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1.
The epoxidation of cyclohexene with hydrogen peroxide in a biphase medium (H2O/CHCl3) was carried out with the reaction-controlled phase transfer catalyst composed of quaternary ammonium heteropolyoxotungstates [π-C5H5N(CH2)15CH3]3[PW4O16]. A conversion of about 90% and a selectivity of over 90% were obtained for epoxidation of cyclohexene on the catalyst. The fresh catalyst, the catalyst under reaction conditions and the used catalysts were characterized by FT-IR, Raman and 31P NMR spectroscopy. It appears that the insoluble catalyst could degrade into smaller species, [(PO4){WO(O2)2}4]3−, [(PO4){WO(O2)2}2{WO(O2)2(H2O)}]3−, and [(PO3(OH)){WO(O2)2}2]2− after the reaction with hydrogen peroxide and becomes soluble in the CHCl3 solvent. The active oxygen in the [W2O2(O2)4] structure unit of these soluble species reacts with olefins to form the epoxides and consequently the corresponding W---Ob---W (corner-sharing) and W---Oc---W (edge-sharing) bonds are formed. The peroxo group [W2O2(O2)4] can be regenerated when the W---Ob---W and W---Oc---W bonds react with hydrogen peroxide again. These soluble species lose active oxygen and then polymerize into larger compounds with the W---Ob---W and W---Oc---W bonds and then precipitate from the reaction solution after the hydrogen peroxide is consumed up. Part of the used catalyst seems to form more stable compounds with Keggin structure under the reaction conditions.  相似文献   

2.
The H2O2-based epoxidation of bridged cyclic alkenes in a monophasic system containing low concentrations (<2 mM) of [Bu4nN]4[Pr2iNH3]2H[P{Ti(O2)}2W10O38]·H2O (1) (with two η2-peroxotitanium sites in the anion) has been studied in search of the catalytically active species involved. 31P NMR spectra of 1, measured under a variety of conditions, revealed that the active species was not hydroperoxotitanium complex [P{Ti(OOH)}2W10O38]7−or [P{Ti(OOH)}Ti(O2)W10O38]7−. The reaction pathways for the alkene epoxidation are discussed to understand the kinetics (especially the initial [H2O2] dependence). It was concluded that the net catalytic reaction for the epoxidation occurred through the two-electron oxidation at the hydroperoxotitanium site in the catalyst.  相似文献   

3.
The vanadium(V) peroxo phosphato complex K7[V4O4(O2)8(PO4)]·9H2O has been obtained from the KVO3---KH2PO4---KOH---H2O2---H2O---C2H5OH system. The X-ray structural analysis revealed a tetranuclear anionic structure in which two dinuclear [V2O2(O)2)2(μ-η1 : η2-O2)2] units are connected by the μ4-PO4 group.  相似文献   

4.
A new family of heteropolytungstate complexes (NH4)21[Ln(H2O)5{Ni(H2O)}2As4W40O140xH2O(Ln=Y, Ce, Pr, Nd, Sm, Eu, Gd) were prepared by the reaction of Na27[NaAs4W40O140]·60H2O with NiCl2·6H2O and Ln(NO3)3·xH2O at pH≈4.5. The crystal structures of (NH4)21[Gd(H2O)5{Ni(H2O)}2As4W40O140]·51H2O was determined by X-ray diffraction analysis and element analysis. The compound crystallizes in the monoclinic space group P21/n with a=19.754(3), b=24.298(4), c=39.350(6) Å, β=100.612(3)°, V=18564(5) Å3, Z=2, R1(wR2)=0.0544(0.0691). The central site S1 and two opposite sites S2 of the big cyclic ligand [As4W40O140]28− are occupied by one Ln3+and two Ni2+, respectively, each site supply four Od coordinating to metal ion, another one water molecule and other five water molecules coordinate, respectively, to Ni2+and Ln3+. Polyanion [Ln(H2O)5{Ni(H2O)}2As4W40O140]21− has C2v symmetry. IR and UV–vis spectra of [NaAs4W40O140]27− of the title compounds are discussed.  相似文献   

5.
The compounds K4Ti(O2)4·2H2O, K3Ta(O2)2F4 and K2V2O3(O2)2F2 undergo photolysis in the solid state. The photolysis kinetics obey the parabolic rate equation p = kt1/2 and indicate a monoexcitation process for the photolysis. These features are similar to those reported previously for peroxo complexes. The mechanism of evolution of oxygen reported earlier appears to be the same in all these solids.  相似文献   

