Página 1 dos resultados de 2015 itens digitais encontrados em 0.008 segundos

Estudo teórico de propriedades químicas de sistemas hetero-macrocíclos que complexam metais de transição divalentes da primeira e segunda filas; Theoretical study of chemistry proprieties of the hetero-macrocycle systems that complex bivalentes transition metals of the first and second-row

Lima, Francisco das Chagas Alves
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 06/05/2008 PT
Relevância na Pesquisa
486.4647%
Um estudo teórico detalhado das estruturas e energias do ligante 1, 7, 11, 17-tetraoxa-2, 6, 12, 16-trazaocicloocsano ([20]aneN4O4) coordenado com íons metálicos de transição Fe2+, Co2+, Ni2+, Ru2+, Rh2+ e Pd2+ foi realizado em nível de teoria B3LYP/Lanl2DZ. As geometrias dos complexos foram totalmente otimizados em simetria Cs com os íons metálicos coordenados com quatro átomos de nitrogênio (complexos 1a e 1aq) ou quatro átomos de oxigênios (complexos 1b e 1bq) e duas moléculas de água. Os arranjos octaédricos (1a e 1b) e quadrado-planares (1aq e 1bq) foram consideremos neste trabalho. A estrutura teórica está em excelente acordo com a estrutura de difração de raio-x experimental determinada para o complexo octaédrico de Ni2+ de [20]AneN4O4. Os cátions M2+ ligam-se preferencialmente aos átomos de nitrogênios com energia de ligação que aumenta na ordem Fe2+ < Ru2+ < Co2+ < Ni2+ < Rh2+ < Pd2+. Para os metais de transição da primeira fila, os complexos de spin alto são mais estáveis que os complexos de spin baixo. Em contraste, para os metais de transição da segunda fila, os estados de spin baixo mostraram-se mais estáveis que os estados de spin alto. As ligações metal-ligante nos complexos foram analisadas em termo das interações covalentes e iônicas e ajudaram a entender porque os complexos (1a e 1aq) são mais estáveis que os complexos (1b e 1bq). Os complexos poliaminas [20]aneN4 e poliéteres [20]aneO4 foram obtidos substituindo os átomos de nitrogênio e oxigênio da posição alfa dos macrociclos [20]aneN4O4 e [20]aneO4N4...

Estudo de dispositivos orgânicos emissores de luz empregando complexos de terras raras e de metais de transição.; Study of organic light-emitting devices using rare earth and transition metals complexes.

Santos, Gerson dos
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 21/08/2008 PT
Relevância na Pesquisa
568.59027%
Neste trabalho foram projetados, fabricados e caracterizados funcionalmente dispositivos eletroluminescentes empregando complexos de Terras Raras (TR) e de Metais de Transição (MT) tanto como em filmes finos termicamente evaporados quanto formados através da técnica de spin-coating. O estudo foi iniciado com os complexos de TRs (especificamente o complexo de Európio e de Térbio) com filmes termicamente evaporados, com vistas à análise da eficiência externa dos dispositivos em função do ligante principal (CL). Desta análise observou-se que a particular estrutura química do CL resulta em diferenças perceptíveis ao nível da caracterização eletro-óptica (de 0,73x10-3 [BTA] para 1,05x10-3 [DBM]). Dando seqüência à análise de dispositivo com camada emissiva termicamente evaporada, foi realizada a análise do complexo de Térbio com dois tipos de ligante neutro (NL). Com base nos resultados obtidos, neste foco do estudo, observou-se que a configuração estrutural do NL implica em diferenças na eficiência externa (de 0,8x10-3 [PHEN] para 4,1x10- 3 [BIPY]) e no comprimento de onda dominante emitido (de 542 nm [BIPY] para 563 [PHEN]). Ainda explorando os complexos de TRs, foram estudados dispositivos empregando estes dispersos em um polímero com função de matriz...

