Ultraviolet Spectra and Electronic Structure of Metallic Complexes. I. Chloroammine Cobalt (III) Complexes

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Abstract
In order to study the nature of the so‐called ``first, second, third, and specific bands'' of the metallic complexes, the semiempirical M.O. method has been applied to a series of [Co(NH3)6—nCln](3—n) + (n=0, 1, 2 (cis, trans)) type complexes taking π electrons of the ligands into consideration. The agreement between the calculated and observed energies of transition is satisfactory partly due to the appropriate values of the parameters used. Moreover, the following conclusions have been obtained by the present calculation: (1) The magnitude of the splitting of the first band depends upon the overlap integral, S(3dπ, npπ) and also the ionization potential of the ligand (π). (2) The splitting of the first band in the cis‐complex is small compared to that of the trans‐complex, since, in the former, the three orbitals, from which electrons are excited to produce the low‐energy absorptions, lie at nearly the same energy. (3) Two strong bands in the ultraviolet region are due to the transitions approximately from the ligand level to the metal level, and therefore, correspond to the so‐called ``third bands.'' They will show ``blue‐shift'' in polar media. (4) The general rule that the trans‐complex shows the third bands at longer wavelength than that of the cis‐complex can be accounted for more satisfactorily if the Cl–Cl interaction in the cis‐complex is considered. (5) The spectra of other halogenoammine complexes are reasonably interpreted in a similar manner.

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