Oxo-vanadium(IV) dihydrogen phosphate: preparation, magnetic study, and heterogeneous catalytic epoxidation

A layered oxo-vanadium(IV) dihydrogen phosphate, {VO(H2PO 4)2} n has been synthesized hydrothermally and characterized by several physicochemical methods. Single-crystal X-ray analysis (crystal system, tetragonal; space group, P4/ ncc; unit cell dimensions, a = b = 8.9632(4), c = 7.9768(32) A) of {VO(H2PO4) 2} n reveals that the compound has an extended two-dimensional structure. The VO2+ moieties are connected through bridging H 2PO4 (-) ions, and this type of connection propagates parallel to the crystallographic ab plane which gives rise to a layered structure. The layers are staked parallel to the crystallographic c axis with a separation between the layers of ca. 4.0 A. Magnetic susceptibility of {VO(H2PO4)2} n has been measured in the temperature range 2-300 K on a SQUID magnetometer. The magnetic property of {VO(H2PO4)2} n is explicable in the light of a two-dimensional quantum Heisenberg antiferromagnet model. Magnetic pathways are available through the dihydrogen-phosphato bridges within the layer and provide for weak antiferromagnetic interactions. Notably {VO(H2PO4)2} n catalyzes the epoxidation reaction of alkenes with tert-BuOOH in acetonitrile medium under heterogeneous condition.     

Design, synthesis, and conformational dynamics of a gated molecular basket

We have developed a synthesis and examined the conformational behavior and recognition properties of dynamic molecular containers 1-3. As follows from the 1H NMR dilution, diffusion NMR, and vapor pressure osmometry measurements, compound 1 has a low affinity for intermolecular aggregation and is mostly present in monomeric form in dilute chloroform solutions. Inspecting the O-H chemical shift resonances of 1, 3, and model compound 4 as a function of temperature afforded the deltadelta/deltaT coefficients of 17.0, 17.3, and 4.7 ppb K(-1), respectively. In combination with the results from variable temperature 1H NMR and IR measurements, the existence of conformers of 1 and 3 in equilibrium, each having a different extent of hydrogen bonding, was confirmed. Molecular mechanics calculations suggested 1a as the most favorable conformation, with three additional conformers, 1b, 1c, and 1d, populating local energy minima. Further optimization of each of the four conformers using semiempirical PM3 and ab initio (HF/6-31G) methods allowed a determination of their relative free energies and the corresponding Boltzmann population distributions which were heavily weighted toward 1a. A computed composite IR spectrum of a fraction-weighted mixture of the conformers of 1 reproduced the experimentally observed IR spectrum in its structural features, leading to a conclusion that conformer 1a indeed dominates the equilibrium. The egg-shaped cavity of 1 (136.6 angstroms3) is complementary in size, shape, and electrostatic potential to chloroform (74.9 angstroms3). A single-crystal X-ray study of 2 revealed a disordered chloroform molecule positioned inside the cavitand along its C3 axis.     

Composites of polyaniline and lead dioxide: preparation,characterization, and catalytic activity

This paper is devoted to the preparation of polyaniline/lead dioxide composites (PANI/PbO₂) via chemical oxidation of aniline in H₂SO₄ medium using β-PbO₂ as an oxidant. The parameters affecting the polymerization reaction are considered. These parameters are [aniline], amount of β-PbO₂, stirring time, and different acids. The prepared composites were characterized by SEM, FT-IR, XRD, TGA, DTA, and elemental analysis. From XRD and FT-IR spectra, it was concluded that high molecular weight polymer could be obtained with high aniline concentration, high amount of β-PbO₂, increasing polymerization time and polymerization of ANI at lower temperatures. Thermogravimetric study exhibited that the composite prepared using high amount of β-PbO₂ has a higher thermal stability. The application of the composites in the oxidative degradation of Alizarin yellow G and Acid alizarin violet N dyes exhibited good catalytic activity in presence of H₂O₂ as an oxidant. The reactions followed first-order kinetics and the rate constants were determined.     

Iron-oxide-modified nanosized diamond: preparation, characterization, and catalytic properties in methanol decomposition

Nanosized diamond (UDD), obtained by a detonation procedure, was modified with iron from the corresponding acetylacetonate precursor under various pretreatment conditions. Nitrogen physisorption, X-ray diffraction, temperature-programmed reduction, and FTIR and M?ssbauer spectroscopy were used for their characterization. The samples' catalytic behavior in methanol decomposition was also studied. The physicochemical and catalytic properties of the obtained materials (Fe/UDD) were compared with those of other iron-oxide-modified mesoporous supports with different nature and functionality (MCM-48 silica and CMK-1 carbon). The highest catalytic activity and stability was achieved with air-pretreated Fe/UDD.     

