Synthesis and properties of nano-cadmium oxide and its size-dependent responses by barley plant.

Present study included technological methods that made it possible to synthesize CdO nanoparticles and carry out their qualitative and quantitative diagnostics, confirming the as-prepared CdO nanoparticles (NPs) were spherical and had a size of 25 nm. Then, under the conditions of the model experiment the effect of CdO in macro and nanosized particles on absorption, transformation, and structural and functional changes occurring in cells and tissues of Hordeum vulgare L. (spring barley) during its ontogenesis was analyzed. Different analytical techniques were used to detect the transformation of CdO forms: Fourier-transform infrared spectroscopy (FTIR), Dynamic light scattering (DLS), X-ray fluorescence analysis (XRF), Scanning electron microscopy (SEM-EDXMA and TEM), X-ray diffraction (XRD), and X-ray absorption fine structure, consists of XANES - X-ray absorption near edge structure, and EXAFS - Extended X-ray absorption fine structure. Quantitative differences in the elemental chemical composition of barley root and leaf samples were observed. The predominant root uptake of Cd was revealed. CdO-NPs were found to penetrate deeply into barley plant tissues, where they accumulated and formed new mineral phases such as Cd5(PO4)3Cl and CdSO4 according to XRD analysis. The molecular-structural state of the local Cd environment in plant samples corresponding to Cd-O and Cd-Cd. The toxicity of CdO-NPs was found to significantly affect the morphology of intracellular structures are the main organelles of photosynthesis therefore, destructive changes in them obviously reduce the level of metabolic processes ensuring the growth of plants. This study is an attempt to show results how it is possible to combine some instrumental techniques to characterize and behavior of NPs in complex matrices of living organisms.

Stokes and Anti-Stokes Luminescent Rare-Earth-Doped Tantalum Oxide Nanoparticles.

Doping of nano- and microparticles of oxides with rare earth elements (REEs) is used to fine-tune their structural, optical, and electrochemical properties. On the way to establish the structure-property relationship, we dope tantalum oxide (Ta2O5) particles with REEs to study their effect on the oxide structure and luminescence. Ta2O5 is highly perspective in medicine, catalysis, and optics, but its crystal structure is insufficiently studied. Two synthesis approaches (sol-gel and solvothermal) were used to obtain powders with different textures. Experimental and theoretical studies of amorphous and crystallized tantalum oxide NPs by means of X-ray powder diffraction, Rietveld analysis, EXAFS/XANES spectroscopy, and density functional theory calculations were performed. All samples (doped and undoped) crystallized in orthorhombic phase with no admixtures. It was demonstrated that Ta2O5 is a promising wide-spectrum luminescent material: by combining REEs, both Stokes and anti-Stokes luminescence in the visible region were obtained. By means of optical absorption spectroscopy, it was shown that the prepared samples could be classified as wide band gap semiconductors.

Synthesis, crystal polymorphism and spin crossover behavior of adamantylboron-capped cobalt(II) hexachloroclathrochelate and its transformation into the CoIIICoIICoIII-bis-macrobicyclic derivative.

Fast crystallization of the monoclathrochelate cobalt(II) intracomplex [Co(Cl2Gm)3(BAd)2] (where Cl2Gm2- is a dichloroglyoxime dianion and BAd is an adamantylboron capping group, 1), initially obtained by the direct template condensation of the corresponding chelating α-dioximate and cross-linking ligand synthons on the Co2+ ion as a matrix, from benzene or dichloromethane afforded its structural triclinic and hexagonal polymorphs. Its prolonged recrystallization from dichloromethane under air atmosphere and sunlight irradiation unexpectedly gave the crystals of the CoIIICoIICoIII-trinuclear dodecachloro-bis-clathrochelate intracomplex [[CoIII(Cl2Gm)3(BAd)]2CoII] (2), the molecule of which consists of two macrobicyclic frameworks with encapsulated low-spin (LS) Co3+ ions, which are cross-linked by a µ3-bridging Co2+ ion as a bifunctional Lewis-acidic center. The most plausible pathway of such a 1 → 2 transformation is based on the photoinitiated radical oxidation of dichloromethane with air oxygen giving the reactive species. Cobalt(II) monoclathrochelate 1 was found to undergo a temperature-induced spin crossover (SCO) both in its solutions and in the solid state. In spite of the conformational rigidity of the corresponding quasiaromatic diboron-capped tris-α-dioximate framework, the main parameters of this SCO transition (i.e., its completeness and gradual character) are strongly affected by the nature of the used solvent (in the case of its solutions) and by the structural polymorphism of its crystals (in the solid state). In the latter case, the LS state (S = 1/2) of this complex is more thermally stable and, therefore, the cobalt(II)-centered 1/2 → 3/2 SCO is more gradual than that in solutions.

