Many organic coordination compounds occur in nature. For example, hemoglobin and myoglobin contain an iron center coordinated to the nitrogen atoms of a porphyrin ring; magnesium is the center of a chlorin ring in chlorophyll. The field of such inorganic compounds is known as bioinorganic chemistry. However, methylcobalamin (a form of Vitamin B), with a cobalt-methyl bond, is a true organometallic complex, one of the few known in biology. 