ELECTRONIC STRUCTURE AND ELECTRONIC SPECTRUM OF DICHLORODIPYRIDINECOBALT(2) . CHARGE-TRANSFER BAND DUE TO INTERACTION BETWEEN HALIDE ION AND COBALT(2) CATION

The ultraviolet absorption spectrum of dichlorodipyridinecobalt(II) complex was measured in solution and in the crystal form. The solution spectrum exhibits a strong band at 256 mμ and a shoulder on the longer wavelength side. The former band was interpreted to be the local excitation band of pyridine. The shoulder band was found to shift to longer wavelengths and to increase in intensity in the order dichloro-< dibromo-< diiododipyridinecobalt(II). Furthermore, the band was found to split into two peaks for the diiodo complex. The separation of 5200 cm-1 may correspond to the energy difference between the 2P3/2 and 2P1/2 states of the free iodine atom. From these experimental facts and the theoretical studies, it was shown that the shoulder band may be regarded as the charge-transfer absorption accompanying the π-electron migration from the ligand halide ion to the metal cation. The dichroism observed in a single crystal of the dichloro complex supports this interpretation of the weak absorption at 300 mμ. The Davydov splitting was observed with the local excitation band of the ligand pyridine molecule. © 1968, American Chemical Society. All rights reserved.