Cobalt electronic structures

The electronic structure of cobalt(II) complexes with Schiff bases and related ligands. C. Daul, C. W. Schlapfer and A. von Zelewsky, Struct. Bonding (Berlin), 1979,36,129-171 (76). 

Daul C, Schlapfer CW, von Zelewsky A (1979) The Electronic Structure of Cobalt(II) Complexes with Schiff Bases and Related Ligands. 36 129-171 Davidson G, see also Maroney MJ (1998) 92 1-66 Dawson JH, see Andersson LA (1991) 74 1-40... 

Daul, C., Schlapfer, C. W., von Zelewsky, A. The Electronic Structure of Cobalt (II) Complexes with Schifl Bases and Related Ligands. Vol. 36, pp. 129—171. 

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. 

Alike metallocomplex anion-radicals, cation-radicals of odd-electron structure exhibit enforced reactivity. Thus, the 17-electron cyclopentadienyl dicarbonyl cobalt cation-radical [CoCp(CO)2] undergoes an unusual organometallic chemical reaction with the neutral parent complex. The reaction leads to [Co2Cp2(CO)4]. This dimeric cation-radical contains a metal-metal bond unsupported by bridging ligands. The Co—Co bond happens to be robust and persists in all further transformations of the binuclear cation-radical (Nafady et al. 2006). 

The addition of promoter elements to cobalt-based Fischer-Tropsch catalysts can affect (1) directly the formation and stability of the active cobalt phase structural promotion) by altering the cobalt-support interfacial chemistry, (2) directly affect the elementary steps involved in the turnover of the cobalt active site by altering the electronic properties of the cobalt nanoparticles electronic promotion) and (3) indirectly the behaviour of the active cobalt phase, by changing the local reaction environment of the active site as a result of chemical reactions performed by the promoter element itself synergistic promotion). 

It is far from easy to distinguish structural, electronic and synergistic promotion effects. Structural promotion is, in this respect, the most easily to observe. Most synergistic elfects are also widely discussed in the literature in enhancing the catalytic performance of supported cobalt nanoparticles. Instead, promotion as a result of electronic effects are much more difficult to detect. The main reason is that one has to discriminate between the number of surface cobalt sites and the intrinsic activity of a surface cobalt site (turnover frequency). This is especially difficult in view of the complexity of the catalyst material. It also requires spectroscopic tools, which are able to detect changes in the electronic structure of the supported cobalt nanoparticles. 

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 reversible formation of a low-spin [Co (III) (NHS) n02 ]2+ complex within a Co (II) Y zeolite has been demonstrated by EPR spectroscopy. In this complex n is probably equal to five. A maximum of one cobalt complex per large cavity was farmed. The cobalt hyperfine structure shows that the unpaired electron is only 8% on the metal ion. Experiments utilizing 170 indicate that 02 enters the coordination sphere of the Co2+ ions and that the unpaired electron is largely associated with the oxygen molecule. The oxygen-17 hyperfine structure reveals that the two oxygen atoms are not equivalent hence, it is concluded that the oxygen is bonded as a peroxy-type superoxide ion. 

Compensation behavior found for the decomposition of hydrogen peroxide on preparations of chromium (III) oxide, which had previously been annealed to various temperatures, was attributed to variations in the energy states of the active centers (here e 0.165). Compensation behavior has also been observed (284) in the decomposition of hydrogen peroxide on cobalt-iron spinels the kinetic characteristics of reactions on these catalysts were ascribed to the electronic structures of the solids concerned. 

ESR studies also show the similarity between oxycoboglobin and oxygenated cobalt porphyrin, and suggest that the protein does not measurably influence the electronic structure of the heme group, although the protein does control the extent to which dioxygen is bound. 

---