Direct Synthesis of Bimetallic Pd3Ag Nanoalloys from Bulk Pd3Ag Alloy

In the article of the ACS “Direct Synthesis of Bimetallic Pd₃Ag Nanoalloys from Bulk Pd₃Ag Alloy”, it is reported a transformative, all inorganic synthesis method of preparing supported bimetallic Pd₃Ag alloy nanoparticles. The method involves breaking down bulk Pd₃Ag alloy into the nanoparticles in liquid lithium, converting metallic Li to LiOH, and transferring Pd₃Ag nanoparticles/LiOH mixture onto non-water-soluble supports, followed by leaching off the LiOH with water under ambient conditions. The size of the resulting Pd₃Ag nanoparticles was found narrowly distributed around 2.3 nm characterized by transmission electron microscope (TEM). In addition, studies by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy, and X-ray absorption near edge structure (XANES) spectroscopy showed that the resulting Pd₃Ag nanoparticles inherited similar atomic ratio and alloy structure as the starting material. The synthesized Pd₃Ag nanoparticles exhibited excellent catalytic activity toward hydrogenation of acrolein to propanal.

Chi-Kai Lin, Yan-Gu Lin, Tianpin Wu, Heather M. Barkholtz, Qiyin Lin, Haojuan Wei, Dale L. Brewe, Jeffrey T. Miller, Di-Jia Liu, Yang Ren, Yasuo Ito, Tao Xu. (2012). Direct Synthesis of Bimetallic Pd3Ag Nanoalloys from Bulk Pd3Ag Alloy.  Journal Of The American Chemical Society, DOI: 10.1021/ic301940g

A Bis(ferrocenyl)phenanthroline Iridium(III) Complex as a Lab-on-a-Molecule for Cyanide and Fluoride in Aqueous Solution

The bis(ferrocenyl)phenanthroline iridium(III) complex 1 is synthesized and elaborated as a lab-on-a-molecule for the competitive and quantitative determination of cyanide and fluoride in aqueous solution. 1 exhibits a strong OFF–ON photoluminescence (PL) response upon addition of cyanide with a good selectivity over other anions. The mechanism involves nucleophilic displacement of the phenanthroline ligand, which quenches PL, to furnish a strongly photoluminescent dicyano iridium complex. In contrast, in the electrochemiluminescence (ECL) channel, cyanide undergoes oxidation and a different selectivity is observed. The strong ferrocenium–fluoride interaction is exploited for the first time in ECL to selectively monitor fluoride by a >60-fold enhancement. In both PL and ECL channels, anion selectivity is further challenged by competitive assays in the presence of other anions. Quantitative determination of CN^– and F^– is achieved in both channels.

Qinghai Shu, Lars Birlenbach, Michael SchmittelA. (2012).  Bis(ferrocenyl)phenanthroline Iridium(III) Complex as a Lab-on-a-Molecule for Cyanide and Fluoride in Aqueous Solution. Journal Of The American Chemical Society, DOI: 10.1021/ic301256g

Nuevo catalizador para la fabricación de bolsas de plástico

Si no fuera por el hecho de que la industria química normalmente utiliza al paladio como reactivo para el polietileno, las bolsas de plástico serían muy deficientes, ya que se romperían con una carga de apenas un par de manzanas y un cartón de leche.

Sin embargo, gracias al trabajo eficaz de ese metal precioso, no sufrimos este problema. El paladio convierte al acetileno en etileno, el cual es usado para crear polietileno. El etileno siempre contiene trazas de acetileno, porque ambas sustancias se obtienen a partir del petróleo crudo y no es fácil separarlas. Sin embargo, el acetileno interfiere en la conversión del etileno en polietileno. Por tanto, a menos que primero se le convierta en etileno mediante la unión de dos átomos de hidrógeno en presencia de paladio, el plástico resultante es de mala calidad. La producción mundial de polietileno es de 80 millones de toneladas al año, por lo que los costos de conversión del acetileno son considerables.

Estos costos podrían reducirse significativamente reemplazando al paladio por otros materiales más baratos pero igual de eficientes.

