Ni Atoms (ni + atom)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Unusual Magnetism of an Unsymmetrical Trinickel Chain

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2008
F. Albert Cotton
Abstract An extended metal atom chain (EMAC) compound with an unsymmetrical trinickel core and the formula [Ni3(dpa)4(CH3CN)](PF6)2·2CH2Cl2 (1·2CH2Cl2, dpa is the anion of 2,2,-dipyridylamine) has the central Ni atom in an essentially square-planar configuration. Besides having four equatorial nitrogen atoms, the two terminal metal centers have axial interactions that are notably different with one having a strongly bound acetonitrile molecule with a Ni(3),N(3) distance of 2.108(5) Å while the other unit has a very weak interaction with an axial PF6 anion [Ni(1)···F(1) separation of 2.690 Å]. In these outer units, the Ni(3) atom is pulled out of the idealized plane of the four equatorial nitrogen atoms by 0.239 Å, while in the one with an axial PF6 anion the metal atom is pulled from the plane of the equatorial nitrogen atoms by only 0.097 Å. In 1 there are two unpaired electrons and an S = 1 state prevails from ca. 25 to 300 K. This magnetic behavior differs considerably from that of symmetrical trinickel EMACs with two strongly pyramidal terminal nickel atoms. A discussion of the effect of various axial ligands on the geometry of the terminal nickel atoms is provided. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


Anion-Directed Template Synthesis and Hydrolysis of Mono-Condensed Schiff Base of 1,3-Pentanediamine and o -Hydroxyacetophenone in NiII and CuII Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2008
Pampa Mukherjee
Abstract Bis(o -hydroxyacetophenone)nickel(II) dihydrate, on reaction with 1,3-pentanediamine, yields a bis-chelate complex [NiL2]·2H2O (1) of mono-condensed tridentate Schiff baseligand HL {2-[1-(3-aminopentylimino)ethyl]phenol}. The Schiff base has been freed from the complex by precipitating the NiII as a dimethylglyoximato complex. HL reacts smoothly with Ni(SCN)2·4H2O furnishing the complex [NiL(NCS)] (2) and with CuCl2·2H2O in the presence of NaN3 or NH4SCN producing [CuL(N3)]2 (3) or [CuL(NCS)] (4). On the other hand, upon reaction with Cu(ClO4)2·6H2O and Cu(NO3)2·3H2O, the Schiff base undergoes hydrolysis to yield ternary complexes [Cu(hap)(pn)(H2O)]ClO4 (5) and [Cu(hap)(pn)(H2O)]NO3 (6), respectively (Hhap = o -hydroxyacetophenone and pn = 1,3-pentanediamine). The ligand HL undergoes hydrolysis also on reaction with Ni(ClO4)2·6H2O or Ni(NO3)2·6H2O to yield [Ni(hap)2] (7). The structures of the complexes 2, 3, 5, 6, and 7 have been confirmed by single-crystal X-ray analysis. In complex 2, NiII possesses square-planar geometry, being coordinated by the tridentate mono-negative Schiff base, L and the isothiocyanate group. The coordination environment around CuII in complex 3 is very similar to that in complex 2 but here two units are joined together by end-on, axial-equatorial azide bridges to result in a dimer in which the geometry around CuII is square pyramidal. In both 5 and 6, the CuII atoms display the square-pyramidal environment; the equatorial sites being coordinated by the two amine groups of 1,3-pentanediamine and two oxygen atoms of o -hydroxyacetophenone. The axial site is coordinated by a water molecule. Complex 7 is a square-planar complex with the Ni atom bonded to four oxygen atoms from two hap moieties. The mononuclear units of 2 and dinuclear units of 3 are linked by strong hydrogen bonds to form a one-dimensional network. The mononuclear units of 5 and 6 are joined together to form a dimer by very strong hydrogen bonds through the coordinated water molecule. These dimers are further involved in hydrogen bonding with the respective counteranions to form 2-D net-like open frameworks. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


