Halogen-free water-immiscible ionic liquids based on tetraoctylammonium cation and dodecylsulfate and dodecylbenzenesulfonate anions, and their application as chelate extraction solvent.

The tetraoctylammonium cation forms water-immiscible room temperature ionic liquids with dodecylsulfate and dodecylbenzenesulfonate anions. The ionic liquids are halogen-free and can be considered environmentally friendly solvents. At 25 degrees C, the solubilities of water in tetraoctylammonium dodecylsulfate and tetraoctylammonium dodecylbenzenesulfonate were 2.8 and 4.0%, respectively, and the densities were 0.92 and 0.93 g cm(-3). The ionic liquids formed stable interfaces with water at 25 degrees C. The possible use of tetraoctylammonium dodecylsulfate as chelate extraction solvent was evaluated by using 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione as extractant. Tetraoctylammonium dodecylsulfate showed high extraction performance for divalent transition metal cations.     

Use of dipotassium cyanamide for the synthesis of cyanoimido (NCN2-) complexes of tungsten and cobalt

Three transition metal cyanoimido (NCN2-) complexes, (Cp*WS2)2(mu-NCN) (1) (Cp* = eta 5-C5Me5), K[(Cp*WS2)2(NCN)] (2) and ([bipy)2Co]2(mu-NCN)2)(ClO4)2 (3), were synthesized from dipotassium cyanamide, and their structures were determined.     

An intermolecular perturbation approach to the cycloaddition of carbenes toward olefins. Reaction Path and Stereoselectivity

The perturbation theory of Murrell, Randi and Williams for intermolecular interaction has been combined with the assumption of local zero-differential overlaps. The theory has been applied to the cycloadditions of singlet methylene and halocarbenes toward olefins. The results, obtained by use of the CNDO/2 energies and wave functions for isolated molecules, quantitatively assess the roles of various types of energies influencing the stereochemical courses of reaction. The syn/anti stereoselectivities of halocarbenes in their cycloadditions toward cis-butene-2 are found to be governed by the Coulombic, dispersion, charge-transfer and exchange-repulsion energies altogether. Participation of the d orbitals of the chlorine atom in charge transfer is emphasized.

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Zusammenfassung Die Störungsrechnung von Murrell, Randic und Williams für intermolekulare Wechselwirkung wurde in Verbindung mit der Annahme von lokalen ZDO zur Berechnung der Cycloaddition von Singulett-Methylen oder -Halogencarbenen an Olefine angewendet. Die Resultate, die über die CNDO/2-Ergebnisse für die isolierten Moleküle erhalten wurden, lassen die Rolle der einzelnen Energieanteile erkennen, die die Stereochemie der Reaktion beeinflussen. Die syn/anti-Stereoselektivität der Halogencarbene gegenüber cis-2-Buten wird durch die Coulomb-, Dispersions-, Charge-transfer- und Austausch-Wechselwirkung gemeinsam bestimmt. Auch die d-Orbitale von Chlor sind für den Charge transfer von Bedeutung.

     

Searching ultimate nanometrology for AlOx thickness in magnetic tunnel junction by analytical electron microscopy and X-ray reflectometry.

