Localized versus Delocalized Electrons

Given the relative success of the above point defect scheme to model the experimental data of oxygen nonstoichiometry and electrical conductivity for Lai xSrxFe03 [165,166] and Lai.j rxCrOs [167], its use is less satisfactory for La].xSrxCo03 and Laj.xSrxMnOa which compoimds show notably high values for the electronic conductivity. 

A proper description of electronic defects in terms of simple point defect chemistry is even more complicated as the d electrons of the transition metals and their compounds are intermediate between localized and delocalized behaviour. Recent analysis of the redox thermodynamics of Lao.8Sro,2Co03. based upon data from coulometric titration measurements supports itinerant behaviour of the electronic charge carriers in this compound [172]. The analysis was based on the partial molar enthalpy and entropy of the oxygen incorporation reaction, which can be evaluated from changes in emf with temperature at different oxygen (non-)stoichiometries. The experimental value of the partial molar entropy (free formation entropy) of oxygen incorporation, Asq, could be 

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An overview of electron transport from water to NADP will be presented, and a discussion of photophosphorylation. This will include an appraisal of the recent observations and controversies about the localized versus delocalized nature of the proton pool(s) contributing to the proton electrochemical gradient involved in the mitchellian coupling of electron transport to ATP synthesis [5,6]. 

Localized Versus Delocalized Description of the Two-Electron/Two-Orbital Problem... 

Lindenberg and Ratner have discussed the question of localized versus delocalized valency states by using a four-site model. In the simplest case, this is the system H2 H2, in which the two H-H distances can be varied to provide different values of the coupling parameter. The criteria for valence trapping, and rates of intramolecular electron transfer are discussed in terms of the model. ... 

It is generally accepted nowadays that the sequentially increasing occupation of 5f states dominates the electronic properties in the series of actinide elements (see table 2.1). The analogy with lanthanides, in which the 4f states are gradually filled, is not complete. The 4f electronic states are confined deeply in the core of the lanthanide ion and can be treated in most cases as localized. On the other hand, a non-negligi-ble overlap of the more extended 5f wave functions belonging to neighbouring actinide atoms in a solid leads to the delocalization of the 5f states which resembles the formation of the d band in transition metals. The question about the localized versus itinerant 5f electron behaviour has become one of the most central ones within electronic structure considerations. This controversial behaviour is quite well... 

As to the electronic effect of the nitrogen atoms adjacent to the benzylic center in the diaza derivative 7d, semiempirical calculations show that only 2% of the a. spin density is delocalized onto the nitrogens of the urazole moiety. Therefore, the urazole-bridged derivatives 7 are localized triplet diradicals and their lower D values (Table 5) derive from the slightly lower spin densities and the somewhat higher interradical distance dAB. The latter is a consequence of angle widening due to the shorter N—N versus C—C distance ( 144 vs. 154 pm [67]). 

In contrast to all other rare earth metal compounds discussed so far, the hydride halides contain mobile interstitial atoms that can be added or (partly) removed at will in a topochemical reaction. These compounds therefore offer a unique possibility to study the delocalization of electrons in extended metal-metal bonds versus the localization at interstitial atoms. The known compounds are summarized in table 7. 

Bultinck P, Fias S, Ponec R (2006) Local aromaticity in polycyclic aromatic hydrocarbons electron delocalization versus magnetic indices. Chem Eur J 12 8813-8818... 

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