Synthesis and characterisation of TlLn(SO4)2·xH2O (Ln=La-Tb)

The compounds TlLn(SO₄)₂·2H₂OLn=La, Ce, Pr, Nd and Tl[Ln(SO₄)₂(H₂O)₃]·H₂OLn=Nd, Sm, Eu, Gd, Tb have been isolated from aqueous solutions of the corresponding sulfates. The dihydrates are all isomorphous and crystallize monoclinic, space groupP2₁/n,Z=4. The compounds which belong to the second type are also isomorphous and crystallize in monoclinic space groupP 2₁/c withZ=4.The dehydration has been studied by thermogravimetry, differential scanning calorimetry and isothermal weight change determination. The dihydrates dehydrate in a single step. For the tetrahydrates the reaction is more complex, however no intermediate phases could be isolated.The unit cell parameters, the dehydration temperatures and the dehydration enthalpies are correlated to the ionic radii ofLn ³⁺.

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Synthese und Charakterisierung von TlLn(SO₄)₂·xH₂O (Ln=La-Tb)

Zusammenfassung Die Verbindungen TlLn(SO₄)₂·2H₂OLn=La, Ce, Pr, Nd und Tl[Ln(SO₄)₂(H₂O)₃]·H₂OLn=Nd, Sm, Eu, Gd, Tb wurden aus wäßrigen Lösungen der entsprechenden Sulfate isoliert. Die Dihydrate sind alle isomorph und kristallisieren monoklin, RaumgruppeP 2₁/n,Z=4. Die Verbindungen des zweiten Typs sind auch isomorph und kristallisieren in der monoklinen RaumgruppeP 2₁/c mitZ=4.Die Dehydration wurde mit TG, DSC und dem isothermalen Gewichtsverlust untersucht. Die Entwässerung der Dihydrate verläuft in einer Stufe, die von Tetrahydraten aber in mehreren Stufen mit keiner isolierbaren Zwischenphase.Die Gitterkonstanten, die Dehydratations-Temperaturen und -Enthalpien wurden mit den Ionenradien vonLn ³⁺ korreliert.

     

The influence of oxygen pressure on phase equilibria in the Ln-Mn-O (Ln = Sm, Tb, Dy, Yb, and Lu) systems

The influence of oxygen pressure on phase equilibria during thermal dissociation in the Ln-Mn-O (Ln = Sm, Tb, Dy, Yb, and Lu) systems was studied by the static method on a vacuum circulation unit with subsequent X-ray analysis of quenched solid phases. The reduction of the double oxides was found to occur according to the reactions LnMn₂O₅ = LnMnO₃ + (1/3)Mn₃O₄ + (1/3)O₂, LnMnO₃ = (1/2)Ln₂O₃ + MnO + (1/4)O₂, for which the temperature dependences of equilibrium oxygen pressure were determined over the temperature range 973–1220 K. The Gibbs energies of dissociation of the double oxides were calculated. Interrelation between the type of lanthanides and the thermal properties of the compounds was analyzed.     

Crystal structure and magnetism of layered Ln2Ca2MnNiO8 (Ln=Pr,Nd, Sm,and Gd) compounds

We report the syntheses, crystal structure, and magnetic properties of a series of distorted K₂NiF₄-type oxides Ln₂Ca₂MnNiO₈ (Ln=Pr, Nd, Sm, and Gd) in which Ln/Ca and Mn/Ni atoms randomly occupy the K and Ni sites respectively. The Ln=La compound does not form. These compounds show systematic distortions from the ideal tetragonal K₂NiF₄ structure (space group I4/mmm) to an orthorhombic structure (space group Pccn) with buckled MO₂ (M=Mn/Ni) layers. The degree of distortion is increased as the size of Ln decreases. Based on the magnetic data and X-ray absorption near edge spectra, we assigned Mn^IV and Ni^II. The Curie–Weiss plots of the high temperature magnetic data suggest strong ferromagnetic interactions probably due to Mn^IV–O–Ni^II linkages, implying local ordering of Mn/Ni ions to form ferromangnetic clusters in the MO₂ layers. At low temperatures below 110–130 K, these compounds show antiferromagnetic behaviors because of Mn^IV–O–Mn^IV and/or Ni^II–O–Ni^II contacts between the ferromagnetic clusters. The Ln=Pr and Nd compounds show additional antiferromagnetic signals that we attribute to the interlayer interactions between the clusters mediated by the Pr³⁺ and Nd³⁺ ions in the interlayer spaces. The present compounds show many parallels with the previously reported Ln₂Sr₂MnNiO₈ compounds.     