Impurezas de metais de transição 3d em SiC: cálculos de primeiros princípios; Impurities of 3d transition metals in SiC: first principles calculations

Barbosa, Karina de Oliveira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/02/2003 PT
Relevância na Pesquisa
574.11258%
A tecnologia dos semicondutores tem exigido materiais alternativos para substituir a silício em aplicações a altas temperaturas, altas potências e altas frequências. O carbeto de silício (SiC) emergiu como um dos sérios candidatos que poderiam operar sob extremas condições. O carbeto de silício é um semicondutor que apresenta uma grande faixa proibida de energia e possui mais de 200 politipos. Dentre esses politipos, a maioria das pesquisas tem sido focada nos politipos hexagonais (4H e 6H) e cúbico (3C). Com o objetivo de desenvolver novos dispositivos baseados em SiC, é importante obter um controle bastante rígido sobre os defeitos nativos e as impurezas no material. Os metais de transição tais como titânio, vanádio e cromo são impurezas residuais comuns que são incorporadas durante o crescimento e podem afetar as propriedades eletrônicas do material. Vanádio e cromo são conhecidos como geradores de centros eletricamente ativos em todos os politipos até agora investigados. Por outro lado , a atividade elétrica das impurezas de titânio dependem do politipo de SiC. Apesar do grande interesse que as impurezas de metais de transição despertam devido a suas aplicações tecnológicas associadas a produção de dispositivos eletrônicos...

APLICACAO DO METODO DE RECORRENCIA PARA O CALCULO DE GRADIENTE DE CAMPO ELETRICO NO NUCLEO EM METAIS DE TRANSICAO; Application of recurrence method for calculating the electric field gradient in the nucleus of transition metals

Petrilli, Helena Maria
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 30/09/1985 PT
Relevância na Pesquisa
568.59027%
Neste trabalho apresentamos um procedimento que utiliza o método de recorrência aliado a uma Hamiltoniana LCAO parametrizada, para avaliar a contribuição dos elétrons d locais ao gradiente de campo elétrico no núcleo (GCE) em ligas de metal de transição. Esta contribuição é geralmente a dominante nestes materiais e de difícil descrição, uma vez que depende das funções de onda eletrônicas que normalmente não são conhecidas. Usamos o método de recorrência para obter a densidade de estados local em torno do átomo considerado e determinamos a ocupação de cada orbital d deste átomo. Calculamos, então, a contribuição eletrônica ao GCE como a soma sobre os orbitais d locais das contribuições de cada orbital. Como ilustração do procedimento sugerido calculamos a contribuição eletrônica para o GCE numa impureza de Fe colocada substitucionalmente numa rede hexagonal de Zr. No cálculo da contribuição de cada orbital d da impureza de Fe para o GCE tomamos funções atômicas, utilizando como parte radial os resultados tabelados por Herman e Skilman por se mostrarem bem representativos na região de interesse. Avaliamos a contribuição da rede ao GCE e verificamos neste caso, como era esperado, que a contribuição eletrônica devido aos elétrons d do Fe é dominante. Nossos resultados se apresentaram em boa concordância com o valor experimental existente na literatura. Uma vez que o método de recorrência não requer periodicidade este tratamento pode ser extendido para investigar a distribuição de GCE em materiais amorfos.; We present here a procedure which uses the recursion method parametrized LCAO Hamiltonian to calculate the electric field gradient (EFG) at the nucleus in transition metal alloys. The main contribution to the EFG in these materials is generally the electronic contribution due to the local d electrons. This contribution is usually difficult to describe since it requires a detailed knowledge of the electronic wave function which are...

Thermal behaviour of nicotinic acid, sodium nicotinate and its compounds with some bivalent transition metal ions

Nascimento, A. L. C. S. do; Caires, F. J.; Gomes, D. J. C.; Gigante, A. C.; Ionashiro, M.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 212-218
ENG
Relevância na Pesquisa
572.45273%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Solid-state M(L)(2)center dot nH(2)O compounds, where M stands for bivalent transition metals (Mn, Fe, Co, Ni, Cu and Zn), L is nicotinate and n = 0-4.5, have been synthesized. Characterization and thermal behaviour of these compounds were investigated employing elemental analysis based on the mass losses observed in the TG-DTA curves, complexometry, X-ray diffractometry, infrared spectroscopy (FTIR), simultaneous thermogravimetric and differential thermal analysis (TG-DTA) and TG-DSC coupled to FTIR. The thermal behaviour of nicotinic acid and its sodium salt was also investigated. For the hydrated transition metal compounds, the dehydration and thermal decomposition of the anhydrous compounds occur in a single step. For the sodium nicotinate, the final residue up to 765 degrees C is sodium carbonate and for the transition metal nicotinates, the final residues are Mn3O4, Fe2O3, Co3O4, NiO, CuO and ZnO. The results also provided information concerning the thermal stability, thermal decomposition and identification of the gaseous products evolved during the thermal decomposition of the compounds. (C) 2013 Published by Elsevier B.V.

