The spectra of complexes of conjugated ligands. Part V. Zero differential overlap calculations on α-di-imine and its iron(II) complexes

Abstract

Calculations at the level of intermediate neglect of different overlap, including only π-electrons, have been performed on an aliphatic α-di-imine and its iron(II) complexes, to interpret the available absorption spectra. Calculations on the isolated ligand gave good agreement with the observed spectrum, and a treatment of a hypothetical low-spin mono-complex showed that this ligand is a useful analogue of phenanthroline.

The choice of a basis and of the excited configurations to be taken into account in calculations on tris-complexes are discussed. The origin of c.d. and the mixing of the various classes of excited configurations are discussed within the framework of a basis of localised ligand and metal orbitals, and the results of different calculations are compared. Previous assignment of the absorption spectrum is confirmed. Inter-ligand charge-transfer configurations have a large effect on the predicted c.d. of the metal–ligand charge-transfer band, but their influence on the first π→π* band is unimportant. The results of an SCF calculation are compared; the predicted c.d. of the charge-transfer band does not agree with the previous predictions. The predicted structure of the π→π* band agrees well with the previous results, but its energy is better predicted by the SCF calculation.

The effect of the flow of electrons from the σ system of the ligand on complex formation is considered, and the effective charge on the iron atom estimated as +0·86.