Cyclooctatetraenyl-komplexe der frühen übergangsmetalle und lanthanoide: IV. Strukturchemie des anionisichen sandwich-komplexes [Ce(COT)2]−

The cerocene(III) derivatives [Li(THF)₄][Ce(COT)₂] (1) and (THF)₃Na(μ-COT)Ce(COT) (2) have been prepared and characterized structurally by an X-ray diffraction study (COT  η⁸-cycloocta-tetraenyl(2−)). The molecular structures differ significantly, depending on the nature of the alkali metal cation. In the solid state, compound 1 consists of separated ion pairs. In 2 a cyclooctatetraenyl ligand bridges cerium and sodium to give a linear (COT)Ce(μ-COT)Na arrangement.     

Aktivierungsanalise von Luminophoren des Typs K3La1-x-yCexTby(PO4)2

Instrumental Neutron Activation Analysis (INAA) of potassium lanthanum double phosphates of the type K₃SE(PO₄)₂, where lanthanum is partially or completely substituted by cerium and/or terbium, is reported. Several lanthanum and terbium preparates were tested and one of each element was used as a standard, while cerium was based on (NH₄)₂ Ce(NO₃)₆. The phosphates are prepared by solid state reaction (powders) or grown from a flux of K₄P₂O₇ (crystals). It could be shown that the composition of the solid flux grown phosphate mixtures is different from those of the starting mixtures. The content of terbium differs most clearly, while lanthanum gives nearly the expected values. The results demonstrate the occurrence of nonstoichiometric lattices in compounds of this type.     

Inductively Coupled Plasma Synthesis of CeO<Subscript>2</Subscript>-based Powders from Liquid Solutions for SOFC Electrolytes

Doped cerium oxide (CeO₂) based electrolytes are attractive alternative materials to replace the existing yttria-stabilized zirconia (YSZ) used as electrolyte for SOFC (solid oxide fuel cells). Cerium oxide electrolytes offer a similar performance to YSZ electrolytes at a lower cell operating temperature (~600--800 ^°C), therefore reducing thermal stresses and solid state reactions among the cell components.Doped Ce_1-xMe_xO_2-x/2(Me = Gd, Sm or Y) fine \hbox{powders} were synthesized from nitrate salts dissolved in water using a radio frequency inductively coupled plasma reactor. It was demonstrated that the relative concentrations of Ce and dopants fed in the solutions were retained in the synthesized powders. The products were all nano-crystalline with the basic crystal structure of CeO₂ and the crystal size of the products was essentially independent of the dopant used. The particle size distributions obtained were multimodal and in most cases trimodal. The results obtained differ from a previously reported mechanism of particle synthesis from liquid precursors.     

Cerium(IV) Nitrate Complexes With Bidentate Phosphine Oxides

The reactions between ceric ammonium nitrate, (NH₄)₂Ce(NO₃)₆, (CAN) and the bidentate phosphine oxides, 4,5-bis(diphenylphosphine oxide)-9,9-dimethylxanthene (L¹), oxydi-2,1-phenylene bis(diphenylphosphine dioxide) (L²), 1,2-bis(diphenylphosphino)ethane dioxide (L³) and 1,4-bis(diphenylphosphino)butane dioxide, L⁴ have been investigated. The crystal structures of the molecular Ce(NO₃)₄L¹ ( 1 ), and ionic [Ce(NO₃)₃L³₂][NO₃]⋅CHCl₃ ( 3 ), [Ce(NO₃)₃L³₂][NO₃] ( 4 ) and the polymeric [Ce(NO₃)₃L⁴_1.5] [NO₃] ( 5 ) and the cerium(III) complex [Ce(NO₃)₂L¹₂][NO₃] ( 2 ) are reported. The thermal stability of the complexes has been examined by thermogravimetry with the gaseous decomposition products analysed by infrared spectroscopy. Evolution of CO₂ is found for both Ce(III) and Ce(IV) complexes with the later also forming NO₂. The formation of the complexes in solution has been studied by ³¹P NMR spectroscopy and further complexes [Ce(NO₃)₃L¹₂]⁺[NO₃]⁻ and [Ce(NO₃)₂L¹₃]²⁺2[NO₃]⁻ identified in CD₃CN solution. The complex ( 1 ) exists as a single molecular species in solution and is stable in dichloromethane whilst ( 3 ) decomposes on standing in both CD₂Cl₂ and CD₃CN to Ce(III) containing species. Complexes of L² have been identified by solution ³¹P NMR spectroscopy and these decompose in solution to give Ce(NO₃)₃L²₂. This study represents the first structural characterisations of Ce(IV) complexes with bidentate phosphine oxides.     

