Kinetics of the thermal dehydration of potassium titanium oxalate, K2TiO(C2O4)2·2H2O

The thermal dehydration reaction of potassium titanium oxalate, K₂TiO(C₂O₄)₂·2H₂O, has been studied by means of thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC) in nitrogen atmosphere at different heating rates. K₂TiO(C₂O₄)₂·2H₂O dehydrates in a single step through a practically irreversible process. The activation energy involved and its dependence on the conversion degree were estimated by evaluating the thermogravimetric data according to model-free methods, and values of activation energy were determined for the dehydration reaction. Activation energy values were also evaluated from DSC data using isoconversional methods. The complexity of the dehydration of K₂TiO(C₂O₄)₂·2H₂O is illustrated by the dependence of E on the extent of conversion, ?? (0.05??????????0.95).     

Heat capacity and thermodynamic functions of MnCl2·2H2O and MnCl2·2D2O

The heat capacities of MnCl₂·2H₂O and MnCl₂·2D₂O have been experimentally determined from 1.4 to 300 K. The smooth heat capacity and the thermodynamic functions (H°_T − H°₀) and S°_T are reported for the two compounds over the 10 and 300 K temperature range. The error in the thermodynamic functions at 10 K is estimated at 3%. Additional error in the tabulated values arising from the heat capacity data above 10 K is thought to be less than 1%. Lambda-shaped heat capacity features associated with antiferromagnetic ordering were observed at 6.67 ± 0.08 and 6.61 ± 0.08 K for the dihydrate and dideuterate, respectively. In addition, compound heat capacity anomalies consisting of a small lambda-shaped feature at 57.7 ± 0.5 K with a comparably large high-temperature shoulder extending to approximately 70 K were observed in both the dihydrate and dideuterate. The entropies associated with these anomalies are 0.42 ± 0.04 and 1.04 ± 0.04 J/mole-K, respectively.     

Synthesis and characterization of substitutional solid solutions aLn2O3 · (1 − a)Bi2O3 · 4TiO2

The solubility of 10 lanthanide elements and of scandium is solid Bi₂Ti₄O₁₁ has been determined using Raman spectroscopy and X-ray diffraction. The data obtained were used to construct a diagram of solubility as a function of the ionic radii of bismuth and the lanthanide elements. The thermal stability of the solid solutions as a function of temperature and duration of thermal treatment has been qualitatively established.     

Synthesis and thermochemical characteristics of Na2O · Al2O3 · 2.5H2O

A pure phase of monosodium aluminate hydrate Na₂O · Al₂O₃ · 2.5H₂O (MAH) is synthesized and characterized by means of XRD, IR, SEM, TGA, and DSC. The heat capacity of the compound is measured in the temperature range of ?100 to 100°C, and the thermal contributions to enthalpy and entropy are calculated. The standard entropy, enthalpy, and Gibbs energy of formation of MAH at 298 K are estimated.     

Syntheses and Structural Researches of Nine-coordinate K3[TbIII(nta)2(H2O)]·5.5H2O and Eight-coordinate K3[YbIII(nta)2]·5H2O

The crystal and molecular structures of K3[TbIII(nta)2(H2O)](5.5H2O (nta = nitrilotriacetic acid) and K3[YbIII(nta)2](5H2O complexes have been determined by single-crystal Xray structural analyses. Because TbIII and YbIII have different ionic radii and electronic configura- tions, they take nine- and eight-coordinate structures with two nta ligands, respectively. The crystal of K3[TbIII(nta)2(H2O)](5.5H2O belongs to orthorhombic, space group Pccn with a = 1.6374(7), b = 1.9913(8), c = 1.5068(6) nm, V = 4.913(3) nm3, Z = 8, Mr = 769.54, Dc = 2.081 g/cm3, μ= 3.476 mm-1 and F(000) = 3048. The final R and wR are 0.0432 and 0.0916 for 4961 observed reflections (I > 2.0(σI)), and 0.0814 and 0.1042 for all 21921 reflections, respectively. The [TbIII(nta)2(H2O)]3- complex anion has a nine-coordinate pseudo-monocapped square anti-prismatic structure, in which two N and six O coordinated atoms are from two nta ligands and the left ninth O atom from one water molecule. The crystal of K3[YbIII(nta)2]·5H2O is of monoclinic, space group P21/c with a = 1.5579(5), b = 0.9981(3), c = 1.5956(5) nm, β = 109.776(5), V = 2.3348(13) nm3, Z = 4, Mr = 756.62, Dc = 2.153 g/cm3, μ= 4.624 mm-1 and F(000) = 1484. The final R and wR are 0.0253 and 0.0657 for 4123 observed reflections (I > 2.0(σI)), and 0.0320 and 0.0731 for all 9414 reflections, respectively. The [YbIII(nta)2]3- complex anion has an eight-coordination structure with a distorted square antiprismatic prism, in which each nta acts as a tetradentate ligand with one N atom from the amino group and three O atoms from the carboxylic groups.     

