Hemoglobin-iron coordination complex

Coordination compounds play important roles in nature. Chlorophyll, which is involved in photosynthesis in plants, is a coordination complex of magnesium. Hemoglobin, the oxygen transporter in the human body, is a coordination complex of iron. Vitamin B12, necessary for the prevention and cure of pernicious anemia, is a coordination complex of cobalt. In all three compounds, the metal ion is in an approximately octahedral environment, its coordination number is 6, and bonded to it are the four nitrogen atoms of a planar porphyrin-hke ring. The basic planar ring structure is closely related to that of the extremely stable blue pigment, Cu(II)phthalo-cyanine. 

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