and Mn(III)/(II) couples (bis terpyridyl tri-N-oxide complex in MeCN), respectively, to −0.96 V for the Mn(IV)/(III) couple (tris 3,5,-di-tert-butylcatecholate complex in Me₂SO). The redox reactions between manganese complexes and dioxygen species (O₂, O₂, and H₂O₂) also are reviewed.     

Pyridin‐, Quinolin‐ and Acridinylidene Palladium Carbene Complexes as Highly Efficient C–C Coupling Catalysts

A series of four new complexes bearing N‐heterocyclic carbene ligands (NHCs) as well as four compounds bearing N‐heterocyclic carbene ligands with remote heteroatoms (rNHCs) of the general types [(NHC)(PPh₃)₂PdCl]⁺BF₄⁻ and [(rNHC)(PPh₃)₂PdCl]⁺BF₄⁻, respectively, have been prepared in high yields. Crystal and molecular structures have been determined for four representative examples. These compounds proved to be efficient catalysts for aryl coupling reactions of the Heck and Suzuki types (reaching TONs of as high as 6,200,000). Both aryl bromides and aryl chlorides can be used as substrates. Like the well known mixed, standard (NHC)(phosphine) compounds, the new six‐numbered, one‐N‐heterocyclic carbene complexes (and in particular certain rNHC‐containing ones) also combine the advantageous stability of bis(carbene) and the high activity of bis(phosphine) complexes. Furthermore, their good catalytic performance and, especially, their easy synthesis based on cheap and commercially available starting materials, make them by far superior when compared to the mixed (NHC)(phosphine) catalysts known thus far.     

C–S bond cleavage in pyridylmethylthioether systems promoted by oxorhenium(V) ion

C–S bond cleavage in pyridylmethylthioether systems promoted by oxorhenium(V) ion has been established performing the reaction of 1,2-bis(2-pyridylmethylthio)ethane(BPT¹), 1,3-bis(2-pyridyl-methylthio)propane(BPT²) and 3,4-bis(2-pyridylmethylthio)-5-methyltoluene (BPT³) with Bu₄N[ReOCl₄] in dry alcoholoic medium. In case of BPT¹ and BPT², new 2-(2-pyridylmethylthio)ethane-1-thiol (L¹H) and 3-(2-pyridylmethylthio)propane-1-thiol (L²H) ligand, respectively were formed in situ through cleavage of one C–S(thioether) bond, resulting in the neutral oxorhenium(V) complexes of formulation [ReO(L¹)Cl₂] (1a) and [ReO(L²)Cl₂] (1b); where as in case of BPT³, binary oxorhenium(V) complex of 3,4-dimercapto-toluene ligand (L³H₂), formulated as Bu₄N[ReO(L³)₂] (1c) through cleavage of two C–S(thioether) bonds. The presence of picolinic acid, as by-product in the filtrates of the C–S bond cleavage reactions in dry alcohol, was detected by treatment of copper(II) salts and GC–MS techniques. But in hydrated alcoholic medium no C–S bond cleavage induced by ReO(V) ion occurred in any of the BPT systems rather the conversion of ReO(V) into perrhenate salt was observed; this reaction mixture, in turn on reaction with copper(II) nitrate trihydrate salt, produce [Cu(BPT)Cl]ReO₄ (2) type complexes. The solid-state structures of complexes 1a and 2a were established by X-ray crystallography.     

Deposition of thin TiO2 layers on platinum by means of cyclic voltammetry of selected complex Ti(IV) media leading to anatase

Thin layers of anatase TiO₂, up to 1 μm, were produced on the surface of a platinum electrode by means of cycling voltammetry from the aqueous solutions of the peroxo-oxalate complexes and the oxalate complexes of titanium(IV). Mechanisms of TiO₂ electrodeposition as well as different electrochemical reactions causing pH changes at the electrode were studied. The electroreduction processes of hydrogen peroxide and nitrite ion on platinum cause the highest pH changes. Values of the molar ratio of Ti(IV)/H₂O₂ should be kept closely to 0.5.In all cases studied, the electrodeposition led to the partially decomposed amorphous oxalate compounds of titanium(IV), which can be converted into crystalline anatase above 500 °C in air. The thermal behaviour of TiO₂ precursor compounds was examined by DRIFTS and TG-DTA methods. Strong effects of K⁺ and NH₄⁺ ions on the electrodeposition process were found by using of the EQCM technique, Raman spectroscopy and XRD measurements. The ammonium electrolyte warrants purity of the anatase phase.Morphology of the oxide films produced in different solvents was examined by SEM.     