Fe2O3—TiO2—K2O复合氧化物体系结构与湿敏性能

Ｆｅ２Ｏ３┐ＴｉＯ２┐Ｋ２Ｏ复合氧化物体系结构与湿敏性能储向峰刘杏芹＊王弘（中国科学技术大学材料科学与工程系合肥２３００２６）关键词Ｆｅ２Ｏ３－ＴｉＯ２－Ｋ２Ｏ，复合氧化物，湿度传感器１９９７－０４－３０收稿，１９９７－０９－２９修回Ｆｅ２Ｏ３是一种...     

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%).     

Synthesis and Crystal Structure of K3[HO{VO(O2)2}2]·H2O

The title compound K3[HO{VO(O2)2}2]·H2O has been synthesized and its crystal structure was determined by X-ray diffraction method. The crystal is of monoclinic, space group P21/c with a = 6.7078(3), b = 9.9539(6), c = 15.8182(9)A, β = 93.702(3)0, V = 1053.96(10)A3, Mr = 414.20, Dc = 2.610 g/cm3, Z = 4, λ(MoKα) = 0.71073A, F(000) = 808, μ = 3.014 mm-1, the final R = 0.0173 and wR = 0.0466 for 2178 observed reflections with I > 2σ(I). X-ray diffraction reveals that the coordination polyhedra of V atoms are not chemically equivalent: the V(1) and V(2) polyhedra can be described as pentagonal pyramid and pentagonal bipyramid, respectively.     

Preparation and Characterization of Nano-ZnFe2O4/TiO2 Films

The nano-ZnFe2O4/TiO2 films possess the functions of desulfurization and degradation for organic pollutants. The sols of ZnFe2O4/TiO2 were prepared by sol-gel method and coated on glass and porous ceramic by vertical coating and dipping-lift processes, respectively, and the samples were obtained after drying and sintering. The composition, appearance, absorption spectrum of the films, and the influence of the film on porous ceramic performances were analyzed using SEM, AFM, UV-Vis spectrometer, and mercury porosimeter, respectively, to determine the operation parameters of the multifunction porous ceramic elements for gas-purification.     

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.     

Crystal structures of MnNbOF5 · 4H2O at 153 and 297 K

Crystals of MnNbOF₅ · 4H₂O were studied by X-ray diffraction, differential scanning calorimetry (DSC) and thermogravimetry. DSC showed a phase transition in the temperature range of 282 to 296.3 K. The compound is dehydrated in two stages in the temperature ranges of 65–131.1 and 131.1–190°C, two H₂O molecules being removed in each stage. The structure of MnNbOF₅ · 4H₂O was determined at 153 K (α phase; space group P2₁/c) and at 297 K (β phase, space group C2/m). The structure of both phases is formed of the octahedral complexes [NbF₄(O/F)_2/2]^0.5? and [Mn(H₂O)₄(O/F)_2/2]^0.5+ linked by bridging O and F atoms to infinite chains. The isolated niobium-manganese chains are connected by O-H…F hydrogen bonds. In the α phase, the Nb, O, and F atoms in the trans position relative to O are disordered with respect to the inversion center of the structure. Transition to the β phase is accompanied by splitting of all ligand positions at the Nb and Mn atoms into two equally probable positions.     

Pressure dependent Raman studies in the K2Mo2O7·H2O crystal

The pressure dependent Raman scattering in the potassium molybdenum oxide hydrate crystal, K₂Mo₂O₇·H₂O, was measured. The high pressure Raman study showed, that the compound remains in the triclinic structure within the 0.0–3.81 GPa range and undergoes a structural phase transition between 3.81 and 4.13 GPa. This particular phase transition is most likely connected with changes in the Raman spectrum, in which the number of modes associated originally with the stretching vibrations in the MoO₅ and MoO₆ units is increased. However, the phase at atmospheric pressure shows bands due to the presence of only one equivalent site, while in the high-pressure phase, two bands are associated with the stretching modes. Continuing the pressure evolution up to 17.04 GPa, two further phase transitions occurred in this crystal in the 6.3–8.1 GPa and the 12.3–14.0 GPa range, respectively. The Raman spectra measured at about 17.04 GPa presented a crystal structure, which experienced a pre-amorphization with a total loss of all lattice modes. This particular result is indicative that this material may have undergone a complete amorphization at pressures larger than 17.04 GPa. Then, the reversible character in the triclinic P-1 (C_i¹) structure was recovered after releasing the pressure.     

IR and polarized Raman spectra of K2Mg(SO4)2 · 6H2O

IR and polarized Raman spectra of K₂Mg(SO₄)₂ · 6H₂O have been recorded and analyzed. From the spectra, the vibrations due to SO²⁻₄ ion, the complex [Mg(H₂O)₆]²⁺ and the water molecules have been identified. The splitting of the nondegenerate ν₁ mode of the SO²⁻₄ ion indicates the presence of a factor group interaction between vibrating ions in the crystal. It has been inferred that the angular distortion of SO²⁻₄ is greater than the bond distortion. Separate bands for the three different water molecules have been observed.     

