Post–Hartree–Fock MP2 and density functional theory derived structure and vibrations of 1,2-dithiole-2-thione and 1,2-dithiole-3-one

Abstract

Post–Hartree–Fock MP2 and density functional theory (DFT) calculations with the combined B3LYP functional using the 6-31G(d) basis set were carried out to investigate structure and vibrational spectra of 3H-1,2-dithiole-3-thione and 3H-1,2-dithiole-3-one. Theory predicts planar structures of C s symmetry in both cases. The geometric parameters and the results of the Natural Bond Orbital (NBO) and Natural Resonance Theory (NRT) calculations are compatible with structures with localized rather than delocalized bonds. Schleyer's Nuclear Independent Chemical Shielding (NICS) criterion also indicates relatively low aromatic delocalization. Both the MP2 and DFT calculations provided consistent results about the fundamental vibrational modes and their assignment. Uniformly scaled DFT frequencies reproduce the experimental data in CCl 4 and CS 2 solutions not as well as uniformly scaled MP2 frequencies. The extension of the standard basis set of DFT calculations from 6-31G(d) to 6-311+G(2df,2p) affects vibrational frequencies and intensities to a minor extent.