A model of heme.The Merk index says,
"mol. wt. 616.48 C34H32FeN4O4; It is the color furnishing portion of hemoglobin. Absorption max in phosphate buffer at ph 7 is ~550, 575 nm. Sparingly soluble in glacial acetic acid; freely soluble in presence of oxygen. Very unstable."
Heme is very similar to protoporphyrin IX. See below.