ESR Study of a Complex Formation Between HO2 Radical and Peroxy-Vanadium (V) Ion

HO₂ radicals were generated in a flow system by the reaction: Ce⁴⁺ + H₂O₂→ Ce³⁺ +HO₂ + H⁺. The HO₂ radicals were mixed with V - H₂O₂ solutions and ESR spectroscopy was used to follow the reaction. It was shown that HO₂ reacts with both VO(O₂)⁺ and VO(O₂)^?₂ complexes. The ESR signal of the complexed radical consists of eight lines, indicating that the unpaired electron interacts with the Vanadium nucleus. The kinetics of the formation and decay reactions of the complexed radical were studied.     

N-Hydroxy-N,N'-diarylbenzamidine as a New Extraction System for Vanadium(V) in the Presence of Carboxylic Acids,Phenols, Aldehydes,Thiocyanate, and Azide

Abstract

N- Hydroxy- N -m-tolyl-N'-(2-methyl-5-chloro) phenyl-p-toluamidine hydrochloride (HTMCPTH) has been used as a new and convenient extraction system for vanadium(V) in the presence of all organic compounds containing -COOH, -CHO, -OH (phenolic) groups, and also in SCN^? and N₃ ^? media. HTMCPTH reacts with vanadium(V) to give a 1:2 complex (having a flat peak in the region 550–590 nm with 750 l/mole/cm). In the presence of various adduct-forming substances, a quantitative recovery of metal and marked absorbance enhancement into chloroform have been observed on the basis of formation and hyper- and bathochromic shift of the hydrophobic species formed. The extracting species is found to be 1:2:1 (V: HTMCPTH: RCOOH/ ArCOOH/ArOH/ArCHO) and 1:2:2 (V: HTMCPTH: SCN^?/N₃ ^?) mixed complexes. The nature of adduct-forming substances has a large effect on absorbance and the λ_max of mixed complexes. The effective molar absorbances lie between 3500 to 8000 l/mole/cm. Fe^{3 +}, Cu^{2 +}, Zn^{2 +}, Ni^{2 +}, Co^{2 +}, Mn^{2 +}, Al^{3 +}, Cr^{3 +}, Ti^{4 +}, Zr^{4 +}, Mo^{6 +}, etc. do not interfere. The method is accurately applied for determination of vanadium content in BCS steels.     

Organofunctionalized catalyst surfaces highly active and selective for carbon–carbon bond-forming reactions

This article illustrates two types of organofunctionalized heterogeneous catalysts for variety of organic carbon–carbon bond-forming reactions, summarizing our previous reports and also presenting new data. Organic amines with an alkoxysilane moiety were immobilized on inorganic silica-alumina surfaces (SA-NR₂) by simple silane-coupling reactions between the silica-alumina surface (SA) and the alkoxysilane. This SA-NR₂ acted as acid–base bifunctional heterogeneous catalysts for carbon–carbon bond-forming reactions, such as cyano-ethoxycarbonylation, Michael reaction of nitriles, and nitro-aldol reaction. These reactions did not occur with either SA or homogeneous amine compounds. In addition, the mixture of SA and homogeneous amine showed low catalytic activity due to undesirable acid–base neutralization reaction. Achiral organic silane-coupling reagents with a variety of functional groups were also immobilized on a SiO₂ surface that had been immobilized with chiral bis(oxazoline) (BOX), to which Cu ions were coordinated to make chiral Cu–BOX complexes on the SiO₂ surface. The SiO₂-supported Cu–BOX complex catalyst functionalized with achiral 3-methacryloxypropyltrimethoxysilane dramatically increased enantioselectivity in the asymmetric Diels–Alder reaction of cyclopentadiene and 3-acryloyl-2-oxazolidinone. The organofunctionalized catalysts showed much better performances for the C–C bond-forming reactions compared to the corresponding homogeneous systems. The heterogeneous catalysts thus obtained were characterized by solid-state ¹³C and ²⁹Si MAS NMR, FT-IR, UV/vis, XAFS, ESR, XRF, and elemental analysis.     

