Stability constants of the aqueous mono-fluoride complexes of Pu(III) and Am(III) and their correlation with other metal ions

The stability constants of the aqueous mono-fluoride complexes of Pu(III) and Am(III) have been measured using the distribution method. A correlation of the available stability constants of fluoride complexes of trivalent actinides, up to Cf, with fundamental properties like charge and radii of the metal ion has been discussed. Good correlation within the group and as a part of other metal ions was obtained only for transplutonium elements. The reported stability constant values measured by potentiometry and the value obtained by distribution for Pu³⁺ appear to be much higher than expected from this correlation. However, a better correlation was obtained with transplutonium elements when effective charge instead of formal charge was considered for Pu³⁺ in the BSE function.     

Stabilisation of tetravalent cerium in perchloric acid medium and measurement of the stability constants of its fluoride complexes using ion selective potentiometry

The stability constants of the fluoride complexes of cerium(IV) in 1 M (HClO(4), NaClO(4)) medium have been measured potentiometrically using a fluoride ion-selective electrode. Quantitative oxidation of cerium to its tetravalent state and its stabilisation in the perchlorate medium were accomplished by oxidation with AgO followed by quick addition of a known amount of fluoride ion. This procedure ensures stability of the oxidation state and prevents hydrolysis and polymerisation of Ce(IV). Logarithms of the average values of beta(1), beta(2), beta(3) and beta(4) were estimated to be 7.57+/-0.04, 14.50+/-0.03, 20.13+/-0.37 and 24.14+/-0.10 respectively.     

A rapid, selective and sensitive spectrophotometric method for the determination of Ce(III) using some bisazophenyl-beta-diketone derivatives

A rapid, simple, selective and sensitive spectrophotometric method for the determination of cerium(III) using the title azo dyes [1,3-phenylenediamine bisazoacetylacetone (I(a));1,3-phenylenediamine bisazobenzoylacetone (I(b));1,4-phenylenediamine bisazoacetylacetone (I(c)); and 1,4-phenylenediamine bisazobenzoylacetone (I(d))] has been developed in neutral and slightly alkaline (pH 7.00, 7.50, 8.00 and 7.00) media. The 1:1 and 2:1 (M:L) complexes formed exhibit their highest absorbances in 30% (v/v) dioxane solutions, having formation constants (log K) of 4.44, 4.95. 5.63 and 5.22 and 8.51, 8.76, 9.73 and 9.37 respectively. Beer's law is obeyed over the concentration ranges 0.10-2.50, 0.05-3.00, 0.05-3.75 and 0.10-3.50 mug ml(-1) of cerium(III). More accurately, Ringbom optimum concentration ranges are 0.2-2.25, 0.2-2.6, 0.2-3.5 and 0.2-3.3 mug ml(-1) for the complexes of reagents I(a),I(b),I(c) and I(d) respectively. The molar absorptivities, Sandell sensitivities and relative standard deviations were also calculated. The interferences of 50 foreign ions on the determination of cerium(III) were studied. The method allows the determination of cerium(IV) after prior reduction to the trivalent state. The proposed method was used for cerium determination in two different monazite samples and the results were compared with certified values obtained using atomic absorption spectrometry, indicating that the procedure provided accurate and precise results.     

Ce(C_8H_8)_2和Ce(C_8H_8)_2~-的化学键性质

结合改进的重叠模型Xa-SW法和Ziegler过渡态法,通过将中心原子与配体的作用选成离子聚集、中心原子只有s和p轨道参与成键、中心原子只有d轨道参与成键、中心原子只有f轨道参与成键、中心原子的s、p、d和f轨道同时参与成键5种类型,从能量角度分析了Ce(C_8H_8)_2和Ce(C_8H_8)~-_2的化学键性质。     

Determination of the stability constant of Np(V) fluoride complex using a fluoride ion selective electrode

Fluoride complexing of Np(V) has been studied using fluoride ion selective electrode (F-ISE). Free fluoride ion concentrations in the presence of Np(V) were measured at 0.1 and 1.0M ionic strength. The data were used to calculate the stability constant of the fluoride complex of Np(V) and the values obtained are reported here.     

