α-H6P2W18O62·37H2O的热稳定性

通过溶解性实验、变温红外、紫外光谱、X射线粉末衍射(XRD)和热重-差热分析(TG DTA)等手段,对Dawson结构钨磷酸的热稳定性进行了较系统的研究,结果表明,阴离子骨架在360℃左右开始分解,并提出了化合物热分解的可能机理.     

Reduction potential and oxidation catalysis of vanadium-containing H6+x P2Mo18−x V x O62 Wells-Dawson heteropolyacid (HPA) catalysts

Vanadium-containing H_6+x P₂Mo_18?x V _x O₆₂ (x=0?3) Wells-Dawson heteropolyacid (HPA) catalysts were prepared. The successful formation of the Wells-Dawson HPAs was confirmed by FT-IR and ICP-AES analyses. The reduction potential of the H_6+x P₂Mo_18?x V _x O₆₂ (x=0?3) catalysts was determined by temperature-programmed reduction measurements. The Wells-Dawson HPA catalysts were applied to the vapor-phase oxidation of methacrolein and benzyl alcohol. The reduction potential, conversion of methacrolein, and conversion of benzyl alcohol showed volcano-shaped curves with respect to vanadium substitution, and decreased in the order of H₈P₂Mo₁₆V₂O₆₂>H₇P₂Mo₁₇V₁O₆₂>H₉P₂Mo₁₅V₃O₆₂>H₆P₂Mo₁₈O₆₂. A correlation between reduction potential and catalytic activity clearly showed that the conversion was monotonically increased with increasing reduction potential of the HPA catalyst in both oxidation reactions.     

Thermal Dehydration and Infrared Studies of Mg 2 P 2 O 7 · 6H 2 O Diphosphate

The thermal dehydration of Mg 2 P 2 O 7 ·; 6H 2 O were studied, in the range 25-800°;C, by thermogravimetric analysis (TG-DSC), x-ray diffraction, and infrared spectroscopy. According to the TG-DSC curves, the dehydration of this salt takes place in two stages. The results of thermal analysis, x-ray patterns, and infrared spectra of this compound heated at different temperatures showed that, after dehydration, Mg 2 P 2 O 7 ·; 6H 2 O decomposes into dihydrate Mg 2 P 2 O 7 ·; 2H 2 O diphosphate then to an amorphous Mg 2 P 2 O 7 product which crystallises at 665°;C to give anhydrous diphosphate f Mg 2 P 2 O 7 . The j H enthalpy of the dehydration of Mg 2 P 2 O 7 ·; 6H 2 O and of the formation of f Mg 2 P 2 O 7 have been calculated from thermogravimetric data. The infrared spectroscopic study of Mg 2 P 2 O 7 ·; 6H 2 O and of its heated products, reveals the existence of the characteristic bands of the P 2 O 7 group ( x as POP and x s POP) and showed that the POP angle is bent in these salts. In these compounds, the POP angle values are estimated using the Lazarev's relationship.     

Inhibition of α/β-K6P2W18O62· 10H2O on the Activity of Mushroom Tyrosinase and Its Antimicrobial Effects

Dawson-type phosphotungstic polyoxometalate α/β-K₆P₂W₁₈O₆₂·10H₂O(P₂W₁₈) was synthesized and its inhibitory effect on the mushroom tyrosinase was investigated. It could inhibit diphenolase activity of mushroom tyrosinase as an irreversible inhibitor. When the concentration of the enzyme reached 0.0176 mg/mL, the concentration of P₂W₁₈ leading to 50% activity lost(IC₅₀) was 0.05 mmol/L for monophenolase and 0.64 mmol/L for diphenolase. In addition, the antimicrobial activity of P₂W₁₈ was evaluated by zone of inhibition test. The results show that P₂W₁₈ possesses effective antimicrobial ability against Escherichia coli, Bacillus subtilis, yeast, especially Escherichia coli and yeast.     