Oxadiazoline and Ketoimine Palladium(II) Complexes as Highly Efficient Catalysts for Suzuki–Miyaura Cross‐Coupling Reactions in Supercritical Carbon Dioxide

The [2+3] cycloaddition of nitriles (RCN) with 2,2‐dimethyl‐3,4‐dihydro‐2H‐pyrrole 1‐oxide, in the presence of palladium dichloride (PdCl₂) gives the corresponding 2,3‐dihydro[1.2.4]oxadiazole (Δ⁴‐1,2,4‐oxadiazoline) palladium(II) complexes 1 – 4 in good yields. However, the Pd(II)‐assisted reaction of pentafluorobenzonitrile with the same pyrroline N‐oxide gives a mixture of oxadiazoline 5 , ketoimine 6 and pyrrolylbenzamide‐ketoimine 7 Pd(II) complexes, which affords upon heating in refluxing acetone the unprecedented fused tricyclic ketoimine complex 8 as the exclusive product. Under heating, compounds 5 and 7 transform to 6 , the latter undergoing intramolecular cyclization by nucleophilic attack of the amino moiety to the ortho carbon of the pentafluorophenyl ring leading ultimately to 8 . The compounds were characterized by IR, ¹H and ¹³C NMR, ESI⁺‐MS, elemental analyses and, in the cases of 3 , 6 , 7 and 8 , also by X‐ray diffraction analyses. The catalytic properties of the Pd complexes were evaluated in Suzuki–Miyaura cross‐coupling reactions, using supercritical carbon dioxide (scCO₂) as a green solvent. Cross‐couplings of aryl halides with phenylboronic acid give the desired biaryl products in quantitative yields, in a short reaction time, for substrate‐to‐catalyst molar ratios as high as 4.0⋅10⁴.     

Redox chemistry of H2S oxidation by the British gas Stretford process part V: Aspects of the process chemistry

Stretford processes use air to oxidize H₂S in process and natural gases to elemental sulphur, by absorption in aqueous solution at about pH 9 and reaction of the resulting HS^– ions with dissolved oxygen, in the presence of anthraquinone disulphonates (AQDS) and vanadium (v) species, which act as catalysts. Kinetic measurements of the reactions (AQ27DS + HS^– ions), (V(v) + HS^– ions) and (AQ27DSH^– + O₂), primarily used stopped flow spectrophotometry, as reported here, following papers on the electrochemical behaviour of the individual redox couples in Stretford Processes. The course of reaction (AQ27DS + HS^– ions) was also followed with a gold bead indicator electrode, the potential of which was determined essentially by the AQ27DS/AQ27DSH^– couple as the former species were reduced to the latter. Attempts to use⁵¹V NMR to characterize aqueous vanadium-sulphur complexes were inconclusive. A possible mechanism for Stretford Processes is postulated, involving polysulphide (S _n ^2–) ions as intermediates, which are oxidized to elemental sulphur by another intermediate, H₂O₂, formed by reaction of AQ27DSH^– ions and dissolved oxygen.     

Photoelectrochemical reaction of biomass-related compounds in a biophotochemical cell comprising a nanoporous TiO<Subscript>2</Subscript> film photoanode and an O<Subscript>2</Subscript>-reducing cathode

Photoelectrochemical decomposition of bio-related compounds such as ammonia, formic acid, urea, alcohol, and glycine by a biophotochemical cell (BPCC) comprising a nanoporous TiO₂ film photoanode and an O₂-reducing cathode generating simultaneously electrical power was investigated. The bio-related compounds studied were all photodecomposed by the present BPCC when they were either liquid or soluble in water. It was shown that ethanol exhibits similar characteristics both under 1 atm O₂ and air as studied by cyclic voltammograms. Although the present BPCC utilizes only UV light, a solar simulator at AM 1.5G and 100 mW cm⁻² light intensity gave also moderate photocurrent–photovoltage (J–V) characteristics with about 2/5 of the short circuit photocurrent (J _sc) values (J _sc) of that under a Xe lamp irradiation at the intensity of 503 mW cm⁻². It was demonstrated that varieties of bio-related compounds can be used as a direct fuel simultaneously for photodecomposition and electrical power generation. The charge transport processes in the BPCC operation were analyzed using glycine by an alternating current impedance spectroscopy, showing that the charge transfer reactions on the photoanode and the cathode surfaces compose the major resistance for the cell performance.     

