Theoretical Study of the Formation of Three-Electron Bonds in Some F-Substituted Thiol and Sulfide Anions

Abstract

The possibility of formation of stable unsymmetrical three-electron (3e) bonds of the type {RS··(−)··R‘} was theoretically studied by ab initio SCF-CI quantum calculations. It was predicted, on the basis of a classical resonance scheme, that a 3e bond was the most likely to be observed when both constituting fragments RS and R‘ had the same electron affinity (EA). In this context the CH3-nFnSH and CH3-nFnSCH3-nFn (n = 0, 3) molecules were tested. The results support the prediction for the CF3/SH- and CF3/SCH3- anions. By comparing results from different types of basis sets, for describing the valence part of the reaction coordinate or providing the system with the possibility of electron attachment (or detachment) via a very diffuse available space, we were able to propose a qualitative model which accounts for the general features of these processes, in each type of molecule. Semiquantitative data are offered for further experimental testing of our findings with molecules such as CHnX3-nSH and CHnX3-nSCH3 (X = F, Cl, Br; n = 0,1).