Porphyrin-like macrocyclic complexes: a spectroscopic and theoretical study of dibenzo [b,i] [1,4,8,11] tetraaza [14] annulenenickel (II)

Abstract

The electronic structure of dibenzo [b,i][1,4,8,11]tetraaza [14]annulenenickel(II), Nidbtaa, is studied by density functional LCAO approach and is presented together with a detailed description of the bonding. A quantitative analysis of the energetic contributions of the σ and π components to the metal-macrocycle total bond strength points out that the σ contribution is by far dominant. The π-back donation appears to have little energetic contribution. Ultraviolet photoelectron and optical spectra are reported for Nidbtaa and, for comparison purpose, for the free ligand, H 2dbtaa. Satisfactory assignments of the spectra are provided by ΔSCF density functional calculations. Similarities and differences with the spectroscopical behaviour and metal porphyrins, MP, are highlighted. It is stressed that a not negligible π metal-macrocycle interaction is responsible for the red shift of the Soret and Q bands in Nidbtaa, not observed in porphyrins. The gross population analysis of the excited states shows that, as in porphyrins, these bands are due to transitions which consists of a charge rearrangement occurring only within the macrocycle π system.