Compound and solid-solution formation in the system Li2ONb2O5TiO2

A systematic study of compound and solid-solution formation in the system Li₂ONb₂O₅TiO₂ has been made. Several solid-solution series, based on LiNbO₃, LiNb₃O₈, Li₂Nb₂₈O₇₁, Li₂TiO₃, phase M, Li₂Ti₃O₇, and TiO₂, have been characterized. In all cases, the principal solid-solution mechanism appears to involve stoichiometric formulae with constant overall cation content. One new phase, of approximate formula Li₁₃TiNb₅O₂₁, has been prepared. A subsolidus phase diagram for the ternary system is presented.     

Syntheses and structures of seven-coordinate K3[Cd(Dtpa)], K2[Cd(H2O)4][Cd(Edta)(H2O)]2 · 2H2O, and Na2[Cd(H2O)4][Cd(Edta)(H2O)]2 · 2H2O complexes

The title complexes, K₃[Cd(Dtpa)] (H₅Dtpa = diethylenetriamine-N,N,N,N′,N′-pentaacetic acid, (I)), K₂[Cd(H₂O)₄][Cd(Edta)(H₂O)]₂ · 2H₂O (H₄Edta = ethylenediamine-N,N,N′,N′-tetraacetic acid, (II)), and Na₂[Cd(H₂O)₄][Cd(Edta)(H₂O)]₂ · 2H₂O (III), were prepared, and their compositions and structures were determined by elemental analyses, IR spectra, and single-crystal X-ray diffraction techniques, respectively. In complex I, the Cd is seven-coordinated by one Dtpa ligand yielding a pseudo-monocapped trigonal prism conformation, and the complex crystallizes in the triclinic crystal system with the Pi space group. The crystal data are as follows: a = 8.7300(17), b = 9.1200(18), c = 15.110(3) Å, α = 95.52(3)°, β = 96.59(3)°, γ = 99.63(3)°, V = 1170.0(4) ų, Z = 2, ρ = 1.754 g/cm³, μ = 1.519 mm^?1, F(000) = 616, R = 0.0644 and wR = 0.1712 for 3842 observed reflections with I ≥ 2σ(I). For complex II, in the [Cd(Edta)(H₂O)]^2? complex anion the Cd²⁺ ion is seven-coordinated by one Edta ligand and one water molecule, yielding a pseudo-pentagonal bipyramid conformation. In the [Cd(H₂O)₄]²⁺ cation, the bridged Cd is six-coordinated, yielding an almost standard octahedral conformation. The complex crystallizes in the monoclinic system with P2₁/n space group. The crystal data are as follows: a = 9.098(3), b = 16.442(6), c = 12.023(4) Å, β = 91.053(6)°, V = 1798.3(12) ų, Z = 2, ρ = 2.098 g/cm³, μ = 2.086 mm^?1, F(000) =1124, R = 0.0406 and wR = 0.1152 for 3680 observed reflections with I ≥ 2σ(I). In complex III, the conformations of Cd²⁺ ions are similar to those of the potassium salt complex, and the complex also crystallizes in the monoclinic crystal system with the P2₁/n space group. The crystal data are as follows: a = 9.134(7), b = 16.500(13), c = 12.075(10) Å, β = 91.054(12)°, V = 1820(2) ų, Z = 2, ρ = 2.015 g/cm³, μ = 1.856 mm^?1, F(000) = 1092, R = 0.0363 and wR = 0.0879 for 3707 observed reflections with I ≥ 2σ(I).     

Buckled layers in K0.66Mn2O4·0.28H2O and K0.99Mn3O6·1.25H2O synthesized at high pressure: implication for the mechanism of layer-to-tunnel transformation in manganese oxides

A 2 × 2 layer-buckled manganese oxide, K(0.66)Mn(2)O(4)·0.28H(2)O (I), has been synthesized under high pressure and retained at ambient pressure; it is metastable and will finally transform to a 2 × 1 layer-buckled K(0.99)Mn(3)O(6)·1.25H(2)O (II) in 1 year. Both crystal structures were determined by single-crystal X-ray diffraction. On the basis of these buckled layers, which are a result of ordering of Mn(3+)/Mn(4+) in separate rows and cooperative Jahn-Teller distortion of Mn(3+)O(6) octahedra, a mechanism of structure transformation from birnessite to tunnel structures was proposed.     

Phase diagram and IR spectral investigations of the 2TeO2 · V2O5Li2O · V2O5 · 2TeO2 system

By means of X-ray phase analysis, IR spectroscopy, and DTA, the system 2TeO₂ · V₂O₅Li₂O · V₂O₅ · 2TeO₂ was investigated and its phase diagram was constructed. The formation of a new compound with composition Li₂O · 3V₂O₅ · 6TeO₂, melting incongruently was documented. A comparison of the bands in the IR spectrum was made. Stable glasses in the whole range of concentrations were prepared. From the IR spectra of the glasses, the corresponding crystallization products, and the data of known crystal structures, a model of the short-range order in the glasses was proposed.