Abstract
We have for the first time measured and analyzed the Raman spectra of the model hydroporphyrins nickel(II) and copper(II) 2,2,7,8,12,13,17,18-octamethylchlorin in CS2. A detailed spectral analysis of the fingerprint region of nickel(II) chlorin revealed that a band at 1654 cm-1 is composed of two sublines at 1654 and 1662 cm-1. A novel normal coordinate analysis based on a transferrable force field derived from nickel(II) porphin, propane, and 2,2-dimethylpropane revealed that the respective normal mode is comparable with the porphyrin mode ν10 despite significant localization effects due to the reduction of a pyrrole ring. The resonance excitation profile of the low-frequency subline of ν10 is red-shifted with respect to that at higher frequencies. Hence, the two sublines can be interpreted as resulting from the coexistence of a nonplanar (ruffled) and a more planar conformer. The analysis of the ν10 band of the copper(II) octamethylchlorin revealed that it is also composed of two sublines. The frequenci...
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