X-ray powder structure determination of Li6P6O18·3H2O

Preparation, characterization by X-ray diffraction, IR absorption, DTA-GTA analysis and ab-initio crystal structure determination are reported for a new lithium cyclohexaphosphate hydrate Li₆P₆O₁₈·3H₂O. It crystallizes in a trigonal (rhomboedral) cell (space group R 3¯m No 166, Z = 6) with a = 15.7442(2) Å, c = 12.5486(2) Å. X-ray powder diffraction pattern data was refined by Rietveld profile technique and lead to R_Bragg = 0.09. The crystal structure of Li₆P₆O₁₈·3H₂O is built up from [P₆O₁₈]^6- ring anions, having the 3m symmetry, alternating along the 3¯ axis with rings made of six LiO₄ tetrahedra and six LiO₅ pseudo square pyramids sharing common edges.     

Dawson结构α-H6P2W18O62·3(CH3)2NH·H2O的合成、表征和晶体结构

由二甲胺与H6P2W18O62·nH2O合成了电荷转移化合物α-H6P2W18O62·3(CH3)2NH·H2O.单晶结构解析结果表明晶体属单斜晶系,空间群为P21/c,晶胞参数a=1.2964(3)nm,b=1.3621(3)nm,c=4.1559(8)nm,β=90.02(3)°,V=7.338(3)nm3,Z=4.标题化合物具有可逆光色性.热分析表明,化合物阴离子在430.5℃左右分解.     

STM and AFM characterization of thin metal oxide films electrodeposited from [P2Mo18O62]6−

Two groups of techniques have been devised for the electrodeposition of new electroactive oxide films from [P₂Mo₁₈O₆₂]⁶⁻. In the first group, two adsorption procedures were used: simple immersion of the electrode in a solution containing 10⁻⁴M [P₂Mo₁₈O₆₂]⁶⁻ in a pH 3.50 medium or cycling of the electrode in this solution in the potential domain of the first three two-electron waves of the heteropolyanion results in surfaces which retain the oxometalate by mere adsorption. Strikingly, during the cycling, it was found that a fourth wave appears in the potential domain of the first three two-electron waves of [P₂Mo₁₈O₆₂]⁶⁻, indicating an evolution of the heteropolyanion in the solution. Such an evolution was also observed with aged solutions. Then, the potential program for the actual modification step was run by cycling either of these electrodes from −0.2 V to −0.87 V vs. SCE in pure supporting electrolyte. Analysis of the STM images of the surfaces show essentially monomers 1.2–1.5 nm in diameter just after adsorption and a sizeable increase of the dimensions of the patterns after modification. The predominant sizes of these aggregates after modification remain in the range 10–12 nm. The second group of techniques consists in a modification of the electrode surface directly in the solution containing the heteropolyanion. A fixed potential as well as cycling prove efficient. Thick films are obtained readily, which are better imaged by tapping mode AFM. An increase of the pH to 4.50, in appropriate conditions, seems to be favourable to the deposition kinetics. The aggregates in the topmost layers are up to 40 nm in diameter and are assembled in interconnected islands. As a whole, these two groups of techniques appear to exert an important influence on the aggregate sizes. The paper demonstrates that these sizes might be relatively well controlled by the choice of experimental conditions. Received: 4 January 2000 / Accepted: 15 February 2000     

Mechanism of formic acid decomposition on P?Mo heteropolyacid

Hydrated (undecomposed) form of heteropolyacid H₃PMo₁₂O₄₀/SiO₂ exhibits a higher activity in the formic acid decomposition than the corresponding dehydrated sample. The formic acid decomposition takes place on strong Br?nsted acid sites of the heteropolyacid.Ab initio SCF MO LCAO method was used for the calculation of the electronic state of two surface complexes of HCOOH molecule (S1 and S2) coordinated to a proton H⁺. The S1 complex is formed by proton addition to the carbonyl oxygen, whereas the S2 complex is formed proton addition to the oxygen atom of the C−O−H fragment of HCOOH. The selective weakening of the C−O bond and localization of the positive charge on the (O=C−H) fragment in the protonated complex S2 are favorable for the decomposition of formic acid to CO and H₂O.     

