928 resultados para Ni^2


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An equimolar mixture of Ni(NO(3))(2)center dot 6H(2)O and pyridine-2-aldehyde with two equivalents of NaN(3) in methanol in the presence of NaOMe resulted in the formation of light green precipitate which upon crystallization from dimethylformamide (DMF) yielded light green single crystals [{Ni(2)Na(2)(pic)(4)(N(3))(2)(H(2)O)(2)(MeOH)}center dot MeOH center dot 3H(2)O](n) (1) and [{Ni(2)Na(2)(pic)(4)(N(3))(2)(H(2)O)(4)}center dot 2DMF center dot H(2)O](n) (2) (pic = pyridine-2-carboxylate) at room temperature and high temperature (100 degrees C), respectively. Variable temperature magnetic studies revealed the existence of overall ferromagnetic behaviour with J approximate to + 10 cm(-1) and D approximate to -2 to -7 cm(-1) for 1 and 2, respectively. Negative D values as well as variation of D upon slight distortion of structure by varying reaction temperature were observed. The X-band Electron Paramagnetic Resonance (EPR) spectra of both 2 and 3 were recorded below 50 K. The structural distortion was also implicated from the EPR spectra. Density Functional Theory (DFT) calculations on both complexes were performed in two different ways to corroborate the magnetic results. Considering only Ni(2)(II) dimeric unit, results were J = + 20.65 cm(-1) and D = -3.16 cm(-1) for 1, and J = +24.56 cm(-1) and D = -4.67 cm(-1) for 2. However, considering Ni(2)(II)Na(2)(I) cubane as magnetic core the results were J = +16.35 cm(-1) (1), +19.54 cm(-1) (2); D = -3.05 cm(-1) (1), -4.25 cm(-1) (2).

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Ni^2ZnO-Al2O3-SiO2X-Ni^2ZnO-Al2O3-SiO2X-ZnAl2O413nmNi^2^3T2g^3F^3A2g^3F

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Ni2+Er3+.

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SRBSRBNi^2qm9319mgNi^2gSRBSRBNi^2

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Structural and magnetic characterization of compound {[Ni-2(L)(2)(OAC)(2)][Ni-3(L)(2) (OAc)(4)]) center dot 2CH(3)CN (3) (HL = the tridentate Schiff base ligand, 2-[(3-methylaminb-propylimino)-methyl]-phenol) shows that it is a rare example of a crystal incorporating a dinuclear Ni(II) compound, [Ni-2(L)(2)(OAc)(2)], and a trinuclear one, [Ni-3(L)(2)(OAC)(4)]. Even more unusual is the fact that both Ni (II) complexes, [Ni-2(L)(2)(OAc)(2)] (1) and [Ni-3(L)(2)(OAc)(4)(H2O)(2)] center dot CH2Cl2 center dot 2CH(3)OH (2), have also been isolated and structurally and magnetically characterized. The structural analysis reveals that the dimeric complexes [Ni-2(L)(2)(OAc)(2)] in cocrystal 3 and in compound 1 are almost identical-in both complexes, the Ni(II) ions possess a distorted octahedral geometry formed by the chelating tridentate ligand (L), a chelating acetate ion, and a bridging phenoxo group with very similar bond angles and distances. On the other hand, compound 2 and the trinuclear complex in the cocrystal 3 show a similar linear centrosymmetric structure with the tridentate ligand coordinated to the terminal Ni(II) and linked to the central Ni(II) by phenoxo and carboxylate bridges. The only difference is that a water molecule found in 2 is not present in the trinuclear unit of complex 3; instead, the coordination sphere is completed by an additional bridging oxygen atom from an acetate ligand. Variable-temperature (2-300 K) magnetic susceptibility measurements show that the dinuclear unit is antiferromagnetically coupled in both compounds (2J = -36.18 and -29.5 cm(-1) in 1 and 3, respectively), whereas the trinuclear unit shows a very weak ferromagnetic coupling in compound 3 (2J = 0.23 cm(-1)) and a weak antiferromagnetic coupling in 2 (2J = -8.7(2) cm(-1)) due to the minor changes in the coordination sphere.

