The C2S2H2 molecular system may adopt several stable conformations. The relative stability of the two which are presumably the most stable ones, namely, dithiete and dithioglyoxal have been the subject of some controversy regarding their relative stabilities. Experimental findings favoured the dithiete structure, while ab initio calculations privileged the dithioglyoxal form. Recently this controversy was solved by Jonas and Frenking [1], who show that inclusion of f polarization functions in the basis set results in an enhanced stability of the cyclic dithiete form in agreement with experimental evidence. One of our goals is to provide a reliable estimation of the stability difference between both conformers by means of G2 ab initio calculations. We have considered also of interest to investigate all the stationary points of the corresponding potential energy surface at the same level of accuracy. For this purpose we have also calculated the gauge, cis and trans isomers of dithioglyoxal, the other two four membered cyclic structures which can be defined for the C2S2H2 besides dithiete and the transition states between the different local minima. We have also investigated the performance of three different density functional approaches, namely, BLYP, B3LYP and B3P86 for the correct description of these systems. Finally, we have estimated the possible influence of polar solvents, by means of the SCRF theory, on the structure and relative stabilities of dithiete and dithioglyoxal.
This work has been partially supported by the D.G.I.C.Y.T Project No. PB93-0142-C03-02.