Nickel electronic band structure

Early work on electron band structure by soft X-ray spectroscopy was concentrated on pure metals, and it was not until the advent of photoelectron spectroscopies that alloys started to be examined. It soon became clear that small additions of nickel to copper resulted in the appearance of electrons having energies close to the Fermi value there was no common d-band, but each component exhibited its own band structure (Figure 1.17). Many other kinds of physical measurement confirmed this, and corresponding behaviour was observed with the palladium-silver system (Figure 1.18). It became necessary to find a new and better theory. 

Calculated band structures of aU these compounds feature the fermi level above a density-of-state peak that is consistent with the 3d bands for nickel. The [BN]" anion in CaNi(BN) compromises an electronic situation with a filled 3(7 (HOMO) level that is B-N anti-bonding (Fig. 8.13). Any additional electron will... 

It is unnecessary to provide details of the results of such calculations, or of their comparison with experimental determinations by for example soft X-ray spectroscopy band structures for Transition Metals can adopt quite complex forms, so we must content ourselves with a few qualitative observations. For the metals of catalytic interest, the nrf-electron band is narrow but has a high density of states (Figure 1.8), because these electrons are to some degree localised about each ion core, whereas the (n + l)s band is broad with a much lower density of states because s-electrons extend further and interact more. On progressing from iron through to copper, the d-band occupancy increases quickly, and the level density at the Fermi surface falls. The extent of vacancy of the d-band is provided by the saturation moment of magnetisation thus for example the electronic structure of metallic nickel is (Ar core) and is said to have 0.6 holes in the d-band . 

Recently, a spin-orbit split structure was observed in the case of cerium for the peak near Ep by Patthey et al. (1985) which can be interpreted with a modified G-S model which includes spin-orbit effects. Inclusion of spin-orbit splitting in the screening model can also explain this spectrum (Norman 1986). Recently, a two-peak structure has been resolved in uranium compounds by Arko (1986). The data also seems to be consistent with a screening model interpretation. Finally, we need to emphasize that although the two-peak structure seen in all of these cases is considered to be an exotic effect, such structure is also seen in the case of nickel, where the peak away from Ep is actually a satellite below the nickel d-band. And, of course, this multiple peak structure is seen in core level spectroscopy all over the periodic table. As we shall see, the observation of such structure in the valence emission of f-electron compounds is merely a reflection of the localization of such electrons as compared to the other valence electrons. 

For a very few metals, however, the unpaired electrons in the conduction band can lead to ferromagnetism. In the whole of the Periodic Table, only iron, cobalt, nickel, and a few of the lanthanides (Gd, Tb) possess this property. So, what is so special about these elements that confers this uniqueness on them It is not their crystal structure they each have different structures and the structures are similar to those of other non-ferromagnetic metals. Iron, cobalt, and nickel, however, all have a nearly full, narrow 3c/band. 

The [Ni(CN)4]2 anion is one of the most stable nickel(II) complexes and an overall formation constant as high as about 1030 has been determined.627,62 The structure of the complex is square planar with the nickel(II) bound to carbon atoms of cyanides and with linear Ni—C—N linkages (Table 37).629 630 The planar [Ni(CN)4]2 units are stacked in columns in the crystal lattice with Ni—Ni interlayer distances as short as 330 pm. C-bonded CN- is a strong field donor and the electronic spectrum of [Ni(CN)4]2 shows two weak d-d bands at 444 and 328 nm. 

The ligand field strength of the ligands is between that of the dithiocarbamates and water.49 IR studies show characteristic bands near 1250, 1100, 1020 and 550 cm-1.93 The contribution of the resonance form (85) in transition metal complexes is less than that of the analogous structure in the dithiocarbamates.60 The electron density on the metal is not very high, which accounts for the fact that abnormal high oxidation states are exceptional and a strong interaction of bases with the square planar nickel (and some other metal) xanthates is found.94... 

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