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In Leishmania, arginase is responsible for the production of ornithine, a precursor of polyamines required for proliferation of the parasite. In this work, the activation kinetics of immobilized arginase enzyme from L. (L.) amazonensis were studied by varying the concentration of Mn(2+) applied to the nickel column at 23 degrees C. The intensity of the binding of the enzyme to the Ni(2+) resin was directly proportional to the concentration of Mn(2+). Conformational changes of the enzyme may occur when the enzyme interacts with immobilized Ni(2+), allowing the following to occur: (1) entrance of Mn(2+) and formation of the metal bridge; (2) stabilization and activation of the enzyme at 23 degrees C; and (3) an increase in the affinity of the enzyme to Ni(2+) after the Mn(2+) activation step. The conformational alterations can be summarized as follows: the interaction with the Ni(2+) simulates thermal heating in the artificial activation by opening a channel for Mn(2+) to enter. (C) 2010 Elsevier Inc. All rights reserved.

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Neste trabalho apresentamos os resultados experimentais da medida do calor especfico dos compostos Heusler da srie Ni2TA1, onde T =Ti, Zr,Hf,V,Nb, Ta. Estas medidas foram feitas utilizando-se um calormetro adiabtico que atua na faixa de 1,84 K a 10,3 K e visaram o estudo da estrutura eltrnica dos compostos em termos da densidade de estados eletrnicos nvel de Fermi, bem como da dinmica da rede cristalina, com o uso dos modelos de Debye e de Einstein para o calor especfico. Apresentamos, tambm, uma descrio do calormetro, seu funcionamento e as alteraes ocorridas em funo deste trabalho.

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Conselho Nacional de Desenvolvimento Cientfico e Tecnolgico (CNPq)

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Coordenao de Aperfeioamento de Pessoal de Nvel Superior (CAPES)

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Gegenstand dieser Arbeit ist die Prparation und die ausfhrliche Charakterisierung epitaktischer Dnnschicht-Proben der Heusler Verbindung Ni2MnGa. Diese intermetallische Verbindung zeigt einen magnetischen Formgedchtnis-Effekt (MFG), der sowohl im Bezug auf mgliche Anwendungen, als auch im Kontext der Grundlagenforschung uerst interessant ist. In Einkristallen nahe der Stchiometrie Ni2MnGa wurden riesige magnetfeldinduzierte Dehnungen von bis zu 10 % nachgewiesen. Der zugrundeliegende Mechanismus basiert auf einer Umverteilung von kristallographischen Zwillings-Varianten, die eine tetragonale oder orthorhombische Symmetrie besitzen. Unter dem Einfluss des Magnetfeldes bewegen sich die Zwillingsgrenzen durch den Kristall, was eine makroskopische Formnderung mit sich bringt. Die somit erzeugten reversiblen Lngennderungen knnen mit hoher Frequenz geschaltet werden, was Ni2MnGa zu einem vielversprechenden Aktuatorwerkstoff macht. rnDa der Effekt auf einem intrinsischen Prozess beruht, eignen sich Bauteile aus MFG Legierungen zur Integration in Mikrosystemen (z.B. im Bereich der Mikrofluidik). rnrnBislang konnten groe magnetfeldinduzierte Dehnungen nur fr Einkristalle und Polykristalle mit hoher Porositt (foams") nachgewiesen werden. Um den Effekt fr Anwendungen nutzbar zu machen, werden allerdings Konzepte zur Miniaturisierung bentigt. Eine Mglichkeit bieten epitaktische dnne Filme, die im Rahmen dieser Arbeit hergestellt und untersucht werden sollen. Im Fokus stehen dabei die Optimierung der Herstellungsparameter, sowie die Prparation von freitragenden Schichten. Zudem werden verschiedene Konzepte zur Herstellung freistehender Mikrostrukturen erprobt. Mittels Rntgendiffraktometrie konnte die komplizierte Kristallstruktur fr verschiedene Wachstumsrichtungen verstanden und die genaue Verteilung der Zwillingsvarianten aufgedeckt werden. In Verbindung mit Mikroskopie-Methoden konnte so die Zwillingsstruktur auf verschiedenen Lngenskalen geklrt werden. Die Ergebnisse erklren das Ausbleiben des MFG Effekts in den Proben mit (100) Orientierung. Andererseits wurde fr Schichten mit (110) Wachstum eine vielversprechende Mikrostruktur entdeckt, die einen guten Ausgangspunkt fr weitere Untersuchungen bietet.rnDurch die spezielle Geometrie der Proben war es mglich, Spektroskopie-Experimente in Transmission durchzufhren. Die Ergebnisse stellen den ersten experimentellen Nachweis der nderungen in der elektronischen Struktur einer metallischen Verbindung whrend des martensitischen Phasenbergangs dar. Durch Messen des magnetischen Zirkulardichroismus in der Rntgenabsorption konnten quantitative Aussagen ber die magnetischen Momente von Ni und Mn getroffen werden. Die Methode erlaubt berdies die Beitrge von Spin- und Bahn-Moment separat zu bestimmen. Durch winkelabhngige Messungen gelang es, die mikroskopische Ursache der magnetischen Anisotropie aufzuklren. Diese Ergebnisse tragen wesentlich zum Verstndnis der komplexen magnetischen und strukturellen Eigenschaften von Ni2MnGa bei.rn

