Density functional theory analysis of structure and vibrational spectra of nickel octaethylporphyrin

A procedure combining density functional theory (DFT) with quantum mechanical scaling (SQM) has been applied to obtain the vibrational force field for several conformers of nickel octaethylporphyrin (NiOEP). The results of these calculations have been compared with crystallographic and spectroscopic data to verify accuracy of the calculations and applicability of the DFT-SQM approach to NiOEP. Calculated energies of NiOEP conformers showed that those conformers with a ruffled porphyrin macrocycle were energetically favored over their planar counterparts by about 0.2 kcal/mol.; Infrared and off-resonance Raman spectra were simulated from DFT-SQM calculated frequencies and compared with experimental data. Descriptions for infrared and Raman active modes were developed through normal coordinate analysis of the DFT-SQM force field, and these were evaluated against those proposed earlier based strictly on empirical methods. Calculated isotope shifts were also compared to existing experimental data.; Based upon normal coordinate analysis of the DFT-SQM force field for NiOEP, a{09} complete vibrational assignment for all in-plane and out-of-plane modes of the porphyrin macrocycle was generated. (Abstract shortened by UMI.)...