Theoretical study on the structures, stabilities and electronic properties of S₂O₅^2- isomers in the gas and solution phases

Different theoretical levels of theory including B3LYP/6-311+G(3df,3pd), MP2/6-311+G(3df,3pd), QCISD/6-311+G(d,p), CBS-QB3 and CCSD(T)/6-311+(d,p)//B3LYP/6-311+G(3df,3pd) have been employed to determine the structures, relative stabilities, electronic properties and thermochemistry of the selected S₂O₅^2- isomers in the gas phase and aqueous solution. Atoms in molecules (AIM) method and natural bonding orbital (NBO) were used to characterize the origin of atomic bonds. The NBO and AIM calculations showed that the strength of S-O and S-S bonds in the (O₃SSO₂)^2-, (O₂SOSO₂)^2- and (OSOSO₃)^2- isomer are relatively weak and go toward dissociation to form , SO₃^-SO₂-, SO^- and SO₄^- radical anions. For more confirmation, the dissociation equilibrium constant (K _diss) of each isomer were calculated at 298K and showed that by increasing the dielectric constant of the solvent, the stability of the S₂O^2/5- isomer increases. Based on these result, the isomers are considerably unstable and dissociate in the gas phase compared with solution.