[masaa]

Hi

I had a lesson about porphyrin, but I would like to know how metals such as zinc or iron could be inserted into porphyrin, and what is the mechanism for this reaction?
I read as a conformation of a successful reaction , they use U.V. spec as there will be a reduction in the number of Q bands from four to two, I do not understand why?

could you explain it to me, Please?"

[Corribus]

Inserting zinc is fairly easy. Usually you just reflux in a suitable solvent for about an hour, then purify.  Inserting other metals uses generally the same procedure, but they aren't quite as stable and you also have to worry about axial ligand.

The reason the number of Q-bands reduces from 4 to 2 is that inserting a metal ion increases the symmetry of the porphyrin ring, which causes the x- and y-polarized π-π* transitions to become degenerate (have the same energy). Without the metal ion present, two of the central nitrogens are usually protonated. So draw the free base form and the coordinated form of porphine ring and look at how the symmetry changes.

Note that UV-Vis is not sensitive to impurities, so more sensitive methods are generally needed to confirm that the reaction yield is satisfactory.

(By the way, this forum encourages users to show work before they receive help. So, I gave you a freebee. Make sure you try to explain your thinking in the future.)

[masaa]

Thx Corribus
what I thought is that zinc is easier than other such as Fe ...etc due to its size. However, porphyrin is planar ligand, it is well-known that metal ions with different sizes can coordinate the porphyrins due to the electronic effect. but how is that as the oxidation number of zinc is two.

[kriggy]

Im not sure why there should be a problem with zinc having oxidation number of 2? Could you explain your thought in bit more detail?

[masaa]

Amm

What I meant is that the how is the coordination will occur as the zinc atoms have an electronic configuration of [Ar]3d¹⁰4s2. When compounds in the +2 oxidation state are formed the s electrons are lost, so the bare zinc ion has the electronic configuration [Ar]3d10.

[Corribus]

Thx Corribus
what I thought is that zinc is easier than other such as Fe ...etc due to its size. However, porphyrin is planar ligand, it is well-known that metal ions with different sizes can coordinate the porphyrins due to the electronic effect. but how is that as the oxidation number of zinc is two.

Size is probably the most important factor determining how easily a metal coordinates to a porphyrin, and how stable it ultimately is. If the ion is too big or too small, the metal ion is far more acid labile.

[masaa]

Kriggy

What I meant how the coordination of the zinc will occur with porphyrin as its d orbital is fully occupied?
in porphyrin , there are four nitrogen.