Magnetic X-ray absorption fine structure for Ni,Mn alloys

JOURNAL OF SYNCHROTRON RADIATION, Issue 2 2003
T. Miyanaga
Magnetic X-ray absorption fine-structure (XAFS) spectra have been measured for Ni,Mn alloys. The magnetic XAFS in the near-edge region (X-ray absorption near-edge structure, XANES) and X-ray magnetic circular dichroism (XMCD) of the Mn and Ni K -edge for Ni1,xMnx (x = 0.25, 0.24 and 0.20) show that (i) the local magnetic structure around the Mn atom is quite different from that around the Ni atom, and (ii) the peak intensity in the magnetic XANES of the Mn K -edge depends on the magnetization of the sample in contrast to the Ni K -edge. The Mn K -edge magnetic EXAFS (extended XAFS) for Ni0.76Mn0.24 is also measured. The second and fourth peaks in the Fourier transform are observed to be enhanced in comparison with the non-magnetic EXAFS, indicating that the second- and fourth-shell Ni atoms are replaced by Mn atoms due to heat treatment (atomic ordering). Semi-relativistic theoretical calculation explains the observed magnetic EXAFS. [source]


A square-planar NiII complex with an asymmetric coordination of a novel polynucleative 2,6-diacetylpyridine bis{[2-(hydroxyimino)propanoyl]hydrazone} ligand

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2008
Maxym V. Plutenko
The title compound, (2,6-diacetylpyridine bis{[2-(hydroxyimino)propanoyl]hydrazone}(2,))nickel(II) dimethyl sulfoxide solvate monohydrate, [Ni(C15H17N7O4)]·C2H6OS·H2O, represents the first example of square-planar N4 coordination via N atoms with four different functions, namely amide, azomethine, hydroxyimino and pyridine. The coordination polyhedron of the central Ni atom has a slightly distorted square-planar geometry. The 2,6-diacetylpyridine bis{[2-(hydroxyimino)propanoyl]hydrazone} ligand forms one six- and two five-membered chelate rings, and a pseudo-chelate ring through an intramolecular hydrogen bond with an amide group as donor and a deprotonated hydroxyimino group as acceptor, resulting in a pseudomacrocyclic arrangement. [source]


Poly[,-aqua-diaqua-,4 -malonato-,3 -malonato-barium(II)nickel(II)]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2008
Ming-Lin Guo
The title complex, [BaNi(C3H2O4)2(H2O)3]n, is polymeric, with two non-equivalent malonate dianions bridging one Ni atom and five different Ba atoms. The Ni atoms have a distorted octahedral (NiO6) environment, and are coordinated by four malonate O atoms in a planar arrangement and two water molecules in axial positions. The Ba atom may be described as a BaO9 polyhedron in a monocapped square-antiprismatic environment, which involves two water molecules and seven O atoms from different malonate ligands. The three-dimensional structure is further maintained and stabilized by hydrogen bonds. [source]


Ni(bipy)2Ni(CN)4, a new type of one-dimensional square tetra­cyano complex

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2000
Juraj, ernák
The one-dimensional structure of catena -poly­[[bis(2,2,-bi­pyri­dyl-1,2N,N,)-,-cyano-1:2,2N:C -di­cyano-2,2C -di­nickel(II)]-,-cyano- C:N], [Ni2(CN)4(C10H8N2)2]n, consists of infinite zigzag chains running parallel to the c axis. The chains are composed of paramagnetic [Ni(bipy)2]2+ cations (bricks; nickel on a twofold axis) linked by diamagnetic [Ni(CN)4]2, anions (mortar; nickel on an inversion center) via bridging cyano groups. The bridging cyano groups occupy cis positions in the cation and trans positions in the anion, giving rise to a new previously unknown CT-type chain (i.e. cis,trans -type) among square tetra­cyano complexes. The coordination polyhedron of the paramagnetic Ni atom (twofold symmetry) is a slightly deformed octahedron with the two Ni,N(bipy) bonds in cis positions being somewhat longer [2.112,(3),Å] than the remaining four Ni,N bonds with a mean value of 2.065,(6),Å. The bond distances and angles in the anion have typical values. [source]


New Insight into the Mode of Action of Nickel Superoxide Dismutase by Investigating Metallopeptide Substrate Models

CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2009
Daniel Tietze M.
Abstract For the first time, the existence of a substrate adduct of a nickel superoxide dismutase (NiSOD) model, based on the first nine residues from the N terminus of the active form of Streptomyces coelicolor NiSOD, has been proven and the adduct has been isolated. This adduct is based on the cyanide anion (CN,), as a substrate analogue of the superoxide anion (O2.,), and the nickel metallopeptide H-HCDLPCGVY-NH2 -Ni. Spectroscopic studies, including IR, UV/Vis, and liquid- and solid-state NMR spectroscopy, show a single nickel-bound cyanide anion, which is embedded in the metallopeptide structure. This complex sheds new light on the question of whether the mode of action of the NiSOD enzyme is an inner- or outer-sphere mechanism. Whereas discussion was previously biased in favor of an outer-sphere electron-transfer mechanism due to the fact that binding of cyanide or azide moieties to the nickel active site had never been observed, our results are a clear indication in favor of the inner-sphere electron-transfer mechanism for the disproportionation of the O2., ion, whereby the substrate is attached to the Ni atom in the active site of the NiSOD. [source]


Germanates of 1D Chains, 2D Layers, and 3D Frameworks Built from Ge,O Clusters by Using Metal-Complex Templates: Host,Guest Symmetry and Chirality Transfer

CHEMISTRY - AN ASIAN JOURNAL, Issue 10 2007
Guang-Zhen Liu
Abstract The self-assembly of Ge,O polyhedra by metal-complex templates leads to initial examples of open germanate structures under mild solvothermal conditions. These materials are constructed from Ge,O cluster building bocks (Ge7X19 (X=O, OH, or F) or Ni@Ge14O24(OH)3) and span the full range of dimensionalities from 1D chains of Ge7O13(OH)2F3,Cl,2[Ni(dien)2] (FJ- 6) to 2D layers of Ge7O14F3,0.5[In(dien)2],0.5H3dien, 2H2O (1) and 3D frameworks of Ni@ Ge14O24(OH)3,2[Ni(L)3] (FJ- 1,a/FJ- 1,b) (dien=diethylenetriamine, L=ethylenediamine (en) or 1,2-diaminopropane (enMe)). The Ge7X19 cluster in FJ- 6 and 1 is formed by condensation of four GeX4 tetrahedra, two GeX5 trigonal bipyramids, and one GeX6 octahedron with a ,3 -O atom at the center of the cluster, whereas the Ni@ Ge14O24(OH)3 cluster in FJ- 1,a/FJ- 1,b is formed by condensation of nine peripheral GeO4 tetrahedra and five interior GeO3Ni units with one ,5 -Ni atom at the center of the cluster. FJ- 6 is characterized by a pair of racemic Ge7O14(OH)2F3 cluster chains and represents only one example of 1D germanates; 1 exhibits unique germanate layers with uniform 10-membered-ring apertures encapsulating an unknown indium complex, and the framework structure of FJ- 1,a/FJ- 1,b with large 24-membered-ring channels is the first example of porous materials that contain metal,metal bonds (Ge2+Ni+). These initial examples of germanates from metal-complex templates provide a useful model system for understanding the mechanisms of host,guest interactions, which may further facilitate the design and development of new porous materials "on demand". It is shown that the symmetry and configuration of the guest metal complex can be imprinted onto the host inorganic framework through hydrogen bonding between host and guest. [source]


A Binuclear Phthalocyanine Containing Two Different Metals

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2003
Mario Calvete
Abstract The unsymmetrical binuclear phthalocyanine 4a and the symmetrical binuclear phthalocyanine 4b with two different metals (Ni and Cu), as well as the correspondent binuclear phthalocyanines with two Ni atoms (4c and 4d) were synthesized from the benzoannulated dicyano-substituted Ni phthalocyanine 2. Atomic absorption spectroscopy verified unambiguously the presence of Ni and Cu in the binuclear phthalocyanines. The proposed synthetic route demonstrates great versatility towards substitution at the peripheral positions of the ring and the variation of the chelating central metal. Complexes 4a,4d are soluble in common organic solvents of medium polarity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine-based polyethenes ,