6.
TiO2 nanoparticles and H2Ti2O5·H2O, Na2Ti2O4(OH)2 nanotubes were synthesized by solvothermal method and their applications in the degradation of active Brilliant-blue (KN-R) solution were investigated. The experimental results revealed that the synthesized TiO2 nanoparticles had a good crystallinity and a narrow size distribution (about 4–5 nm); the obtained H2Ti2O5·H2O, Na2Ti2O4(OH)2 were tubelike products with an average diameter of 20–30 and 200–300 nm length. The three catalysts we synthesized had some hydroxyl groups and the maximum absorption boundaries of the samples were all red-shifted, which indicated the samples had a promising prospect in photocatalysis.

The results of the photocatalytic experiments indicated that the photocatalytic activity of the samples was: TiO2 > H2Ti2O5·H2O > Na2Ti2O4(OH)2, which was in good accordance with the fact of FTIR and UV–vis absorption spectra. The formation mechanism of these nanostructures was also discussed.  相似文献   


7.
The compound [Zn(H2O)4]2[H2As6V15O42(H2O)]·2H2O (1) has been synthesized and characterized by elemental analysis, IR, ESR, magnetic measurement, third-order nonlinear property study and single crystal X-ray diffraction analysis. The compound 1 crystallizes in trigonal space group R3, a=b=12.0601(17) Å, c=33.970(7) Å, γ=120°, V=4278.8(12) Å3, Z=3 and R1(wR2)=0.0512 (0.1171). The crystal structure is constructed from [H2As6V15O42(H2O)]4− anions and [Zn(H2O)4]2+ cations linked through hydrogen bonds into a network. The [H2As6V15O42(H2O)]6− cluster consists of 15 VO5 square pyramids linked by three As2O5 handle-like units.  相似文献   

8.
Three hydrated uranyl arsenates, (UO2)3(AsO4)2 · 11 H2O, UO2HAsO4 · 4 H2O, and UO2(H2AsO4)2 · 1 H2O, have been prepared. The dehydration of these compounds has been studied by thermal analysis. Three crystalline anhydrous uranyl arsenates, (UO2)3(AsO4)2, (UO2(AsO3)2, have been found. These show melting phenomena and lose arsenic oxide vapour at high temperatures to result, finally, in U3O8 at 1500°C in air. The anhydrous compounds have been prepared under isothermal conditions and the strongest X-ray reflections are given. A tentative phase diagram in the composition range UO3 to As2O5 has been constructed.  相似文献   

9.
Hydrated strontium borate, SrB4O7·3H2O, has been synthesized and characterized by XRD, FT-IR, DTA-TG and chemical analysis. The molar enthalpy of solution of SrB4O7·3H2O in 1 mol dm−3 HCl(aq) was measured to be (21.15 ± 0.29) kJ mol−1. With incorporation of the previously determined enthalpies of solution of Sr(OH)2·8H2O(s) in [HCl(aq) + H3BO3(aq)] and H3BO3 in HCl(aq), and the enthalpies of formation of H2O(l), Sr(OH)2·8H2O(s) and H3BO3(s), the enthalpy of formation of SrB4O7·3H2O was found to be −(4286.7 ± 3.3) kJ mol−1.  相似文献   

10.
We reported here four structures of lanthanide–amino acid complexes obtained under near physiological pH conditions and their individual formula can be described as [Tb2(dl-Cys)4(H2O)8]Cl2 (1), [Eu43-OH)4(l-Asp)2(l-HAsp)3(H2O)7] Cl · 11.5H2O (2), [Eu8(l-HVal)16(H2O)32]Cl24 · 12.5H2O (3), and [Tb2(dl-HVal)4(H2O)8]Cl6 · 2H2O (4). These complexes showed diverse structures and have shown potential application in DNA detection. We studied the interactions of the complexes with five single-stranded DNA and found different fluorescence enhancement, binding affinity and binding stoichiometry when the complexes are bound to DNA.  相似文献   

11.
The stabilities of the hydrated uranyl phosphates (UO2)3(PO4)2 · 4 H2O, UO2HPO4 · 4 H2O, and UO2(H2PO4) · 3 H2O have been reinvestigated. The compounds identified by thermal analysis have been prepared isothermally and characterized by their strongest X-ray reflections. During dehydration, oxygen was not evolved and the crystalline compounds (UO2)3(PO4)2, (UO2)2P2O7, UO2(PO3)2, and probably (UO2)3P4O)13 were found.

