In this work, we synthesized two new benzo-18-azacrown-6 ethers bearing picolinate and pyridine pendant arms and studied the copper complexes of these ligands, as well as those of an acetate analog. ...All considered ligands were capable of forming mono- and dinuclear complexes due to their large size and large number of donor sites. Among all forms of complexes, the coordination of cations inside the macrocycle has only been shown for the mononuclear form of the acetate complex, while out-cage coordination has been observed for other forms. Electrochemical studies have shown the instability of the mononuclear form of the complex with the pyridine ligand to the reduction in the range of redox potentials of bioreductants. The stabilities of labeled acetate complexes with "in-cage" coordination of the cation and picolinate with "out-cage" coordination were compared in an excess of serum and superoxide dismutase; while the former turned out to be unstable to transchelation, the latter was stable throughout the experiment. Additional studies in biologically relevant media were performed for the picolinate complex and demonstrated its stability
. The biodistribution of this complex in mice after 6 hours post-injection demonstrates a slow excretion from the body; however, the accumulation is noticeably lower than that of free copper cations.
The reduction of high-active FeAl and CuFeAl composite catalysts was investigated in situ by XRD and XAS in the temperature range between 100 and 600 °C. It was found that the fresh catalysts consist ...of Fe2O3 and Al2O3 phases only. The Al3+ cations partially dissolute in the Fe2O3 lattice. The addition of copper to the Fe-Al catalyst leads to formation of highly dispersed CuO nanoparticles and mixed oxide with a spinel-type crystalline structure similar to that of CuFe2O4. The low-temperature reduction of Cu2+ to Cu0 accelerates the Fe2O3 → Fe3O4 and FeO → Fe0 transformations. In the presence of oxygen we did not observe the reduction of Cu and Fe to the metallic state. This means that the oxidation of CO over FeAl and CuFeAl composite catalysts proceeds via a redox mechanism.
•High-active FeAl and CuFeAl composite catalysts were investigated by XAS and XRD.•Copper leads to increase the catalytic activity of iron based catalysts.•Oxidation of CO over FeAl and CuFeAl catalysts proceeds via redox mechanism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Single crystals of of the warwickites Mn2-xFexBO4 (x=0.3, 0.5, 0.7) have been synthesized.•Crystal and local atomic structure has been studied through X-ray diffraction and X-ray absorption ...spectroscopy.•The Fe-doping was found to enhance the magnetic frustation giving rise to the supression of the long-range magnetic order.
Single crystalline Mn2-xFexBO4 with x=0.3, 0.5, 0.7 grown by the flux method have been studied by means of X-ray diffraction and X-ray absorption spectroscopy at both Mn and Fe K edges. The compounds were found to crystallize in an orthorhombic warwickite structure (sp. gr. Pnam). The lattice parameters change linearly with x thus obeying the Vegard’s law. The Fe3+ substitution for Mn3+ has been deduced from the X-ray absorption near-edge structure (XANES) spectra. Two energy positions of the absorption edges have been observed in Mn K-edge XANES spectra indicating the presence of manganese in two different oxidation states. Extended X-ray absorption fine structure (EXAFS) analysis has shown the reduction of local structural distortions upon Fe substitution. The magnetization data have revealed a spin-glass transition at TSG=11, 14 and 18K for x=0.3, 0.5 and 0.7, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The implantation of 57Fe atoms into refractory metals Mo and Ta was studied by X-ray diffraction, Mössbauer spectroscopy, and EXAFS. When irradiated with 57Fe ions with energy of 1 MeV and fluence of ...5 × 1016 ions/cm2, Fe implantation occurred to a depth of about 600 nm, while creating an extremely strong level of radiation damage with DPA ≥100. Experimental data have confirmed the preservation of the original bcc crystal structure. The localization of 57Fe atoms in the Mo and Ta was studied by Mössbauer spectroscopy and by the EXAFS method in the Fe K-edge region. Both methods give consistent results. In Mo, Fe atoms are predominantly localized in substitutional positions with 1.4 atomic vacancies localized in the first coordinate sphere. Fe atoms in the Ta matrix have a more complex localization. The model spectra for typical atomic configurations of Fe in the Ta were calculated by the density functional theory. Comparison of the experimental spectra with the calculated ones showed that Fe atoms are localized in Ta in several positions, including interstitial and substitutional positions. It is shown that the EXAFS method more accurately determines the configurations of defects caused by irradiation.