Ribbons, vesicles, and baskets: supramolecular assembly of a coil-plate-coil emeraldicene derivative

Concentration matters: the self-assembly of title compound 1 evolves from well-defined ribbons to vesicles to baskets, upon simply decreasing the concentration of 1 in tetrahydrofuran. Electron microscopy revealed a unique self-assembled structure: baskets are formed by curved and self-wrapped nanometer-thin ribbons. The self-assembly of π-conjugated molecule 1 enables to construct nano/micro structures with desired optoelectronic properties.     

Convenient preparation of cyclic acetals,using diols,TMS-source,and a catalytic amount of TMSOTf

With use of diol, alkoxysilane, and a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf), carbonyl compounds are converted to acetals in good yields under mild conditions. This procedure, which was carried out without synthesizing the silylated diols, is a more convenient adaptation of Noyori's method. This acetalization applies to not only simple but also conjugated carbonyl compounds. Moreover, various TMS compounds, including solid supported compounds, are effective for this method instead of alkoxylsilane.     

Structures, preparation and catalytic activity of ruthenium cyclopentadienyl complexes based on pyridyl-phosphine ligand

Ruthenium complexes [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(PPh₃)Cl] (1) and [(η⁵-C₅H₅)Ru(κ²-P-N-PPh₂Py)(PPh₃)]⁺ (1a) containing diphenyl-2-pyridylphosphine (PPh₂Py) are reported. Coordinated PPh₂Py in the complex [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(PPh₃)Cl] (1) exhibits monodentate behavior. In presence of NH₄PF₆ in methanol at room temperature it afforded chelated complex [(η⁵-C₅H₅)Ru(κ²-P,N-PPh₂Py)(PPh₃)]⁺ (1a). Further, 1 reacted with various species viz., CH₃CN, NaCN, NH₄SCN and NaN₃ to afford cationic and neutral complexes [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(PPh₃)L]⁺ and [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(PPh₃)L] [L = CH₃CN (1b); CN⁻ (1c); N₃⁻ (1d) and SCN⁻ (1e)] and it’s reaction with N,N-donor chelating ligands dimethylglyoxime (H₂dmg) and 1,2-phenylenediamine (pda) gave cationic complexes [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(κ²-N-N)]PF₆ [κ²-N-N = dmg (1f) and pda (1g)]. The complexes 1-1g have been characterized by physicochemical techniques and crystal structures of 1, 1a, 1c, 1e and 1f have been determined by single crystal X-ray analyses. Catalytic potential of the complex 1 has been evaluated in water under aerobic conditions. It was observed that the complex 1 selectively catalyzes reduction of aldehyde into alcohol.     

Tungstate sulfuric acid: preparation, characterization, and application in catalytic synthesis of novel benzimidazoles

Tungstate sulfuric acid (TSA) was prepared, characterized, and applied for direct synthesis of novel and known benzimidazoles through a condensation reaction of o-phenylenediamines with orthoesters under solvent-free conditions. TSA was characterized by powdered X-ray diffraction (XRD), X-ray fluorescence (XRF), and FTIR spectroscopy. This novel and eco-friendly method is very cheap and has many advantages such as excellent yields, recyclable and eco-friendly catalyst, and simple work-up procedure.     

Cages, baskets, ladders, and tubes: conformational studies of polyhedral oligomeric silsesquioxanes

The conformational flexibility of a series of cage, basket, ladder, and tube polyhedral oligomeric silsesquioxanes (POSS) has been examined using the Low Mode:Monte Carlo conformational search method in conjunction with the MM3/GBSA(CHCl3) surface. An ensemble of low energy structures was generated and used to explore the molecular shape and flexibility of each system. The results indicate that, except for the ladder molecule, the incompletely condensed systems that are studied are relatively rigid. Even in cases where the molecule is able to adopt numerous low energy conformations, the overall shape remains cage-like and the conformations differ only by small angles or substituent orientations. The ladder molecule is the most flexible and this ensemble clusters into two families: one that is cage-like and the other that is more open and ladder-like. The conformational flexibilities in the gas and solvent phases, as approximated using the GBSA continuum solvent model, are very similar.     

Method for catalytic preparation of ethyl 2-thienylacetate

Conclusions Using Re₂S₇ as the catalyst, the optimum conditions were found for the selective reduction of the carbonyl group in ethyl 2-thienylglyoxylate to the CH₂ group with the formation of ethyl 2-thienylacetate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2152–2154, September, 1977.     