The Structure Stability of Metal Diffusion Membrane-Filters in the Processes of Hydrogen Absorption/Desorption.

The evolution of a nanostructured state of palladium-lead membrane alloys during their interaction with hydrogen was studied using precision X-ray diffraction with synchrotron radiation (SR) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDXS). The importance of this topic is due to the need and demand for improving the performance characteristics of dense metal diffusion filters for high purity hydrogen separation processes. Palladium-based membrane filters with lead concentrations of 5 and 20 wt.% were prepared via electric arc melting from high purity metals (99.95%). The thickness of the filters was 50 µm. Hydrogenation was carried out from a gas medium at 573 K and the pressure of 16 atm. within 150 min. The focus of the study is on the structural state of diffusion filter membranes depending on the content of the palladium-alloying element-lead-and on analysis of the substructure of alloys before and 5300 h relaxation after hydrogenation is carried out. Specific features of the surface morphology and the structure of the membrane filters depending on the concentration of lead in the alloys are determined. The formation and development of deformation processes in metal systems upon the hydrogenation is shown. The establishment of peculiarities of hydrogen interaction with metals will contribute to obtaining new potentially important characteristics of membrane filters.

Ni/(R2O3,CaO) Nanocomposites Produced by the Exsolution of R1.5Ca0.5NiO4 Nickelates (R = Nd, Sm, Eu): Rare Earth Effect on the Catalytic Performance in the Dry Reforming and Partial Oxidation of Methane.

In order to clarify the role of R2O3 in the metal-oxide catalysts derived from complex oxide precursors, a series of R1.5Ca0.5NiO4 (R = Nd, Sm, Eu) complex oxides was obtained. A significant systematic increase in the orthorhombic distortion of the R1.5Ca0.5NiO4 structure (K2NiF4 type, Cmce) from Nd to Eu correlates with a corresponding decrease in their ionic radii. A reduction of R1.5Ca0.5NiO4 in the Ar/H2 gas mixture at 800 °C causes a formation of dense agglomerates of CaO and R2O3 coated with spherical 25-30 nm particles of Ni metal. The size of metal particles and oxide agglomerates is similar in all Ni/(R2O3,CaO) composites in the study. Their morphology is rather similar to the products of redox exsolution obtained by the partial reduction of complex oxides. All obtained composites demonstrated a significant catalytic activity in the dry reforming (DRM) and partial oxidation (POM) of methane at 700-800 °C. A systematic decrease in the DRM catalytic activity of composites from Nd to Eu could be attributed to the basicity reduction of R2O3 components of the composite catalysts. The maximum CH4 conversion in POM reaction was observed for Ni/(Sm2O3,CaO), while the maximum selectivity was demonstrated by Nd2O3-based composite. The possible reasons for the observed difference are discussed.

Revealing the peculiar local behavior of manganese and cobalt in diffusion-doped calcium orthovanadate Ca3(VO4)2.

