Stabilization energy applications

The same conclusion is not applicable to the NO+ complexes, in which the magnitudes of the formation constants are much more strongly dependent on the ionization potential of the arene donor (see Fig. 10A). Thus the factor of >104 that separates the formation constant of the benzene complex with NO+ from that of the hexamethylbenzene complex corresponds to more than 5 kcal mol-1 of extra stabilization energy in the... 

Perhaps a more fundamental application of crystal field spectral measurements, and the one that heralded the re-discovery of crystal field theory by Orgel in 1952, is the evaluation of thermodynamic data for transition metal ions in minerals. Energy separations between the 3d orbital energy levels may be deduced from the positions of crystal field bands in an optical spectrum, malting it potentially possible to estimate relative crystal field stabilization energies (CFSE s) of the cations in each coordination site of a mineral structure. These data, once obtained, form the basis for discussions of thermodynamic properties of minerals and interpretations of transition metal geochemistry described in later chapters. 

One of the most successful applications of crystal field theory to transition metal chemistry, and the one that heralded the re-discovery of the theory by Orgel in 1952, has been the rationalization of observed thermodynamic properties of transition metal ions. Examples include explanations of trends in heats of hydration and lattice energies of transition metal compounds. These and other thermodynamic properties which are influenced by crystal field stabilization energies, including ideal solid-solution behaviour and distribution coefficients of transition metals between coexisting phases, are described in this chapter. 

Trends in CFSE data derived from the absorption spectral measurements described in chapter 5 may be used to predict or interpret element partitioning involving AT3 cations between coexisting aluminosilicate minerals. In many cases, however, the CFSE data represent average values for cations in several Al3+ sites in individual crystal structures. Nevertheless, the stabilization energies are applicable to interphase partitioning trends based on bulk chemical data for coexisting minerals. 

It is possible to describe the site preference of metals for nitrogen or carbon coordination in a Prussian blue analog in terms of ligand field stabilization energies Shriver, Shriver and Anderson, 1965). In application, even this simple treatment requires a number of estimates nevertheless, it affords reasonable agreement with experimentally determined structures and provides a framework for the systemization of Prussian blue type structures. One expectation from this approach is that if one of the two metal ions has more than six d electrons and the other has six or less, the latter will be carbon coordinated and the former nitrogen coordinated. 

This is only valid if A Ht s 35.6 kcal mol-1. It allows us to determine 2S °(R ) - 5E°(R—R) and so, to calculate BDE(C—C) and Ea. Moreover, if the heat of formation and therefore the stabilization energy of the dimer are known, one readily obtains the SE° and the heat of formation of the corresponding radical. The reverse is also obviously true. Three specific applications of Eq. (121) are given below ... 

We have also proposed a general definition of the concept of stabilization energy applying to any compound, as shown by the numerous applications described in this survey article. Using this concept, we have been able to carry out a critical analysis and to offer a unified definition of various former notions such as hyperconjugation, resonance, ring strain, and steric repulsion energies. 

However, the application of such a concept to the transition state of [47t+2jt] cycloadditions is controversial because the stabilizing energy involved may be too weak [46-49] ( 9.3). 

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