Preparation of Ammonium Cerium Phosphate via Low-heating Solid State Reaction and Its Catalysis for Benzyl Acetate Synthesis

Ammonium cerium phosphate was prepared with (NH₄)₃PO₄·3H₂O and Ce(SO₄)₂·4H₂O as raw materials and PEG‐400 as surfactant via a solid state reaction at low‐heating temperature. The characterization result of XRD indicates that the molecular formula of the product was (NH₄)₂Ce(PO₄)₂·H₂O. The synthesis of benzyl acetate was carried out with H₂SO₄/ammonium cerium phosphate as catalyst, and uniform experimental design as well as data mining technology was applied to the experiments, in which the effect of the reaction time, the molar ratio of acid to alcohol and the amount of catalyst on the conversion yield of acetic acid were studied. When benzalcohol was 0.10 mol, under the optimal reaction conditions, i.e. reaction time of 174 min, 2.02 of molar ratio of acid to alcohol and 0.5 g of catalyst, the esterification rate of acetic acid was 97.9%. The ammonium cerium phosphate had potential for industry application since it not only was feasible and simple in synthesis technics, but also had good catalysis activity for the synthesis of benzyl acetate.     

Specifics of pyrohydrolytic and solid-phase syntheses of solid solutions in the (MgGa2O4)x(MgFe2O4)1 ? x system

This work demonstrates the possibility of preparing solid solutions in the (MgGa₂O₄) _x (MgFe₂O₄)_{1 − x} system by pyrohydrolytic and solid-phase methods. It is shown that the products obtained have different specific surface areas depending on the ratio between metal nitrates and citric acid. The composition dependence of the unit cell parameter deviates considerably from the Vegard’s rule. The compounds obtained are found to be stable up to 300°C, which makes them candidate materials for electronics.     

Microstructural characteristics of Ce conversion coatings on Cf/Al composite or Ni?P plated Cf/Al composite

The microstructural characteristics of Ce conversion coatings on carbon fiber reinforced Al matrix (Cf/Al) composites and Ce conversion coatings on Ni? P plated Cf/Al composites were studied by SEM, AFM, TEM and XPS. The Ce conversion coating on the Ni? P plated composite does not have obvious microcracks, which can be found easily in Ce conversion coatings. The Ce conversion coating on Ni? P plated composite has a lower surface roughness profile arithmetic mean deviation (R_a) than Ce conversion coating, as seen by AFM. Because of the inhomogeneity of the material surface and the different levels of deposition of Ce conversion coatings at the different sites, nonhomogeneous sites would promote microcrack formation of the Ce conversion coatings. The Cf/Al composite surface has lessuniformity than Ni? P plated composite, leading to more prominent microcracks. Selected area electron diffraction (SAED) patterns of Ce conversion coating could not be indexed nor matched closely to any of the oxides (Ce₂O₃, Ce₇O₁₂, Ce₆O₁₁) or hydroxides (Ce(OH)₃) that are listed in the Powder Diffraction File maintained by Diffraction Data, but for Ce conversion coating on the Ni? P plated composite the data matched closely with that of CeO₂ or Ce₆O₁₁. The XPS results showed that the Ce conversion coating mainly contained both Ce³⁺ and Ce⁴⁺ species, but Ce⁴⁺ species were the dominant oxidation state on Ni? P coating with Ce conversion deposition. Copyright © 2008 John Wiley & Sons, Ltd.     