Kinetics of the transformation of Ln2O2SO4 into Ln2O2S (Ln = La, Pr, Nd, and Sm) in a hydrogen flow

The kinetic dependences of the yield of Ln₂O₂S (Ln = La, Pr, Nd, and Sm) upon the treatment of Ln₂O₂SO₄ in a hydrogen flow at 950, 1120, and 1170 K are constructed. The plots are approximated by Avrami-Erofeev equations, equations of compressed volume and compressed surface, and Jander’s equation. The correctness of choosing these equations is evaluated using the numerical values of Fisher’s criterion. Images of the particles of Nd₂O₂SO₄ → Nd₂O₂S transformation in the flow are obtained on an Ntegra Aura atomic force probe microscope. A mechanism of the crystal growth of the Nd₂O₂S phase from the nucleation site of the Nd₂O₂SO₄ and Nd₂O₂S phase boundaries is proposed.     

Synthesis, identification and thermal decomposition of double sulfates of La, Ce, Pr or Nd with ethanolammonium

On evaporation at room temperature of an aqueous reaction mixture of Ln(III) sulfate and ethanolammonium sulfate in a molar ratio higher than 1∶16, crystal products with a waxy feel were obtained. They were identified by means of the X-ray powder diffraction patterns and it was concluded that they are isostructural. The results of elemental analysis and the mass losses by TG analysis indicated the formation of double sulfates with general formula: (HOCH₂CH₂NH₃)₄Ln₂(SO₄)5·4.5H₂O (Ln=La, Ce, Pr or Nd) Their thermal decompositions in static atmosphere in the temperature range from ambient up to 1173 K took place in a similar way, and mainly Ln₂O₂SO₄ was obtained as final product. The exception was the Ce compound, which decomposed to CeO₂. The double sulfates decomposed in many not well-differentiated steps. From the mass losses occurring during thermal decomposition, the mode of thermal decomposition was presumed. The X-ray powder diffraction patterns of Ln₂O₂SO₄ (Ln=La, Pr and Nd) show that they are also isostructural.     

Syntheses, crystal structures and vibrational spectra of KLn(SO4)2·H2O (Ln=La, Nd, Sm, Eu, Gd, Dy)

The potassium lanthanide double sulphates KLn(SO₄)₂·H₂O (Ln=La, Nd, Sm, Eu, Gd, Dy) were obtained by evaporation of aqueous reaction mixtures of rare earth (III) sulphates and potassium thiocyanate at 298 K. X-ray single-crystal investigations show that KLn(SO₄)₂·H₂O (Ln=Nd, Sm, Eu, Gd, Dy) crystallise monoclinically (Ln=Sm: P2₁/c, Z=4, a=10.047(1), b=8.4555(1), c=10.349(1) Å, wR2=0.060, R1=0.024, 945 reflections, 125 parameters) while KLa(SO₄)₂·H₂O adopts space group P3₂21 (Z=3, a=7.1490(5), c=13.2439(12) Å, wR2=0.038, R1=0.017, 695 reflections, 65 parameters). The coordination environment of the lanthanide ions in KLn(SO₄)₂·H₂O is different in the case of the Nd/Sm/Gd and the Eu/Dy compounds, respectively. In the first case the Ln atoms are nine-fold coordinated in contrast to the latter where the Ln ions are eight-fold coordinated by oxygen atoms. The vibrational spectra of KLn(SO₄)₂·H₂O and the UV-vis reflection spectra of KEu(SO₄)₂·H₂O and KNd(SO₄)₂·H₂O are also reported.     

