Density carbon-rich structures

Redox reactions can induce significant redistribution of n electron density along the metal-carbon backbone when conjugated or cumulated carbon-rich ligands are present and may thus lead to major bonding changes. Particularly common are interconversions between alkynyl and cumulenic structures. 

In each case, it is the carbon atom that has the negative formal charge that makes it the "electron-rich" end of the structure. Moreover, there are antibonding orbitals in both CO and CN that can accept electron density transferred from the nonbonding d orbitals on the metal (as described in Section 16.10). Because of the nature of these ligands, it is not uncommon for them to function also as bridging groups in which they are bonded to two metal atoms or ions simultaneously. 

Nanocarbon emitters behave like variants of carbon nanotube emitters. The nanocarbons can be made by a range of techniques. Often this is a form of plasma deposition which is forming nanocrystalline diamond with very small grain sizes. Or it can be deposition on pyrolytic carbon or DLC run on the borderline of forming diamond grains. A third way is to run a vacuum arc system with ballast gas so that it deposits a porous sp2 rich material. In each case, the material has a moderate to high fraction of sp2 carbon, but is structurally very inhomogeneous [29]. The material is moderately conductive. The result is that the field emission is determined by the field enhancement distribution, and not by the sp2/sp3 ratio. The enhancement distribution is broad due to the disorder, so that it follows the Nilsson model [26] of emission site distributions. The disorder on nanocarbons makes the distribution broader. Effectively, this means that emission site density tends to be lower than for a CNT array, and is less controllable. Thus, while it is lower cost to produce nanocarbon films, they tend to have lower performance. 

ENDOR frequency determination with the aid of ENDOR-induced ESR in cis-rich samples gives the half-width of the spin distribution of 18 carbon sites and the ratio of the peak value of the negative density to that of the positive density of p(l)/p(0)%0.44 [104,105], Similar results to those in cis-rich samples, that is similar spectra with resolved structures for the stretch direction and similar spectral frequencies, have been reported for stretch-oriented trans-polyacetylene prepared by the Durham route using pulsed ENDOR techniques [99,106,107], The unpaired electrons observed in Durham samples were conjectured to be trapped solitons from nearly temperature-independent ENDOR spectra. In the studies of this system the first successful application of TRIPLE resonance in polyacetylene has been reported [99,107], Readers can find reviews on the results of Durham samples [2,99] as... 

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