The Effect of Bonding Characteristic of Axial Ligand on the Electronic Structure of Iron(Ⅲ) Porphyrins
| Autor: | Chia-Wei Chao, 趙家緯 |
|---|---|
| Rok vydání: | 2006 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 Recent researches demonstrate that porphyrin distortion is mainly divided into two kinds: saddle and ruffle. The saddle distortion in OETPP increases basicity. The phenomenon promotes dx2-y2 orbital energy and decreases dz2 orbital energy relatively in metalloporphyrin. Porphyrin’s a1u orbital has the same symmetry as dxy orbital in saddle distortions. Iron (III) porphyrin is advantageous to intermediate-spin under crystal field intensity change. The ruffle distortion in TiPP decreases porphyrin core and creates dxy orbital bonding interaction with porphyrin’s a2u orbital. Iron (III) porphyrin becomes the unusual (dxz, dyz)4(dxy)1 electronic state. Beside this substituents effect, we are focusing on axial ligand in this report. It is generally believed that a strong field ligand is a good σ- donor and is also a good π-acceptor. Through the bonding analysis, it has been found that CN- is a good σ- donor but the π-acceptor of neutral HNC is better than CN- which make large difference in their electronic properties in metalloporphyrin. The electronic state of planar [Fe(TPP)(HNC)2]+ is (dxz, dyz)4(dxy)1 and exhibits Jahn-Teller distortion. In case of [Fe(OETPP)(HNC)2]+ the unpair electron is unusually present on the porphyrin’s a2u orbital and make [FeII(OETPP)+•(HNC)2]+. The electronic state of [Fe(TPP)(Im)2]+ is (dxy)2(dxz, dyz)3 in many evidential demonstrations where Im is mainly good σ- donor. But [Fe(TPP)(Py)2]+ is more complex where Py is also good σ- donor as well as π-acceptor. However, the π-acceptor properties of Py is not better than HNC but it still has a little ruffle distortion because two pys are peripendicular to meso porphyrin which lead the electronic state to (dxz, dyz)4(dxy)1. At last, we tried to explain, by using of Ramsey equations and 59Co chemical shift, why the weak field axial ligand low-spin Co(II) porphyrin oxidizes on the porphyrin ring which become π cation radical. But we found another way to determine the crystal field energy by accident. |
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