Nickel atomic properties

Complex 4a (see Fig. 1) differs from these catalytically active complexes only in the substitution of the complexed olefin molecules and hydrogen atom by a 7r-allyl group. The ligands in these square-planar molecules can adopt two different arrangements around the central nickel atom The olefin can either be trans (31a) or cis (31b) to the phosphine molecule. Because precedent exists for both these arrangements [e.g., 12 (84) and 30 (82)]. it is difficult to decide which of the two structures (31a or 31b) represents the catalytically active species. It is of course possible that the differences observed in the catalytic properties of systems having different ligands L and Y (Section IV) is due (at least in part) to differences in the population of 31a and 31b. 

Figure 7.21 STM image ot a nickel(ll I) surface containing a few gold atoms. The nickel nearest-neighbor atoms of gold are seen to have different electronic properties from those of the other nickel atoms (from Besenbacher et at. [63]).

German team of physicists at GSI, Darmstadt, Germany Highly unstable and presumed to be a metal, but little else is known of its properties produced by bombarding bismuth with accelerated nickel atoms. 

The structure and properties of the initial nickel atom-propene complex has received detailed attention by Skell. The use of isotopically labeled propenes demonstrated that exchange occurs between the 1- and 3-positions but not between either the 1- and 2- or 2- and 3-positions (10) ... 

In anhydrous NiX2 (X = halides), the nickel atom is octahedrally coordinated by six halogen atoms. Their relevant properties and synthetic procedures are reported in Table 94.2220,2221... 

In contrast to the dithiolenes, we refer to dithiolato complexes as those in which the typical dithiolene resonance (and the properties which are associated with it) are absent because the ligand exists entirely in its dinegative form. In the neutral compound (22) above, the 2 — charge of the ethylenedithiolato ligand is balanced by the 2 + charge of the nickel atom and approximately square planar coordination is provided by the neutral dithiooxamide-type ligand. 

Another distorted variant of the NiAs structure occurs in NiP which is stable only above 850° C (159). In the orthorhombic NiP structure the distortions are stronger than in the MnP type (Fig. 44) but like in MnP the metal atoms form zig-zag chains with Ni—Ni = 2.53 A. The coordination of the nickel atoms is modified insofar as they are shifted towards a comer of the distorted anion octahedra. As a result there are only five phosphorus atoms in contact with the central nickel atom. The anions themselves are arranged in pairs with a P—P distance of 2.43 A, which roughly corresponds to the length of a half bond. In the absence of cation-cation bonds the P—P pairs would lead to divalent Ni and non-metallic properties would be possible. In the actual structure the Ni—Ni bonds exclude semiconductivity which, moreover, cannot be expected in a high-temperature phase. 

In contrast, when Ni(CT)Cl2 or Ni(CT)Br2 is dissolved in water, it converts to a planar, diamagnetic complex which acts as a di-univalent electrolyte. Also, the nickel (II) ion in Ni(CT)2+ will not combine with NH3 when dissolved in aqueous solution 11). These observations present a number of disturbing features. The failure of H2O and NH3 to coordinate is inferred from the fact that the solution properties are typical of planar nickel(II). Both NH3 and H2O occupy positions much higher in the spectrochemical series than Cl or Br. Consequently, if either of these neutral molecules were coordinated, the nickel atom would surely exist in its paramagnetic triplet state. 

For a better understanding of the role of rare earth elements in the catalytic properties of the amorphous alloy-derived catalysts, characterization of the catalysts was carried out. Figure 3shows the change in the number of surface nickel atoms,... 

In the case of the nickel-copper system, which can form solid solutions over the whole range of compositions, the substitution of copper atoms for nickel atoms in the metal lattice adds electrons to the system. According to Mott and Jones (5), nickel-copper alloys would possess (/-bands with fewer unoccupied states than would pure nickel. In this view a nickel-copper alloy would possess a single (/-band rather than separate bands for the two components, and the additional electrons introduced with the copper would lead to an alloy with a more completely filled (/-band. In this model of the electronic structure of a nickel-copper alloy, no distinction was made between the chemical properties of nickel and copper atoms in the alloy. 

The environment about the nickel atom, and its isomorphous analogs, may therefore be regarded as six-coordinate Da, but with two long interactions perpendicular to the molecular plane. This result has important implications in the study of the magnetic (see Section V,D) and electrical (see Section VI,D) properties of the phthalocyanines. 

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