The spectra of complexes of conjugated ligands. Part VI. Zero differential overlap calculations on tris(phenanthroline)iron(II)

Abstract

The absorption and c.d. of tris(phenanthroline)iron(II) have been interpreted using a π-electron treatment. An SCF basis with interaction among 162 excited configurations was used, and compared with a basis of orbitals localised on the ligands or the metal ion. Calculations on a hypothetical mono-complex were used to choose the configurations. Oscillator and rotational strengths were calculated with both dipole length and velocity operators and reasonable bandshapes used to simulate absorption and c.d. envelopes. The results are compared with experiment, and with those of other workers. The visible charge-transfer band contains transitions to both the two lowest empty ligand orbitals, and these apparently have different bandshapes. Only our SCF calculation gives a qualitatively correct prediction of the c.d. envelope of this band. Magnetic c.d. is briefly discussed. The SCF calculation gives an excellent prediction of the absorption and c.d. in the π→π* region; a localised basis is less satisfactory. A bandshape with a greater halfwidth on the high-energy side gives better results than does a symmetrical one. The first band in this region and its shoulders contain the α, p, β, and β′ ligand transitions; the c.d. arises primarily from the β′ transition. Our results are only approximately in agreement with those of a simple exciton model. The relation of the π→π* spectrum of the complex to those of phenanthroline and of phenanthrene, in which p and β′ bands are well separated, is discussed. The effective charge on the iron atom is estimated as +0·77.