Nickel electronic structure

H. Basch, M. D. Newton and J. W. Moskowitz, The electronic structure of small nickel atom clusters , J. Chem. Phys. 73 4492 (1980). 

This review aims to present an account of the catalytic properties of palladium and nickel hydrides as compared with the metals themselves (or their a-phase solid solutions with hydrogen). The palladium or nickel alloys with the group lb metals, known to form /8-phase hydrides, will be included. Any attempts at commenting on the conclusions derived from experimental work by invoking the electronic structure of the systems studied will of necessity be limited by our as yet inadequate knowledge concerning the electronic structure of the singular alloys, which the hydrides undoubtedly are. 

The screened proton model of nickel or palladium hydrides and Switendick s concept of the electronic structure do not constitute a single approach sufficient to explain the observed facts. In this review, however, such a model will be used as the basis for further discussions. It allows for the explanation and general interpretation of the observed change of catalytic activity of the metals, when transformed into their respective hydrides. 

Figure 9.3 Images of an Ni(l 11) surface (A) with 2% and (B) with 7% of a monolayer of gold. The gold atoms appear black in the images and the nickel atoms adjacent to the gold atoms are brighter (yellow) because of a change in their electronic structure. (Reproduced from Ref. 12).

Oxygenation of the Ni1 complex (39) leads to 02 activation and 0-0 bond rupture with formation of a deep purple bis(/i-oxo)nickel(III) complex (40) supported by thioether ligands.184 Its electronic structure has been investigated by spectroscopic and DFT methods.185... 

Bis( 73-allyl)nickel(0) and bis( 75-pentadienyl)iron(II) have been used as starting materials in the preparation of [Ni(PF3)4] and [Ni(PF2H)4], 0 The electronic structure of the fluorophosphine com-... 

The structures of metal-complex dyes, which must exhibit a high degree of stability during synthesis and application, is limited to certain elements in the first transition series, notably copper, chromium, iron, cobalt and nickel. The remaining members of the transition series form relatively unstable chelated complexes. The following description of the influence of electronic structure, however, is applicable to all members of the series. 

Physics of Nickel Clusters. 2. Electronic Structure and Magnetic Properties. 

In Situ Spectroscopy—Electronic Structure and Redox Behavior of Nickel... 

Recent studies using high resolution electron energy loss and photoelectron spectroscopy to investigate the effect of sulfur on the CO/Ni(100) system are consistent with an extended effect by the impurity on the adsorption and bonding of CO. Sulfur levels of a few percent of the surface nickel atom concentration were found sufficient to significantly alter the surface electronic structure as well as the CO bond strength. 

NiOi45o appears to be independent of temperature below room temperature and above 100°C with a linear region of log (charge) versus jT between 30 and 100°C. The process of charge removal is clearly thermally activated and intimately related to the electronic structure of the nickel oxide. 

Recall that the saturation magnetization, Mj, is the maximum possible magnetization in the material, and is simply the prodnct of the net magnetic moment per atom. Pm, and the number of atoms per unit volnme, N. The net magnetic moment, in turn, is related to the electronic structure (paired or unpaired electrons), although a number of other factors come into play. Use this information to calculate the saturation magnetization for nickel. 

Fig. 3. Two STM images of the nickelfl 1 1) surface with 2% (right) and 7% (left) gold coverage, respectively. Au is imaged as dark depressions in the surface. The nickel atoms surrounding the gold appear brighter owing to a local modification of the electronic structure, indicating a changed chemical reactivity of these. Adapted from Reference (79).

Percentage d-character Considering the electronic structure of metals thus derived, Pauling then calculates the percentage d-character of the metallic bonds, the percentage d-character being an indication of bond strength. As examples, we have chosen cobalt, nickel and copper (Table I). 

The oxidation of carbon monoxide on nickel oxide has often been investigated (4, 6, 8, 9, II, 16, 17, 21, 22, 26, 27, 29, 32, 33, 36) with attempts to correlate the changes in the apparent activation energy with the modification of the electronic structure of the catalyst. Published results are not in agreement (6,11,21,22,26,27,32,33). Some discrepancies would be caused by the different temperature ranges used (27). However, the preparation and the pretreatments of nickel oxide were, in many cases, different, and consequently the surface structure of the catalysts—i.e., their composition and the nature and concentration of surface defects— were probably different. Therefore, an explanation of the disagreement may be that the surface structure of the semiconducting catalyst (and not only its surface or bulk electronic properties) influences its activity. 

Nature of Active Sites. There is no apparent correlation between the increase of catalytic activity and a modification of the electronic structure of nickel oxide, since the electrical properties of both catalysts are identical. It is probable that local modifications of the nickel oxide surface are responsible for the change of its activity and of the reaction mechanism. It should be possible to associate these structural modification with local modifications of the height of the Fermi level, but it would be difficult to explain the results by the electronic theory of catalysis which considers only collective electrons or holes. A discussion based only on the influence of surface defects seems, therefore, to be more straightforward. 

The discovery that the iron-group elements can form bonds which have in part the character of multiple bonds by making use of the orbitals and electrons of the 3d subshell, whilq surprising, need not be greeted with skepticism the natural formula for a compound ECO is that with a double bond from R to C, and the existence of the metal carbonyls might well have been interpreted years ago as evidence for double-bond formation by metals. The double-bond structure for nickel tetracarbonyl (structure E) was in fact first proposed by Langmuir62 in 1921, on the basis of the electroneutrality principle, but at that time there was little support for the new idea. 

Electronic Structure and Methods of Study of Nickel(III) and Nickel(IV) Complexes 288... 

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