Synthesis and Crystal Structure of Commensurate Polymorph of Ln4AlCu2B9O23 (Ln=Lu,Ho) and Refinement of Cu2Al6B4O17

Single crystals of new Cu,Lu(Ho)–alumoborate and known Cu,Al–borate were synthesized through reaction between CuB₂O₄ and LnBO₃ on the Al₂O₃ surface by annealing at 1100 °C. Structure of commensurate modification of Ln₄AlCu₂B₉O₂₃, (Ln = Lu,Ho), sp. gr. , was solved at room temperature. It was found that a low–temperature (110 K) modification possesses incommensurate modulations with modulation vector q =(0, 0, 0.132). The nonaborate block – [B₉O₂₃]^19– – 9[6T+3Δ] forms an isolated unique dense closed anionic unit. This block is terminated by Al–tetrahedrons in the chessboard pattern, resulting in formation of complex alumoborate layer [AlB₉O₂₃]^16–. Apical oxygen of central BO₃ triangle of the nonaborate block seems to be the source of modulations observed in low temperature polymorph. Cationic layers with the Ln and Cu atoms are alternating along c axis with anionic layers. The structure Cu₂Al₆B₄O₁₇, previously studied by the Rietveld method, was corroborated by single crystal data and was compared with LiAl₇B₄O₁₇.     

The thermodynamic properties of Ln2BaO4 (Ln = Sm, Dy, Ho)

The thermodynamic properties of the Ln₂BaO₄ phases (Ln = Dy, Ho, Sm) were studied by the electromotive force method with a fluoride electrolyte (890–1180 K), solution calorimetry in 1.07 N hydrochloric acid at 298.15 K, and differential scanning calorimetry (298–860 K). The experimental data were jointly processed, and the thermodynamic functions of the compounds over the temperature range 298–1200 K were calculated.     

Octanuclear Ni4Ln4 Coordination Aggregates from Schiff Base Anion Supports and Connecting of Two Ni2Ln2 Cubes: Syntheses,Structures, and Magnetic Properties

A family of 3d–4f aggregates have been reported through guiding the dual coordination modes of ligand anion (HL^?) and in situ generated ancillary bridge driven self‐assembly coordination responses toward two different types of metal ions. Reactions of lanthanide(III) nitrate (Ln=Gd, Tb, Dy, Ho and Yb), nickel(II) acetate and phenol‐based ditopic ligand anion of 2‐[{(2‐hydroxypropyl)imino}methyl]‐6‐methoxyphenol (H₂L) in MeCN‐MeOH (3 : 1) mixture and LiOH provided five new octanuclear Ni‐4f coordination aggregates from two Ni₂Ln₂ cubanes. Single‐crystal X‐ray diffraction analysis reveals that all the members of the family are isostructural, with the central core formed from the coupling of two distorted [Ni₂Ln₂O₄] heterometallic cubanes [Ni₂Ln₂(HL)₂(μ₃‐OH)₂(OH)(OAc)₄]⁺ (Ln=Gd ( 1 ), Tb ( 2 ), Dy ( 3 ), Ho ( 4 ) and Yb ( 5 )). Higher coordination demand of 4f ions induced the coupling of the two cubes by (OH)(OAc)₂ bridges. Variable temperature magnetic study reveals weak coupling between the Ni²⁺ and Ln³⁺ ions. For the Tb ( 2 ) and Dy ( 3 ) analogs, the compounds are SMMs without an applied dc field, whereas the Gd ( 1 ) analogue is not an SMM. The observation revealed thus that the anisotropy of the Ln³⁺ ions is central to display the SMM behavior within this structurally intriguing family of compounds.     

An Exploratory Flow Reactor Study of H2S Oxidation at 30–100 Bar

Hydrogen sulfide oxidation experiments were conducted in O₂/N₂ at high pressure (30 and 100 bar) under oxidizing and stoichiometric conditions. Temperatures ranged from 450 to 925 K, with residence times of 3–20 s. Under stoichiometric conditions, the oxidation of H₂S was initiated at 600 K and almost completed at 900 K. Under oxidizing conditions, the onset temperature for reaction was 500–550 K, depending on pressure and residence time, with full oxidization to SO₂ at 550–600 K. Similar results were obtained in quartz and alumina tubes, indicating little influence of surface chemistry. The data were interpreted in terms of a detailed chemical kinetic model. The rate constants for selected reactions, including SH + O₂ ⇄ SO₂ + H, were determined from ab initio calculations. Modeling predictions generally overpredicted the temperature for onset of reaction. Calculations were sensitive to reactions of the comparatively unreactive SH radical. Under stoichiometric conditions, the oxidation rate was mostly controlled by the SH + SH branching ratio to form H₂S + S (promoting reaction) and HSSH (terminating). Further work is desirable on the SH + SH recombination and on subsequent reactions in the S₂ subset of the mechanism. Under oxidizing conditions, a high O₂ concentration (augmented by the high pressure) causes the termolecular reaction SH + O₂ + O₂ → HSO + O₃ to become the major consumption step for SH, according to the model. Consequently, calculations become very sensitive to the rate constant and product channels for the H₂S + O₃ reaction, which are currently not well established.     

