A peroxo- ligand in this coordination complex is degraded to a single redox-active oxygen atom in “compound I,” which goes on to hydroxylate C-H bonds. Unlike typical square planar complexes, this complex’s d-z-squared orbital lies above the d-sub-xy orbital in energy due to repulsion from a proximal histidine. This complex’s transition from a high-spin domed configuration to a low-spin planar configuration corresponds to a larger system’s T state and (*) R state. (-5[1])This cofactor for cytochrome P450s is metabolized to a “verdo-“ form before being cleaved to form biliverdin and then excreted as bilirubin. Due to pi backbonding, this complex undesirably binds very strongly to CO. For 10 points, name (-5[1])this iron-porphyrin complex, four of which appear in a namesake protein that binds molecular oxygen in red blood cells. (10[1])■END■ (10[1])