Electronic spectra of square-planar halides and cyanides

2 Electronic spectra of square-planar halides and cyanides 

With the energy level scheme shown in Fig. 8.9.2, we can easily derive two types of energy level diagrams those for halides, as shown in Fig. 8.9.3, and those for cyanides, as shown in Fig. 8.9.4. We will make use of these results to interpret some spectral data for square-planar ML4 complexes. 

Schematic energy level diagram for square-planar cyanides. 

The d-d spectrum of [P1.CI4I2- in solution is shown in Fig. 8.9.5. Note that the bands are relatively weak, signifying that they are due to symmetry-forbidden transitions. As mentioned previously, three d-d bands are expected indeed, three are observed. Hence the assignment is relatively straightforward  

Two intense bands are observed in the spectrum of [PtCU]2-, as shown in Fig 8.9.6. They are charge transfer bands, as characterized by their energies and intensities. Compared to the d-d transitions shown in Fig. 8.9.5, the charge transfer bands are seen at much higher energy and are more intense by a factor of nearly 103. Hence these transitions must be symmetry allowed. With the aid of Fig. 8.9.3, as well as some computational treatments, the following assignments have been made  

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