•EXAFS method allows more accurate determination of the configuration of radiation defects.•Fe atoms implanted in Mo predominantly occupy the substitution positions.•Fe atoms implanted in Ta occupy the interstitial and substitution positions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The valence states and local structure around Mn atoms in mixed-valence Mn2BO4 have been studied by temperature dependent X-ray powder diffraction (XRPD), X-ray photoelectron (XPS) and Mn K-edge ...X-ray absorption (XAFS) spectroscopies measurements. X-ray absorption near-edge structure (XANES) and XPS have been used to measure the average oxidation state of Mn in bulk and near-surface of the material. The edge position, peak shapes and pre-edge features of Mn K-edge XANES spectra have been discussed. The pronounced temperature dependence of the Debye-Waller (DW) factor corresponding to the MnO coordination shell has been found from the extended x-ray absorption fine structure (EXAFS) analysis and has been associated with variations in the local distortions in MnO6 octahedra and emergence of short-range magnetic correlations at low temperatures. The XRPD measurements have been carried out at 298, 523 and 773 K. The monoclinic symmetry (P21/n) was found to persist up to highest temperature measured. The BVS calculations have revealed large valence difference between two manganese sites that strongly supports the presence of charge ordering up to high temperatures.
•The monoclinic symmetry was found to persist up to 973 K.•The large bond-valence difference between Mn1 and Mn2 sites suggests the presence of the charge ordering up to highest temperature measured.•The DW factor is progressively reduced below 100 K and goes through a minimum at the TN.•The average manganese oxidation state in bulk was found to be Mn(2.55±0.08)+.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Radiation defects arising from the high-dose implantation of
57
Fe
+
ions into matrices of refractory Mo and Ta metals are studied by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy in ...the region of the Fe
K
-edge Fe. The concentration of Fe atoms, which is calculated using the SRIM program, is 2.5 at % at a depth of ≈300 nm. The concentration of radiation-induced defects exceeds 100 dpa. The positions of Fe atoms are determined in the samples after implantation and additional annealing at 700°C. In Mo, Fe atoms are predominantly located in substitution positions in a body-centered cubic (bcc) crystal lattice. An analysis of the EXAFS spectra shows that, on average, 1.4 atomic vacancies are in the first coordination sphere of Fe, which corresponds to a vacancy concentration of about 24 at %. In the Ta matrix, Fe atoms are located in a more complex manner. To analyze the data, model EXAFS spectra are calculated for typical atomic configurations of Fe atoms in a Ta matrix, which form as a result of irradiation. Relaxation of the crystal environment of Fe atoms is taken into account by the density-functional-theory method. Comparison of the experimental spectra with the calculated ones shows that Fe atoms are located in several positions in Ta, including interstitial and substitution positions. Annealing leads to a change in the coordination and partial segregation of Fe atoms. The EXAFS data are consistent with previously published Mössbauer-spectroscopy data. It is demonstrated that the EXAFS method makes it possible to more accurately determine the configurations of defects arising from irradiation.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The redox state of hydrothermal fluids, which form economic deposits of noble metals, varies in wide limits – from oxidized ones typical for porphyry mineralization to reduced, which form ...volcanogenic massive sulfide deposits. Sulfur-bearing species, along with chloride, are the most important ligands that form stable aqueous complexes with Au and determine the concentration of the latter in natural ore-generating fluids. Depending on the oxygen fugacity, in high-temperature fluids (t>300°C) the dominant forms of sulfur are sulfides (H2S, HS−), sulfites (SO2, HSO3−, SO32−), sulfates (HSO4−, SO42−), and the radical species (S2−, S3−). Here we report an investigation of Au complexation in high-temperature sulfide-bearing fluids of contrasting redox states. The solubility of Au was measured in a relatively oxidized sulfide fluid (H2S/SO42− buffer controls the redox state) at 450°C, 1000bar, and compared with the Au solubility in the “reduced” sulfide systems (H2S/HS− predominate) reported in the literature. The measured values of the Au solubility matches best the model of the formation of Au(HS)2− at near-neutral to weakly acidic pH, and AuHS° in acidic solutions. The solubility constants have been determined for the reactionsAucr+H2S°aq+HS−=AuHS2−+0.5H2glogKAuHS2−=−0.9±0.1,Aucr+H2S°aq=AuHS°aq+0.5H2glogKAuHS=−6.5±0.1.
