MACROCYCLE AND SUBSTITUENT VIBRATIONAL-MODES OF NONPLANAR NICKEL(II) OCTAETHYLTETRAPHENYLPORPHYRIN FROM ITS RESONANCE RAMAN, NEAR-INFRARED-EXCITED FT RAMAN, AND FT-IR SPECTRA AND DEUTERIUM-ISOTOPE SHIFTS

We have employed Raman dispersion, FT Raman, and FT-IR spectroscopy to identify a large number of resonance Raman lines of Ni(II) octaethylt etraphenylporphyrin dissolved in CS2. The Raman depolarization dispers ion technique was used to derive the symmetry of the normal modes givi ng rise to the observed Raman lines. By combining this information and the already available normal coordinates of Ni(II) tetraphenylporphyr in and Ni(II) octaethylporphyrin, many of the Raman-active modes of th e macrocycle could be assigned. Some resonance-enhanced Raman lines we re found to arise from vibrations of the ethyl and phenyl substituents . They were identified by comparing resonance Raman, FT Raman, and FT infrared spectra of the Ni(II) octaethyltetraphenylporphyrin and its d 20 isotopomer. All Raman lines normally referred to as core-size marke rs are found to be significantly shifted to lower frequencies with res pect to their positions in Ni(II) octaethylporphyrin, in accordance wi th earlier findings (Shelnutt et al., J. Am. Chem. Soc. 113, 4077, 199 1). This suggests that the molecule is in a highly nonplanar conformat ion. This notion is further corroborated by the strong dispersion of t he depolarization ratio observed for nearly all A1g and A2g modes of t he macrocycle.