Un equipo de científicos del Instituto Max Planck de Física Química de los Sólidos en Dresde, el Instituto Fritz Haber de la Sociedad Max Planck en Berlín y otras instituciones alemanas ha desarrollado un catalizador usando hierro y aluminio que hace un trabajo igual de bueno que el del catalizador de paladio convencional, pero que obviamente cuesta mucho menos.

En la labor de investigación y desarrollo han participado, entre otros, Marc Armbrüster y Juri Grin del Instituto Max Planck de Física Química de los Sólidos, y Robert Schloegl del Instituto Fritz Haber.

Amazings / NCYT. (2012). Nuevo catalizador para abaratar costos en la fabricación de bolsas de plástico. Recuperado 27/nov/2012, de: http://noticiasdelaciencia.com/not/4699/nuevo_catalizador_para_abaratar_costos_en_la_fabricacion_de_bolsas_de_plastico/

Role of Fe–N–C Geometry Flip-Flop in Bistability in Fe(tetrazol-2-yl)4(C2H5CN)2-Type Core Based Coordination Network

One of the most interesting phenomena, the thermal induced spin crossover (SCO), arises from an ability of the transition metal octahedral complexes with 3d⁴-3d⁷ configuration to adopt two different electronic states. In iron(II) complexes, the high spin (HS) to low spin (LS) HS(S = 2)LS(S = 0) transition triggered by a change of temperature, an application of pressure, magnetic field, or by light irradiation involves severe alterations of magnetic, optical, and dielectric properties which are the basis of potential applications. For practical applications, SCO materials have to exhibit an abrupt spin transition with a wide loop of hysteresis. According to the model of elastic interactions developed by Spiering, a perturbation produced by shortening of the Fe–N bond length involves a compression of a crystal lattice contributing additionally to a stabilization of the LS form of iron(II).

[Fe(ebtz)₂(C₂H₅CN)₂](ClO₄)₂ was prepared in the reaction of 1,2-di(tetrazol-2-yl)ethane (ebtz) with Fe(ClO₄)₂·6H₂O in propionitrile. The compound crystallizes as a one-dimensional (1D) network, where bridging of neighboring iron(II) ions by two ebtz ligand molecules results in formation of a [Fe(ebtz)₂]_∞ polymeric skeleton. The 1D chains are assembled into supramolecular layers with axially coordinated nitrile molecules directed outward. The complex in the high spin (HS) form reveals a very rare feature, namely, a bent geometry of the Fe–N–C(propionitrile) fragment (149.1(3)° at 250 K). The HS to low spin (LS) HS→LS transition triggers reorientation of the propionitrile molecule resulting in accommodation of a typical linear geometry of the Fe–N–C(nitrile) fragment. The switching of the propionitrile molecule orientation in relation to the coordination octahedron is associated with increase of the distance between the supramolecular layers. When the crystal is in the LS phase, raising the temperature does not cause reduction of the distance between supramolecular layers, which contributes to further stabilization of the more linear geometry of Fe–N–C(C₂H₅) and the LS form of the complex. Thus, a combination of Fe–N–C(C₂H₅) geometry lability and lattice effects contributes to the appearance of hysteretic behavior (T_1/2^↓ ≈ 112 K, T_1/2^↑ ≈ 141 K).

Agata Białońska, Robert Bronisz. (2012). Role of Fe–N–C Geometry Flip-Flop in Bistability in Fe(tetrazol-2-yl)4(C2H5CN)2-Type Core Based Coordination Network Journal Of The American Chemical Society, DOI: 10.1021/ic300880w

Reactivity of Diphenylpropynone Derivatives Toward Metal-Associated Amyloid-β Species