Laser Ca3(VO4)2 single crystals (СVO; space group R3c, Z = 21) with crystallochemical formula Ca118Ca218Ca318Ca46(Ca5 + Са5А)3(V118V218V36)O168 grown by the Czochralski method were doped with Мn2O3 (CVO:Мn2O3) and Сo3O4 (CVO:Co3O4) by high-temperature diffusion annealing. Statistical and local structures were comprehensively studied by single-crystal and powder synchrotron X-ray diffraction and conventional single-crystal X-ray diffraction as well as by X-ray absorption spectroscopy for the first time. The presence of Mn(2+δ)+ ions with a mixed formal charge and Co2+ ions in the Ca2 (monocapped trigonal prism), Ca3 (two-capped trigonal prism), and Ca4 (octahedron) sites was revealed by diffraction methods. The tetrahedral coordination and the coordination intermediate between tetrahedral and octahedral were established for Mn(2+δ)+ and Co2+ ions, respectively. A fundamentally different structural behavior of dopant ions (concentration, formal charge, and coordination environment) in the CVO crystals doped with manganese in the form of Mn2O3 during the crystal growth or by high-temperature diffusion annealing was observed. The relationship between characteristic bands in the absorption, fluorescence, and excitation spectra of CVO:Мn2O3 and CVO:Co3O4 samples and transition metals with specific formal charges is discussed.

Change in the Electronic Structure of the Cobalt(II) Ion in a One-Dimensional Polymer with Flexible Linkers Induced by a Structural Phase Transition.

A new 1D-coordination polymer [Co(Piv)2(NH2(CH2)6NH2)]n (1, Piv is Me3CCO2- anion) was obtained, the mononuclear fragments {Co(O2CR)2} within which are linked by µ-bridged molecules of hexamethylenediamine (NH2(CH2)6NH2). For this compound, two different monoclinic C2/c (α-1) and P2/n (ß-1) phases were found at room temperature by single-crystal X-ray diffraction analysis, with a similar structure of chains and their packages in unit cells. The low-temperature phase (γ-1) of crystal 1 at 150 K corresponds to the triclinic space group P-1. As the temperature decreases, the structural phase transition (SPT) in the α-1 and ß-1 crystals is accompanied by an increase in the crystal packing density caused by the rearrangements of both H-bonds and the nearest ligand environment of the cobalt atom ("octahedral CoN2O4 around the metal center at room temperature" → "pseudo-tetrahedral CoN2O2 at 150 K"). The SPT was confirmed by DSC in the temperature range 210-150 K; when heated above 220 K, anomalies in the behavior of the heat flow are observed, which may be associated with the reversibility of SPT; endo effects are observed up to 300 K. The SPT starts below 200 K. At 100 K, a mixture of phases was found in sample 1: 27% α-1 phase, 61% γ-1 phase. In addition, at 100 K, 12% of the new δ-1 phase was detected, which was identified from the diffraction pattern at 260 K upon subsequent heating: the a,b,c-parameters and unit cell volume are close to the structure parameters of γ-1, and the values of the α,ß,γ-angles are significantly different. Further heating leads to a phase transition from δ-1 to α-1, which both coexist at room temperature. According to the DC magnetometry data, during cooling and heating, the χMT(T) curves for 1 form a hysteresis loop with ~110 K, in which the difference in the χMT values reaches 9%. Ab initio calculations of the electronic structure of cobalt(II) in α-1 and γ-1 have been performed. Based on the EPR data at 10 K and the ab initio calculations, the behavior of the χMT(T) curve for 1 was simulated in the temperature range of 2-150 K. It was found that 1 exhibits slow magnetic relaxation in a field of 1000 Oe.

Peculiar Spin-Crossover Behavior in the 2D Polymer K[FeIII(5Cl-thsa)2].

