The geometric structure optimization of iron-tetraphenylporphyrin chloride (Fe(TPP)Cl) and a number of its halogenated complexes have been performed by PM3 semi-empirical quantum calculations. Using molecular modelling based on HF/6-31G* ab initio calculation the activation Of O-2 on the surfaces of these complexes has been modeled. The negative Mulliken charge on the Fe atoms obtained in the complexes studied meet the condition of attraction Of O-2 molecules to the activation center in molecular modeling of the activation Of O-2 on the surface of the complexes. These results were compared with the modeling of Fe(TPP)Cl with a positive Mulliken charge on Fe atom given by ZINDO/1. The similar modeling for the latter case shows even if the O-2 molecule was put closely over the Fe atom, O-2 would also depart away from the Fe atom. When hydrogen atoms on Fe(TPP)Cl are replaced by fluorine or bromine atoms, the electronic densities on Fe are increased. The spin population shows that partial spin is transferred from the Fe atom to the porphyrin ring. The data also indicate the spin transfer increases with increasing degree of halogenation on the porphyrin ring. A low HOMO and high electronic density on Fe atom have been shown to favor the enhanced catalytic activity of halogenated iron-tetraporphyrin complexes, with a paddle structure especially prefer-red holding the phenyl groups crossing with the porphyrin's saddle surface. The chemometric quantitative structure activity relationship (QSAR) studies using quantum chemistry parameters as feature variables have been shown as very promising for catalyst design. (C) 2003 Elsevier Science B.V. All rights reserved.