Tuning the valence of the cerium center in (Na)phthalocyaninato and porphyrinato cerium double-deckers by changing the nature of the tetrapyrrole ligands

A series of 7 cerium double-decker complexes with various tetrapyrrole ligands including porphyrinates, phthalocyaninates, and 2,3-naphthalocyaninates have been prepared by previously described methodologies and characterized with elemental analysis and a range of spectroscopic methods. The molecular structures of two heteroleptic [(na)phthalocyaninato](porphyrinato) complexes have also been determined by X-ray diffraction analysis which exhibit a slightly distorted square antiprismatic geometry with two domed ligands. Having a range of tetrapyrrole ligands with very different electronic properties, these compounds have been systematically investigated for the effects of ligands on the valence of the cerium center. On the basis of the spectroscopic (UV-vis, near-IR, IR, and Raman), electrochemical, and structural data of these compounds and compared with those of the other rare earth(III) counterparts reported earlier, it has been found that the cerium center adopts an intermediate valence in these complexes. It assumes a virtually trivalent state in cerium bis(tetra-tert-butylnaphthalocyaninate) as a result of the two electron rich naphthalocyaninato ligands, which facilitate the delocalization of electron from the ligands to the metal center. For the rest of the cerium double-deckers, the cerium center is predominantly tetravalent. The valences (3.59-3.68) have been quantified according to their L(III)-edge X-ray absorption near-edge structure (XANES) profiles.     

Extraction of thorium and cerium (III) chlorides by neutral organophosphorus solvents

Summary The extraction of thorium and trivalent cerium chlorides by tri-n-butyl phosphate and di-isoamylmethyl phosphonate has been investigated as a function of hydrochloric acid molarity in the aqueous phase and solvent concentration in the organic phase. The comparative stability of the extractable metal complexes with the two solvents has been also estimated. The second solvent has been recommended, instead of the first, for the separation of thorium and the rare earth elements from hydrochloric acid media.

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Zusammenfassung Die Extraktion von Thorium- und Cer(III)-chloriden mit Hilfe von Tri-n-butylphosphat und Di-isoamylmethyl-phosphonat wurde in Abhängigkeit von der HCl-Konzentration in der wäßrigen und der Lösungsmittelkonzentration in der organischen Phase untersucht. Die Stabilität der gebildeten Metallkomplexe wurde bestimmt. Zur Abtrennung von Thorium und Seltenen Erden aus salzsaurem Medium wird Di-isoamylmethyl-phosphonat empfohlen.

     

Radiolyse des solutions aqueuses du complexe cerium(III)-acide triethylene tetraaminehexaacetique

Irradiation of cerium III-triethylenetetraaminehexaacetic acid (TTHA) solutions was done. The degradation of the metal chelate was determined. A radiolytic mechanism has been proposed where it has been showed that the degradation is due to the OH radical, while oxidation of trivalent cerium to tetravalent cerium is due to the hydrogen peroxide molecule.      

Oxygen exchange properties in the new pyrochlore solid solution Ce2Sn2O7-Ce2Sn2O8

The phase-pure cerium stannate pyrochlore (Ce₂Sn₂O₇) has been prepared for the first time. The structure and oxidation states of both cations were carefully reviewed, and the compound was unambiguously replaced within the rare-earth stannate series. As a consequence of the low stability of trivalent cerium in oxide phases, one oxygen per formula unit could be intercalated by calcination under O₂ at 400 °C, leading to the new Ce₂Sn₂O₈ pyrochlore. This latter phase is subject to oxygen under-stoichiometry from 400 to 700 °C. However, oxygen deintercalation seems to be in competition with cerium oxide segregation at high temperature, leading to the formation of cerium deficient pyrochlore phases.     