Synthesis of guanidine from ammonium thiocyanate in solid state

Zaia,Dimas A. M.; Santana,Henrique de; Toppan,Rodrigo; Zaia,Cássia T. B. V.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2004 EN
Relevância na Pesquisa
488.5736%
Guanidine is an important substance for modern living beings as well as for the prebiotic chemistry. We studied the reaction between ammonium and thiocyanate species in solid state with different substances (river sand, kaolin, transition metals, salts of seawater) and temperatures (80, 120 and 150 ºC). The recoveries of thiocyanate and ammonium in the samples with river sand or kaolin at 150 ºC were statistically different (p<0.05) from the recoveries of thiocyanate and ammonium in the sample without them. The decomposition of ammonium thiocyanate in the samples river sand or kaolin at 150 ºC was about 40%. Kaolin showed to have more effect on the synthesis guanidine than river sand, because, the concentrations of guanidine in the samples with kaolin were always bigger than in the samples with river sand. The decomposition of ammonium thiocyanate in the samples with transition metals plus river sand at 120 ºC was about 30%. The salts of seawater or transition metals plus ammonium thiocyanate plus river sand (120 ºC) showed to increase the concentration of thiourea (seawater: 538%; transition metals: 357%) or guanidine (seawater: 393%, transition metals: 806%) when they were compared to the samples without them. When the results obtained with sample of ammonium thiocyanate were compared to the samples of ammonium thiocyanate (at 120 ºC) plus salts of seawater or transition metals also an increased on the production of thiourea (168%) and guanidine (268%) was obtained...

A systems view of haloarchaeal strategies to withstand stress from transition metals

Kaur, Amardeep; Pan, Min; Meislin, Megan; Facciotti, Marc T.; El-Gewely, Raafat; Baliga, Nitin S.
Fonte: Cold Spring Harbor Laboratory Press Publicador: Cold Spring Harbor Laboratory Press
Tipo: Artigo de Revista Científica
Publicado em /07/2006 EN
Relevância na Pesquisa
483.7783%
Given that transition metals are essential cofactors in central biological processes, misallocation of the wrong metal ion to a metalloprotein can have resounding and often detrimental effects on diverse aspects of cellular physiology. Therefore, in an attempt to characterize unique and shared responses to chemically similar metals, we have reconstructed physiological behaviors of Halobacterium NRC-1, an archaeal halophile, in sublethal levels of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II). Over 20% of all genes responded transiently within minutes of exposure to Fe(II), perhaps reflecting immediate large-scale physiological adjustments to maintain homeostasis. At steady state, each transition metal induced growth arrest, attempts to minimize oxidative stress, toxic ion scavenging, increased protein turnover and DNA repair, and modulation of active ion transport. While several of these constitute generalized stress responses, up-regulation of active efflux of Co(II), Ni(II), Cu(II), and Zn(II), down-regulation of Mn(II) uptake and up-regulation of Fe(II) chelation, confer resistance to the respective metals. We have synthesized all of these discoveries into a unified systems-level model to provide an integrated perspective of responses to six transition metals with emphasis on experimentally verified regulatory mechanisms. Finally...

Increased inflammation and intracellular calcium caused by ultrafine carbon black is independent of transition metals or other soluble components

Brown, D; Stone, V; Findlay, P; MacNee, W; Donaldson, K
Fonte: BMJ Group Publicador: BMJ Group
Tipo: Artigo de Revista Científica
Publicado em /10/2000 EN
Relevância na Pesquisa
484.80203%
OBJECTIVES—Particulate air pollution has been shown to cause adverse health effects, and the ultrafine particle component has been implicated. The aim of the present study was to investigate whether an ultrafine particle exerted its effects through transition metals or other soluble factors released from the surface of the particles.
METHODS—Both in vitro and in vivo models were used to test the imflammogenicity of carbon black (CB) and ultrafine carbon black (UfCB) and the role of transition metals was investigated by treating the particles with desferrioxamine mesylate (desferal), a transition metal chelator. Rats were instilled with particles and the cell population assessed by bronchoalveolar lavage (BAL). Calcium homeostasis in macrophages was assessed with a fluorimetric technique.
RESULTS—UfCB was inflammogenic compared with CB when instilled into Wistar rat lungs, an effect which could not be ameliorated by desferal treatment of the particles. Particle leachates produced no significant inflammation in vivo. In vitro experiments showed that the cytosolic calcium ion concentration in Mono Mac 6 cells was increased significantly after UfCB treatment and treatment of particles with desferal did not alter these effects. Particle leachates had no effect on cytosolic calcium ion concentration. Iron was not detected in leachates of the particles with the desferal assay...