At still higher temperatures, the uranyl phosphates are reduced. The decomposition products lose phosphorus oxide above 1300–1400°C. The present results are summarized in a tentative pseudo-binary phase diagram UOx(x = 3 to 2)—UO2(PO3)2.  相似文献   


12.
This work presents chemical modeling of solubilities of metal sulfates in aqueous solutions of sulfuric acid at high temperatures. Calculations were compared with experimental solubility measurements of hematite (Fe2O3) in aqueous ternary and quaternary systems of H2SO4, MgSO4 and Al2(SO4)3 at high temperatures. A hybrid model of ion-association and electrolyte non-random two liquid (ENRTL) theory was employed to fit solubility data in three ternary systems H2SO4–MgSO4–H2O, H2SO4–Al2(SO4)3–H2O at 235–270 °C and H2SO4–Fe2(SO4)3–H2O at 150–270 °C. Employing the Aspen Plus™ property program, the electrolyte NRTL local composition model was used for calculating activity coefficients of the ions Al3+, Mg2+ Fe3+ and SO42−, HSO4, OH, H3O+, respectively, as well as molecular species. The solid phases were hydronium alunite (H3O)Al3(SO4)2(OH)6, hematite Fe2O3 and magnesium sulfate monohydrate (MgSO4)·H2O which were employed as constraint precipitation solids in calculating the metal sulfate solubilities. A correlation for the equilibrium constants of the association reactions of complex species versus temperature was implemented. Based on the maximum-likelihood principle, the binary interaction energy parameters for the ionic species as well as the coefficients for equilibrium constants of the reactions were obtained simultaneously using the solubility data of the ternary systems. Following that, the solubilities of metal sulfates in the quaternary systems H2SO4–Fe2(SO4)3–MgSO4–H2O, H2SO4–Fe2(SO4)3–Al2(SO4)3–H2O at 250 °C and H2SO4–Al2(SO4)3–MgSO4–H2O at 230–270 °C were predicted. The calculated results were in excellent agreement with the experimental data.  相似文献   

13.
The complexes, M[M(C2O4)3xH2 O, where x=4 for M=Cr(III), x=2 for M=Sb(III) and x=9 for M=La(III) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR and electronic spectral data, conductivity measurement and powder X-ray diffraction (XRD) studies. The chromium(III)tris(oxalato)chromate(III)tetrahydrate (COT), Cr[Cr(C2 O4)3]·4H2O, released water in a stepwise fashion. Removal of the last trace of water was accompanied by a partial decomposition of the oxalate group. Thermal investigation using TG, DTG and DTA techniques in air produced Cr2O3 at 858°C through the intermediate formation of Cr2O3 and CrC2O4 at around 460°C. While DSC study in nitrogen up to 670°C produced a mixture of Cr2O3 and CrC2O4. In antimony(III)tris(oxalato)antimonate(III)dihydrate (AOD), Sb[Sb(C2O4)3]·3H2O the dehydration took place during the decomposition of precursor at 170–290°C and finally at ca. 610°C Sb2 O5 along with trace amounts of Sb2O4 were produced. Trace amount of Sb2O3 and Sb along with Sb2O is proposed as the end product at 670°C of AOD in nitrogen. The oxide La2O3 is formed at 838°C from the study with TG, DTG and DTA in air of lanthanum(III)tris(oxalato)lanthanum(III)nonahydrate (LON), La[La(C2O4)3]·9H2O. Intermediate dioxycarbonate, La2O2CO3 was generated at 526°C prior to its decomposition to lanthanum oxide in air; whereas in N2 the formation of La2(CO3)3 at 651°C was proposed. The thermal parameters have been evaluated for each step of the dehydration and decomposition of COT, AOD and LON using five non-mechanistic equations i.e. Flynn and Wall, Freeman and Carroll, Modified Freeman and Carroll, Coats–Redfern and MacCallum–Tanner equations. Kinetic parameters, such as, E*, ko, ΔH*, ΔS* etc. were also supplemented by DSC studies in nitrogen for all the three complexes. Some of the intermediate species have been identified by analytical and powder XRD studies. Tentative schemes has been proposed for the decomposition of all three compounds in air and nitrogen.  相似文献   

