Eu8(NCN)5-deltaI6+2delta (delta= 0.05): a novel rare-earth carbodiimide iodide containing oligomeric tritetrahedral Eu8 clusters

Eu8(NCN)4.95I6.10 is the first compound with discrete tritetrahedral Eu8 clusters which are interconnected by coordinating NCN2- carbodiimide anions on their triangular faces to form separated layers, the latter being bridged by iodide and carbodiimide anions.     

Extraction-separation of Eu(III) and Th(IV) ions from nitrate media into a room-temperature ionic liquid

Application of a room-temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim⁺][PF₆ ^?]), in the extraction of Eu(III) and Th(IV) ions from nitrate media using tri-n-octylphosphine oxide (TOPO) as extractant is investigated. The results are compared with those obtained in dichloromethane. It is shown that the europium ions are extracted via a solvation mechanism by formation of [Eu(TOPO) ₃ ³⁺ ](NO₃ ^?)₃ species in both [C₄mim⁺][PF₆ ^?] and dichloromethane. Nevertheless, application of the studied RTIL makes a significant improvement in the extraction efficiency of europium ions. A different attitude was observed for the extraction of thorium ions. In fact, although the analysis of the extraction data of these ions from sodium nitrate solutions confirms the formation of [Th(TOPO) ₃ ⁴⁺ ](NO₃ ^?)₄ species in dichloromethane, the extraction of these ions into the ionic liquid was not affected by the presence of TOPO. This latter outcome states the process takes place by a cation-exchange mechanism. It is found that the extraction of thorium ions diminishes in the presence of nitric acid. Interestingly, in contrast to the results observed in the extraction of thorium ions from sodium nitrate solutions, TOPO shows a co-operative effect on the extraction of these ions from nitric acid media. This allows considering the mechanism of the extraction of Th⁴⁺ ions from nitric acid media as a mixed ion exchange-solvation mechanisms by formation of [Th(TOPO)⁴⁺](NO₃ ^?)(PF₆ ^?)₃ species.     

Luminescence properties of sol-gel derived silica gels doped and undoped with RE-complexes(RE=Eu,Tb)

The luminescence properties of silica gels and silica gels doped with two rare earth complexes,Eu(TTA)3 and Tb(o-CBA)3 (TTA=thenoyltrifluocetate,o-CBA=o-chlorobenzoic acid) are reported and discussed.Pure silica gels show a blue luminescence,and the maximum excitation and emission wavelengths depend strongly on the solvents used.Both of the studied rare earth complexes exhibit the characteristic emissions of the rare earth ions in silica gels,i.e.,Eu3+5 Do→7 FJ(J=0,1,2,3,4),Tb3+5D4→7FJ(J=3,4,5,6) transitions.Compared with the pure RE-complexes powder,the silica gels doped with RE-complexes show fewer emission lines of the rare earth ions.Furthermore the rare earth ion (Tb3+) presents a longer lifetime (1346μs) in silica gel doped with Tb(o-CBA)3 than in pure Tb(o-CBA)3 powder (744μs).The reasons responsible for these results are discussed in the context.     

Characteristics of dye-impregnated tetraethylorthosilane (TEOS) derived sol-gel coatings

An investigation has been carried out on a cross-comparison study into several sol-gel coatings, impregnated with a pH-sensitive fluorescent dye, to determine their optimum characteristics, with the aim of their application as thin film sensor elements in fibre optic chemical sensors. In this test of the coatings, they were applied to standard, cleaned microscope slides and several characteristics, such as the ability of the sol to wet the glass substrate and the optical clarity of the subsequent coating were investigated and found to depend mainly on the water: tetraethylorthosilane (H₂O: TEOS) ratio used in their preparation but also on the extent of aging and the level of catalyst used. It was found that thicker coatings could be created through the use of suitable chemical additives in the preparation process.     