铈铬比例对CeO2-CrOx复合氧化物催化剂上1,2-二氯乙烷催化氧化性能的影响

采用共沉淀法制备了不同铈铬比例的CeO₂-CrO_x复合氧化物(Ce/Cr 摩尔比分别为9/1、4/1、2/1、1/1、1/2、1/4、1/8)以及单纯的CeO₂和Cr₂O₃, 并研究了各催化剂对1,2-二氯乙烷(DCE)的催化氧化性能. 结果表明,相较于单纯的CeO₂, 不同铈铬比例的复合氧化物催化剂对DCE的催化氧化活性有明显提高, 其中Ce/Cr 摩尔比为2/1的CeO₂-CrO_x复合氧化物上DCE的氧化活性最好, 且只有极微量的含氯等副产物产生; 随着Ce/Cr 摩尔比减小, 对HCl的选择性有下降的趋势. 通过X射线衍射(XRD)、N₂吸附/脱附(BET)、紫外拉曼(UV-Raman)光谱、H₂程序升温还原(H₂-TPR)、NH₃程序升温脱附(NH₃-TPD)等实验技术, 研究了铈铬比例对铈铬复合氧化物的物理化学性质的影响. 结果表明, 适当比例Ce-Cr的复合, 形成了结构较稳定的Ce-Cr-O固溶体, 提高了催化剂活性氧物种的流动性, 催化剂表面酸量及强弱酸比例, 从而有利于DCE的吸附活化, 进一步脱氯降解以及深度氧化.     

Modified Pechini synthesis of Na3Ce(PO4)2 and thermochemistry of its phase transition

Effect of the synthesis conditions of Pechini technique on crystallinity and purity of Na₃Ce(PO₄)₂ compound was investigated. Nano-sized cerium-sodium phosphate obtained when EDTA was used as an additional chelating agent for Ln³⁺. The total enthalpy change of Na₃Ce(PO₄)₂ phase transition was determined as 14.2±0.7 kJ mol⁻¹ for sample synthesized by conventional solid-solid reaction. The phase transition process was confirmed to occur at 1060°C or in temperature range 920–1060°C depending on thermal treatment of powders.     

Thermal behaviour of sulphato and nitrato complexes of cerium(IV)

Four sulphato and nitrato complexes of cerium(IV),viz. (NH₄)₄Ce(SO₄)₄·2H₂O (1), (NH₄)₂Ce(SO₄)₃ (2), (NH₄)₂Ce(NO₃)₆ (3) and Cs₂Ce(NO₃)₆ (4) were studied by simultaneous TG/DTA under various experimental conditions in order to establish their decomposition mechanism and to compare the results with the literature data which have been reviewed. In the case of the ammonium compounds (1, 2 and3) the decompositions are accompanied by changes in the oxidation state of cerium; the presence of Ce(III) and Ce(IV) were studied byex situ magnetic susceptibility and XPS measurements. The crystal structure of (1) was determined as well. It forms monoclinic crystals with space groupP2₁/c; the parameters of the unit cell are:a=12.638(18) Å,b=11.362(10) Å,c=13.607(11) Å, β=110.17(9)°,V=1834.05 ų.     

Sol–gel synthesis and optical behavior of Mg–Ce–O nano-crystallites

The Mg–Ce–O powder are shown to contain periclase-type MgO and/or fluoride-type cerium oxide (CeO₂) depending upon the composition (x) defined by Ce/(Ce + Mg) atomic ratio. Lattice contraction of pariclase phase of MgO (average crystallite size ~8.8 nm) at Ce content of ‘x’ = 0.20 in comparison to pure MgO (crystallite size ~9.5 nm) has been realized due to oxygen vacancy formation. The optical band gap values of CeO₂ varies (3.0–3.2 eV) due to oxygen vacancy formation in CeO₂ phase, crystallite size and/or Ce³⁺/Ce⁴⁺ ratio. Further, the addition of Ce has shown to reduce the physisorption and chemisorption of water significantly as reflected by (1) suppression of related absorption peaks and (2) absence of magnesium hydroxide, Mg(OH)₂, bands in Fourier transform infrared spectra.     

Synthesis of ceria nanosheets on the surface of Ce(NO3)3 solution by interaction with gaseous ammonia

The surfactant-free synthesis of a solid film of ceria was carried out at the air–water interface from an aqueous solution of Ce(NO₃)₃ and gaseous NH₃ as reactants. The synthesized CeO_2?x ? n H₂O film consists of 2D nanocrystals with a fluorite structure. The film can form a planar coating on the surface of a solid substrate or transform into curved fragments upon drying, depending on the synthesis conditions.     

Double sulfates of some rare earths with tetramethylammonium

Double sulfates of rare earths and tetramethylammonium with empirical formula (CH₃)₄NLn(SO₄)₂ · 3H₂O (Ln=Ce, Pr, Nd, Eu, Gd, Tb and Dy) were synthesized and studied by the methods of TG, DTG and DTA in the temperature range from 20 to 500°C, and by X-ray powder diffraction and chemical analysis. Two isostructural groups were obtained: one from Ce to Eu and another from Gd to Dy. It was found that rare earth sulfates are obtained as final products at 500°C. For comparison, TG, DTG and DTA curves of the thermal decomposition of tetramethylammonium sulfate are given.

