Microstructure and electrical properties of IrO2 prepared by thermal decomposition of IrCl3·x H2O: Role played by the conditions of thermal treatment

Some features of the thermal decomposition of IrCl₃·3 H₂O in an oxygen atmosphere are presented. The formation of IrO₂ phases has been followed by X-ray diffractometry, and the onset of definite reflections has been documented for samples pyrolyzed at 350° C, although moderate weight losses are observed by thermogravimetry at this temperature. The effect of the thermal history of iridium oxide coatings on their structure has been studied by means of electrical resistance measurements. An explanation of the results has been attempted in terms of impurity segregation to the oxide grain boundaries.     

Synthesis and electrochemical properties of sulfur doped-LixMnO2−ySy materials for lithium secondary batteries

Sulfur doped lithium manganese oxides (Li_xMnO_2−yS_y) were prepared by ion exchange of sodium for lithium in Na_xMnO_2−yS_y precursors obtained by a sol–gel method. These materials had the nano-crystallite size, which was composed of grain size of about 100–200 nm. Especially, Li_0.56MnO_1.98S_0.02 delivered the initial discharge capacity of 170 mAh g⁻¹ and gradually increased the discharge capacity of 220 mAh g⁻¹ until 50 cycles. Moreover, it showed an excellent cycling behavior, although its original structure transformed into the spinel phase during cycling.     

Synthesis and crystal structure of the lithium perrhenate monohydrate LiReO4·H2O

A new monohydrate of lithium perrhenate LiReO₄·H₂O was prepared by dehydration of LiReO₄·1.5H₂O at room temperature. The single crystals of LiReO₄·H₂O were obtained by crystallisation from the isoamyl acetate solution of LiReO₄·1.5H₂O. The structure of monohydrate (a=5.6674(4), b=10.771(1), c=7.4738(7) Å, β=102.422(7)°, R₁=0.0414, space group P2₁/a, Z=4) is built up from LiO₃(H₂O)₂ trigonal bipyramids and ReO₄ tetrahedra sharing common edges and corners inside the layers. The layers are connected together by hydrogen bonds. The relationships between the structures of sesquihydrate, monohydrate and anhydrous LiReO₄ are discussed.     

Effects of oxygen vacancy on the electrochemical properties of γ-V2O5 as cathode material for lithium-ion batteries: a first-principle study

Generating oxygen vacancies is an effective way to improve the lithium-ion storage performance of V₂O₅. However, the mechanism has not been theoretically investigated. In this study, first-principle calculations were performed to study the effect of oxygen vacancy on electrochemical properties of γ-V₂O₅ as cathode material for lithium-ion batteries. γ-V₂O₅ with oxygen vacancy mole fraction of 1.67% shows an open circuit voltage about 0.1 V lower than that of the perfect γ-V₂O₅. Oxygen vacancies generates gap states, which is beneficial to the electronic conductivity of γ-V₂O₅ and γ-LiV₂O₅. In addition, the activation energies for lithium-ion diffusion along [010] in both γ-V₂O₅ and γ-LiV₂O₅ are increased by oxygen vacancy, which might lead to the decrease of diffusion coefficient. Our results will provide guidance for further improving the lithium-ion storage performance of γ-V₂O₅.

     

Theoretical studies of the g factors and local structures of the Ni3+ centers in Na2Zn(SO4)2·4H2O and K2Zn(SO4)2·6H2O crystals

The local structures and the g factors g_i (i = x, y, z) for Ni³⁺ centers in Na₂Zn(SO₄)₂·4H₂O (DPPH) and K₂Zn(SO₄)₂·6H₂O (PHZS) crystals are theoretically studied by using the perturbation formulas of the g factors for a 3d⁷ ion with low spin (S = 1/2) in orthorhombically compressed octahedra. In these formulas, the contributions to g factors from both the spin-orbit coupling interactions of the central ion and ligands are taken into account, and the required crystal-field parameters are estimated from the superposition model and the local geometry of the systems. Based on the calculations, the Ni-O bonds are found to suffer the axial compression δz (or Δz) of about 0.111 Å (or 0.036 Å) along the z-axis for Ni³⁺ centers in DPPH (or PHZS) crystals. Meanwhile, the Ni-O bonds may experience additional planar bond length variation δx (≈0.015 Å) along x- and y-axes for the orthorhombic Ni³⁺ center in DPPH. The theoretical g factors agree well with the experimental data. The obtained local structural parameters for both Ni³⁺ centers are discussed.     