Water incorporation into a micellar-lamellar phase (dodecyl maltoside-water)

Many alkylated sugars are surfactants, and show lamellar phases which prove to be identical to those of more conventional surfactants. Most, if not all, previous investigations focus on the behaviour of these compounds in pure form. Dodecyl maltoside shows the same lamellar phase as when dry, but on the addition of water the layer spacing expands, and on addition of more water, a hexagonal phase forms. The area per head group increases substantially with water addition, indicating that the water is incorporated into the layers, possibly at the head groups. We suggest that the hexagonal phase is the system's answer to the frustration caused by a large head group area compared with that of the tails.     

Electrochemical synthesis of rare-earth metal (Eu,Nd) borides in molten salts

Rare-earth metal borides are widely used in different fields of modern techniques. Electrochemical synthesis at moderate temperatures (973–1023 K) is a cost-effective alternative to direct reaction techniques. The present work reports the mechanism and kinetics of boron and europium, boron and neodymium joint electrodischarge in chloride-fluoride molten systems. The optimum regimes of europium and neodymium borides electrodeposition are worked out on the base of voltammetric experiments. Europium compound is synthesized as a single-phase EuB₆ product, while neodymium compounds is co-deposited as NdB₄ and NdB₆. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 8, pp. 978–984. The article was translated by the authors.     

Study on the energy transfer between UO_2~(2 ) and Eu~(3 ) in sol-gel derived titania matrix by luminescence spectroscopy

The TiO2 gel doped with UO22 and Eu3 has been prepared by a sol-gel method. The quenching of the UO22 emission by Eu3 and the energy transfer from the excited state of UO22 to the ground state of Eu3 have been investigated. The energy transfer has been studied by the measurement of luminescence lifetime τ, calculations of energy transfer efficiency ηET and energy transfer rate WET. The experimental results indicated that the quenching is combined static and dynamic mechanism, but the static mechanism is dominant.     

Enhanced luminescence of rare-earth complexes Tb(1-x)Eu(x)(m-NBA)3Phen in ZnS

Rare-earth ternary complexes Tb(1-x)Eu(x)(m-NBA)(3)Phen (X=1, 0.25, 0.5, 0.75, 1.0) were synthesized and characterized by IR, DTA-TG, UV, fluorescent spectra and elemental analysis. It was found that luminescence of Eu(3+) complex was enhanced by doped with Tb(3+). It is proved by TG curve that the complexes are stable, ranging from ambient temperature to 360 degrees C in air. The organic-inorganic combined structural device was fabricated, and the electroluminescence intensity of the combined structural device was improved compared with the device of the purely organic components.     

Oxoneptunium(v) as part of the framework of a polyoxometalate

(NH4)14Na4[(Np3W4O15)(H2O)3(BiW9O33)3].62H2O (1) and (NH4)14.5Na3.5[(Np3W4O15)(H2O)3(SbW9O33)3].40.5H2O (2) each contain three neptunyl(v) moieties encapsulated within heteropolyoxotungstate frameworks in which axial {NpO2}+ oxygens form one face of a WO6 octahedron.     

Optical determination of Cr(VI) using regenerable, functionalized sol-gel monoliths

Transparent, pyridine-functionalized sol-gel monoliths have been formed and their use in Cr(VI) sensing applications is demonstrated. The monoliths were immersed in acidic Cr(VI)-containing solutions, and the Cr(VI) uptake was monitored using UV-vis and atomic absorption spectroscopies. At concentrations at the ppm level, the monoliths exhibit a yellow color change characteristic of Cr(VI) uptake, and this can be measured by monitoring the absorption change at about 350 nm using UV-vis spectroscopy. Concentrations at the ppb level are below the limit of detection using this wavelength of 350 nm for measurement. However, by adding a diphenylcarbazide solution to monoliths that have been previously immersed in ppb-level Cr(VI) solutions, a distinct color change takes place within the gels that can be measured at about 540 nm using UV-vis spectroscopy. Concentrations as low as 10 ppb Cr(VI) can be measured using this method. The monoliths can then be regenerated for subsequent sensing cycles by thorough washing with 6.0 M HCl. The factors affecting monolith uptake of Cr(VI) have been explored. In addition, the gels have been characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) measurements.     