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2001
J. O. Liimatta
Abstract Dynamic mechanical thermoanalysis showed that polyethene, prepared under suitable polymerization conditions with the Brookhart-type catalyst dibromo- N,N,-1,2-acenaphthylenediylidenebis[2,6-bis(1-methylethyl)benzeneamine]Ni(II)/methylaluminoxane (MAO), behaved like an elastomer, even though no comonomer was added. A structural characterization showed that the polymers contained methyl to hexyl branches and some longer branches. The effect of the polymerization conditions on branching was investigated through variations in the pressure and temperature of the polymerization. Depending on the degree and type of branching, polyethene was either quite amorphous or highly crystalline with a high melting temperature. The solid-state structure of the catalyst dibromo- N,N,-1,2-acenaphthylenediylidenebis[2,6-bis(1-methylethyl)benzeneamine]Ni(II) consisted of two centrosymmetrically related monomeric moieties, where Ni atoms were bridged by two bromide ligands. The Ni atom was five-coordinated, with a square pyramidal coordination polyhedron. The sixth coordination site of the octahedral geometry was effectively blocked by the isopropyl groups of the 2,6-C6H3(i -Pr) substituents of the diimine ligand. In solution in the presence of MAO, the longer bridging NiBr bonds broke, and the complex dissociated to a monomeric species. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1426,1434, 2001 [source]


Magnetic X-ray absorption fine structure for Ni,Mn alloys

JOURNAL OF SYNCHROTRON RADIATION, Issue 2 2003
T. Miyanaga
Magnetic X-ray absorption fine-structure (XAFS) spectra have been measured for Ni,Mn alloys. The magnetic XAFS in the near-edge region (X-ray absorption near-edge structure, XANES) and X-ray magnetic circular dichroism (XMCD) of the Mn and Ni K -edge for Ni1,xMnx (x = 0.25, 0.24 and 0.20) show that (i) the local magnetic structure around the Mn atom is quite different from that around the Ni atom, and (ii) the peak intensity in the magnetic XANES of the Mn K -edge depends on the magnetization of the sample in contrast to the Ni K -edge. The Mn K -edge magnetic EXAFS (extended XAFS) for Ni0.76Mn0.24 is also measured. The second and fourth peaks in the Fourier transform are observed to be enhanced in comparison with the non-magnetic EXAFS, indicating that the second- and fourth-shell Ni atoms are replaced by Mn atoms due to heat treatment (atomic ordering). Semi-relativistic theoretical calculation explains the observed magnetic EXAFS. [source]


The electronic and electrochemical properties of the TiFe1,xNix alloys

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
A. Szajek
Abstract Mechanical alloying (MA) process was introduced to produce nanocrystalline TiFe1,xNix alloys (0 , x , 1). XRD analysis showed that, firstly, after 25 h of milling, the starting mixture of the elements had decomposed into an amorphous phase and, secondly, the annealing in high purity argon at 750 °C for 0.5 h led to formation of the CsCl-type (B2) structures with a crystallite sizes of about 30 nm. These materials, used as negative electrodes for Ni,MH batteries, showed an increase in discharge capacity with a maximum for x = 3/4. The band structure has been studied by the Tight Binding version of the Linear Muffin-Tin method in the Atomic Sphere Approximation (TB LMTO ASA). Increasing content of Ni atoms intensified charge transfer from Ti atoms, extended valence bands and increased the values of the densities of electronic states at the Fermi level. [source]