超分子化合物[C6H11NH3]6[P2Mo18O62]·4H2O的水热法合成及结构

超分子化合物[C6H11NH3]6[P2Mo18O62]·4H2O的水热法合成及结构;Wells-Dawson结构;杂多化合物     

Y2P2W18O62?nH2O/4A-分子筛的研制及其催化合成乙酰水杨酸

以4A-分子筛为载体,Dawson结构磷钨酸钇（Y2P2W18O62?nH2O）为活性组分,采用浸渍法制备出负载型40% Y2P2W18O62?nH2O/4A-分子筛,并通过FT-IR、EDS、SEM、NH3-TPD及N2吸附-脱附等方法对催化剂进行表征。将其用于催化水杨酸和乙酸酐反应制备乙酰水杨酸,考察了各因素对反应的影响。结果表明：负载前后磷钨酸钇均保持Dawson结构,Y2P2W18O62?nH2O和40% Y2P2W18O62?nH2O/4A-分子筛均呈球形,负载后催化剂的比表面积增大,酸强度和酸量均明显提高。在优化反应条件下,即水杨酸与乙酸酐摩尔比为1:3,反应时间为30min,催化剂用量为反应物质量分数的2.3%,乙酰水杨酸收率为95.2%。催化剂重复使用6次,乙酰水杨酸收率仍保持为77.9%。     

X-Ray Photoelectron Study of Thorium Silicate ThSiO4 · nH2O and Uranium Silicate USiO4·nH2O

The naturally occurring compounds of thorium ThSiO₄, ThSiO₄· nH₂O, and (Th, Fe)SiO₄ and uranium USiO₄· nH₂O have been studied by X-ray photoelectron spectroscopy in the range of electron binding energies from 0 to 1200 eV. The oxidation state of Th in the natural compounds is close to that in Th(OH)₄; for uranium, it is similar to that in UO₂. Based on the structure of the low-energy electron spectra it is assumed that the electrons of the filled Th6p- and O2s-atomic orbitals take an active part in chemical bonding. Fine structure was observed in the Th(U)6s-, 5d-, 5p-, 4f-, 4d-, and 4p _3/2 electron spectra of all substances under study. Mechanisms of fine structure formation are discussed and the fine structure parameters are correlated with the physicochemical properties of the compounds.     

H6P2W18O62·18H2O–Catalyzed,Three-Component,One-Pot Synthesis of Indeno[1,2-b]quinoline-7-one Derivatives

In this work, a rapid and efficient one-pot method for the synthesis of indeno[1,2-b]quinoline-7-one derivatives by condensation of 1-naphthylamine, 1,3-indanedione, and different aldehydes in the presence of H₆P₂W₁₈O₆₂·18H₂O as a green and reusable catalyst in refluxing acetic acid is described.     

一个新的超分子化合物(C10H18N)6As2Mo18O62·6CH3CN·8H2O的合成、结构及性质

以Dawson型砷钼酸、金刚烷胺为原料,合成了一个新的超分子化合物(C1oH18N)6As2Mo1gO62·6CH3CN·8H2O.通过元素分析,IR,1H NMR等方法对合成的化合物进行了表征.X射线衍射晶体解析表明,金刚烷胺与Dawson型多阴离子以静电力和分子间力(氢键)结合,并且在新化合物中,金刚烷胺及多阴离子结构基本保持不变.该化合物均具有可逆的光致变色特性,基于变色后样品的电子自旋共振(ESR)谱提出一个可能变色机理.以该类化合物为修饰剂的本体修饰碳糊电极(APM-CPE)对过氧化氢还原有很好的电催化活性.     

Dimerization in Acetonitrile of [H6PMo9O34]3− into [P2Mo18O62]6−: Structural Characterization of the Tetrabutyl Ammonium Salt

The trivacant heteropolyanion A-α[PMo₉O₃₁(OH₂)₃]³⁻ spontaneously dimerizes in acetonitrile to form the Dawson complex [P₂Mo₁₈O₆₂]⁶⁻. A rapid new quantitative preparation of the sodium salt of this Dawson complex is described. In addition, the structure of TBA₅[HP₂Mo₁₈O₆₂] is given and the featuring data compared with the isomorphous sodium salt (space group C2/c).