Transport mechanisms for iron and other transition metals in rat and rabbit erythroid cells

Savigni, Donna L; Morgan, Evan H
Fonte: Blackwell Science Inc Publicador: Blackwell Science Inc
Tipo: Artigo de Revista Científica
Publicado em 01/05/1998 EN
Relevância na Pesquisa
488.37%
Earlier studies have shown that Fe2+ transport into erythroid cells is inhibited by several transition metals (Mn2+, Zn2+, Co2+, Ni2+) and that Fe2+ transport can occur by two saturable mechanisms, one of high affinity and the other of low affinity. Also, the transport of Zn2+ and Cd2+ into erythroid cells is stimulated by NaHCO3 and NaSCN. The aim of the present investigation was to determine whether all of these transition metals can be transported by the processes described for Fe2+, Zn2+ and Cd2+ and to determine the properties of the transport processes.Rabbit reticulocytes and mature erythrocytes and reticulocytes from homozygous and heterozygous Belgrade rats were incubated with radiolabelled samples of the metals under conditions known to be optimal for high- and low-affinity Fe2+ transport and for the processes mediated by NaHCO3 and NaSCN.All of the metals were transported by the high- and low-affinity Fe2+ transport processes and could compete with each other for transport. The Km and Vmax values and the effects of incubation temperature and metabolic inhibitors were similar for all the metals. NaHCO3 and NaSCN increased the uptake of Zn2+ and Cd2+ but not the other metals.The uptake of all of the metals by the high-affinity process was much lower in reticulocytes from homozygous Belgrade rats than in those from heterozygous animals...

Impacts of Antioxidants on Hydroxyl Radical Production from Individual and Mixed Transition Metals in a Surrogate Lung Fluid

Charrier, Jessica G.; Anastasio, Cort
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/2011 EN
Relevância na Pesquisa
482.7328%
Inhalation of ambient particulate matter causes morbidity and mortality in humans. One hypothesized mechanism of toxicity is the particle-induced formation of reactive oxygen species (ROS) – including the highly damaging hydroxyl radical (·OH) – followed by inflammation and a variety of diseases. While past studies have found correlations between ROS formation and a variety of metals, there are no quantitative measurements of ·OH formation from transition metals at concentrations relevant to 24-hour ambient particulate exposure. This research reports specific and quantitative measurements of ·OH formation from 10 individual transition metals (and several mixtures) in a cell-free surrogate lung fluid (SLF) with four antioxidants: ascorbate, citrate, glutathione, and uric acid. We find that Fe and Cu can produce ·OH under all antioxidant conditions as long as ascorbate is present and that mixtures of the two metals synergistically increase ·OH production. Manganese and vanadium can also produce ·OH under some conditions, but given that their ambient levels are typically very low, these metals are not likely to chemically produce significant levels of ·OH in the lung fluid. Cobalt, chromium, nickel, zinc, lead, and cadmium do not produce ·OH under any of our experimental conditions. The antioxidant composition of our SLF significantly affects ·OH production from Fe and Cu: ascorbate is required for ·OH formation...

On dithiothreitol (DTT) as a measure of oxidative potential for ambient particles: evidence for the importance of soluble transition metals

Charrier, J. G.; Anastasio, C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 03/05/2012 EN
Relevância na Pesquisa
487.45984%
The rate of consumption of dithiothreitol (DTT) is increasingly used to measure the oxidative potential of particulate matter (PM), which has been linked to the adverse health effects of PM. While several quinones are known to be very reactive in the DTT assay, it is unclear what other chemical species might contribute to the loss of DTT in PM extracts. To address this question, we quantify the rate of DTT loss from individual redox-active species that are common in ambient particulate matter. While most past research has indicated that the DTT assay is not sensitive to metals, our results show that seven out of the ten transition metals tested do oxidize DTT, as do three out of the five quinones tested. While metals are less efficient at oxidizing DTT compared to the most reactive quinones, concentrations of soluble transition metals in fine particulate matter are generally much higher than those of quinones. The net result is that metals appear to dominate the DTT response for typical ambient PM2.5 samples. Based on particulate concentrations of quinones and soluble metals from the literature, and our measured DTT responses for these species, we estimate that for typical PM2.5 samples approximately 80 % of DTT loss is from transition metals (especially copper and manganese)...