---

Zusammenfassung Doppelsulfate von Seltenerden und Tetramethylammonium der empirischen Formel (CH₃)₄NLn(SO₄)₂ · 3H₂O mit Ln=Ce, Pr, Nd, Eu, Gd, Tb und Dy wurden synthetisiert und im Temperaturbereich 20–500°C mittels TG, DTG und DTA, weiterhin mittels Röntgenpulverdiffraktion und chemischer Analyse untersucht. Es wurden zwei isostrukturelle Gruppen erhalten, die eine von Ce bis Eu, die andere von Gd bis Dy. Man fand, daß man bei 500°C als Endprodukt die Seltenerdensulfate erhält. Zum Vergleich wurden die TG-, DTG- und DTA-Kurven der thermischen Zersetzung von Tetramethylammoniumsulfat gegeben.

---

---

Financial support by the Research Council of Slovenia is gratefully acknowledged.     

Facile synthesis of 1-(arylimino)naphthalen-2(1H)-ones from anilines and 2-naphthols promoted by NaBr/K2S2O8/CAN

An efficient method has been developed for the synthesis of 1-(arylimino)naphthalen-2(1H)-ones through the cascade reaction of anilines and 2-naphthols promoted by NaBr/K₂S₂O₈/Ce(NH₄)₂(NO₃)₆. Using this protocol, a series of 1-(arylimino)naphthalen-2(1H)-ones was obtained in good to excellent yields (17 examples, 70–92% yields). The reactions may proceed through the following steps: bromination of 2-naphthols by in-situ-generated bromine from NaBr and K₂S₂O₈ to afford 1-bromonaphthalen-2-ols, coupling of 1-bromonaphthalen-2-ols with anilines to afford the corresponding amines, and subsequent oxidation of the amines into the products by Ce(NH₄)₂(NO₃)_6. These newly obtained α-imine ketones have great potentials for synthesis of special optical materials bearing naphthalene moiety.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. XLIX. Reaktionen von Cerium(IV)-acetylacetonat mit Lithium- und Magnesiumorganylen

Contributions to the Chemistry of Organo Transition Metal Compounds. XLIX. Reactions of Cerium(IV) Acetylacetonate with Organolithium and Organomagnesium Compounds Reacting Ce(acac)₄ with lithium organyls RLi (R = CH₃ 1-Nor¹), ((CH₃)₂NCH₂CH₂CH₂) in the molar ratio 1:1 the cerium compound is reduced with formation of Li[Ce(acac)₄]. Using a molar ratio of Ce:Li = 1:4 organocerium complexes of the composition R₃Ce · 3 Li(acac) or Li₃[R₃Ce(acac)₃] are formed. From reactions with excess CH₃Li (Ce: Li = 1:7) Li₃[Ce(CH₃)₆] · 3 Li(acac) could be isolated. All cerium complexes are characterized by elementary analysis, hydrolysis products, i.r. spectra, and molecular weight determination.     

Preparation and characterization of poly(2′-aminomethyl-3,4-ethylenedioxythiophene) by chemical oxidative polymerization

Poly(2′-aminomethyl-3,4-ethylenedioxythiophene) was synthesized by the chemical oxidative polymerization of 2′-aminomethyl-3,4-ethylenedioxythiophene in the presence of different oxidants, such as FeCl₃, Ce(SO₄)₂, (NH₄)₂Ce(NO₃)₆, and (NH₄)₂S₂O₈. The as-formed polymer was investigated by FTIR, UV–Vis, and Raman spectroscopy, fluorescence, thermogravimetry, and X-ray diffraction to determine the structure, photophysical properties, thermal stability, and polymer phase. FTIR and Raman spectra measurements indicated that the formation of macromolecules occurred exclusively via α,α-coupling of thiophene rings. Moreover, polymer obtained in polymerization using Ce(SO₄)₂ as the oxidant displayed superior thermal stability. All the characterizations indicated that FeCl₃ was the more suitable oxidant for oxidative polymerization of the monomer and provided formation of polymer with higher yield.     

