Ab initio determination of geometries and vibrational characteristics of building blocks of organic superconductors: 4,5-Ethylenedithio-1,3-dithiole-2-thione, and 4,5-ethylenedithio-1,3-dithiole-2-one

RHF and DFT calculations were carried out to study the optimized molecular geometries and vibrational characteristics of the 4,5-ethylenedithio-1,3-dithiole-2-thione (EDT-DTT) and 4,5-ethylenedithio-1,3-dithiole-2-one (EDT-DTO) molecules and their radical cations and anions. It is found that the anionic radical of the EDT-DTO molecule is unstable. Both the neutral molecules and their radical cations have non-planar structures with C2 symmetry while the radical anion of the EDT-DTT molecule has non-planar structure with C1 symmetry. It is found that the most of the vibrational characteristics of the radicals are similar to their corresponding neutral molecules, however, for some of the modes significant changes are noticed. As a result of anionic radicalization of EDT-DTT, the IR intensity and Raman activity increase and Raman band becomes polarized for both the CH2 twisting modes. Drastic enhancements in the Raman activity and reduced IR intensity are noticed for the CS/O stretching mode in going from neutral molecules to their radical ions consistent with charge separation along this bond. The CS and CC stretching wavenumber changes are consistent with corresponding bond length changes in going from neutral to their radical ions.