Preparation of 2CaO·3B2O3·H2O nanomaterials and evaluation of their flame retardant properties by a thermal analysis method

Different morphologies of calcium borate 2CaO·3B₂O₃·H₂O, nanoribbon, bundle-like nanostructure and fan-shaped non-nanostructure, have been prepared under hydrothermal conditions, which were characterized by XRD, FT-IR, TGA and SEM. Their flame retardant properties to the polypropylene were investigated by thermal analysis method (including TG, DSC and non-isothermal decomposition kinetics) and oxygen index method. With the decrease in TG mass loss, the increase in heat absorption for DSC in N₂ atmosphere, the increase in LOI values, and the increase in apparent activation energy E_a, the flame retardant properties of prepared 2CaO·3B₂O₃·H₂O samples increased gradually from non-nanostructure to bundle-like nanostructure and then to nanoribbon. This trend may be ascribed to their sizes being decreased accordingly. The flame retarding mechanism has been proposed. The mechanical property of polypropylene/2CaO·3B₂O₃·H₂O composite material has also been evaluated. It can be predicted that 2CaO·3B₂O₃·H₂O nanoribbon could serve as an excellent flame retardant.

     

Syntheses and structures of p-HOOCC6F4COOH · H2O (H2L · H2O) and luminescent coordination polymers [Tb2(H2O)4(L)3 · 2H2O] n and Tb2(Phen)2(L)3 · 2H2O

Compounds p-HOOCC₆F₄COOH · H₂O (H₂L · H₂O), [Tb₂(H₂O)₄(L)₃ · 2H₂O] _n (I), and Tb₂(Phen)₂(L)₃ · 2H₂O (II) are synthesized. According to the X-ray structure analysis data, the crystal structure of H₂L · H₂O is built of centrosymmetric molecules H₂L and molecules of water of crystallization. The crystal structure of compound I is built of layers of coordination 2D polymer [Tb₂(H₂O)₄(L)₃] _n and molecules of water of crystallization. The ligands are the L^2? anions performing both the tetradentate bridging and pentadentate bridging-chelating functions. The coordination polyhedron TbO₉ is a distorted three-capped trigonal prism. Acid H₂L manifests photoluminescence in the UV region (??_max = 368 nm). Compounds I and II have the green luminescence characteristic of the Tb³⁺ ions, and the band with ??_max = 545 nm (transition ⁵ D ₄?? ⁷ F ₅) is maximum in intensity. The photoluminescence intensity of compound II is higher than that for compound I.     

The layer crystal structure of [In2(C2O4)3(H2O)3]·7H2O and microstructure of nanocrystalline In2O3 obtained from thermal decomposition

A new indium oxalate, [In₂(C₂O₄)₃(H₂O)₃]·7H₂O, with a layered structure has been synthesised from precipitation methods at room temperature. It crystallises with a monoclinic symmetry, space group P2₁/c (No. 14), a=8.7456(1) Å, b=11.1479(2) Å, c=21.9376(4) Å, β=112.1(1)°, V=1979.98(6) ų and Z=4. The structure is built from neutral [In₂(C₂O₄)₃(H₂O)₃] corrugated layers, between which water molecules are intercalated. The layers are built from chains with two different sequences of indium atoms and bichelating oxalate groups. Two independent indium atoms are present in the structure with two coordination polyhedra, i.e., InO₈ as a distorted square-based antiprism and InO₇ as a nearly regular pentagonal-based bipyramid. The thermal decomposition has been studied in situ by temperature dependent X-ray diffraction and thermogravimety. The final product is nanocrystalline indium oxide. The microstructure of the oxide has been characterised with both the Voigt/Langford method based on the integral breadth and the whole pattern fitting approach. The size of the isotropic crystallites increases from 322 to 924 Å, while microstrains decrease, in the annealing temperature range 500–750 °C.     

