SINGLE-CRYSTAL MOLECULAR-STRUCTURE .55. DITHIOLO-DITHIOL-DITHIONE C4S6 AND DITHIOLO-DITHIOL-DIONE C4S2S4

The two iso(valence)electronic molecules, the violet-blue 3H,6H-1,2-Dithiolo[4,3-c]-1,2-dithione-3,6-dithione and its yellow oxygen analogue, the corresponding dione, are characterized by single crystal structure determinations and quantum chemical calculations to gain information on similarities and differences: The molecular structures are comparable except for the O perturbation, which causes short C=O and long (O)C-S bonds; the carbon chain CC bond lengths alternate between 143 and 134 pm. The crystal lattices are both monoclinic (P2(1)/c), but with molecules arranged differently in beta-type and gamma-type layered staples due to 293 pm short (S ... O), dimer contacts. The color differences can be rationalized by extensive PM3/Cl-calculations: Accordingly, both molecules exhibit long wavelength pi --> pi*-transitions X((1)A(g)) --> A(B-1(u)), with the one of the sulfur derivative further lowered by a strong n(s)(sigma) --> sigma(ss)*, admixture. In addition, structural changes are discussed, which are expected for potentially conducting polymers containing disulfide-bridged chains on doping with suitable accepters.