14.
In this paper, we summarise our recent research interest in the hydrothermal synthesis and structural characterisation of multi-dimensional coordination polymers. The use of N-(phosphonomethyl)iminodiacetic acid (also referred to as H4pmida) in the literature as a versatile chelating organic ligand is briefly reviewed. This molecule plays an important role in the formation of centrosymmetric dimeric [V2O2(pmida)2]4− anionic units, which were first used by us as building blocks to construct novel coordination polymers. Starting with [V2O2(pmida)2]4− in solution, we have isolated [M2V2O2(pmida)2(H2O)10] species (where M2+ = Mn2+, Co2+ or Cd2+) via the hydrothermal synthetic approach, which were then employed for the construction of [CdVO(pmida)(4,4′-bpy)(H2O)2]·(4,4′-bpy)0.5·(H2O), [CoVO(pmida)(4,4′-bpy)(H2O)2]·(4,4′-bpy)0.5, [Co(H2O)6][CoV2O2(pmida)2(pyr)(H2O)2]·2(H2O) and [Cd2V2O2(pmida)2(pyr)2(H2O)4]·4(H2O) by the inclusion of bridging organic ligands in the reactive mixtures, such as pyrazine (pyr) and 4,4′-bipyridine (4,4′-bpy). These materials can contain channel systems, and exhibit magnetic behaviour, not only due to the V4+ centres but also to the transition metal centres which establish the links between neighbouring dimeric [V2O2(pmida)2]4− anionic units. A closely related anionic moiety, [Ge2(pmida)2(OH)2]2−, was engineered to allow the study of such crystalline hybrid materials using one- and two-dimensional high-resolution solid-state NMR.  相似文献   

15.
Thermal decomposition of mixed ligand thymine (2,4-dihydroxy-5-methylpyrimidine) complexes of divalent Ni(II) with aspartate, glutamate and ADA (N-2-acetamido)iminodiacetate dianions was monitored by TG, DTG and DTA analysis in static atmosphere of air. The decomposition course and steps of complexes [Ni(C5H6N2O2)(C4H5NO4)2−(H2O)2]·H2O, [Ni(C5H6N2O2)(C5H7NO4)2−(H2O)2]·H2O and [Ni(C5H6N2O2)(C6H8N2O5)2−(H2O)2]·1.5H2O were analyzed. The final decomposition products are found to be the corresponding metal oxides. The kinetic parameters namely, activation energy (E*), enthalpy (ΔH*), entropy (ΔS*) and free energy change of decomposition (ΔG*) are calculated from the TG curves using Coats–Redfern and Horowitz–Metzger equations. The stability order found for these complexes follows the trend aspartate > ADA > glutamate.  相似文献   

16.
Three interpenetrated polymeric networks, {[Co(bpp)(OH-BDC)] · H2O}n (1) [Ni(bpp)1.5(H2O)(OH-BDC)]n (2) and {[Cd(bpp)(H2O)(OH-BDC)] · 2H2O}n (3), have been prepared by hydrothermal reactions of 1,3-bis(4-pyridyl)propane (bpp), 5-hydroxyisophthalic acid (OH-H2BDC), with Co(NO3)2 · 6H2O, Ni(NO3)2 · 6H2O and Cd(NO3)2 · 4H2O, respectively. Single-crystal X-ray diffraction analyses reveal that the three compounds all exhibit interpenetrated but entirely different structures. Compound 1 is a fourfold interpenetrated adamantanoid structure with water molecules as space fillers, in which bpp adopts a TG conformation (T = trans, G = gauche). Compound 2 is an interdigitated structure from the interpenetrated long arms of one-dimensional molecular ladders, while bpp in 2 adopts both TT and TG conformations. Compound 3 is a twofold interpenetrated three-dimensional network from a one-dimensional metal-carboxylate chain bridged by TG conformational bpp. The hydrogen bonding interactions in 1–3 further stabilize the whole structural frameworks and play critical roles in their constructions.  相似文献   

