Electronic structures stability factors

Trends in the electronic structure of the chalcogenide catalysts have proved to be helpful in the design and understanding of the catalyst clusters. During ORR, the molecular oxygen has been found to react with the cluster as a whole, rather than individual metal atoms.177 The overall number of electrons per cluster unit (NEC) in the valence bond has been shown to have a factor in the activity and stability of the cluster catalysts.177,181 The unsubstituted Chevrel phases have a NEC of 20.177,181 Substituting or intercalating other transition metals into the crystal lattice to make ternary or pseudo-binary Chevrel phases allows for the increase of NEC. It has been found that as the NEC approaches 24, the catalytic activity improves.181 Alonso-Vante compiled the results from his previous studies to show the effect of NEC in... 

Delocalization of charge in the conjugate base anion through resonance is a stabilizing factor and will be reflected by an increase in acidity. Drawing resonance structures allows us to rationalize that the negative charge is not permanently localized on a particular atom, but may be dispersed to other areas of the structure. We should appreciate that a better interpretation is that the electrons are contained in a molecular orbital that spans several atoms. 

Thus, the apparent stability of a cluster ion in any specific CMS may arise from a combination of one or more of the following factors, such as structural stability, electronic bonding pattern, and dynamics of unimolecular dissociation. 

The quantum-chemical calculations play an important role in investigation of electronic structure and stability of fullerenes. The relative positioning of the pentagons which set the surface curvature of fullerene molecule, presence of condensed hexagons, electronic effects - all of these factors define a total energy of a fullerene molecule and its stability or instability. The analysis has shown that the most stable fullerenes have minimal total energies among their isomers. Nevertheless, the reasons of why some fullerenes can be obtained and others cannot are not clear yet. 

As has been previously mentioned, the two most important electronic structure factors that have been suggested to stabilize the TP geometry in... 

Hexafluoroacetone has been found to be a very interesting synthon on the borderline between inorganic and organic chemistry, and has established its own chemistry with various nonmetallic and metallic substrates only a few types of reactions resemble those of a regular ketone. The electron-withdrawing properties of the CFj groups are the stabilizing factor for structures that would otherwise be inaccessible. Only a few cases are known in which the electronic properties of HFA have inhibited any reaction. 

However, it is sometimes profitable to compare the relative stabilities of ions differing by unit charge when surrounded by similar ligands with similar stereochemistry, as in the case of the Fe3+—Fe2+ potentials (Table 17-1), or with different anions. In these cases, as elsewhere, many factors are usually involved some of these have already been discussed, but they include (a) ionization enthalpies of the metal atoms, (b) ionic radii of the metal ions, (c) electronic structure of the metal ions, (d) the nature of the anions or ligands involved with respect to their polarizability, donor pir- or acceptor d77-bonding capacities, (e) the stereochemistry either in a complex ion or a crystalline lattice, and (f) nature of solvents or other media. In spite of the complexities there are a few trends to be found, namely ... 

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