A theoretical procedure to determine interaction energies in complex systems:: application to the oxygen-iron tetraazaporphyrin interaction

In this paper we present a theoretical model to determine interaction energies from the profiles of electronic global properties such as chemical potential and hardness, The procedure is based upon already established relationships among these properties and is applied to the qualitative analysis of the reduction mechanism of oxygen by the iron tetraazaporphyrin (FeTAP). As a result, the interaction is qualitatively rationalized in terms of a [physisorption] --> [chemisorption] process where at O-2... FeTAP distances larger than 1.9 Angstrom the oxygen is physisorbed and the adduct is characterized by weak intermolecular interactions. For distances smaller than 1.9 Angstrom, the oxygen is chemisorbed, and the adduct is characterized by a complex with a formal Fe-O bond, The adduct structures generated from these mechanisms are separated by a potential barrier of about 6 kJ/mol. (C) 1999 Elsevier Science B.V. All rights reserved.