Thermodynamic properties of nonsuperconducting Ln2CuO4 (Ln = Nd, Sm, Eu), Ho2Cu2O5 and Ln2BaCuO5 (Ln = Nd, Sm, Eu, Ho, Yb) cuprates

Thermodynamic properties of rare-earth Ln₂CuO₄ (Ln = Nd, Sm, Eu), Ho₂Cu₂O₅ and Ln₂BaCuO₅ (Ln = Nd, Sm, Eu, Ho, Yb) cuprates were determined using the electromotive force method with a fluorine-ion electrolyte in the temperature interval of 1000–1230 K. The thermodynamic data obtained by different experimental methods were compared.     

Kinetic modeling of the CO/H2O/O2/NO/SO2 system: Implications for high‐pressure fall‐off in the SO2 + O(+M) = SO3(+M) reaction

Flow reactor experiments were performed to study moist CO oxidation in the presence of trace quantities of NO (0–400 ppm) and SO₂ (0–1300 ppm) at pressures and temperatures ranging from 0.5–10.0 atm and 950–1040 K, respectively. Reaction profile measurements of CO, CO₂, O₂, NO, NO₂, SO₂, and temperature were used to further develop and validate a detailed chemical kinetic reaction mechanism in a manner consistent with previous studies of the CO/H₂/O₂/NO_X and CO/H₂O/N₂O systems. In particular, the experimental data indicate that the spin‐forbidden dissociation‐recombination reaction between SO₂ and O‐atoms is in the fall‐off regime at pressures above 1 atm. The inclusion of a pressure‐dependent rate constant for this reaction, using a high‐pressure limit determined from modeling the consumption of SO₂ in a N₂O/SO₂/N₂ mixture at 10.0 atm and 1000 K, brings model predictions into much better agreement with experimentally measured CO profiles over the entire pressure range. Kinetic coupling of NO_X and SO_X chemistry via the radical pool significantly reduces the ability of SO₂ to inhibit oxidative processes. Measurements of SO₂ indicate fractional conversions of SO₂ to SO₃ on the order of a few percent, in good agreement with previous measurements at atmospheric pressure. Modeling results suggest that, at low pressures, SO₃ formation occurs primarily through SO₂ + O(+M) = SO₃(+M), but at higher pressures where the fractional conversion of NO to NO₂ increases, SO₃ formation via SO₂ + NO₂ = SO₃ + NO becomes important. For the conditions explored in this study, the primary consumption pathways for SO₃ appear to be SO₃ + HO₂ = HOSO₂ + O₂ and SO₃ + H = SO₂ + OH. Further study of these reactions would increase the confidence with which model predictions of SO₃ can be viewed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 317–339, 2000     

Ln0.5A0.5MnO3 (Ln=Lanthanide,A= Ca,Sr) Perovskites Exhibiting Remarkable Performance in the Thermochemical Generation of CO and H2 from CO2 and H2O

Perovskite oxides of the Ln_0.5A_0.5MnO₃ (Ln=lanthanide, A=Sr, Ca) family have been investigated for the thermochemical splitting of H₂O and CO₂ to produce H₂ and CO respectively. The amounts of O₂ and CO produced strongly depend on the size of the rare earth ions and alkaline earth ions. The manganite with the smallest rare earth possessing the highest distortion and size disorder as well as the smallest tolerance factor, gives out the maximum amount of O₂, and, hence, the maximum amount of CO. Thus, the best results are found with Y_0.5Sr_0.5MnO₃, which possesses the highest distortion and size disorder. Y_0.5Sr_0.5MnO₃ shows remarkable fuel production activity even at the reduction and oxidation temperatures as low as 1200 °C and 900 °C, respectively.     