Transition metals and mitochondrial metabolism in the heart

Rines, Amy K.; Ardehali, Hossein
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
485.0354%
Transition metals are essential to many biological processes in almost all organisms from bacteria to humans. Their versatility, which arises from an ability to undergo reduction–oxidation chemistry, enables them to act as critical cofactors of enzymes throughout the cell. Accumulation of metals, however, can also lead to oxidative stress and cellular damage. The importance of metals to both enzymatic reactions and oxidative stress makes them key players in mitochondria. Mitochondria are the primary energy-generating organelles of the cell that produce ATP through a chain of enzymatic complexes that require transition metals, and are highly sensitive to oxidative damage. Moreover, the heart is one of the most mitochondrially-rich tissues in the body, making metals of particular importance to cardiac function. In this review, we focus on the current knowledge about the role of transition metals (specifically iron, copper, and manganese) in mitochondrial metabolism in the heart. This article is part of a Special Issue entitled ‘Focus on Cardiac Metabolism’.

Superconductivity in Transition Metals with Nonmagnetic Impurities

Kusakabe, Takashi
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
EN
Relevância na Pesquisa
481.3734%
The two-band model proposed by Suhl, Matthias and Walker for the theory of superconductivity of pure transition metals is extended to the transition metals in the presence of nonmagnetic impurities. It is found that the theory of superconductivity in the two-band model is rather sensitive to the choice of the cutoffs of the pairing interactions, in contrast to our expectations in the one-band model. That is, if ωss = ωdd = ωsd ≡ωD, Tc always decreases with increasing impurity concentration and has a complete isotope effect. Furthermore if ωss = ωdd ≠ωsdss = ωD), Tc always decreases of increases with the impurity concentration according to the case of |α| ≪ 1 or α> 1, respectively, and does not necessarily have the complete isotope effect, where ωss, ωdd and ωsd are the cutoffs for interactions giving a pairing of s-s, d-d and s-d electrons and α is a certain constant given by the pairing interaction...

Studies in the mass spectra of perfluoroaromatic derivatives of phosphorus and some selected transition metals

Jones, Timothy R. B.
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
568.59027%
The mass spectra and fragmentation of a variety of fluoroaromatic compounds of Group V and some selected transition elements are discussed in some detail, aided by data from metastable defocussed experiments. Results of ,studies on the coupling reaction using unstable organotitanium chloride intermediate species are reported. The preparation of some 5-substituted octafluorodibenzophospho1es is also discussed. Rearrangements under electron bombardment resulting in the loss of heteroatom-fluoride fragments are discussed in the light of presently accepted mechanisms for these processes as are rearrangements observed in compounds involving thionophosphoryl bonds ( p=s ).

Exploring Thermal and Mechanical Properties of Selected Transition Elements under Extreme Conditions: Experiments at High Pressures and High Temperatures

Hrubiak, Rostislav
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
589.2402%
Transition metals (Ti, Zr, Hf, Mo, W, V, Nb, Ta, Pd, Pt, Cu, Ag, and Au) are essential building units of many materials and have important industrial applications. Therefore, it is important to understand their thermal and physical behavior when they are subjected to extreme conditions of pressure and temperature. This dissertation presents: An improved experimental technique to use lasers for the measurement of thermal conductivity of materials under conditions of very high pressure (P, up to 50 GPa) and temperature (T up to 2500 K). An experimental study of the phase relationship and physical properties of selected transition metals, which revealed new and unexpected physical effects of thermal conductivity in Zr, and Hf under high P-T. New phase diagrams created for Hf, Ti and Zr from experimental data. P-T dependence of the lattice parameters in α-hafnium. Contrary to prior reports, the α-ω phase transition in hafnium has a negative dT/dP slope. New data on thermodynamic and physical properties of several transition metals and their respective high P-T phase diagrams. First complete thermodynamic database for solid phases of 13 common transition metals was created. This database has: All the thermochemical data on these elements in their standard state (mostly available and compiled). All the equations of state (EoS) formulated from pressure-volume-temperature data (measured as a part of this study and from literature). Complete thermodynamic data for selected elements from standard to extreme conditions. The thermodynamic database provided by this study can be used with available thermodynamic software to calculate all thermophysical properties and phase diagrams at high P-T conditions. For readers who do not have access to this software...

