A complete characterization of vibrational IR and Raman spectra of the highly-symmetrical octathia[8]circulene

The highly-symmetrical octathia[8]circulene molecule (8S) was synthesized and well studied 10 years ago in Moscow, including X-ray diffraction, IR and Raman spectra assignment on the ground of molecular DFT calculation. Nevertheless, this comprehensive study could not explain a big number of interesting deviations from the DFT predictions based on the molecular Dsh symmetry restriction being specific for a free species in a gas phase. In present work we have performed DFT optimization of the 8S tetramer starting with the X-ray diffraction analysis of a similar crystal structure. DFT calculation of IR and Raman spectra of such a huge system provides a good assignment of the crystal-field splitting and new band occurrence. The force-field distortions, electric charges and polarizability dependence on the tetramer structure are well reproduced by the B3LYP functional with the dispersion correction. Thus, the small shifts of IR and Raman bands, their splitting and intensity redistribution upon weak intermolecular interactions in crystal packing are explained and full assignment of all observed bands is presented.