Highly electrophilic metallocenes and their role in alkene polymerizations

This summary explores three main topics: (1) zwitterionic alternatives to cationic metallocene alkyl complexes as olefin polymerization catalysts, based on borato (–BR ₃ ^- ) and boryl (–BR₂) substituted cyclopentadienyl ligands (R = C₆F₅); including zwitterionic zirconium allyl complexes of the type CpZr(η³-allyl){η³-allyl–CH₂B(C₆F₅)₃}; (2) reactions which contribute to catalyst deactivation, notably aluminum alkyl mediated C₆F₅ transfer reactions as well as C–H activation reactions including an unusual case of catalyst self-reactivation; (3) the role of highly electrophilic metallocene complexes of aluminum, zirconium and yttrium in combination with weakly coordinating anions as initiators for the carbocationic polymerization of isobutene and isobutene–isoprene copolymerizations is discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis of pentavalent imidovanadium complexes and their catalyses for the polymerization of ethylene and propylene

Imidovanadium complexes with cyclopentadienyl (Cp) ligands—(Cp)V(?NC₆H₄Me‐4)Cl₂ (1), (Cp)V(?N^tBu)Cl₂ (2), and (^tBuCp)V(?N^tBu)Cl₂ (3; ^tBuCp = tert‐butylcyclopentadienyl)—were synthesized through the reaction of imidovanadium trichloride with (trimethylsilyl)cyclopentadiene derivatives. The molecular structure of 3 was determined by X‐ray crystallography. The monocyclopentadienyl complex 1 exhibited moderate activity in combination with methylaluminoxane [MAO; 10.3 kg of polyethylene (mol of V)^?1 h^?1 atm^?1], whereas similar complexes with bulky ^tBu groups, 2 and 3, were less active. (2‐Methyl‐8‐quinolinolato)imidovanadium complexes, V(?NR)(O ?N)Cl₂ (R = C₆H₃ⁱPr₂‐2,6 (4) or n‐hexyl (5), O ?N = 2‐methyl‐8‐quinolinolato), were obtained from the reaction of imidovanadium trichloride with 2‐methyl‐8‐quinolinol. Upon activation with modified MAO, complex 4 showed moderate activities for the polymerization of ethylene at room temperature. The complex 5/MAO system also exhibited moderate activity at 0°C. The polyethylenes obtained by these complexes had considerably high melting points, which indicated the formation of linear polyethylene. Moreover, the 5/dried MAO system showed propylene polymerization activities and produced polymers with considerably high molecular weights and narrow molecular weight distributions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1008–1015, 2005     

Evaluation on the optical properties of Ga2O3−x thin films co-doped with Tb and transition metals (Mn,Cr) prepared by a photochemical route

Gallium β-diketonate complexes were studied as precursors for the photochemical deposition of amorphous thin films of gallium oxide doped with terbium and co-doped with chromium or manganese. Solutions of the inorganic complexes were spin coated on Si(100) and quartz substrates and photolyzed at room temperature using 254 nm UV light. The photolysis of these films induces the fragmentation of the complexes and the partial reduction of the metal ion together with the release of volatile organic compounds as sub-products. When the metallic complexes are irradiated under air, the products of the reactions are metal oxide thin films. The photochemical reactivity of these films was monitored by UV–vis spectroscopy, followed by a post-annealing treatment. The obtained films were characterized by X-ray photoelectron spectroscopy and X-ray diffraction. The optical properties of the films showed that these are highly transparent in the visible spectrum but decrease significantly in doped and co-doped films. Under UV light excitation (254 nm) the doped films (Ga₂O_3−x/Tb) show the characteristic emissions at 486, 530, 542 and 610 nm associated to ⁵D₄→⁷F_J (J=6,5,4,3) transitions of Tb⁺³ ion. However, these emissions decrease and deteriorate in the co-doped films (Ga₂O_3−x/Tb/M, where M=Mn or Cr). A possible emission mechanism and energy transfer have been proposed.     

Complexation of titanium alkoxides with pentenoic acid and allylacetoacetate and their hydrolysis and addition reactions with H‐silanes

Complexation reactions of titanium tetraethoxide [Ti(OEt)₄] and titanium tetra‐n‐butoxide [Ti(OBuⁿ)₄] with 3‐pentenoic acid (PA) and allylacetoacetate (AAA), in a 1 : 1M ratio, were studied in ethanol solution at room temperature. ¹³C‐NMR and FTIR spectra showed that all PA and AAA completely reacted with both titanium alkoxides. Hydridosilane compounds such as triethoxysilane and triethylsilane were added to titanium chelate complexes in a 1 : 1M ratio. The investigation of products by ¹³C‐ and ²⁹Si‐NMR and FTIR showed additions of ? SiH to the C?C double bond. The hydrolysis of titanium–PA and AAA complexes, by water in 1 : 4 ratios, resulted in released PA in an amount of 10% and AAA of 20%. The stability of hydrolyzed products was investigated by ¹³C‐NMR, ²⁹Si‐NMR, and FTIR. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 790–796, 2005     

