Chlorophyll and Coordination Chemistry for Non-Transition Metals

[Hanyi Jia 3B]

When we talked about myoglobin that has a porphyrin ligand surrounding the Fe atom, I was reminded of chlorophyll which also has a porphyrin ligand surrounding an Mg atom. https://en.wikipedia.org/wiki/Chlorophyll

This raised the questions:
1. Does the central atom of a coordination compound have to be a transition metal? (Mg is alkaline earth metal.)
2. Does the coordination chemistry also apply to other metals like alkali and alkaline earth?
3. Does Chlorophylls (all types through a to f) count as examples of coordination compounds?
4. If not, how should chlorophyll be categorized?
5. What crucial rules does the existing valence d-shells play for the coordinate bonds? (As focus 9 is about d-block)

Thank you!

[Mari Masunaga 1G]

Hi! In response to your first question I believe more coordination complexes are made up off transition metals however it is possible for other elements to form complexes too. I found that complexes can also be formed from aluminum, tin, and lead. Hope this helps!

[Chem_Mod]

1. The central atom of a coordination compound does not have to be a d block transition metal. It must be a metal with access to it's d-orbitals

2. Coordination chemistry applies to any metal that has access to it's d-orbitals this includes late block alkali and alkali earth metals (though it is very rare with alkali metals)

3. All chlorophyll compounds would count as coordination compounds when there is a Mg at the center of the porphyrin ring coordinated to the larger chlorophyll structure. You can think of the chlorophyll a-f as different ligands that coordinate Mg

5. d orbitals are required for coordination compounds as they allow metals to create bonding orbitals with ligands using the donated electron pair from the ligands. This eventually gets into molecular orbital theory which is beyond the scope of chem 14A

[Hanyi Jia 3B]

1. The central atom of a coordination compound does not have to be a d block transition metal. It must be a metal with access to it's d-orbitals

2. Coordination chemistry applies to any metal that has access to it's d-orbitals this includes late block alkali and alkali earth metals (though it is very rare with alkali metals)

3. All chlorophyll compounds would count as coordination compounds when there is a Mg at the center of the porphyrin ring coordinated to the larger chlorophyll structure. You can think of the chlorophyll a-f as different ligands that coordinate Mg

5. d orbitals are required for coordination compounds as they allow metals to create bonding orbitals with ligands using the donated electron pair from the ligands. This eventually gets into molecular orbital theory which is beyond the scope of chem 14A

Thank you so much! You are the best!
As for "access to d-orbitals", can I assume that refers to any metals with n>=3? Just like how atoms with n>=3 are allowed to have expanded octet as they can use d shells for hybridization?
And Magnesium definitely can use 3d orbitals for coordination right?

[Chem_Mod]

This NIH link has details and papers you can read on chlorophyll:

https://pubchem.ncbi.nlm.nih.gov/compound/Chlorophyll