In Alzheimer’s disease (AD), metal-associated amyloid-β (metal–Aβ) species have been suggested to be involved in neurotoxicity; however, their role in disease development is still unclear. To elucidate this aspect, chemical reagents have been developed as valuable tools for targeting metal–Aβ species, modulating the interaction between the metal and Aβ, and subsequently altering metal–Aβ reactivity. In the article of the ACS journal: “Reactivity of Diphenylpropynone Derivatives Toward Metal-Associated Amyloid-β Species”, it is reported  the design, preparation, characterization, and reactivity of two diphenylpropynone derivatives (DPP1 and DPP2) composed of structural moieties for metal chelation and Aβ interaction (bifunctionality). The interactions of these compounds with metal ions and Aβ species were confirmed by UV–vis, NMR, mass spectrometry, and docking studies. The effects of these bifunctional molecules on the control of in vitro metal-free and metal-induced Aβ aggregation were investigated and monitored by gel electrophoresis and transmission electron microscopy (TEM). Both DPP1 and DPP2 showed reactivity toward metal–Aβ species over metal-free Aβ species to different extents. In particular, DPP2, which contains a dimethylamino group, exhibited greater reactivity with metal–Aβ species than DPP1, suggesting a structure-reactivity relationship. Overall, our studies present a new bifunctional scaffold that could be utilized to develop chemical reagents for investigating metal–Aβ species in AD.

Resource:

Reactivity of Diphenylpropynone Derivatives Toward Metal-Associated Amyloid-β Species. Amit S. Pithadia, Akiko Kochi, Molly T. Soper, Michael W. Beck, Yuzhong Liu, Sanghyun Lee, Alaina S. DeToma, Brandon T. Ruotolo, and Mi Hee Lim. Inorganic Chemistry. Article ASAP

Structural and Spectroscopic Trends in a Series of Half-Sandwich Scorpionate Complexes

Hydrotris(pyrazol-1-yl)borates (i.e., HB{pz}₃^–, Tp) and tris(pyrazol-1-yl)methanes (i.e., HC(pz)₃, Tpm) are tridentate face-capping ligands, formally isolobal to the cyclopentadienyl anion (C₅H₅^–, Cp), that have been extensively utilized in bioinorganic and organometallic chemistry. A wide variety of half-sandwich complexes can be supported, which have been exploited as enzyme active site models and as functional catalysts. For example, Tp-supported copper complexes (i.e., [Tp^Br3Cu(NCMe)]) have been used as nitrene transfer catalysts, promoting olefin aziridination and amination of aliphatic and aromatic C–H bonds. Analogous catalysis was also reported using [Tpm^RCu(NCMe)]BF₄ in ionic liquids. Fifteen half-sandwich scorpionate complexes [(L)M(NCMe)₃](BF₄)_n (L = tris(3,5-dimethylpyrazol-1-yl)methane, Tpm^Me,Me, n = 2, 1^M, M = Mn, Fe, Co, Ni; L = tris(3-phenylpyrazol-1-yl)methane, Tpm^Ph, n = 2, 2^M, M = Mn, Fe, Co, Ni; L = hydrotris(3,5-dimethylpyrazol-1-yl)borate, [Tp^Me,Me]⁻, n = 1, 3^M, M = Fe, Co, Ni; L = hydrotris(3-phenyl-5-methylpyrazol-1-yl)borate, [Tp^Ph,Me]⁻, n = 1, 4^M, M = Mn, Fe, Co, Ni) were prepared by addition of the tripodal ligands to solvated [M(NCMe)_x]²⁺ (M = Mn, x = 4; M = Fe, Co, Ni, x = 6) precursor complexes. The product complexes were characterized by ¹H NMR (except M = Mn), UV–vis–NIR, and FTIR spectroscopy. The structures of 2^Mn, 2^Ni, 3^Fe, 3^Co, and 4^Fe were determined by X-ray crystallography. The data were consistent with complexes of high-spin divalent metal ions in idealized piano-stool geometries in all cases. Consequent lability of the acetonitrile ligands will enable use of these complexes as synthetic precursors and as catalysts. Comparison to previously reported structures of 1^Fe, 1^Co, 2^Fe, and 2^Co, the triflate salt analogues of 4^Co and 4^Ni, as well as related sandwich complexes (e.g., [(Tp^Me,Me)₂M]) and solvated metal dications [M(NCMe)₆]²⁺ reveals numerous trends in M–N bond lengths. Primary among these are the Irving–Williams series, with significant structural effects also arising from ligand charge and sterics. Systematic trends in spectroscopic data were also observed which further elucidate these issues,

Structural and Spectroscopic Trends in a Series of Half-Sandwich Scorpionate ComplexesShengwen Liang, Haoshuang Wang, Tapash Deb, Jeffrey L. Petersen, Gordon T. Yee, and Michael P. Jensen. Inorganic Chemistry Article ASAP