Organic‐inorganic Hybrid Lanthanide‐Silver Heterometallic Coordination Frameworks Constructed from Oxalate and Sulfate Anion: Syntheses,Structures, and Photoluminescent Properties

The first four examples of organic‐inorganic hybrid lanthanide‐silver heterometallic frameworks, namely, [AgLn(μ₅‐C₂O₄)(SO₄)(H₂O)₂] [Ln = Eu ( 1 ) and Sm ( 2 )] and [AgLn(μ₄‐C₂O₄)_0.5(μ₆‐C₂O₄)_0.5(SO₄)(H₂O)] [Ln = Tb ( 3 ) and Dy ( 4 )] based on oxalate and sulfate anions were synthesized by hydrothermal reactions of lanthanide oxide, silver nitrate, oxalic acid and sulfuric acid. All structures contain ladder‐like inorganic lanthanide sulfato chains, which are further connected together through silver atoms by oxalate anions with different coordination behavior (μ₅‐C₂O₄: 1 and 2 , μ₆‐C₂O₄ mixed μ₄‐C₂O₄: 3 and 4 ) to generate two types of 3D networks. The luminescent properties of these compounds were also studied.     

Mössbauer study of the thermal decomposition of co-precipitated Fe/NH4/2/SO4/2.6H2O and Ni/NH4/2/SO4/2.6H2O

Using Mössbauer spectroscopy, the thermal decomposition products of co-precipitated Fe/NH_4/2/SO_4/2.6H₂O and Ni/NH_4/2/SO_4/2.6H₂O for two hours at various temperatures in open air have been studied and identified. It has been found that NiFe₂O₄, formed at 900 °C and 1100 °C, has been the final product.     

Metastable phase equilibria in the systems K2SO4 + K2B4O7 + H2O and KCl + K2B4O7 + H2O at 308.15 K

Experimental studies on the metastable solubilities and physicochemical properties (density and refractive index) in the ternary systems K₂SO₄ + K₂B₄O₇ + H₂O and KCl + K₂B₄O₇ + H₂O at 308.15 K were determined with the method of isothermal evaporation. According to the experimental results, the phase diagrams of the two ternary systems were plotted. In the phase diagrams, there are both two isotherm evaporation curves, one eutectic point corresponding to K₂SO₄ + K₂B₄O₇ · 4H₂O, and KCl + K₂B₄O₇ · 4H₂O, respectively. Both of the ternary systems belong to a simple eutectic type, and neither double salts nor solid solutions formed in the ternary systems. A comparison of the stable and metastable phase diagrams of the ternary systems K₂SO₄ + K₂B₄O₇ + H₂O and KCl + K₂B₄O₇ + H₂O shows that the supersaturated phenomenon of potassium borate tetrahydrate is significant and easier to appear the metastable behavior.     

Chemiluminescence in the reaction of LnI<Subscript>2</Subscript> (Ln = Dy,Nd) with water

Chemiluminescence (CL) upon the reaction of crystalline LnI₂ (Ln = Dy, Nd) with water was found. The CL emitters are the Ln³⁺* electron-excited ions (Dy³⁺*, λ_max = 470, 570 nm; Nd³⁺*, λ = 700–1200 nm) generated by the electron transfer from the Ln^II ions to the H₂O molecules. The identified reaction products are H₂, dissolved LnI₃, and insoluble LnI(OH)₂ (49–51% and 48–50% yield for DyI₂ and NdI₂, respectively). The treatment of NdI₂ with an H₂O solution in THF gives the NdI₂OH(thf)₂·3H₂O complex and hydrogen. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1890–1893, October, 2007.     

