Absorption of SO2(g) by TDAE[O2SSO2](s) to Give TDAE[O2SS(O)2SO2](s): Related Reactions of [NR4]2[O2SSO2](s) (R = CH3, C2H5)

One mole equivalent of gaseous SO, is absorbed by purple TDAE[O2SSO2](s), producing red, essentially spectroscopically pure TDAE[O2SS(O)(2)SO2](s); under prolonged evacuation, the product loses SO2(g), regenerating TDAE [O2SSO2] (s). Similarly, [NR4](2) [O2SS-(O)(2)SO2] (S) (R = Et, Me) can be prepared, albeit at lower purity, from the corresponding tetraalkylammonium dithionites (prepared by a modification of the known [NEt4](2)[O2SSO2] (s) preparation). While the [NEt4](+) salt is stable at rt; the [NMe4](+) salt has only limited stability at 78 degrees C. Vibrational spectra assignments for the anion in these salts were distinctly different from those for the anion in salts containing the long -known [O3SSSO3](2-) dianion, the most thermodynamically stable form of [S3O6](2-) (we prepared TDAE[O3SSSO3]center dot H2O(s) and obtained its structure by X-ray diffraction and vibrational analyses). The best fit between the calculated ((B3PW91/6-311+G(3de and PBE0/6-311G(d)) and experimental vibrational spectra were obtained with the dianion having the [O2SS(O)(2)SS2](2-) structure. Vibrational analyses of the three [O2SS(O)(2)SO2](2-) salts prepared in this work showed that the corresponding [O3SSO2](2-) salts were present as a ubiquitous decomposition product. The formation of these new [O2SS(O)(2)SO2](2-) dianion salts was predicted to be favorable for [NMe4](+) and larger cations using a combination of theoretical calculations (B(3)PW91/6-311+G(3df)) and volume based thermodynamics (VBT). Similar methods accounted for the greater stabilities of the TDAE(2+) and [NEt4](+) salts of [O2SS(O)(2)SO2](2-) compared to [NMe4](2)[O2SS(O)(2)SO2](s) toward irreversible decomposition to the corresponding [O3SSO2](2-) salts. These salts represent the first known examples of a new class of poly(sulfur dioxide) dianion, [SO2](2-) in which n > 2.