Hydrogen and carbon interaction in a FeNi alloy with a vacancy

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2009
Estela Gonzalez
Abstract The bonding of hydrogen and carbon to Fe and Ni in a 50:50 alloy is analysed using density functional calculations. The changes in the electronic structure of a L10 alloy upon C and H introduction at a vacancy region are addressed and a comparison with H or C in pure metals is drawn. H in bulk FeNi alloy with a vacancy locates at a tetrahedral site shifted towards the vacancy. Instead, C prefers an octahedral site (Fe based). The vacancy acts as strong traps of both C and H. Fe,Ni atoms are initially more strongly bonded to each other due to the vacancy formation. Consequently, the Fe,Fe, Fe,Ni and Ni,Ni bond strengths are diminished as new metal,C or metal,H bonds are formed. The most affected bond is the Fe,Ni, whose overlap population decreases by 72%. An analysis of the orbital interaction reveals that the Fe,H bonding involves mainly the Fe 4s, H 1s and Ni 4s orbitals. In the case of the sequential absorption, the C,H interaction is almost zero at a distance of 2.72 Å. The main interactions of these interstitials are developed with either Fe or Ni. We also consider the absorption sequence (H first or C first) and its influence on the electronic structure. Our results could be relevant to understand some steps of the carburization process during thermal cracking operations where hydrogen atoms are present. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Synthesis of single-walled carbon nanotubes with the laser vaporization method: Ex situ and in situ measurements

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006
M. Cau
Abstract In situ measurements were executed in the continuous wave CO2 -laser vaporization synthesis of single-walled carbon nanotubes (SWCNTs). The results were compared with the findings of the ex situ analysis of the product. Different catalysts (Co, Ni, Co/Ni, Ni/Y and Co/Y) were used and the temperature of the target surface (Ts) changed to compare the efficiency of the synthesis process. Our main results are related to the SWCNTs diameter which is depending on Ts and on the catalysts nature. The targets containing Y with Co or Ni atoms produce more and larger SWCNTs than Co/Ni targets. The SWCNTs' diameter is seen to increase with Ts. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Soft X-ray absorption spectroscopy and magnetic circular dichroism study of electroless-deposited CoNiFe ternary alloy soft magnetic films

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006
Masahito Tanaka
Abstract We studied microscopic magnetic properties of each consistent atom in boron added CoNiFe electroless-deposited soft magnetic films, which is a promising candidate for the soft magnetic underlayer of the perpendicular magnetic recording medium, by X-ray absorption spectra (XAS) and magnetic circular dichroism (MCD) measurement. It was found that various monoxides and Fe sesquioxide coexisted with the metals at the upper part of the films. The results of MCD sum rule showed the expected values of orbital angular moment ,Lz, for the film with macroscopic magnetic domain boundaries were larger than those of without domains at Co and Ni atoms and smaller at Fe atom. The appearance of macroscopic magnetic domain boundaries probably originated from the increase in ,Lz, of Co and/or Ni atoms. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Space group and atomic structure determination of a nano-sized ordered phase derived from a f.c.c. structure in maraging steel 12Cr,9Ni,4Mo,2Cu using transmission electron microscopy

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2003
Ping Liu
The unique properties of maraging steel Sandvik 1RK91 were attributed to unique precipitation: a nano-sized L phase in addition to the quasi-crystalline R, phase, which differs from any precipitation system in conventional maraging steels. The L phase was observed after ageing at either 748 or 823,K. It has flake morphology with dimensions ,100 × 500 × 500,Å. In the present study the structure of the L phase was examined using convergent-beam electron diffraction (CBED), energy-dispersive X-ray analysis (EDX) and high-resolution electron microscopy (HREM). The L phase could be described as Ti19Fe9Mo9Al8Cr5Ni50 or simply M50Ni50 (M = Ti, Fe, Mo, Al and Cr). The L phase is isostructural to FeNi. Its crystal structure was determined to have the ordered structure of the uAu-I type (L10, P4/mmm, a = 3.52, c = 3.63,Å and Z = 2) with two Ni atoms at ½ 0 ½ and 0 ½½, and two M atoms at 0 0 0 and ½½ 0. The crystal structure of the L phase can also be described using a primitive tetragonal cell and lattice parameters: a = 2.49 and c = 3.63,Å, Z = 1. The volume of the primitive tetragonal unit cell is 22.5,Å3 and the density is ,6.98,g,cm,3. The present study has demonstrated the possibility of determining the structure of an extremely small crystal by utilizing the information from CBED, EDX analysis and HREM. [source]


Two polymeric nickel(II) complexes with aromatic benzene-1,2,4,5-tetracarboxylate and pyridine-2,5-dicarboxylate linkers