Decomposition of methane on polycrystalline thick films of Ga2O3 investigated by thermal desorption spectroscopy with a mass spectrometer

Methane in air can be detected by the conductivity increase of Ga₂O₃ films. Films (200 μm) of β-Ga₂O₃ were prepared by depositing a suspension of β-Ga₂O₃ powder (Johnson Matthey; 32102; 99,99%) on alumina substrates. The films were exposed to 20 kPa O₂ for 15 min at 934 K. In thermal desorption spectroscopy (TDS, β = 4,6 K/s, UHV conditions) only O₂ occured at temperatures above 934 K. On reduction in 100 Pa H₂ for 5 min at 800 K, only a suboxide, Ga₂O (above 880 K), indicating a destabilisation of the lattice [1], a broad hydrogen peak (440–930 K) and the formation of water (700–900 K) were observed. No Ga₂O₃ and O₂ were found in desorption. At temperatures between 260 K and 934 K the film was exposed to methane (100 Pa, 5 min). For exposure temperatures between 630 K and 934 K, CO, CO₂, H₂, and small amounts of CH₄ and the suboxide Ga₂O appeared in desorption. A reaction scheme for the decomposition of methane is proposed. It includes the adsorption of CH₄, the dissociation of CH₄, the desorption of H₂O and the formation of oxygen vacancies. These vacancies and the adsorbed hydrogen both acting as donors may explain the conductance increase on exposure to methane observed by other authors.     

Rate constants for the reactions of C2H5O,i‐C3H7O,and n‐C3H7O with NO and O2 as a function of temperature

The rate constants of the reactions of ethoxy (C₂H₅O), i‐propoxy (i‐C₃H₇O) and n‐propoxy (n‐C₃H₇O) radicals with O₂ and NO have been measured as a function of temperature. Radicals have been generated by laser photolysis from the appropriate alkyl nitrite and have been detected by laser‐induced fluorescence. The following Arrhenius expressions have been determined: (R₁) C₂H₅O + O₂ → products k₁ = (2.4 ± 0.9) × 10⁻¹⁴ exp(−2.7 ± 1.0 kJmol⁻¹/RT) cm³ s⁻¹ 295K < T < 354K p = 100 Torr (R₂) i‐C₃H₇O + O₂ → products k₂ = (1.6 ± 0.2) × 10⁻¹⁴ exp(−2.2 ± 0.2 kJmol⁻¹/RT) cm³ s⁻¹ 288K < T < 364K p = 50–200 Torr (R₃) n‐C₃H₇O + O₂ → products k₃ = (2.5 ± 0.5) × 10⁻¹⁴ exp(−2.0 ± 0.5 kJmol⁻¹/RT) cm³ s⁻¹ 289K < T < 381K p = 30–100 Torr (R₄) C₂H₅O + NO → products k₄ = (2.0 ± 0.7) × 10⁻¹¹ exp(0.6 ± 0.4 kJmol⁻¹/RT) cm³ s⁻¹ 286K < T < 388K p = 30–500 Torr (R₅) i‐C₃H₇O + NO → products k₅ = (8.9 ± 0.2) × 10⁻¹² exp(3.3 ± 0.5 kJmol⁻¹/RT) cm³ s⁻¹ 286K < T < 389K p = 30–500 Torr (R₆) n‐C₃H₇O + NO → products k₆ = (1.2 ± 0.2) × 10⁻¹¹ exp(2.9 ± 0.4 kJmol⁻¹/RT) cm³s⁻¹ 289K < T < 380K p = 30–100 Torr All reactions have been found independent of total pressure between 30 and 500 Torr within the experimental error. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 860–866, 1999     

H3OLa(SO4)2 · 3 H2O: Ein neues saures Sulfat der Selten‐Erd‐Elemente

H₃OLa(SO₄)₂ · 3 H₂O: A New Acidic Sulfate of the Rare Earth Elements Colorless single crystals of H₃OLa(SO₄)₂ · 3 H₂O have been obtained by the reaction of La₂O₃ and sulfuric acid (80% H₂SO₄) at 150 °C. In the crystal structure (monoclinic, P2₁/c, Z = 4, a = 1119.5(5), b = 693.3(2), c = 1357.4(4) pm, β = 110.94(4)°) La³⁺ is ninefold coordinated by oxygen atoms which belong to five SO₄^– ions and three H₂O molecules. One of sulfate groups acts as a bidentate ligand. Hydrogen bonding is observed with H₂O molecules as donors and acceptors. Furthermore, strong hydrogen bonds are formed between the H₃O⁺ ions and oxygen atoms of the SO₄^2– groups.