# How does ferrous iron coordinate nitrogen in a porphyrin ring?

In first semester biochemistry, my professor said that iron forms a coordination complex with nitrogens in the heme group.

I'm failing to understand what this even means since the charge on nitrogen does not change as a result of this bond. My organic chemistry textbook and biochemistry textbook do not even have a basic explanation of what is meant by this, and I can't find anything on the web.

How does iron form a bond with two of the nitrogens in the porphyrin ring, the histidine, and the oxygen?

• Nitrogen is coordinating iron; not the other way around. You should look up coordination compounds in general inorganic textbooks. $\ce{[Fe(haem)(His)(O2)]}$ is similar enough to $\ce{[Fe(NH3)6]^2+}$ as a starting point. I’m not sure if this site is the best place to answer the question. By the way, the porphyrinic nitrogens (two of the four) do have a charge associated with them; they are rendered in the image as forming a single bond to iron.
– Jan
Feb 12, 2017 at 20:00