Table 3.
Calculated normal mode dependence on peripheral substituent configuration. Mode labels in the first column refer to porphyrin core modes with large Fe amplitudes. The porphyrin core normal mode analysis (second column) lists the wave number (cm−1) calculated for these modes for the D4h 25-atom skeletal structure (1 Fe, 4 N, 20 C; hydrogen masses are added to the 8 pyrrole carbons), using the force field derived from the Ci best fit to the NRVS data on Fe(OEP). The next column reprints a published DFT calculation on the porphyrin core plus eight methyl substituents in a planar D4h conformation10. These are in generally good agreement with the porphyrin core NMA results. The final column summarizes results from Table 1 for the Ci point group (Ci1 space group) structure. Including the true symmetry and non-planar structure of the ethyl substituents eliminates any direct correspondence with core modes for several normal modes, including the absence of any mode with significant ν8 symmetry.
| Mode | Porphyrin core (D4h) (NMA) | Core + methyls (D4h) (DFT) | FeOEP (Ci) (NMA) |
|---|---|---|---|
| γ9 | 70 | 65 | 54 |
| γ8 | 245 | 234 | - |
| γ7 | 345 | 380 | 168,256,305 |
| ν53 | 282 | 290 | 296 |
| ν52 | 188 | 178 | 153,256 |
| ν51 | 240 | 233 | 254 |
| ν50 | 368 | 343 | 354 |