A potassium salt of the N2S2O2-coordination Fe(III) anion K[Fe(5Cl-thsa)2] (1) (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) is synthesized and characterized structurally and magnetically over a wide temperature range. Two polymorphs of salt 1 characterized by the common 2D polymer nature and assigned to the same orthorhombic Pbcn space group have been identified. The molecular structure of the minor polymorph of 1 was solved and refined at 100, 250, and 300 K is shown to correspond to the LS configuration. The dominant polymorph of 1 features K+ cations disordered over a few crystallographic sites, while the minor polymorph includes fully ordered K+ cations. The major polymorph exhibits a complete three-step cooperative spin-crossover transition both in the heating and cooling modes: The first step occurs in a temperature range from 2 to 50 K; the second abrupt hysteretic step occurs from 200 to 250 K with T1/2 = 230 K and a 6 K hysteresis loop. The third gradual step occurs from 250 to 440 K. According to 57Fe Mössbauer, XRPD, and EXAFS data, the spin-crossover transition for the dominant polymorph is quite peculiar. Indeed, the increase in the HS concentration by 57% at the second step does not result in the expected significant increase in the iron(III)-ligand bond lengths. In addition, the final step of the spin conversion (ΔγHS = 26%) is associated with a structural phase transition with a symmetry lowering from the orthorhombic (Pbcn) to the monoclinic (P21/n) space group. This nontrivial phenomenon was investigated in detail by applying magnetization measurements, electron spin resonance, 57Fe Mössbauer spectroscopy, and DFT calculations. These results provide a new platform for understanding the multistep spin-crossover character in the Fe(III) thsa-complexes and related compounds.

Partitioning of uranium in contaminated bottom sediments: The meaning of fractionation.

Sequential extraction tests were used to study partitioning of U in the bottom sediments of two reservoirs that have been used for the temporary storage of nuclear waste at the "Mining and Chemical Combine" (Zheleznogorsk, Krasnoyarsk region, Russia). Various sequential extraction protocols were applied to the bottom sediment samples and the results compared with those obtained for laboratory-prepared simulated samples with different speciation and partitioning, e.g., U(VI) sorbed onto various inorganic minerals and organic matter, as well as uranium oxides. The distributions of uranium in fractions extracted from simulated and actual contaminated samples were compared to shed light on the speciation of U in the bottom sediments. X-ray absorption spectroscopy, X-ray diffraction, and scanning electron microscopy were also used to analyze the partitioning of U in contaminated sediments. We also compared the results obtained using the spectroscopic and microscopic techniques, as well as sequential extraction.

End-to-End Azido-Bridged Lanthanide Chain Complexes (Dy, Er, Gd, and Y) with a Pentadentate Schiff-Base [N3O2] Ligand: Synthesis, Structure, and Magnetism.

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N3)C2H5OH]C2H5OH}n where H2DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N3O2] ligand and Ln = Dy (1), Y0.930Dy0.070 (2), Er (3), Y0.923Er0.077 (4), and Gd (5). X-ray diffraction analysis of 1-5 show that the central lanthanide atoms are eight-coordinated with the N5O3 donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N3- bridges connecting the metal centers into infinite chain. The [LnN5O3] coordination polyhedron can be regarded as a distorted dodecahedron (D2d). AC magnetic measurements revealed that compounds 1-4 show field-induced single-molecule magnet behavior, with estimated energy barriers Ueff ≈ 47-17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln3+ ions mediated by the end-to-end azide bridging groups (J ≈ -0.015 cm-1 for 5). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated (1, 3) and diluted (2, 4) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln3+ ions.

Spin-crossover behavior of neutral iron(iii) complexes with salicylaldehyde thio-, seleno- and semicarbazone ligands: experiment and theoretical analysis.

The iron(iii) complex [Fe(Hsemsal)(semsal)]·3H2O (1) (H2semsal - salicylaldehyde semicarbazone) has been synthesized and characterized by powder and single crystal X-ray diffraction, and magnetic susceptibility measurements. Crystal structure analysis showed that the complex forms neat stacks stabilized by hydrogen-bonding through water molecules and π-π interactions between phenolate rings of ligands. The complex does not exhibit spin-crossover phenomena and remains in the high-spin state down to 2 K. DFT calculations were performed for a series of neutral Fe(iii) complexes, and the influence of the N2S2O2, N2Se2O2 and N2O4 coordination environment on the spin transition in these complexes was traced. The effect of substituents in the benzene ring of salicylaldehyde on the stabilization of the HS or LS states in complexes of this type was analyzed.