Polarographic determination of fluoride using the adsorption wave of the Ce(III)-alizarin complexone-fluoride complex

A very sensitive electrochemical method for trace measurement of fluoride in water is discussed. The complex of cerium(III) with alizarin complexone (ALC) and fluoride ion is adsorbed at the dropping mercury electrode. In cathodic sweeps, the peak height is directly proportional to the concentration of fluoride over the range 8 x 10(-8)-5 x 10(-6)M (1.5 x 10(-9)-9.5 x 10(-8) g/ml), and the detection limit is 5 x 10(-8)M (9.5 x 10(-10) g/ml). The proposed method was applied to the determination of fluoride in water.     

Micellar catalysis in the oxidation of acetophenones by Ce(IV)

Rate of oxidation of acetophenones by Ce(IV) in aqueous acetic acid 80:20 (v/v) either slows down or remains constant over a range of cetyltrimethyl ammonium bromide (CTAB) concentration exceeding the cmc value. The rate is then found to increase sharply as the surfactant concentration increases with no sign of reaching a maximum or constant value. From Fluorescence quenching, binding constant for p-nitro acetophenone has been evaluated. The rate data have been rationalized on the basis of a reaction between the acetophenones situated on the micelle surface and active Ce(IV) species in the bulk aqueous phase.     

水溶液法制备CeF3纳米颗粒

氟化铈(CeF3)具有很高的离子电导率［1］和独特的光学特性［2］, 可用于制作化学传感器和光学元器件. CeF3还是良好的固体润滑剂［3］. 近年来的研究结果表明, 与氟化物粗晶材料相比, 纳米尺度的氟化物的性能有显著的提高， 因此, 其制备方法也很受关注. 目前, 制备氟化物纳米颗粒的方法有蒸发法［4］、 微乳液法［2, 5~8］、 水醇混合溶液法［3,9］和微波固相氧化还原合成法［10］等. 但是, 水溶液直接沉淀法作为一种操作简单, 成本低, 适合批量生产的制备方法尚未见用于制备纳米CeF3颗粒.     

Einkristalle des Cer(III)‐Borosilicats Ce3[BSiO6][SiO4]

Single Crystals of the Cerium(III) Borosilicate Ce₃[BSiO₆][SiO₄] Colorless, lath‐shaped single crystals of Ce₃[BSiO₆]‐ [SiO₄] (orthorhombic, Pbca; a = 990.07(6), b = 720.36(4), c = 2329.2(2) pm, Z = 8) were obtained in attempts to synthesize fluoride borates with trivalent cerium in evacuated silica tubes by reaction of educt mixtures of elemental cerium, cerium dioxide, cerium trifluoride, and boron sesquioxide (Ce, CeO₂, CeF₃, B₂O₃; molar ratio 3 : 1 : 3 : 3) in fluxing CsCl (700 °C, 7 d) with the glass wall. The crystal structure contains eight‐ (Ce1) and ninefold coordinated Ce³⁺ cations (Ce2 and Ce3) surrounded by oxygen atoms. Charge balance is achieved by both discrete borosilicate ([BSiO₆]^5– ≡ [O₂BOSiO₃]^5–) and ortho‐silicate anions ([SiO₄]^4–). The former consists of a [BO₃] triangle linked to a [SiO₄] tetrahedron by a single vertex. The anions form layers in [001] direction alternatingly built up from [BSiO₆]^5– and [SiO₄]^4– groups while Ce³⁺ cations are located in between.     

Synthesis and characterization of single-crystal Ce(OH)CO3 and CeO2 triangular microplates

Single-crystal cerium hydroxide carbonate (Ce(OH)CO3) triangular microplates with the hexagonal phase have been successfully synthesized by a hydrothermal method at 150 degrees C using cerium nitrate (Ce(NO3)3.6H2O) as the cerium source, aqueous carbamide as both an alkaline and carbon source, and cetyltrimethylammonium bromide (CTAB) as a surfactant. Single-crystal ceria (CeO2) triangular microplates have been fabricated by a thermal decomposition-oxidation process at 650 degrees C for 7 h using single-crystal Ce(OH)CO3 microplates as the precursor. The shape of the Ce(OH)CO3 microplate was sustained after thermal decomposition-oxidation to CeO2. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TG).     