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009
Ana María Atria
(,-Benzene-1,2,4,5-tetracarboxylato-,2O1:O4)bis[aquabis(2,2-methylpropane-1,3-diamine-,2N,N,)nickel(II)] methanol disolvate tetrahydrate, [Ni2(C10H2O8)(C5H14N2)4(H2O)2]·2CH4O·4H2O, (I), is dinuclear, with elemental units built up around an inversion centre halving the benzene-1,2,4,5-tetracarboxylate (btc) anion, which bridges two symmetry-related NiII cations. The octahedral Ni polyhedron is completed by two chelating 2,2-methylpropane-1,3-diamine (dmpda) groups and a terminal aqua ligand. Two methanol and four water solvent molecules are involved in a number of N,H...O and O,H...O hydrogen bonds which define a strongly bound two-dimensional supramolecular structure. The structure of catena -poly[[[bis(2,2-methylpropane-1,3-diamine-,2N,N,)nickel(II)]-,-pyridine-2,5-dicarboxylato-,3O5:N,O2 -[(2,2-methylpropane-1,3-diamine-,2N,N,)nickel(II)]-,-pyridine-2,5-dicarboxylato-,3N,O2:O5] octahydrate], {[Ni2(C7H3NO4)2(C5H14N2)3]·8H2O}n, (II), is polymeric, forming twisted chains around three independent Ni centres, two of which lie on inversion centres and the third in a general position. There are three chelating dmpda ligands (one disordered over two equally populated positions), which are each attached to a different cation, and two pyridine-2,5-dicarboxylate (pdc) anions, both chelating the Ni centre in general positions through an ,O,C,C,N, loop, while acting as bridges to the remaining two centrosymmetric Ni atoms. There are, in addition, eight noncoordinated water molecules in the structure, some of which are disordered. [source]


Dy2Ni7Sn3: a new member of the CaCu5 family of intermetallics

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2008
V. Romaka
Single crystals of didysprosium heptanickel tritin were synthesized from the constituent elements by arc-melting. Two of the five Ni atoms are at general sites and all other atoms are at sites with either twofold or m symmetry. The structure contains `DyNi5Sn' and `DyNi2Sn2' fragments and represents a new member of the CaCu5 series of intermetallics. [source]


Tb2Ni2Mg3: a new structure type derived from the Ru3Al2B2 type

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2007
Pavlo Solokha
Single crystals of diterbium dinickel trimagnesium, Tb2Ni2Mg3, were synthesized from the elements by induction melting. The novel compound crystallizes in the space group Cmmm with one Mg atom of site symmetry mmm and the Tb, Ni and other Mg atom in m2m positions. This ternary compound represents a new structure type that is derived from Ru3Al2B2 by way of Wyckoff site distribution. The two-layer structure of Tb2Ni2Mg3 is a new representative of a homologous linear structure series of general formula R,k+nX2nR,,2m+k based on structural fragments of the ,-Fe, CsCl and AlB2 structure types. The Tb atoms in the structure are enclosed in 17-vertex polyhedra, while rhombododeca­hedra and distorted rhombododeca­hedra surround the Mg atoms, and equatorially tricapped trigonal prisms form around the Ni atoms. All inter­atomic distances indicate metallic type bonding. [source]


Structure-sensitivity of CH3 dissociation on Ni(100)from first-principles calculations

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009
Yi-An Zhu
Abstract First-principles calculations are performed to explore the CH3 dissociation on Ni(100). The CH2 species bind most strongly to the hollow site with two CH bonds pointing toward the neighboring surface Ni atoms. Through the calculations of local density of states (LDOSs) and partial charge density, the CHNi three-center bond is regarded as the key factor determining the CH3 adsorption. The CH3 dissociation on Ni(100) is investigated along two different reaction pathways. After zero-point energy (ZPE) correction considered, the energy barriers for the CH3 dehydrogenation are calculated to be 0.46 and 0.54 eV. Because these barriers are much lower than that for the CH3 dissociation on Ni(111), the CH3 dehydrogenation is found to be structure-sensitive. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]