Density Functional Study of the Stable Oxidation States and the Binding of Oxygen in MO4 Clusters of the 3d Elements

12/marzo/2012
By Maximiliano De La Higuera Macías

The tetraoxide clusters with stoichiometry MO4, and the structural isomers with side-on and end-on bonded dioxygen, are studied by DFT with the B1LYP functional. Diperoxides M (O2)2 are the most stable clusters at the beginning (Sc, Ti) and at the end of the row (Co_Cu), the latter being planar. For V, Cr, and Mn, the dioxoperoxides O2M (O2) are the most stable isomers. Low-spin states are dominant for the nonplanar diperoxides M (O2)2 and dioxoperoxides O2M (O2), and the local magnetic moment at the metal cations is small.

The local charge on the metal cation center is higher in the diperoxides of Sc and Ti; it drops significantly in the dioxoperoxides of V and Cr. The iron dioxosuperoxide in the 3A00 state, which contains end-on bonded dioxygen, OOFeO2, is an exception with higher charge on Fe. In the planar diperoxides of Co, Ni, and Cu, oxygen-to-metal charge transfer is significant, and the local charge on the metal cation is close to 1.

In all tetraoxygen clusters of the 3d elements, the cation center remains strongly electrophilic and interacts with Ar atoms from the inertgas matrix, where the clusters are trapped for IR spectral studies. Significant frequency shifts in the matrix are found for the dioxoperoxide of vanadium, O2V (O2), the dioxosuperoxide of iron, OOFeO2, and the nickel diperoxide, Ni(O2)2

.L. Uzunova, Ellie. Density Functional Study of the Stable Oxidation States and the
Binding of Oxygen in MO4 Clusters of the 3d Elements. Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 11, Sofia 1113, Bulgaria. 2012. http://pubs.acs.org/doi/pdfplus/10.1021/jp2034888

Facile Solvothermal Synthesis of Phase-Pure Cu4O3 Microspheres and Their Lithium Storage Properties

In order to tackle new challenges met in the development of modern industry and society, it is imperative to develop materials with high energy and power density, particular electrodes in Li-ion batteries. Transition-metal oxides (TMOs, where TM = Co, Fe, Ni, Cu, etc.) have been regarded as potential candidates for anode materials. This is because lithium can be stored reversibly in TMOs through a heterogeneous conversion reaction: Li + TMO → Li₂O + TM, which involves the formation and decomposition of Li₂O via the reduction and oxidation of metal nanoparticles, different from the classical Li insertion/desertion or Li-alloying processes. Although CuO (tenorite or cupric oxide) and Cu₂O (cuprite or cuprous oxide) have been extensively investigated as potential anode materials for Li-ion batteries, the electrochemical lithium storage properties of Cu₄O₃ have never been reported.

Phase-pure Cu4O3 microspheres were synthesized for the first time via a facile solvothermal method, using Cu(NO3)2·3H2O as the precursor. A formation mechanism was proposed based on the observation of a series of reaction intermediates. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, temperature-programmed reduction and oxidation, X-ray photoelectron spectroscopy, and nitrogen adsorption. It was found that the composition of the prepared products were highly dependent on the synthesis conditions, particularly the hydrate water content in the copper precursor of Cu(NO3)2. Pure Cu4O3 microspheres with a diameter of 2–10 μm could be obtained via the symproportionation reaction (2CuO + Cu2O → Cu4O3), which was regarded not being feasible in aqueous media under mild synthesis conditions. The electrochemical properties of the Cu4O3 microspheres as anode materials for Li-ion batteries were also investigated. Compared to the simple physical mixture of CuO and Cu2O with an equivalent atomic ratio of 2:1, the as-prepared Cu4O3 exhibited unique lithium storage behaviors at a low voltage range and superior electrochemical performances as an anode material for Li-ion batteries. The successful preparation of pure Cu4O3 material could provide opportunities to further explore its physicochemical properties and potential applications.

Zhao, L. Chen, H. Wang, Y.(et.al.) Facile Solvothermal Synthesis of Phase-Pure Cu4O3 Microspheres and Their Lithium Storage Properties. February 23 , 2012. http://pubs.acs.org/doi/full/10.1021/cm203589h

Comparison of Cu(II)-Promoted Leaving Group Stabilization of the Cleavage of a Homologous Set of Phosphate Mono-, Di-, and Triesters in Water,Methanol

