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The influence of Yb3+ cations substitution for Pr3+ on the structure and catalytic activity of (Pr1−xYbx)2Zr2O7 powders synthesized via coprecipitation followed by calcination is studied using a combination of long- (s-XRD), medium- (Raman, FT-IR, and SEM-EDS) and short-range (XAFS) sensitive methods, as well as adsorption and catalytic techniques. It is established that chemical composition and calcination temperature are the two major factors that govern the phase composition, crystallographic, and local-structure parameters of these polycrystalline materials. The crystallographic and local-structure parameters of (Pr1−xYbx)2Zr2O7 samples prepared at 1400 °C/3 h demonstrate a tight correlation with their catalytic activity towards propane cracking. The progressive replacement of Pr3+ with Yb3+ cations gives rise to an increase in the catalytic activity. A mechanism of the catalytic cracking of propane is proposed, which considers the geometrical match between the metal–oxygen (Pr–O, Yb–O, and Zr–O) bond lengths within the active sites and the size of adsorbed propane molecule to be the decisive factor governing the reaction route. [ABSTRACT FROM AUTHOR]

The effect of synthesis conditions on the features of the long- and short-range order of Ln 2 (WO 4 ) 3 (Ln = Gd, Dy, Ho, Yb) powders synthesized via coprecipitation of salts has been studied by a complex of physico-chemical techniques including synchrotron X-ray powder diffraction, X-ray absorption spectroscopy, Raman and infrared spectroscopy, and simultaneous thermal analysis. It was found that crystallization of amorphous precursors begins at 600 °C/3 h and leads to the formation of the monoclinic structure with sp. gr. C12/c1(15) for Ln 2 (WO 4 ) 3 (Ln = Gd, Dy) and with sp. gr. P12 1 /a1(14) for Ln = Yb, whereas crystallization of Ho precursor requires even higher temperature. After annealing at 1000 °C, the P12 1 /a1(14) phase becomes the dominant phase component for all heavy lanthanoid types except for Ln = Gd. It was shown that the Ln (Ln = Dy, Ho, and Yb) tungstates with the P12 1 /a1(14) monoclinic structure correspond to trihydrates Ln 2 (WO 4 ) 3 ·3H 2 O formed due to a rapid spontaneous hydration under ambient conditions. It was concluded that the proneness to hydration is due to a specific structure of the P12 1 /a1(14) phase with large voids available to water molecules. Modifications in the local structure of Ln-O coordination shell accompanying the structure type change and hydration are monitored using EXAFS spectroscopy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The local environment of Mo6+ ions in the structures of scheelite-type crystals (space group I41/a) with the initial compositions (Na1/2Gd1/2)MoO4 (NGM 1:1) and (Na2/7Gd4/7□1/7)MoO4 (NGM 1:2; □ - vacancies) was determined by X-ray absorption spectroscopy (XAS) for the first time. Different coordination environments of Na1+ and Gd3+ ions caused primarily by the difference in their formal charges have been established based on the comparison of Mo–Gd and Mo–Na interatomic distances. According to resent results and structural data known for the (Na1-хREx)MO4 crystals (RE3+ = rare-earth cations), the character of distribution of different Na1+ and RE3+ polyhedra over NGM crystal structures is influenced by the sizes and electronegativities of Na1+, RE3+, and М6+ (M6+ = Mo, W) ions, the Na1+:RE3+ ratio, and vacancies in the M site. Disordered distribution of Na1+ and RE3+ polyhedra in NGM occurs without changing the symmetry of crystals (space group I41/a) and ordered one is accompanied by reduction of crystal symmetry. [ABSTRACT FROM AUTHOR]

Bismuth germanate Bi4Ge3O12 single crystals doped with 0.1 and 1.0 wt% Dy2O3 have been successfully grown by the Czochralski method. The actual compositions of the Dy3+-doped Bi4Ge3O12 crystals have been refined for the first time using single-crystal and synchrotron powder X-ray diffraction. Different local structural behavior of the Dy3+ and Bi3+ ions in the Bi4Ge3O12 crystal matrix depending on the initial Dy3+ content has been revealed by X-ray absorption spectroscopy. In the crystal with the refined composition (Bi3.996(11)Dy0.004)Ge3O12 (0.1 wt% Dy2O3), the octahedron Dy3+O7 with a split vertex and vacancy octahedron Bi3+O5 are formed in adjacent octahedra. In the crystal with the refined composition (Bi3.952(47)Dy0.048)Ge3O12 (1.0 wt% Dy2O3), the semi-octahedron Dy3+O5 and distorted octahedron Bi3+O6 are realized. A character of distribution of the residual electron density showed a probable decrease in the symmetry of Dy3+-doped Bi4Ge3O12 crystals that limits the possible maximum Dy3+ content in the Bi4Ge3O12 crystal matrix. Noticeable fluctuations were not revealed in the absorption and luminescence spectra of Dy3+-doped Bi4Ge3O12 crystals. [ABSTRACT FROM AUTHOR]