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Three-dimensional oxalate-based {[Ru(bpy)3][Cu2xNi2(1-x)(ox)3]}n (0 x 1, ox = C2O42-, bpy = 2,2bipyridine) were synthesized. The structure was determined for x = 1 by X-ray diffraction on single crystal. The compound crystallizes in the cubic space group P4132. It shows a three-dimensional 10-gon 3-connected (10,3) anionic network where copper(II) has an unusual tris(bischelated) environment. X-ray powder diffraction patterns and their Rietveld refinement show that all the compounds along the series are isostructural and single-phased. According to X-ray absorption spectroscopy, copper(II) and nickel(II) have an octahedral environment, respectively elongated and trigonally distorted. As shown by natural circular dichroism, the optically active forms of {[Ru(bpy)3][CuxNi2(1-x)(ox)3]}n are obtained starting from resolved - or -[Ru(bpy)3]2+. The CurieWeiss temperatures range between 55 (x = 1) and 150 K (x = 0). The antiferromagnetic exchange interaction thus decreases when the copper contents increases in agreement with the crystallographic structure of the compounds and the electronic structure of the metal ions. At low temperature, the compounds exhibit complex long-range ordered magnetic behavior.

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Reaction of [Ph(4)P]2WS4 With NiCl2 in methanol solution in the presence of NaOCH3 leads to the formation of [Ph(4)P](2) [S2W(mu-S)(2)Ni(S-2)] (I) A Similar reaction between (NH4)(2)WS4 and NiCl2 under O-2 atmosphere in the presence of Ph(4)PCl or (n)Bu(4)NCl affords [Ph(4)P](2)([(S-2)W(O)(mu-S)(2)]Ni-2] (IIa) and [(n)Bu(4)N](2)([(S-2)W(O)(mu-S)(2)]Ni-2} (IIb) Under argon the same reaction gives [Ph(4)P](2)[Ni(WS4)(2)] (IIIa) and [(n)Bu(4)N](2)[Ni(WS4)(2)] (IIIb). [Ph(4)P](2)[Ni(WOS3)(2)] (IV) and [Ph(4)P](2)[Ni(WO2S2)(2)] (V) can be prepared from the reaction of [Ph(4)P]2WOS3 and [Ph(4)P]2WO2S2 with NiCl2. Treatment of (NH4)(2)WS4 with CuCl in the presence of PPh(3) in boiling pyridine produces W(mu-S)(4)Cu-2(PPh(3))(3) (VI), which can further react with excess PPh(3) to give W(mu-S)(4)Cu-2(PPh(3))(4) . py (VII). Complex I crystallizes in the space group P2(1)/n with the cell parameters: a = 20.049(4), b = 17.010(4), c = 14.311(7) Angstrom; beta = 110.24(3)degrees and Z = 4; R = 0.058 for 4267 independent reflections. The structural study confirms that complex I contains two terminal sulfide ligands, two bridging sulfide ligands, a side-on disulfide ligand, and a planar central W(mu-S)(2)Ni four membered ring. Complex VII crystallizes in the space group C2/c with the cell parameters: a = 26.436(8), b = 20.542(6), c = 19.095(8) Angstrom; beta = 125.00(3)degrees and Z = 4; R = 0.080 for 3802 independent reflections. The structural study reveals a perfect linear arrangement of the three metal atoms Cu-W-Cu.