The thermal dehydration and decomposition of Ba[Cu(C2O4)2(H2O)]·5H2O

The thermal behaviour of Ba[Cu(C₂O₄)₂(H₂O)]·5H₂O in N₂ and in O₂ has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively low temperatures (about 80°C), but continues until the onset of the decomposition (about 280°C). The decomposition takes place in two major stages (onsets 280 and 390°C). The mass of the intermediate after the first stage corresponded to the formation of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The enthalpy for the dehydration was found to be 311±30 kJ mol^–1 (or 52±5 kJ (mol of H₂O)^–1). The overall enthalpy change for the decomposition of Ba[Cu(C₂O₄)₂] in N₂ was estimated from the combined area of the peaks of the DSC curve as –347 kJ mol^–1. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly deceleratory and the -time curves could be described by the three dimensional diffusion (D3) model. The values of the activation energy and the pre-exponential factor for the dehydration were 125±4 kJ mol^–1 and (1.38±0.08)×10¹⁵ min^–1, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry model withn=5. The other process was slow and could also be described by the contracting-geometry model, but withn=2.The values ofE _a andA were 206±23 kJ mol^–1 and (2.2±0.5)×10¹⁹ min^–1, respectively, for the fast process, and 259±37 kJ mol^–1 and (6.3±1.8)×10²³ min^–1, respectively, for the slow process.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Reactions of ZrOCl2·8H2O with carboxylic acids and thionyl chloride: crystal and molecular structures of K4[Zr(mal)4]·2H2O and K4[Zr(dipic)3]2·13.5H2O

Reactions of ZrOCl₂·8H₂O in aqueous solution with a carboxylic acid in the presence of K₂CO₃ have been studied as a route to Zr^IV-carboxylates. With malonic acid (HO₂CCH₂CO₂H) (H₂mal) the product has been identified as K₄[Zr(mal)₄]·2H₂O (1) by X-ray crystallography. The individual eight-coordinate zirconium anions contain four bidentate (OO) malonate anions with the metal geometry approximating to a square antiprism with each chelating ligand spanning the two square faces, Zr—O 2.091(3)–2.288(3) Å. The four potassium cations feature irregular coordination spheres of oxygen atoms [from both H₂O and (mal) ligand molecules] with a 7–9 coordination range. With 2,6-dicarboxypicolinicacid (HO₂CC₅NH₃CO₂H) (H₂dipic) the product has been characterised as K₄[Zr(dipic)₃]₂·13.5H₂O (2) following X-ray diffraction studies. The structure consists of two [Zr(dipic)₃]^2- anions, four potassium cations and lattice solvate (H₂O) molecules. Individual anions feature nine-coordinate zirconium in which each dipic ligand is terdentate, being bonded via one N (pyridine) and two O (carboxylate) atoms. The metal geometry approximates to tricapped trigonal prismatic with each nitrogen atom capping a regular face of four oxygen atoms, Zr—O, 2.216(6)–2.261(6) Å; Zr—N, 2.343(8)–2.361(7) Å. The potassium cations show similar environments to those observed in structure (1). Dehydration of ZrOCl₂·8H₂O using SOCl₂ in the presence of an excess of THF effects removal of coordinated H₂O molecules and hydroxy bridging groups to provide the anhydrous bis-adduct ZrCl₄(thf)₂ in good yield (72%).     

Researches on crystal and molecular structures of nine-coordination mononuclear K[Eu III 2 (Edta)(H2O)3]·3.5H2O and binuclear K4[(HTtha)2]·13.5H2O