Phosphoesterase activity of polyoxomolybdates: diffusion ordered NMR spectroscopy as a tool for obtaining insights into the reactivity of polyoxometalate clusters

Diffusion ordered NMR spectroscopy (DOSY NMR) is shown to be an excellent tool for observing reactive transients in the hydrolysis of the phosphatase model substrate (p-nitrophenyl)phosphate (NPP) promoted by polyoxomolybdate.     

两个多酸基镧系(Eu、Tb)双膦酸酯配合物的合成、物化性质和太赫兹时域光谱

在乙腈和去离子水的混合溶剂中合成了2个新的多酸基镧系双膦酸酯配合物[Eu (L)₄]PW₁₂O₄₀·2CH₃CN (1)和[Tb (L)₃(H₂O)]PW₁₂O₄₀(2)(L=亚乙基二膦酸四乙酯),并通过单晶X射线衍射、元素分析、红外光谱、粉末X射线衍射、热重分析和太赫兹时域光谱对2个配合物的性质进行了表征,分析了配合物的晶体结构及分子间弱作用力,研究了配合物的发光等性能。单晶结构表明,配合物1是以Eu (Ⅲ)为中心、L为配体螯合形成的扭曲四方反棱柱结构。配合物2是以Tb (Ⅲ)为中心、L和H₂O为配体形成的扭曲单帽八面体结构。发光光谱表明配合物1和2所有的发射峰来源于金属内部的电荷迁移。此外,太赫兹时域光谱对配合物1和2的结构和发光的分析提供了帮助。     

Enlightening the journey of metal-organic framework (derived) catalysts during the oxygen evolution reaction in alkaline media via operando X-ray absorption spectroscopy

The development of catalysts with enhanced activity for the oxygen evolution reaction (OER) compared to the traditionally used metal oxide catalysts is crucial for further commercialization of electrolyzers. Because of their high surface area and adjustable pore structure, metal-organic framework (MOF)-based catalysts represent a promising alternative. During the OER in alkaline media, the initial MOF structure is susceptible to transformations including the decomposition of the organic backbone and/or the formation of oxide, hydroxide and oxyhydroxide intermediates. Hence, operando characterizations of MOF catalysts during OER are essential to understand the material's progressive changes and extract the OER catalytic mechanism. This article discusses existing operando X-ray absorption spectroscopy studies of MOF(-derived) catalysts during OER and extracts important parameters for future research regarding operando X-ray absorption spectroscopy characterizations of MOFs during alkaline electrolysis.     

Effect of incorporation of sodium into copper(II) oxide

Copper(II) oxide containing different amounts of sodium has been prepared. Thermo-analytical studies reveal differences in behaviour between sodium-incorporated samples and the control sample. A strong esr signal withg=2.1 is explained by assuming a square planar configuration around the Cu²⁺ ion. The spin concentration is found to vary linearly with the sodium content, each sodium decoupling the spins of 40 Cu²⁺ ions in CuO. The signal is found to be present even in a reduced sample. The origin of such species is explained on the basis of antiferromagnetic decoupling of spins.The authors are grateful to Mr. A. N. Dutta for carrying out the DTA and TG experiments, to Dr. P. C. Srivastava for sodium analysis and to Dr. S. K. Ghosh, M. L. Kundu and G. Sengupta for helpful discussions.     

Probing the binding of Tb(III) and Eu(III) to the hammerhead ribozyme using luminescence spectroscopy

BACKGROUND: Divalent metal ions serve as structural as well as catalytic cofactors in the hammerhead ribozyme reaction. The natural cofactor in these reactions is Mg(II), but its spectroscopic silence makes it difficult to study. We previously showed that a single Tb(III) ion inhibits the hammerhead ribozyme by site-specific competition for a Mg(II) ion and therefore can be used as a spectroscopic probe for the Mg(II) it replaces. RESULTS: Lanthanide luminescence spectroscopy was used to study the coordination environment around Tb(III) and Eu(III) ions bound to the structurally well-characterized site on the hammerhead ribozyme. Sensitized emission and direct excitation experiments show that a single lanthanide ion binds to the ribozyme under these conditions and that three waters of hydration are displaced from the Tb(III) upon binding the RNA. Furthermore, we show that these techniques allow the comparison of binding affinities for a series of ions to this site. The binding affinities for ions at the G5 site correlates linearly with the function Z(2)/r of the aqua ion (where Z is the charge and r is the radius of the ion). CONCLUSIONS: This study compares the crystallographic nature of the G5 metal-binding site with solution measurements and gives a clearer picture of the coordination environment of this ion. These results provide one of the best characterized metal-binding sites from a ribozyme, so we use this information to compare the RNA site with that of typical metalloproteins.     

