Chromophore metal-ligating atom

Such a definition is a crucial assumption in the approach that follows and, somewhat surprisingly, is not commonly exploited in alternative approaches. Consider, for example, the d-d transitions. If the metal ion is taken as the chromophore, it is generally inpossible to get realistic energies and intensities for the normal absorption because of the importance of the metal-ligating atom overlap. Thus it is unlikely to provide a satisfactory basis for a CD model. On the other hand, if the chromo-phore is taken to include both the metal and the ligating atom system, both the d-d and charge transfer regions in the normal absorption spectrum may be exploited to parametrize the chromophore as much as possible. The remainder of the complex (the chelate system) then constitutes another chromophoric system. 

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