Studies of systems incorporating metal ions that provide leaving group assistance (LGA) in the reactions of small molecules is documented in only a few cases. Herein they reported on an expanded study where the reaction medium changes from methanol to both ethanol and water, how these solvents affect the reaction mechanisms, and the acceleration provided by LGA.The cleavage of a set of phosphate mono-, di-, and triesters having a Cu(II)-complexed 2-phenanthrolyl group at the ortho-position of a departing phenoxide was studied in water and ethanol. Experimentally observed pH/rate profiles, solvent deuterium kinetic isotope effects, and activation parameters are compared with those obtained in methanol. The pH/rate profile in each solvent exhibits an extended plateau due to solvent attack on forms designated as [Cu(II):1b/c]⁰ for the monoester, [Cu(II):2b]⁺, for the diester, and [Cu(II):3a]²⁺for the triester. The solvent dkie values (k_H/k_D) for the three complexes are 0.91, 0.95, and 0.83 for decomposition of [Cu(II):1b/c]⁰ in water (W), methanol (M), and ethanol (E), 1.22, 1.09, and 1.29 for [Cu(II):2b]⁺ in W, M, and E, and 1.94, 2.2, and 1.96 for [Cu(II):3a]²⁺ in W, M, and E. Near unit, or slightly inverse values for the monoester are taken as evidence for little involvement of solvent in a highly dissociative TS for P–OAr cleavage, with slightly higher solvent dkie values for the diester signifying the onset of some solvent participation in assisting the nucleophilic displacement. The larger primary dkie for the triester gives evidence for a solvent-assisted delivery of ROH in the cleavage through a more associative mechanism. Activation parameters for each substrate in the solvents are compared, indicating that the transition from methanol to ethanol for each substrate involves a near cancellation of the ΔΔH^‡ and –TΔΔS^‡ values (25 °C) so that the respective rates in both solvents are very similar. The transition from alcohol to water produces variable effects, with ΔΔH^‡ and –TΔΔS^‡ values canceling for cleavage of the triester and being additive for the mono and diester, explaining their 100–500 rate reduction in passing from methanol to water. The rate enhancing effects of the Cu(II)-promoted leaving group assistance in all three solvents are substantial and estimated at 10¹²–10¹⁵ for the monoester, 10¹²–10¹⁴ for the diester, and 10⁵ for the triester relative to their background reactions.

Mark A. R. Raycroft, C. Tony Liu, and R. Stan Brown. Comparison of Cu(II)-Promoted Leaving Group Stabilization of the Cleavage of a Homologous Set of Phosphate Mono-, Di-, and Triesters in Water, Methanol, and Ethanol. Inorganic Chemistry. March 7, 2012 ASAP. http://pubs.acs.org/doi/full/10.1021/ic300059e

Tris(diethylamino)silane-A new precursor compound for obtaining layers of silicon carbonitride

Silicon carbonitride layers have been obtained by chemical deposition from the gas phase with thermal (LPCVD) and plasma (PECVD) activation of the gas mixture of helium with the new volatile siliconorganic compound tris(diethylamino)silane ( EtN)SiH (TDEAS) in the temperature region 373-1173 K. Thermodynamic simulation of the deposition processes from the gas mixture (TDEAS + He) in the temperature interval 300-1300 K and pressure interval P from 1 × 10 to 10 mm Hg has revealed the possibility of varying the equilibrium composition of the condensed phase depending on the synthesis temperature and the composition of the initial gas mixture. Physicochemical and functional properties of obtained layers were studied by complex of modern methods. It has been established that the chemical composition of the silicon carbonitride layers obtained by the PECVD method, depending on the deposition conditions, approaches that of silicon oxynitride or nitride, and the composition of those obtained by the LPCVD method approaches that of silicon carbide. The presence of nanocrystals with a phase composition close to the standard α-SN phase and of carbon inclusions has been found in the layers.

Fainer, N. N., Golubenko, A. A., Rumyantsev, Y. u., Kesler, V. V., Ayupov, B. B., Rakhlin, V. V., & Voronkov, M. M. (2012). Tris(diethylamino)silane-A new precursor compound for obtaining layers of silicon carbonitride. Glass Physics & Chemistry, 38(1), 15-26.

Salicylimine-Based Fluorescent Chemosensor for Aluminum Ions and Application to Bioimaging

Chemosensors for selective detection of various biologically and environmentally relevant metal ions have recently attracted great attention. The widespread use of aluminum in food additives, aluminum-based pharmaceuticals, and storage/cooking utensils often exposes people to aluminum ions. In addition, frequent use of aluminum foil, vessels, and trays for convenience results in moderate increases in the Al3+ concentration in food. After absorption, aluminum ions would be distributed to all tissues in humans and animals and eventually accumulate in the bone. The iron binding protein is known to be the main carrier of Al3+ in plasma, and Al3+ can enter the brain and reach the placenta and fetus. Aluminum ions may stay for a very long time in various organs and tissues before being excreted through the urine. In addition, aluminum ions have been implicated as a causative factor of Alzheimer’s disease and associated with damage to the central nervous system in humans. Although trace amounts of aluminum ions are present in the drinking water, low-dose chronic exposure to the ions may cause Alzheimer’s disease possibly due to accumulation of oxidative damage induced by the ions. Sensitive bioimaging of Al3+ in the cell is a prerequisite for understanding the underlying mechanism about how aluminum ions cause aluminum-induced human diseases including Alzheimer’s disease.Thus, detection of Al3+ is important to control the concentration levels in the biosphere and minimize direct affects on human health.

