The electronic spectra of the dithiolato nickel complexes have been calculated with a PPP-CI type program developed for including variable β approximation. This calculation was based on the assumption that the nickel atom have a π-orbital and two π electrons.
The calculated longest-wavelengths, λ
max′s'of the dithiolato nickel complexes were in good agreement with the observed values. The orbital assignment of the molecular orbitals for bis (ethylene-1, 2-dithiolato) nickel calculated by the PPP-method is in reasonable agreement with them calculated by the INDO-method or the Extended-Huckel-method. The first λ
max of the dithiolato nickel complexes was assigned to the HOMO-LUMO transition, as a π-π* transition
The bathochromic shift caused by the substitution with the electron-donating group at the 4-position of the phenyl group of bis (1, 2-diary1-1, 2-ethylenedithiolato) nickels might be mainly due to the increase of HOMO energy levels.
A linear relationship between experimental longest-wavelengths of the nickel complexes and calculated λ
max′s' of the ligand in the nickel complexes was observed.
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