An INDO-CI method in π-approximation for the calculation of transition metal complexes with organic ligands—application to iron(II)-trisdiimine complexes

An INDO-CI method in π-approximation extended for transition metal complexes with organic ligands is presented. The σ-polarization in the complex is estimated using a two-dimensional EHT calculation and considered in the π-calculation by means of the diagonal Fock matrix elements. The method is tested for four trisdiimine iron(II) complexes. In agreement with the experimental absorption spectra the calculations show that diimine complexes with non-heterocyclicly bound nitrogen atoms exhibit a large red-shift of the characteristic charge-transfer transition increasing the number of aromatic rings. Contrarily, for diimine complexes with heterocyclicly bound nitrogen atoms no shift of the charge-transfer transition was obtained.