In recent years, fluorescent chemosensors have attracted significant interest because of their potential use in medicinal and environmental research. The most commonly employed method used for chemosensor detection is the development of probe molecules that consist of a photon interaction site as a fluorophore and a metal binding site. In the presence of specific metal ions, the fluorophore–receptor communication gets turned on as a result of the binding of the metal ions at the receptor site. Until recently, only a few fluorescent chemosensors have been developed for detection of Al3+.Most fluorescent sensors for Al3+ have good selectivity, but this approach has several disadvantages including complicated synthetic procedures and poor water solubility. Meanwhile, some Schiff base compounds coordinated to metal ions were reported to have antitumor and antioxidative activities. Although many Schiff base derivatives incorporating a fluorescent moiety have been used to detect various metal ions, Schiff base-type Al3+ chemosensors are very rare and no examples of water-soluble devices as well as sensors that can be used for cell imaging have been developed. Possible utilization of PSI (o-phenolsalicylimine) as intracellular sensors of Al3+ was also examined by confocal fluorescence microscopy.

Kim, S. Young, J. Kim, Ka(et.al.).Salicylimine-Based Fluorescent Chemosensor for Aluminum Ions and Application to Bioimaging March 2, 2012. Inorg. Chem,Article ASAP. http://pubs.acs.org/doi/suppl/10.1021/ic2024583

Effects of Surface Heterogeneity on the Adsorption of CO(2) in Microporous Carbons.

Carbon capture combined with utilization and storage has the potential to serve as a near-term option for CO(2) emissions reduction. CO(2) capture by carbon-based sorbents and CO(2) storage in geologic formations such as coal and shale both require a thorough understanding of the CO(2) adsorption properties in microporous carbon-based materials. Complex pore structures for natural organic materials, such as coal and gas shale, in addition to general carbon-based porous materials are modeled as a collection of independent, noninterconnected, functionalized graphitic slit pores with surface heterogeneities. Electronic structure calculations coupled with van der Waals-inclusive corrections have been performed to investigate the electronic properties of functionalized graphitic surfaces. With Bader charge analysis, electronic structure calculations can provide the initial framework comprising both the geometry and corresponding charge information required to carry out statistical modeling. Grand canonical Monte Carlo simulations were carried out to determine the adsorption isotherms for a given adsorbent-adsorbate interaction at temperature/pressure conditions relevant to carbon capture applications to focus on the effect of the surface functionalities. On the basis of the current work, oxygen-containing functional groups were predicted to enhance CO(2) adsorption in microporous carbon materials in the absence of water vapor, and the hydrated graphite was found to hinder CO(2) adsorption.

Como podemos leer en este artículo cada vez estamos mas cerca de la remediación ambiental, no obstante aun quedan muchos retos políticos, culturales y tecnológicos pero de granito en granito se podrá lograr un cambio.

Liu Y, Wilcox J. SourceDepartment of Energy Resources Engineering, School of Earth Sciences, Stanford University , Green Earth Sciences 065, 367 Panama Street, Stanford, California 94305, United States.

Una mirada al futuro desde el pasado.

Por lo visto, de las tantas fuentes renovables y eficientes de energía. El hidrógeno esta ganando campo para las producción energética casera. En Japón,Matsushita Electronic, el fabricante de Panasonic ha podido producir una celda de combustible de hidrogeno muy eficiente.

"El sistema de Matsushita está basado en una tecnología de electrolitos polímeros que, según el Nikkei, es más eficiente que los modelos existentes. De esta manera, por medio de una reacción química, el nuevo sistema es capaz de convertir más del 39% para generar un máximo de 750 vatios de energía hasta un 37% menos de emisiones contaminantes que los generadores tradicionales."

Por lo visto, iban a hacer pruebas de eficiencia(2009) y si todo quedaba dentro de los estándares de producción y eficiencia las iban a sacar al mercado.Ya han pasado tres años, y tal parece que el poder de tomar la abundancia del elemento mas simple a nuestro favor y en nuestras casas aun esta lejos. Aunque a veces pareciera que no tanto.

Desde el lado de vista económico-gubernamental hay una disruptiva entre eficiencia e interés. Si todos los hogares tuvieran celdas de hidrogeno u otra fuente de energia renovable entonces serian eficientes y no se desperdiciarian recursos. Pero por otro lado el gobienro no tendria las recaudaciones de impuestos de compañias paraestatales o privadas energéticas. No se puede tener a todos contentos.

Para el paper original consulten:

http://web.ebscohost.com/ehost/pdfviewer/pdfviewer?sid=f9e6ae45-6b45-4e2c-99bc-9c151fbe415e%40sessionmgr4&vid=2&hid=17

ADN,"CREAN UNA BATERÍA DE HIDRÓGENO CAPAZ DE SUMINISTRAR EL 60% DE LA

ENERGÍA DE UNA CASA", ADYN, Mayo 2008, pps.N85