And so we have to be able to somehow stabilize this diatomic oxygen inside that heme group. And in fact, what happens is we have another histidine residue that is part of the polypeptide chain inside that protein. Either myoglobin or hemoglobin that binds creates a hydrogen bond with that negative charge. And this is shown in the following diagram. So the actual structure of the iron oxygen complex is resonant stabilized as shown in this diagram. One of it consists of this structure, and the other one consists of this structure here.