The crystal and molecular structures of the K[Eu^III(Edta)(H₂O)₃] 3.5H₂O (I) (H₄Edta = ethylenediaminetetraacetic acid) and K₄[Eu₂^III(HTtha)₂] 13.5H₂O (II) (H₆Ttha = triethylenetetraminehexaacetic acid) complexes have been determined by single-crystal X-ray diffraction analyses. The crystal of I belongs to orthorhombic crystal system and Fdd2 space group. The crystal data are as follows: a = 1.9849(6)nm, b = 3.5598(11)nm, c = 1.2222(4)nm, V = 8.636(5)nm³, Z = 16, M = 596.37, (calcd) = 1.835g/cm³, µ= 3.166mm^–1, and F (000) = 4752. The final R and wR values are 0.0269 and 0.0692 for 2936 (I > 2.0 (I)) reflections and 0.0317 and 0.0708 for all 7284 unique reflections, respectively. The [Eu^III(Edta)(H₂O)₃]^– complex anion has a nine-coordination pseudo-monocapped square antiprismatic structure in which the nine coordinated atom are two N and seven O atoms (four from one Edta ligand and three water molecules). The crystal of II belongs to monoclinic system and P2¹/n space group. The crystal data are as follows: a = 1.1337(3)nm, b = 2.5753(6)nm, c = 2.2138(6) nm, = 102.871(5)°, V = 6.301(3) nm³, Z = 4, M = 1682.33, (calcd) = 1.773g/cm³, = 2.339mm^–1, and F(000) = 3404. The final R and wR are 0.0514 and 0.0906 for 11144 (I> 2.0(I)) reflections and 0.0976 and 0.1068 for all 26 048 unique reflections, respectively. The whole complex molecule is composed of two close parts in which every one has a nine-coordination structure as a distorted monocapped square antiprism. The Ttha ligand in the [Eu ₂^III(HTtha)₂]^4– complex anion coordinates to one central Eu ³⁺ ion with three N atoms and four O atoms and to the other Eu³⁺ ion with two O atoms.From Koordinatsionnaya Khimiya, Vol. 30, No. 12, 2004, pp. 901–909.Original English Text Copyright © 2004 by J. Wang, X. Zhang, Y. Zhang, Y. Wang, X. Liu, Z. Liu.This article was submitted by the authors in English.     

Syntheses and structures of nine-coordinate NH4[HoIII(Edta)(H2O)3] · 1.5H2O, (NH4)4[Ho 2 III (Dtpa)2] · 9H2O, and (NH4)3[HoIII(Ttha)] · 5H2O complexes

The three title complexes, NH₄[Ho^III(Edta)(H₂O)₃] · 1.5H₂O (I) (H₄Edta = ethylenedianine-N,N,N′,N′-tetraacetic acid), (NH₄)₄[Ho ₂ ^III (Dtpa)₂] · 9H₂O (II) (H₅Dtpa = diethylenetriamine-N,N,N′,N″,N″-entaacetic acid), and (NH₄)₃[Ho^III(Ttha)] · 5H₂O (III) (H₆ Ttha = triethylenetetramine-N,N,N′,N″,N?,N?-hexaacetic acid), have been prepared and characterized by FT-IR, elemental analyses, and single-crystal X-ray diffraction technique. Complex I has a nine-coordinate mononuclear structure with distorted monocapped square antiprismatic conformation and its crystal structure belongs to orthorhombic system and Fdd2 space group. The crystal data are as follows: a = 19.343(9), b = 35.125(17), c = 12.364(6) Å, V = 8400(7) ų, Z = 16, M = 552.26, ρ_calcd = 1.747 g cm^?3 μ = 3.828 mm^?1, and F(000) = 4368. Complex II has a binuclear nine-coordinate pseudomonocapped square antiprismatic conformation and its crystal structure belongs to triclinic system and space P1 group. The crystal data are as follows: a = 9.7637(16), b = 9.9722(16), c = 12.945(2) Å, α= 85.853(2)°, β = 77. 140(2)°, γ = 77.140(2)°, V = 1198.4(3) ų, Z = 1, M = 1340.80, ρ_calcd = 1.858 g cm^?3, μ = 3.380 mm^?1, and F(000) = 674. As for complex III, it also has nine-coordinate mononuclear structure with distorted tricapped trigonal prism and its crystal structure belongs to monoclinic system andP2₁/c space group. The crystal data are as follows: a = 10.349(3), b = 12.760(4), c = 23.142(7) Å, β = 91.020(6)°, V = 3055.6(16) ų, Z = 2, M = 797.55, ρ_calcd = 1.734 g cm^?3, μ = 2.674 mm^?1, and F(000) = 1624. The results showed that although the ligands are different from one another in the shape and the numbers of coordination atoms, they all have nine-coordinate structures. However, one of them has binuclear structure and the other two have mononuclear structures because of the difference of the ligands.