Characterization of the Weak SS Bonds in the OSSSO and O2SSSO2 Molecules

The weak S1-S3 bonds in the OSSSO trans-disulfoxide and the corresponding sulfone, O 2 SSSO 2 , are readdressed at the B3LYP/6-31+G(d) level using both the atoms-in-molecules (AIM) and the electron localization function (ELF) approaches. The S1-S3 bonds are clearly characterized as fractional (i.e., with a bond number or bond order which is less than unity) or protocovalent and are very similar in nature to the weak N-N bond in O 2 NNO 2 . These results are in accord with what is obtained by inspection of valence bond structures of the increased-valence type.