On the O 2 binding of Fe–porphyrin, Fe–porphycene, and Fe–corrphycene complexes

Abstract Based on our previous study for the O 2 binding of the Fe–Por complex, this study investigates the O 2 binding mechanism in the Fe–porphyrin isomers, Fe–porphycene (FePc), and Fe–corrphycene (FeCor) complexes. By calculating the potential energy surface of the O 2 binding, the present study explains the reason for the dramatic increase of O 2 affinities observed in the FePc complex. In the case of FeCor–O 2 , the O 2 binding process includes the intersystem crossing from a triplet to singlet state, as in the FePor–O 2 complex. However, FePc–O 2 uses only a singlet surface. This is because the ground state of the FePc complex in the deoxy state is a triplet state, while those of FePor and FeCor are a quintet state. Such difference originates from character of the SOMO. We estimated an equilibrium constant for the O 2 binding that reasonably reproduced the trend observed in the experiments. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1363–1372, 2006