GENERALIZED MOLECULAR-ORBITAL CALCULATIONS ON TRANSITION-METAL DIOXYGEN COMPLEXES - MODELS FOR IRON AND COBALT PORPHYRINS
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Generalized molecular orbital calculations with configuration interaction are reported for the dioxygen complexes of Co and Fe. The other ligands include a model ligand to represent the porphyrin ring system and a trans ammonia. The Co-O2 system is best described as a superoxide complex, Co3+-O2-, with the unpaired electron in a nearly pure g O2 orbital. The Fe-02 system is best described as a singlet dioxygen, O2 (1g) donating to and x accepting from an Fe2+. All of the experimental results for both systems can be rationalized with these descriptions. The calculations predict a low-lying triplet state for the Fe02 system, but not low enough in energy to explain the recently reported paramagnetism of hemoglobin. 1984, American Chemical Society. All rights reserved.