This article presents a crystal chemical analysis, generalization, and systematization of structural characteristics of metal-organic polymers MIL-53(M3+) with M = Al, Cr, Ga, and Fe. The division of the MIL-53(M3+) structures into a morphotropic series was performed, which made it possible to predict the formation of new compounds or solid solutions with the corresponding composition and structure. The change in the symmetry of MIL-53(M3+) and the causes of polymorphs formation are explained on the basis of crystal chemical rules. The efficiency of the revealed regularities in the structural characteristics of the MIL-53(M3+) phases were experimentally confirmed for MIL-53(Fe) and composite MIL-53(Fe)/GO (GO-graphene oxide) by several methods (powder X-ray, X-ray absorption, and photoelectron spectroscopy). For the first time, different coordination numbers (CN) (CNFe = 4.9 for MIL-53(Fe)—two types of coordination polyhedra with CNFe = 6 and CNFe = 4; CNFe = 4 for MIL-53 (Fe3+)/GO) and the formal charges (FC) of iron ions (variable FC of Fe (2+δ)+ in MIL-53(Fe3+) and Fe2+ in MIL-53(Fe3+)/GO) were found. These experimental data explain the higher photocatalytic activity of MIL-53(Fe3+)/GO in photo-Fenton reactions—RR195 decomposition. [ABSTRACT FROM AUTHOR]

A series of oxidative treatments of PdIn-supported intermetallic nanoparticles at different temperatures were performed. The bulk and surface structure of catalyst during phase transformation was investigated by bulk- and surface-sensitive techniques (in situ XAFS, DRIFTS of adsorbed CO). It was found that comparison of palladium and indium fractions in bulk and on the surface suggests the formation of a «core-shell» structure. According to obtained results, the core consists of In-depleted intermetallic compound or inhomogeneous bimetallic phase with the inner core of metallic Pd, when a mixture of indium oxide, metallic palladium and small part of PdIn is present on the surface. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Nanocomposites based on nickel sulfate hexahydrate α-NiSO 4 ·6H 2 O (NSH) with titanium (IV) oxide introduced in the form of nanoparticles (Hombifine N: anatase; Degussa P25: 85 % anatase + 15 % rutile; η-phase: 86 % η - phase + 14 % anatase, NSH:Ti(1)) or sols (NSH:Ti(2)) are synthesized for the first time. X-ray diffraction study reveals a single-phase nature of samples, the full occupancy of all crystallographic sites in the NSH:Ti(1) structures, and the presence of Ti4+ ions in interstitial sites near the vacant Ni site in the NSH:Ti(2) structures. A crystallization of the nanosized η-phase of the composition TiO 2- x × m H 2 O directly in the NSH:Ti(1) crystalline matrix with the formation of TiO 2 with the rutile structure, facilitated by the structural-geometric correspondence of 2D projections of NSH and rutile, is observed for the first time. The presence of TiO 2 in the interblock space of NSH:Ti(1) crystals affects the unit cell parameters due to the induced stresses, which is practically not described in the literature. The intensity of SHG signals of NSH:Ti varies depending on both the prehistory of TiO 2 samples and the crystal state, single-crystal or powdered, of the object under study: the highest values were observed for the NSH:Ti(2) powder with the lowest content of titanium ions. The UV–VIS study reveals similar absorption and transmission bands, but with little difference in band width and intensity, for NSH, NSH:Ti(1) and NSH:Ti(2), which can be perspective for UV filters operating in the solar-blind range. • Nanocomposites based on NiSO 4 ·6H 2 O with TiO 2 nanoparticles or sols are synthesized. • The presence of Ti4+ ions in interstitial sites near the vacant Ni site is found. • Rutile structure with Ti4+ octahedra is formed in the interblock space of NSH. • Intensity of SHG signals varies depending on prehistory of TiO 2 samples. • NSH:Ti possesses promising spectroscopic properties for solar-blind UV filters. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ca 3 (VO 4) 2 crystals doped with 0.1 and 1.0 wt.%Mn were grown by Czochralski method. • Crystals were first studied by single-crystal X-ray diffraction and EXAFS/XANES. • The presence of Mn3+ in several Ca2+ sites and vacancies in V5+ sites were found. • Mn3+ form elongated octahedron (tetragonal bipyramid) typical for Jahn-Teller ions. • Optical spectroscopy showed the presence of Mn3+ and low amounts of Mn2+ and Mn5+. Calcium orthovanadate Ca 3 (VO 4) 2 (CVO) is an efficient media for laser applications. Czochralski-grown green CVO single crystals doped with over-stoichiometric 0.1 (CVO:0.1Mn) and 1.0 wt.%Mn (CVO:1.0Mn) were studied by X-ray diffraction and X-ray absorption spectroscopy for the first time. In the CVO:1.0Mn, an occurrence of Mn3+ in Ca3 (two-capped trigonal prism), Ca4 (distorted octahedron), and defective Ca5 and Ca5 A (highly-distorted octahedron) sites and vacancies in V2 and V3 sites (distorted tetrahedra) were revealed. In the CVO:0.1Mn, a presence of Mn3+ in Ca3 and Ca5 A sites and vacancies in V2 site were found. In the CVO, the Mn3+ form elongated octahedra (tetragonal bipyramid; coordination number, 4 + 2) typical for the Jahn-Teller ions. Models for the rearrangement of Ca3 and Ca4 polyhedra into a tetragonal bipyramid are proposed. Along with the Mn3+, the Mn2+ and Mn5+ ions were observed by optical spectroscopy in CVO:0.1Mn (predominantly Mn2+ ions) and CVO:1.0Mn (only Mn5+ ions). [ABSTRACT FROM AUTHOR]