Beiträge zur Chemie der Alkylverbindungen von Übergangsmetallen. 52. Darstellung,Charakterisierung und Reaktionen von (C5H5)3Ce · THF und Na[Ce(C5H5)4] · THF

Contributions to the Chemistry of Organo Transition Metal Compounds. 52. Preparation, Characterization, and Reactions of (C₅H₅)₃Ce · THF and Na[Ce(C₅H₅)₄] · THF (C₅H₅)₃ · THF ( I ) was synthesized in a simple manner by reaction of (NH₄)₂[Ce(NO₃)₆] with C₅H₅Na. With excess C₅H₅Na the complex Na[Ce(C₅H₅)₄] · THF ( II ) could be obtained. In addition of cyclovoltammetric and polarographic measurements it was tried without success to transfer I and II into organocerium( IV ) compounds by means of different oxidizing agents. II reacts with I₂ and (C₆H₅)₃CCl forming Na[(C₅H₅)₃CeI] · THF or Na[(C₅H₅)₂CeI₂] · 4 THF and I besides of (C₆H₅)₃CCl respectively. At interaction of I with Co(acac)₃ the cobalticinium salt [(C₅H₅)₂Co][C₅H₅Ce(acac)₃] is formed. The compounds obtained were characterized by elementary analysis, hydrolysis products, magnetic moments, i.r., ¹H-n.m.r. und u.v.-vis spectra, and measurements of electric conductivity.     

Synthesis and dehydration of double oxalates of rare earths(III) with some monovalent metals

The synthesis of double oxalates of rare earths(III) and potassium with empirical formulae K₄Ln₂(C₂O₄)₅·10H₂O (Ln=La, Ce) and KLn(C₂O₄)₂· nH₂O (wheren=4 for Pr-Dy andn=4.5 for Ho-Lu, Y) is described. The compounds obtained were studied by TG, DTG and DTA over the temperature interval 25–500C and by X-ray powder diffraction and chemical analysis. Three structurally different groups were recognized. It was found that either rare earth oxide or basic carbonate (Ln₂O₂·CO₃) and potassium carbonate were obtained as final product at 500C, depending on the rare earth element. The thermal decomposition takes place in two well-resolved stages.     

Thermal decomposition course of Eu(CH3COO)3·4H2O and the reactivity at the gas/solid interface thus established

The thermal decomposition course of europium acetate tetrahydrate (Eu(CH₃COO)₃·4H₂O) was probed on heating up to 1000 °C in a dynamic atmosphere of air by thermogravimetry and differential thermal analysis. The solid- and gas-phase decomposition products were identified by X-ray diffractometry, ex- and in situ infrared spectroscopy and mass spectrometry. Results obtained showed the acetate to dehydrate stepwise at 145-283 °C, and then decompose stepwise to yield eventually cubic-Eu₂O₃ at ≥663 °C encompassing the formation of intermediate oxycarbonate (Eu₂O(CO₃)₂/Eu₂O₂(CO₃) solid products (at 347-466 °C)) and H₂O, (CH₃)₂CO and CO₂ as primary gaseous products. A considerable enhancement of the production of the primary gas phase products at 400-450 °C and the emergence of (CH₃)₂CCH₂, CH₄ and CO molecules in the gas phase are ascribed to reactions occurring at the gas/solid interface at the expense of some of the primary products. These interfacial activities impart application-worthy adsorptive and catalytic functions for the associated solid products.     

Physico-chemical characterization of thermal decomposition course in zinc nitrate-copper nitrate hexahydrates

This study reports experimental investigations by non-isothermal TG/DSC analysis of Zn(NO₃)₂·4H₂O, Cu(NO₃)₂·4H₂O and their mixtures of known compositions in the temperature range 30–1200°C. Solid/liquid transitions in the sealed samples of the hexahydrate salts and their mixtures were also studied by DSC in the temperature range 0–60°C. The mixture with composition 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O showed single melting peak at 29°C. This mixture was chosen for detailed studies. Melting temperature and heat of fusion of single salt hexahydrates and of the mixture were calculated from DSC endotherms. The different stages in the thermal decomposition processes have been established. The intermediate and the final solid products of the thermal decomposition were analyzed by XRD. The scheme and the decomposition temperature depended on the composition of the starting material. The final decomposition products were CuO (monoclinic), Cu₂O (cubic), ZnO (hexagonal) and their mixtures with the defined crystalline structures. Possible influence of the addition of CuCl₂·2H₂O into the mixture 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O and a gel combustion technique of the precursor preparation, on the composition and morphology of the solid decomposition products, were also studied. The gel combustion technique, using citric acid added to a mixture of 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O, was applied in an attempt to obtain mixed Zn/Cu oxides of a particular mole ratio. The morphology of the solid decomposition products was examined by SEM.