Conformational Distortions of Metalloporphyrins with Electron-Withdrawing NO2 Substituents at Different Meso Positions. A Structural Analysis by Polarized Resonance Raman Dispersion Spectroscopy and Molecular Mechanics Calculations

Abstract

The meso substituted Ni(II)(5,15-diNO2−octaethylporphyrin) coexists in at least three different conformers in CS2. To explore the structural properties of these conformers, we measured the resonance excitation profiles and depolarization ratio dispersions of various prominent Raman lines of Ni(5,15-diNO2−octaethylporphyrin) in CS2. The data were analyzed by a theoretical approach, which formulates the Raman tensor in terms of vibronic coupling parameters that depend on static deformations along the normal coordinates. The coupling parameters were determined by simultaneously fitting the depolarization ratio dispersion data and the corresponding resonance excitation profiles. We have also performed molecular mechanics calculations to identify all possible stable conformers of the molecule. To quantify the out-of-plane distortions of the calculated structures, we subjected them to normal coordinate deformation analysis (Jentzen, W.; Song, X.-Z.; Shelnutt, J. A. J. Phys. Chem. B 1997, 101, 1684). The results...