Deoxyhemoglobin iron-porphyrin complex

A close-up view of the iron-porphyrin complex with the F helix in deoxyhemoglobin. Note that the iron atom is displaced slightly above the plane of the porphyrin. (Illustration copyright by Irving Geis. Reprinted by permission.)... 

For example, in mononitrosyl complexes, most M-N-O interactions are linear for hexacoordinate complexes containing the configuration M(NO) . Thus, Fe(NO) possesses a linear coordination [53, 58] and such a compound would form with an Fe(III) porphyrinate (where iron is 3d ) which binds to NO. By contrast, the primary NO adduct of Fe(II) porphyrinates (3d ), such as is found in the reduced heme which binds O2 in blood or muscle (deoxyhemoglobin or deoxymyoglobin, respectively) possesses the (Fe(NO) configuration and such species are bent see examples with structural and spectroscopic data (Table 2.2). 

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