Practical analyses of the structures of ultrathin multilayers in tunneling magneto resistance (TMR) and Magnetic Random Access Memory (MRAM) devices have been a challenging task because layers are very thin, just 1-2 nm thick. Particularly, the thinness (approximately 1 nm) and chemical properties of the AlOx barrier layer are critical to its magnetic tunneling property. We focused on evaluating the current TEM analytical methods by measuring the thickness and composition of an AlOx layer using several TEM instruments, that is, a round robin test, and cross-checked the thickness results with an X-ray reflectometry (XRR) method. The thickness measured by using HRTEM, HAADF-STEM, and zero-loss images was 1.1 nm, which agreed with the results from the XRR method. On the other hand, TEM-EELS measurements showed 1.8 nm for an oxygen 2D-EELS image and 3.0 nm for an oxygen spatially resolved EELS image, whereas the STEM-EDS line profile showed 2.5 nm in thickness. However, after improving the TEM-EELS measurements by acquiring time-resolved images, the measured thickness of the AlOx layer was improved from 1.8 nm to 1.4 nm for the oxygen 2D-EELS image and from 3.0 nm to 2.0 nm for the spatially resolved EELS image, respectively. Also the observed thickness from the EDS line profile was improved to 1.4 nm after more careful optimization of the experimental parameters. We found that EELS and EDS of one-dimensional line scans or two-dimensional elemental mapping gave a larger AlOx thickness even though much care was taken. The reasons for larger measured values can be found from several factors such as sample drift, beam damage, probe size, beam delocalization, and multiple scattering for the EDS images, and chromatic aberration, diffraction limit due to the aperture, delocalization, alignment between layered direction in samples, and energy dispersion direction in the EELS instrument for EELS images. In the case of STEM-EDS mapping with focused nanoprobes, it is always necessary to reduce beam damage and sample drift while trying to maintain the signal-to-noise (S/N) ratio as high as possible. Also we confirmed that the time-resolved TEM-EELS acquisition technique improves S/N ratios of elemental maps without blurring the images.     

Al-RUB-41: a shape-selective zeolite catalyst from a layered silicate

A new zeolite catalyst, Al-RUB-41, was synthesized for the first time. It was tested as a catalyst in methanol amination, and showed a shape-selective performance that results in a highly favorable product distribution. The shape-selective nature was also evidenced by using Pt-Al-RUB-41 as a bifunctional catalyst for decane hydroconversion. With its unique pore architecture and remarkable shape-selective character, Al-RUB-41 presents a significant commercial potential in industrial catalysis.     

Synthesis of chiral mesoporous silica and its potential application to asymmetric separation

Chiral mesoporous silica (CMS) has been successfully synthesized in the presence of basic amino acids; the use of basic amino acids in combination with the chiral anionic surfactant is advantageous for the formation of CMS in terms of uniformity in the twisted morphology. We first demonstrate that thus obtained chiral mesoporous silicas can be used for the enantioselective separation of racemic compounds; the helical rod-shaped CMS is found to be capable of asymmetric separation of racemic N-trifluoroacetylalanine ethyl ester (CF₃CO-Ala-OEt). The left handedness-rich CMS shows asymmetric preferential adsorption of the L isomer and vice versa.     

Cyclic quaternary ammonium ionic liquids with perfluoroalkyltrifluoroborates: synthesis, characterization, and properties

New cyclic quaternary ammonium salts, composed of N-alkyl(alkyl ether)-N-methylpyrrolidinium, -oxazolidinium, -piperidinium, or -morpholinium cations (alkyl = nC4H9, alkyl ether = CH3OCH2, CH3OCH2CH2) and a perfluoroalkyltrifluoroborate anion ([R(F)BF3]-, R(F) = CF3, C2F5, nC3F7, nC4F9), were synthesized and characterized. Most of these salts are liquids at room temperature. The key properties of these salts--phase transitions, thermal stability, density, viscosity, conductivity, and electrochemical windows--were measured and compared to those of their corresponding [BF4]- and [(CF3SO2)2N]- salts. The structural effect on all the above properties was intensively studied in terms of the identity of the cation and anion, variation of the side chain in the cation (i.e., alkyl versus alkyl ether), and change in the length of the perfluoroalkyl group (R(F)) in the [R(F)BF3]- ion. The reduction of Li+ ions and reoxidation of Li metal took place in pure N-butyl-N-methylpyrrolidinium pentafluoroethyltrifluoroborate as the supporting electrolyte. Such comprehensive studies enhance the knowledge necessary to design and optimize ionic liquids for many applications, including electrolytes. Some of these new salts show desirable properties, including low melting points, high thermal stabilities, low viscosities, high conductivities, and wide electrochemical windows, and may thus be potential candidates for use as electrolytes in high-energy storage devices. In addition, many salts are ionic plastic crystals.     

Synthesis of crystallized mesoporous transition metal oxides by silicone treatment of the oxide precursor

Ordered mesoporous transition metal oxides were successfully crystallized after strengthening the amorphous framework by a silica layer, which efficiently protected the original mesoporous structure against crystallization and resulting mass transfer.