17.
Six mononuclear complexes [M(L1)2(H2O)4] (M = Co(II), 1a and M = Mn(II), 1b), [Cu(L1)2(H2O)2] (1c), [Cu(L1)2(H2O)(Py)2] (1d), [Cu(L3)(H2O)Cl] · H2O (3a) and [Co(Sal)(H2O)(Py)3] · 2ClO4 · H2O (3b) of phenoxyacetic acid derivatives and Schiff base were determined by single crystal X-ray diffraction. The Co(II) (1a) and Mn(II) (1b) complexes are isomorphous. X-ray crystal structural analyses reveal that these coordination complexes form polymeric structure via formation of different types of hydrogen bonding and π-stacking interactions in solid. Thermal analysis along with the powder X-ray diffraction data of these complexes shows the importance of the coordinated and/or crystal water molecules in stabilizing the MOF structure. Complexes 1a, 1c, 3a show marginal catalytic activity in the oxidation of olefins to epoxides in the presence of i-butyraldehyde and molecular oxygen.  相似文献   

18.
Polyoxoanions of tungsten, molybdenum, and vanadium have been the subject of interest since their wide variety of compositions, structures, and properties give rise to numerous important applications[1]. From the NH4VO3/Na2Sx (or (NH4)2Sx) reaction system we synthesized several spherical octadecavanadates with Na+,K+, NH4+ or I encapsulated using hydrothermal method. These complexes include (NH4)11[V18O42(Na)]·(H2O)20 1; (NH4)11[V18O42(K)]·(H2O)6, 2; (NH4)10(Na)[V18O42(Na)]·(H2O)26, 3; (NH4)11[V18O42(NH4]·(H2O)20, 4; and (NH4)20(I)7[V18O42(I)]·(H2O)12, 5, in which the structures of 1, 2, 3, and 5 have been determined by X-ray analyses. In the analogous reaction system of (NH4)2MoS4/(NH4)2Sx, we also obtained one ellipsoidal octadecamolybdate, (NH4)4[Mo18O54(2SO4)]·(H2O)4, 6 with a standard Wells-Dawson structure[2]. The Ortep drawings of the two kinds of structures are viewed as follows.  相似文献   

19.
A series of chromium(III) complexes [Cr(bipy)(HC2O4)2]Cl·3H2O (1), [Cr(phen)(HC2O4)2]Cl·3H2O (2), [Cr(phen)2(C2O4)]ClO4 (3), [Cr2(bipy)4(C2O4)](SO4)·(bipy)0.5·H2O (4) and [Mn(phen)2(H2O)2]2[Cr(phen)(C2O4)2]3ClO4·14H2O (5) were synthesized (bipy=4,4′-bipyridine, phen=1,10-phenanthroline), while the crystal structures of 1 and 3–5 have been determined by X-ray analysis. 1 and 3 are mononuclear complexes, 4 contains binuclear chromium(III) ions and 5 is a 3D supromolecule formed by complicated hydrogen bonding. 1–3 are potential molecular bricks of chromium(III) building blocks for synthesis heterometallic complexes. When we use these molecular bricks as ligands to react with other metal salts, unexpected complexes 4 and 5 are isolated in water solution. The synthesis conditions and reaction results are also discussed.  相似文献   

20.
在水热条件下,Cu(Ⅱ)-H2biim配合物与Dawson型钨磷酸盐构筑了1个无机-有机杂化化合物[Cu(H2biim)2(H2O)][{Cu(H2biim)2}2(P2W18O62)]·11H2O(1)(H2biim=2,2'-联咪唑)。 通过单晶X射线衍射、红外光谱(IR)、X射线粉末衍射(XRD)、元素分析、电化学分析等技术手段对其进行了表征。 结构分析表明,在化合物1分子中,[P2W18O62]6-单元作为双齿配体与2个Cu2+离子配位形成双支撑的杂多阴离子[{Cu(H2biim)2}2(P2W18O62)]2-,在其外部有1个游离的[Cu(H2biim)2(H2O)]2+ 和11个H2O分子。 H2biim分子与杂多阴离子/H2O分子间存在氢键,通过氢键、静电和π-π堆积作用,进一步构成具有3D结构的晶体材料。 该晶体化合物对H2O2和NaNO2的还原具有良好的电催化作用;同时,作为酸催化剂用于合成环己酮乙二醇缩酮反应,催化活性高,可重复使用。  相似文献   

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