Ammonolysereaktionen von ternären Thiovanadaten und Übergangsmetallthiocyanaten; Ammonolysisreactions of ternary Thiovanadates and Transition Metals Thiocyanates

Jakovleva, Irina
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
674.1126%
Inhalt der Arbeit war die Untersuchung der Ammonolyse von ternären Sulfiden und Thiocyanaten der Übergangsmetalle. Es wurden einige neue Verbindungen synthetisiert. Die Charakterisierung erfolgte mittels Einkristalldiffraktometrie und anderen analytischen Methoden. Bei der Ampullenreaktion von Li2S und VN bei 850°C entstehen rhomboedrische Kristalle von „LixV2O3-xNx“ mit den Gitterkonstanten a = b = 494,40(2) pm, c = 1397,15(11) pm und der Raumgruppe R . Bei der Ampullenreaktion von NbCl5 mit NH4SCN und I2 bei 330°C entstehen Kristalle von (NH4)5[Nb2(S2)2Cl8]I. Die Verbindung kristallisiert orthorhombisch innenzentriert in der Raumgruppe Immm mit den Gitterkonstanten a = 707,97(17) pm, b = 974,2(3) pm und c = 1614,2(4) pm. Durch die Reaktion von NiCl2 und LiSCN in Acetonitril konnte das bisher unbekannte Ni(NCS)2(CH3CN)4 synthetisiert werden. Diese Verbindung kristallisiert kubisch in der Raumgruppe Pm mit der Gitterkonstante a = 1289,80(9) pm. Ni(NCS)2(CH3CN)4 ist nur unterhalb -30°C stabil. Für die weitere Ammonolysereaktion wurde zunächst das CH3CN unter Bildung von Ni(NCS)2(CH3CN)2 abgezogen. Ni(NCS)2(CH3CN)2 wurde dann im Ammoniakstrom bei 150°C ammonolysiert. Die Strukturanalyse ergab, dass Li[Ni(NH3)6](SCN)3 • NH3 • 1/6H2O entsteht. Diese Verbindung kristallisiert monoklin in der Raumgruppe Cc mit den Gitterkonstanten a = 1737...

Reactions and Photochemistry of Transition Metals with Methanol, Water, Hydrogen, and Carbon Monoxide via FTIR Matrix Isolation Spectroscopy

Park, Mingue
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
568.59027%
The reactions and photochemistry of atomic and diatomic transition metals with methanol, water, hydrogen, and carbon monoxide in noble gas matrices at cryogenic temperatures have been studied with the use of Fourier Transform infrared inert matrix spectroscopy. Atoms and dimers of iron and cobalt reacted with methanol to form the adducts, M(CH30H) and M2(CH30H), respectively. M(CH30H) underwent metal insertion into the 0-H bond of methanol to yield methoxymetal hydride, CH3OMH, with irradiation of the matrix in the violet (400 nm < λ < 500 nm) region. Ultraviolet (280 nm < λ < 360 nm) photolysis of the matrix rearranged CH30MH to yield the methylmetal hydroxide species, CH3MOH. CH30MH dissociated into carbon monoxide and hydrogen after prolonged irradiation in the ultraviolet region. Surprisingly, nickel atoms reacted spontaneously to insert into the 0-H bonds of methanol and water to form CH30NiH and HONiH, respectively. Violet photolysis caused CH30NiH to rearrange to form methylnickel hydroxide, CH3NiOH. This is effectively a two step process of the C-0 activation of methanol by a nickel atom. In addition to rearrangement, CH30NiH dissociates into carbon monoxide and hydrogen with violet photolysis. Nickel dimers also reacted spontaneously with water to form both an adduct and insertion products. Atomic nickel spontaneously inserts into the H-H bond of molecular hydrogen to yield a bent nickel dihydride...