Synthesis of Calix[4]arene-Based Thiourea Derivatives for Extraction of Toxic Dichromate and Arsenate Ions

In the environment, the presence of toxic oxyanions such as Cr(VI) and As(V), especially in drinking water, creates serious hazards to human health. For efficient and selective detection of these species; novel calix[4]arene-based thiourea derivatives which obtained using p-tert-butylcalix[4]arene as starting material have been prepared from m-aniline or o-aniline or o-aminophenol in moderate yield. The structures of all new synthesized compounds obtained from these reactions were determined by using FTIR, ¹H, and ¹³C NMR spectroscopy. The complexing properties of calix[4]arene-based thiourea derivatives have been studied towards the As(V) and Cr(VI). It was found that calix[4]arene-based thiourea derivative 5,11,17,23-tetra-tert-butyl-25,27-bis(o-amino-phenylthioureido propoxy)-26,28-hydroxycalix[4]arene is an effective extractant for carrying HCr₂O₇^2? anions.     

Electrochemical reactivity of aromatic compounds for use in Li cells

The electrochemical reactivity of aromatic compounds coupled with Li in LiClO₄-propylene carbonate was studied. Simple aromatic compounds, triphenylmethane compounds and quinone imine dyes were used. Discharge results for aromatic cathode-Li cells indicated that the relation between discharge voltage measured and reduction potential reported was approximately linear, which suggested that the discharge products were ion complexes. Also, the discharge voltage increased with an increase of their electron accepting groups and with a decrease of the electron donating strength of alkyl groups in their amino end groups. Among these compounds, rosaniline derivatives, bromo-substituted phenol red and thiazine dyes showed higher discharge voltages than 2.5 V. Methylene blue (MB) showed the largest energy density of 363 Wh kg^–1. Details of MB charge-discharge behavior were examined. The dynamic charge-discharge tests and cyclic voltammetry results suggested that the MB-Li cell could be cycled up to 2e per mol of MB depth. Direct reaction between the Li anode and dissolved MB seemed to be small as indicated by the Li⁺ ion conductive film formation on the Li anode.     

Exhaustive oxidation/reduction of nitrite, nitrate and hydrazine using a square wave potential regime

Exhaustive oxidation–reduction of nitrite, nitrate and hydrazine was achieved by application of a square wave potential regime to a platinum electrode. The parameters of the square wave were chosen after investigation of the adsorption behaviour of the three compounds. The three compounds were found to adsorb and desorb at a platinum electrode in the potential window from –0.2 V to 1.3 V and hence the lower potential of the square wave was –0.2 V while the upper potential was 1.3 V. The square wave was applied to a solution containing the test compound for 10 h. The results of analysis indicated a decrease in the concentration of the tested compounds with respect to the control sample. The optimal frequencies for the conversion were 10, 50 and 10 for nitrite, nitrate and hydrazine, respectively. Analysis of solutions for possible products of the exhaustive oxidation gave negative tests for NO^– ₂, NO^– ₃, and NH₃ leaving the possibility of conversion to nitrogen as the end product.     

Fluoro-Boron Complexes as Biocides: Synthetic,structural and biological aspects

The present account deals with the synthesis, stereochemistry and biological properties of coordinatively saturated difluoroboron(III) compounds. The ligands used during the present investigations were prepared by the condensation of [1-(thien-2-yl)-ethanone], [1-(pyridin-2-yl)ethanone], [1-(furan-2-yl)ethanone], [1-(naphthen-2-yl)ethanone] and [(thien-2-yl)methanal] with 2-mercapto-aniline. The unimolar reactions between borontrifluoride-acetic acid and these ligands have produced BF₂(NS) type of biologically active complexes. The quantitative and spectral analyses comprising u.v., i.r. and n.m.r. (¹H, ¹¹B, ¹³C and ¹⁹F) helped in establishing the structures of the resulting complexes. In the quest for better fungicides and bactericides, studies were conducted to assess the growth inhibiting potential of the synthesized complexes against various fungal and bacterial strains. The studies demonstrate that the concentration reached levels which are sufficient to inhibit and kill the pathogens.