Bonding considerations crystal field theory

In the final section of this chapter, we shall attempt to give a brief rationalization of the regularities and peculiarities of the reactions of non-labile complexes which have been discussed in the previous sections. The theoretical framework in which the discussion will be conducted is that of molecular orbital theory (mot). The MOT is to be preferred to alternative approaches for it allows consideration of all of the semi-quantitative results of crystal field theory without sacrifice of interest in the bonding system in the complex. In this enterprise we note the apt remark d Kinetics is like medicine or linguistics, it is interesting, it js useful, but it is too early to expect to understand much of it . The electronic theory of reactivity remains in a fairly primitive state. However, theoretical considerations may not safely be ignored. They have proved a valuable stimulus to incisive experiment. 

The analogy between the two theories is only formal. Crystal field theory is a purely electrostatic approach that does not take into consideration the formation of MOs and the nature of the bond. According to crystal field theory, optical and magnetic properties are ascribed to crystal field splitting between two AOs, whereas in ligand field theory energy splitting occurs between AOs, and... 

The electronic structures of the [Mo(CN)8]" (n = 3 or 4) ions have been calculated using a SCCC-MO method and the d-orbital splittings shown to be nearly identical with those calculated by crystal-field theory. Bonding considerations suggest that the stable forms of [Mo(CN)g] and [MofChOg] ... 

The transition metals are characterized by the fact that not only the s and p electrons of the outermost shell but also the d electrons of the penultimate shell are available for bonding. As a result, the theory of the interatomic binding in these elements is particularly complex and certainly cannot be regarded as having reached a state of finality. Some of the considerations involved have already been outlined in chapter 5, but here, where we are concerned primarily with structure, it would be quite inappropriate to attempt a detailed review of the great volume of work in this field, especially as many such reviews are readily available (see appendix 1). It is sufficient for our purpose to emphasize that crystal structure alone is far from a complete characterization of the properties of the elements concerned, and that metals with the same crystal structure may, nevertheless, differ profoundly in their physical properties. 

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