On the incorporation of geraniol and farnesol into cantharidin (author's transl)

On the incorporation of geraniol and farnesol into cantharidin Earlier investigations [1] have shown that cantharidin (1) is biosynthesized by the male Lytta vesicatoria L. (Meloidae, Coleoptera) from the common terpenoid precursors mevalonate and farnesol (3) . To prove if geraniol (2) is incorporated via farnesol (3) into cantharidin (1) the following geraniols have been synthesized and injected into either larvae or male adult Lytta vesicatoria, partly in a mixture with synthetic 11′, 12-[³H]-farnesol as an internal standard: 2-[¹⁴C]-, 7-[¹⁴C]-, 7′, 8-[¹⁴C]-, 7′, 8-[³H]-geraniol. Unexpectedly, geraniol (2) was not specifically incorporated into cantharidin (1) perhaps due to its higher toxicity or its faster degradation relative to the other precursors before incorporation. The incorporation of U-[¹⁴C]-leucine, U-[¹⁴C]-isoleucine and 1-[¹⁴C]-glucose into cantharidin (1) via their metabolites is evident by degradation studies, whereas 1-[¹⁴C]- and 2-[¹⁴C]-glycine do not serve as precursors for cantharidin (1) .     

Stabilization of plutonium(III) in the Preyssler polyoxometalate

The Na(+) ion encapsulated within the Preyssler heteropolyoxoanion, [NaP5W30O110](14-), was exchanged with Pu(III) under hydrothermal conditions to obtain [Pu(III)P5W30O110](12-) (abbreviated [PuPA](12-)) with hybrid electrochemical properties resulting from the combination of the key redox behaviors of the Pu cation and the P-W-O anion. The electroanalytical chemistry of this two-center, multielectron redox system in a 1 M HCl electrolyte shows that Pu(III) is oxidized to Pu(IV) at the half-wave potential, E(1/2), of +0.960 V versus Ag/AgCl, which is 0.197 V more positive than the corresponding electrode potential for the Pu(III) aqua ion also in 1 M HCl, indicating the stabilization of the trivalent Pu cation by its encapsulation in the Preyssler polyoxometalate (POM). This effect is uncommon in actinide-POM chemistry, wherein electrode potential shifts of the opposite nature (to more negative values), leading to the stabilization of the tetravalent ions by complexation, are renowned. Moreover, in cyclic voltammetry measurements of the Pu(III) aqua ion and [PuPA](12-), the peak currents, i(p), for the one-electron Pu(III)/Pu(IV) processes show different dependencies with the scan rate, nu. The former shows proportionality with nu(1/2), indicating freely diffusing species, whereas the latter shows proportionality with nu, indicating a surface-confined one. The first of the five successive two-electron, W-centered reduction processes in [PuPA](12-) occurs at E(1/2) = -0.117 V versus Ag/AgCl, which is 1.077 V less than the E(1/2) for the Pu(III)/Pu(IV) oxidation, thereby providing an experimental, electrochemical measure of the highest occupied molecular orbital/lowest unoccupied molecular orbital energy gap, which compares well with values previously obtained by density-functional theory, complete active space-self consistent field, and post-Hartree-Fock calculations for a series of M(n+)-exchanged systems, [MPA](n-15) for 1 < or = n < or = 4 (Fernandez, J. A.; Lopez, X.; Bo, C.; de Graff, C.; Baerends, E. J.; Poblet, J. M. J. Am Chem. Soc. 2007, 129, 12244-12253). It was not possible to prepare the Np-exchanged Preyssler anion in the manner of [PuPA](12-), because of the instability of tri- and tetravalent Np to oxidation and the formation of the neptunyl(V) ion, which also could not be exchanged for Na(+).