Low-temperature catalytic preparation of multi-wall MoS_2 nanotubes

Since the first report on inorganic fullerene-like WS2 polyhedra and nanotubes by Tenne et al.[1] in 1992, this kind of nanostructural materials have become extensive research topics owing to their unique electronic structures. WS2 and MoS2 nanomaterials have shown potential applications in the fields of scanning probe microscopy[2], solid-state lubrication[3], heterogeneous catalysis[4], and electrochemical hydrogen storage[5]. Up to now, a great deal of progress has been achieved in the st…     

生物医用磷脂化聚氨酯的设计、制备与性能

聚氨酯因其具有优异的力学性能和良好的生物相容性广泛地应用于医疗领域.但医用聚氨酯常常会引起蛋白吸附、血小板激活、凝血、血栓和补体激活等不良生物学反应,使其应用受到限制.仿生物膜的磷脂表面被认为是和人体最亲和的表面,聚氨酯磷脂化是提高医用聚氨酯材料生物相容性的非常有效的手段之一.近年来国内外课题组在生物医用磷脂化聚氨酯的设计、制备与生物相容性等方面开展了大量的工作,取得了重要的研究进展.本文综述了磷脂改进医用聚氨酯的最新研究成果,指出含氟磷脂化聚氨酯和可降解的磷脂聚氨酯因其优异的性能,代表了该领域的发展方向并具有重要的应用前景.     

二维分子筛的制备及其催化应用研究进展

沸石分子筛是一种具有独特孔道结构的硅铝酸盐晶体,因其具有较大的比表面积、优异的孔道择形性、良好的热稳定性以及适宜的酸性质等特点,被广泛应用于催化、吸附、分离等领域。与常规三维沸石分子筛相比,二维分子筛由于其独特的形貌结构带来的可调变的多级孔结构、适宜的表面酸性以及良好的扩散传质性能等优点,已在吸附和催化领域显示出巨大的应用潜力。本文系统总结了二维MFI、SAPO-34、MCM-n、Y型分子筛等的合成以及此类分子筛催化应用研究方面的最新进展。最后,对二维沸石分子筛材料的新合成方法及新应用领域进行了展望。     

V-Mo-O催化剂的制备及催化甲苯合成苯甲醛的研究

在低温液相条件下,催化氧化甲苯合成苯甲醛是具有竞争力的苯甲醛合成路线。采用溶胶凝胶法制备了V-Mo-O催化剂,评估了在液相低温条件下选择性氧化甲苯的催化性能。研究表明,钒钼配比和焙烧温度对催化剂性能影响显著,适宜的钒钼物质量的配比为6:7,适宜的焙烧温度为500℃。扫描电镜实验表明,该条件下合成的催化剂呈棒状结构,直径约700nm,长度约6µm。X射线衍射观测到催化剂中拥有Mo6V9O40和MoO3物相。X光电子能谱表征,棒状催化剂外表面覆盖一层主含MoO3物种的薄层,这种不同氧化态钼物种的分层组装可能有助于氧物种的传递,提高了其催化性能。当反应温度为80℃,氧化剂为双氧水,溶剂为冰乙酸时,甲苯在该催化剂上的转化率为38.9%,苯甲醛的选择性为69.7%。     

The regio- and stereoselective one-pot catalytic preparation of beta-selenyl acrylamides

Pd(PPh(3))(4) is found to catalytically assemble sulfenamides, terminal aliphatic alkynes, carbon monoxide, and diphenyl diselenides regio- and stereoselectively in a single-pot reaction to produce good yields of beta-selenyl acrylamides. [reaction: see text]     

含Mo介孔复合材料的一步制备及催化性能表征

在强碱性条件下,通过加入辅助模板剂HAcac,制备得到高Mo掺杂的MoSiO_x介孔复合材料。XRD、N₂吸附 脱附、ICP AES、Py FTIR表征结果表明,MoSiO_x具有较规整的孔道结构、较大孔道尺寸、很大的孔容以及大的比表面积。MoSiO_x中Mo物种高度分散,且载量最高可达6.3%以上。以L酸中心为主的酸分布特征使MoSiO_x材料呈中强酸 强酸酸性。柴油HDS性能评价结果表明,MoSiO_x具有很高的柴油HDS活性,加氢后柴油中含硫化合物的质量分数低于10×10^-6。对合成影响因素的分析表明,HAcac及NaOH用量对复合材料的物化性能影响很大。因此,合成时应严格控制HAcac以及NaOH的用量。     

含膦配体的羰基钼(O)和钨(O)化合物的改进合成,反应及催化活性

MoCl5或WCl6与锌粉及适当的膦配体和CO在常压常温进行反应,合成了含膦配体的炭基钼和钨的化合物(Ph2PR)nM(CO)6-n(M=Mo,W;R=ME,Et,n-Pr,Ph;n=2,3),用该方法也成功地将M(CO)5(M=Mo,W)单元负载到含膦的高分子链上,化合物(Ph2PEt)2Mo(CO)4与HgCl2反应得到含Mo-Hg键的化合物。用(Ph3P)2Mo(CO)4和(Ph3P)2Ni(CO)2二元催化体系,在适当温度和压力下对甲醇羰基化反应进行初步研究,得到了初步研究,得到了醋酸和醋酸甲酯。该催化过程对甲醇的转化率可达92%,对醋酸和醋酸甲酯的选择性可达68%。