Resonance Raman spectra for nickel octaethylporphyrin (NiOEP) in solution are compared with triclinic and tetragonal crystalline forms containing flat and ruffled porphyrin. The appearance in solution of several bands that are activated only in the crystals containing ruffled porphyrin and that have been assigned to porphyrin out-of-plane modes provides clear evidence for a ruffled structure in solution. The in-plane porphyrin skeletal modes and their isotope shifts are catalogued for the triclinic and tetragonal crystals. The similarities in isotope shift pattern and relative RR intensities show that the normal-mode compositions are not significantly altered by ruffling, even though there are appreciable frequency shifts. The solution frequencies are intermediate between those of the triclinic and tetragonal crystals, indicating that the degree of ruffling is diminished in solution relative to the ruffled NiOEP crystals. The structure-sensitive v10 band has been examined in detail. It is much broader in solution than in either of the crystals. The band profile covers the frequency range from the flat (1663 cm'1) to the ruffled (1642 cm'1) structures, peaking at ~1653 cm'1; a range of solution structures is inferred. The previous treatment by Asher and Murtaugh of the temperature dependence of v10 in terms of anharmonic coupling with a low-frequency mode is explicitly related to the Blu pyrrole swiveling mode, 12 = 610 cm'1 in the tetragonal crystals, which is involved in the ruffling distortion.
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