Supersaturating silicon with transition metals by ion implantation and pulsed laser melting

Recht, Daniel; Smith, Matthew J.; Charnvanichborikarn, Supakit; Sullivan, Joseph T.; Winkler, Mark T.; Mathews, Jay; Warrender, Jeffrey M.; Buonassisi, Tonio; Williams, James S.; Gradečak, Silvija; Aziz, Michael J.
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica Formato: 8 pages
Relevância na Pesquisa
485.33812%
We investigate the possibility of creating an intermediate band semiconductor by supersaturating Si with a range of transition metals (Au, Co, Cr, Cu, Fe, Pd, Pt, W, and Zn) using ion implantation followed by pulsed laser melting (PLM). Structural characterization shows evidence of either surface segregation or cellular breakdown in all transition metals investigated, preventing the formation of high supersaturations. However, concentration-depth profiling reveals that regions of Si supersaturated with Au and Zn are formed below the regions of cellular breakdown. Fits to the concentration-depth profile are used to estimate the diffusive speeds, v D, of Au and Zn, and put lower bounds on v D of the other metals ranging from 10² to 10⁴ m/s. Knowledge of v D is used to tailor the irradiation conditions and synthesize single-crystal Si supersaturated with 10¹⁹ Au/cm³ without cellular breakdown. Values of v D are compared to those for other elements in Si. Two independent thermophysical properties, the solute diffusivity at the melting temperature, D s(T m), and the equilibrium partition coefficient, k e, are shown to simultaneously affect v D. We demonstrate a correlation between v D and the ratio D s(T m)/k e ⁰·⁶⁷, which is exhibited for Group III...

Surprisingly large inverse spin Hall effect and systematic variation of spin-orbit coupling with d-orbital filling in 3d transition metals

Du, Chunhui; Wang, Hailong; Yang, Fengyuan; Hammel, P. Chris
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/10/2014
Relevância na Pesquisa
481.47566%
It is generally believed that spin-orbit coupling (SOC) follows Z4 (atomic number) dependence and becomes significant only in heavy elements. Consequently, SOC in 3d transition metals should be negligible given their small Z. Using dynamic spin pumping of Y3Fe5O12-based structures, we uncover a systematic evolution of spin Hall angle with d-orbital filling in a series of 3d metals, reminiscent of behavior observed in 5d metals. In particular, Cr and Ni show very large spin Hall angle (half of that for Pt), indicating that d-orbital filling rather than Z plays a dominant role in spin Hall effect (SHE) in 3d metals. This result enriches our understanding of SHE and broadens the scope of materials available for exploring the rich phenomena enabled by SOC as well as presenting a guidepost for testing theoretical models of spin-orbit coupling in transition metals.; Comment: 17 pages, 4 figures, 1 table

Study of Intrinsic Spin Hall Effect and Orbital Hall Effect in 4d- and 5d- Transition Metals

Tanaka, T.; Kontani, H.; Naito, M.; Naito, T.; Hirashima, D. S.; Yamada, K.; Inoue, J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
487.7218%
We study the intrinsic spin Hall conductivity (SHC) in various $5d$-transition metals (Ta, W, Re, Os, Ir, Pt, and Au) and 4d-transition metals (Nb, Mo, Tc, Ru, Rh, Pd, and Ag) based on the Naval Research Laboratory tight-binding model, which enables us to perform quantitatively reliable analysis. In each metal, the obtained intrinsic SHC is independent of resistivity in the low resistive regime ($\rho < 50 \mu\Omega\text{cm}$) whereas it decreases in proportion to $\rho^{-2}$ in the high resistive regime. In the low resistive regime, the SHC takes a large positive value in Pt and Pd, both of which have approximately nine $d$-electrons per ion ($n_d=9$). On the other hand, the SHC takes a large negative value in Ta, Nb, W, and Mo where $n_d<5$. In transition metals, a conduction electron acquires the trajectory-dependent phase factor that originates from the atomic wavefunction. This phase factor, which is reminiscent of the Aharonov-Bohm phase, is the origin of the SHC in paramagnetic metals and that of the anomalous Hall conductivity in ferromagnetic metals. Furthermore, each transition metal shows huge and positive $d$-orbital Hall conductivity (OHC), independently of the strength of the spin-orbit interaction (SOI). Since the OHC is much larger than the SHC...