Synthesis and crystal structure of ((NH3CH2CH2)3N)2P6O18·6H2O

Chemical preparation and crystal structure are given for a new cyclohexaphosphate: ((NH₃CH₂CH₂)₃N)₂P₆O₁₈·6H₂O. This compound is triclinic P¯1 with the following unit-cell parameters: a = 10,281(1)Å, b = 11.083(1)Å, c = 9.307(2)Å, α = 103.83(1) °, β = 108.56(1) °, γ = 68.11(1) °, Z = 1, V = 924.2(3)ų and pcal. = 1.582 g.cm⁻³. Its atomic arrangements contain layers built by P₆O₁₈ ring anions spreading in the plans (001). Between these layers are located the organic groups which form hydrogen bonds with oxygen atoms of P₆O₁₈ rings and water molecules. Crystal structure has been solved and refined to R = 0.028 using 4540 independent reflections. The thermal behavior has been investigated and interpreted by comparison with IR absorption spectroscopy and X-ray diffraction experiments.     

Syntheses and Crystal Structures of (H3O)(C3H5N2)[Mn(OH)6 Mo6O18]·3.5H2O and (H3O)3[Co(OH)6Mo6O18]·7H2O

The crystals of the title compounds (H3O)(C3H5N2)[Mn(OH)6Mo6O18]·3.5H2O 1 and (H3O)3[Co(OH)6Mo6O18]·7H2O 2 have been prepared and structurally determined by X-ray single-crystal diffraction. Compound 1 crystallizes in monoclinic, space group C2/c with a = 21.5018(9), b = 10.9331(5), c = 11.8667(5)A,β = 95.3570(10)o, V = 2777.5(2)A3, Z = 4, Dc = 2.802 g/cm3, Mr = 1171.80,μ(MoKα) = 3.173 mm-1, F(000) = 223, the final R = 0.0458 and wR = 0.1041 for 2093 observed reflections (I>2σ(I)); Compound 2 crystallizes in monoclinic, space group P21/c with a = 11.4042(12), b = 10.9481(11), c = 11.6722(12)A, β= 99.948(2)o, V = 1435.4(3)A3, Z = 2, Dc = 2.794 g/cm3, Mr = 1207.80,μ(MoKα) = 3.223 mm-1, F(000) = 1160, the final R = 0.0544 and wR = 0.1066 for 1906 observed reflections (I > 2σ(I)). Both compounds 1 and 2 adopt the Anderson structure, in which the anion is of centrosymmetry and formed by six octahedral edge-sharing MoO6 units surrounding the central MO6 (M = Mn or Co) octahedron.     

Efficient and suitable preparation of N-sulfonyl-1,2,3,4-tetrahydroisoquinolines and ring analogues using recyclable H6P2W18O62·24H2O/SiO2 catalyst

Silica gel-supported H₆P₂W₁₈O₆₂·24H₂O is an efficient and recyclable catalyst for the synthesis of biologically important molecules. Several substituted N-sulfonyl-1,2,3,4-tetrahydroisoquinolines and ring analogues can be prepared in very good yields and purity by direct reaction of N-aralkylsulfonamides and sym-trioxane by a Pictet-Spengler reaction in the presence of a catalytic amount of silica gel-supported H₆P₂W₁₈O₆₂·24H₂O. Reactions were performed in a low volume of toluene, at 70 °C and for a short time, typically 15 to 30 min. The title heterocyclic compounds were prepared in very good yields (60%–95%) using the described procedure results in a clean and useful alternative, which has the advantages of a greener methodology with operative simplicity, use of a reusable and non-corrosive solid catalyst, soft reaction conditions, low reaction times, and good yields.     

Thermal properties of Na2O–P2O5–Fe2O3 polyphosphate glasses

Journal of Thermal Analysis and Calorimetry - Iron phosphate glasses are materials that can have many applications like durable matrixes in waste immobilization techniques, biomaterials,...