Hexagonally Ordered KLaF4 Host: Phase-Controlled Synthesis and Luminescence Studies

Research on the lanthanide-doped upconversion (UC) energy systems continues to be a vibrant and growing interdisciplinary field, essentially in two directions. One of them is tuning of the optical properties such as the high UC efficiency and emission profile in well-established energy UC systems, adopting different synthetic strategies, surface modification, and multicolor emission optimization. The other direction has been controlling the size, shape, and phase purity of the crystals of these systems from the applications point of view. In addition, the search for newer host fluoride lattices that are more effective for the UC process is also being pursued with the concomitant aim of understanding its role.

Experiments resulting in the successful synthesis of hexagonally ordered KLaF4 have been described for the first time. Syntheses from three different lanthanum precursors and KF under nonaqueous conditions and at atmospheric pressure are presented. The temperature, time of the fluorination reactions, and lanthanum precursor influenced the formation of hexagonal KLaF4. While La(OiPr)3 and La(acac)3 yielded hexagonal KLaF4 by their reaction with KF in methanol at 65 °C, LaCl3 favored only the formation of cubic KLaF4 at 25 °C (room temperature). Size-induced phase transformation from cubic KLaF4 to its hexagonal polymorph has been proposed for the reactions involving La(acac)3 and La(OiPr)3 and KF. Rietveld refinement of the powder X-ray diffraction pattern of the hexagonally ordered KLaF4 was successfully carried out in space group P6̅2m (No. 189) with lattice constants a = 6.5842(3) Å and c = 3.8165(3) Ǻ. A relatively lower effective phonon energy of 262 cm–1 observed for the hexagonally ordered KLaF4 (determined from its Raman spectrum) suggests its potential as a host for optically active elements with the possibility of minimized nonradiative processes. The hexagonal KLaF4 sample was doped with Er3+ ion (3 mol %) and systematically investigated by diffuse reflectance, normal emission, and upconversion studies. Strong green emission (4S3/2, 2H11/2 → 4I15/2) has been observed upon 980 and 460 nm excitation. A highly transparent light-emitting polymer [poly(methyl methacrylate)] composite containing hexagonal KLaF4:Er3+ phosphor has also been effectively demonstrated for many potential applications

Fuente:

Shahzad, A.; Vijaya P.; Nagarajan. Hexagonally Ordered KLaF4 Host: Phase-Controlled Synthesis and Luminescence Studies. J. Am. Chem. Soc., 2012, 10.1021

Plástico con propiedades comparables a las del acero

El reciente proyecto de desarrollo de un plástico tan robusto que será capaz de reemplazar al acero en algunas aplicaciones ofrece interesantes perspectivas para sectores industriales como el automovilístico. Reemplazar piezas metálicas por piezas hechas con este nuevo plástico mantendría la funcionalidad del vehículo y reduciría su peso, con el consiguiente ahorro de combustible.

El químico Moshe Kol de la Universidad de Tel Aviv en Israel está desarrollando una variedad hiperrobusta de polipropileno, uno de los plásticos más usados en el mundo. Esta nueva variedad de polipropileno tendrá el potencial de reemplazar al acero y a otros materiales usados en productos comunes. Esto podría tener repercusiones a largo plazo para muchas industrias, incluyendo a la del automóvil, en la cual sería factible reemplazar diversas piezas metálicas de automóviles por piezas de plástico.

Otra aplicación que Kol considera muy prometedora es usar el nuevo plástico para fabricar tuberías destinadas al suministro de agua potable. Para las redes de suministro doméstico de agua tradicionalmente se han usado tuberías de cemento y cañerías metálicas, unas y otras susceptibles de sufrir fugas, con el consiguiente desperdicio de agua. Sin embargo, reemplazar una tubería que pierde agua no es tarea fácil debido en buena parte a que las tuberías tradicionales son muy pesadas.

Amazings / NCYT.(07/2012). Plástico con propiedades comparables a las del acero. Recuperado 24/Nov/2012, de: http://noticiasdelaciencia.com/not/4686/plastico_con_propiedades_comparables_a_las_del_acero/