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 energ ies from the profiles of electronic global properties such as chemical pote ntial and hardness, The procedure is based upon already established relatio nships among these properties and is applied to the qualitative analysis of the reduction mechanism of oxygen by the iron tetraazaporphyrin (FeTAP). A s a result, the interaction is qualitatively rationalized in terms of a [ph ysisorption] --> [chemisorption] process where at O-2... FeTAP distances la rger than 1.9 Angstrom the oxygen is physisorbed and the adduct is characte rized by weak intermolecular interactions. For distances smaller than 1.9 A ngstrom, the oxygen is chemisorbed, and the adduct is characterized by a co mplex with a formal Fe-O bond, The adduct structures generated from these m echanisms are separated by a potential barrier of about 6 kJ/mol. (C) 1999 Elsevier Science B.V. All rights reserved.