Ligand complexes, high-complexation intensity systems

Attempts have been made to understand the electronic spectra and, particularly, the high-intensity bands in the visible region and the very low ligand field band ( >, 12kK) in the perthiocarboxylate complexes of Ni(II) (246). It is conceded that the use of ligand field treatment in this system, where mixing of electronic states occurs in the higher excited states, is only of limited value (246). 

So far, we have briefly touched upon the ligand field approach and AI calculation on transition metal complexes. In our view, it is important to realize that these two approaches have fundamentally different goals. LFT aims at providing a conceptual framework which qualitatively describes the properties of a class of compounds in as-simple-as-possible terms. It is not meant to be a theory that lets one to predict the properties of a given compound accurately without any external input. Thus, using LFT, it is possible to predict how many absorption bands are expected in the UV-vis spectra of, say, high-spin d3 systems, which of them are spin-allowed. Only after adjustment of certain parameters (to be described later), one can make semiquantitative estimates of the positions - and perhaps also the intensities - of these bands. However, importantly, LFT makes the statement that there are many properties that are common to the class of high-spin d3 systems - or, in fact, that any d" share a number of physical properties. 

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