Waste-activated sludge (WAS) as Cr(III) sorbent biosolid from wastewater effluent

A biological sludge – waste-activated sludge (WAS) – from a dairy filtering station was investigated for the removal of trivalent chromium from aqueous solution. Kinetic results revealed that chromium adsorption was instantaneous. The removal rate increases up to pH 4 for contact times beyond 20 min. The equilibrium state is attained in 30 min in all the considered systems. The reaction orders as well as the diffusion rate constant were determined. Values adsorption isotherms measured at pH 3 generally followed the Langmuir model. The maximum uptake capacity was 25.64 mg/g. Values of thermodynamic parameters show that chromium (III) sorption on WAS is an exothermic process.This study provides an opportunity for the removal of heavy metals such as chromium from aqueous solutions using a low-cost biosolid as adsorbent support.     

Extractive spectrophotometric determination of micro and sub-micro amounts of fluoride

A simple and sensitive extractive spectrophotometric determination of fluoride with the cerium(III)-alizarin complexan chelate has been investigated. The fluoro chelate formed is extracted into n-pentanol containing triethylamine. It is possible to achieve under selected conditions a selective extraction of the cerium(III)alizarin complexan-fluoride chelate. The stability of the chelate, the effect of temperature and the low absorbance of the blank are discussed. It is found that it is necessary to add a pH 9 buffer before the extraction. Procedures are given for the determination of 0.1-1 mug of fluoride in a 4-ml sample and 5-25 mug of fluoride in a 90-ml sample.     

Nitroxide chemistry XXII. Oxidation of N,N-bis(trifluoromethyl)hydroxylamine

A number of cheap oxidising agents have been found to be effective for the conversion of N,N-bis(trifluoromethyl)hydroxylamine into bis(trifluoromethyl)nitroxide. The best of these are cerium(IV) salts either in the solid state or in aqueous acid solution. Efficient, self-indicating processes have been developed using either catalytic amounts of silver(II) picolinate and aqueous potassium persulphate solutions, or electrochemical oxidation with cerium(III) nitrate and sodium nitrate in dilute nitric acid.     

Kinetics of Cerium(IV) Extraction from H(2)SO(4)-HF Medium with Cyanex 923

Studies of the extraction kinetics of cerium(IV) from H(2)SO(4)-HF solutions with Cyanex 923 in n-heptane have been carried out using a constant interfacial area cell with laminar flow. The experimental hydrodynamic conditions were chosen so that the contribution of diffusion to the measured rate of reaction was minimized. The data were analyzed in terms of pseudo-first order constants. The results were compared with those of the system without HF. It was concluded that the addition of HF reduces the activation energy for the forward rate from 46.2 to 36.5 kJ mol(-1) while it has an opposite effect on the activation energy for the reverse process(the activation energy increased from 23.3 to 90.8 kJ mol(-1)). Thus, HF can accelerate the rate of cerium(IV) extraction. At the same time, the extraction rate is controlled by a mixed chemical reaction-diffusion rather than by a chemical reaction alone. A rate equation has also been obtained.     

Radiolysis of aqueous solutions of cobalt(II) and cobalt(III)

Radiolysis of aqueous solution of di and trivalent cobalt with 1:2 (bis) carboxymethylaminodiethyltetraacetic acid (EGTA) was investigated, both in absence and in presence of oxygen. A radiolytic mechanism has been proposed. It has been shown that the degradation at the ligand of the chelate is due to OH only.     

Photometric determination of the stability constant of the palladium(II)-pyridine-2,6-dicarboxylate complex

From the absorption spectra it has been concluded that Pd(II) forms a 1:1 complex with pyridine-2,6-dicarboxylic acid in aqueous solution at pH 2. The influence of various concentrations of chloride on the spectr has been examined. Ternary complex formation with chloride does not occur to a measurable extent. The conditional stability constant has been determined from data collected near the equivalence point of the titration curve. With allowance for the different side-reactions in this medium at an ionic strength of 0.2, a value of log K = 16.0 +/- 0.2 has been found for the stability constant.