Pure and Tm3+-doped Ca 3 (VO 4) 2 crystals (CVO and CVO:Tm) were grown by the Czochralski method. Activator ions were introduced in the form of Tm 2 O 3 (0.5 and 1.0 wt%) over CVO stoichiometry. The single-crystal X-ray diffraction analysis revealed for the first time the actual crystal compositions with a splitting of one Ca5 site into two, Ca5 and Ca5 A , defective sites and a partial occurrence of Tm3+ ions in two, Ca3 and Ca4, sites. X-ray absorption spectroscopy showed that the Tm3+ ions have octahedral coordination with an additional oxygen atom (coordination number, 6 + 1) and the V5+ ions have tetrahedral coordination (coordination number, 4). The structure of CVO:Tm crystals is proposed based on the local structure of Tm3+ ions, taking into account their structural organization in Tm 2 O 3 and structural features of the CVO crystal matrix. Spectral-luminescent properties of CVO:1.0 wt%Tm crystal are consistent with structural results obtained: two pronounced peaks at λ = 470.5 and 473.5 nm in the absorption spectra (77 K), two different fluorescence spectra for different excitation wavelengths, and two components with significantly different lifetimes (1380 and 370 μs) in the decay curves indicate the presence of two different Tm3+ optical centers in the Ca 3 (VO 4) 2 crystal with excellent spectroscopic properties. • Pure and Tm-doped Ca 3 (VO 4) 2 crystals were grown by the Czochralski method. • X-ray diffraction revealed a splitting of Ca5 site into two defective sites. • The Tm3+ ions partially occupy two, Ca3 and Ca4, crystallographic sites. • The Tm3+ ions have octahedral coordination with an additional oxygen atom. • The Tm-doped Ca 3 (VO 4) 2 demonstrate excellent spectral-luminescent properties. [ABSTRACT FROM AUTHOR]

The crystal and local structures of Czochralski-grown calcium orthovanadate (Ca 3 (VO 4 ) 2 ) single crystals doped with over-stoichiometric 0.05 wt % Mn 2 O 3 (CVO:0.05Mn) and annealed under different conditions are studied by single-crystal conventional and synchrotron X-ray diffraction, X-ray absorption spectroscopy, and electron paramagnetic resonance for the first time. Bottom (annealing in air) and top (annealing in air and in vacuum) parts of the CVO:0.05Mn crystal differ in the manganese content (higher in the bottom part), formal charge (Mn 4+ and Mn (3+δ)+ , respectively), and color (orange bottom part; light orange and yellow top parts annealed in air and vacuum, respectively). Manganese ions are located in one (Ca3, distorted two-capped trigonal prism) of five crystallographic Ca sites and have octahedral coordination, which is consistent with crystal-chemical properties of transition-metal ions. The presence of vacancies in one of three V sites is revealed. Formal charge 5+ for vanadium ions is confirmed by X-ray photoelectron spectroscopy. Different colors of CVO:Mn crystals and different formal charges of manganese are explained depending on the growth and post-growth treatment conditions.

The reaction of Pd 3 (OOCMe) 6 with indium(III) and gallium(III) acetates was studied to prepare new Pd II -based heterometallic carboxylate complexes with group 13 metals. The heterometallic palladium(II)-indium(III) acetate-bridged complexes Pd(OOCMe) 4 In(OOCMe) (1) and Pd(OOCMe) 4 In(OOCMe)·MeCOOH (1a) were synthesized and structurally characterized with X-ray crystallography and extended X-ray absorption fine structure in the solid state and solution. A similar Pd-Ga heterometallic complex formed by the reaction of Pd 3 (OOCMe) 6 with gallium(III) acetate in a dilute acetic acid solution, as evidenced by atmospheric pressure chemical ionization mass and UV-vis spectrometry, was unstable at higher concentrations and in the solid state. Complex 1 catalyzes the liquid-phase-selective phenylacetylene and styrene hydrogenation (1 atm of H 2 at 20 °C) in acetic acid, ethyl acetate, and N, N-dimethylformamide solutions, while no Pd metal was formed until alkyne and alkene hydrogenation ceased.