Infrared Spectra of Nickel Octaethylporphyrin and Its Isotopomers Computed via Density Functional Theory−Scaled Quantum Mechanical (DFT−SQM) Method

Abstract

Gradient-corrected density functional theory (DFT) calculations were carried out to develop a scaled quantum mechanical (SQM) force field for nickel octaethylporphyrin (NiOEP). Frequencies for all vibrations were calculated for several conformers and isotopomers of NiOEP. Assignments of infrared active vibrations were made upon the basis of normal coordinate analysis of the resulting DFT−SQM force field. The spectra and vibrational assignments agree well with previously reported experimental infrared data for NiOEP, with only eight of the peaks in the simulated natural abundance spectrum being more than 10 cm-1 apart from their counterparts on the experimental natural abundance spectrum. Theoretically calculated isotopic shifts on simulated spectra resemble isotopic shifts observed experimentally. All but four shifts in the simulated meso-deuterated spectrum are within the same order of magnitude and in the same direction as those reported for experimental meso-deuteration, and none of the simulated 15N shifts were more than 2 cm-1 larger or smaller than their respective experimental shifts.