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Apresentamos neste trabalho os resultados de um estudo experimental e terico dos compostos borocarbetos supercondutores da srie Y(Ni1-xMnx)2B2C com x = 0; 0,01; 0,025; 0,05; 0,10; 0,15. A principal motivao para este trabalho foi investigar a estrutura eletrnica e a possvel formao do momento magntico sobre os tomos de impureza de Mn nos compostos Y(Ni1- xMnx)2B2C. O aparecimento do momento magntico localizado no stio da impureza possibilitou estudar a influncia do Mn sobre o mecanismo de quebra de pares supercondutores e sobre as propriedades magnticas do composto. Os borocarbetos so compostos de estrutura cristalina tetragonal de corpo centrado e altamente anisotrpicos (c/a~3). So intermetlicos de alta temperatura crtica supercondutora Tc, com forte acoplamento eltron-fonon. Em alguns casos podem apresentar ordem magntica, supercondutividade e tambm coexistncia ou competio energtica entre ambos. As medidas de transporte eletrnico, em funo da temperatura, foram feitas utilizando-se um detector sncroton baseado na tcnica de quatro pontos operando na faixa de 4,2K at 300K. Essas medidas possibilitaram o estudo das propriedades relacionadas ao transporte eletrnico na fase supercondutora. Na fase normal, extraiu-se a dependncia em energia da funo espectral de fonons F () para alguns compostos da srie estudada. As medidas magnticas em funo da temperatura e do campo magntico foram feitas utilizando-se um SQUID (Superconducting Quantun Interference Device Quantun Design Model MPMS XL). Tais medidas permitiram a caracterizao das propriedades magnticas de nossas amostras. Em particular determinou-se o valor, em regime de saturao, do momento magntico associado ao stio cristalino do Mn. Foram determinadas tambm as correntes crticas supercondutoras usando o Modelo de estado crtico de Bean e a variao da temperatura crtica supercondutora (Tc) com a mudana do campo externo aplicado. As medidas magnticas permitiram a obteno do diagrama que relaciona o campo crtico inferior (HC1) e a temperatura, variando-se a concentrao do tomo dopante de mangans. Foi feito um esforo terico no sentido de interpretar os resultados experimentais. Para isso foram usados trs modelos: O modelo de estado crtico de Bean j citado acima e um modelo baseado na frmula de Ziman usando uma aproximao para a funo espectral de fonons para descrever a resistividade no regime de alta temperatura. Alm disto, usou-se o modelo de duas sub-redes para a descrio do momento magntico das impurezas de Mn, em funo da concentrao, na srie Y(Ni ) ( 2 F 1-xMnx)2B2C.

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This work deals with the synthesis, spectroscopic and structural investigation of pyrazolyl complexes of the type trans-[M(NCS)(2)(HPz)(4)] {M=Co (1), Ni (2); HPz=pyrazole}. Single crystal X-ray studies on 1 and 2 reveal the formation of similar supramolecular arrangements derived from self-assembly of monomers linked together through intermolecular N-H center dot center dot center dot SCN hydrogen bonds, C-H center dot center dot center dot pi interactions and pi-pi stacking. (c) 2005 Elsevier B.V. All rights reserved.