Synthesis Of (Tdae)(O2sso2)(S) And Discovery Of (Tdae)(O2sssso2)(S) Containing The First Polythionite, [O2sssso2](2-)

Gaseous SO2 reacts with tetrakis(dimethylamino)ethylene (TDAE) in acetonitrile in a 2:1 stoichiometric ratio to give analytically pure insoluble purple (TDAE)(O2SSO2) (1) in about 80% yield. Crystals of (TDAE)(O2SSSSO2) (2) were obtained from orange solution over the purple solid. The Raman spectrum of [TDAE](2+) was established using (TDAE)(A) salts [A = 2Br(-), 2Br(-)center dot 2H(2)O (X-ray), 2[Br-3](-) (X-ray)]. Vibrational spectroscopy showed that [O2SSO2](2-) in 1 has C-2h geometry. The X-ray structure of 2 showed that it contained [O2SSSSO2](2-), the first example of a new class of sulfur oxyanions, the polythionites. The geometry of [O2SSSSO2](2-) consists of S-2 with an S-S bond length of 2.003(1) angstrom connected to two terminal SO2 moieties by much longer S-S bonds of 2.337(1) angstrom. Calculations (B3PW91/6-311+G(3df) show that the structural units in [O2SSSSO2](2-) are joined by the interaction of electrons in two mutually perpendicular pi* SOMOs of the triplet-state diradical S-2 with unpaired electrons in the pi*-antibonding orbitals of the two terminal [SO2](center dot-) and polarized to delocalize the negative charge equally onto the three fragments. Thermodynamic estimates show 2 to be stable with respect to loss of sulfur and formation of 1, in contrast to [O2SSSSO2](2-) salts of small cations that are unstable toward the related dissociation. Reaction of TDAE with an excess of liquid SO2 led to (TDAE)(O3SOSO3)center dot SO2 (preliminary X-ray, Raman), (TDAE)(O3SSSSO3)center dot 2SO(2) (preliminary X-ray, Raman), and (TDAE)(O3SSO2) (Raman).