Reactivity descriptors applied to the study of cobalt porphyrin and their aza derivatives

A theoretical study at the density functional level of theory (ROBLYP/3-21G*) of the reactivity of cobalt porphyrin (CoP) and their aza derivatives (CoP(xN)) by using global and local indexes is presented. First, vertical ionization potentials and electronic affinities are calculated to determine global reactivity descriptors such as the chemical potential (mu), molecular hardness (eta), and electrophilicity (omega). In general, it is found that eta and omega increase with the inclusion of aza-N atoms in the cobalt porphyrin. The cobalt condensed Fukui function (f(Co)) and cobalt condensed electrostatic potential (EPCo) for the set of CoP(xN) are also determined. We obtained that f(Co)(-) decreases with the increase of aza-N atoms, which indicates that a minimum Fukui function is preferred for hard-hard interactions, in agreement with previous results (Cardenas-jiron, G. J. J Phys Chem A 2002, 106, 3202). Results obtained for EPCo indicates that the increase of aza-N atoms leads to a more electrophilic site for the cobalt atom that is also stated at a global level through the results of omega, which are referred to the molecule as a whole. It is concluded that global and local descriptors are complementary in this reactivity study and both give enough information to rationalize the effect of the inclusion of aza-N atoms in the porphyrin upon the reactivity. (C) 2002 Wiley Periodicals, Inc.