The average value of log KAu(HS)2−=−1.3±0.5 was calculated for 450°C (P=500–1500bar) using all the available Au solubility constants obtained in both “reduced” and “oxidized” sulfide systems. The local atomic environment and electronic structure of Au in high-temperature hydrothermal fluids have been studied using X-ray absorption spectroscopy (XAS) in high energy resolution fluorescence detection (HERFD) mode in combination with ab initio molecular dynamics (AIMD) and Reverse Monte Carlo (RMC) simulations. Interpretation of Au L3-edge extended X-ray absorption fine structure (EXAFS) spectra showed that, independently of the redox (sulfide or sulfide/sulfate systems) and PT – conditions (350–450°C, 500bar) two S atoms are located in the first coordination sphere of Au at 2.29±0.02Å. Comparison of the experimental spectra with those simulated by means of AIMD revealed that EXAFS spectroscopy is not sensitive to the presence of light atoms like S in the distant coordination spheres of Au. However, theoretical calculations indicated that the shape of Au L3-edge X-ray absorption near edge structure spectra (HERFD-XANES) depends upon the composition of the distant coordination spheres and, therefore, can be used to discriminate between Au(HS)2−, Au-(HS)-S3− and, probably, other complexes with distant-coordination-sphere anions. Experimental Au L3-edge HERFD-XANES spectra are identical for all studied redox- and PT-parameters. These results allowed us to conclude that Au(HS)2− complex predominates Au speciation in weakly acidic to weakly alkaline pH independently from the redox state of the fluid. Besides that, the EXAFS spectra analysis demonstrated that the formation of mixed Au-HS-Cl complex can be neglected. Due to increase of the concentration of S species in intermediate oxidation states, with increasing pressure (to n⋅kbar) or decreasing temperature (to <300°C), formation of the Au-HS complexes can be accompanied by the formation of other species with (hydro) sulfite, thiosulfate, (hydro) polysulfide, and sulfur radicals, which would enhance the hydrothermal Au mobility. Stability of these complexes needs further experimental and theoretical examination.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Azomethines were synthesized from 2,4,6-trimethylaniline, salicylaldehyde, and its 3(5)-halogen derivatives, as well as their complexes with zinc(II) (ZnL
2
). The structure and composition of the ...compounds were determined by elemental analysis, IR,
1
H NMR, and X-ray spectroscopy. The ZnL
2
complexes have a tetrahedral structure. The photoluminescent properties of azomethines and their zinc complexes in methylene chloride solutions and in solid state have been studied. The photoluminescence quantum yields of azomethines lie in the range 4.66–12.16%; for zinc complexes they decrease to 0.45–2.02%. The average photoluminescence lifetimes for azomethines and their complexes range from 2.00 to 2.87 ns. Azomethine, obtained from 2,4,6-trimethylaniline and dichlorosalicylic aldehyde, and its complex with zinc have significant protistocidal activity.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A heterometallic phenylsilsesquioxane (PhSiO1,5)22(CoO)3(NaO0.5)6⋅(EtOH)6⋅(H2O) 1 cage architecture of CoII ions in a triangular topology exhibits a slow dynamic behavior in its magnetization, ...induced by the freezing of the spins of individual molecules.
A cobalt(II) phenylsilsesquioxane (PhSiO1,5)22(CoO)3(NaO0.5)6⋅(EtOH)6⋅(H2O) in a triangular topology exhibits a slow dynamic behavior in its magnetization, induced by the freezing of the spins of individual molecules.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Complexing of organic ligands with actinides plays a key role in the processes of spent nuclear fuel reprocessing in the final stages of the nuclear fuel cycle. N,O-Donor ligands based on ...phenanthroline diamides are promising for group isolation and separation of actinides in hydrometallurgical approaches that are alternative to the PUREX process (such as the GANEX process). Understanding of the specific features of actinide ions complexing in an organic solvent may explain the mechanisms of extraction and be useful to find an “ideal” extractant for uranium extraction. Specific features of metal coordination in the presence of perchlorate anion have been studied by the example of a UO
2
(ClO
4
)
2
complex with pyrrolidine-substituted 1,10-phenanthroline-diamide in an organic solvent, and the structure of the complex compound has been compared with that for a similar compound with nitrate anion as a counter ion.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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